Science.gov

Sample records for horizontal flow regime

  1. A mechanistic determination of horizontal flow regime bound using void wave celerity

    SciTech Connect

    Park, J.W.

    1995-09-01

    The two-phase flow regime boundaries in a horizontal channel has been investigated by using the behavior of the second order void wave celerities. The average two-fluid model has been constituted with closure relations for horizontally stratified and bubbly flows. A vapor phase turbulent stress model for a smooth interface geometry has been included. It is found that the second order waves (i.e., eigenvalues) propagate in opposite direction with almost the same speed when the liquid phase is stationary. Using the well-posedness limit of the two-phase system, the dispersed-stratified flow regime boundary has been modeled. Two-phase Froude number has been theoretically found to be a convenient parameter in quantifying the flow regime boundary as a function of the void fraction. It is found that interaction between void wave celerities become stronger as the two-phase Froude number is reduced. This result should be interpreted as that gravity and the relative velocity are key parameters in determining flow regime boundaries in a horizontal flow. The influence of the vapor phase turbulent stress found to stabilize the flow stratification. This study clearly shows that the average two-fluid model is very effective for a mechanistic determination of horizontal flow regimes if appropriate closure relations are developed.

  2. Experimental investigation of the two-phase flow regimes and pressure drop in horizontal mini-size rectangular test section

    NASA Astrophysics Data System (ADS)

    Elazhary, Amr Mohamed; Soliman, Hassan M.

    2012-10-01

    An experimental study was conducted in order to investigate two-phase flow regimes and fully developed pressure drop in a mini-size, horizontal rectangular channel. The test section was machined in the form of an impacting tee junction in an acrylic block (in order to facilitate visualization) with a rectangular cross-section of 1.87-mm height on 20-mm width on the inlet and outlet sides. Pressure drop measurement and flow regime identification were performed on all three sides of the junction. Air-water mixtures at 200 kPa (abs) and room temperature were used as the test fluids. Four flow regimes were identified visually: bubbly, plug, churn, and annular over the ranges of gas and liquid superficial velocities of 0.04 ≤ JG ≤ 10 m/s and 0.02 ≤ JL ≤ 0.7 m/s, respectively, and a flow regime map was developed. Accuracy of the pressure-measurement technique was validated with single-phase, laminar and turbulent, fully developed data. Two-phase experiments were conducted for eight different inlet conditions and various mass splits at the junction. Comparisons were conducted between the present data and former correlations for the fully developed two-phase pressure drop in rectangular channels with similar sizes. Wide deviations were found among these correlations, and the correlations that agreed best with the present data were identified.

  3. Experimental Study on the Flow Regimes and Pressure Gradients of Air-Oil-Water Three-Phase Flow in Horizontal Pipes

    PubMed Central

    Al-Hadhrami, Luai M.; Shaahid, S. M.; Tunde, Lukman O.; Al-Sarkhi, A.

    2014-01-01

    An experimental investigation has been carried out to study the flow regimes and pressure gradients of air-oil-water three-phase flows in 2.25 ID horizontal pipe at different flow conditions. The effects of water cuts, liquid and gas velocities on flow patterns and pressure gradients have been studied. The experiments have been conducted at 20°C using low viscosity Safrasol D80 oil, tap water and air. Superficial water and oil velocities were varied from 0.3 m/s to 3 m/s and air velocity varied from 0.29 m/s to 52.5 m/s to cover wide range of flow patterns. The experiments were performed for 10% to 90% water cuts. The flow patterns were observed and recorded using high speed video camera while the pressure drops were measured using pressure transducers and U-tube manometers. The flow patterns show strong dependence on water fraction, gas velocities, and liquid velocities. The observed flow patterns are stratified (smooth and wavy), elongated bubble, slug, dispersed bubble, and annular flow patterns. The pressure gradients have been found to increase with the increase in gas flow rates. Also, for a given superficial gas velocity, the pressure gradients increased with the increase in the superficial liquid velocity. The pressure gradient first increases and then decreases with increasing water cut. In general, phase inversion was observed with increase in the water cut. The experimental results have been compared with the existing unified Model and a good agreement has been noticed. PMID:24523645

  4. Experimental study on the flow regimes and pressure gradients of air-oil-water three-phase flow in horizontal pipes.

    PubMed

    Al-Hadhrami, Luai M; Shaahid, S M; Tunde, Lukman O; Al-Sarkhi, A

    2014-01-01

    An experimental investigation has been carried out to study the flow regimes and pressure gradients of air-oil-water three-phase flows in 2.25 ID horizontal pipe at different flow conditions. The effects of water cuts, liquid and gas velocities on flow patterns and pressure gradients have been studied. The experiments have been conducted at 20 °C using low viscosity Safrasol D80 oil, tap water and air. Superficial water and oil velocities were varied from 0.3 m/s to 3 m/s and air velocity varied from 0.29 m/s to 52.5 m/s to cover wide range of flow patterns. The experiments were performed for 10% to 90% water cuts. The flow patterns were observed and recorded using high speed video camera while the pressure drops were measured using pressure transducers and U-tube manometers. The flow patterns show strong dependence on water fraction, gas velocities, and liquid velocities. The observed flow patterns are stratified (smooth and wavy), elongated bubble, slug, dispersed bubble, and annular flow patterns. The pressure gradients have been found to increase with the increase in gas flow rates. Also, for a given superficial gas velocity, the pressure gradients increased with the increase in the superficial liquid velocity. The pressure gradient first increases and then decreases with increasing water cut. In general, phase inversion was observed with increase in the water cut. The experimental results have been compared with the existing unified Model and a good agreement has been noticed. PMID:24523645

  5. Experimental study on the flow regimes and pressure gradients of air-oil-water three-phase flow in horizontal pipes.

    PubMed

    Al-Hadhrami, Luai M; Shaahid, S M; Tunde, Lukman O; Al-Sarkhi, A

    2014-01-01

    An experimental investigation has been carried out to study the flow regimes and pressure gradients of air-oil-water three-phase flows in 2.25 ID horizontal pipe at different flow conditions. The effects of water cuts, liquid and gas velocities on flow patterns and pressure gradients have been studied. The experiments have been conducted at 20 °C using low viscosity Safrasol D80 oil, tap water and air. Superficial water and oil velocities were varied from 0.3 m/s to 3 m/s and air velocity varied from 0.29 m/s to 52.5 m/s to cover wide range of flow patterns. The experiments were performed for 10% to 90% water cuts. The flow patterns were observed and recorded using high speed video camera while the pressure drops were measured using pressure transducers and U-tube manometers. The flow patterns show strong dependence on water fraction, gas velocities, and liquid velocities. The observed flow patterns are stratified (smooth and wavy), elongated bubble, slug, dispersed bubble, and annular flow patterns. The pressure gradients have been found to increase with the increase in gas flow rates. Also, for a given superficial gas velocity, the pressure gradients increased with the increase in the superficial liquid velocity. The pressure gradient first increases and then decreases with increasing water cut. In general, phase inversion was observed with increase in the water cut. The experimental results have been compared with the existing unified Model and a good agreement has been noticed.

  6. Non-invasive classification of gas–liquid two-phase horizontal flow regimes using an ultrasonic Doppler sensor and a neural network

    NASA Astrophysics Data System (ADS)

    Musa Abbagoni, Baba; Yeung, Hoi

    2016-08-01

    The identification of flow pattern is a key issue in multiphase flow which is encountered in the petrochemical industry. It is difficult to identify the gas–liquid flow regimes objectively with the gas–liquid two-phase flow. This paper presents the feasibility of a clamp-on instrument for an objective flow regime classification of two-phase flow using an ultrasonic Doppler sensor and an artificial neural network, which records and processes the ultrasonic signals reflected from the two-phase flow. Experimental data is obtained on a horizontal test rig with a total pipe length of 21 m and 5.08 cm internal diameter carrying air-water two-phase flow under slug, elongated bubble, stratified-wavy and, stratified flow regimes. Multilayer perceptron neural networks (MLPNNs) are used to develop the classification model. The classifier requires features as an input which is representative of the signals. Ultrasound signal features are extracted by applying both power spectral density (PSD) and discrete wavelet transform (DWT) methods to the flow signals. A classification scheme of ‘1-of-C coding method for classification’ was adopted to classify features extracted into one of four flow regime categories. To improve the performance of the flow regime classifier network, a second level neural network was incorporated by using the output of a first level networks feature as an input feature. The addition of the two network models provided a combined neural network model which has achieved a higher accuracy than single neural network models. Classification accuracies are evaluated in the form of both the PSD and DWT features. The success rates of the two models are: (1) using PSD features, the classifier missed 3 datasets out of 24 test datasets of the classification and scored 87.5% accuracy; (2) with the DWT features, the network misclassified only one data point and it was able to classify the flow patterns up to 95.8% accuracy. This approach has demonstrated the

  7. Non-invasive classification of gas-liquid two-phase horizontal flow regimes using an ultrasonic Doppler sensor and a neural network

    NASA Astrophysics Data System (ADS)

    Musa Abbagoni, Baba; Yeung, Hoi

    2016-08-01

    The identification of flow pattern is a key issue in multiphase flow which is encountered in the petrochemical industry. It is difficult to identify the gas-liquid flow regimes objectively with the gas-liquid two-phase flow. This paper presents the feasibility of a clamp-on instrument for an objective flow regime classification of two-phase flow using an ultrasonic Doppler sensor and an artificial neural network, which records and processes the ultrasonic signals reflected from the two-phase flow. Experimental data is obtained on a horizontal test rig with a total pipe length of 21 m and 5.08 cm internal diameter carrying air-water two-phase flow under slug, elongated bubble, stratified-wavy and, stratified flow regimes. Multilayer perceptron neural networks (MLPNNs) are used to develop the classification model. The classifier requires features as an input which is representative of the signals. Ultrasound signal features are extracted by applying both power spectral density (PSD) and discrete wavelet transform (DWT) methods to the flow signals. A classification scheme of ‘1-of-C coding method for classification’ was adopted to classify features extracted into one of four flow regime categories. To improve the performance of the flow regime classifier network, a second level neural network was incorporated by using the output of a first level networks feature as an input feature. The addition of the two network models provided a combined neural network model which has achieved a higher accuracy than single neural network models. Classification accuracies are evaluated in the form of both the PSD and DWT features. The success rates of the two models are: (1) using PSD features, the classifier missed 3 datasets out of 24 test datasets of the classification and scored 87.5% accuracy; (2) with the DWT features, the network misclassified only one data point and it was able to classify the flow patterns up to 95.8% accuracy. This approach has demonstrated the

  8. The transition between stratified and annular regimes for horizontal two-phase flow in small diameter tubes

    SciTech Connect

    Galbiati, L.; Andreini, P. )

    1992-03-01

    In this paper a modification to the model of Taitel and Dukler to include the effect of surface tension in transition between stratified and annular regimes is proposed. The predictions of the modified theory given in this paper are compared with empirical boundaries presented in literature. A good agreement has been found.

  9. Environment Flow Assessment with Flow Regime Transition

    NASA Astrophysics Data System (ADS)

    Su, J.; Ho, C. C.; Chang, L. C.

    2015-12-01

    To avoid worsen river and estuarine ecosystems cause by overusing water resources, environmental flows conservation is applied to reduce the impact of river environment. Environmental flows refer to water provided within a river, wetland or coastal zone to sustain ecosystems and benefits to human wellbeing. Environment flow assessment is now widely accepted that a naturally variable flow regime, rather than just a minimum low flow. In this study, we propose four methods, experience method, Tenant method, hydraulic method and habitat method to assess the environmental flow of base flow, flush flow and overbank flow with different discharge, frequency and occurrence period. Dahan River has been chosen as a case to demonstrate the assessment mechanism. The alternatives impact analysis of environment and human water used provides a reference for stakeholders when holding an environmental flow consultative meeting.

  10. Merging of Rhine flow regimes

    NASA Astrophysics Data System (ADS)

    Boessenkool, Berry; Bronstert, Axel; Bürger, Gerd

    2016-04-01

    The Rhine flow regime is changing: (a) in the alpine nival regime, snow melt floods occur earlier in the year and (b) in the pluvial middle-Rhine regime, rainfall induced flood magnitudes rise. The seasonality of each is currently separated in time, but it is conceivable that this may shift due to climate change. If extremes of both flood types coincide, this would create a new type of hydrologic extreme with disastrous consequences. Quantifying the probability for a future overlap of pluvial and nival floods is therefore of high relevance to society and particularly to reinsurance companies. In order to investigate possible changes in magnitude and timing of flood types, we are developing a chain of physical models for spatio-temporal combination of flood probabilities. As input, we aim to use stochastically downscaled temperature and rainfall extremes from climate model weather projections. Preliminary research shows a six-week forward-shift of peak discharge at the nival gauge Maxau in the past century. The aim of presenting our early-stage work as a poster is to induce an exchange of ideas with fellow scientists in close research disciplines.

  11. Capacitance densitometer for flow regime identification

    DOEpatents

    Shipp, Jr., Roy L.

    1978-01-01

    This invention relates to a capacitance densitometer for determining the flow regime of a two-phase flow system. A two-element capacitance densitometer is used in conjunction with a conventional single-beam gamma densitometer to unambiguously identify the prevailing flow regime and the average density of a flowing fluid.

  12. Horizontal slug flow modeling and metering

    SciTech Connect

    Kouba, G.E.

    1986-01-01

    An experimental and theoretical investigation of horizontal two-phase slug flow was performed with the purpose of developing a method to measure the in-situ flow rates of the liquid and the gas phases using non-intrusive devices. A microcomputer based data acquisition system was used to acquire slug flow data on a 3 in.(76.2 mm) diameter, 1370 ft (418 m) long, horizontal pipeline. These data include the following slug characteristics: liquid holdups in the slug and film, slug and gas pocket lengths, and slug translational velocity. The data were gathered over a wide range of flow conditions in groups of constant superficial liquid and mixture velocities. The volumetric phase flow rate equation, for either liquid or gas, was developed for slug flow conditions. Within the flow rate equation, a key flow distribution parameter was defined that related the phase velocity in the slug to the translational velocity of the slug.

  13. Numerical simulation of flow in a horizontal channel with multiple cross-flow inlets

    NASA Astrophysics Data System (ADS)

    Jha, Pranab N.; Smith, Chuck; Metcalfe, Ralph W.

    2014-11-01

    Flow in a horizontal channel with multiple cross-flow inlets was studied numerically. Based on Reynolds and Mach number analysis of data obtained from a horizontal natural gas well having 31 completion stages, measured at two different times in the production cycle, it was determined that an incompressible flow model may be applied to study a large fraction of the wellbore. Using five cross-flow inlets, the existence of three basic flow regimes - trickle flow, partially blocked flow and fully blocked flow - were identified with respect to the blocking of upstream inlets by the downstream ones. The existence of these flow regimes is consistent with field data. A lumped-parameter model for pressure drop was used to simulate large axial distances between two inlets. A pressure boundary condition was employed at each inlet to simulate a linearly depleting reservoir. This was used to study the dynamic interaction between the inlets in the channel. The characteristic time scales related to the transient depletion were identified and analyzed. The transition of flow regimes is consistent with the trends observed from field data and gives an insight into the behavior of horizontal wells. Supported in part by Apache Corp., Houston.

  14. Dual permeability flow behavior for modeling horizontal well production in fractured-vuggy carbonate reservoirs

    NASA Astrophysics Data System (ADS)

    Guo, Jian-Chun; Nie, Ren-Shi; Jia, Yong-Lu

    2012-09-01

    SummaryFractured-vuggy carbonate reservoirs are composed of by matrix, fracture, and vug systems. This paper is the first investigation into the dual permeability flow issue for horizontal well production in a fractured-vuggy carbonate reservoir. Considering dispersed vugs in carbonate reservoirs and treating media directly connected with horizontal wellbore as the matrix and fracture systems, a test analysis model of a horizontal well was created, and triple porosity and dual permeability flow behavior were modeled. Standard log-log type curves were drawn up by numerical simulation and flow behavior characteristics were thoroughly analyzed. Numerical simulations showed that type curves are dominated by external boundary conditions as well as the permeability ratio of the fracture system to the sum of fracture and matrix systems. The parameter κ is only relevant to the dual permeability model, and if κ is one, then the dual permeability model is equivalent to the single permeability model. There are seven main flow regimes with constant rate of horizontal well production and five flow regimes with constant wellbore pressure of horizontal well production; different flow regimes have different flow behavior characteristics. Early radial flow and linear flow regimes are typical characteristics of horizontal well production; duration of early radial flow regime is usually short because formation thickness is generally less than 100 m. Derivative curves are W-shaped, which is a reflection of inter-porosity flows between matrix, fracture, and vug systems. A distorted W-shape, which could be produced in certain situations, such as one involving an erroneously low time of inter-porosity flows, would handicap the recognition of a linear flow regime. A real case application was successfully implemented, and some useful reservoir parameters (e.g., permeability and inter-porosity flow factor) were obtained from well testing interpretation.

  15. Identifying natural flow regimes using fish communities

    NASA Astrophysics Data System (ADS)

    Chang, Fi-John; Tsai, Wen-Ping; Wu, Tzu-Ching; Chen, Hung-kwai; Herricks, Edwin E.

    2011-10-01

    SummaryModern water resources management has adopted natural flow regimes as reasonable targets for river restoration and conservation. The characterization of a natural flow regime begins with the development of hydrologic statistics from flow records. However, little guidance exists for defining the period of record needed for regime determination. In Taiwan, the Taiwan Eco-hydrological Indicator System (TEIS), a group of hydrologic statistics selected for fisheries relevance, is being used to evaluate ecological flows. The TEIS consists of a group of hydrologic statistics selected to characterize the relationships between flow and the life history of indigenous species. Using the TEIS and biosurvey data for Taiwan, this paper identifies the length of hydrologic record sufficient for natural flow regime characterization. To define the ecological hydrology of fish communities, this study connected hydrologic statistics to fish communities by using methods to define antecedent conditions that influence existing community composition. A moving average method was applied to TEIS statistics to reflect the effects of antecedent flow condition and a point-biserial correlation method was used to relate fisheries collections with TEIS statistics. The resulting fish species-TEIS (FISH-TEIS) hydrologic statistics matrix takes full advantage of historical flows and fisheries data. The analysis indicates that, in the watersheds analyzed, averaging TEIS statistics for the present year and 3 years prior to the sampling date, termed MA(4), is sufficient to develop a natural flow regime. This result suggests that flow regimes based on hydrologic statistics for the period of record can be replaced by regimes developed for sampled fish communities.

  16. Learning Flow Regimes from Snapshot Data

    NASA Astrophysics Data System (ADS)

    Hemati, Maziar

    2015-11-01

    Fluid flow regimes are often categorized based on the qualitative patterns observed by visual inspection of the flow field. For example, bluff body wakes are traditionally classified based on the number and groupings of vortices shed per cycle (e.g., 2S, 2P, P+S), as seen in snapshots of the vorticity field. Subsequently, the existence and nature of these identified flow regimes can be explained through dynamical analyses of the fluid mechanics. Unfortunately, due to the need for manual inspection, the approach described above can be impractical for studies that seek to learn flow regimes from large volumes of numerical and/or experimental snapshot data. Here, we appeal to established techniques from machine learning and data-driven dynamical systems analysis to automate the task of learning flow regimes from snapshot data. Moreover, by appealing to the dynamical structure of the fluid flow, this approach also offers the potential to reveal flow regimes that may be overlooked by visual inspection alone. Here, we will introduce the methodology and demonstrate its capabilities and limitations in the context of several model flows.

  17. Constructing an interdisciplinary flow regime recommendation

    USGS Publications Warehouse

    Bartholow, J.M.

    2010-01-01

    It is generally agreed that river rehabilitation most often relies on restoring a more natural flow regime, but credibly defining the desired regime can be problematic. I combined four distinct methods to develop and refine month-by-month and event-based flow recommendations to protect and partially restore the ecological integrity of the Cache la Poudre River through Fort Collins, Colorado. A statistical hydrologic approach was used to summarize the river's natural flow regime and set provisional monthly flow targets at levels that were historically exceeded 75% of the time. These preliminary monthly targets were supplemented using results from three Poudre-specific disciplinary studies. A substrate maintenance flow model was used to better define the high flows needed to flush accumulated sediment from the river's channel and help sustain the riparian zone in this snowmelt-dominated river. A hydraulic/habitat model and a water temperature model were both used to better define the minimum flows necessary to maintain a thriving cool water fishery. The result is a range of recommended monthly flows and daily flow guidance illustrating the advantage of combining a wide range of available disciplinary information, supplemented by judgment based on ecological principles and a general understanding of river ecosystems, in a highly altered, working river. ?? 2010 American Water Resources Association.

  18. Forest damage and snow avalanche flow regime

    NASA Astrophysics Data System (ADS)

    Feistl, T.; Bebi, P.; Christen, M.; Margreth, S.; Diefenbach, L.; Bartelt, P.

    2015-01-01

    Snow avalanches break, uproot and overturn trees causing damage to forests. The extent of forest damage provides useful information on avalanche frequency and intensity. However, impact forces depend on avalanche flow regime. In this paper, we define avalanche loading cases representing four different avalanche flow regimes: powder, intermittent, dry and wet. In the powder regime, the blast of the cloud can produce large bending moments in the tree stem because of the impact area extending over the entire tree crown. We demonstrate that intermittent granular loadings are equivalent to low-density uniform dry snow loadings under the assumption of homogeneous particle distributions. In the wet snow case, avalanche pressure is calculated using a quasi-static model accounting for the motion of plug-like wet snow flows. Wet snow pressure depends both on avalanche volume and terrain features upstream of the tree. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest damage. We find (1) powder clouds with velocities over 20 m s-1 can break tree stems, (2) the intermittent regime seldom controls tree breakage and (3) quasi-static pressures of wet snow avalanches can be much higher than pressures calculated using dynamic pressure formulas.

  19. Forest damage and snow avalanche flow regime

    NASA Astrophysics Data System (ADS)

    Feistl, T.; Bebi, P.; Christen, M.; Margreth, S.; Diefenbach, L.; Bartelt, P.

    2015-06-01

    Snow avalanches break, uproot and overturn trees causing damage to forests. The extent of forest damage provides useful information on avalanche frequency and intensity. However, impact forces depend on avalanche flow regime. In this paper, we define avalanche loading cases representing four different avalanche flow regimes: powder, intermittent, dry and wet. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest damage. First we show that in the powder regime, although the applied impact pressures can be small, large bending moments in the tree stem can be produced due to the torque action of the blast. The impact area of the blast extends over the entire tree crown. We find that, powder clouds with velocities over 20 m s-1 can break tree stems. Second we demonstrate that intermittent granular loadings are equivalent to low-density uniform dry snow loadings under the assumption of homogeneous particle distributions. The intermittent regime seldom controls tree breakage. Third we calculate quasi-static pressures of wet snow avalanches and show that they can be much higher than pressures calculated using dynamic pressure formulas. Wet snow pressure depends both on avalanche volume and terrain features upstream of the tree.

  20. Fluid flow through a vertical to horizontal 90 elbow bend III three phase flow

    SciTech Connect

    Spedding, P.L.; Benard, E.; Crawford, N.M.

    2008-01-15

    Three phase water/oil/air flow was studied around a vertical upward to horizontal 90 elbow bend of R/d = 0.654. The results were more complex than corresponding two phase data. The pressure drop recorded for the two tangent legs sometimes showed significant variations to the straight pipe data. In most cases this variation was caused by differences in the flow regimes between the two systems. The elbow bend tended to constrict the flow presented by the vertical inlet tangent leg while sometimes acting as a wave and droplet generator for the horizontal outlet tangent leg. It could be argued that the inclusion of the elbow bend altered the flow regime map transitional boundaries but it also is possible that insufficient settling length was provided in the apparatus design. The elbow bend pressure drop was best presented as l{sub e}/d the equivalent length to diameter ratio using the actual total pressure drop in the vertical inlet tangent leg. Generally l{sub e}/d values rose with gas rate, but exhibited an increasingly complex relation with f{sub o} the oil to liquid volumetric ratio as liquid rate was increased. A significant maximum in l{sub e}/d was in evidence around the inversion from water dominated to oil dominated flows. Several models are presented to predict the data. (author)

  1. Flow regimes in a trapped vortex cell

    NASA Astrophysics Data System (ADS)

    Lasagna, D.; Iuso, G.

    2016-03-01

    This paper presents results of an experimental investigation on the flow in a trapped vortex cell, embedded into a flat plate, and interacting with a zero-pressure-gradient boundary layer. The objective of the work is to describe the flow features and elucidate some of the governing physical mechanisms, in the light of recent investigations on flow separation control using vortex cells. Hot-wire velocity measurements of the shear layer bounding the cell and of the boundary layers upstream and downstream are reported, together with spectral and correlation analyses of wall-pressure fluctuation measurements. Smoke flow visualisations provide qualitative insight into some relevant features of the internal flow, namely a large-scale flow unsteadiness and possible mechanisms driving the rotation of the vortex core. Results are presented for two very different regimes: a low-Reynolds-number case where the incoming boundary layer is laminar and its momentum thickness is small compared to the cell opening, and a moderately high-Reynolds-number case, where the incoming boundary layer is turbulent and the ratio between the momentum thickness and the opening length is significantly larger than in the first case. Implications of the present findings to flow control applications of trapped vortex cells are also discussed.

  2. River Flow Regimes and Effective Discharge

    NASA Astrophysics Data System (ADS)

    Basso, S.; Sprocati, R.; Frascati, A.; Marani, M.; Schirmer, M.; Botter, G.

    2015-12-01

    The concept of effective discharge is widespread in geomorphology and river engineering and restoration. For example, it is used to design the most stable channel configuration, to estimate sedimentation rate and lifespan of reservoirs and to characterize the hydrologic forcing in models studying long-term evolution of rivers. Accordingly, the effective discharge has been the focus of countless empirical, theoretical and numerical studies, which found it to vary among catchments as a function of climate, landscape and river morphology, type of transport (dissolved, suspended or bedload), and of streamflow variability. The heterogeneity of the effective discharge values observed in different catchments challenges a thorough understanding of its pivotal drivers, and a consistent framework which explains observations carried out in different geographic areas is still lacking. In the present work, the observed diversity is explained in terms of the underlying heterogeneity of river flow regimes, by linking effective discharge to attributes of the sediment rating curve and to streamflow variability, as resulting from climatic and landscape drivers. An analytic expression of the effective ratio (i.e. the ratio between effective discharge and mean streamflow) is provided, which captures observed values of effective discharge for suspended sediment transport in a set of catchments of the continental United States. The framework disentangles hydrologic and landscape controls on effective discharge, and highlights distinct effective ratios of persistent and erratic hydrologic regimes (respectively characterized by low and high flow variability), attributable to intrinsically different streamflow dynamics. Clusters of river catchments characterized by similar streamflow dynamics can be identified. The framework provides an opportunity for first-order estimates of effective discharge in rivers belonging to different areas, based on the type of flow regime.

  3. The relationship between void waves and flow regime transition

    SciTech Connect

    Lahey, R.T. Jr.; Drew, D.A.; Kalkach-Navarro, S.; Park, J.W.

    1992-12-31

    The results of an extensive experimental and analytical study on the relationship between void waves and flow regime transition are presented, in particular, the bubbly/slug flow regime transition. It is shown that void wave instability signals a flow regime transition.

  4. Formation damage effects on horizontal-well flow efficiency

    SciTech Connect

    Renard, G.; Dupuy, J.M. )

    1991-07-01

    Wellbore damage commonly is accounted for by an apparent skin factor. A better relative index for determining the efficiency with which a well has been drilled and completed is the flow efficiency, the ration of a well's actual PI to ideal PI. The flow efficiency of horizontal wells is derived assuming steady-state flow of an incompressible fluid in a homogeneous, anisotropic medium. A comparison between the flow efficiencies of vertical and horizontal wells indicates that permeability reduction around the wellbore is less detrimental to horizontal wells. This paper shows that the effect of damage around a horizontal wellbore is reduced slightly by increasing the well length. Conversely, if the vertical permeability is less than the horizontal permeability, the anisotropy ratio, {radical} k{sub H}/k{sub V}, magnifies the influence of formation damage near the horizontal wellbore. Examples of flow efficiency calculations assuming a formation damage or a formation collapse around a liner in poorly consolidated formations are provided for horizontal and vertical wells.

  5. A criterion for the onset of slugging in horizontal stratified air-water countercurrent flow

    SciTech Connect

    Chun, Moon-Hyun; Lee, Byung-Ryung; Kim, Yang-Seok

    1995-09-01

    This paper presents an experimental and theoretical investigation of wave height and transition criterion from wavy to slug flow in horizontal air-water countercurrent stratified flow conditions. A theoretical formula for the wave height in a stratified wavy flow regime has been developed using the concept of total energy balance over a wave crest to consider the shear stress acting on the interface of two fluids. From the limiting condition of the formula for the wave height, a necessary criterion for transition from a stratified wavy flow to a slug flow has been derived. A series of experiments have been conducted changing the non-dimensional water depth and the flow rates of air in a horizontal pipe and a duct. Comparisons between the measured data and the predictions of the present theory show that the agreement is within {plus_minus}8%.

  6. SATURATED-SUBCOOLED STRATIFIED FLOW IN HORIZONTAL PIPES

    SciTech Connect

    Richard Schultz

    2010-08-01

    Advanced light water reactor systems are designed to use passive emergency core cooling systems with horizontal pipes that provide highly subcooled water from water storage tanks or passive heat exchangers to the reactor vessel core under accident conditions. Because passive systems are driven by density gradients, the horizontal pipes often do not flow full and thus have a free surface that is exposed to saturated steam and stratified flow is present.

  7. Online recognition of the multiphase flow regime and study of slug flow in pipeline

    NASA Astrophysics Data System (ADS)

    Liejin, Guo; Bofeng, Bai; Liang, Zhao; Xin, Wang; Hanyang, Gu

    2009-02-01

    Multiphase flow is the phenomenon existing widely in nature, daily life, as well as petroleum and chemical engineering industrial fields. The interface structure among multiphase and their movement are complicated, which distribute random and heterogeneously in the spatial and temporal scales and have multivalue of the flow structure and state[1]. Flow regime is defined as the macro feature about the multiphase interface structure and its distribution, which is an important feature to describe multiphase flow. The energy and mass transport mechanism differ much for each flow regimes. It is necessary to solve the flow regime recognition to get a clear understanding of the physical phenomena and their mechanism of multiphase flow. And the flow regime is one of the main factors affecting the online measurement accuracy of phase fraction, flow rate and other phase parameters. Therefore, it is of great scientific and technological importance to develop new principles and methods of multiphase flow regime online recognition, and of great industrial background. In this paper, the key reasons that the present method cannot be used to solve the industrial multiphase flow pattern recognition are clarified firstly. Then the prerequisite to realize the online recognition of multiphase flow regime is analyzed, and the recognition rules for partial flow pattern are obtained based on the massive experimental data. The standard templates for every flow regime feature are calculated with self-organization cluster algorithm. The multi-sensor data fusion method is proposed to realize the online recognition of multiphase flow regime with the pressure and differential pressure signals, which overcomes the severe influence of fluid flow velocity and the oil fraction on the recognition. The online recognition method is tested in the practice, which has less than 10 percent measurement error. The method takes advantages of high confidence, good fault tolerance and less requirement of

  8. Cluster analysis of multiple planetary flow regimes

    NASA Technical Reports Server (NTRS)

    Mo, Kingtse; Ghil, Michael

    1987-01-01

    A modified cluster analysis method was developed to identify spatial patterns of planetary flow regimes, and to study transitions between them. This method was applied first to a simple deterministic model and second to Northern Hemisphere (NH) 500 mb data. The dynamical model is governed by the fully-nonlinear, equivalent-barotropic vorticity equation on the sphere. Clusters of point in the model's phase space are associated with either a few persistent or with many transient events. Two stationary clusters have patterns similar to unstable stationary model solutions, zonal, or blocked. Transient clusters of wave trains serve as way stations between the stationary ones. For the NH data, cluster analysis was performed in the subspace of the first seven empirical orthogonal functions (EOFs). Stationary clusters are found in the low-frequency band of more than 10 days, and transient clusters in the bandpass frequency window between 2.5 and 6 days. In the low-frequency band three pairs of clusters determine, respectively, EOFs 1, 2, and 3. They exhibit well-known regional features, such as blocking, the Pacific/North American (PNA) pattern and wave trains. Both model and low-pass data show strong bimodality. Clusters in the bandpass window show wave-train patterns in the two jet exit regions. They are related, as in the model, to transitions between stationary clusters.

  9. Two-phase flow in horizontal pipes

    SciTech Connect

    Maeder, P.F.; Michaelides, E.E.; DiPippo, R.

    1981-09-01

    A method is developed in this paper which calculates the two-phase flow friction factor at any state of the fluid in the pipe. The mixing-length theory was employed for the calculation of the Reynolds stresses in turbulent two-phase flow. The friction factors obtained this way are in good agreement with experimental data. It is clear that the choice of the parameter m, or the density distribution, is rather arbitrary. Careful experimentation is required to refine the analysis given in this study, and in particular to provide guidance in the proper selection of the parameter m.

  10. Horizontal Information Flow in Spoken Sentence Production

    ERIC Educational Resources Information Center

    Smith, Mark; Wheeldon, Linda

    2004-01-01

    In 4 experiments the authors used a variant of the picture-word interference paradigm to investigate whether there is a temporal overlap in the activation of words during sentence production and whether there is a flow of semantic and phonological information between them. Experiments 1 and 2 demonstrate that 2 semantically related nouns produce…

  11. Flow regimes in a single dimple on the channel surface

    NASA Astrophysics Data System (ADS)

    Kovalenko, G. V.; Terekhov, V. I.; Khalatov, A. A.

    2010-12-01

    The boundaries of the domains of existence of flow regimes past single dimples made as spherical segments on a flat plate are determined with the use of available experimental results. Regimes of a diffuser-confuser flow, a horseshoe vortex, and a tornado-like vortex in the dimple are considered. Neither a horseshoe vortex nor a tornado-like vortex is observed in dimples with the relative depth smaller than 0.1. Transformations from the diffuser-confuser flow regime to the horseshoe vortex regime and from the horseshoe vortex flow to the tornado-like vortex flow are found to depend not only on the Reynolds number, but also on the relative depth of the spherical segment. Dependences for determining the boundaries of the regime existence domains are proposed, and parameters at which the experimental results can be generalized are given.

  12. Regular flow reversals in Rayleigh-Bénard convection in a horizontal magnetic field.

    PubMed

    Tasaka, Yuji; Igaki, Kazuto; Yanagisawa, Takatoshi; Vogt, Tobias; Zuerner, Till; Eckert, Sven

    2016-04-01

    Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two-dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q. We explored convection regimes in a parameter range, at 2×10^{3}regime diagram provided by Yanagisawa et al. [T. Yanagisawa et al., Phys. Rev. E 88, 063020 (2013)PLEEE81539-375510.1103/PhysRevE.88.063020]. Three regimes were identified, of which the regime of regular flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra/Q=10, where irregular flow reversals were observed in Yanagisawa et al. We performed the proper orthogonal decomposition (POD) analysis on the spatiotemporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a four-roll state in a dominant five-roll state. The POD analysis also provides the definition of the effective number of rolls as a more objective approach. PMID:27176392

  13. Regular flow reversals in Rayleigh-Bénard convection in a horizontal magnetic field

    NASA Astrophysics Data System (ADS)

    Tasaka, Yuji; Igaki, Kazuto; Yanagisawa, Takatoshi; Vogt, Tobias; Zuerner, Till; Eckert, Sven

    2016-04-01

    Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two-dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q . We explored convection regimes in a parameter range, at 2 ×103regime diagram provided by Yanagisawa et al. [T. Yanagisawa et al., Phys. Rev. E 88, 063020 (2013), 10.1103/PhysRevE.88.063020]. Three regimes were identified, of which the regime of regular flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra /Q =10 , where irregular flow reversals were observed in Yanagisawa et al. We performed the proper orthogonal decomposition (POD) analysis on the spatiotemporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a four-roll state in a dominant five-roll state. The POD analysis also provides the definition of the effective number of rolls as a more objective approach.

  14. Regular flow reversals in Rayleigh-Bénard convection in a horizontal magnetic field.

    PubMed

    Tasaka, Yuji; Igaki, Kazuto; Yanagisawa, Takatoshi; Vogt, Tobias; Zuerner, Till; Eckert, Sven

    2016-04-01

    Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two-dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q. We explored convection regimes in a parameter range, at 2×10^{3}regime diagram provided by Yanagisawa et al. [T. Yanagisawa et al., Phys. Rev. E 88, 063020 (2013)PLEEE81539-375510.1103/PhysRevE.88.063020]. Three regimes were identified, of which the regime of regular flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra/Q=10, where irregular flow reversals were observed in Yanagisawa et al. We performed the proper orthogonal decomposition (POD) analysis on the spatiotemporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a four-roll state in a dominant five-roll state. The POD analysis also provides the definition of the effective number of rolls as a more objective approach.

  15. Estuarine versus transient flow regimes in Juan de Fuca Strait

    NASA Astrophysics Data System (ADS)

    Thomson, Richard E.; MiháLy, Steven F.; Kulikov, Evgueni A.

    2007-09-01

    Residual currents in Juan de Fuca Strait are observed to switch between two fundamental states: estuarine and transient. The estuarine regime, which prevails roughly 90% of the time in summer and 55% of the time in winter, has a fortnightly modulated, three-layer structure characterized by strong (˜50 cm s-1) outflow above 60 ± 15 m depth, moderate (˜25 cm s-1) inflow between 60 and 125 m depth, and weak (˜10 cm s-1) inflow below 125 ± 10 m depth. Rotation increases the upper layer depth by 40 m on the northern side of the channel and upwelling-favorable coastal winds augment inflow in the bottom layer by as much as 5 cm s-1. Rotation, combined with modulation of the estuarine currents by tidal mixing in the eastern strait, leads to fortnightly variability in the along-channel velocity and cross-channel positioning of the core flow regions. Transient flows, which occur roughly 10% of the time in summer and 45% of the time in winter, are rapidly evolving, horizontally and vertically sheared "reversals" in the estuarine circulation generated during poleward wind events along the outer coast. Major events can persist for several weeks, force a net inward transport, and give rise to an O(10) km wide, surface-intensified, O(100) cm s-1 inflow along the southern (Olympic Peninsula) boundary of the strait. This "Olympic Peninsula Countercurrent" is typically accompanied by an abrupt decrease in salinity, indicating that it is a buoyancy flow originating with low-density water on the northern Washington shelf.

  16. On chaotic flow regimes in a rotating spherical layer

    NASA Astrophysics Data System (ADS)

    Zhilenko, D. Yu.; Krivonosova, O. É.; Nikitin, N. V.

    2008-12-01

    We present results of an experimental investigation and numerical simulations of chaotic flow regimes in a layer of a viscous incompressible fluid confined between counter-rotating spherical boundaries. The turbulent flow velocity pulsation profiles obtained by straightforward calculations are qualitatively similar to the analogous profiles known for a flat mixing layer. At the boundaries of their formation, chaotic flow regimes are characterized by a continuous spectrum of velocity pulsations and a high correlation dimension ( D > 8), in contrast to the chaotic regimes observed in an analogous layer with one (inner) rotating boundary.

  17. Rheological equations in asymptotic regimes of granular flow

    USGS Publications Warehouse

    Chen, C.-L.; Ling, C.-H.

    1998-01-01

    This paper assesses the validity of the generalized viscoplastic fluid (GVF) model in light of the established constitutive relations in two asymptotic flow regimes, namely, the macroviscous and grain-inertia regimes. A comprehensive review of the literature on constitutive relations in both regimes reveals that except for some material constants, such as the coefficient of restitution, the normalized shear stress in both regimes varies only with the grain concentration, C. It is found that Krieger-Dougherty's relative viscosity, ??*(C), is sufficiently coherent among the monotonically nondecreasing functions of C used in describing the variation of the shear stress with C in both regimes. It not only accurately represents the C-dependent relative viscosity of a suspension in the macroviscous regime, but also plays a role of the radial distribution function that describes the statistics of particle collisions in the grain-inertia regime. Use of ??*(C) alone, however, cannot link the two regimes. Another parameter, the shear-rate number, N, is needed in modelling the rheology of neutrally buoyant granular flows in transition between the two asymptotic regimes. The GVF model proves compatible with most established relations in both regimes.

  18. DIVERGENT HORIZONTAL SUB-SURFACE FLOWS WITHIN ACTIVE REGION 11158

    SciTech Connect

    Jain, Kiran; Tripathy, S. C.; Hill, F. E-mail: stripathy@nso.edu

    2015-07-20

    We measure the horizontal subsurface flow in a fast emerging active region (AR; NOAA 11158) using the ring-diagram technique and the Helioseismic and Magnetic Imager high spatial resolution Dopplergrams. This AR had a complex magnetic structure and displayed significant changes in morphology during its disk passage. Over a period of six days from 2011 February 11 to 16, the temporal variation in the magnitude of the total velocity is found to follow the trend of magnetic field strength. We further analyze regions of individual magnetic polarity within AR 11158 and find that the horizontal velocity components in these sub-regions have significant variation with time and depth. The leading and trailing polarity regions move faster than the mixed-polarity region. Furthermore, both zonal and meridional components have opposite signs for trailing and leading polarity regions at all depths showing divergent flows within the AR. We also find a sharp decrease in the magnitude of total horizontal velocity in deeper layers around major flares. It is suggested that the re-organization of magnetic fields during flares, combined with the sunspot rotation, decreases the magnitude of horizontal flows or that the flow kinetic energy has been converted into the energy released by flares. After the decline in flare activity and sunspot rotation, the flows tend to follow the pattern of magnetic activity. We also observe less variation in the velocity components near the surface but these tend to increase with depth, further demonstrating that the deeper layers are more affected by the topology of ARs.

  19. On the prediction of horizontal bubbly flows using the interfacial area transport equation

    SciTech Connect

    Talley, J. D.; Kim, S.

    2012-07-01

    To solve the two-fluid model utilized in current nuclear reactor system analysis codes, the interfacial area concentration (a i) is estimated through flow regime dependent correlations that rely on static regime transition criteria. This approach does not capture the continuous evolution of the interfacial structures, and thus, it can pose numerical issues near the transition boundaries. The interfacial area transport equation (IATE) can help address these shortcomings by providing a dynamic prediction of a a{sub i} through mechanistic source and sink terms that account for bubble coalescence and breakup. Most of the previous work for this approach has focused on vertical two-phase flow. However, relatively few studies have been performed for horizontal two-phase flows, where buoyancy strongly affects the phase distribution. To develop a one-dimensional, area-averaged form of the IATE for adiabatic, horizontal bubbly flows the following considerations are necessary: (1) pressure drop estimation, (2) bubble velocity/void fraction estimation, (3) determination of bubble interaction mechanisms, and (4) treatment of the asymmetric phase distribution. In the current work, treatment of the asymmetric phase distribution is presented. (authors)

  20. Predictive mapping of the natural flow regimes of France

    NASA Astrophysics Data System (ADS)

    Snelder, Ton H.; Lamouroux, Nicolas; Leathwick, John R.; Pella, Hervé; Sauquet, Eric; Shankar, Ude

    2009-06-01

    SummaryHydrologic variability is important in sustaining a variety of ecological processes in streams and rivers. Natural flow regime classifications group streams and rivers that are relatively homogeneous with respect to flow variability and have been promoted as a method of defining units for management of river flows. Although there has been considerable interest in classifying natural flow regimes, there has been less emphasis given to developing accurate methods of extrapolating these classifications to locations without flow data. We developed a method of mapping flow regime classes using boosted regression trees (BRT) that automatically fits non-linear functions and interactions between explanatory variables of flow regimes, both of which can be expected when comparing responses between complex systems such as watersheds. A natural flow regimes classification of continental France was developed from cluster analysis of 157 hydrological indices derived from 763 gauging stations representing unmodified flows. BRT models were used to predict the likelihood of gauging stations belonging to each class based on the watershed characteristics. These models were used to extrapolate the natural flow regime classification to all segments of a national river network. The performance of the BRT models were compared with other methods of assigning locations to flow regime classes, including the use of geographically contiguous regions, linear discriminant analysis (LDA) and classification and regression trees (CART). The "fitted" misclassification rate (associated with model fits) for assignment based on the BRT models was 13% whereas the fitted misclassification rates for geographically contiguous regions, LDA and CART were 52%, 44% and 39% respectively. A "predictive" misclassification rate (calculated for new cases) was estimated for assignments based on the BRT, LDA and CART models using cross validation analysis. For assignment based on the BRT models, the mean

  1. SPRITE MRI of bubbly flow in a horizontal pipe.

    PubMed

    Sankey, Mark; Yang, Zhi; Gladden, Lynn; Johns, Michael L; Lister, Derek; Newling, Benedict

    2009-08-01

    Bubble flow is characterised by numerous phase interfaces and turbulence, leading to fast magnetic resonance signal decay and artefacts in spin-warp imaging. In this paper, the SPRITE MRI pulse sequence, with its potential for very short encoding times, is demonstrated as an ideal technique for studying such dynamic systems. It has been used to acquire liquid velocity and relative intensity maps of two-phase gas-liquid dispersed bubble flow in a horizontal pipe at a liquid Reynolds number of 14,500. The fluids were air and water and a turbulence grid was used to generate a dispersed bubble flow pattern. The SPRITE technique shows promise for future research in gas-liquid flow. PMID:19481190

  2. River flow regimes and vegetation dynamics along a river transect

    NASA Astrophysics Data System (ADS)

    Doulatyari, Behnam; Basso, Stefano; Schirmer, Mario; Botter, Gianluca

    2014-11-01

    Ecohydrological processes occurring within fluvial landscapes are strongly affected by natural streamflow variability. In this work the patterns of vegetation biomass in two rivers characterized by contrasting flow regimes were investigated by means of a comprehensive stochastic model which explicitly couples catchment-scale hydroclimatic processes, morphologic attributes of the river transect and in-stream bio-ecological features. The hydrologic forcing is characterized by the probability distribution (pdf) of streamflows and stages resulting from stochastic precipitation dynamics, rainfall-runoff transformation and reach scale morphologic attributes. The model proved able to reproduce the observed pdf of river flows and stages, as well as the pattern of exposure/inundation along the river transect in both regimes. Our results suggest that in persistent regimes characterized by reduced streamflow variability, mean vegetation biomass is chiefly controlled by the pattern of groundwater availability along the transect, leading to a marked transition between aquatic and terrestrial environments. Conversely, erratic regimes ensure wider aquatic-terrestrial zones in which optimal elevation ranges for species with different sensitivity to flooding and access to groundwater are separated. Patterns of mean biomass in erratic regimes were found to be more sensitive to changes in the underlying hydroclimatic conditions, notwithstanding the reduced responsiveness of the corresponding flow regimes. The framework developed highlights the important role played by streamflow regimes in shaping riverine environments, and may eventually contribute to identifying the influence of landscape, climate and morphologic features on in-stream ecological dynamics.

  3. Horizontal flow and capillarity-driven redistribution in porous media.

    PubMed

    Doster, F; Hönig, O; Hilfer, R

    2012-07-01

    A recent macroscopic mixture theory for two-phase immiscible displacement in porous media has introduced percolating and nonpercolating phases. Quasi-analytic solutions are computed and compared to the traditional theory. The solutions illustrate physical insights and effects due to spatiotemporal changes of nonpercolating phases, and they highlight the differences from traditional theory. Two initial and boundary value problems are solved in one spatial dimension. In the first problem a fluid is displaced by another fluid in a horizontal homogeneous porous medium. The displacing fluid is injected with a flow rate that keeps the saturation constant at the injection point. In the second problem a horizontal homogeneous porous medium is considered which is divided into two subdomains with different but constant initial saturations. Capillary forces lead to a redistribution of the fluids. Errors in the literature are reported and corrected.

  4. Early regimes of water capillary flow in slit silica nanochannels.

    PubMed

    Oyarzua, Elton; Walther, Jens H; Mejía, Andrés; Zambrano, Harvey A

    2015-06-14

    Molecular dynamics simulations are conducted to investigate the initial stages of spontaneous imbibition of water in slit silica nanochannels surrounded by air. An analysis is performed for the effects of nanoscopic confinement, initial conditions of liquid uptake and air pressurization on the dynamics of capillary filling. The results indicate that the nanoscale imbibition process is divided into three main flow regimes: an initial regime where the capillary force is balanced only by the inertial drag and characterized by a constant velocity and a plug flow profile. In this regime, the meniscus formation process plays a central role in the imbibition rate. Thereafter, a transitional regime takes place, in which, the force balance has significant contributions from both inertia and viscous friction. Subsequently, a regime wherein viscous forces dominate the capillary force balance is attained. Flow velocity profiles identify the passage from an inviscid flow to a developing Poiseuille flow. Gas density profiles ahead of the capillary front indicate a transient accumulation of air on the advancing meniscus. Furthermore, slower capillary filling rates computed for higher air pressures reveal a significant retarding effect of the gas displaced by the advancing meniscus.

  5. DYNAMIC MODELING STRATEGY FOR FLOW REGIME TRANSITION IN GAS-LIQUID TWO-PHASE FLOWS

    SciTech Connect

    X. Wang; X. Sun; H. Zhao

    2011-09-01

    In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in

  6. Temporal evolution of flow regimes in urbanizing basins

    NASA Astrophysics Data System (ADS)

    Mejia, A.; Rossel, F.; Gironas, J. A.; Jovanovic, T.

    2014-12-01

    We characterize the temporal evolution of the flow regime of urbanizing basins. By urbanizing basins, we mean basins that have experienced urban growth during their observation period. To represent the flow regime, we use flow duration curves (FDCs). We compute the FDCs using a stochastic model of daily streamflow for urban basins. In this case, the model aids in discerning the influence of key factors (e.g., climate, land use change, stormwater managenment conditions, and the slow and fast properties of the hydrologic response) on streamflow. To implement the model, we first divide the complete observation period of a given urban basin into intervals of equal duration, e.g. 5 years. Subsequently, we apply the model to each interval and this is how we capture the influence of land use changes and climatic fluctuations on the flow regime. We apply this modeling framework to 14 urbanizing basins in the Baltimore-Washington DC region. Results from this application indicate consistent changes in the temporal evolution of the altered flow regimes, which can largely be explained by the progressive redistribution with urban growth of water from slow subsurface runoff and evapotranspiration to fast urban runoff. We also use the modeling framework to determine indicators of ecohydrological alteration for urbanizing basins. The application of these indicators to our study area suggests that the flow regime is sensitive to alterations up to a certain level of urbanization after which sensitivity seems to level off. The flow regime also seems to be relatively more resistant to alterations for both the smaller and larger levels of urbanization considered. In the future, we would like to extend the application of the proposed modeling framework to other metropolitan areas.

  7. Microgravity Flow Regime Data: Buoyancy and Mixing Apparatus Effects

    NASA Astrophysics Data System (ADS)

    Shephard, Adam; Best, Frederick

    2010-01-01

    Zero-g two-phase flow data set qualification and flight experiment design have not been standardized and as a result, agreement among researchers has not been reached regarding what experimental conditions adequately approximate those of microgravity. The effects of buoyancy forces and mixing apparatus on the flow regime transitions are presented in this study. The gravity conditions onboard zero-g aircraft are at best 10-3 g which is used to approximate the 10-5 g conditions of microgravity, thus the buoyancy forces present on zero-g aircraft can become significantly large and unrepresentative of microgravity. When buoyancy forces approach those of surface tension forces, buoyancy induced coalescence occurs. When discussing flow regime transitions, these large buoyancy forces lead to flow regime transitions which otherwise would not occur. The buoyancy attributes of the two-phase flow data sets available in the literature are evaluated to determine which data sets exhibit buoyancy induced transitions. Upon comparison of the representative data sets, the affects of different mixing apparatus can be seen in the superficial velocity flow regime maps.

  8. Direct numerical simulation of interfacial wave generation in turbulent gas-liquid flows in horizontal channels

    NASA Astrophysics Data System (ADS)

    Campbell, Bryce; Hendrickson, Kelli; Liu, Yuming; Subramani, Hariprasad

    2014-11-01

    For gas-liquid flows through pipes and channels, a flow regime (referred to as slug flow) may occur when waves form at the interface of a stratified flow and grow until they bridge the pipe diameter trapping large elongated gas bubbles within the liquid. Slug formation is often accompanied by strong nonlinear wave-wave interactions, wave breaking, and gas entrainment. This work numerically investigates the fully nonlinear interfacial evolution of a two-phase density/viscosity stratified flow through a horizontal channel. A Navier-Stokes flow solver coupled with a conservative volume-of-fluid algorithm is use to carry out high resolution three-dimensional simulations of a turbulent gas flowing over laminar (or turbulent) liquid layers. The analysis of such flows over a range of gas and liquid Reynolds numbers permits the characterization of the interfacial stresses and turbulent flow statistics allowing for the development of physics-based models that approximate the coupled interfacial-turbulent interactions and supplement the heuristic models built into existing industrial slug simulators.

  9. Experimental investigation of ice slurry flow pressure drop in horizontal tubes

    SciTech Connect

    Grozdek, Marino; Khodabandeh, Rahmatollah; Lundqvist, Per

    2009-01-15

    Pressure drop behaviour of ice slurry based on ethanol-water mixture in circular horizontal tubes has been experimentally investigated. The secondary fluid was prepared by mixing ethyl alcohol and water to obtain initial alcohol concentration of 10.3% (initial freezing temperature -4.4 C). The pressure drop tests were conducted to cover laminar and slightly turbulent flow with ice mass fraction varying from 0% to 30% depending on test conditions. Results from flow tests reveal much higher pressure drop for higher ice concentrations and higher velocities in comparison to the single phase flow. However for ice concentrations of 15% and higher, certain velocity exists at which ice slurry pressure drop is same or even lower than for single phase flow. It seems that higher ice concentration delay flow pattern transition moment (from laminar to turbulent) toward higher velocities. In addition experimental results for pressure drop were compared to the analytical results, based on Poiseulle and Buckingham-Reiner models for laminar flow, Blasius, Darby and Melson, Dodge and Metzner, Steffe and Tomita for turbulent region and general correlation of Kitanovski which is valid for both flow regimes. For laminar flow and low buoyancy numbers Buckingham-Reiner method gives good agreement with experimental results while for turbulent flow best fit is provided with Dodge-Metzner and Tomita methods. Furthermore, for transport purposes it has been shown that ice mass fraction of 20% offers best ratio of ice slurry transport capability and required pumping power. (author)

  10. Steady particulate flows in a horizontal rotating cylinder

    NASA Astrophysics Data System (ADS)

    Yamane, K.; Nakagawa, M.; Altobelli, S. A.; Tanaka, T.; Tsuji, Y.

    1998-06-01

    Results of discrete element method (DEM) simulation and magnetic resonance imaging (MRI) experiments are compared for monodisperse granular materials flowing in a half-filled horizontal rotating cylinder. Because opacity is not a problem for MRI, a long cylinder with an aspect ratio ˜7 was used and the flow in a thin transverse slice near the center was studied. The particles were mustard seeds and the ratio of cylinder diameter to particle diameter was approximately 50. The parameters compared were dynamic angle of repose, velocity field in a plane perpendicular to the cylinder axis, and velocity fluctuations at rotation rates up to 30 rpm. The agreement between DEM and MRI was good when the friction coefficient and nonsphericity were adjusted in the simulation for the best fit.

  11. Analysis of horizontal flows in the solar granulation

    NASA Astrophysics Data System (ADS)

    Quintero Noda, C.; Shimizu, T.; Suematsu, Y.

    2016-04-01

    Solar limb observations sometimes reveal the presence of a satellite lobe in the blue wing of the Stokes I profile from pixels belonging to granules. The presence of this satellite lobe has been associated in the past to strong line-of-sight gradients and, as the line-of-sight component is almost parallel to the solar surface, to horizontal granular flows. We aim to increase the knowledge about these horizontal flows studying a spectropolarimetric observation of the north solar pole. We will make use of two state of the art techniques, the spatial deconvolution procedure that increases the quality of the data removing the stray light contamination, and spectropolarimetric inversions that will provide the vertical stratification of the atmospheric physical parameters where the observed spectral lines form. We inverted the Stokes profiles using a two component configuration, obtaining that one component is strongly blueshifted and displays a temperature enhancement at upper photospheric layers while the second component has low redshifted velocities and it is cool at upper layers. In addition, we examined a large number of cases located at different heliocentric angles, finding smaller velocities as we move from the centre to the edge of the granule. Moreover, the height location of the enhancement on the temperature stratification of the blueshifted component also evolves with the spatial location on the granule being positioned on lower heights as we move to the periphery of the granular structure.

  12. Model for sweet corrosion in horizontal multiphase slug flow

    SciTech Connect

    Jepson, W.P.; Stitzel, S.; Kang, C.; Gopal, M.

    1997-08-01

    A model has been developed that can predict the corrosion rate in horizontal slug flows. The effect of the slug frequency and oil type on corrosion rate have been included. The model has been compared to experimental data, and, to the model and field data of Gunaltun (1996). For all conditions, the corrosion rate increased with increase in slug frequency until a maximum in corrosion rate is reached at approximately 35 slugs/minute. At 60 C, the model compares well with that of Gunaltun (1996) if a slug frequency of 10 to 12 is used. For 80 C, the Gunaltun model is in good agreement if a frequency of 1 slug/minute is used. His model does not include a term that predicts a maximum in the corrosion rate between 60 and 80 C. This has not been noticed in this laboratory for slug flows. For horizontal pipelines, field data suggests that, the slug frequency is usually in the range of 1 to 20 slugs/minute, depending on the liquid velocity. When the pipe is inclined, the slug frequency can increase to values much greater than these and this may lead to higher levels of corrosion. The oil type is accounted for using the suggestion of Efird (1989) based on the product of oil acid number and % nitrogen. When this relation is used, the results compare very well with those of Efird for the oils he studied.

  13. Stability of stratified two-phase flows in horizontal channels

    NASA Astrophysics Data System (ADS)

    Barmak, I.; Gelfgat, A.; Vitoshkin, H.; Ullmann, A.; Brauner, N.

    2016-04-01

    Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems, the stratified flow with a smooth interface is stable only in confined zone of relatively low flow rates, which is in agreement with experiments, but is not predicted by long-wave analysis. Depending on the flow conditions, the critical perturbations can originate mainly at the interface (so-called "interfacial modes of instability") or in the bulk of one of the phases (i.e., "shear modes"). The present analysis revealed that there is no definite correlation between the type of instability and the perturbation wavelength.

  14. The flow of slugs in horizontal, two-phase pipelines

    SciTech Connect

    Kouba, G.E. ); Jepson, W.P. . Dept. of Chemical Engineering)

    1990-03-01

    The flow characteristics in horizontal slug flow are studied experimentally in a 150-mm-dia pipeline. If a frame of reference is taken as moving with the translational velocity of the slug, measurements of the Froude number in the liquid film ahead of the slug were always greater than unity while the Froude number within the slug was in general less than unity. This illustrates a change in flow from super to subcritical flow and the presence of a hydraulic jump. Different types of flow are noticed using high-speed video equipment and these types closely resemble those reported by open-channel hydraulics tests. The distribution of gas in the slug body is only homogeneous at high-mixture velocities and the effect of buoyancy on the gas is more noticeable at low gas velocities. The liquid fraction in the slug is shown to be directly dependent on the Froude number in the liquid film. The ratio of the translational velocity of the slug to the mixture velocity decreases continuously from 2.0 at low-mixture velocities to 1.25 and a mixture velocity of approximately 3 m/s. After this point, it remains constant at 1.25.

  15. Pressure gradient phenomena during horizontal oil-water flow

    SciTech Connect

    Angeli, P.; Hewitt, G.F.

    1996-12-01

    Pressure gradients were measured during the cocurrent dispersed flow of oil (1.6 mPa viscosity) and water in two 1 inch nominal bore horizontal test sections made from stainless steel and acrylic resin. Measurements were made for mixture velocities above 1.1 m/s in the steel pipe and above 1.7 m/s in the acrylic pipe and up to 3.9 m/s, where fully dispersed flow exists (Angeli, 1996). Water volume fractions ranged from 5% to 85%, while phase inversion appeared between 37% and 40% water volume fraction in both pipes. Analysis of the results showed that the homogeneous model, where the mixture of the two fluids is treated as one pseudofluid with properly averaged physical properties, cannot satisfactorily predict the pressure gradients occurring during the dispersed flow. Pressure gradients increased suddenly at the phase inversion point, while the experimental friction factors, especially in the oil continuous flows, appeared to be lower than the predictions of the homogeneous model or sometimes even lower than the single phase oil and water flow friction factors.

  16. Determination of flow-regime boundaries for cohesive particles

    SciTech Connect

    Knowlton, T.M.; Findlay, J.G.

    1992-01-01

    The overall objective of this program is the development of a hydrodynamic model to predict the choking/non-choking flow regime boundary of fine, cohesive (i.e., Geldart Group C) powders. Specific objectives are to: (1) Develop a two-dimensional hydrodynamic model that can be applied to cohesive solids. (2) Generate large-scale solids-flows data that will be used to verify the model.

  17. Analytic expression for poloidal flow velocity in the banana regime

    SciTech Connect

    Taguchi, M.

    2013-01-15

    The poloidal flow velocity in the banana regime is calculated by improving the l = 1 approximation for the Fokker-Planck collision operator [M. Taguchi, Plasma Phys. Controlled Fusion 30, 1897 (1988)]. The obtained analytic expression for this flow, which can be used for general axisymmetric toroidal plasmas, agrees quite well with the recently calculated numerical results by Parker and Catto [Plasma Phys. Controlled Fusion 54, 085011 (2012)] in the full range of aspect ratio.

  18. Proper horizontal photospheric flows in a filament channel

    NASA Astrophysics Data System (ADS)

    Schmieder, B.; Roudier, T.; Mein, N.; Mein, P.; Malherbe, J. M.; Chandra, R.

    2014-04-01

    Context. An extended filament in the central part of the active region NOAA 11106 crossed the central meridian on Sept. 17, 2010 in the southern hemisphere. It has been observed in Hα with the THEMIS telescope in the Canary Islands and in 304 Å with the EUV imager (AIA) onboard the Solar Dynamic Observatory (SDO). Counterstreaming along the Hα threads and bright moving blobs (jets) along the 304 Å filament channel were observed during 10 h before the filament erupted at 17:03 UT. Aims: The aim of the paper is to understand the coupling between magnetic field and convection in filament channels and relate the horizontal photospheric motions to the activity of the filament. Methods: An analysis of the proper photospheric motions using SDO/HMI continuum images with the new version of the coherent structure tracking (CST) algorithm developed to track granules, as well as the large scale photospheric flows, was performed for three hours. Using corks, we derived the passive scalar points and produced a map of the cork distribution in the filament channel. Averaging the velocity vectors in the southern hemisphere in each latitude in steps of 3.5 arcsec, we defined a profile of the differential rotation. Results: Supergranules are clearly identified in the filament channel. Diverging flows inside the supergranules are similar in and out of the filament channel. Converging flows corresponding to the accumulation of corks are identified well around the Hα filament feet and at the edges of the EUV filament channel. At these convergence points, the horizontal photospheric velocity may reach 1 km s-1, but with a mean velocity of 0.35 km s-1. In some locations, horizontal flows crossing the channel are detected, indicating eventually large scale vorticity. Conclusions: The coupling between convection and magnetic field in the photosphere is relatively strong. The filament experienced the convection motions through its anchorage points with the photosphere, which are

  19. Nozzle Free Jet Flows Within the Strong Curved Shock Regime

    NASA Technical Reports Server (NTRS)

    Shih, Tso-Shin

    1975-01-01

    A study based on inviscid analysis was conducted to examine the flow field produced from a convergent-divergent nozzle when a strong curved shock occurs. It was found that a certain constraint is imposed on the flow solution of the problem which is the unique feature of the flow within this flow regime, and provides the reason why the inverse method of calculation cannot be employed for these problems. An approximate method was developed to calculate the flow field, and results were obtained for two-dimensional flows. Analysis and calculations were performed for flows with axial symmetry. It is shown that under certain conditions, the vorticity generated at the jet boundary may become infinite and the viscous effect becomes important. Under other conditions, the asymptotic free jet height as well as the corresponding shock geometry were determined.

  20. Intermittency of rheological regimes in uniform liquid-granular flows.

    PubMed

    Armanini, Aronne; Larcher, Michele; Fraccarollo, Luigi

    2009-05-01

    We present a detailed analysis of a free surface-saturated liquid-granular mixture flowing over a static loose bed of grains, where the coexistence of layers dominated by collisional and frictional interactions among particles was observed. Kinetic theory was applied to the flow described above and it proved suitable for describing a realistic behavior of the collisional layers, although it failed to interpret the regions of the flow domain dominated by the frictional contacts. The paper provides a conceptual scheme with which to overcome this problem by focusing on the mechanisms governing the transition from the frictional to the collisional regime. In particular we observed that in highly concentrated flows the transition layer exhibits a typical intermittency of the dominating rheological regime, switching alternately from the frictional to the collisional one. By filtering the velocity signal, we introduced an intermittency function that made it possible to extend the validity of the equations derived from dense gas analogy, typical of the collisional regimes, also in the intermittent phase of the flow. Owing to the small values of the Stokes number, in the application of the kinetic theory we accounted for the possible variation of the elastic restitution coefficient along the flow depth. PMID:19518448

  1. A Cahn-Hilliard framework for thin-film flows in the partial-wetting regime

    NASA Astrophysics Data System (ADS)

    Pahlavan, A. A.; Chen, M.; Cueto-Felgueroso, L.; McKinley, G. H.; Juanes, R.

    2014-12-01

    Traditional mathematical descriptions of multiphase flow in porous media rely on a multiphase extension of Darcy's law, and lead to nonlinear second-order (advection-diffusion) partial differential equations for fluid saturations. Here, we study horizontal redistribution of immiscible fluids. The traditional Darcy-flow model predicts that the spreading of a finite amount of liquid in a horizontal porous medium never stops; a prediction that is not substantiated by observation. To help guide the development of new models of multiphase flow in porous media [1], we draw an analogy with the flow of thin films. The flow of thin films over flat surfaces has been the subject of much theoretical, experimental and computational research [2]. Under the lubrication approximation, the classical mathematical model for these flows takes the form of a nonlinear fourth-order PDE, where the fourth-order term models the effect of surface tension [3]. This classical model, however, effectively assumes that the film is perfectly wetting to the substrate and, therefore, does not capture the partial wetting regime. Partial wetting is responsible for stopping the spread of a liquid puddle. Here, we present experiments of (large-volume) liquid spreading over a flat horizontal substrate in the partial wetting regime, and characterize the spreading regimes that we observe. We extend our previous theoretical work of two-phase flow in a capillary tube [4], and develop a macroscopic phase-field model of thin-film flows with partial wetting. Our model naturally accounts for the dynamic contact angle at the contact line, and therefore permits modeling thin-film flows without invoking a precursor film, leading to compactly-supported solutions that reproduce the spreading dynamics and the static equilibrium configuration observed in the experiments. We anticipate that this modeling approach will provide a natural mathematical framework to describe spreading and redistribution of immiscible fluids

  2. Characterization of flow regimes in the post-dryout region

    SciTech Connect

    Obot, N.T.; Ishii, M.

    1988-01-01

    A visual study of film boiling using photographic and high speed motion-picture methods was carried out to determine the flow regime transition criteria in the post-CHF region. An idealized inverted annular flow was obtained by introducing a liquid jet of Freon 113 through a nozzle, precisely centered with respect to the internal diameter of the test section, with an annual gas flow. The respective ranges for liquid and gas exit velocities were 0.05-0.5 and 0.03-8.2 m/s. Nitrogen and helium were used in the study.

  3. Regimes of axisymmetric flow in a rotating annulus with local convective forcing

    NASA Astrophysics Data System (ADS)

    Scolan, Helene; Su, Sylvie; Young, Roland M. B.; Read, Peter L.

    2015-11-01

    We present a numerical study of axisymmetric flows in a rotating annulus convectively forced by local thermal forcing via a heated annular ring at the bottom near the external wall and a cooled circular disk near the centre at the top surface. This new configuration is a variant of the classical thermally-driven annulus analogue of the atmosphere circulation, where thermal forcing was previously applied on the sidewalls. Two vertically and horizontally displaced heat sources/sinks are arranged so that, in the absence of rotation, statically unstable convection would be induced above the source and beneath the sink, thereby relaxing strong constraints placed on background temperature gradients in previous setup. By using the Met Office/ Oxford Rotating Annulus Laboratory code, we investigated a series of equilibrated, 2D axisymmetric flows for a large range of dimensionless parameters and characterized them in terms of velocity and temperature fields. Several distinct flow regimes were identified, depending upon the rotation rate and strength of differential heating. These regimes will be presented with reference to variations of horizontal Ekman layer thickness versus the thermal boundary layer thickness and corresponding scalings for various quantities such as the heat transport. Grants: EPSRC EP/K029428/1 and studentship Met Office/Oxford

  4. Dairy washwater treatment using a horizontal flow biofilm system.

    PubMed

    Rodgers, M; de Paor, D; Clifford, E

    2008-01-01

    In Ireland, dairy farmyard washwater commonly comprises farmyard run-off and dairy parlour washings. Land-spreading is the most widely used method for treating this wastewater. However, this method can be labour intensive and can cause, in some cases, the degradation of surface and ground waters, mainly due to nitrogen contamination. In this study, a horizontal flow biofilm reactor (HFBR) with step-feed was constructed and tested in the laboratory, to remove organic carbon and nitrogen from a agricultural strength synthetic washwater (SWW). The HFBR had an average top plan surface area (TPSA) of 0.1002 m(2) and consisted of a stack of 45 polystyrene horizontal sheets--15 sheets embedded with 25 mm deep frustums above 30 sheets with 10 mm deep frustums. The frustums acted as miniature reservoirs. The sheets were alternately offset to allow the wastewater to flow horizontally along each sheet and vertically from sheet to sheet down through the reactor. Biofilms developed on the sheets and treated the wastewater. During the 212-d study, the total hydraulic loading rate based on the TPSA of the sheets was 35 l m(-2) d(-1). SWW was pumped for 10 min each hour, in a step feed arrangement at a rate of 23.33 l m(-2) d(-1) on to the top sheet during Phases 1 and 2, and 11.67 l m(-2) d(-1) onto Sheet 16 during Phase 1 (days 1-92) and onto Sheet 30 during Phase 2 (days 93-212). The substrate loading rate during Phases 1 and 2 was 94.8 g total chemical oxygen demand (COD) m(-2) d(-1) and 10.5 g total nitrogen (TN) m(-2) d(-1), based on the TPSA. At steady state in Phase 2, the unit achieved excellent carbon removal of 99.7% 5-day biochemical oxygen demand (BOD(5)) and 96.7% total COD, equivalent to TPSA removal rates of 67.5 g BOD(5)m(-2)d(-1) and 91.7 g COD m(-2) d(-1). The nitrogen removal percentages were 98.3% total ammonium-nitrogen (NH(4)-N(t)) and 72.8% TN, which equated to TPSA removal rates of 4.8 g NH(4)-N(t) m(-2) d(-1) and 7.6g TN m(-2) d(-1). No sloughing of

  5. Classification of the stratified fluid flows regimes around a square cylinder

    NASA Astrophysics Data System (ADS)

    Gushchin, V. A.; Matyushin, P. V.

    2015-10-01

    The 2D density stratified (in vertical direction) viscous fluid flows around a square cylinder with diameter d (moving in horizontal direction with the velocity U) have been simulated on the basis of the Navier-Stokes equations in the Boussinesq approximation. For solving of the Navier-Stokes equations the Splitting on physical factors Method for Incompressible Fluid flows (SMIF) with hybrid explicit finite difference scheme (second-order accuracy in space, minimum scheme viscosity and dispersion, monotonous) has been used. The numerical method SMIF has been successfully applied for solving of the different problems: 2D and 3D separated homogeneous and stratified fluid flows around a sphere and a circular cylinder; the flows with free surface including regimes with broken surface wave; the air, heat and mass transfer in the clean rooms. At the present paper the original refined classification of 2D stratified viscous fluid flow regimes around a square cylinder at Re ≤ 200 has been obtained and the interesting fluid flows with two hanging vortices in the wake and with two wavy hanging sheets of density (connected with two hanging vortices) have been investigated in details at Fr = 0.1, Re = 50, where Re = U.d/ν is the Reynolds number, Fr = U/(N.d) is the internal Froude number, ν is the kinematical viscosity coefficient, N is the buoyancy frequency.

  6. Regimes of flow induced vibration for tandem, tethered cylinders

    NASA Astrophysics Data System (ADS)

    Nave, Gary; Stremler, Mark

    2015-11-01

    In the wake of a bluff body, there are a number of dynamic response regimes that exist for a trailing bluff body depending on spacing, structural restoring forces, and the mass-damping parameter m* ζ . For tandem cylinders with low values of m* ζ , two such regimes of motion are Gap Flow Switching and Wake Induced Vibration. In this study, we consider the dynamics of a single degree-of-freedom rigid cylinder in the wake of another in these regimes for a variety of center-to-center cylinder spacings (3-5 diameters) and Reynolds numbers (4,000-11,000). The system consists of a trailing cylinder constrained to a circular arc around a fixed leading cylinder, which, for small angle displacements, bears a close resemblance to the transversely oscillating cylinders found more commonly in existing literature. From experiments on this system, we compare and contrast the dynamic response within these two regimes. Our results show sustained oscillations in the absence of a structural restoring force in all cases, providing experimental support for the wake stiffness assumption, which is based on the mean lift toward the center line of flow.

  7. Particle seeding flow system for horizontal shock tube

    SciTech Connect

    Johnston, Stephen; Garcia, Nicolas J.; Martinez, Adam A.; Orlicz, Gregory C.; Prestridge, Katherine P.

    2012-08-01

    The Extreme Fluids Team in P-23, Physics Division, studies fluid dynamics at high speeds using high resolution diagnostics. The unsteady forces on a particle driven by a shock wave are not well understood, and they are difficult to model. A horizontal shock tube (HST) is being modified to collect data about the behavior of particles accelerated by shocks. The HST has been used previously for studies of Richtmyer-Meshkov instability using Planar Laser-Induced Fluorescence (PLIF) as well as Particle Image Velocimetry (PIV), diagnostics that measure density and velocity. The purpose of our project is to design a flow system that will introduce particles into the HST. The requirements for this particle flow system (PFS) are that it be non-intrusive, be able to introduce either solid or liquid particles, have an exhaust capability, not interfere with existing diagnostics, and couple with the existing HST components. In addition, the particles must flow through the tube in a uniform way. We met these design criteria by first drawing the existing shock tube and diagnostics and doing an initial design of the ducts for the PFS. We then estimated the losses through the particle flow system from friction and researched possible fans that could be used to drive the particles. Finally, the most challenging component of the design was the coupling to the HST. If we used large inlets, the shock would lose strength as it passed by the inlet, so we designed a novel coupling inlet and outlet that minimize the losses to the shock wave. Our design was reviewed by the Extreme Fluids Team, and it is now being manufactured and built based upon our technical drawings.

  8. Couette flow regimes with heat transfer in rarefied gas

    SciTech Connect

    Abramov, A. A. Butkovskii, A. V.

    2013-06-15

    Based on numerical solution of the Boltzmann equation by direct statistic simulation, the Couette flow with heat transfer is studied in a broad range of ratios of plate temperatures and Mach numbers of a moving plate. Flow regime classification by the form of the dependences of the energy flux and friction stress on the Knudsen number Kn is proposed. These dependences can be simultaneously monotonic and nonmonotonic and have maxima. Situations are possible in which the dependence of the energy flux transferred to a plate on Kn has a minimum, while the dependence of the friction stress is monotonic or even has a maximum. Also, regimes exist in which the dependence of the energy flux on Kn has a maximum, while the dependence of the friction stress is monotonic, and vice versa.

  9. Three-dimensional numerical simulations of three-phase slug flows in horizontal pipes

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Yang, Junfeng; Matar, Omar

    2015-11-01

    One of the most common flow regimes in pipelines is that of slug flow: slug bodies corresponding to alternating blocks of aerated liquid which bridge the pipe, separated by elongated bubbles; the latter ride atop a liquid layer. The slugs travel at velocities that exceed the mixture superficial velocity; this can potentially cause structural damage, particularly at pipe bends and junctions. Two-phase slug flows have received considerable attention in the literature both experimentally and computationally but there has been very little work carried out on three-phase slugging. In the present work, the evolution of oil-water-air three-phase slug flow in a horizontal cylindrical pipe is investigated using two-dimensional and three-dimensional computational fluid dynamics simulations. The parameters characterising three-phase slug flow, e.g. slug length, propagation velocity, and slug formation frequency, are determined for various gas and liquid superficial velocities for a given pipe geometry. The results of this work are compared to available experimental data and numerical solutions based on approximate, one-dimensional models relying on the use of empirical correlations. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.

  10. compartment transfer rates in horizontal flow constructed wetlands

    NASA Astrophysics Data System (ADS)

    Maier, Uli; Oswald, Sascha; Thullner, Martin; Grathwohl, Peter

    2010-05-01

    A conceptual computer model has been constructed to simulate the compartment transfer rates in horizontal flow constructed wetlands. The model accounts for flow and transport in the variably saturated porous medium as well as biogeochemical change reactions. The most concentrated contaminants such as BTEX, MTBE and gasoline hydrocarbons and dissolved as well as mineral phase electron acceptors are considered. Also of major interest are reduced species with high oxygen demand such as ammonium. The influence of marsh plants on microbial activity, gas transport, water balance and contaminant fate in general is matter of current investigation. The constructed wetlands consist of a coarse sand or fine gravel porous medium. Marsh plants were introduced after installation, however, a number of control basins are operated unplanted. Water levels and through flow rates are adjusted to optimize the remediation efficiency. The system is likely to be neither reaction nor mixing limited, thus both, values of dispersivity and degradation kinetics may be crucial for remediation efficiency. Biogeochemical modelling is able to delineate in detail (i) the zonation of processes, (ii) temporal variation (breakthrough curves) and (iii) mass balance information. The contributions of biodegradation and volatilisation and the influence of plants (compartment transfer) can generally best be evaluated by the component's mass balance. More efficient mixing is expected in the wetlands with open water body which leads to both, more biodegradation and volatilisation. An important task is to quantify the role of plants and root systems for contaminant attenuation in constructed wetlands. The long term goal of investigation is to allow for predictions for the design of large scale compartment transfer wetlands that may be applied to remediate the site as a whole.

  11. Response of the Patterson probe in the transition flow regime

    NASA Astrophysics Data System (ADS)

    Grabe, Martin

    2012-11-01

    The free-molecular impact pressure probe, also known as Patterson probe, is known and applied for more than half a century now to deduce the number flux of a single species in highly rarefied inert flow. While the working principle is conceptually simple, interpretation of the gauge readings may not be, but approximate formulas for evaluation exist. In the context of cold-gas plume flow and interaction experiments with the obvious large variations in Mach and Knudsen numbers, it may not be clear initially, whether the signals measured with the Patterson probe are obtained in free-molecular flow environment, and hence, whether the mentioned evaluation techniques may be employed. A series of numerical experiments have been conducted using the Direct Simulation Monte-Carlo method, to study the response of the Patterson probe to prescribed free-stream conditions in the transitional flow regime. From the computational results we infer analytical expressions that describe the probe response in transitional regime at zero angle of attack.

  12. Characterization of river flow fluctuations via horizontal visibility graphs

    NASA Astrophysics Data System (ADS)

    Braga, A. C.; Alves, L. G. A.; Costa, L. S.; Ribeiro, A. A.; de Jesus, M. M. A.; Tateishi, A. A.; Ribeiro, H. V.

    2016-02-01

    We report on a large-scale characterization of river discharges by employing the network framework of the horizontal visibility graph. By mapping daily time series from 141 different stations of 53 Brazilian rivers into complex networks, we present a useful approach for investigating the dynamics of river flows. We verified that the degree distributions of these networks were well described by exponential functions, where the characteristic exponents are almost always larger than the value obtained for random time series. The faster-than-random decay of the degree distributions is an another evidence that the fluctuation dynamics underlying the river discharges has a long-range correlated nature. We further investigated the evolution of the river discharges by tracking the values of the characteristic exponents (of the degree distribution) and the global clustering coefficients of the networks over the years. We show that the river discharges in several stations have evolved to become more or less correlated (and displaying more or less complex internal network structures) over the years, a behavior that could be related to changes in the climate system and other man-made phenomena.

  13. Linear stability of cylindrical Couette flow in the convection regime

    NASA Astrophysics Data System (ADS)

    Ali, Mohamed E.; McFadden, G. B.

    2005-05-01

    The instability of steady circular Couette flow with radial heating across a vertically oriented annulus with a rotating inner cylinder and a stationary outer cylinder is investigated using a linear stability analysis. The convection regime base flow is developed for an infinite aspect ratio geometry and constant fluid properties with buoyancy included through the Boussinesq approximation. The base flow is characterized by a dimensionless stratification parameter γ that is proportional to the vertical temperature gradient. Critical stability boundaries are calculated for this assumed base flow with respect to both toroidal and helical disturbances. The numerical investigation is primarily restricted to a radius ratio of 0.6 at a Prandtl number of 100. Critical stability boundaries in Taylor-Grashof number space are presented for two values of the stratification parameter γ (4 and 13). The results follow the development of critical stability from Taylor cells at small Grashof numbers up to a maximum Grashof number used in this calculation of 20 000 and 80 000 for γ =4 and 13, respectively. Results show that increasing the stratification parameter stabilizes the isothermal Taylor vortices, followed by a destabilization at higher azimuthal mode numbers (n>0). The results also show that for γ =4 (close to the conduction regime), two modes are obtained: one is axisymmetric and the other is nonaxisymmetric. However, for the convection regime (large γ) six asymmetric modes are obtained. Finally, the disturbance wavelength, phase speed, and spiral inclination angle are presented as a function of the critical Grashof number for the stratification parameters considered in this work.

  14. Modelling Air and Water Two-Phase Annular Flow in a Small Horizontal Pipe

    NASA Astrophysics Data System (ADS)

    Yao, Jun; Yao, Yufeng; Arini, Antonino; McIiwain, Stuart; Gordon, Timothy

    2016-06-01

    Numerical simulation using computational fluid dynamics (CFD) has been carried out to study air and water two-phase flow in a small horizontal pipe of an inner diameter of 8.8mm, in order to investigate unsteady flow pattern transition behaviours and underlying physical mechanisms. The surface liquid film thickness distributions, determined by either wavy or full annular flow regime, are shown in reasonable good agreement with available experimental data. It was demonstrated that CFD simulation was able to predict wavy flow structures accurately using two-phase flow sub-models embedded in ANSYS-Fluent solver of Eulerian-Eulerian framework, together with a user defined function subroutine ANWAVER-UDF. The flow transient behaviours from bubbly to annular flow patterns and the liquid film distributions revealed the presence of gas/liquid interferences between air and water film interface. An increase of upper wall liquid film thickness along the pipe was observed for both wavy annular and full annular scenarios. It was found that the liquid wavy front can be further broken down to form the water moisture with liquid droplets penetrating upwards. There are discrepancies between CFD predictions and experimental data on the liquid film thickness determined at the bottom and the upper wall surfaces, and the obtained modelling information can be used to assist further 3D user defined function subroutine development, especially when CFD simulation becomes much more expense to model full 3D two-phase flow transient performance from a wavy annular to a fully developed annular type.

  15. Observations on preferential flow and horizontal transport of nitrogen fertilizer in the unsaturated zone

    USGS Publications Warehouse

    Wilkison, D.H.; Blevins, D.W.

    1999-01-01

    A study site underlain by a claypan soil was instrumented to examine the transport of fertilizer nitrogen (N) under corn (Zea mays L.) cultivation. The study was designed to examine N transport within the unsaturated zone and in interflow (the saturated flow of water on top of the claypan). A 15N- labeled fertilizer (labeled N), bromide (Br), and chloride (Cl) were used as field tracers. Rapid or prolonged infiltration events allowed water and dissolved solutes to perch on the claypan for brief periods. However, a well- developed network of preferential flow paths quickly diverted water and solutes through the claypan and into the underlying glacial till aquifer. Excess fertilizer N in the unsaturated zone supplied a continuous, but declining input of N to ground water for a period of 15 mo after a single fertilizer application. Calculated solute velocities through the claypan matrix (6.4 x 10-6 cm s-1) were similar to horizontal transport rates along the claypan (3.5 to 7.3 x 10-6 cm s-1) but much slower than infiltration rates determined for preferential flow paths (1.67 x 10-3 cm s-1). These flow paths accounted for 35% of the transport. A seasonally variable, dual mode of transport (matrix and preferential flow) prevented the claypan from being an effective barrier to vertical transport. Simulations of selected field observations, conducted using the variably saturated two- dimensional flow and transport model, VS2DT, confirmed the presence of a dual flow regime in the claypan.

  16. Dairy washwater treatment using a horizontal flow biofilm system.

    PubMed

    Clifford, E; Rodgers, M; Paor, D de

    2008-01-01

    In Ireland, land-spreading is the most widely used method for treating dairy wastewaters. This can be labour intensive and can cause, in some cases, nitrate contamination of groundwater. In this study a simple pilot-scale horizontal flow biofilm reactor (HFBR) with a step-feed was developed and tested at a dairy farm site in County Offaly, Ireland for partial remediation of this soiled water prior to landspreading.During the 122-day study, the top surface plan area (TSPA) hydraulic loading rate was 50 L/m2/day. Influent concentrations averaged: 2904.2 mg total chemical oxygen demand (COD)/L, 950 mg 5-day biochemical oxygen demand (BOD5)/L and 177.9 mg total nitrogen (TN)/L. Between Days 1 and 45 frequent ambient temperatures below 4 degrees C inhibited the build-up of biomass resulting in low removals. From Day 45 the HFBR unit removed 74.9% total COD and 69.6% BOD5, equivalent to TSPA removals of 108.8 g COD/m2/day and 33.1 g BOD5/m2/day. On Sheet 29, by the end of the study, the NH4-N had reduced from 123.1 mg/L in the influent to 37.0 mg/L. TN removal in the reactor averaged 56.0% equating to a TSPA removal rate of 5.0 g TN/m2/day.The HFBR does not require any mechanical aeration, was simple and inexpensive to construct and can provide a robust and economical alternative for the remediation of agricultural soiled water before landspreading.

  17. Venturi flow meter and Electrical Capacitance Probe in a horizontal two-phase flow

    NASA Astrophysics Data System (ADS)

    Monni, G.; Caramello, M.; De Salve, M.; Panella, B.

    2015-11-01

    The paper presents the results obtained with a spool piece (SP) made of a Venturi flow meter (VMF) and an Electrical Capacitance Probe (ECP) in stratified two-phase flow. The objective is to determine the relationship between the test measurements and the physical characteristics of the flow such as superficial velocities, density and void fraction. The outputs of the ECP are electrical signals proportional to the void fraction between the electrodes; the parameters measured by the VFM are the total and the irreversible pressure losses of the two- phase mixture. The fluids are air and demineralized water at ambient conditions. The flow rates are in the range of 0,065-0,099 kg/s for air and 0- 0,039 kg/s (0-140 l/h) for water. The flow patterns recognized during the experiments are stratified, dispersed and annular flow. The presence of the VFM plays an important role on the alteration of the flow pattern due to wall flow detachment phenomena. The signals of differential pressure of the VFM in horizontal configuration are strongly dependent on the superficial velocities and on the flow pattern because of a lower symmetry of the flow with respect to the vertical configuration.

  18. Flow regimes and heat transfer in vertical narrow annuli

    SciTech Connect

    Ulke, A.; Goldberg, I.

    1993-11-01

    In shell side boiling heat exchangers narrow crevices that are formed between the tubes and the tube support structure provide areas for local thermal-hydraulic conditions which differ significantly from bulk fluid conditions. Understanding of the processes of boiling and dryout in flow restricted crevices can help in designing of tube support geometries to minimize the likelihood of tube support plate and tube corrosion observed in commercial power plant steam generators. This paper describes a one dimensional thermal-hydraulic model of a vertical crevice between a tube and a support plate with cylindrical holes. The annulus formed by the support plate hole and an eccentrically located tube has been represented by vertical strips. The formation, growth and collapse of a steam bubble in each strip has been determined. Based on the bubble history, and flow regimes characterized by ``isolated`` bubbles, ``coalesced`` bubbles and liquid deficient regions have been defined.

  19. Resonant phenomenon of elliptical cylinder flows in a subcritical regime

    NASA Astrophysics Data System (ADS)

    Chen, Shih-Sheng; Yen, Ruey-Hor

    2011-11-01

    The resonant phenomena in the wake behind a transversely vibrating elliptical cylinder with different axis ratios from Ar = 0.01 to Ar = 2.0 in the subcritical regime is numerically investigated. Navier-Stokes equations are solved by a spectral element code with a triangular mesh. Reynolds numbers range from 15 to 60 and the Roshko numbers range from 0.5 to 8 for different elliptical cylinders. Both the velocity and pressure responses in the wake are measured and analyzed. The investigations of the drag coefficients and the wake streamlines indicate that the cylinder's axis ratio has a minor effect on the resonant frequency, Ron. However, the cylinder's axis ratio is found to have a prominent effect on the resonant amplitude; namely, the smaller the cylinder's axis ratio, the stronger the occurrence of resonant amplitude. The investigations of resonant responses of both the velocity and pressure and the probe locations may provide information for designing a flow meter based on pressure responses in the subcritical regime. It shows that the ratio of velocity and pressure responses poses a great linear relationship against the probe distance behind the vibrating cylinder. Moreover, a resonant method based on the different resonant frequencies at different probed locations in the subcritical regime to predict the critical conditions is examined and verified for different elliptical cylinders. Finally, based on the critical values found, a reduced Reynolds number and a reduced Roshko number are proposed to unify the different linear relationships resulting from different elliptical cylinder flows. The result indicates that the effect of axis ratio can be stripped off in the reduced plane, which may be applied to a more generalized cylinder shape.

  20. Measurement of interfacial structures in horizontal air-water bubbly flows

    SciTech Connect

    Talley, J. D.; Worosz, T.; Dodds, M. R.; Kim, S.

    2012-07-01

    In order to predict multi-dimensional phenomena in nuclear reactor systems, methods relying on computational fluid dynamics (CFD) codes are essential. However, to be applicable in assessing thermal-hydraulic safety, these codes must be able to accurately predict the development of two-phase flows. Therefore, before practical application these codes must be assessed using experimental databases that capture multi-dimensional phenomena. While a large database exists that can be employed to assess predictions in vertical flows, the available database for horizontal flows is significantly lacking. Therefore, the current work seeks to develop an additional database in air-water horizontal bubbly flow through a 38.1 mm ID test section with a total development length of approximately 250 diameters. The experimental conditions are chosen to cover a wide range of the bubbly flow regime based upon flow visualization using a high-speed video camera. A database of local time-averaged void fraction, bubble velocity, interfacial area concentration, and bubble Sauter mean diameter are acquired throughout the pipe cross-section using a four-sensor conductivity probe. To investigate the evolution of the flow, measurements are made at axial locations of 44, 116, and 244 diameters downstream of the inlet. In the current work, only measurements obtained at L/D = 244 are presented. It is found that increasing the liquid superficial velocity tends to reduce both the bubble size and the degree of bubble packing near the upper wall. However, it is observed that the position of the maximum void fraction value remains nearly constant and is located approximately one bubble diameter away from the upper wall. It is also found that the bubble velocity exhibits a power law behavior resembling a single phase liquid turbulent velocity profile. Moreover, the local bubble velocity tends to decrease as the local void fraction increases. Conversely, increasing the gas superficial velocity is found to

  1. Assessing temporal and spatial alterations of flow regimes in the regulated Huai River Basin, China

    NASA Astrophysics Data System (ADS)

    Zhang, Yongyong; Zhai, Xiaoyan; Shao, Quanxi; Yan, Ziqi

    2015-10-01

    The assessment of flow regime alterations is fundamental in understanding the potential impact of reservoirs and other water infrastructures on aquatic ecosystems and biota. Previously used methods to classify flow regimes have not captured temporal changes between unregulated and regulated flow regimes at individual stations. In this study, a combination of hierarchical classification and trend analysis was used to assess spatial and temporal flow regime alterations in the Huai River Basin, China. Two categories of flow regime indices were selected to characterize the impacts of reservoir and sluice regulation, including the basic flow indices for mean variation, and the cumulative variation indices for long-term alteration. The overall impact of reservoirs and sluices on flow regime included the decrease of high flow magnitudes but the increase of low flow magnitudes through time. Moreover, on average, the flow variability, and the high and low flow frequencies were reduced, while their durations were increased. Reservoirs had a greater impact on flow regimes than sluices. The flow regimes at 18 of 30 stations were altered significantly from a pre-regulation condition and were divided into three main types of alteration corresponding to operational rules of reservoirs and sluices. From a management perspective, water projects in China should address the environmental flow requirements of the rivers, particularly in terms of the hydrologic indices affected mostly by reservoirs and sluices. This study will promote the application of flow regime classification and river restoration in highly regulated basins in China.

  2. Wind-Driven Ecological Flow Regimes Downstream from Hydropower Dams

    NASA Astrophysics Data System (ADS)

    Kern, J.; Characklis, G. W.

    2012-12-01

    challenge, the following study was designed to investigate the potential for wind power integration to alter riparian flow regimes below hydroelectric dams. A hydrological model of a three-dam cascade in the Roanoke River basin (Virginia, USA) is interfaced with a simulated electricity market (i.e. a unit commitment problem) representing the Dominion Zone of PJM Interconnection. Incorporating forecasts of electricity demand, hydro capacity and wind availability, a mixed-integer optimization program minimizes the system cost of meeting hourly demand and reserve requirements by means of a diverse generation portfolio (e.g. nuclear, fossil, hydro, and biomass). A secondary 'balancing' energy market is executed if real-time wind generation is less than the day-ahead forecast, calling upon reserved generation resources to meet the supply shortfall. Hydropower release schedules are determined across a range of wind development scenarios (varying wind's fraction of total installed generating capacity, as well as its geographical source region). Flow regimes for each wind development scenario are compared against both historical and simulated flows under current operations (negligible wind power), as well as simulated natural flows (dam removal), in terms of ecologically relevant flow metrics. Results quantify the ability of wind power development to alter within-week stream flows downstream from hydropower dams.

  3. Effect of horizontal heat and fluid flow on the vertical temperature distribution in a semiconfining layer

    USGS Publications Warehouse

    Lu, N.; Ge, S.

    1996-01-01

    By including the constant flow of heat and fluid in the horizontal direction, we develop an analytical solution for the vertical temperature distribution within the semiconfining layer of a typical aquifer system. The solution is an extension of the previous one-dimensional theory by Bredehoeft and Papadopulos [1965]. It provides a quantitative tool for analyzing the uncertainty of the horizontal heat and fluid flow. The analytical results demonstrate that horizontal flow of heat and fluid, if at values much smaller than those of the vertical, has a negligible effect on the vertical temperature distribution but becomes significant when it is comparable to the vertical.

  4. A hydrometeorological forecasting approach for basins with complex flow regime

    NASA Astrophysics Data System (ADS)

    Zarkadoulas, Akis; Mantesi, Konstantina; Efstratiadis, Andreas; Koussis, Antonis; Mazi, Aikaterini; Katsanos, Demetris; Koukouvinos, Antonis; Koutsoyiannis, Demetris

    2015-04-01

    The combined use of weather forecasting models and hydrological models in flood risk estimations is an established technique, with several successful applications worldwide. However, most known hydrometeorological forecasting systems have been established in large rivers with perpetual flow. Experience from small- and medium-scale basins, which are often affected by flash floods, is very limited. In this work we investigate the perspectives of hydrometeorological forecasting, by emphasizing two issues: (a) which modelling approach can credibly represent the complex dynamics of basins with highly variable runoff (intermittent or ephemeral); and (b) which transformation of point-precipitation forecasts provides the most reliable estimations of spatially aggregated data, to be used as inputs to semi-distributed hydrological models. Using as case studies the Sarantapotamos river basin, in Eastern Greece (145 km2), and the Nedontas river basin, in SW Peloponnese (120 km2), we demonstrate the advantages of continuous simulation through the HYDROGEIOS model. This employs conjunctive modelling of surface and groundwater flows and their interactions (percolation, infiltration, underground losses), which are key processes in river basins characterized by significantly variability of runoff. The model was calibrated against hourly flow data at two and three hydrometric stations, respectively, for a 3-year period (2011-2014). Next we attempted to reproduce the most intense flood events of that period, by substituting observed rainfall by forecast scenarios. In this respect, we used consecutive point forecasts of a 6-hour lead time, provided by the numerical weather prediction model WRF (Advanced Research version), dynamically downscaled from the ~1° forecast of GSF-NCEP/NOAA successively first to ~18 km, then to ~6 km and ultimately at the horizontal grid resolution of 2x2 km2. We examined alternative spatial integration approaches, using as reference the rainfall stations

  5. Controls of wellbore flow regimes on pump effluent composition.

    PubMed

    Martin-Hayden, James M; Plummer, Mitchell; Britt, Sanford L

    2014-01-01

    Where well water and formation water are compositionally different or heterogeneous, pump effluent composition will vary due to partial mixing and transport induced by pumping. Investigating influences of purging and sampling methodology on composition variability requires quantification of wellbore flow regimes and mixing. As a basis for this quantification, analytical models simulating Poiseuille flow were developed to calculate flow paths and travel times. Finite element modeling was used to incorporate influences of mixing. Parabolic velocity distributions within the screened interval accelerate with cumulative inflow approaching the pump intake while an annulus of inflowing formation water contracts uniformly to displace an axial cylinder of pre-pumping well water as pumping proceeds. Increased dispersive mixing forms a more diffuse formation water annulus and the contribution of formation water to pump effluent increases more rapidly. Models incorporating viscous flow and diffusion scale mixing show that initially pump effluent is predominantly pre-pumping well water and compositions vary most rapidly. After two screen volumes of pumping, 94% of pump effluent is inflowing formation water. Where the composition of formation water and pre-pumping well water are likely to be similar, pump effluent compositions will not vary significantly and may be collected during early purging or with passive sampling. However, where these compositions are expected to be considerably different or heterogeneous, compositions would be most variable during early pumping, that is, when samples are collected during low-flow sampling. Purging of two screen volumes would be required to stabilize the content and collect a sample consisting of 94% formation water.

  6. Controls of Wellbore Flow Regimes on Pump Effluent Composition

    SciTech Connect

    James Martin-Hayden; plummer; Sanford Britt

    2014-01-01

    Where well water and formation water are compositionally different or heterogeneous, pump effluent composition will vary due to partial mixing and transport induced by pumping. Investigating influences of purging and sampling methodology on composition variability requires quantification of wellbore flow regimes and mixing. As a basis for this quantification, analytical models simulating Poiseuille flow were developed to calculate flow paths and travel times. Finite element modeling was used to incorporate influences of mixing. Parabolic velocity distributions within the screened interval accelerate with cumulative inflow approaching the pump intake while an annulus of inflowing formation water contracts uniformly to displace an axial cylinder of pre-pumping well water as pumping proceeds. Increased dispersive mixing forms a more diffuse formation water annulus and the contribution of formation water to pump effluent increases more rapidly. Models incorporating viscous flow and diffusion scale mixing show that initially pump effluent is predominantly pre-pumping well water and compositions vary most rapidly. After two screen volumes of pumping, 94% of pump effluent is inflowing formation water. Where the composition of formation water and pre-pumping well water are likely to be similar, pump effluent compositions will not vary significantly and may be collected during early purging or with passive sampling. However, where these compositions are expected to be considerably different or heterogeneous, compositions would be most variable during early pumping, that is, when samples are collected during low-flow sampling. Purging of two screen volumes would be required to stabilize the content and collect a sample consisting of 94% formation water.

  7. Turbulence- and buoyancy-driven secondary flow in a horizontal square duct heated from below

    NASA Astrophysics Data System (ADS)

    Sekimoto, A.; Kawahara, G.; Sekiyama, K.; Uhlmann, M.; Pinelli, A.

    2011-07-01

    Direct numerical simulations of fully developed turbulent flows in a horizontal square duct heated from below are performed at bulk Reynolds numbers Reb = 3000 and 4400 (based on duct width H) and bulk Richardson numbers 0≤Ri≤1.03. The primary objective of the numerical simulations concerns the characterization of the mean secondary flow that develops in this class of flows. On one hand, it is known that turbulent isothermal flow in a square duct presents secondary mean motions of Prandtl's second kind that finds its origin in the behavior of turbulence structures. On the other hand, thermal convection drives a mean secondary motion of Prandtl's first kind directly induced by buoyancy. As far as the mean structure of the cross-stream motion is concerned, it is found that different types of secondary flow regimes take place when increasing the value of the Richardson number. The mean secondary flow in the range 0.025≲Ri≲0.25 is characterized by a single large-scale thermal convection roll and four turbulence-driven corner vortices of the opposite sense of rotation to the roll, as contrasted with the classical scenario of the eight-vortex secondary flow pattern typical of isothermal turbulent square-duct flow. This remarkable structural difference in the corner regions can be interpreted in terms of combined effects, on instantaneous streamwise vortices, of the large-scale circulation and of the geometrical constraint by the duct corner. When further increasing the Richardson number, i.e., Ri ≳ 0.25, the structure of the mean secondary flow is solely determined by the large-scale circulation induced by the buoyancy force. In this regime, the additional mean cross-stream motion is characterized by the presence of two distinct buoyancy-driven vortices of opposite sense of rotation to the circulation only in two of the four corner regions. With increasing Ri, the large-scale circulation is found to enhance the wall skin friction and heat transfer. In the

  8. Vertical Subsurface Flow Mixing and Horizontal Anisotropy in Coarse Fluvial Aquifers: Flow Field

    NASA Astrophysics Data System (ADS)

    Huber, E.; Huggenberger, P.

    2014-12-01

    A stochastic object-based model for hydrogeological aquifer characterization of coarse braided-river deposits has been developed based (1) on sedimentological observations of ancient coarse braided-river deposits and ground penetrating radar surveys on the floodplain of the Tagliamento River (Northeast Italy) and (2) on observations of the morphodynamics of the Tagliamento River. We assume that at each large flow event, flow-confluence scours are formed and filled during their migration, and subsequently covered by downstream moving gravel sheets of poorly sorted sediments. The object-based model mimics this behaviour: at each iteration truncated ellipsoids (scour-fill deposits) are distributed, as a marked point process, at the previous simulated floodplain surface and are followed on top by a layer with a specified thickness (gravel sheets) that define the next floodplain topography. The truncated ellipsoids have erosional and depositional properties. Compared with the scour-fills, the gravel sheets show much less variability and a much smaller hydraulic conductivities with only a vertical anisotropy. Accordingly, specific three-dimensional hydraulic conductivity tensors and porosity values are stochastically attributed to the truncated ellipsoids and the horizontal layers. This object-based model is able to simulate a large range of the morphodynamics of braided-river systems (scenarios) that result in different sediment sorting processes and, in turn, in specific hydraulic heterogeneity and connectivity patterns of high permeable units. In the context of surface water-groundwater interaction the model is used to assess the impact of some scenarios on the groundwater flow field as well as on solute transport. We evaluate the vertical mixing of the groundwater flows, the horizontal flow deviation caused by the anisotropy of the scour-fill deposits as well as the solute transport behaviour. We discuss the specific hydraulic responses in relation with the

  9. Flow visualization study of post critical heat flux region for inverted bubbly, slug and annular flow regimes

    SciTech Connect

    Denten, J.G.; Ishii, M.

    1988-11-01

    A visual study of film boiling using still photographic and high- speed motion picture methods was carried out in order to analyze the post-CHF hydrodynamics for steady-state inlet pre-CHF two-phase flow regimes. Pre-CHF two-phase flow regimes were established by introducing Freon 113 liquid and nitrogen gas into a jet core injection nozzle. An idealized, post-CHF two-phase core initial flow geometry (cylindrical multiphase jet core surrounded by a coaxial annulus of gas) was established at the nozzle exit by introducing nitrogen gas into the annular gap between the jet nozzle two-phase effluent and the heated test section inlet. For the present study three basic post-CHF flow regimes have been observed: the rough wavy regime (inverted annular flow preliminary break down), the agitated regime (transition between inverted annular and dispersed droplet flow), and the dispersed ligament/droplet regime. For pre-CHF bubbly flow in the jet nozzle, the post-CHF flow (beginning from jet nozzle exit/heated test section inlet) consists of the rough wavy regime, followed by the agitated and then the dispersed ligament/droplet regime. In the same way, for pre-CHF slug flow in the jet core, the post-CHF flow is comprised of the agitated regime at the nozzle exit, followed by the dispersed regime. Pre-CHF annular jet core flow results in a small, depleted post-CHF agitated flow regime at the nozzle exit, immediately followed by the dispersed ligament/droplet regime. Observed post dryout hydrodynamic behavior is reported, with particular attention given to the transition flow pattern between inverted annular and dispersed droplet flow. 43 refs., 20 figs., 5 tabs.

  10. Flow Visualization Study of a 1/48-Scale AFTI/F111 Model to Investigate Horizontal Tail Flow Disturbances

    NASA Technical Reports Server (NTRS)

    Bjarke, Lisa J.

    1991-01-01

    During flight testing of the AFTI/F111 aircraft, horizontal tail buffet was observed. Flutter analysis ruled out any aeroelastic instability, so a water-tunnel flow visualization study was conducted to investigate possible flow disturbances on the horizontal tail which might cause buffet. For this study, a 1/48-scale model was used. Four different wing cambers and one horizontal tail setting were tested between 0 and 20 deg angle of attack. These wing cambers corresponded to the following leading training edge deflections: 0/2, 10/10, 10/2, and 0/10. Flow visualization results in the form of still photographs are presented for each of the four wing cambers between 8 and 12 deg angle of attack. In general, the horizontal tail experiences flow disturbances which become more pronounced with angle of attack or wing trailing-edge deflection.

  11. The effect of the scale of horizontal subsurface flow constructed wetlands on flow and transport parameters.

    PubMed

    Suliman, F; French, H; Haugen, L E; Kløve, B; Jenssen, P

    2005-01-01

    Horizontal subsurface flow constructed wetlands have proven their efficiency in treating wastewater and removing the pollutants of concern. Treatment efficiency depends on the wastewater residence time, which is a function of the hydraulic loading and the physical conditions of the constructed filter system, which can be described with effective parameters such as: hydraulic conductivity, porosity, dispersivity etc. Because spatial variability is often scale dependent, these effective parameters may be affected by the scale of the system being studied. In this paper the results of tracer experiments in constructed filters using saturated horizontal flow at three scales (small and medium lab scales and full-scale system) using the same filter media is reported. Light-weight aggregate (filter media termed Filtralite-P) was used at all scales. Increasing the scale was associated with increasing dispersivity, meanwhile hydraulic conductivity experienced dramatic reduction and variation by increasing the examined scale. Observed changes in the hydraulic parameters indicate that heterogeneity at different scales should be taken into account when the performance of LWA filters are evaluated from small-scale experiments. PMID:16042266

  12. Flow regimes and mechanistic modeling of critical heat flux under subcooled flow boiling conditions

    NASA Astrophysics Data System (ADS)

    Le Corre, Jean-Marie

    Thermal performance of heat flux controlled boiling heat exchangers are usually limited by the Critical Heat Flux (CHF) above which the heat transfer degrades quickly, possibly leading to heater overheating and destruction. In an effort to better understand the phenomena, a literature review of CHF experimental visualizations under subcooled flow boiling conditions was performed and systematically analyzed. Three major types of CHF flow regimes were identified (bubbly, vapor clot and slug flow regime) and a CHF flow regime map was developed, based on a dimensional analysis of the phenomena and available data. It was found that for similar geometric characteristics and pressure, a Weber number (We)/thermodynamic quality (x) map can be used to predict the CHF flow regime. Based on the experimental observations and the review of the available CHF mechanistic models under subcooled flow boiling conditions, hypothetical CHF mechanisms were selected for each CHF flow regime, all based on a concept of wall dry spot overheating, rewetting prevention and subsequent dry spot spreading. It is postulated that a high local wall superheat occurs locally in a dry area of the heated wall, due to a cyclical event inherent to the considered CHF two-phase flow regime, preventing rewetting (Leidenfrost effect). The selected modeling concept has the potential to span the CHF conditions from highly subcooled bubbly flow to early stage of annular flow. A numerical model using a two-dimensional transient thermal analysis of the heater undergoing nucleation was developed to mechanistically predict CHF in the case of a bubbly flow regime. In this type of CHF two-phase flow regime, the high local wall superheat occurs underneath a nucleating bubble at the time of bubble departure. The model simulates the spatial and temporal heater temperature variations during nucleation at the wall, accounting for the stochastic nature of the boiling phenomena. The model has also the potential to evaluate

  13. Hot-wire calibration in subsonic/transonic flow regimes

    NASA Technical Reports Server (NTRS)

    Nagabushana, K. A.; Ash, Robert L.

    1995-01-01

    A different approach for calibrating hot-wires, which simplifies the calibration procedure and reduces the tunnel run-time by an order of magnitude was sought. In general, it is accepted that the directly measurable quantities in any flow are velocity, density, and total temperature. Very few facilities have the capability of varying the total temperature over an adequate range. However, if the overheat temperature parameter, a(sub w), is used to calibrate the hot-wire then the directly measurable quantity, voltage, will be a function of the flow variables and the overheat parameter i.e., E = f(u,p,a(sub w), T(sub w)) where a(sub w) will contain the needed total temperature information. In this report, various methods of evaluating sensitivities with different dependent and independent variables to calibrate a 3-Wire hot-wire probe using a constant temperature anemometer (CTA) in subsonic/transonic flow regimes is presented. The advantage of using a(sub w) as the independent variable instead of total temperature, t(sub o), or overheat temperature parameter, tau, is that while running a calibration test it is not necessary to know the recovery factor, the coefficients in a wire resistance to temperature relationship for a given probe. It was deduced that the method employing the relationship E = f (u,p,a(sub w)) should result in the most accurate calibration of hot wire probes. Any other method would require additional measurements. Also this method will allow calibration and determination of accurate temperature fluctuation information even in atmospheric wind tunnels where there is no ability to obtain any temperature sensitivity information at present. This technique greatly simplifies the calibration process for hot-wires, provides the required calibration information needed in obtaining temperature fluctuations, and reduces both the tunnel run-time and the test matrix required to calibrate hotwires. Some of the results using the above techniques are presented

  14. Regimes of two-phase flow in micro- and minichannels ( review)

    NASA Astrophysics Data System (ADS)

    Chinnov, E. A.; Ron'shin, F. V.; Kabov, O. A.

    2015-05-01

    The review deals with the analysis of the factors affecting the boundaries of two-phase regimes in the channels of different cross sections, whose minimal size is less than the capillary constant. The channels are classified by size. Data for two-phase flow regimes are systematized and summarized in tables for the round and rectangular tubes. It is indicated that the most studies identify the following two-phase flow regimes: bubble, slug and annular. The regimes found in some papers are described. The terminology used to describe the regimes is kept. Here we analyze the main factors affecting the structure of the two-phase flow, such as gas and liquid flow rates, parameters of the channel and input section, wettability of the inner surface of channels, liquid properties, and gravitational forces. It is shown that development of instability of the two-phase flow has a significant impact on formation, evolution, and change of the flow regimes.

  15. Magneto-polar fluid flow through a porous medium of variable permeability in slip flow regime

    NASA Astrophysics Data System (ADS)

    Gaur, P. K.; Jha, A. K.; Sharma, R.

    2016-05-01

    A theoretical study is carried out to obtain an analytical solution of free convective heat transfer for the flow of a polar fluid through a porous medium with variable permeability bounded by a semi-infinite vertical plate in a slip flow regime. A uniform magnetic field acts perpendicular to the porous surface. The free stream velocity follows an exponentially decreasing small perturbation law. Using the approximate method the expressions for the velocity, microrotation, and temperature are obtained. Further, the results of the skin friction coefficient, the couple stress coefficient and the rate of heat transfer at the wall are presented with various values of fluid properties and flow conditions.

  16. Zonal flow regimes in rotating anelastic spherical shells (Invited)

    NASA Astrophysics Data System (ADS)

    Gastine, T.; Wicht, J.; Aurnou, J. M.; Heimpel, M. H.

    2013-12-01

    The surface zonal winds observed in the giant planets form a complex jet pattern with alternating prograde and retrograde direction. While the main equatorial band is prograde on the gas giants, both ice giants have a pronounced retrograde equatorial jet. The depth of these jets is however poorly known and highly debated. Theoretical scenarios range from "shallow models", that assume that these zonal flows are restricted to the outer stably stratified layer; to "deep models" that hypothesise that the surface winds are the signature of deep-seated convection. Most of the numerical models supporting the latter idea employed the Boussinesq approximation where compressibility effects are ignored. While this approximation is suitable for modelling the liquid iron core of terrestrial planets, this becomes questionable in the gas giants interiors, where density increases by several orders of magnitude. To tackle this problem, several numerical models using the "anelastic approximation" have been recently developed to study the compressibility effects while filtering out the fast acoustic waves. Here, we consider such anelastic models of rapidly-rotating spherical shells to explore the properties of the zonal winds in different regimes where either rotation or buoyancy dominates the force balance. We conduct several parameter studies to quantify the dependence of zonal flows on the background density stratification and the driving of convection. We find that the direction of the equatorial wind is controlled by the ratio of buoyancy and Coriolis force. The prograde equatorial band maintained by Reynolds stresses is found in the rotation-dominated regime. At low Ekman numbers, several alternating jets form at high latitude in a similar way to some previous Boussinesq calculations. In cases where buoyancy dominates Coriolis force, the angular momentum per unit mass is homogenised and the equatorial band is retrograde, reminiscent to those observed in the ice giants

  17. Flooding characteristics of gas-liquid two-phase flow in a horizontal U bend pipe

    SciTech Connect

    Sakaguchi, T.; Hosokawa, S.; Fujii, Y.

    1995-09-01

    For next-generation nuclear reactors, hybrid safety systems which consist of active and passive safety systems have been planned. Steam generators with horizontal U bend pipelines will be used as one of the passive safety systems. It is required to clarify flow characteristics, especially the onset of flooding, in the horizontal U bend pipelines in order to examine their safety. Flooding in vertical pipes has been studied extensively. However, there is little study on flooding in the horizontal U bend pipelines. It is supposed that the onset of flooding in the horizontal U bend pipelines is different from that in vertical pipes. On the other hand, liquid is generated due to condensation of steam in pipes of the horizontal steam generators at the loss of coolant accident because the steam generators will be used as a condenser of a cooling system of steam from the reactor. It is necessary to simulate this situation by the supply of water at the middle of horizontal pipe. In the present paper, experiments were carried out using a horizontal U bend pipeline with a liquid supply section in the midway of pipeline. The onset of flooding in the horizontal U bend pipeline was measured. Effects of the length of horizontal pipe and the radius of U bend on the onset of flooding were discussed.

  18. Multiphase flow-enhanced corrosion mechanisms in horizontal pipelines

    SciTech Connect

    Jiang, L.; Gopal, M.

    1998-12-31

    Previous work has demonstrated the mechanism of enhanced corrosion in slug flow due to entrained pulses of bubbles. Corrosion rate measurements have been made at pressures up to 0.79 MPa, and temperatures up to 90 C and it has been shown that the effect of these pulses of bubbles increases with pressure and Froude number. This paper describes mass transfer measurements under multiphase slug and annular flows using the limiting current density technique. The experiments are carried out in a 10 cm diameter pipe using a 0.1 M potassium ferro-ferricyanide solution in 1.3 N sodium hydroxide for the liquid phase and nitrogen in the gas phase. Froude numbers of 4, 6 and 9 in slug flow have been studied, while gas velocities up to 10 m/s are investigated in annular flows. The results show instantaneous peaks in the mass transfer rates corresponding to the pulses of bubbles in slug flow. Instantaneous increases of 10--100 times the average values in single phase flow are seen. Peaks are also seen in instantaneous mass transfer rates in some annular flows.

  19. Separated two-phase flow regime parameter measurement by a high speed ultrasonic pulse-echo system.

    PubMed

    Masala, Tatiana; Harvel, Glenn; Chang, Jen-Shih

    2007-11-01

    In this work, a high speed ultrasonic multitransducer pulse-echo system using a four transducer method was used for the dynamic characterization of gas-liquid two-phase separated flow regimes. The ultrasonic system consists of an ultrasonic pulse signal generator, multiplexer, 10 MHz (0.64 cm) ultrasonic transducers, and a data acquisition system. Four transducers are mounted on a horizontal 2.1 cm inner diameter circular pipe. The system uses a pulse-echo method sampled every 0.5 ms for a 1 s duration. A peak detection algorithm (the C-scan mode) is developed to extract the location of the gas-liquid interface after signal processing. Using the measured instantaneous location of the gas/liquid interface, two-phase flow interfacial parameters in separated flow regimes are determined such as liquid level and void fraction for stratified wavy and annular flow. The shape of the gas-liquid interface and, hence, the instantaneous and cross-sectional averaged void fraction is also determined. The results show that the high speed ultrasonic pulse-echo system provides accurate results for the determination of the liquid level within +/-1.5%, and the time averaged liquid level measurements performed in the present work agree within +/-10% with the theoretical models. The results also show that the time averaged void fraction measurements for a stratified smooth flow, stratified wavy flow, and annular flow qualitatively agree with the theoretical predictions.

  20. Natural flow regimes of the Ozark-Ouachita Interior Highlands region

    USGS Publications Warehouse

    Leasure, D. R.; Magoulick, Daniel D.; Longing, S. D.

    2016-01-01

    Natural flow regimes represent the hydrologic conditions to which native aquatic organisms are best adapted. We completed a regional river classification and quantitative descriptions of each natural flow regime for the Ozark–Ouachita Interior Highlands region of Arkansas, Missouri and Oklahoma. On the basis of daily flow records from 64 reference streams, seven natural flow regimes were identified with mixture model cluster analysis: Groundwater Stable, Groundwater, Groundwater Flashy, Perennial Runoff, Runoff Flashy, Intermittent Runoff and Intermittent Flashy. Sets of flow metrics were selected that best quantified nine ecologically important components of these natural flow regimes. An uncertainty analysis was performed to avoid selecting metrics strongly affected by measurement uncertainty that can result from short periods of record. Measurement uncertainties (bias, precision and accuracy) were assessed for 170 commonly used flow metrics. The ranges of variability expected for select flow metrics under natural conditions were quantified for each flow regime to provide a reference for future assessments of hydrologic alteration. A random forest model was used to predict the natural flow regimes of all stream segments in the study area based on climate and catchment characteristics, and a map was produced. The geographic distribution of flow regimes suggested distinct ecohydrological regions that may be useful for conservation planning. This project provides a hydrologic foundation for future examination of flow–ecology relationships in the region. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

  1. Slug-plug flow analyses of stratified flows in a horizontal duct by means of MARS

    SciTech Connect

    Kunugi, T.; Ose, Y.; Banat, M.

    1999-07-01

    The objectives of this study are to perform the slug-plug flow analyses of stratified flows in a horizontal duct by means of the MARS (Multi-interfaces Advection and Reconstruction Solver) developed by the author which based on the piece-wise linear calculation as a volume tracking procedure and the continuum surface force model (CSF) for the surface tension, and to investigate the effect of the Bernoulli term for slug-plug flows, i.e., so-called the topological law, on the competition between inertial forces and gravitation forces. Some discussion on the primary jump condition at the interface in the MARS is described in the paper. The results of the direct numerical simulation (DNS) by the MARS are compared with the experimental one. The slugging positions obtained by the DNS are in good agreement with the experimental one. Since the mass conservation between before the plugging and after slugging can be shown by the DNS here, the authors may conclude that this physical/numerical model based on the MARS is reliable.

  2. Interfacial characteristic measurements in horizontal bubbly two-phase flow

    NASA Astrophysics Data System (ADS)

    Wang, Z.; Huang, W. D.; Srinivasmurthy, S.; Kocamustafaogullari, G.

    1990-10-01

    Advances in the study of two-phase flow increasingly require detailed internal structure information upon which theoretical models can be formulated. The void fraction and interfacial area are two fundamental parameters characterizing the internal structure of two-phase flow. However, little information is currently available on these parameters, and it is mostly limited to vertical flow configurations. In view of the above, the internal phase distribution of concurrent, air-water bubbly flow in a 50.3 mm diameter transparent pipeline has been experimentally investigated by using a double-sensor resistivity probe. Liquid and gas volumetric superficial velocities ranged from 3.74 to 5.60 m/s and 0.25 to 1.59 m/s, respectively, and average void fractions ranged from 2.12 to 22.5 percent. The local values of void fractions, interfacial area concentration, mean bubble diameter, bubble interface velocity, bubble chord-length and bubble frequency distributions were measured. The experimental results indicate that the void fraction interfacial area concentration and bubble frequency have local maxima near the upper pipe wall, and the profiles tend to flatten with increasing void fraction. The observed peak void fraction can reach 0.65, the peak interfacial area can go up to 900 approximately 1000 sq m/cu m, and the bubble frequency can reach a value of 2200 per s. These ranges of values have never been reported for vertical bubbly flow. It is found that either decreasing the liquid flow rate or increasing the gas flow would increase the local void fraction, the interfacial area concentration and the bubble frequency.

  3. Numerical simulation of flows from free molecular regime to continuum regime by a DVM with streaming and collision processes

    NASA Astrophysics Data System (ADS)

    Yang, L. M.; Shu, C.; Wu, J.; Wang, Y.

    2016-02-01

    A discrete velocity method (DVM) with streaming and collision processes is presented in this work for simulation of flows from free molecular regime to continuum regime. The present scheme can be considered as a semi-Lagrangian like scheme. At first, we follow the conventional DVM to discretize the phase velocity space by a number of discrete velocities. Then, for each discrete velocity, the kinetic equation with BGK-Shakhov model is integrated in space and time within one time step. As a result, a simple algebraic formulation can be obtained, and its solution can be marched in time by the streaming and collision processes. However, differently from the conventional semi-Lagrangian scheme, the present scheme uses the MUSCL approach with van Albada limiter in the process of reconstructing the distribution function at the surrounding points of the cell center, and the transport distance is controlled in order to avoid extrapolation. This makes the present scheme be capable of simulating the hypersonic rarefied flows. In addition, as compared to the unified gas kinetic scheme (UGKS), the present scheme is simpler and easier for implementation. Thus, the computational efficiency can be improved accordingly. To validate the proposed numerical scheme, test examples from free molecular regime to continuum regime are simulated. Numerical results showed that the present scheme can predict the flow properties accurately even for hypersonic rarefied flows.

  4. A kinematic investigation of the influence of anvil air flow over convective nephsystems on high-level horizontal flow

    NASA Technical Reports Server (NTRS)

    Balogun, E. E.

    1977-01-01

    The interactions between horizontal ambient flow and divergent wind fields, such as those that obtain atop cumulonimbus complexes, were investigated (theoretically) kinematically. The following were observed from the results of the analyses. First, for a particular divergent field, the relative mass flux over the area of the nephsystem decreased as the strength of the horizontal flow increased. Secondly, while in some of the cases analyzed the interaction between the two flows only resulted in the fanning out of streamlines and a slight redistribution in the wind speed, in many cases backflows and a total reorganization of the wind field occurred. Backflows have a blocking effect on the horizontal flow. Some of the computed patterns were compared with upper level cloud vectors (from geostationary satellite photographs). The comparison indicated that the computed resultant wind field could be used to explain some features of such satellite-derived wind fields.

  5. Basic principles and ecological consequences of altered flow regimes for aquatic biodiversity.

    PubMed

    Bunn, Stuart E; Arthington, Angela H

    2002-10-01

    The flow regime is regarded by many aquatic ecologists to be the key driver of river and floodplain wetland ecosystems. We have focused this literature review around four key principles to highlight the important mechanisms that link hydrology and aquatic biodiversity and to illustrate the consequent impacts of altered flow regimes: Firstly, flow is a major determinant of physical habitat in streams, which in turn is a major determinant of biotic composition; Secondly, aquatic species have evolved life history strategies primarily in direct response to the natural flow regimes; Thirdly, maintenance of natural patterns of longitudinal and lateral connectivity is essential to the viability of populations of many riverine species; Finally, the invasion and success of exotic and introduced species in rivers is facilitated by the alteration of flow regimes. The impacts of flow change are manifest across broad taxonomic groups including riverine plants, invertebrates, and fish. Despite growing recognition of these relationships, ecologists still struggle to predict and quantify biotic responses to altered flow regimes. One obvious difficulty is the ability to distinguish the direct effects of modified flow regimes from impacts associated with land-use change that often accompanies water resource development. Currently, evidence about how rivers function in relation to flow regime and the flows that aquatic organisms need exists largely as a series of untested hypotheses. To overcome these problems, aquatic science needs to move quickly into a manipulative or experimental phase, preferably with the aims of restoration and measuring ecosystem response. PMID:12481916

  6. Methodology Development of a Gas-Liquid Dynamic Flow Regime Transition Model

    NASA Astrophysics Data System (ADS)

    Doup, Benjamin Casey

    Current reactor safety analysis codes, such as RELAP5, TRACE, and CATHARE, use flow regime maps or flow regime transition criteria that were developed for static fully-developed two-phase flows to choose interfacial transfer models that are necessary to solve the two-fluid model. The flow regime is therefore difficult to identify near the flow regime transitions, in developing two-phase flows, and in transient two-phase flows. Interfacial area transport equations were developed to more accurately predict the dynamic nature of two-phase flows. However, other model coefficients are still flow regime dependent. Therefore, an accurate prediction of the flow regime is still important. In the current work, the methodology for the development of a dynamic flow regime transition model that uses the void fraction and interfacial area concentration obtained by solving three-field the two-fluid model and two-group interfacial area transport equation is investigated. To develop this model, detailed local experimental data are obtained, the two-group interfacial area transport equations are revised, and a dynamic flow regime transition model is evaluated using a computational fluid dynamics model. Local experimental data is acquired for 63 different flow conditions in bubbly, cap-bubbly, slug, and churn-turbulent flow regimes. The measured parameters are the group-1 and group-2 bubble number frequency, void fraction, interfacial area concentration, and interfacial bubble velocities. The measurements are benchmarked by comparing the prediction of the superficial gas velocities, determined using the local measurements with those determined from volumetric flow rate measurements and the agreement is generally within +/-20%. The repeatability four-sensor probe construction process is within +/-10%. The repeatability of the measurement process is within +/-7%. The symmetry of the test section is examined and the average agreement is within +/-5.3% at z/D = 10 and +/-3.4% at z/D = 32

  7. Multiple planetary flow regimes in the Southern Hemisphere

    NASA Technical Reports Server (NTRS)

    Yoden, Shigeo; Shiotani, Masato; Hirota, Isamu

    1987-01-01

    Low-frequency variations in the general circulation of the Southern Hemisphere during 1983 were studied using daily geopotential height and temperature analyses for 12 pressure levels from 1000 mb up to 50 mb, performed by the National Meteorological Center of Japan. Results disclosed the presence, in the Southern Hemisphere troposphere, of an irregular fluctuation of two zonal mean geostrophic wind patterns (named single-jet and double-jet regimes) during wintertime. The fluctuation is characterized by the persistence of one geostrophic wind regime, with characteristic duration of a month, followed by a rather rapid transition to another regime.

  8. Counter-current flow in a vertical to horizontal tube with obstructions

    SciTech Connect

    Tye, P.; Matuszkiewicz, A.; Teyssedou, A.

    1995-09-01

    This paper presents experimental results on counter-current flow and flooding in an elbow between a vertical and a horizontal run. The experimental technique used allowed not only the flooding limit to be determined, but also the entire partial delivery region to be studied as well. The influence that various size orifices placed in the horizontal run have on both the delivered liquid flow rates and on the flooding limits is also examined. It is observed that both the flooding limits and the delivered liquid flow rates decrease with decreasing orifice size. Further, it is also observed that the mechanisms that govern the partial delivery of the liquid are significantly different when an orifice is present in the horizontal leg as compared to the case when no orifice is present.

  9. Flow and habitat effects on juvenile fish abundance in natural and altered flow regimes

    USGS Publications Warehouse

    Freeman, Mary C.; Bowen, Z.H.; Bovee, K.D.; Irwin, E.R.

    2001-01-01

    Conserving biological resources native to large river systems increasingly depends on how flow-regulated segments of these rivers are managed. Improving management will require a better understanding of linkages between river biota and temporal variability of flow and instream habitat. However, few studies have quantified responses of native fish populations to multiyear (>2 yr) patterns of hydrologic or habitat variability in flow-regulated systems. To provide these data, we quantified young-of-year (YOY) fish abundance during four years in relation to hydrologic and habitat variability in two segments of the Tallapoosa River in the southeastern United States. One segment had an unregulated flow regime, whereas the other was flow-regulated by a peak-load generating hydropower dam. We sampled fishes annually and explored how continuously recorded flow data and physical habitat simulation models (PHABSIM) for spring (April-June) and summer (July-August) preceding each sample explained fish abundances. Patterns of YOY abundance in relation to habitat availability (median area) and habitat persistence (longest period with habitat area continuously above the long-term median area) differed between unregulated and flow-regulated sites. At the unregulated site, YOY abundances were most frequently correlated with availability of shallow-slow habitat in summer (10 species) and persistence of shallow-slow and shallow-fast habitat in spring (nine species). Additionally, abundances were negatively correlated with 1-h maximum flow in summer (five species). At the flow-regulated site, YOY abundances were more frequently correlated with persistence of shallow-water habitats (four species in spring; six species in summer) than with habitat availability or magnitude of flow extremes. The associations of YOY with habitat persistence at the flow-regulated site corresponded to the effects of flow regulation on habitat patterns. Flow regulation reduced median flows during spring and

  10. Aerothermodynamics of compressible flow past a flat plate in the slip-flow regime

    NASA Astrophysics Data System (ADS)

    Cheng, Chi-Yang; Dai, Yi; Li, Genong; Hu, Yitao; Lai, Ming-Chia

    2015-11-01

    Compressible flow past a flat plate in the slip-flow regime features a very simple geometry and flow field, but it retains the most relevant and interesting physics in high-speed rarefied gas dynamics. In the slip-flow regime, the aerothermodynamic issues, especially the recovery factors and the convection heat transfer correlation, are the focus of this presentation. We first present the detailed similarity equations, especially the transformed Maxwell's slip and jump boundary conditions, and the equations for the Chapman-Rubesin parameter as well as how we incorporate the variable gas properties and the constitutive scaling model for the Knudsen layer in the similarity equations. The similarity solutions are compared with results published by E. R. van Driest [NACA Technical Note 2597, 1952]. We point out that van Driest's solutions were computed by using no-slip and no-jump boundary conditions. The recovery factor and Nusselt number of the plate are shown as functions of the Reynolds number and the Mach number. Finally, the similarity solutions are also compared with simulations of a two-dimensional computational fluid dynamics model solving the full Navier-Stokes-Fourier equations with slip and jump boundary conditions.

  11. LHe Flow Regime/Pressure Drop for D0 Solenoid at Steady State Conditions

    SciTech Connect

    Rucinski, R.; /Fermilab

    1993-03-03

    This paper describes in a note taking format what was learned from several sources on two phase liquid helium flow regimes and pressure drops as applied to the D-Zero solenoid upgrade project. Calculations to estimate the steady state conditions for the D-Zero solenoid at 5, 10 and 15 g/s are also presented. For the lower flow rates a stratified type regime can be expected with a pressure drop less than 0.5 psi. For the higher flow rate a more homogeneous flow regime can be expected with a pressure drop between 0.4 to 1.5 psi.

  12. Laboratory and numerical evaluation of borehole methods for subsurface horizontal flow characterization.

    SciTech Connect

    Pedler, William H. (Radon Abatement Systems, Inc., Golden, CO); Jepsen, Richard Alan (Sandia National Laboratories, Carlsbad, NM)

    2003-08-01

    The requirement to accurately measure subsurface groundwater flow at contaminated sites, as part of a time and cost effective remediation program, has spawned a variety of flow evaluation technologies. Validation of the accuracy and knowledge regarding the limitations of these technologies are critical for data quality and application confidence. Leading the way in the effort to validate and better understand these methodologies, the US Army Environmental Center has funded a multi-year program to compare and evaluate all viable horizontal flow measurement technologies. This multi-year program has included a field comparison phase, an application of selected methods as part of an integrated site characterization program phase, and most recently, a laboratory and numerical simulator phase. As part of this most recent phase, numerical modeling predictions and laboratory measurements were made in a simulated fracture borehole set-up within a controlled flow simulator. The scanning colloidal borescope flowmeter (SCBFM) and advanced hydrophysical logging (NxHpL{trademark}) tool were used to measure velocities and flow rate in a simulated fractured borehole in the flow simulator. Particle tracking and mass flux measurements were observed and recorded under a range of flow conditions in the simulator. Numerical models were developed to aid in the design of the flow simulator and predict the flow conditions inside the borehole. Results demonstrated that the flow simulator allowed for predictable, easily controlled, and stable flow rates both inside and outside the well. The measurement tools agreed well with each other over a wide range of flow conditions. The model results demonstrate that the Scanning Colloidal Borescope did not interfere with the flow in the borehole in any of the tests. The model is capable of predicting flow conditions and agreed well with the measurements and observations in the flow simulator and borehole. Both laboratory and model results showed a

  13. Modality transition-based network from multivariate time series for characterizing horizontal oil-water flow patterns

    NASA Astrophysics Data System (ADS)

    Ding, Mei-Shuang; Jin, Ning-De; Gao, Zhong-Ke

    2015-11-01

    The simultaneous flow of oil and water through a horizontal pipe is a common occurrence during petroleum industrial processes. Characterizing the flow behavior underlying horizontal oil-water flows is a challenging problem of significant importance. In order to solve this problem, we carry out experiment to measure multivariate signals from different flow patterns and then propose a novel modality transition-based network to analyze the multivariate signals. The results suggest that the local betweenness centrality and weighted shortest path of the constructed network can characterize the transitions of flow conditions and further allow quantitatively distinguishing and uncovering the dynamic flow behavior underlying different horizontal oil-water flow patterns.

  14. Horizontal Flows in the Photosphere and Subphotosphere of Two Active Regions

    NASA Technical Reports Server (NTRS)

    Liu, Yang; Zhao, Junwei; Schuck, P. W.

    2012-01-01

    We compare horizontal flow fields in the photosphere and in the subphotosphere (a layer 0.5 megameters below the photosphere) in two solar active regions: AR11084 and AR11158. AR11084 is a mature, simple active region without significant flaring activity, and AR11158 is a multipolar, complex active region with magnetic flux emerging during the period studied. Flows in the photosphere are derived by applying the Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) on HMI-observed vector magnetic fields, and the subphotospheric flows are inferred by time-distance helioseismology using HMI-observed Dopplergrams. Similar flow patterns are found for both layers for AR11084: inward flows in the sunspot umbra and outward flows surrounding the sunspot. The boundary between the inward and outward flows, which is slightly different in the photosphere and the subphotosphere, is within the sunspot penumbra. The area having inward flows in the subphotosphere is larger than that in the photosphere. For AR11158, flows in these two layers show great similarities in some areas and significant differences in other areas. Both layers exhibit consistent outward flows in the areas surrounding sunspots. On the other hand, most well-documented flux-emergence-related flow features seen in the photosphere do not have counterparts in the subphotosphere. This implies that the horizontal flows caused by flux emergence do not extend deeply into the subsurface.

  15. System-focused environmental flow regime prescription, monitoring and adaptive management

    NASA Astrophysics Data System (ADS)

    Hetherington, David; Lexartza Artza, Irantzu

    2016-04-01

    The definition of appropriate environmental flow regimes through hydropower schemes and water storage reservoirs is key part of mitigation. Insufficient (magnitude and variability) environmental flows can result in much environmental harm with negative impacts being encountered by morphological, ecological and societal systems. Conventionally, environmental flow regimes have been determined by using generic protocols and guidance such as the Tennant method of environmental flow estimation. It is generally accepted that such approaches to minimum environmental flow definition, although being a useful starting point, are not universally applicable across catchment typologies and climatic regions. Such approaches will not always produce conditions that would be associated with 'Good Ecological Status' under the Water framework Directive (or equivalent). Other similar approaches to minimum environmental flow estimation are used that are specific to geographies, yet still the associated guidance rarely thoroughly covers appropriate definition for healthy holistic systems across the flow regime. This paper draws on experience of system-focused environmental flow regime determination in the UK and the Georgian Caucasus Mountains, which allowed for a critical analysis of more conventional methods to be undertaken. The paper describes a recommended approach for determining appropriate environmental flow regimes based on analysis of the impacted geomorphological, ecological and societal systems in a way which is sensitive to the local holistic environment and associated complexities and interactions. The paper suggests that a strong understanding of the local geomorphology in key in predicting how flows will manifest habitat differently across the flow regime, and be spatially dynamic. Additionally, an understanding of the geomorphological system allows the flow of course and fine sediment to be factored into the initial suggested environmental flow regime. It is suggested

  16. Borehole flowmeter measurements of horizontal groundwater flow before and during an aquifer test in central Indiana

    NASA Astrophysics Data System (ADS)

    Lampe, D. C.

    2009-12-01

    Horizontal borehole flowmeters will be used by the U.S. Geological Survey’s Indiana Water Science Center during an aquifer test in an outwash aquifer adjacent to the White River in central Indiana to determine directions and velocities of horizontal groundwater flow. Borehole flowmeters will provide point measurements of horizontal groundwater flow direction and velocity in four observation wells installed around the producing well. The point flow directions and velocities will be used to evaluate whether the aquifer test induces flow from the direction of nearby hydrologic boundaries: a river, and two adjacent tributaries, and/or from normally upgradient parts of the outwash aquifer system. Final calculations of flow velocity in the formation will include a correction factor based on laboratory flowmeter data. Correction factor data will be collected in the same type of well screen as the observation wells that is emplaced in a laboratory simulator packed with sand from the outwash aquifer and operated at known flow volumes and directions. Flowmeter-based groundwater flow directions and velocities that are made before and during the aquifer test, in combination with recorded water-level fluctuations, will be evaluated to understand groundwater/surface-water interactions and sources of groundwater to the producing well.

  17. Homogenization of precipitation and flow regimes across China: Changing properties, causes and implications

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Gu, Xihui; Singh, Vijay P.; Xu, Chong-Yu; Kong, Dongdong; Xiao, Mingzhong; Chen, Xiaohong

    2015-11-01

    Homogenization and similarities of precipitation and flow regimes across China are thoroughly investigated using Gini coefficient analysis method and the Analysis Of Similarity (ANOSIM) technique, respectively based on daily precipitation data from 554 meteorological stations and monthly streamflow data from 370 hydrological stations covering the period of 1960-2000. The results indicate that: (1) Homogenization of precipitation regimes is increasing from the northwest to the southeast China. However, different spatial patterns of homogenization of flow regions are identified. Spatially, lower homogenization of flow regimes is detected in the northeast China and higher homogenization of flow regimes in the central and southeast China. Temporally, flow regimes during 1961-2000 are characterized mainly by increasing homogenization, and it is particularly true after 1980; (2) precipitation regimes during 1961-2000 are characterized by decreasing dissimilarities. Larger areas of China are characterized by decreasing dissimilarities of precipitation regimes during 1980-2000 when compared to those during 1961-1980, which should be due to increasing precipitation concentration and intensifying precipitation regimes in recent years; (3) distinctly dissimilar precipitation and flow regimes can be identified between geographically separate river basins. Interregional similarities of flow regimes are enhancing after 1980 when compared to those before 1980 though interregional similarities of precipitation regimes are not changed much; and (4) spatial mismatch is evident in terms of spatial range and changing degree of flow and precipitation regimes. Roughly spatial match can be observed between changes of flow and precipitation indicates and it is particularly the case for precipitation and flow changes in dry season such as winter in China. However, influences of human activities and precipitation changes on streamflow are varying as for specific river basins, such as the

  18. Aircraft wake flow effect and horizontal tail buffet. [pressure distribution and responses of fighter aircraft in transonic maneuvers

    NASA Technical Reports Server (NTRS)

    Hwang, C.; Pi, W. S.

    1979-01-01

    As part of a program to investigate the fluctuating pressure distribution and response behavior of a fighter aircraft in transonic maneuver, an F-5A scale model has previously been tested in an 11-ft transonic wind tunnel. The model, with a number of static and dynamic pressure transducers imbedded in the lifting surfaces was tested at various angles of attack up to 16 deg. In this paper, test results of particular interest to wake flow and horizontal tail buffet are described. It is shown that the dynamic pressure data on the tail surface at the specified flight conditions serve to determine the local dynamic loads. They also influence the control performance of the aircraft under maneuver conditions where buffet is encountered. The data presented demonstrate a number of contributing factors that affect the tail dynamic pressures in the transonic regime.

  19. Experimental on two sensors combination used in horizontal pipe gas-water two-phase flow

    SciTech Connect

    Wu, Hao; Dong, Feng

    2014-04-11

    Gas-water two phase flow phenomenon widely exists in production and living and the measurement of it is meaningful. A new type of long-waist cone flow sensor has been designed to measure two-phase mass flow rate. Six rings structure of conductance probe is used to measure volume fraction and axial velocity. The calibration of them have been made. Two sensors have been combined in horizontal pipeline experiment to measure two-phase flow mass flow rate. Several model of gas-water two-phase flow has been discussed. The calculation errors of total mass flow rate measurement is less than 5% based on the revised homogeneous flow model.

  20. Horizontal Flow of Semantic and Phonological Information in Chinese Spoken Sentence Production

    ERIC Educational Resources Information Center

    Yang, Jin-Chen; Yang, Yu-Fang

    2008-01-01

    A variant of the picture--word interference paradigm was used in three experiments to investigate the horizontal information flow of semantic and phonological information between nouns in spoken Mandarin Chinese sentences. Experiment 1 demonstrated that there is a semantic interference effect when the word in the second phrase (N3) and the first…

  1. Two Phase Flow Modeling: Summary of Flow Regimes and Pressure Drop Correlations in Reduced and Partial Gravity

    NASA Technical Reports Server (NTRS)

    Balasubramaniam, R.; Rame, E.; Kizito, J.; Kassemi, M.

    2006-01-01

    The purpose of this report is to provide a summary of state-of-the-art predictions for two-phase flows relevant to Advanced Life Support. We strive to pick out the most used and accepted models for pressure drop and flow regime predictions. The main focus is to identify gaps in predictive capabilities in partial gravity for Lunar and Martian applications. Following a summary of flow regimes and pressure drop correlations for terrestrial and zero gravity, we analyze the fully developed annular gas-liquid flow in a straight cylindrical tube. This flow is amenable to analytical closed form solutions for the flow field and heat transfer. These solutions, valid for partial gravity as well, may be used as baselines and guides to compare experimental measurements. The flow regimes likely to be encountered in the water recovery equipment currently under consideration for space applications are provided in an appendix.

  2. The dynamical regime of fluid flow at the core surface

    NASA Astrophysics Data System (ADS)

    Bloxham, Jeremy

    1988-06-01

    An alternative method for determining the fluid motion immediately beneath the core-mantle boundary is presented which is based on solving the full nonlinear core motions problem. This method is used to examine three dynamical hypotheses about the flow: (1) the steady motions hypothesis; (2) the geostrophic hypothesis; and (3) the toroidal flow hypothesis. Better fits to the field are obtained with the toroidal flows than with geostrophic flows, casting considerable doubt on the validity of the geostrophic hypothesis. Additionally, some indication is found that failure of the frozen-flux approximation, a concomitant assumption, may be a serious obstacle to obtaining reliable maps of the core fluid flow.

  3. Optimal Ranking Regime analysis of TreeFlow dendrohydrological reconstructions

    NASA Astrophysics Data System (ADS)

    Mauget, S. A.

    2015-03-01

    The Optimal Ranking Regime (ORR) method was used to identify 6-100 year time windows containing significant ranking sequences in 55 western US streamflow reconstructions, and reconstructions of the level of the Great Salt Lake and San Francisco Bay salinity during 1500-2007. The method's ability to identify optimally significant and non-overlapping runs of low and high rankings allows it to re-express a reconstruction time series as a simplified sequence of regime segments marking intra- to multi-decadal (IMD) periods of low or high streamflow, lake level, or salinity. Those ORR sequences, referred to here as Z lines, can be plotted to identify consistent regime patterns in the analysis of numerous reconstructions. The Z lines for the 57 reconstructions evaluated here show a common pattern of IMD cycles of drought and pluvial periods during the late 16th and 17th centuries, a relatively dormant period during the 18th century, and the reappearance of alternating dry and wet IMD periods during the 19th and early 20th centuries. Although this pattern suggests the possibility of similarly active and inactive oceanic modes in the North Pacific and North Atlantic, such centennial-scale patterns are not evident in the ORR analyses of reconstructed Pacific Decadal Oscillation (PDO), El Niño-Southern Oscillation, and North Atlantic seas-surface temperature variation. But given the inconsistency in the analyses of four PDO reconstructions the possible role of centennial-scale oceanic mechanisms is uncertain. In future research the ORR method might be applied to climate reconstructions around the Pacific Basin to try to resolve this uncertainty. Given its ability to compare regime patterns in climate reconstructions derived using different methods and proxies, the method may also be used in future research to evaluate long-term regional temperature reconstructions.

  4. Optimal ranking regime analysis of TreeFlow dendrohydrological reconstructions

    NASA Astrophysics Data System (ADS)

    Mauget, S. A.

    2015-08-01

    The optimal ranking regime (ORR) method was used to identify 6-100-year time windows containing significant ranking sequences in 55 western US streamflow reconstructions, and reconstructions of the level of the Great Salt Lake and San Francisco Bay salinity during 1500-2007. The method's ability to identify optimally significant and non-overlapping runs of low- and high-rankings allows it to re-express a reconstruction time series as a simplified sequence of regime segments marking intra- to multi-decadal (IMD) periods of low or high streamflow, lake level, and salinity. Those ORR sequences, referred to here as Z-lines, can be plotted to identify consistent regime patterns in the analysis of numerous reconstructions. The Z-lines for the 57 reconstructions evaluated here show a common pattern of IMD cycles of drought and pluvial periods during the late 16th and 17th centuries, a relatively dormant period during the 18th century, and the reappearance of alternating dry and wet IMD periods during the 19th and early 20th centuries. Although this pattern suggests the possibility of similarly active and inactive oceanic modes in the North Pacific and North Atlantic, such centennial-scale patterns are not evident in the ORR analyses of reconstructed Pacific Decadal Oscillation (PDO), El Niño-Southern Oscillation, and North Atlantic sea-surface temperature variation. However, given the inconsistency in the analyses of four PDO reconstructions, the possible role of centennial-scale oceanic mechanisms is uncertain. In future research the ORR method might be applied to climate reconstructions around the Pacific Basin to try to resolve this uncertainty. Given its ability to compare regime patterns in climate reconstructions derived using different methods and proxies, the method may also be used in future research to evaluate long-term regional temperature reconstructions.

  5. Flow regime transitions in a bubble column with a paraffin wax as the liquid medium

    SciTech Connect

    Bukur, D.B.; Petrovic, D.; Daly, J.G.

    1987-06-01

    Gas hold-up measurements were made in a 0.051-m-diameter by 3.05-m-long glass bubble column with a molten paraffin wax as the liquid medium. For temperatures between 230 and 280/sup 0/C, there is a range of gas velocities where two modes of operation are possible, and they are referred to as the foamy and the turbulent bubbling flow regimes. The start-up velocity determines which flow regime are obtained. Transitions between these two flow regimes occur and are influenced by the temperature (i.e., the liquid viscosity) and the gas distributor design. Lower temperatures and/or perforated plate distributors with larger holes favor the existence of the turbulent bubbling flow regime.

  6. Venus' nighttime horizontal plasma flow, 'magnetic congestion', and ionospheric hole production

    NASA Technical Reports Server (NTRS)

    Grebowsky, J. M.; Mayr, H. G.; Curtis, S. A.; Taylor, H. A., Jr.

    1983-01-01

    A simple rectilinear, two-dimensional MHD model is used to investigate the effects of field-aligned plasma loss and cooling on a dense plasma convecting across a weak magnetic field, in order to illumine the Venus nighttime phenomena of horizontal plasma flow, magnetic congestion and ionospheric hole production. By parameterizing field-aligned variations and explicitly solving for cross magnetic field variations, it is shown that the abrupt horizontal enhancements of the vertical magnetic field, as well as sudden decreases of the plasma density to very low values (which are characteristic of ionospheric holes), can be produced in the presence of field-aligned losses.

  7. Salix response to different flow regimes in controlled experiments: first results

    NASA Astrophysics Data System (ADS)

    Gorla, Lorenzo; Signarbieux, Constant; Buttler, Alexandre; Perona, Paolo

    2013-04-01

    Dams and water management for hydropower production, agriculture and other human activities alter the natural flow regime of rivers. The new river hydrograph components depend on the type of impoundment and the policy of regulation but such a different flow regime will likely affect the riparian environment. The main challenge in order to define sustainable flow releases is to quantify hydrological effects in terms of geomorphology and ecosystem response. A considerable lack of knowledge still affects the link hydrology-ecology and inadequate flow rules (e.g., minimal or residual flows) are consequently still widespread: further research in this direction is urgently required. We present an experiment, which aims to investigate the effects of different water stage regimes on riparian vegetation (salix Viminalis cuttings) development in a temperate region (Switzerland). This work describes the installation setup, together with the first results concerning the first of the two scheduled seasons of campaign. Sixty Salix cuttings were planted in non-cohesive sandy-gravel sediment within 1 meter tall plastic pots installed outside in the EPFL campus. After grouping them in three batteries, the water level within them has been varying following three river regimes simulated by adjusting the water level within the pots by means of an automatic hydraulic system. The three water level regimes reproduce a natural flow regime, a minimum residual flow policy, which only conserves peaks during flooding conditions, and an artificial regime conserving only low frequencies (e.g., seasonality) of the natural dynamic. The natural flow regime of the first battery has been applied for two months to the entire system; the three regimes above said started in June 2012. This triggered a plant response transitory regime, which we monitored by measuring plant growth, soil and atmospheric variables. Particularly, measures concern with branches development leaves photosynthesis and

  8. Possible flow regimes of adiabatic one-dimensional compressible fluid flow with friction in convergent and divergent ducts.

    NASA Technical Reports Server (NTRS)

    Shouman, A. R.; Garcia, C. E.

    1971-01-01

    An analytical solution for the compressible one-dimensional flow in convergent and divergent ducts with friction is obtained. It is found that a nondimensional parameter, N, can be formed using the friction factor, duct half-angle and the ratio of specific heats of the gas. Seven flow regimes are describable with the solution, based on certain bounds on the magnitude of N. The regimes are discussed and corollary data are presented graphically.

  9. Two-phase slug flow splitting phenomenon at a regular horizontal side-arm tee

    SciTech Connect

    Arirachakaran, S.

    1990-01-01

    An experimental and theoretical investigation of two-phase slug flow splitting at a regular horizontal side-arm tee was performed. A new test facility was designed and constructed, suitable for acquiring pertinent slug flow splitting data. Elaborate measurement techniques and sophisticated instrumentation and computerized data acquisition system were implemented to assure high-quality data for this complex flow pattern. Splitting data were acquired for a wide range of slug flow conditions. Data analysis showed a steep-slope trend, exhibited by the splitting curves. Under these conditions, liquid preferentially flows into the run arm due to its high inertia forces associated with slug flow. A model which describes preferential liquid movement under slug flow conditions in a regular horizontal pipe tee has been developed from physical principles. The model consists of two splitting mechanisms. These include the Breaking-of-a-Dam mechanism for the slug body, and the Equilibrium Stratified Film concept for the gas pocket-liquid film region. The proposed slug flow splitting model along with other published splitting prediction methods are tested against new data acquired in the present study, and additional data available in the literature. Good agreement was found between the proposed model and the data. The present model also outperforms other available methods.

  10. The impact of stormwater source-control strategies on the (low) flow regime of urban catchments.

    PubMed

    Hamel, Perrine; Fletcher, Tim D

    2014-01-01

    Stormwater management strategies increasingly recognise the need to emulate the pre-development flow regime, in addition to reducing pollutant concentrations and loads. However, it is unclear whether current design approaches for stormwater source-control techniques are effective in restoring the whole flow regime, and in particular low flows, towards their pre-development levels. We therefore modelled and compared a range of source-control stormwater management strategies, including some specifically tailored towards enhancing baseflow processes. The strategies were assessed based on the total streamflow volume and three low flow metrics. Strategies based on harvesting tanks showed much greater volume reduction than those based on raingardens. Strategies based on a low flow rate release, aimed at mimicking natural baseflow, failed to completely restore the baseflow regime. We also found that the sensitivity of the low flow metrics to the proportion of catchment treated varied amongst metrics, illustrating the importance of metrics selection in the assessment of stormwater strategies. In practice, our results suggest that realistic scenarios using low flow release from source-control techniques may not be able to fully restore the low flow regime, at least for perennial streams. However, a combination of feasibly-sized tanks and raingardens is likely to restore the baseflow regime to a great extent, while also benefitting water quality through the retention and filtration processes.

  11. Scaling laws and flow structures of double diffusive convection in the finger regime

    NASA Astrophysics Data System (ADS)

    Yang, Yantao; Verzicco, Roberto; Lohse, Detlef

    2016-09-01

    Direct numerical simulations are conducted for double diffusive convection (DDC) bounded by two parallel plates, with fluid properties similar to the values of seawater. The DDC flow is driven by an unstable salinity difference and stabilized at the same time by a temperature difference. For these conditions the flow can be in the finger regime. We develop scaling laws for three key response parameters of the system: The non-dimensional salinity flux $Nu_S$ mainly depends on the salinity Rayleigh number $Ra_S$, which measures the strength of the salinity difference, and exhibits a very weak dependence on the density ratio $\\Lambda$, which is the ratio of the buoyancy forces induced by two scalar differences. The non-dimensional flow velocity $Re$ and the non-dimensional heat flux $Nu_T$ are dependent on both $Ra_S$ and $\\Lambda$. However, the rescaled Reynolds number $Re\\Lambda^{\\alpha^{\\rm eff}_u}$ and the rescaled convective heat flux $(Nu_T-1)\\Lambda^{\\alpha^{\\rm eff}_T}$ depend only on $Ra_S$. The two exponents are dependent on the fluid properties and are determined from the numerical results. Moreover, the behaviors of $Nu_S$ and $Re\\Lambda^{\\alpha^{\\rm eff}_u}$ agree with the predictions of the Grossmann-Lohse theory which was originally developed for the Rayleigh-B\\'{e}nard flow. The non-dimensional salt-finger width and the thickness of the velocity boundary layers, after being rescaled by $\\Lambda^{\\alpha^{\\rm eff}_u/2}$, collapse and obey a similar power-law scaling relation with $Ra_S$. When $Ra_S$ is large enough, salt fingers do not extend from one plate to the other and horizontal zonal flows emerge in the bulk region. We then show that the current scaling strategy can be successfully applied to the experimental results of a heat-copper-ion system~(Hage and Tilgner, Phys. Fluids, 22, 076603, 2010).

  12. A model for fluid flow during saturated boiling on a horizontal cylinder

    NASA Technical Reports Server (NTRS)

    Kheyrandish, K.; Dalton, C.; Lienhard, J. H.

    1987-01-01

    A model has been developed to represent the vapor removal pattern in the vicinity of a cylinder during nucleate flow boiling across a horizontal cylinder. The model is based on a potential flow representation of the liquid and vapor regions and an estimate of the losses that should occur in the flow. Correlation of the losses shows a weak dependence on the Weber number and a slightly stronger dependence on the saturated liquid-to-vapor density ratio. The vapor jet thickness, which is crucial to the prediction of the burnout heat flux, and the shape of the vapor film are predicted. Both are verified by qualitative experimental observations.

  13. Prediction of slug frequency in horizontal two-phase slug flow

    SciTech Connect

    Tronconi, E. )

    1990-05-01

    In this paper available data on slug frequency in horizontal two-phase intermittent flow are predicted with adequate accuracy by assuming that the slug frequency is one half of the frequency of the unstable waves precursors slugs, as determined according to published analyses of finite amplitude waves in conduits. The experimental effects of gas and liquid flow rates, pipe diameter, gas density and liquid viscosity on slug frequency are explained by modifications of the wave properties due to changes in the liquid level of the stratified flow existing in the pipe inlet region prior to slug formation. Simple generalized equations are proposed to estimate the slug frequency for engineering calculations.

  14. Observational evidence of preferred flow regimes in the Northern Hemisphere winter stratosphere

    NASA Technical Reports Server (NTRS)

    Pierce, R. B.; Fairlie, T. D. A.

    1993-01-01

    Ten years of stratospheric geopotential height data are analyzed in an attempt to determine whether there are preferred flow regimes in the Northern Hemisphere winter stratosphere. The data are taken from Stratospheric Sounding Units on board NOAA satellites. The probability density estimate of the amplitude of the wavenumber 1 10-mb height is found to be bimodal. The density distribution is composed of a dominant large-amplitude mode and a less frequent low-amplitude mode. When the wavenumber 1 10-mb height data are projected onto the phase plane defined by the 10-mb zonal-mean winds and wavenumber 1 100-mb heights, three preferred regimes are evident. The small-amplitude mode separates into a strong zonal wind-weak wave regime and a weak zonal wind-weak wave regime. The large-amplitude mode is an intermediate zonal wind-strong wave regime. Transitions between the large-amplitude regime and the weak zonal wind-weak wave regime are found to be associated with major stratospheric warmings. The clustering of the stratospheric data into the preferred flow regimes is interpreted in light of the bifurcation properties of the Holton and Mass model. The interannual variability of the Northern Hemisphere winter stratosphere is interpreted in terms of the relative frequency of the observed preferred regimes.

  15. The expanding thermal arc plasma: the low-flow regime

    NASA Astrophysics Data System (ADS)

    van de Sanden, M. C. M.; Tobin, J. A.

    1998-02-01

    This paper reports on experiments on an expanding thermal arc plasma using pure argon flows in the 50 to 500 sccm range. From pressure and voltage measurements on the arc it is verified that the arc plasma is still a thermal plasma at these low flows. Langmuir probe measurements of the radial profiles downstream using different flows and chamber pressures are presented and discussed. These measurements indicate an enhanced ion loss for low flows at constant pressure. The enhanced loss is explained by the increase in residence time and due to this a relatively large volumetric recombination. The sputter etch rate of PECVD deposited silicon oxide at 100 mTorr and 400 V DC bias is measured and compared with the results of the Langmuir probe.

  16. Intermittent flow regimes near the convection threshold in ferromagnetic nanofluids.

    PubMed

    Krauzina, Marina T; Bozhko, Alexandra A; Putin, Gennady F; Suslov, Sergey A

    2015-01-01

    The onset and decay of convection in a spherical cavity filled with ferromagnetic nanofluid and heated from below are investigated experimentally. It is found that, unlike in a single-component Newtonian fluid where stationary convection sets in as a result of supercritical bifurcation and where convection intensity increases continuously with the degree of supercriticality, convection in a multicomponent ferromagnetic nanofluid starts abruptly and has an oscillatory nature. The hysteresis is observed in the transition between conduction and convection states. In moderately supercritical regimes, the arising fluid motion observed at a fixed temperature difference intermittently transitions from quasiharmonic to essentially irregular oscillations that are followed by periods of a quasistationary convection. The observed oscillations are shown to result from the precession of the axis of a convection vortex in the equatorial plane. When the vertical temperature difference exceeds the convection onset value by a factor of 2.5, the initially oscillatory convection settles to a steady-state regime with no intermittent behavior detected afterward. The performed wavelet and Fourier analyses of thermocouple readings indicate the presence of various oscillatory modes with characteristic periods ranging from one hour to several days. PMID:25679711

  17. Instability of a thin film flowing on a rotating horizontal or inclined plane.

    PubMed

    Dávalos-Orozco, L A; Busse, F H

    2002-02-01

    In this paper the instability of a thin fluid film flowing under the effects of gravity, Coriolis, and centrifugal forces is investigated. It is supposed that the film flows far from the axis of rotation on a plane which may be horizontal or inclined with respect to the horizontal. In the former case, the flow is only driven by the centrifugal force while in the latter case, the flow is driven by the components of centrifugal force and gravity along the plane. This case may also be considered as the flow down a rotating cone but far from the apex. The stabilizing influence of rotation on the film flow increases with the rotation rate. Up to a certain critical rate of rotation, the film flowing down the rotating inclined plane (or cone) is more stable than the flow on the horizontal rotating plane while above this rate of rotation the situation is reversed. The instability above the critical rate is associated with a finite wave number in contrast to the vanishing wave number of the instability below the critical rate. The possibility of Ekman layer instabilities is also investigated. An equation describing the nonlinear evolution of surface waves is also obtained. Moreover, this equation is simplified for the case in which the amplitudes are very small. An equation including dissipation as well as dispersion is derived whose solutions may possess solitary waves, as in the case of similar equations considered in the literature. These solutions are likely to correspond to the solitary spiral waves observed in experiments.

  18. Wind Tunnel Investigation of the Near-wake Flow Dynamics of a Horizontal Axis Wind Turbine

    NASA Astrophysics Data System (ADS)

    Hashemi-Tari, P.; Siddiqui, K.; Refan, M.; Hangan, H.

    2014-06-01

    Experiments conducted in a large wind tunnel set-up investigate the 3D flow dynamics within the near-wake region of a horizontal axis wind turbine. Particle Image Velocimetry (PIV) measurements quantify the mean and turbulent components of the flow field. Measurements are performed in multiple adjacent horizontal planes in order to cover the area behind the rotor in a large radial interval, at several locations downstream of the rotor. The measurements were phase-locked in order to facilitate the re-construction of the threedimensional flow field. The mean velocity and turbulence characteristics clearly correlate with the near-wake vortex dynamics and in particular with the helical structure of the flow, formed immediately behind the turbine rotor. Due to the tip and root vortices, the mean and turbulent characteristics of the flow are highly dependent on the azimuth angle in regions close to the rotor and close to the blade tip and root. Further from the rotor, the characteristics of the flow become phase independent. This can be attributed to the breakdown of the vortical structure of the flow, resulting from the turbulent diffusion. In general, the highest levels of turbulence are observed in shear layer around the tip of the blades, which decrease rapidly downstream. The shear zone grows in the radial direction as the wake moves axially, resulting in velocity recovery toward the centre of the rotor due to momentum transport.

  19. Horizontal flow of semantic and phonological information in Chinese spoken sentence production.

    PubMed

    Yang, Jin-Chen; Yang, Yu-Fang

    2008-01-01

    A variant of the picture-word interference paradigm was used in three experiments to investigate the horizontal information flow of semantic and phonological information between nouns in spoken Mandarin Chinese sentences. Experiment 1 demonstrated that there is a semantic interference effect when the word in the second phrase (N3) and the first noun in the initial phrase (N1) are semantically related, while there is no effect when N3 and the second noun in the initial phrase (N2) are semantically related. Experiments 2 and 3 showed that there is a phonological facilitation effect only when the two phonologically related words are both in the initial phrase, and there is no effect when they are in different phrases. Reinforcing the findings of an earlier study of horizontal information flow by Smith and Wheeldon (2004), our results indicate that there is a temporal overlap in the access of the nouns in spoken Mandarin Chinese sentences and a flow of semantic and phonological information between these nouns. Moreover, our results are incompatible with a wholly parallel view of horizontal information flow and instead provide support for a view which is partly serial and partly parallel in nature. PMID:19626927

  20. Separation in the mixed convection boundary-layer radial flow over a constant temperature horizontal plate

    NASA Astrophysics Data System (ADS)

    Fernandez-Feria, R.; del Pino, C.; Fernández-Gutiérrez, A.

    2014-10-01

    The boundary-layer flow of a horizontal current emerging radially from a cylindrical vertical surface of radius r0 with a constant velocity over a heated horizontal wall at constant temperature is analyzed. The boundary-layer equations are made dimensionless with a radial characteristic length in which natural and forced convection become of the same order of magnitude, so that the Prandtl (Pr) number and Gr2/Re5 are the only nondimensional parameters governing the problem, where Gr and Re are the Grashof and Reynolds numbers based on r0, respectively. A similarity solution valid at the leading edge of the boundary-layer flow is obtained. It contains, as the first order correction to Blasius' thermal boundary layer solution, the effect of buoyancy, and as the second order correction the effect of the radial divergence of the flow. This solution is used to start the numerical integration of the equations to provide a criterion for when separation occurs. It is found that separation, based on the boundary layer model, occurs for Gr < B(Pr)Re5/2, where the Prandtl's number function B is characterized numerically and found to be almost constant. This separation location law is compared with experimental results for air flowing over a heated horizontal plate at constant temperature, finding a qualitative good agreement.

  1. Lava Fountaining Discharge Regime driven by Slug-to-Churn Flow Transition. (Invited)

    NASA Astrophysics Data System (ADS)

    Ripepe, M.; Pioli, L.; Marchetti, E.; Ulivieri, G.

    2013-12-01

    Lava fountaining episodes at Etna volcano appear characterized by the transition between Strombolian and Hawaiian end-member eruptive styles. There is no evidence for this transition in the seismic (i.e. seismic tremor) signal. However, infrasonic records provide unprecedented evidence on this flow transition. Each eruptive episode is characterized by distinctive common trend in the amplitude, waveform and frequency content of the infrasonic wavefield, which evidences the shift from discrete, and transient, strombolian to sustained, and oscillatory, lava fountain dynamics. Large scale experiments on the dynamics of two-phase flow of basaltic magmas show how the transition between different regimes mainly depends on gas volume flow, which in turn controls pressure distribution within the conduit and also magma vesicularity. In particular, while regular large bubble bursting is associated with slug flow regime, large amplitude and low frequency column oscillations are associated with churn flow. In large pipes, transition from slug to churn flow regime is independent on conduit diameter and it is reached at high superficial gas velocity. Lava fountaining episodes at Etna can be thus interpreted as induced by the transition from the slug (discrete strombolian) to churn flow (sustained lava fountain) regimes that is reflecting an increase in the gas discharge rate. Based on laboratory experiments, we calculate that transition between these two end-member explosive regimes at Etna occurs when gas superficial velocity is 76 m/s for near-the-vent stagnant magma conditions.

  2. Comparison of the transport of the aggregates of nanoscale zerovalent iron under vertical and horizontal flow.

    PubMed

    Li, Jing; Ghoshal, Subhasis

    2016-02-01

    Direct injection of nanoscale zerovalent iron (NZVI) particles is being considered for remediation of contaminated sites. However, the transport characteristics of NZVI under horizontal flow conditions are not fully understood. In this study, NZVI particles were stabilized with carboxymethyl cellulose (CMC) and injected in vertical and horizontal columns to compare the effects of the flow direction on the transport. Columns were packed with sand of mean grain diameters of 180, 340 or 1140 µm (referred to as fine, intermediate and coarse sand, respectively), and were injected with CMC-NZVI suspensions of 0.3, 1 or 3 g Fe L(-1). Experimental breakthrough curves showed that with the coarse and intermediate sands, the steady-state effluent concentration in the horizontal column were up to 84% lower than those in the vertical column regardless of the initial NZVI concentration. However, in the fine sand the differences were insignificant, except at the highest NZVI particle concentration. Additionally, in the horizontally-oriented columns containing the coarse or intermediated sand, NZVI aggregates particles were non-uniformly distributed in the cross-section of the columns and there higher deposition in the bottom-half of the cross-section due to gravity effects. These deposition patterns can be accounted for, in part, by the gravitational settling of the large aggregates of NZVI, especially at high NZVI concentrations. A particle trajectory analysis in three dimensions demonstrated that under horizontal flow, gravity forces resulted in lower deposition of NZVI on the bottom-half of a single collector, as particles approaching the bottom-half of the collector were deflected by gravity to collectors below. PMID:26498094

  3. Comparison of the transport of the aggregates of nanoscale zerovalent iron under vertical and horizontal flow.

    PubMed

    Li, Jing; Ghoshal, Subhasis

    2016-02-01

    Direct injection of nanoscale zerovalent iron (NZVI) particles is being considered for remediation of contaminated sites. However, the transport characteristics of NZVI under horizontal flow conditions are not fully understood. In this study, NZVI particles were stabilized with carboxymethyl cellulose (CMC) and injected in vertical and horizontal columns to compare the effects of the flow direction on the transport. Columns were packed with sand of mean grain diameters of 180, 340 or 1140 µm (referred to as fine, intermediate and coarse sand, respectively), and were injected with CMC-NZVI suspensions of 0.3, 1 or 3 g Fe L(-1). Experimental breakthrough curves showed that with the coarse and intermediate sands, the steady-state effluent concentration in the horizontal column were up to 84% lower than those in the vertical column regardless of the initial NZVI concentration. However, in the fine sand the differences were insignificant, except at the highest NZVI particle concentration. Additionally, in the horizontally-oriented columns containing the coarse or intermediated sand, NZVI aggregates particles were non-uniformly distributed in the cross-section of the columns and there higher deposition in the bottom-half of the cross-section due to gravity effects. These deposition patterns can be accounted for, in part, by the gravitational settling of the large aggregates of NZVI, especially at high NZVI concentrations. A particle trajectory analysis in three dimensions demonstrated that under horizontal flow, gravity forces resulted in lower deposition of NZVI on the bottom-half of a single collector, as particles approaching the bottom-half of the collector were deflected by gravity to collectors below.

  4. Impurity flows and plateau-regime poloidal density variation in a tokamak pedestal

    SciTech Connect

    Landreman, M.; Fueloep, T.; Guszejnov, D.

    2011-09-15

    In the pedestal of a tokamak, the sharp radial gradients of density and temperature can give rise to poloidal variation in the density of impurities. At the same time, the flow of the impurity species is modified relative to the conventional neoclassical result. In this paper, these changes to the density and flow of a collisional impurity species are calculated for the case when the main ions are in the plateau regime. In this regime, it is found that the impurity density can be higher at either the inboard or outboard side. This finding differs from earlier results for banana- or Pfirsch-Schlueter-regime main ions, in which case the impurity density is always higher at the inboard side in the absence of rotation. Finally, the modifications to the impurity flow are also given for the other regimes of main-ion collisionality.

  5. Laminar, turbulent, and inertial shear-thickening regimes in channel flow of neutrally buoyant particle suspensions.

    PubMed

    Lashgari, Iman; Picano, Francesco; Breugem, Wim-Paul; Brandt, Luca

    2014-12-19

    The aim of this Letter is to characterize the flow regimes of suspensions of finite-size rigid particles in a viscous fluid at finite inertia. We explore the system behavior as a function of the particle volume fraction and the Reynolds number (the ratio of flow and particle inertia to viscous forces). Unlike single-phase flows, where a clear distinction exists between the laminar and the turbulent states, three different regimes can be identified in the presence of a particulate phase, with smooth transitions between them. At low volume fractions, the flow becomes turbulent when increasing the Reynolds number, transitioning from the laminar regime dominated by viscous forces to the turbulent regime characterized by enhanced momentum transport by turbulent eddies. At larger volume fractions, we identify a new regime characterized by an even larger increase of the wall friction. The wall friction increases with the Reynolds number (inertial effects) while the turbulent transport is weakly affected, as in a state of intense inertial shear thickening. This state may prevent the transition to a fully turbulent regime at arbitrary high speed of the flow.

  6. Multiple Regimes of Flow, Stratification, and Turbulence in the Stable Boundary Layer

    NASA Astrophysics Data System (ADS)

    Monahan, A. H.; Rees, T.

    2014-12-01

    It is well established that the atmospheric Stable Boundary Layer (SBL) can display distinct regimes of flow. In the weakly stable boundary layer, turbulence is weak but continuous and the surface flow is coupled to that aloft. In the very stable boundary layer, turbulence collapses and the surface flow becomes decoupled from the flow above.This study demonstrates the clear presence of two distinct SBL regimes in a long record of observations from the 213m tower in Cabauw, Netherlands. These regimes are found in the joint distribution of near-surface stratification, shear, and vertically-averaged wind speed. Hidden Markov model (HMM) analysis is used to distinguish these regimes and objectively classify states as being in one regime or the other. This classification allows for a detailed diagnosis of the flow, stratification, and turbulence structures within each of the two regimes, as well as their relation to large-scale forcing through the geostrophic wind and cloud cover. Observational evidence is presented that the very stable boundary layer is produced by a previously-discussed positive feedback associated with a maximum sustainable turbulent heat flux.

  7. Using regional flow classes as references to analyse flow regime anomalies across a set of regulated Canadian rivers

    NASA Astrophysics Data System (ADS)

    McLaughlin, Fraser; Lapointe, Michel; Bourque, Guillaume; Boisclair, Daniel

    2014-11-01

    It is well established that a river's natural flow regime is a key determinant of ecological integrity and that dam regulated-flow releases can be detrimental to biotic communities and even affect river ecosystem structure (e.g. Poff and Zimmerman, 2010). Regional flow classes, groups of rivers that share similar natural flow regimes (called ‘river types' by Poff and Zimmerman (2010)) and to which regional fish communities are ‘adapted', have been proposed as units of analysis to identify significant damming related flow alteration (e.g. Poff, 1996; Poff and Zimmerman, 2010; McManamay et al., 2012a). Specifically, the natural range of flow behaviour within regional classes can be used to identify clearly anomalous flow features in rivers regulated by dams. Through ordination analysis on 70 ecologically important flow indices, we isolated five distinctive regional groupings of natural flow regimes among the 96 unregulated rivers located in study regions of South Eastern and South Western Canada, selected based on watershed characteristics as possible references for the 13 hydro-regulated, NSERC-HydroNet study rivers in British Columbia, Alberta, Ontario, Quebec and New Brunswick. The distinguishing characteristics of natural flow regimes within each flow class are explored through visualization in principal component space. The 16 regulated HydroNet sites were assigned to appropriate regional flow classes through discriminant function analysis based on shared geographic location and watershed characteristics. Anomalous flow features in the regulated rivers are then characterized by type and strength, based on identification of flow indices that are significantly different from observed natural variability in the relevant regional class. The magnitude distributions and the main axes of variability in index anomalies are analysed, across regions and regulation types (storage, peaking and run-of-the-river (RoR)). We also discuss the potential biological

  8. Multi-metric calibration of hydrological model to capture overall flow regimes

    NASA Astrophysics Data System (ADS)

    Zhang, Yongyong; Shao, Quanxi; Zhang, Shifeng; Zhai, Xiaoyan; She, Dunxian

    2016-08-01

    Flow regimes (e.g., magnitude, frequency, variation, duration, timing and rating of change) play a critical role in water supply and flood control, environmental processes, as well as biodiversity and life history patterns in the aquatic ecosystem. The traditional flow magnitude-oriented calibration of hydrological model was usually inadequate to well capture all the characteristics of observed flow regimes. In this study, we simulated multiple flow regime metrics simultaneously by coupling a distributed hydrological model with an equally weighted multi-objective optimization algorithm. Two headwater watersheds in the arid Hexi Corridor were selected for the case study. Sixteen metrics were selected as optimization objectives, which could represent the major characteristics of flow regimes. Model performance was compared with that of the single objective calibration. Results showed that most metrics were better simulated by the multi-objective approach than those of the single objective calibration, especially the low and high flow magnitudes, frequency and variation, duration, maximum flow timing and rating. However, the model performance of middle flow magnitude was not significantly improved because this metric was usually well captured by single objective calibration. The timing of minimum flow was poorly predicted by both the multi-metric and single calibrations due to the uncertainties in model structure and input data. The sensitive parameter values of the hydrological model changed remarkably and the simulated hydrological processes by the multi-metric calibration became more reliable, because more flow characteristics were considered. The study is expected to provide more detailed flow information by hydrological simulation for the integrated water resources management, and to improve the simulation performances of overall flow regimes.

  9. Assessment of flow regime alterations over a spectrum of temporal scales using wavelet-based approaches

    NASA Astrophysics Data System (ADS)

    Wu, Fu-Chun; Chang, Ching-Fu; Shiau, Jenq-Tzong

    2015-05-01

    The full range of natural flow regime is essential for sustaining the riverine ecosystems and biodiversity, yet there are still limited tools available for assessment of flow regime alterations over a spectrum of temporal scales. Wavelet analysis has proven useful for detecting hydrologic alterations at multiple scales via the wavelet power spectrum (WPS) series. The existing approach based on the global WPS (GWPS) ratio tends to be dominated by the rare high-power flows so that alterations of the more frequent low-power flows are often underrepresented. We devise a new approach based on individual deviations between WPS (DWPS) that are root-mean-squared to yield the global DWPS (GDWPS). We test these two approaches on the three reaches of the Feitsui Reservoir system (Taiwan) that are subjected to different classes of anthropogenic interventions. The GDWPS reveal unique features that are not detected with the GWPS ratios. We also segregate the effects of individual subflow components on the overall flow regime alterations using the subflow GDWPS. The results show that the daily hydropeaking waves below the reservoir not only intensified the flow oscillations at daily scale but most significantly eliminated subweekly flow variability. Alterations of flow regime were most severe below the diversion weir, where the residual hydropeaking resulted in a maximum impact at daily scale while the postdiversion null flows led to large hydrologic alterations over submonthly scales. The smallest impacts below the confluence reveal that the hydrologic alterations at scales longer than 2 days were substantially mitigated with the joining of the unregulated tributary flows, whereas the daily-scale hydrologic alteration was retained because of the hydropeaking inherited from the reservoir releases. The proposed DWPS approach unravels for the first time the details of flow regime alterations at these intermediate scales that are overridden by the low-frequency high-power flows when

  10. A rapid numerical method for horizontal fluid flow in unsaturated soils

    NASA Astrophysics Data System (ADS)

    Kirby, J. M.

    1984-06-01

    A rapid numerical method for the horizontal flow of water is presented, based on the approximation for conductivity k = k0 exp (αψ). A simple expression for the velocity of flow is obtained, which produces accurate solutions to horizontal infiltration problems even with very large time and length steps. The method is compared with previous solutions, including the much studied Yolo light clay infiltration problems. These examples are used to demonstrate the accuracy and economy (in terms of the time and necessary computer power) of the solution. The method is accurate for any choice of length step, provided that the time step is below a certain limit which is related to the length step. An expression for estimating the maximum permissible time step is presented and its use demonstrated via one of the examples.

  11. Linear mechanism of surface gravity wave generation in horizontally sheared flow

    SciTech Connect

    Kalashnik, M. V.

    2008-01-15

    An analysis is presented of a linear mechanism of surface gravity wave generation in a horizontally sheared flow in a fluid layer with free boundary. A free-surface flow of this type is found to be algebraically unstable. The development of instability leads to the formation of surface gravity waves whose amplitude grows with time according to a power law. Flow stability is analyzed by using a nonmodal approach in which the behavior of a spatial Fourier harmonic of a disturbance is considered in a semi-Lagrangian frame of reference moving with the flow. Shear-flow disturbances are divided into two classes (wave and vortex disturbances) depending on the value of potential vorticity. It is shown that vortex disturbances decay with time while the energy of wave disturbances increases indefinitely. Transformation of vortex disturbances into wave ones under strong shear is described.

  12. Investigation of flow regimes affecting the Mexico city region

    SciTech Connect

    Bossert, J.E.

    1997-02-01

    The Regional Atmospheric Modeling System (RAMS) in used to investigate the detailed mesoscale flow structure over the Mexico City region for a 3-day period in February 1991. The model simulation is compared with rawinsonde and tethersonde profile data and measurements from two surface stations in the southwestern part of Mexico City. The model results show that show that downward momentum transfer from aloft increases southerly winds near the surface on the first case day, effectively sweeping pollution from the basin surrounding Mexico City. Thermally driven circulations within the basin, in adjacent valleys, and over the slope of the Mexican Plateau strongly influence winds within the Mexico City basin on the second case day. These wind systems produce a complex interaction of flows, culminating in the propagation of a 1-km-deep density current circulation through Mexico City that displaces the polluted basin air mass aloft. Regional northeasterly flows develop early in the morning of the third case day and force the polluted basin air mass toward the southwestern portion of the basin where observed ozone concentrations are highest. The results show that both regional- and synoptic-scale flows influence the meteorology within the Mexico City basin over the 3-day period. The simulated circulation also provide a physical basis for understanding the high spatial and temporal variability of ozone concentrations observed over the city. 27 refs., 17 figs.

  13. Determination of flow-regime boundaries for cohesive particles

    NASA Astrophysics Data System (ADS)

    Knowlton, T. M.; Findlay, J. G.; Arastoopour, H.; Gidaspow, D.

    1992-10-01

    Cohesive particles (Geldart Group C powders) are fine particles generally less than 30 microns in size. Interparticle forces are large relative to inertial forces in these particles, and cause clumping, sticking, and channeling when attempts are made to fluidize them. These solids do not flow easily through pipes, and bridge extremely easily. The objectives of the work in this program were (1) to develop a hydrodynamic model which can be applied to cohesive solids, and (2) to obtain data in a large-scale (30-cm-diameter) riser to test the model. The work was divided into six tasks: Task 1. Preparation of a Project Work Plan; Task 2. Hydrodynamic Model Development; Task 3. Determination of Rheological Properties for Incorporation into the Model; Task 4. Small-Scale Flow Tests; Task 5. Large-Scale Flow Tests; and Task 6. Comparison of Model With Data. The work was conducted by the Institute of Gas Technology (IGT) in collaboration with the Illinois Institute of Technology (IIT). This work combined the expertise of IIT in model development, with the large-scale experimental capabilities of IGT. IIT researchers developed the hydrodynamic model in the program, while the large-scale data were generated by IGT. Following the preparation of the Project Work Plan in Task 1, work was started on the development of a two-dimensional hydrodynamic model to enable the behavior of cohesive solids in a dilute-phase riser to be simulated. In Task 2, two hydrodynamic models were developed based on the kinetic theory model of granular flow. The models were used to predict data presented in the literature, as well as data generated in Task 5 of this study. In Task 3, rheological data on cohesive oil shale with an average particle size of approximately 12 microns was obtained using a unique device called a cohetester.

  14. Triple-decker: Interfacing atomistic-mesoscopic-continuum flow regimes

    SciTech Connect

    Fedosov, Dmitry A.; Karniadakis, George Em

    2009-03-01

    Multiscale flow phenomena in microfluidic and biomedical applications require the use of heterogeneous modeling approaches. In this paper we present a hybrid method based on coupling the Molecular Dynamics (MD) method, the Dissipative Particle Dynamics (DPD) method, and the incompressible Navier-Stokes (NS) equations. MD, DPD, and NS are formulated in separate subdomains and are coupled via an overlapping region by communicating state information at the subdomain boundaries. Imposition of boundary conditions in the MD and DPD systems involves particle insertion and deletion, specular wall reflection and body force terms. The latter includes a boundary pressure force in order to minimize near-boundary density fluctuations, and an adaptive shear force which enforces the tangential velocity component of boundary conditions. The triple-decker algorithm is verified for prototype flows, including simple and multi-layer fluids (Couette, Poiseuille, and lid-driven cavity), using highly accurate reference solutions. A zero-thickness interface is also possible if it is aligned with the flow streamlines.

  15. Interfacial shear stress in stratified flow in a horizontal rectangular duct

    SciTech Connect

    Lorencez, C.; Kawaji, M.; Murao, Y.

    1995-09-01

    Interfacial shear stress has been experimentally examined for both cocurrent and countercurrent stratified wavy flows in a horizontal interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress values at high gas flow rates which could be attributed to the assumptions and procedures involved in each method. The interfacial waves and secondary motions were also found to have significant effects on the accuracy of Reynolds stress and turbulence kinetic energy extrapolation methods.

  16. Velocity and temperature profiles in near-critical nitrogen flowing past a horizontal flat plate

    NASA Technical Reports Server (NTRS)

    Simoneau, R. J.

    1977-01-01

    Boundary layer velocity and temperature profiles were measured for nitrogen near its thermodynamic critical point flowing past a horizontal flat plate. The results were compared measurements made for vertically upward flow. The boundary layer temperatures ranged from below to above the thermodynamic critical temperature. For wall temperatures below the thermodynamic critical temperature there was little variation between the velocity and temperature profiles in three orientations. In all three orientations the point of crossing into the critical temperature region is marked by a significant flattening of the velocity and temperature profiles and also a decrease in heat transfer coefficient.

  17. Pattern recognition techniques for horizontal and vertically upward multiphase flow measurement

    NASA Astrophysics Data System (ADS)

    Arubi, Tesi I. M.; Yeung, Hoi

    2012-03-01

    The oil and gas industry need for high performing and low cost multiphase meters is ever more justified given the rapid depletion of conventional oil reserves that has led oil companies to develop smaller and marginal fields and reservoirs in remote locations and deep offshore, thereby placing great demands for compact and more cost effective solutions of on-line continuous multiphase flow measurement for well testing, production monitoring, production optimisation, process control and automation. The pattern recognition approach for clamp-on multiphase measurement employed in this study provides one means for meeting this need. High speed caesium-137 radioisotope-based densitometers were installed vertically at the top of a 50.8mm and 101.6mm riser as well as horizontally at the riser base in the Cranfield University multiphase flow test facility. A comprehensive experimental campaign comprising flow conditions typical of operating conditions found in the Petroleum Industry was conducted. The application of a single gamma densitometer unit, in conjunction with pattern recognition techniques to determine both the phase volume fractions and velocities to yield the individual phase flow rates of horizontal and vertically upward multiphase flows was investigated. The pattern recognition systems were trained to map the temporal fluctuations in the multiphase mixture density with the individual phase flow rates using statistical features extracted from the gamma counts signals as their inputs. Initial results yielded individual phase flow rate predictions to within ±5% relative error for the two phase airwater flows and ±10% for three phase air-oil-water flows data.

  18. Flow regimes of adiabatic gas-liquid two-phase under rolling conditions

    NASA Astrophysics Data System (ADS)

    Yan, Chaoxing; Yan, Changqi; Sun, Licheng; Xing, Dianchuan; Wang, Yang; Tian, Daogui

    2013-07-01

    Characteristics of adiabatic air/water two-phase flow regimes under vertical and rolling motion conditions were investigated experimentally. Test sections are two rectangular ducts with the gaps of 1.41 and 10 mm, respectively, and a circular tube with 25 mm diameter. Flow regimes were recorded by a high speed CCD-camera and were identified by examining the video images. The experimental results indicate that the characteristics of flow patterns in 10 mm wide rectangular duct under vertical condition are very similar to those in circular tube, but different from the 1.41 mm wide rectangular duct. Channel size has a significant influence on flow pattern transition, boundary of which in rectangular channels tends asymptotically towards that in the circular tube with increasing the width of narrow side. Flow patterns in rolling channels are similar to each other, nevertheless, the effect of rolling motion on flow pattern transition are significantly various. Due to the remarkable influences of the friction shear stress and surface tension in the narrow gap duct, detailed flow pattern maps of which under vertical and rolling conditions are indistinguishable. While for the circular tube with 25 mm diameter, the transition from bubbly to slug flow occurs at a higher superficial liquid velocity and the churn flow covers more area on the flow regime map as the rolling period decreases.

  19. Impact of flow regime on pressure drop increase and biomass accumulation and morphology in membrane systems.

    PubMed

    Vrouwenvelder, J S; Buiter, J; Riviere, M; van der Meer, W G J; van Loosdrecht, M C M; Kruithof, J C

    2010-02-01

    Biomass accumulation and pressure drop development have been studied in membrane fouling simulators at different flow regimes. At linear flow velocities as applied in practice in spiral wound nanofiltration (NF) and reverse osmosis (RO) membranes, voluminous and filamentous biofilm structures developed in the feed spacer channel, causing a significant increase in feed channel pressure drop. Elevated shear by both single phase flow (water) and two phase flow (water with air sparging: bubble flow) caused biofilm filaments and a pressure drop increase. The amount of accumulated biomass was independent of the applied shear, depending on the substrate loading rate (product of substrate concentration and linear flow velocity) only. The biofilm streamers oscillated in the passing water. Bubble flow resulted in a more compact and less filamentous biofilm structure than single phase flow, causing a much lower pressure drop increase. The biofilm grown under low shear conditions was more easy to remove during water flushing compared to a biofilm grown under high shear. To control biofouling, biofilm structure may be adjusted using biofilm morphology engineering combined with biomass removal from membrane elements by periodic reverse flushing using modified feed spacers. Potential long and short term consequences of flow regimes on biofilm development are discussed. Flow regimes manipulate biofilm morphology affecting membrane performance, enabling new approaches to control biofouling.

  20. Lagrangian flows within reflecting internal waves at a horizontal free-slip surface

    NASA Astrophysics Data System (ADS)

    Zhou, Qi; Diamessis, Peter J.

    2015-12-01

    In this paper sequel to Zhou and Diamessis ["Reflection of an internal gravity wave beam off a horizontal free-slip surface," Phys. Fluids 25, 036601 (2013)], we consider Lagrangian flows within nonlinear internal waves (IWs) reflecting off a horizontal free-slip rigid lid, the latter being a model of the ocean surface. The problem is approached both analytically using small-amplitude approximations and numerically by tracking Lagrangian fluid particles in direct numerical simulation (DNS) datasets of the Eulerian flow. Inviscid small-amplitude analyses for both plane IWs and IW beams (IWBs) show that Eulerian mean flow due to wave-wave interaction and wave-induced Stokes drift cancels each other out completely at the second order in wave steepness A, i.e., O(A2), implying zero Lagrangian mean flow up to that order. However, high-accuracy particle tracking in finite-Reynolds-number fully nonlinear DNS datasets from the work of Zhou and Diamessis suggests that the Euler-Stokes cancelation on O(A2) is not complete. This partial cancelation significantly weakens the mean Lagrangian flows but does not entirely eliminate them. As a result, reflecting nonlinear IWBs produce mean Lagrangian drifts on O(A2) and thus particle dispersion on O(A4). The above findings can be relevant to predicting IW-driven mass transport in the oceanic surface and subsurface region which bears important observational and environmental implications, under circumstances where the effect of Earth rotation can be ignored.

  1. Flow regime transitions in dense non-Brownian suspensions: Rheology, microstructural characterization, and constitutive modeling

    NASA Astrophysics Data System (ADS)

    Ness, Christopher; Sun, Jin

    2015-01-01

    Shear flow of dense non-Brownian suspensions is simulated using the discrete element method taking particle contact and hydrodynamic lubrication into account. The resulting flow regimes are mapped in the parametric space of the solid volume fraction, shear rate, fluid viscosity, and particle stiffness. Below a critical volume fraction ϕc, the rheology is governed by the Stokes number, which distinguishes between viscous and inertial flow regimes. Above ϕc, a quasistatic regime exists for low and moderate shear rates. At very high shear rates, the ϕ dependence is lost, and soft-particle rheology is explored. The transitions between rheological regimes are associated with the evolving contribution of lubrication to the suspension stress. Transitions in microscopic phenomena, such as interparticle force distribution, fabric, and correlation length are found to correspond to those in the macroscopic flow. Motivated by the bulk rheology, a constitutive model is proposed combining a viscous pressure term with a dry granular model presented by Chialvo et al. [Phys. Rev. E 85, 021305 (2012), 10.1103/PhysRevE.85.021305]. The model is shown to successfully capture the flow regime transitions.

  2. Vertical two-phase flow regimes and pressure gradients under the influence of SDS surfactant

    SciTech Connect

    Duangprasert, Tanabordee; Sirivat, Anuvat; Siemanond, Kitipat; Wilkes, James O.

    2008-01-15

    Two-phase gas/liquid flows in vertical pipes have been systematically investigated. Water and SDS surfactant solutions at various concentrations were used as the working fluids. In particular, we focus our work on the influence of surfactant addition on the flow regimes, the corresponding pressure gradients, and the bubble sizes and velocity. Adding the surfactant lowers the air critical Reynolds numbers for the bubble-slug flow and the slug flow transitions. The pressure gradients of SDS solutions are lower than those of pure water especially in the slug flow and the slug-churn flow regimes, implying turbulent drag reduction. At low Re{sub air}, the bubble sizes of the surfactant solution are lower than those of pure water due to the increase in viscosity. With increasing and at high Re{sub air}, the bubble sizes of the SDS solution become greater than those of pure water which is attributed to the effect of surface tension. (author)

  3. Economic interpretation of environmental flow regime downstream diverted river reaches.

    NASA Astrophysics Data System (ADS)

    Gorla, Lorenzo; Perona, Paolo

    2013-04-01

    Water demand for hydropower production is increasing together with the consciousness of the importance of riparian ecosystems and biodiversity. Some Cantons in Switzerland and other alpine regions in Austria and in Sud Tirol (Italy) started replacing the inadequate concept of Minimum Flow Requirement (MFR) with a dynamic one, by releasing a fix percentage of the total inflow (e.g. 25 %) to the environment. In the same direction Perona et al. (in revision) mathematically formulated a method particularly suitable for small hydropower plants, handling the environment as a non-traditional water use, which competes with exploitators. This model uses the Principle of Equal Marginal Utility (PEMU) as optimal water allocation rule for generating like-natural flow releases while maximizing the aggregate economic benefit of all uses (Gorla and Perona, in revision). In this paper we show how redistribution policies can be interpreted in terms of PEMU, particularly we focus at traditional water repartition rules, such as the MFR, but also to dynamic ones like proportional redistribution. For the first case we show both ecological and economical arguments suggesting its inappropriateness; in the second case we highlight explicit points of strength and weakness, and suggest ways of improvement. For example the flow release allocation rule can be changed from inflow-independent ones (e.g., proportional redistribution), to inflow-dependent ones (e.g., non-proportional). The latters, having fewer constraints, can generally lead to better both ecological and economical performances. A class of simple functions, based on the PEMU, is then proposed as a suitable solution in run-of-river or small hydropower plants. Each water repartition policy underlies an ecosystem monetization. We explicit the value of the ecosystem health underlying each policy by means of the PEMU under a few assumptions, and discuss how the theoretic efficient redistribution law obtained by our approach is

  4. Effects of inclination and vorticity on interfacial flow dynamics in horizontal and inclined pipes

    NASA Astrophysics Data System (ADS)

    Kiara, Areti; Hendrickson, Kelli; Liu, Yuming

    2015-11-01

    The transport of oil and gas in long horizontal pipelines can be significantly affected by the development of violent roll waves and slugs, but the mechanics causing such transitions have not been well understood. To enable the improvement of the prediction of flow transition criteria in long pipelines we perform theoretical analysis and direct numerical simulations of multiphase pipe flows to quantify the roles of inclination and vorticity in the flow dynamics. We find that backflow or flooding may occur even in the absence of disturbances due to inclination effects and obtain criteria on the maximum pipe length for steady flows. We identify and compare the effects of inclination and vorticity on the stability of interfacial wave disturbances. We discuss the mechanisms of non-linear energy transfer between stable and unstable wave disturbances and present results from direct numerical simulations for the predictions of spectrum evolutions for broad-banded interfacial disturbances in inclined pipes.

  5. Assessment of land use and water management induced changes in flow regime of the Upper Narew

    NASA Astrophysics Data System (ADS)

    Romanowicz, Renata J.; Osuch, Marzena

    Previous studies have shown that it is very difficult to distinguish human-induced changes from those caused by natural forcing. In this paper we try to quantify the influence of land use and water management on flows of the Upper Narew River in north-east Poland. Apart from climatic and land use changes, the Upper Narew catchment was changed by the construction of a storage reservoir at Siemianówka, near Bondary, on the upstream reach of the river. We apply four different approaches to analysing the changes in flow regime and catchment response for the periods before and after reservoir construction. First we estimate the cumulative distribution functions for low and high flow events. The second approach is a time series analysis of flow variation over the whole length of available data and the derivation of cumulative distribution functions for the flows and 0.25-0.75 quantiles followed by a statistical analysis of the number of events below and above the thresholds and their duration. The third approach consists of the application of the Wittenberg baseflow separation method and tests for changes in baseflow indices. In the fourth approach an analysis of changes in flow regime is performed by studying the changes in transfer function-based flow model parameters. Long-term changes in land use are assessed using previous studies of the catchment and the analysis of Corine land cover data and government yearbooks. The results show that different methods explain different aspects of changes in the catchment and flow regime due to climatic changes and changes in land use and water management practices. The analysis of cumulative distribution functions gave evidence of the influence of Siemianówka reservoir on low flows which was also confirmed by the low flow analysis using the Wittenberg approach. The STF analysis of flows indicates the existence of changes in flow regime that can be attributed to the roughness changes in the channel.

  6. Flow regimes for fluid injection into a confined porous medium

    SciTech Connect

    Zheng, Zhong; Guo, Bo; Christov, Ivan C.; Celia, Michael A.; Stone, Howard A.

    2015-02-24

    We report theoretical and numerical studies of the flow behaviour when a fluid is injected into a confined porous medium saturated with another fluid of different density and viscosity. For a two-dimensional configuration with point source injection, a nonlinear convection–diffusion equation is derived to describe the time evolution of the fluid–fluid interface. In the early time period, the fluid motion is mainly driven by the buoyancy force and the governing equation is reduced to a nonlinear diffusion equation with a well-known self-similar solution. In the late time period, the fluid flow is mainly driven by the injection, and the governing equation is approximated by a nonlinear hyperbolic equation that determines the global spreading rate; a shock solution is obtained when the injected fluid is more viscous than the displaced fluid, whereas a rarefaction wave solution is found when the injected fluid is less viscous. In the late time period, we also obtain analytical solutions including the diffusive term associated with the buoyancy effects (for an injected fluid with a viscosity higher than or equal to that of the displaced fluid), which provide the structure of the moving front. Numerical simulations of the convection–diffusion equation are performed; the various analytical solutions are verified as appropriate asymptotic limits, and the transition processes between the individual limits are demonstrated.

  7. Flow regimes for fluid injection into a confined porous medium

    DOE PAGES

    Zheng, Zhong; Guo, Bo; Christov, Ivan C.; Celia, Michael A.; Stone, Howard A.

    2015-02-24

    We report theoretical and numerical studies of the flow behaviour when a fluid is injected into a confined porous medium saturated with another fluid of different density and viscosity. For a two-dimensional configuration with point source injection, a nonlinear convection–diffusion equation is derived to describe the time evolution of the fluid–fluid interface. In the early time period, the fluid motion is mainly driven by the buoyancy force and the governing equation is reduced to a nonlinear diffusion equation with a well-known self-similar solution. In the late time period, the fluid flow is mainly driven by the injection, and the governingmore » equation is approximated by a nonlinear hyperbolic equation that determines the global spreading rate; a shock solution is obtained when the injected fluid is more viscous than the displaced fluid, whereas a rarefaction wave solution is found when the injected fluid is less viscous. In the late time period, we also obtain analytical solutions including the diffusive term associated with the buoyancy effects (for an injected fluid with a viscosity higher than or equal to that of the displaced fluid), which provide the structure of the moving front. Numerical simulations of the convection–diffusion equation are performed; the various analytical solutions are verified as appropriate asymptotic limits, and the transition processes between the individual limits are demonstrated.« less

  8. Obseration of flow regime transition in CFB riser using an LDV

    SciTech Connect

    Yue, Paul C.; Mei, Joseph S.; Shadle, Lawrence J.

    2011-01-01

    The solids flow in a circulating fluidized bed (CFB) riser is often described to have a core-annular structure. For a given superficial gas velocity, at the initial introduction of solids into a riser a flow structure of dilute upflow regime exists. Continuing to increase the solids flow in the riser transitions the flow structure to the core-annular flow regime. However, with further increase of solids flow a condition is reached, depending on the superficial gas velocity, where all the solids across the riser cross section flow upwards, even those at the wall. When the solids flux, solids fraction and gas velocity are relatively high, such a condition is described as the dense phase suspense upflow (DSU) regime. In this paper we report our observations of these flow regime transitions by using a laser Doppler velocimeter (LDV) to monitor the upward and downward particle flow velocities at and near the riser wall of the National Energy Technology Laboratory’s 30.4 centimeters diameter CFB cold flow model. The particles were high density polyethylene (PPE) spheres with a Sauter mean diameter of 861 micron and a density of 800 kg/m3. Three superficial gas velocities of 6.55 m/s, 10.67 m/s and 13.72 m/s were used in this study. For the case of superficial gas velocity 6.55 m/s, the experimental data show that the transition from dilute upflow to core-annular flow occurred when the solids flux was about 7 kg/m{sup 2}-s and the transition from core-annular flow to dense suspension upflow was about 147 kg/m{sup 2}-s. As the superficial gas velocity was increased to 10.67 m/s the corresponding flow regime transitions were at 34 kg/m{sup 2}-s and 205 kg/m{sup 2}-s, respectively. For the case of superficial gas velocity of 13.72 m/s the data showed no distinct transition of flow regimes. The particles were all upflow for the range of solids fluxes from 10 kg/m{sup 2}-s to 286 kg/m{sup 2}-s.

  9. Reconstruction of a constructed wetland with horizontal subsurface flow after 18 years of operation.

    PubMed

    Hudcová, Tereza; Vymazal, Jan; Dunajský, Michal Kriška

    2013-01-01

    The constructed wetland (CW) for 326 PE with horizontal subsurface flow at Kotenčice, Central Bohemia, Czech Republic, was built in 1994. Despite the relatively high efficiency of the CW, the filtration beds suffered from clogging, and therefore it was decided in 2011 to rebuild the whole system. The new treatment system was built as an experimental system consisting of four different combinations of horizontal and vertical beds. The major aim of the design was to determine the best hybrid combination which then could be used in the future for refurbishment of older horizontal flow CWs or for the new systems. The mechanical pretreatment consists of mechanical bar screens, a new Imhoff tank, and the original settling tank which has been converted into the accumulation tank from where the wastewater is pumped into the wetlands. The filters are planted with Phragmites australis, Phalaris arundinacea, Iris pseudacorus, Iris sibirica, Glyceria maxima and Lythrum salicaria in order to evaluate and compare various plant species' effect on the treatment process. The new technology includes a tertiary treatment which consists of a greenhouse with a photo-reactor for the cultivation of algae and hydroponic systems (residual nutrients removal), sludge reed-beds and a composting field. PMID:24037174

  10. Simulation of Flow Regimes to Reduce Habitat for T. tubifex

    USGS Publications Warehouse

    Milhous, Robert T.

    2008-01-01

    Whirling disease has had a significant impact on trout fisheries of the American west by reducing the numbers and quality of rainbow trout in infected streams. A critical factor in the life cycle of the whirling disease parasite is the fine sediment that provides the optimum habitat for Tubifex tubifex, an oligochaete worm that acts as an intermediate host for the disease. This report presents a model for the simulation of flushing flows required to remove undesirable fines and sand from a pool. Undesirable fines may also need to be flushed from runs, the surface layer, and backwater areas. Well-defined links of specific particle sizes to oligochaete worm abundance is needed to justify the use of flushing flows to move sediment. An analytical method for estimating the streamflows needed to remove the fine sediment is demonstrated herein. The overall steps to follow in removing fines from a stream are: Step 1. Determine size of the sediment that is the habitat for oligochaete worms. Step 2. Determine location of the sediment that is the habitat for oligochaete worms. Step 3. Determine streamflows needed to flush (remove) the sediment that is the habitat for oligochaete worms. The case study approach is used to present the method and to demonstrate its application. The case is derived from the sediment and oligochaete worm habitat of Willow Creek, a tributary of the Upper Colorado River located in Grand County, Colo. Willow Creek Reservoir (an element of the Colorado-Big Thompson Project) controls the streamflows of the creek and is just above the study site.

  11. Street canyon flow patterns in a horizontal plane : measurements from the Joint URBAN 2003 field experiment

    SciTech Connect

    Brown, M. J.; Khalsa, H. S.; Nelson, M. A.; Boswell, D.

    2004-01-01

    As part of the larger Joint URBAN 2003 tracer field experiment performed in Oklahoma City from June 29 to July 30, 2003, a collaborative team of government and university researchers instrumented a downtown street canyon with a high density of wind sensor instrumentation (Brown et al., 2003). The goal of the Park Avenue street canyon experiment was to garner flow field information in order to better understand the transport and dispersion of tracers released in the street canyon and to test and improve the next generation of urban dispersion models. In this paper, we focus on describing the mean flow patterns that developed in the street canyon in a horizontal plane near the surface. We look at the patterns that develop over entire Intensive Operating Periods (IOP's) lasting from 6-9 hours in length, and as a function of inflow wind direction. Most prior street canyon experiments have generally focused on the vertical structure of the flow; this work contributes to the understanding of the horizontal nature of the flow.

  12. Flow regime analysis for fluid injection into a confined aquifer: implications for CO2 sequestration

    NASA Astrophysics Data System (ADS)

    Guo, B.; Zheng, Z.; Celia, M. A.; Stone, H.

    2015-12-01

    Carbon dioxide injection into a confined saline aquifer may be modeled as an axisymmetric two-phase flow problem. Assuming the two fluids segregate in the vertical direction due to strong buoyancy, and neglecting capillary pressure and miscibility, the lubrication approximation leads to a nonlinear advection-diffusion equation that describes the evolution of the sharp fluid-fluid interface. The flow behaviors in the system are controlled by two dimensionless groups: M, the viscosity ratio of the displaced fluid relative to injected fluid, and Γ , the gravity number, which represents the relative importance of buoyancy and fluid injection. Four different analytical solutions can be derived as the asymptotic approximations, representing specific values of the parameter pairs. The four solutions correspond to: (1) Γ << 1, M <1; (2) Γ << 1, M =1; (3) Γ << 1, M >1; and (4) Γ >> 1, any M values. The first two of these solutions are new, while the third corresponds to the solution of Nordbotten and Celia (2006) for confined injections and the fourth corresponds to the solution of (Lyle et al., 2005) for gravity currents in an unconfined aquifer. Overall, the various axisymmetric flows can be summarized in a Γ-M regime diagram with five distinct dynamic behaviors including the four asymptotic regimes and an intermediate regime (Fig. 1). Data from a number of CO2 injection sites around the world can be used to compute the two dimensionless groups Γ and M associated with each injection. When plotted on the regime diagram, these values show the flow behavior for each injection and how the values vary from site to site. For all the CO2 injections, M is always larger than 1, while Γ can range from 0.01 up to 100. The pairs of (Γ, M) with lower Γ values correspond to solution (3), while the ones with higher Γ values can move up to the intermediate regime and the flow regime for solution (4). The higher values of Γ correspond to pilot-scale injections with low

  13. Laboratory Validation of Passive Flow Focusing of Horizontal Wells for in Situ Groundwater Remediation

    NASA Astrophysics Data System (ADS)

    DiMarco, A.; Crimi, M.; Holsen, T.; Bellona, C.; Kumarage, P.; Divine, C.; O'Fallon, T.

    2014-12-01

    A new concept for in situgroundwater remediation was recently developed where drilled horizontal wells filled with granular treatment media are installed in the direction of groundwater flow. Due to the differences in hydraulic conductivity (K) of the media in the well and the surrounding aquifer, groundwater is "focused" into the well and treated (Figure 1). Initial computer simulations demonstrate that the horizontal well will have a substantial capture zone making this a viable and appealing remediation strategy. In this work, a laboratory scale model was constructed to validate the computer simulations and determine the expected capture zone of a horizontal well under a range of hydraulic conductivity differentials. We have built a physical model to replicate a horizontal well in a confined aquifer. The model is constructed inside a 55-gallon drum packed with sand and water is pumped into the bottom of the drum and flows upward through the system. Within the aquifer, we installed a 1" screened well packed with lime-soda beads. To define the capture zone, we placed manometers in the aquifer. Finally, a constant head is applied to the system (Figure 2 and 3). Initial tests have shown that the 1" well with a hydraulic conductivity 65 times greater than the surrounding aquifer (kwell= 1.3 cm/sec vs. kaquifer= 0.02cm/sec) will capture a significant percentage (over 80% in some configurations) of the water applied to the system. A tracer test has shown that the water velocity in the well is substantially higher than the aquifer. Manometer readings confirm the flowfield effects of the well and these data are being used to calibrate numerical models. The presentation will focus on the observed behavior of the physical model under varying applied head and hydraulic conductivities and discuss the potential design implications for full-scale application.

  14. Dominating wave regimes in a two-layer film flowing down a vertical wall

    NASA Astrophysics Data System (ADS)

    ćekiç, G.; Sisoev, G. M.

    2014-12-01

    Flows of two-layer falling films are analyzed by an approximate method. Similar to other film flows, there is a non-uniqueness of steady-traveling waves as solutions of the problem. To select the wave regimes developing in two-layer films, systematic transient computations have been carried out to create a map of the attracting wave regimes which can be used to model real-life processes, for example, mass transfer of a gas between the layers or gas absorption into a two-layer film.

  15. Prediction of gas-liquid two-phase flow regime in microgravity

    NASA Technical Reports Server (NTRS)

    Lee, Jinho; Platt, Jonathan A.

    1993-01-01

    An attempt is made to predict gas-liquid two-phase flow regime in a pipe in a microgravity environment through scaling analysis based on dominant physical mechanisms. Simple inlet geometry is adopted in the analysis to see the effect of inlet configuration on flow regime transitions. Comparison of the prediction with the existing experimental data shows good agreement, though more work is required to better define some physical parameters. The analysis clarifies much of the physics involved in this problem and can be applied to other configurations.

  16. Scaling of two-phase flow regimes in a rod bundle with Freon

    SciTech Connect

    Symolon, P.D.

    1990-01-01

    A fundamental requirement of Freon modeling is that the same void fraction and spatial phase distribution will exist in the Freon model as in the steam/water system being simulated. It is shown that this requirement is satisfied by comparing flow regime transitions observed in high-pressure steam/water with transitions observed in the half-scale Freon four-rod test. It is also demonstrated through predictions of a two-fluid model for a one-half geometric scale factor that within each flow regime, a similar slip ratio (vapor-to-liquid-velocity ratio) exists for the Freon and water systems.

  17. Altered stream-flow regimes and invasive plant species: The Tamarix case

    USGS Publications Warehouse

    Stromberg, J.C.; Lite, S.J.; Marler, R.; Paradzick, C.; Shafroth, P.B.; Shorrock, D.; White, J.M.; White, M.S.

    2007-01-01

    Aim: To test the hypothesis that anthropogenic alteration of stream-flow regimes is a key driver of compositional shifts from native to introduced riparian plant species. Location: The arid south-western United States; 24 river reaches in the Gila and Lower Colorado drainage basins of Arizona. Methods: We compared the abundance of three dominant woody riparian taxa (native Populus fremontii and Salix gooddingii, and introduced Tamarix) between river reaches that varied in stream-flow permanence (perennial vs. intermittent), presence or absence of an upstream flow-regulating dam, and presence or absence of municipal effluent as a stream water source. Results: Populus and Salix were the dominant pioneer trees along the reaches with perennial flow and a natural flood regime. In contrast, Tamarix had high abundance (patch area and basal area) along reaches with intermittent stream flows (caused by natural and cultural factors), as well as those with dam-regulated flows. Main conclusions: Stream-flow regimes are strong determinants of riparian vegetation structure, and hydrological alterations can drive dominance shifts to introduced species that have an adaptive suite of traits. Deep alluvial groundwater on intermittent rivers favours the deep-rooted, stress-adapted Tamarix over the shallower-rooted and more competitive Populus and Salix. On flow-regulated rivers, shifts in flood timing favour the reproductively opportunistic Tamarix over Populus and Salix, both of which have narrow germination windows. The prevailing hydrological conditions thus favour a new dominant pioneer species in the riparian corridors of the American Southwest. These results reaffirm the importance of reinstating stream-flow regimes (inclusive of groundwater flows) for re-establishing the native pioneer trees as the dominant forest type. ?? 2007 The Authors Journal compilation ?? 2007 Blackwell Publishing Ltd.

  18. Analysis of basic flow regimes in a human airway model by stereo-scanning PIV

    NASA Astrophysics Data System (ADS)

    Soodt, Thomas; Pott, Desirée; Klaas, Michael; Schröder, Wolfgang

    2013-06-01

    The detailed understanding of the human lung flow is of high relevance for the optimization of mechanical ventilation. Therefore, the spatial and temporal development of the flow field in a realistic human lung model is investigated for several oscillatory flow regimes using stereo-scanning particle-image velocimetry (PIV). The flow in the right primary bronchus is always measured for a complete sinusoidal ventilation cycle. Three Reynolds and Womersley number sets describing viscous ( Re = 10; α = 1.5), unsteady ( Re = 40; α = 5), and convective ( Re = 150; α = 1.5) regimes are defined to cover various dominating fluid mechanical effects. In addition, multi-plane PIV measurements are performed to analyze steady laminar ( Re = 150) and turbulent ( Re = 2,650) flow at inspiration and expiration. The steady results show that the maximum velocity is shifted to the outer wall at inspiration and toward the inner wall of the bronchial bend at expiration. At inhalation, a U-shaped high-speed velocity profile develops only inside the left primary bronchus, whereas both primary bronchi contain one vortex pair. During expiration, the vortex pairs from each main bronchus merge into a two-vortex-pair system inside the trachea. From the oscillatory findings, it is evident that an undersupply for the right upper lobe is noticed at low ventilatory frequencies, whereas high-frequency flow leads to a more homogeneous ventilation. The analysis of the temporal development of the absolute velocity in the center plane shows a variable phase lag. Unlike the flow in the unsteady regime, the flow of the viscous flow domain ( α = 1.5) is in phase with the applied pressure gradient. Additionally, a premature outflow of the upper right lung lobe can be observed in the unsteady flow regime.

  19. An investigation of flow regimes affecting the Mexico City region

    SciTech Connect

    Bossert, J.E.

    1995-05-01

    The Mexico City region is well-known to the meteorological community for its overwhelming air pollution problem. Several factors contribute to this predicament, namely, the 20 million people and vast amount of industry within the city. The unique geographical setting of the basin encompassing Mexico City also plays an important role. This basin covers approximately 5000 km{sup 2} of the Mexican Plateau at an average elevation of 2250 m above sea level (asl) and is surrounded on three sides by mountains averaging over 3500 m asl, with peaks over 5000 m asl. Only to the north is their a significant opening in the mountainous terrain. Mexico City sprawls over 1000 km{sup 2} in the southwestern portion of the basin. In recent years, several major research programs have been undertaken to investigate the air quality problem within Mexico City. One of these, the Mexico City Air Quality Research Initiative (MARI), conducted in 1990--1993, was a cooperative study between researchers at Los Alamos National Laboratory and the Mexican Petroleum Institute. As part of this study, a field campaign was initiated in February 1991 during which numerous surface, upper air, aircraft, and LIDAR measurements were taken. Much of the work to date has focused upon defining and simulating the local meteorological conditions that are important for understanding the complex photochemistry occurring within the confines of the city. It seems reasonable to postulate, however, that flow systems originating outside of the Mexico City basin will influence conditions within the city much of the time.

  20. Experimental observations of pressure oscillations and flow regimes in an analogue volcanic system

    USGS Publications Warehouse

    Lane, S.J.; Chouet, B.A.; Phillips, J.C.; Dawson, P.; Ryan, G.A.; Hurst, E.

    2001-01-01

    Gas-liquid flows, designed to be analogous to those in volcanic conduits, are generated in the laboratory using organic gas-gum rosin mixtures expanding in a vertically mounted tube. The expanding fluid shows a range of both flow and pressure oscillation behaviors. Weakly supersaturated source liquids produce a low Reynolds number flow with foam expanding from the top surface of a liquid that exhibits zero fluid velocity at the tube wall; i.e., the conventional "no-slip" boundary condition. Pressure oscillations, often with strong long-period characteristics and consistent with longitudinal and radial resonant oscillation modes, are detected in these fluids. Strongly supersaturated source liquids generate more energetic flows that display a number of flow regimes. These regimes include a static liquid source, viscous flow, detached flow (comprising gas-pockets-at-wall and foam-in-gas annular flow, therefore demonstrating strong radial heterogeneity), and a fully turbulent transonic fragmented or mist flow. Each of these flow regimes displays characteristic pressure oscillations that can be related to resonance of flow features or wall impact phenomena. The pressure oscillations are produced by the degassing processes without the need of elastic coupling to the confining medium or flow restrictors and valvelike features. The oscillatory behavior of the experimental flows is compared to seismoacoustic data from a range of volcanoes where resonant oscillation of the fluid within the conduit is also often invoked as controlling the observed oscillation frequencies. On the basis of the experimental data we postulate on the nature of seismic signals that may be measured during large-scale explosive activity. Copyright 2001 by the American Geophysical Union.

  1. Flow observation in two immiscible liquid layers subject to a horizontal temperature gradient

    NASA Astrophysics Data System (ADS)

    Someya, Satoshi; Munakata, Tetsuo; Nishio, Masahiro; Okamoto, Koji; Madarame, Haruki

    2002-02-01

    Marangoni convection, driven by an interfacial instability due to a surface tension gradient, has become a significant problem in the crystal growth on the ground or in a microgravity environment. To suppress and control the convection is important for material processing. Especially in the crystal growth by liquid encapsulated czochralski or liquid encapsulated floating zone technique, in which the melt is encapsulated with an immiscible medium, Marangoni convection can occur on the liquid-liquid interface and on the gas-liquid free surface. In the present paper, experiments were carried out with a double liquid layer of silicone oil and fluorinert both in an open-boat system and in an enclosed system. Flow in a cavity subject to a horizontal temperature gradient was observed. An interactive flow near the interface was measured by using particle image velocimetry technique. The measured flow field seemed to agree sufficiently with the numerical prediction.

  2. General slip regime permeability model for gas flow through porous media

    NASA Astrophysics Data System (ADS)

    Zhou, Bo; Jiang, Peixue; Xu, Ruina; Ouyang, Xiaolong

    2016-07-01

    A theoretical effective gas permeability model was developed for rarefied gas flow in porous media, which holds over the entire slip regime with the permeability derived as a function of the Knudsen number. This general slip regime model (GSR model) is derived from the pore-scale Navier-Stokes equations subject to the first-order wall slip boundary condition using the volume-averaging method. The local closure problem for the volume-averaged equations is studied analytically and numerically using a periodic sphere array geometry. The GSR model includes a rational fraction function of the Knudsen number which leads to a limit effective permeability as the Knudsen number increases. The mechanism for this behavior is the viscous fluid inner friction caused by converging-diverging flow channels in porous media. A linearization of the GSR model leads to the Klinkenberg equation for slightly rarefied gas flows. Finite element simulations show that the Klinkenberg model overestimates the effective permeability by as much as 33% when a flow approaches the transition regime. The GSR model reduces to the unified permeability model [F. Civan, "Effective correlation of apparent gas permeability in tight porous media," Transp. Porous Media 82, 375 (2010)] for the flow in the slip regime and clarifies the physical significance of the empirical parameter b in the unified model.

  3. Oscillatory buoyancy-driven flow in horizontal liquid-metal layers

    NASA Astrophysics Data System (ADS)

    Benhadid, Hamda; Roux, Bernard

    1987-02-01

    A two dimensional numerical simulation of the onset of oscillations in horizontal liquid-metal layers (0 is less than Pr is less than 0.1) is described. Layers with upper free surface are treated in order to model horizontal (Bridgman) solidification boat. When this upper surface is assumed conducting, oscillations are found for Pr=0, 0.015, 0.03, and 0.1, when Gr exceeds a critical value, Gr(c,osc). Gr(c,osc) increases with Pr. For Pr=0.03, these oscillations are found to only exist in a limited range of GR (GR(c,osc) is less than or = Gr is less than or = 2 Gr(c,osc)); they are damped when Gr is increased beyond this range. This restabilization phenomenon is not explained. A correlation is found for the theoretical and experimental values of the oscillation frequency in terms of Gr, in the ranges 2 is less than or = Az is less than or = 8 and 0.015 is less than or = Pr is less than or = 0.07. This correlation also includes damped frequencies found in subcritical regimes.

  4. Revisiting Maxwell’s accommodation coefficient: A study of nitrogen flow in a silica microtube across all flow regimes

    SciTech Connect

    Lei, Wenwen McKenzie, David R.

    2014-12-15

    Gas flows have been studied quantitatively for more than a hundred years and have relevance in modern fields such as the control of gas inputs to processes, the measurement of leak rates and the separation of gaseous species. Cha and McCoy have derived a convenient formula for the flow of an ideal gas applicable across a wide range of Knudsen numbers (Kn) that approaches the Navier–Stokes equations at small Kn and the Smoluchowski extension of the Knudsen flow equation at large Kn. Smoluchowski’s result relies on the Maxwell definition of the tangential momentum accommodation coefficient α, recently challenged by Arya et al. We measure the flow rate of nitrogen gas in a smooth walled silica tube across a wide range of Knudsen numbers from 0.0048 to 12.4583. We find that the nitrogen flow obeys the Cha and McCoy equation with a large value of α, unlike carbon nanotubes which show flows consistent with a small value of α. Silica capillaries are therefore not atomically smooth. The flow at small Kn has α=0.91 and at large Kn has α close to one, consistent with the redefinition of accommodation coefficient by Arya et al., which also resolves a problem in the literature where there are many observations of α of less than one at small Kn and many equal to one at large Kn. Silica capillaries are an excellent choice for an accurate flow control system. - Highlights: • First experimental study on flow rate across all flow regimes in a well-defined microtube. • Extend Cha and McCoy theory for molecular flow regime. • Demonstrate the Maxwell accommodation coefficient is different in the slip and molecular flow regimes.

  5. Kinetic modelling of nitrogen and organics removal in vertical and horizontal flow wetlands.

    PubMed

    Saeed, Tanveer; Sun, Guangzhi

    2011-05-01

    This paper provides a comparative evaluation of the kinetic models that were developed to describe the biodegradation of nitrogen and organics removal in wetland systems. Reaction kinetics that were considered in the model development included first order kinetics, Monod and multiple Monod kinetics; these kinetics were combined with continuous-stirred tank reactor (CSTR) or plug flow pattern to produce equations to link inlet and outlet concentrations of each key pollutants across a single wetland. Using three statistical parameters, a critical evaluation of five potential models was made for vertical and horizontal flow wetlands. The results recommended the models that were developed based on Monod models, for predicting the removal of nitrogen and organics in a vertical and horizontal flow wetland system. No clear correlation was observed between influent BOD/COD values and kinetic coefficients of BOD(5) in VF and HF wetlands, illustrating that the removal of biodegradable organics was insensitive to the nature of organic matter. Higher effluent COD/TN values coincided with greater denitrification kinetic coefficients, signifying the dependency of denitrification on the availability of COD in VF wetland systems. In contrast, the trend was opposite in HF wetlands, indicating that availability of NO(3)-N was the main limiting step for nitrogen removal. Overall, the results suggested the possible application of the developed alternative predictive models, for understanding the complex biodegradation routes of nitrogen and organics removal in VF and HF wetland systems.

  6. A nonlinear flow-transition criterion for the onset of slugging in horizontal channels and pipes

    NASA Astrophysics Data System (ADS)

    Campbell, Bryce K.; Liu, Yuming

    2016-08-01

    In this work, the interfacial instability and transition of a two-fluid flow from a stratified state to large amplitude waves or slugs is considered. By combining an asymptotic approximation of the linear Orr-Sommerfeld analysis with nonlinear resonant wave interaction theory, a novel nonlinear slug-transition criterion is derived. This criterion corresponds to a bounding condition on the upper fluid's velocity in order to limit the amount of energy (provided by the linear instability) which is transferred to long waves through resonant wave interactions. It is proposed that such a condition can predict the formation of large-amplitude long waves and/or slugs. Quantitative comparisons of the onset of slugging are made between the prediction by the nonlinear transition criterion and the experimental measurements carried out in a horizontal square channel. Good agreement is observed. An additional heuristic model is developed which generalizes the transition criterion to flow through horizontal pipes. Comparisons are made for flows through different pipe diameters and over a wide range of fluid properties. Good agreement between the present theoretical predictions and the experimental measurements is also observed.

  7. Vertical two-phase flow regimes and pressure gradients: Effect of viscosity

    SciTech Connect

    Da Hlaing, Nan; Sirivat, Anuvat; Siemanond, Kitipat; Wilkes, James O.

    2007-05-15

    The effect of liquid viscosity on the flow regimes and the corresponding pressure gradients along the vertical two-phase flow was investigated. Experiment was carried out in a vertical transparent tube of 0.019 m in diameter and 3 m in length and the pressure gradients were measured by a U-tube manometer. Water and a 50 vol.% glycerol solution were used as the working fluids whose kinematic viscosities were 0.85 x 10{sup -6} and 4.0 x 10{sup -6} m{sup 2}/s, respectively. In our air-liquid annular two-phase flow, the liquid film of various thicknesses flowed adjacent to the wall and the gas phase flowed at the center of the tube. The superficial air velocity, j{sub air}, was varied between 0.0021 and 58.7 m/s and the superficial liquid velocity, j{sub liquid}, was varied between 0 and 0.1053 m/s. In the bubble, the slug and the slug-churn flow regimes, the pressure gradients decreased with increasing Reynolds number. But in the annular and the mist flow regimes, pressure gradients increased with increasing Reynolds number. Finally, the experimentally measured pressure gradient values were compared and are in good agreement with the theoretical values. (author)

  8. Theoretical and pragmatic modeling of governing equations for two-phase flow in bubbly and annular flow regimes

    SciTech Connect

    Bottoni, M.; Ajuha, S.; Sengpiel, W.

    1994-12-31

    Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy derived for a two-phase flow by volume-averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration; bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities makes the rigorously formulated terms useless for computational purposes, modeling of these terms is discussed.

  9. Theoretical and pragmatic modelling of governing equations for a two-phase flow in bubbly and annular flow regimes

    SciTech Connect

    Bottoni, M.; Sengpiel, W.

    1992-12-01

    Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy, derived for a two-phase flow by volume averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration, bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities make the rigorously formulated terms useless for computational purposes, modelling of these terms is discussed. 3 figs., 15 refs.

  10. Theoretical and pragmatic modelling of governing equations for a two-phase flow in bubbly and annular flow regimes

    SciTech Connect

    Bottoni, M. . Materials and Components Technology Div.); Sengpiel, W. . Inst. fuer Reaktorsicherheit)

    1992-01-01

    Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy, derived for a two-phase flow by volume averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration, bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities make the rigorously formulated terms useless for computational purposes, modelling of these terms is discussed. 3 figs., 15 refs.

  11. Experimental investigation of forced convective boiling flow instabilities in horizontal helically coiled tubes

    NASA Astrophysics Data System (ADS)

    Guo, L. J.; Feng, Z. P.; Chen, X. J.; Thomas, N. H.

    1996-07-01

    An experimental investigation is described for the characteristics of convective boiling flow instabilities in horizontally helically coiled tubes using a steam-water two-phase closed circulation test loop at pressure from 0.5 MPa to 3.5 MPa. Three kinds of oscillation are reported: density waves; pressure drop excursions; thermal fluctuations. We describe their dependence on main system parameters such as system pressure, mass flowrate, inlet subcooling, compressible volume and heat flux. Utilising the experimental data together with conservation constraints, a dimensionless correlation is proposed for the occurrence of density waves.

  12. The path to COVIS: A review of acoustic imaging of hydrothermal flow regimes

    NASA Astrophysics Data System (ADS)

    Bemis, Karen G.; Silver, Deborah; Xu, Guangyu; Light, Russ; Jackson, Darrell; Jones, Christopher; Ozer, Sedat; Liu, Li

    2015-11-01

    Acoustic imaging of hydrothermal flow regimes started with the incidental recognition of a plume on a routine sonar scan for obstacles in the path of the human-occupied submersible ALVIN. Developments in sonar engineering, acoustic data processing and scientific visualization have been combined to develop technology which can effectively capture the behavior of focused and diffuse hydrothermal discharge. This paper traces the development of these acoustic imaging techniques for hydrothermal flow regimes from their conception through to the development of the Cabled Observatory Vent Imaging Sonar (COVIS). COVIS has monitored such flow eight times a day for several years. Successful acoustic techniques for estimating plume entrainment, bending, vertical rise, volume flux, and heat flux are presented as is the state-of-the-art in diffuse flow detection.

  13. Natural flow regimes, nonnative fishes, and native fish persistence in arid-land river systems.

    PubMed

    Propst, David L; Gido, Keith B; Stefferud, Jerome A

    2008-07-01

    Escalating demands for water have led to substantial modifications of river systems in arid regions, which coupled with the widespread invasion of nonnative organisms, have increased the vulnerability of native aquatic species to extirpation. Whereas a number of studies have evaluated the role of modified flow regimes and nonnative species on native aquatic assemblages, few have been conducted where the compounding effects of modified flow regimes and established nonnatives do not confound interpretations, particularly at spatial and temporal scales that are relevant to conservation of species at a range-wide level. By evaluating a 19-year data set across six sites in the relatively unaltered upper Gila River basin, New Mexico, USA, we tested how natural flow regimes and presence of nonnative species affected long-term stability of native fish assemblages. Overall, we found that native fish density was greatest during a wet period at the beginning of our study and declined during a dry period near the end of the study. Nonnative fishes, particularly predators, generally responded in opposite directions to these climatic cycles. Our data suggested that chronic presence of nonnative fishes, coupled with naturally low flows reduced abundance of individual species and compromised persistence of native fish assemblages. We also found that a natural flow regime alone was unlikely to ensure persistence of native fish assemblages. Rather, active management that maintains natural flow regimes while concurrently suppressing or excluding nonnative fishes from remaining native fish strongholds is critical to conservation of native fish assemblages in a system, such as the upper Gila River drainage, with comparatively little anthropogenic modification.

  14. EFFECT OF HORIZONTALLY INHOMOGENEOUS HEATING ON FLOW AND MAGNETIC FIELD IN THE CHROMOSPHERE OF THE SUN

    SciTech Connect

    Song, P.; Vasyliūnas, V. M.

    2014-12-01

    The solar chromosphere is heated by damped Alfvén waves propagating upward from the photosphere at a rate that depends on magnetic field strength, producing enhanced heating at low altitudes in the extended weak-field regions (where the additional heating accounts for the radiative losses) between the boundaries of the chromospheric network as well as enhanced heating per particle at higher altitudes in strong magnetic field regions of the network. The resulting inhomogeneous radiation and temperature distribution produces bulk flows, which in turn affect the configuration of the magnetic field. The basic flow pattern is circulation on the spatial scale of a supergranule, with upward flow in the strong-field region; this is a mirror image in the upper chromosphere of photospheric/subphotospheric convection widely associated with the formation of the strong network field. There are significant differences between the neutral and the ionized components of the weakly ionized medium: neutral flow streamlines can form closed cells, whereas plasma is largely constrained to flow along the magnetic field. Stresses associated with this differential flow may explain why the canopy/funnel structures of the network magnetic field have a greater horizontal extent and are relatively more homogeneous at high altitudes than is expected from simple current-free models.

  15. Effect of Horizontally Inhomogeneous Heating on Flow and Magnetic Field in the Chromosphere of the Sun

    NASA Astrophysics Data System (ADS)

    Song, P.; Vasyliūnas, V. M.

    2014-12-01

    The solar chromosphere is heated by damped Alfvén waves propagating upward from the photosphere at a rate that depends on magnetic field strength, producing enhanced heating at low altitudes in the extended weak-field regions (where the additional heating accounts for the radiative losses) between the boundaries of the chromospheric network as well as enhanced heating per particle at higher altitudes in strong magnetic field regions of the network. The resulting inhomogeneous radiation and temperature distribution produces bulk flows, which in turn affect the configuration of the magnetic field. The basic flow pattern is circulation on the spatial scale of a supergranule, with upward flow in the strong-field region; this is a mirror image in the upper chromosphere of photospheric/subphotospheric convection widely associated with the formation of the strong network field. There are significant differences between the neutral and the ionized components of the weakly ionized medium: neutral flow streamlines can form closed cells, whereas plasma is largely constrained to flow along the magnetic field. Stresses associated with this differential flow may explain why the canopy/funnel structures of the network magnetic field have a greater horizontal extent and are relatively more homogeneous at high altitudes than is expected from simple current-free models.

  16. A Regional Hydrologic Classification of Unregulated Rivers: Towards the Development of Natural Flow Regime Characterization and Environmental Flows in California

    NASA Astrophysics Data System (ADS)

    Lane, B.; Sandoval Solis, S.

    2014-12-01

    Alterations to flow regimes from regulation and climate change affect the biophysical functioning of rivers. Re-operating reservoirs to provide environmental flows - the quantity, quality, and timing of water to sustain natural river functions and species - is now widely applied in multi-objective water resources management. However, the absence of a quantitative, transferable framework for evaluating the relationships between hydrologic inputs, geomorphic functions, and ecological responses, remains a major limitation to setting environmental flows standards. This research addresses this gap by developing a hydrologic classification framework for the State of California that balances operational practicality with scientific defensibility. The framework organizes river reaches into: (1) natural flow classes based on (a) a classification model that clusters hydrologic indices calculated directly from unimpaired streamflow data, and (b) a regression model using a set of climatic, landscape, and local geomorphic controls over the flow regime, and (2) functional zones constrained by temporal (seasonal) ranges and hydrologic (average flow percentile-based) thresholds (e.g. summer low flows). The framework is then used to (1) identify major climatic, landscape, and local geomorphic controls over prototypical flow regime signatures, and (2) characterize key natural functions and processes expected of reaches of each flow class and functional zone during wet, dry, and normal water year types. Organizing hydrologic data in this manner provides a means of comparison and transferability of ecologically-significant hydrologic and geomorphic information across reaches of all major flow classes seen in California, both regulated and unregulated. Through this framework, transferable relationships between hydrologic and physiographic conditions, flow alteration, and ecological metrics can be developed and tested on the basis of data obtained from a limited set of study sites.

  17. Lagrangian flows within reflecting internal waves at a horizontal free-slip surface

    SciTech Connect

    Zhou, Qi; Diamessis, Peter J.

    2015-12-15

    In this paper sequel to Zhou and Diamessis [“Reflection of an internal gravity wave beam off a horizontal free-slip surface,” Phys. Fluids 25, 036601 (2013)], we consider Lagrangian flows within nonlinear internal waves (IWs) reflecting off a horizontal free-slip rigid lid, the latter being a model of the ocean surface. The problem is approached both analytically using small-amplitude approximations and numerically by tracking Lagrangian fluid particles in direct numerical simulation (DNS) datasets of the Eulerian flow. Inviscid small-amplitude analyses for both plane IWs and IW beams (IWBs) show that Eulerian mean flow due to wave-wave interaction and wave-induced Stokes drift cancels each other out completely at the second order in wave steepness A, i.e., O(A{sup 2}), implying zero Lagrangian mean flow up to that order. However, high-accuracy particle tracking in finite-Reynolds-number fully nonlinear DNS datasets from the work of Zhou and Diamessis suggests that the Euler-Stokes cancelation on O(A{sup 2}) is not complete. This partial cancelation significantly weakens the mean Lagrangian flows but does not entirely eliminate them. As a result, reflecting nonlinear IWBs produce mean Lagrangian drifts on O(A{sup 2}) and thus particle dispersion on O(A{sup 4}). The above findings can be relevant to predicting IW-driven mass transport in the oceanic surface and subsurface region which bears important observational and environmental implications, under circumstances where the effect of Earth rotation can be ignored.

  18. Accuracy of flowmeters measuring horizontal groundwater flow in an unconsolidated aquifer simulator.

    USGS Publications Warehouse

    Bayless, E.R.; Mandell, Wayne A.; Ursic, James R.

    2011-01-01

    Borehole flowmeters that measure horizontal flow velocity and direction of groundwater flow are being increasingly applied to a wide variety of environmental problems. This study was carried out to evaluate the measurement accuracy of several types of flowmeters in an unconsolidated aquifer simulator. Flowmeter response to hydraulic gradient, aquifer properties, and well-screen construction was measured during 2003 and 2005 at the U.S. Geological Survey Hydrologic Instrumentation Facility in Bay St. Louis, Mississippi. The flowmeters tested included a commercially available heat-pulse flowmeter, an acoustic Doppler flowmeter, a scanning colloidal borescope flowmeter, and a fluid-conductivity logging system. Results of the study indicated that at least one flowmeter was capable of measuring borehole flow velocity and direction in most simulated conditions. The mean error in direction measurements ranged from 15.1 degrees to 23.5 degrees and the directional accuracy of all tested flowmeters improved with increasing hydraulic gradient. The range of Darcy velocities examined in this study ranged 4.3 to 155 ft/d. For many plots comparing the simulated and measured Darcy velocity, the squared correlation coefficient (r2) exceeded 0.92. The accuracy of velocity measurements varied with well construction and velocity magnitude. The use of horizontal flowmeters in environmental studies appears promising but applications may require more than one type of flowmeter to span the range of conditions encountered in the field. Interpreting flowmeter data from field settings may be complicated by geologic heterogeneity, preferential flow, vertical flow, constricted screen openings, and nonoptimal screen orientation.

  19. Validating alternative methodologies to estimate the regime of temporary rivers when flow data are unavailable.

    PubMed

    Gallart, F; Llorens, P; Latron, J; Cid, N; Rieradevall, M; Prat, N

    2016-09-15

    Hydrological data for assessing the regime of temporary rivers are often non-existent or scarce. The scarcity of flow data makes impossible to characterize the hydrological regime of temporary streams and, in consequence, to select the correct periods and methods to determine their ecological status. This is why the TREHS software is being developed, in the framework of the LIFE Trivers project. It will help managers to implement adequately the European Water Framework Directive in this kind of water body. TREHS, using the methodology described in Gallart et al. (2012), defines six transient 'aquatic states', based on hydrological conditions representing different mesohabitats, for a given reach at a particular moment. Because of its qualitative nature, this approach allows using alternative methodologies to assess the regime of temporary rivers when there are no observed flow data. These methods, based on interviews and high-resolution aerial photographs, were tested for estimating the aquatic regime of temporary rivers. All the gauging stations (13) belonging to the Catalan Internal Catchments (NE Spain) with recurrent zero-flow periods were selected to validate this methodology. On the one hand, non-structured interviews were conducted with inhabitants of villages near the gauging stations. On the other hand, the historical series of available orthophotographs were examined. Flow records measured at the gauging stations were used to validate the alternative methods. Flow permanence in the reaches was estimated reasonably by the interviews and adequately by aerial photographs, when compared with the values estimated using daily flows. The degree of seasonality was assessed only roughly by the interviews. The recurrence of disconnected pools was not detected by flow records but was estimated with some divergences by the two methods. The combination of the two alternative methods allows substituting or complementing flow records, to be updated in the future through

  20. Validating alternative methodologies to estimate the regime of temporary rivers when flow data are unavailable.

    PubMed

    Gallart, F; Llorens, P; Latron, J; Cid, N; Rieradevall, M; Prat, N

    2016-09-15

    Hydrological data for assessing the regime of temporary rivers are often non-existent or scarce. The scarcity of flow data makes impossible to characterize the hydrological regime of temporary streams and, in consequence, to select the correct periods and methods to determine their ecological status. This is why the TREHS software is being developed, in the framework of the LIFE Trivers project. It will help managers to implement adequately the European Water Framework Directive in this kind of water body. TREHS, using the methodology described in Gallart et al. (2012), defines six transient 'aquatic states', based on hydrological conditions representing different mesohabitats, for a given reach at a particular moment. Because of its qualitative nature, this approach allows using alternative methodologies to assess the regime of temporary rivers when there are no observed flow data. These methods, based on interviews and high-resolution aerial photographs, were tested for estimating the aquatic regime of temporary rivers. All the gauging stations (13) belonging to the Catalan Internal Catchments (NE Spain) with recurrent zero-flow periods were selected to validate this methodology. On the one hand, non-structured interviews were conducted with inhabitants of villages near the gauging stations. On the other hand, the historical series of available orthophotographs were examined. Flow records measured at the gauging stations were used to validate the alternative methods. Flow permanence in the reaches was estimated reasonably by the interviews and adequately by aerial photographs, when compared with the values estimated using daily flows. The degree of seasonality was assessed only roughly by the interviews. The recurrence of disconnected pools was not detected by flow records but was estimated with some divergences by the two methods. The combination of the two alternative methods allows substituting or complementing flow records, to be updated in the future through

  1. Influence of electrolyte concentration on holdup, flow regime transition and local flow properties in a large scale bubble column

    NASA Astrophysics Data System (ADS)

    Besagni, Giorgio; Inzoli, Fabio

    2015-11-01

    We experimentally investigate the influence of the electrolyte concentration on holdup, flow regime transition and local flow properties in a large scale bubble column, with air and water as working fluids. The column is 0.24 m inner diameter, 5.3 m height and the air is introduced by a spider sparger up to a superficial gas velocity of 0.2 m/s. The influence of five NaCl concentrations are investigated by using gas holdup and optical probe measurements. The gas holdup measurements are used for analysing the flow regime transition between the homogeneous and the transition regime and the optical probe is used for studying the local flow characteristics at different radial positions. The presence of NaCl - up to a critical concentration - increases the gas holdup. The increase in the gas holdup is due to the inhibition of the coalescence between the bubbles and, thus, the extension of the homogeneous regime. The results are in agreement with the previous literature on smaller bubble columns.

  2. Analysis of regimes of magnetogasdynamic interaction between a current layer and an argon flow

    NASA Astrophysics Data System (ADS)

    Vasil'ev, E. N.; Nesterov, D. A.

    2015-03-01

    A nonstationary three-dimensional magnetogasdynamics (MGD) model is used to study the dynamics of a current layer interacting with a transverse magnetic field in a supersonic argon flow through a channel of constant cross section. The MGD interaction regimes and the features of the current layer formation for various external resistances and channel widths are analyzed as based on numerical results.

  3. Flow regime alterations under changing climate in two river basins: Implications for freshwater ecosystems

    USGS Publications Warehouse

    Gibson, C.A.; Meyer, J.L.; Poff, N.L.; Hay, L.E.; Georgakakos, A.

    2005-01-01

    We examined impacts of future climate scenarios on flow regimes and how predicted changes might affect river ecosystems. We examined two case studies: Cle Elum River, Washington, and Chattahoochee-Apalachicola River Basin, Georgia and Florida. These rivers had available downscaled global circulation model (GCM) data and allowed us to analyse the effects of future climate scenarios on rivers with (1) different hydrographs, (2) high future water demands, and (3) a river-floodplain system. We compared observed flow regimes to those predicted under future climate scenarios to describe the extent and type of changes predicted to occur. Daily stream flow under future climate scenarios was created by either statistically downscaling GCMs (Cle Elum) or creating a regression model between climatological parameters predicted from GCMs and stream flow (Chattahoochee-Apalachicola). Flow regimes were examined for changes from current conditions with respect to ecologically relevant features including the magnitude and timing of minimum and maximum flows. The Cle Elum's hydrograph under future climate scenarios showed a dramatic shift in the timing of peak flows and lower low flow of a longer duration. These changes could mean higher summer water temperatures, lower summer dissolved oxygen, and reduced survival of larval fishes. The Chattahoochee-Apalachicola basin is heavily impacted by dams and water withdrawals for human consumption; therefore, we made comparisons between pre-large dam conditions, current conditions, current conditions with future demand, and future climate scenarios with future demand to separate climate change effects and other anthropogenic impacts. Dam construction, future climate, and future demand decreased the flow variability of the river. In addition, minimum flows were lower under future climate scenarios. These changes could decrease the connectivity of the channel and the floodplain, decrease habitat availability, and potentially lower the ability

  4. Flow of a thin liquid film coating a horizontal stationary cylinder.

    PubMed

    Cachile, M; Aguirre, M A; Lenschen, M; Calvo, A

    2013-12-01

    An experimental and theoretical study of the flow of liquid films around a stationary horizontal cylinder is reported. The film presents two different behaviors: The flow is stable in the upper zone (up to ∼150° with the vertical) and Rayleigh-Taylor-like instabilities appear in the lower zone. For the stable region, film thickness evolution could be described by numerically integrating an evolution equation obtained using a lubrication approximation. For the unstable region, a linear stability analysis allows us to determine the maximum growth wavelength for the Rayleigh-Taylor instability. Approximate analytical solutions were obtained for generatrices at an angle with the vertical θ=0 (stable region) and θ=π (where the instability appears).

  5. Flow of a thin liquid film coating a horizontal stationary cylinder.

    PubMed

    Cachile, M; Aguirre, M A; Lenschen, M; Calvo, A

    2013-12-01

    An experimental and theoretical study of the flow of liquid films around a stationary horizontal cylinder is reported. The film presents two different behaviors: The flow is stable in the upper zone (up to ∼150° with the vertical) and Rayleigh-Taylor-like instabilities appear in the lower zone. For the stable region, film thickness evolution could be described by numerically integrating an evolution equation obtained using a lubrication approximation. For the unstable region, a linear stability analysis allows us to determine the maximum growth wavelength for the Rayleigh-Taylor instability. Approximate analytical solutions were obtained for generatrices at an angle with the vertical θ=0 (stable region) and θ=π (where the instability appears). PMID:24483555

  6. Anaerobic treatment of cassava starch extraction wastewater using a horizontal flow filter with bamboo as support.

    PubMed

    Colin, X; Farinet, J-L; Rojas, O; Alazard, D

    2007-05-01

    Small-scale sour starch agroindustry in Colombia suffer from absence of water treatment. Although starch processing plants produce diluted wastewater, it is a source of pollution and cause environmental problems to the nearby rural population. A laboratory scale anaerobic horizontal flow filter packed with bamboo pieces was evaluated for the treatment of cassava starch extraction wastewater. The wastewater used in the experimentation was the draining water of the starch sedimentation basin. The reactor was operated for 6 months. It was inoculated with a semi-granular sludge from an anaerobic UASB reactor of a slaughterhouse. Maximum organic loading rate (OLR) applied was 11.8g COD/L d without dilution of the wastewater. At steady state and maximum OLR applied, 87% of the COD was removed and a gas productivity of 3.7L/L d was achieved. The average biogas yield was 0.36L/g COD removed. Methane content in the biogas was in the range of 69-81%. The total suspended solids (TSS) removed were 67%. The relative high lactic acid content did not negatively influence the performance of the reactor. No perturbation due to cyanide (3-5mg/L) was observed during the reactor operation. The results obtained indicated that the anaerobic horizontal flow filter could be used efficiently for the treatment of wastewater from Colombian starch processing small-scale agroindustry.

  7. Anaerobic treatment of cassava starch extraction wastewater using a horizontal flow filter with bamboo as support.

    PubMed

    Colin, X; Farinet, J-L; Rojas, O; Alazard, D

    2007-05-01

    Small-scale sour starch agroindustry in Colombia suffer from absence of water treatment. Although starch processing plants produce diluted wastewater, it is a source of pollution and cause environmental problems to the nearby rural population. A laboratory scale anaerobic horizontal flow filter packed with bamboo pieces was evaluated for the treatment of cassava starch extraction wastewater. The wastewater used in the experimentation was the draining water of the starch sedimentation basin. The reactor was operated for 6 months. It was inoculated with a semi-granular sludge from an anaerobic UASB reactor of a slaughterhouse. Maximum organic loading rate (OLR) applied was 11.8g COD/L d without dilution of the wastewater. At steady state and maximum OLR applied, 87% of the COD was removed and a gas productivity of 3.7L/L d was achieved. The average biogas yield was 0.36L/g COD removed. Methane content in the biogas was in the range of 69-81%. The total suspended solids (TSS) removed were 67%. The relative high lactic acid content did not negatively influence the performance of the reactor. No perturbation due to cyanide (3-5mg/L) was observed during the reactor operation. The results obtained indicated that the anaerobic horizontal flow filter could be used efficiently for the treatment of wastewater from Colombian starch processing small-scale agroindustry. PMID:16973355

  8. Relationship between first-order decay coefficients in ponds, for plug flow, CSTR and dispersed flow regimes.

    PubMed

    von, Sperling M

    2002-01-01

    Adequate consideration of the hydraulic regime of a pond is essential in the analysis of BOD and coliform removal, and considerable divergence exists in the literature when reporting removal coefficients. This paper aims at integrating the existing approaches, by quantifying the relationship between the first-order removal coefficients K from the three main hydraulic regimes (CSTR, plug flow and dispersed flow) adopted in the design and performance evaluation of ponds. Based on theoretical considerations and statistical regression analyses, the relationship between the K values is investigated, quantified and modelled. Two tables are presented and two equations are proposed, which allow conversion of K values obtained for dispersed flow to (a) K for CSTR and (b) K for plug flow, based on the hydraulic detention time t and the dispersion number d. These coefficients, when applied in the CSTR or plug-flow equations, will give approximately the same prediction of the effluent concentration as that obtained when using the dispersed-flow model with its proper coefficient. With this approach designers can apply, and researchers can report, K values for the two idealised flow patterns (CSTR and plug flow).

  9. Effects of flow regime on stream turbidity and suspended solids after wildfire, Colorado Front Range

    USGS Publications Warehouse

    Murphy, Sheila F.; McCleskey, R. Blaine; Writer, Jeffrey H.

    2012-01-01

    Wildfires occur frequently in the Colorado Front Range and can alter the hydrological response of watersheds, yet little information exists on the impact of flow regime and storm events on post-wildfire water quality. The flow regime in the region is characterized by base-flow conditions during much of the year and increased runoff during spring snowmelt and summer convective storms. The impact of snowmelt and storm events on stream discharge and water quality was evaluated for about a year after a wildfire near Boulder, Colorado, USA. During spring snowmelt and low-intensity storms, differences in discharge and turbidity at sites upstream and downstream from the burned areas were minimal. However, high-intensity convective storms resulted in dramatic increases in discharge and turbidity at sites downstream from the burned area. This study highlights the importance of using high-frequency sampling to assess accurately wildfire impacts on water quality downstream.

  10. Zero-G experiments in two-phase fluids flow regimes

    NASA Technical Reports Server (NTRS)

    Heppner, D. B.; King, C. D.; Littles, J. W.

    1975-01-01

    The two-phase flows studied were liquid and gas mixtures in a straight flow channel of circular cross-section. Boundaries between flow regimes have been defined for normogravity on coordinates of gas quality and total mass velocity; and, when combined with boundary expressions having a Froude number term, an analytical model was derived predicting boundary shifts with changes in gravity level. Experiments with air and water were performed, first in the normogravity environment of a ground laboratory and then in 'zero gravity' aboard a KC-135 aircraft flying parabolic trajectories. Data reduction confirmed regime boundary shifts in the direction predicted, although the magnitude was a little less than predicted. Pressure drop measurements showed significant increases for the low gravity condition.

  11. Design configurations affecting flow pattern and solids accumulation in horizontal free water and subsurface flow constructed wetlands.

    PubMed

    Pedescoll, A; Sidrach-Cardona, R; Sánchez, J C; Carretero, J; Garfi, M; Bécares, E

    2013-03-01

    The aim of this study was to evaluate the effect of different horizontal constructed wetland (CW) design parameters on solids distribution, loss of hydraulic conductivity over time and hydraulic behaviour, in order to assess clogging processes in wetlands. For this purpose, an experimental plant with eight CWs was built at mesocosm scale. Each CW presented a different design characteristic, and the most common CW configurations were all represented: free water surface flow (FWS) with different effluent pipe locations, FWS with floating macrophytes and subsurface flow (SSF), and the presence of plants and specific species (Typha angustifolia and Phragmites australis) was also considered. The loss of the hydraulic conductivity of gravel was greatly influenced by the presence of plants and organic load (representing a loss of 20% and c.a. 10% in planted wetlands and an overloaded system, respectively). Cattail seems to have a greater effect on the development of clogging since its below-ground biomass weighed twice as much as that of common reed. Hydraulic behaviour was greatly influenced by the presence of a gravel matrix and the outlet pipe position. In strict SSF CW, the water was forced to cross the gravel and tended to flow diagonally from the top inlet to the bottom outlet (where the inlet and outlet pipes were located). However, when FWS was considered, water preferentially flowed above the gravel, thus losing half the effective volume of the system. Only the presence of plants seemed to help the water flow partially within the gravel matrix.

  12. Granular flow regimes in rotating drums from depth-integrated theory

    NASA Astrophysics Data System (ADS)

    Hung, C.-Y.; Stark, C. P.; Capart, H.

    2016-03-01

    Granular flows in rotating drums transition between two regimes characterized by straight and curved free surfaces. Here we predict this behavior using a depth-integrated theory applicable to general eroding flows. Closure is achieved by a local μ (I ) rheology and an equation for kinetic energy. Spanning the transition, the theory yields relations for all flow properties in terms of a single dimensionless rotation rate. In accord with experiments, distinct scaling laws are obtained for slow and fast rates, dominated respectively by local energy dissipation and longitudinal energy transfer.

  13. Oxygen transport and cell viability in an annular flow bioreactor: comparison of laminar Couette and Taylor-vortex flow regimes.

    PubMed

    Curran, Stephen J; Black, Richard A

    2005-03-30

    Rotating wall vessel bioreactors have been proposed as a means of controlling the fluid dynamic environment during long-term culture of mammalian cells and engineered tissues. In this study, we show how the delivery of oxygen to cells in an annular flow bioreactor is enhanced by the forced convective transport afforded by Taylor vortex flows. A fiberoptic oxygen probe with negligible lag time was used to measure the dissolved oxygen concentration in real time and under carefully controlled aeration conditions. From these data, the overall mass transfer coefficients were calculated and mass transport correlations determined under laminar Couette flow conditions and discrete Taylor vortex flow regimes, including laminar, wavy, and turbulent flows. While oxygen transport in Taylor vortex flows was significantly greater, and the available oxygen exceeded that consumed by murine fibroblasts in free suspension, the proportion of cells that remained viable decreased with increasing Reynolds number (101.8 < Rei < 1018), which we attribute to the action of fluid shear stresses on the cells as opposed to any limitation in mass transport. Nevertheless, the results of this study suggest that laminar Taylor-vortex flow regimes provide an effective means of maintaining the levels of oxygen transport required for long-term cell culture. PMID:15696514

  14. Implicit unified gas-kinetic scheme for steady state solutions in all flow regimes

    NASA Astrophysics Data System (ADS)

    Zhu, Yajun; Zhong, Chengwen; Xu, Kun

    2016-06-01

    This paper presents an implicit unified gas-kinetic scheme (UGKS) for non-equilibrium steady state flow computation. The UGKS is a direct modeling method for flow simulation in all regimes with the updates of both macroscopic flow variables and microscopic gas distribution function. By solving the macroscopic equations implicitly, a predicted equilibrium state can be obtained first through iterations. With the newly predicted equilibrium state, the evolution equation of the gas distribution function and the corresponding collision term can be discretized in a fully implicit way for fast convergence through iterations as well. The lower-upper symmetric Gauss-Seidel (LU-SGS) factorization method is implemented to solve both macroscopic and microscopic equations, which improves the efficiency of the scheme. Since the UGKS is a direct modeling method and its physical solution depends on the mesh resolution and the local time step, a physical time step needs to be fixed before using an implicit iterative technique with a pseudo-time marching step. Therefore, the physical time step in the current implicit scheme is determined by the same way as that in the explicit UGKS for capturing the physical solution in all flow regimes, but the convergence to a steady state speeds up through the adoption of a numerical time step with large CFL number. Many numerical test cases in different flow regimes from low speed to hypersonic ones, such as the Couette flow, cavity flow, and the flow passing over a cylinder, are computed to validate the current implicit method. The overall efficiency of the implicit UGKS can be improved by one or two orders of magnitude in comparison with the explicit one.

  15. Salinity effect on the characteristics of saturated horizontal flow in small boxes containing Filtralite-P.

    PubMed

    Suliman, Fadi; Haugen, l Lars-Egil; Jenssen, Petter D

    2005-01-01

    Constructed wetlands are ecological systems that have proven their efficiency in treating wastewater and reducing pollutants of concern in both warm and cold climate. Oversizing these systems is common in the design process due to the inadequate knowledge about water movement in the porous media used. This study investigates the saturated horizontal flow pattern in a lightweight aggregates especially made for use in constructed wetlands termed Filtralite P using computer tomography and a chloride tracer under different hydraulic loading rates and inlet concentrations in a laboratory box experiment. The salt concentrations showed a major effect on the retention time and the flow by enhancing short-circuiting, preferential flow pattern. A hydraulic loading rate of 25 cm day(-1) is suggested as the safest loading rate with Filtralite P under different ranges of wastewater concentrations with a possibility to use a loading rate of 50 cm day(-1) only with municipal wastewater and not the industrial wastewater. The computer tomography images indicated that flow was going first to the bottom and then fluidise upward with a sharp boundary between the incoming and ambient water.

  16. Pressure drop reduction phenomenon of slush nitrogen flow in a horizontal pipe

    NASA Astrophysics Data System (ADS)

    Ohira, Katsuhide

    2011-07-01

    Cryogenic slush fluids, such as slush hydrogen and slush nitrogen, are two-phase single-component fluids containing solid particles in a liquid. Their density and refrigerant capacity are greater than those of a liquid-state fluid alone. Owing to these advantages, there are high expectations for use of slush fluids in various applications such as a clean-energy fuel, fuel for space-planes to improve the efficiency of transportation and storage, and as a refrigerant for high-temperature superconducting power machines. Experimental tests were performed with slush nitrogen to obtain the frictional pressure drop flowing in a horizontal pipe with an inner diameter of 15 mm and a length of 400 mm. The primary objective of the study was to investigate the pressure drop reduction phenomenon according to changes in velocity and solid fraction. The pressure drop correlation between the friction factor and the Reynolds number was obtained, and an empirical correlation between them was derived. The flow pattern for slush nitrogen inside a pipe and the behavior of solid particles were observed using a high-speed video camera and the PIV method. From the experimental results, the pressure drop reduction phenomenon emerged clearly when the flow velocity was higher than 3.6 m/s and the flow pattern of solid particles inside the pipe was pseudo-homogeneous.

  17. Orbiter Aerodynamic Acceleration Flight Measurements in the Rarefied-Flow Transition Regime

    NASA Technical Reports Server (NTRS)

    Blanchard, Robert C.; Wilmoth, Richard G.; LeBeau, Gerald J.

    1996-01-01

    Acceleration data taken from the Orbital Acceleration Research Experiment (OARE) during reentry on STS-62 have been analyzed using calibration factors taken on orbit. This is the first Orbiter mission which collected OARE data during the Orbiter reentry phase. The data examined include the flight regime from orbital altitudes down to about 90 km which covers the free-molecule-flow regime and the upper altitude fringes of the rarefied-flow transition into the hypersonic continuum. Ancillary flight data on Orbiter position, orientation, velocity, and rotation rates have been used in models to transform the measured accelerations to the Orbiter center-of-gravity, from which aerodynamic accelerations along the Orbiter body axes have been calculated. Residual offsets introduced in the measurements by unmodeled Orbiter forces are identified and discussed. Direct comparisons are made between the OARE flight data and an independent micro-gravity accelerometer experiment, the High Resolution Accelerometer Package (HiRAP), which also obtained flight data on reentry during the mission down to about 95 km. The resulting OARE aerodynamic acceleration measurements along the Orbiter's body axis, aid the normal to axial acceleration ratio in the free-molecule-flow and transition-flow regimes are presented and compared with numerical simulations from three direct simulation Monte Carlo codes.

  18. Impacts of water resources development on flow regimes in the Brazos River.

    PubMed

    Vogl, Adrian L; Lopes, Vicente L

    2009-10-01

    The Brazos River, the second largest basin in Texas, represents one of the most highly developed river systems in the state. Thirty-nine reservoirs with capacities greater than 5,000 acre-feet are currently in operation in the basin. Impacts on stream ecosystems are evidenced by changes in flow regimes and resulting changes in fish assemblages over the past 50 years. These changes have been widely attributed to human impacts, through the construction of dams, diversion of water supplies for agricultural and municipal uses, and land use change. However, streamflow regimes result from a complex mix of drivers that include climate, topography, land cover, land use practices, reservoir management practices, dam releases, and water consumption patterns, making determination of anthropogenic impacts problematic. This study quantifies changes in flow regime and probable historical drivers including precipitation, dam construction, population growth, and changing water demand in the Brazos River basin over the past 100 years. Results indicate that the climate of the basin has been relatively stable over the study period, while large-scale changes in human population densities and intense water resources development are correlated with impacts on flow regimes, decreasing the frequency and magnitude of high flow events and stabilizing low flows. These changes have resulted in an increase of habitat generalist fish species, a decrease of native obligate riverine fishes, and an overall homogenization of species assemblages. The results of this study indicate the importance of combining ecological data with an assessment of social drivers for a greater understanding of the dynamics of river basin systems.

  19. Thermal and dynamical regimes of single- and two-phase magmatic flow in dikes

    NASA Technical Reports Server (NTRS)

    Carrigan, Charles R.; Schubert, Gerald; Eichelberger, John C.

    1992-01-01

    The coupling between thermal and dynamical regimes of single- and two-phase magmatic flow in dikes, due to temperature-dependent viscosity and dissipation, was investigated using finite element calculations of magma flow in dikelike channels with length-to-width ratios of 1000:1 or more. Solutions of the steady state equations governing magma flow are obtained for a variety of conditions ranging from idealized plane-parallel models to cases involving nonparallel geometry and two-phase flows. The implications of the numerical simulations for the dynamics of flow in a dike-reservoir system and the consequences of dike entrance conditions on magmatic storage are discussed. Consideration is also given to an unmixing/self-lubrication mechanism which may be important for the lubrication of silicic magmas rising to the earth's surface in mixed magma ascent scenarios, which naturally segregates magma mixtures of two components with differing viscosities to minimize the driving pressure gradient.

  20. Numerical and Experimental Studies of the Natural Convection Flow Within a Horizontal Cylinder Subjected to a Uniformly Cold Wall Boundary Condition. Ph.D. Thesis - Va. Poly. Inst. and State Univ.

    NASA Technical Reports Server (NTRS)

    Stewart, R. B.

    1972-01-01

    Numberical solutions are obtained for the quasi-compressible Navier-Stokes equations governing the time dependent natural convection flow within a horizontal cylinder. The early time flow development and wall heat transfer is obtained after imposing a uniformly cold wall boundary condition on the cylinder. Solutions are also obtained for the case of a time varying cold wall boundary condition. Windware explicit differ-encing is used for the numerical solutions. The viscous truncation error associated with this scheme is controlled so that first order accuracy is maintained in time and space. The results encompass a range of Grashof numbers from 8.34 times 10,000 to 7 times 10 to the 7th power which is within the laminar flow regime for gravitationally driven fluid flows. Experiments within a small scale instrumented horizontal cylinder revealed the time development of the temperature distribution across the boundary layer and also the decay of wall heat transfer with time.

  1. Hydrological classification of natural flow regimes to support environmental flow assessments in intensively regulated Mediterranean rivers, Segura River Basin (Spain).

    PubMed

    Belmar, Oscar; Velasco, Josefa; Martinez-Capel, Francisco

    2011-05-01

    Hydrological classification constitutes the first step of a new holistic framework for developing regional environmental flow criteria: the "Ecological Limits of Hydrologic Alteration (ELOHA)". The aim of this study was to develop a classification for 390 stream sections of the Segura River Basin based on 73 hydrological indices that characterize their natural flow regimes. The hydrological indices were calculated with 25 years of natural monthly flows (1980/81-2005/06) derived from a rainfall-runoff model developed by the Spanish Ministry of Environment and Public Works. These indices included, at a monthly or annual basis, measures of duration of droughts and central tendency and dispersion of flow magnitude (average, low and high flow conditions). Principal Component Analysis (PCA) indicated high redundancy among most hydrological indices, as well as two gradients: flow magnitude for mainstream rivers and temporal variability for tributary streams. A classification with eight flow-regime classes was chosen as the most easily interpretable in the Segura River Basin, which was supported by ANOSIM analyses. These classes can be simplified in 4 broader groups, with different seasonal discharge pattern: large rivers, perennial stable streams, perennial seasonal streams and intermittent and ephemeral streams. They showed a high degree of spatial cohesion, following a gradient associated with climatic aridity from NW to SE, and were well defined in terms of the fundamental variables in Mediterranean streams: magnitude and temporal variability of flows. Therefore, this classification is a fundamental tool to support water management and planning in the Segura River Basin. Future research will allow us to study the flow alteration-ecological response relationship for each river type, and set the basis to design scientifically credible environmental flows following the ELOHA framework.

  2. Using Historic Models of Cn2 to predict r0 and regimes affected by atmospheric turbulence for horizontal, slant and topological paths

    SciTech Connect

    Lawson, J K; Carrano, C J

    2006-06-20

    Image data collected near the ground, in the boundary layer, or from low altitude planes must contend with the detrimental effects of atmospheric turbulence on the image quality. So it is useful to predict operating regimes (wavelength, height of target, height of detector, total path distance, day vs. night viewing, etc.) where atmospheric turbulence is expected to play a significant role in image degradation. In these regimes, image enhancement techniques such as speckle processing, deconvolution and Wiener filtering methods can be utilized to recover near instrument-limited resolution in degraded images. We conducted a literature survey of various boundary layer and lower troposphere models for the structure coefficient of the index of refraction (C{sub n}{sup 2}). Using these models, we constructed a spreadsheet tool to estimate the Fried parameter (r{sub 0}) for different scenarios, including slant and horizontal path trajectories. We also created a tool for scenarios where the height along the path crudely accounted for the topology of the path. This would be of particular interest in mountain-based viewing platforms surveying ground targets. The tools that we developed utilized Visual Basic{reg_sign} programming in an Excel{reg_sign} spreadsheet environment for accessibility and ease of use. In this paper, we will discuss the C{sub n}{sup 2} profile models used, describe the tools developed and compare the results obtained for the Fried parameter with those estimated from experimental data.

  3. Mixed convection boundary layer flow over a horizontal elliptic cylinder with constant heat flux

    NASA Astrophysics Data System (ADS)

    Javed, Tariq; Ahmad, Hussain; Ghaffari, Abuzar

    2015-12-01

    Mixed convection boundary layer flow of a viscous fluid over a horizontal elliptic cylinder with a constant heat flux is investigated numerically. The governing partial differential equations are transformed to non-dimensional form and then are solved by an efficient implicit finite different scheme known as Keller-box method. The solutions are expressed in the form of skin friction and Nusselt number, which are plotted against the eccentric angle. The effect of pertinent parameters such as mixed convection parameter, aspect ratio (ratio of lengths of minor axis to major axis), and Prandtl number on skin friction and Nusselt number are illustrated through graphs for both blunt and slender orientations. The increase in the value of mixed convection parameter results in increase in skin friction coefficient and Nusselt number for blunt as well as slender orientations.

  4. Flow Regime Based Climatologies of Lightning Probabilities for Spaceports and Airports

    NASA Technical Reports Server (NTRS)

    Bauman, William H., III; Sharp, David; Spratt, Scott; Lafosse, Richard A.

    2008-01-01

    The objective of this work was to provide forecasters with a tool to indicate the warm season climatological probability of one or more lightning strikes within a circle at a site within a specified time interval. This paper described the AMU work conducted in developing flow regime based climatologies of lightning probabilities for the SLF and seven airports in the NWS MLB CWA in east-central Florida. The paper also described the GUI developed by the AMU that is used to display the data for the operational forecasters. There were challenges working with gridded lightning data as well as the code that accompanied the gridded data. The AMU modified the provided code to be able to produce the climatologies of lightning probabilities based on eight flow regimes for 5-, 10-, 20-, and 30-n mi circles centered on eight sites in 1-, 3-, and 6-hour increments.

  5. A mathematical framework for forcing turbulence applied to horizontally homogeneous stratified flow

    NASA Astrophysics Data System (ADS)

    Rao, K. J.; de Bruyn Kops, S. M.

    2011-06-01

    It is often desirable to study turbulent flows at steady state even if the flow has no inherent source of turbulence kinetic energy. Doing so requires a forcing schema, and various methods applicable to laboratory experiments or numerical simulations have been studied extensively for turbulence that is isotropic and homogeneous in three dimensions. A review of existing schemata for simulations is used to form a framework for more general forcing methods. In this framework, the problem of developing a forcing method is abstracted into the two problems of (1) prescribing the spectrum of the input power and (2) specifying a force that has the desired characteristics and that adds energy to the flow with the correct spectrum. The framework is used to construct three forcing methods for simulating horizontally homogeneous and isotropic, vertically stratified turbulence. They are implemented in a pseudo-spectral large-eddy simulations and their characteristics are analyzed. The framework is then used to characterize existing laboratory experiments. While no exact analogy can be drawn between forcing in esoteric pseudo-spectral simulations and forcing in physical experiments, there are many similarities. It is suggested that the forcing framework can be applied to predict and systematically test the effects of configuration choices made in the design of simulations and laboratory experiments.

  6. One Component Two Phase Flow in Horizontal and Vertical Ducts: Some Basic Considerations

    SciTech Connect

    Maeder, Paul F.; Dickinson, David A.; Nikitopoulos, Dimitris E.

    1983-12-15

    For a description and analysis of the flow they consider the conservation equations of the two phases separately, but in thermal and mechanical equilibrium, coupled by the itnerface shear forces (two fluid model, drift flux model). Coupling may be weak or strong, depending on Froude and Mach numbers of the flow. The fluid is highly compressible, not because the individual phases move at such speeds that their individual density changes are significant but because evapiration (phase change) results in large density changes of the system at moderate pressure or temperature changes once flashing occurs. The slip between the phases is caused by unequal wall shear stress, acceleration of the fluid or gravitational forces and is hindered by the interface interaction. if they denote by {gamma} the ratio of the liquid density to the vapor density and by {sigma} the ratio of the vapor speed to the liquid speed they find that in horizontal flows {sigma} = {gamma}{sup 1/2} yields the maximum slip (neglecting acceleration effects) that can be reached with no interface force acting (assuming equal friction coefficients for both phases at the wall). If one investigates the conditions of thermodynamic flow similarity between different substances in two phase flow, one finds that the latent heat of vaporization is the principal controlling parameter. Thus, a 5 cm diameter test section in two phase R-114, at room temperature, corresponds to a 30 cm diameter duct in water-steam at boiling conditions at high temperatures such as encountered in geothermal and other power production systems.

  7. Pressure-drop reduction and heat-transfer deterioration of slush nitrogen in horizontal pipe flow

    NASA Astrophysics Data System (ADS)

    Ohira, Katsuhide; Nakagomi, Kei; Takahashi, Norifumi

    2011-10-01

    Cryogenic slush fluids such as slush hydrogen and slush nitrogen are two-phase, single-component fluids containing solid particles in a liquid. Since their density and refrigerant capacity are greater than those of liquid-state fluid alone, there are high expectations for the use of slush fluids in various applications such as clean-energy fuels, spacecraft fuels for improved efficiency in transportation and storage, and as refrigerants for high-temperature superconducting equipment. Experimental tests were performed using slush nitrogen to obtain the flow and heat-transfer characteristics in two different types of horizontal circular pipes with inner diameters of 10 and 15 mm. One of the primary objectives for the study was to investigate the effect of pipe diameter on the pressure-drop reduction and heat-transfer deterioration of slush nitrogen according to changes in the pipe flow velocity, solid fraction and heat flux. In the case of an inner diameter of 15 mm, pressure drop was reduced and heat-transfer characteristics deteriorated when the pipe flow velocity was higher than 3.6 m/s. On the other hand, in the case of an inner diameter of 10 mm, pressure drop was reduced and heat-transfer characteristics deteriorated when the pipe flow velocity was higher than 2.0 m/s. From these results, it can be seen that a larger pipe diameter produces a higher onset velocity for reducing pressure drop and deteriorating heat-transfer characteristics. Furthermore, based on observations using a high-speed video camera, it was confirmed that pressure drop was reduced and heat-transfer characteristics deteriorated when the solid particles migrated to the center of the pipe and the flow pattern of the solid particles inside the pipe was pseudo-homogeneous.

  8. Horizontal flow fields observed in Hinode G-band images. II. Flow fields in the final stages of sunspot decay

    NASA Astrophysics Data System (ADS)

    Verma, M.; Balthasar, H.; Deng, N.; Liu, C.; Shimizu, T.; Wang, H.; Denker, C.

    2012-02-01

    Context. Generation and dissipation of magnetic fields is a fundamental physical process on the Sun. In comparison to flux emergence and the initial stages of sunspot formation, the demise of sunspots still lacks a comprehensive description. Aims: The evolution of sunspots is most commonly discussed in terms of their intensity and magnetic field. Here, we present additional information about the three-dimensional flow field in the vicinity of sunspots towards the end of their existence. Methods: We present a subset of multi-wavelengths observations obtained with the Japanese Hinode mission, the Solar Dynamics Observatory (SDO), and the Vacuum Tower Telescope (VTT) at Observatorio del Teide, Tenerife, Spain during the time period 2010 November 18-23. Horizontal proper motions were derived from G-band and Ca ii H images, whereas line-of-sight velocities were extracted from VTT echelle Hα λ656.28 nm spectra and Fe i λ630.25 nm spectral data of the Hinode/Spectro-Polarimeter, which also provided three-dimensional magnetic field information. The Helioseismic and Magnetic Imager on board SDO provided continuum images and line-of-sight magnetograms, in addition to the high-resolution observations for the entire disk passage of the active region. Results: We perform a quantitative study of photospheric and chromospheric flow fields in and around decaying sunspots. In one of the trailing sunspots of active region NOAA 11126, we observe moat flow and moving magnetic features (MMFs), even after its penumbra had decayed. We also detect a superpenumbral structure around this pore. We find that MMFs follow well-defined, radial paths from the spot all the way to the border of a supergranular cell surrounding the spot. In contrast, flux emergence near the other sunspot prevents the establishment of similar well ordered flow patterns, which could be discerned around a tiny pore of merely 2 Mm diameter. After the disappearance of the sunspots/pores, a coherent patch of abnormal

  9. Experimental response of Salix cuttings to different flow regimes due to human activities

    NASA Astrophysics Data System (ADS)

    Gorla, Lorenzo; Signarbieux, Constant; Turberg, Pascal; Buttler, Alexandre; Perona, Paolo

    2014-05-01

    Hydropower production and other human activities change the natural flow regime of rivers, in turn impacting the riparian environment. The main challenge in order to define eco-sustainable flows is to quantify the effects in terms of geomorphology and ecosystem adaptation. We present 2-years controlled experiments to investigate riparian vegetation (Salix Viminalis) response to forced water table changing dynamics, from one water regime to another, in a temperate region (Switzerland). Three synthetic flow regimes have been simulated and applied to three batteries of Salix cuttings growing outdoor within plastic pots, each about 1 meter tall. In 2012 one treatment simulated a minimal flow policy for small run-of-river hydropower plants, which drastically impacts the low and the medium-low components of the hydrograph, but not the extremes. In 2013 we confirmed and completed some of 2012 results, by reproducing typical hydropeaking effects due to dam management and focusing on daily water table variations and offsets. For both the seasons, after an initial period where all pots undergone the same oscillations in order to uniform the plants initial conditions, the experiment started, and the water dynamic was changed. Cuttings transitory response dynamics has been quantified by continuous sap flow and water potential measurements, and by regularly collecting growth parameters, as well as leaves photosynthesis, fluorescence, and pictures of each plant. At the end of the experiment, all cuttings were carefully removed and the both above and below ground biomass analyzed in detail. Particularly, the 3D root structure was obtained by High Resolution Computer Tomography. Our analyses revealed a clear dependence between roots distribution and water regime reflecting the need for adaptation, in agreement with field observations of Pasquale et al. (2012). In particular, an initial strong difference in terms of stress and growth performances was then followed by a later

  10. Validating alternative methodologies to estimate the hydrological regime of temporary streams when flow data are unavailable

    NASA Astrophysics Data System (ADS)

    Llorens, Pilar; Gallart, Francesc; Latron, Jérôme; Cid, Núria; Rieradevall, Maria; Prat, Narcís

    2016-04-01

    Aquatic life in temporary streams is strongly conditioned by the temporal variability of the hydrological conditions that control the occurrence and connectivity of diverse mesohabitats. In this context, the software TREHS (Temporary Rivers' Ecological and Hydrological Status) has been developed, in the framework of the LIFE Trivers project, to help managers for adequately implement the Water Framework Directive in this type of water bodies. TREHS, using the methodology described in Gallart et al (2012), defines six temporal 'aquatic states', based on the hydrological conditions representing different mesohabitats, for a given reach at a particular moment. Nevertheless, hydrological data for assessing the regime of temporary streams are often non-existent or scarce. The scarcity of flow data makes frequently impossible the characterization of temporary streams hydrological regimes and, as a consequence, the selection of the correct periods and methods to determine their ecological status. Because of its qualitative nature, the TREHS approach allows the use of alternative methodologies to assess the regime of temporary streams in the lack of observed flow data. However, to adapt the TREHS to this qualitative data both the temporal scheme (from monthly to seasonal) as well as the number of aquatic states (from 6 to 3) have been modified. Two alternatives complementary methodologies were tested within the TREHS framework to assess the regime of temporary streams: interviews and aerial photographs. All the gauging stations (13) belonging to the Catalan Internal Catchments (NE, Spain) with recurrent zero flows periods were selected to validate both methodologies. On one hand, non-structured interviews were carried out to inhabitants of villages and small towns near the gauging stations. Flow permanence metrics for input into TREHS were drawn from the notes taken during the interviews. On the other hand, the historical series of available aerial photographs (typically 10

  11. Influence of the Regime of Flow of Particles from a Hydrocyclone on its Separation Characteristics

    NASA Astrophysics Data System (ADS)

    Matvienko, O. V.; Andropova, A. O.; Agafontseva, M. V.

    2014-01-01

    The influence of the presence of an air column in a hydrocyclone and the regime of flow of particles through its discharge orifices on the separation characteristics of the hydrocyclone was investigated. It was established that the flow of heavy particles through the lower discharge orifice of the hydrocyclone in the case where its upper discharge orifice is isolated from the atmosphere is larger than that in the case of free flow of particles to the atmosphere though both two orifices of the hydrocyclone. In the case where the lower discharge orifice of the hydrocyclone is isolated from the atmosphere, the involvement of light particles from the lower receiving bin into the reverse fluid flow in the axial zone of the hydrocyclone increases the resulting yield of particles through the upper discharge orifice of the hydrocyclone.

  12. Non-perturbative analysis of space charge limited electron flow in critical regimes

    SciTech Connect

    Rokhlenko, A.; Lebowitz, J. L.

    2014-08-07

    The combined Eulerian-Lagrangian formalism, developed in our previous work for studying the turn on regime of a one-dimensional diode, is extended for wider versatility and better precision in the study of the time dependent space charge limited electron flow with fixed injected current. An analytical analysis is supplemented with an approximate numerical scheme which appears to be sufficiently accurate to calculate the flow evolution until the process approaches stabilization or becomes unstable. This can be compared with properties of stationary flows and showed to be in a good agreement with them. When the stabilization is impossible, the ratio of anode to cathode currents is decreasing and thus the space charge is accumulated in the diode. We discuss the limitations of our approach and give some qualitative estimates for the flow parameters when stabilization is impossible.

  13. Flow regime mapping of vertical two-phase downflow in a ribbed annulus

    SciTech Connect

    Kielpinski, A.L.

    1992-12-01

    Two-phase flow regimes have been mapped for vertical, cocurrent downflow in a narrow annulus which is partially segmented by the presence of longitudinal ribs. This geometry and flow condition has application to the analysis of a Large-Break Loss of Coolant Accident (LB-LOCA) in the production K-Reactor at the Savannah River Site (SRS). The ribbed annular geometry, particularly the presence of non-sealing ribs, gives rise to some unique phenomenological features. The flow behavior is influenced by the partial segmentation of the annulus into four quadrants or subchannels. A random element is induced by the natural bowing of the slender tubes; the width of the azimuthal flow path between two subchannels at a given axial location is indeterminate, and can take on any value between zero and the maximum clearance of 7.6 {times} l0{sup {minus}4} m. When the rib gap is zero at a given location, it is at a maximum 180P away at the same axial location. The range of rib gaps is spanned in a single test section, as it would be also in a reactor assembly. As a result of these effects, flow regime maps obtained by other researchers for downflow in annuli are not accurate for defining flow regimes in a ribbed annulus. Flow regime transitions similar to those noted by, e.g., Bamea, were observed; the locations of these transitions were displaced with respect to the transition equations derived by Bamea. Experimental bubble rise velocity measurements were also obtained in the same test section. The bubble rise velocities were much higher than expected from the theory developed for slug bubbles in tubes, unribbed annuli, and rectangular channels. An elliptical-cap bubble rises faster than a slug bubble of the same area. Large, slug-shaped bubbles injected into the test section were observed to reduce in size as they rose, due to interaction with a longitudinal rib. They thereby adopted a shape more like an elliptical-cap bubble, hence rising faster than the original slug bubble.

  14. Flow regime mapping of vertical two-phase downflow in a ribbed annulus

    SciTech Connect

    Kielpinski, A.L.

    1992-01-01

    Two-phase flow regimes have been mapped for vertical, cocurrent downflow in a narrow annulus which is partially segmented by the presence of longitudinal ribs. This geometry and flow condition has application to the analysis of a Large-Break Loss of Coolant Accident (LB-LOCA) in the production K-Reactor at the Savannah River Site (SRS). The ribbed annular geometry, particularly the presence of non-sealing ribs, gives rise to some unique phenomenological features. The flow behavior is influenced by the partial segmentation of the annulus into four quadrants or subchannels. A random element is induced by the natural bowing of the slender tubes; the width of the azimuthal flow path between two subchannels at a given axial location is indeterminate, and can take on any value between zero and the maximum clearance of 7.6 [times] l0[sup [minus]4] m. When the rib gap is zero at a given location, it is at a maximum 180P away at the same axial location. The range of rib gaps is spanned in a single test section, as it would be also in a reactor assembly. As a result of these effects, flow regime maps obtained by other researchers for downflow in annuli are not accurate for defining flow regimes in a ribbed annulus. Flow regime transitions similar to those noted by, e.g., Bamea, were observed; the locations of these transitions were displaced with respect to the transition equations derived by Bamea. Experimental bubble rise velocity measurements were also obtained in the same test section. The bubble rise velocities were much higher than expected from the theory developed for slug bubbles in tubes, unribbed annuli, and rectangular channels. An elliptical-cap bubble rises faster than a slug bubble of the same area. Large, slug-shaped bubbles injected into the test section were observed to reduce in size as they rose, due to interaction with a longitudinal rib. They thereby adopted a shape more like an elliptical-cap bubble, hence rising faster than the original slug bubble.

  15. Numerical investigations of flow over a sphere in the subcritical and supercritical regimes

    NASA Astrophysics Data System (ADS)

    Constantinescu, George; Squires, Kyle

    2004-05-01

    The flow field around a sphere in an uniform flow has been analyzed numerically for conditions corresponding to the subcritical (laminar separation) and supercritical (turbulent separation) regimes spanning a wide range of Reynolds numbers (104-106). Particular attention has been devoted to assessing predictions of the pressure distribution, skin friction, and drag as well as to understanding the changes in the wake organization and vortex dynamics with the Reynolds number. The unsteady turbulent flow is computed using detached-eddy simulation, a hybrid approach that has Reynolds-averaged Navier-Stokes behavior near the wall and becomes a large eddy simulation in the regions away from solid surfaces. For both the subcritical and supercritical solutions, the agreement with experimental measurements for the mean drag and pressure distribution over the sphere is adequate; differences in skin friction exist due to the simplistic treatment of the attached boundary layers in the computations. Improved agreement in the skin-friction distribution is obtained for the supercritical flows in which boundary layer transition is fixed at the position observed in experiments conducted at the same Reynolds numbers. For the subcritical flows the Strouhal number, St, associated with the large-scale shedding is predicted at St˜0.195 along with a higher frequency component associated with the development of the Kelvin-Helmholtz instabilities in the detached shear layers. If in the subcritical regime the wake assumes a helical-like form due to the shedding of hairpin-like vortices at different azimuthal angles, in the supercritical regime the wake structure is characterized by "regular" shedding of hairpin-like vortices at approximately the same azimuthal angle and at a much higher frequency (St˜1.3) that is practically independent of the Reynolds number and not sensitive to the position of laminar-to-turbulent transition.

  16. Turbulent flow regimes behind a coastal cape in a stratified and rotating environment

    NASA Astrophysics Data System (ADS)

    Magaldi, M. G.; Özgökmen, T. M.; Griffa, A.; Chassignet, E. P.; Iskandarani, M.; Peters, H.

    A numerical study aimed at investigating the roles of both the stratification and topographic slope in generation of turbulent coherent structures in the lee of capes is presented. We consider a steady barotropic current impinging on an obstacle in a rotating and linearly stratified environment. The obstacle is a triangular prism and represents an idealized headland extending from the coast. Numerical experiments are conducted at constant Rossby number Ro=0.06, varying the Burger number, Bu, and the obstacle slope, α. Flow regime diagrams in the Bu- α space are determined. For Bu<0.1, vertical movement over the obstacle is enhanced and a fully attached regime with pronounced internal waves is established. For 0.1⩽Bu<1, fluid parcels flow more around the obstacle than over it. Flow separation occurs and small tip eddies start to shed. For Bu⩾1, tip eddies merge to form larger eddies in the lee of the cape. We find that previous laboratory results cannot be used for gentler slopes, since bottom flow regimes are strongly dependent on α when Bu⩾1. The form drag coefficient exerted by the cape is at least two orders of magnitude larger than the one due to skin friction. It increases with increasing Burger numbers and decreasing slopes. When no separation occurs (low Bu), the increase with decreasing slopes is the result of the mixing associated with hydraulic phenomena. For intermediate and high Bu, form drag coefficients reach larger values as a result of the boundary layer mixing associated with flow separation. We put forth an empirical parametrization of form drag in the Bu- α space.

  17. CFD simulations of the flow control performance applied for inlet of low drag high-bypass turbofan engine at cross flow regimes

    NASA Astrophysics Data System (ADS)

    Kursakov, I. A.; Kazhan, E. V.; Lysenkov, A. V.; Savelyev, A. A.

    2016-10-01

    Paper describes the optimization procedure for low cruise drag inlet of high-bypass ratio turbofan engine (HBRE). The critical cross-flow velocity when the flow separation on the lee side of the inlet channel occurs is determined. The effciency of different flow control devices used to improve the flow parameters at inlet section cross flow regime is analyzed. Boundary layer suction, bypass slot and vortex generators are considered. It is shown that flow control devices enlarge the stability range of inlet performance at cross flow regimes.

  18. Periodic two-dimensional cavity flow: Effect of linear horizontal thermal boundary condition

    SciTech Connect

    Jones, D.N. ); Briggs, D.G. )

    1989-02-01

    A two-dimensional air-filled cavity with isothermal vertical walls adiabatic top and bottom surfaces has been extensively studied both numerically and experimentally. When the aspect ratio is of order one and the Rayleigh number is less than about 10{sup 9} this geometry produces a highly stable and reproducible laminar flow. The result is quite different when the upper and lower surfaces are subjected to a destabilizing boundary condition, i.e., a linear temperature variation between the hot and cold vertical walls. At a critical Rayleigh number between 10{sup 6} and 10{sup 7} the flow becomes periodic and thus appears to fall into the category of instability of the type known as Hopf bifurcation. Briggs and Jones (1985) report velocity variations measured ner the vertical surfaces that vary by nearly {plus minus} 20% about the mean. Other unexplained behavior reported by Briggs and Jones (1985) consisted of jumps exhibited hysteresis effect, which resulted in some overlap between regimes. This paper presents the results of additional measurements, which indicate that the periodic flow is characterized by the convection of hot and cold pairs of thermals around the enclosure.

  19. The Finite Element Analysis for a Mini-Conductance Probe in Horizontal Oil-Water Two-Phase Flow

    PubMed Central

    Kong, Weihang; Kong, Lingfu; Li, Lei; Liu, Xingbin; Xie, Ronghua; Li, Jun; Tang, Haitao

    2016-01-01

    Oil-water two-phase flow is widespread in petroleum industry processes. The study of oil-water two-phase flow in horizontal pipes and the liquid holdup measurement of oil-water two-phase flow are of great importance for the optimization of the oil production process. This paper presents a novel sensor, i.e., a mini-conductance probe (MCP) for measuring pure-water phase conductivity of oil-water segregated flow in horizontal pipes. The MCP solves the difficult problem of obtaining the pure-water correction for water holdup measurements by using a ring-shaped conductivity water-cut meter (RSCWCM). Firstly, using the finite element method (FEM), the spatial sensitivity field of the MCP is investigated and the optimized MCP geometry structure is determined in terms of the characteristic parameters. Then, the responses of the MCP for the oil-water segregated flow are calculated, and it is found that the MCP has better stability and sensitivity to the variation of water-layer thickness in the condition of high water holdup and low flow velocity. Finally, the static experiments for the oil-water segregated flow were carried out and a novel calibration method for pure-water phase conductivity measurements was presented. The validity of the pure-water phase conductivity measurement with segregated flow in horizontal pipes was verified by experimental results. PMID:27563907

  20. The Finite Element Analysis for a Mini-Conductance Probe in Horizontal Oil-Water Two-Phase Flow.

    PubMed

    Kong, Weihang; Kong, Lingfu; Li, Lei; Liu, Xingbin; Xie, Ronghua; Li, Jun; Tang, Haitao

    2016-01-01

    Oil-water two-phase flow is widespread in petroleum industry processes. The study of oil-water two-phase flow in horizontal pipes and the liquid holdup measurement of oil-water two-phase flow are of great importance for the optimization of the oil production process. This paper presents a novel sensor, i.e., a mini-conductance probe (MCP) for measuring pure-water phase conductivity of oil-water segregated flow in horizontal pipes. The MCP solves the difficult problem of obtaining the pure-water correction for water holdup measurements by using a ring-shaped conductivity water-cut meter (RSCWCM). Firstly, using the finite element method (FEM), the spatial sensitivity field of the MCP is investigated and the optimized MCP geometry structure is determined in terms of the characteristic parameters. Then, the responses of the MCP for the oil-water segregated flow are calculated, and it is found that the MCP has better stability and sensitivity to the variation of water-layer thickness in the condition of high water holdup and low flow velocity. Finally, the static experiments for the oil-water segregated flow were carried out and a novel calibration method for pure-water phase conductivity measurements was presented. The validity of the pure-water phase conductivity measurement with segregated flow in horizontal pipes was verified by experimental results.

  1. The Finite Element Analysis for a Mini-Conductance Probe in Horizontal Oil-Water Two-Phase Flow.

    PubMed

    Kong, Weihang; Kong, Lingfu; Li, Lei; Liu, Xingbin; Xie, Ronghua; Li, Jun; Tang, Haitao

    2016-01-01

    Oil-water two-phase flow is widespread in petroleum industry processes. The study of oil-water two-phase flow in horizontal pipes and the liquid holdup measurement of oil-water two-phase flow are of great importance for the optimization of the oil production process. This paper presents a novel sensor, i.e., a mini-conductance probe (MCP) for measuring pure-water phase conductivity of oil-water segregated flow in horizontal pipes. The MCP solves the difficult problem of obtaining the pure-water correction for water holdup measurements by using a ring-shaped conductivity water-cut meter (RSCWCM). Firstly, using the finite element method (FEM), the spatial sensitivity field of the MCP is investigated and the optimized MCP geometry structure is determined in terms of the characteristic parameters. Then, the responses of the MCP for the oil-water segregated flow are calculated, and it is found that the MCP has better stability and sensitivity to the variation of water-layer thickness in the condition of high water holdup and low flow velocity. Finally, the static experiments for the oil-water segregated flow were carried out and a novel calibration method for pure-water phase conductivity measurements was presented. The validity of the pure-water phase conductivity measurement with segregated flow in horizontal pipes was verified by experimental results. PMID:27563907

  2. Quantifying downstream impacts of impoundment on flow regime and channel planform, lower Trinity River, Texas

    NASA Astrophysics Data System (ADS)

    Wellmeyer, Jessica L.; Slattery, Michael C.; Phillips, Jonathan D.

    2005-07-01

    As human population worldwide has grown, so has interest in harnessing and manipulating the flow of water for the benefit of humans. The Trinity River of eastern Texas is one such watershed greatly impacted by engineering and urbanization. Draining the Dallas-Fort Worth metroplex, just under 30 reservoirs are in operation in the basin, regulating flow while containing public supplies, supporting recreation, and providing flood control. Lake Livingston is the lowest, as well as largest, reservoir in the basin, a mere 95 km above the Trinity's outlet near Galveston Bay. This study seeks to describe and quantify channel activity and flow regime, identifying effects of the 1968 closure of Livingston dam. Using historic daily and peak discharge data from USGS gauging stations, flow duration curves are constructed, identifying pre- and post-dam flow conditions. A digital historic photo archive was also constructed using six sets of aerial photographs spanning from 1938 to 1995, and three measures of channel activity applied using a GIS. Results show no changes in high flow conditions following impoundment, while low flows are elevated. However, the entire post-dam period is characterized by significantly higher rainfall, which may be obscuring the full impact of flow regulation. Channel activity rates do not indicate a more stabilized planform following dam closure; rather they suggest that the Trinity River is adjusting itself to the stress of Livingston dam in a slow, gradual process that may not be apparent in a modern time scale.

  3. Horizontal flows concurrent with an X2.2 flare in the active region NOAA 11158

    NASA Astrophysics Data System (ADS)

    Beauregard, L.; Verma, M.; Denker, C.

    2012-02-01

    Horizontal proper motions were measured with local correlation tracking (LCT) techniques in active region NOAA 11158 on 2011 February 15 at a time when a major (X2.2) solar flare occurred. The measurements are based on continuum images and magnetograms of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The observed shear flows along the polarity inversion line were rather weak (a few 100 m s-1). The counter-streaming region shifted toward the north after the flare. A small circular area with flow speeds of up to 1.2 km s-1 appeared after the flare near a region of rapid penumbral decay. The LCT signal in this region was provided by small-scale photospheric brigthenings, which were associated with fast traveling moving magnetic features. Umbral strengthening and rapid penumbral decay was observed after the flare. Both phenomena were closely tied to kernels of white-light flare emission. The white-light flare only lasted for about 15 min and peaked 4 min earlier than the X-ray flux. In comparison to other major flares, the X2.2 flare in active region NOAA 11158 only produced diminutive photospheric signatures.

  4. Nitrogen transforming community in a horizontal subsurface-flow constructed wetland.

    PubMed

    Coban, Oksana; Kuschk, Peter; Kappelmeyer, Uwe; Spott, Oliver; Martienssen, Marion; Jetten, Mike S M; Knoeller, Kay

    2015-05-01

    Constructed wetlands are important ecosystems with respect to nitrogen cycling. Here we studied the activity and abundance of nitrogen transforming bacteria as well as the spatial distribution of nitrification, anaerobic ammonium oxidation (anammox), and denitrification processes in a horizontal subsurface-flow constructed wetland. The functional genes of the nitrogen cycle were evenly distributed in a linear way along the flow path with prevalence at the superficial points. The same trend was observed for the nitrification and denitrification turnover rates using isotope labeling techniques. It was also shown that only short-term incubations should be used to measure denitrification turnover rates. Significant nitrate consumption under aerobic conditions diminishes nitrification rates and should therefore be taken into account when estimating nitrification turnover rates. This nitrate consumption was due to aerobic denitrification, the rate of which was comparable to that for anaerobic denitrification. Consequently, denitrification should not be considered as an exclusively anaerobic process. Phylogenetic analysis of hydrazine synthase (hzsA) gene clones indicated the presence of Brocadia and Kuenenia anammox species in the constructed wetland. Although anammox bacteria were detected by molecular methods, anammox activity could not be measured and hence this process appears to be of low importance in nitrogen transformations in these freshwater ecosystems. PMID:25744184

  5. Treatment of municipal wastewater using horizontal flow constructed wetlands in Egypt.

    PubMed

    Abou-Elela, Sohair I; Golinelli, G; Saad El-Tabl, Abdou; Hellal, Mohammed S

    2014-01-01

    The aim of this study was to evaluate the performance of two pilot horizontal flow constructed wetlands (HFCWs) with and without vegetation. Three types of plants namely Canna, Phragmites australis and Cyprus papyrus were used. The surface area of each plant was 654 m(2). The flow rate was 20 m(3) d(-1) and the organic loading rate range was 1.7-3.4 kg BOD d(-1) with a detention time of 11 days. The results obtained showed that planted HFCW produced high quality effluent in terms of reduction of chemical oxygen demand (COD; 88%), biochemical oxygen demand (BOD; 91%) and total suspended solids (TSS; 92%) as well as nutrient removal. In addition, 4 logs of total coliform were removed from the planted unit compared with only 3 logs in the unplanted one. The phosphate uptake by the plants reached 29, 30.91 and 38.9 g P m(-2) for Canna, Phragmites and Cyprus, respectively, with 60% removal rate in the treated effluent. The nitrogen uptake by the same plants reached 63.1, 49.46 and 82.33 g N m(-2). Although, the unplanted unit proved to be efficient in the removal of COD, BOD and TSS, it lacks efficiency in pathogen and nutrient removal. The reclaimed wastewater, after disinfection, could be reused for non-restricted irrigation purposes. PMID:24434966

  6. Granular-flow rheology: Role of shear-rate number in transition regime

    USGS Publications Warehouse

    Chen, C.-L.; Ling, C.-H.

    1996-01-01

    This paper examines the rationale behind the semiempirical formulation of a generalized viscoplastic fluid (GVF) model in the light of the Reiner-Rivlin constitutive theory and the viscoplastic theory, thereby identifying the parameters that control the rheology of granular flow. The shear-rate number (N) proves to be among the most significant parameters identified from the GVF model. As N ??? 0 and N ??? ???, the GVF model can reduce asymptotically to the theoretical stress versus shear-rate relations in the macroviscous and graininertia regimes, respectively, where the grain concentration (C) also plays a major role in the rheology of granular flow. Using available data obtained from the rotating-cylinder experiments of neutrally buoyant solid spheres dispersing in an interstitial fluid, the shear stress for granular flow in transition between the two regimes proves dependent on N and C in addition to some material constants, such as the coefficient of restitution. The insufficiency of data on rotating-cylinder experiments cannot presently allow the GVF model to predict how a granular flow may behave in the entire range of N; however, the analyzed data provide an insight on the interrelation among the relevant dimensionless parameters.

  7. Numerical investigation of multiple stationary and time-periodic flow regimes in vertical rotating disc CVD reactors

    NASA Astrophysics Data System (ADS)

    Gakis, G. P.; Koronaki, E. D.; Boudouvis, A. G.

    2015-12-01

    The vertical rotating disc CVD reactor problem is revisited with a computational framework that allows systematic parameter continuation along branches of flow regimes over various operating parameter values. The commercial CFD code Fluent is used, enhanced with a home-made module and by appropriate initialization, a P-ω diagram is mapped out. In addition to the well known result where boyancy-induced and rotation-induced regimes exist for low and high rotation rates respectively along with a favorable for film uniformity plug flow regime in between, interesting new flow regimes are computed: Stable time-periodic buoyancy induced flows are found as well as stationary ones. Periodic buoyancy induced flows co-exist with stationary plug flow regimes over a range of ω for pressures higher than 200 Torr. A regime of stationary flows where the effect of buoyancy and rotation is combined is computed at pressures higher than 350 Torr and it shown to co-exist with typical rotation induced flows.

  8. Fibrous filter efficiency and pressure drop in the viscous-inertial transition flow regime.

    SciTech Connect

    Sanchez, Andres L.; Brockmann, John E.; Dellinger, Jennifer Gwynne; Lucero, Daniel A.; Hubbard, Joshua A.; Servantes, Brandon Lee

    2011-10-01

    Fibrous filter pressure drop and aerosol collection efficiency were measured at low air pressures (0.2 to 0.8 atm) and high face velocities (5 to 20 meters per second) to give fiber Reynolds numbers in the viscous-inertial transition flow regime (1 to 16). In this regime, contemporary filtration theory based on Kuwabara's viscous flow through an ensemble of fibers under-predicts single fiber impaction by several orders of magnitude. Streamline curvature increases substantially as inertial forces become dominant. Dimensionless pressure drop measurements followed the viscous-inertial theory of Robinson and Franklin rather than Darcy's linear pressure-velocity relationship (1972). Sodium chloride and iron nano-agglomerate test aerosols were used to evaluate the effects of particle density and shape factor. Total filter efficiency collapsed when plotted against the particle Stokes and fiber Reynolds numbers. Efficiencies were then fitted with an impactor type equation where the cutpoint Stokes number and a steepness parameter described data well in the sharply increasing portion of the curve (20% to 80% efficiency). The cutpoint Stokes number was a linearly decreasing function of fiber Reynolds number. Single fiber efficiencies were calculated from total filter efficiencies and compared to contemporary viscous flow impaction theory (Stechkina et al. 1969), and numerical simulations from the literature. Existing theories under-predicted measured single fiber efficiencies although the assumption of uniform flow conditions for each successive layer of fibers is questionable; the common exponential relationship between single fiber efficiency and total filter efficiency may not be appropriate in this regime.

  9. Gas-kinetic unified algorithm for hypersonic flows covering various flow regimes solving Boltzmann model equation in nonequilibrium effect

    SciTech Connect

    Li, Zhihui; Ma, Qiang; Wu, Junlin; Jiang, Xinyu; Zhang, Hanxin

    2014-12-09

    Based on the Gas-Kinetic Unified Algorithm (GKUA) directly solving the Boltzmann model equation, the effect of rotational non-equilibrium is investigated recurring to the kinetic Rykov model with relaxation property of rotational degrees of freedom. The spin movement of diatomic molecule is described by moment of inertia, and the conservation of total angle momentum is taken as a new Boltzmann collision invariant. The molecular velocity distribution function is integrated by the weight factor on the internal energy, and the closed system of two kinetic controlling equations is obtained with inelastic and elastic collisions. The optimization selection technique of discrete velocity ordinate points and numerical quadrature rules for macroscopic flow variables with dynamic updating evolvement are developed to simulate hypersonic flows, and the gas-kinetic numerical scheme is constructed to capture the time evolution of the discretized velocity distribution functions. The gas-kinetic boundary conditions in thermodynamic non-equilibrium and numerical procedures are studied and implemented by directly acting on the velocity distribution function, and then the unified algorithm of Boltzmann model equation involving non-equilibrium effect is presented for the whole range of flow regimes. The hypersonic flows involving non-equilibrium effect are numerically simulated including the inner flows of shock wave structures in nitrogen with different Mach numbers of 1.5-Ma-25, the planar ramp flow with the whole range of Knudsen numbers of 0.0009-Kn-10 and the three-dimensional re-entering flows around tine double-cone body.

  10. Gas-kinetic unified algorithm for hypersonic flows covering various flow regimes solving Boltzmann model equation in nonequilibrium effect

    NASA Astrophysics Data System (ADS)

    Li, Zhihui; Wu, Junlin; Ma, Qiang; Jiang, Xinyu; Zhang, Hanxin

    2014-12-01

    Based on the Gas-Kinetic Unified Algorithm (GKUA) directly solving the Boltzmann model equation, the effect of rotational non-equilibrium is investigated recurring to the kinetic Rykov model with relaxation property of rotational degrees of freedom. The spin movement of diatomic molecule is described by moment of inertia, and the conservation of total angle momentum is taken as a new Boltzmann collision invariant. The molecular velocity distribution function is integrated by the weight factor on the internal energy, and the closed system of two kinetic controlling equations is obtained with inelastic and elastic collisions. The optimization selection technique of discrete velocity ordinate points and numerical quadrature rules for macroscopic flow variables with dynamic updating evolvement are developed to simulate hypersonic flows, and the gas-kinetic numerical scheme is constructed to capture the time evolution of the discretized velocity distribution functions. The gas-kinetic boundary conditions in thermodynamic non-equilibrium and numerical procedures are studied and implemented by directly acting on the velocity distribution function, and then the unified algorithm of Boltzmann model equation involving non-equilibrium effect is presented for the whole range of flow regimes. The hypersonic flows involving non-equilibrium effect are numerically simulated including the inner flows of shock wave structures in nitrogen with different Mach numbers of 1.5-Ma-25, the planar ramp flow with the whole range of Knudsen numbers of 0.0009-Kn-10 and the three-dimensional re-entering flows around tine double-cone body.

  11. Numerical investigation of flow motion and performance of a horizontal axis tidal turbine subjected to a steady current

    NASA Astrophysics Data System (ADS)

    Li, Lin-juan; Zheng, Jin-hai; Peng, Yu-xuan; Zhang, Ji-sheng; Wu, Xiu-guang

    2015-04-01

    Horizontal axis tidal turbines have attracted more and more attentions nowadays, because of their convenience and low expense in construction and high efficiency in extracting tidal energy. The present study numerically investigates the flow motion and performance of a horizontal axis tidal turbine with a supporting vertical cylinder under steady current. In the numerical model, the continuous equation and incompressible Reynolds-averaged Navier-Stokes equations are solved, and the volume of fluid method is employed to track free surface motion. The RNG k- ɛ model is adopted to calculate turbulence transport while the fractional area/volume obstacle representation method is used to describe turbine characteristics and movement. The effects of installation elevation of tidal turbine and inlet velocity on the water elevation, and current velocity, rotating speed and resultant force on turbine are discussed. Based on the comparison of the numerical results, a better understanding of flow structure around horizontal axis tidal turbine and turbine performance is achieved.

  12. Onset of entrainment and degree of dispersion in dual continuous horizontal oil-water flows

    SciTech Connect

    Al-Wahaibi, Talal; Angeli, Panagiota

    2009-04-15

    The transition from stratified to dual continuous oil-water flow (where each phase retains its continuity but there is dispersion of one phase into the other) as well as the dispersed phase fractions in the layers of the dual continuous pattern, were studied experimentally. Transition to this pattern from stratified flow occurs when drops of one phase appear into the other (onset of entrainment). The studies were carried out in a 38 mm ID horizontal stainless steel test section using two different inlet geometries, a T- and a Y-junction. The patterns were visualized through a transparent acrylic section located at 7 m from the inlet using a high speed video camera. Phase distribution measurements in a pipe cross section were obtained just before the acrylic section with a local impedance probe and the results were used to calculate the volume fraction of each phase entrained into the other. The onset of entrainment was found to occur at lower superficial water velocities as the oil superficial velocities increased. However, the inlet geometry did not affect significantly the transition line. During dual continuous flow, the dispersion of one phase into the opposite was found to extend further away from the interface with increasing water superficial velocity for a certain oil superficial velocity. An increase in the superficial water velocity increased the entrained fraction of water in oil (E{sub w/o}) but there was no trend with the oil velocity. Similarly, an increase in the superficial oil velocity increased the fraction of oil drops in water (E{sub o/w}) but the water velocity had no clear effect. The entrainment fractions were affected by the inlet geometry, with the T-inlet resulting in higher entrainment than the Y-inlet, perhaps because of the increased mixing induced by the T-inlet. The difference between the two inlets increased as the oil and water velocities increased. (author)

  13. Nitrogen transformation in horizontal subsurface flow constructed wetlands I: Model development

    NASA Astrophysics Data System (ADS)

    Mayo, A. W.; Bigambo, T.

    In this paper a mathematical model for prediction of nitrogen transformation in horizontal subsurface flow constructed wetlands was developed. Two horizontal subsurface flow constructed wetlands were designed to receive organic loading rate below 50 kg/ha/d and hydraulic loading rate of 480 m 3/ha/d from a primary facultative pond. Two rectangular shaped units each 11.0 m long, 3.7 m wide and 1.0 m deep and bottom slope of 1% were constructed and filled with 6-25 mm diameter gravel pack to a depth of 0.75 m. Each unit was planted with Phragmites mauritianus with an initial plant density of 29,000 plants/ha. The plants were allowed to grow for about four months before sampling for water quality parameters commenced. Samples were collected daily for about three months. Dissolved oxygen, pH and temperature were measured in situ and ammonia, total Kjeldahl nitrogen, nitrates, nitrite and Chemical Oxygen Demand were measured in the laboratory in accordance with Standard Methods. The mathematical model took into account activities of biomass suspended in the water body and biofilm on aggregates and plant roots. The state variables modelled include organic, ammonia, and nitrate-nitrogen, which were sectored in water, plant and aggregates. The major nitrogen transformation processes considered in this study were mineralization, nitrification, denitrification, plant uptake, plant decaying, and sedimentation. The forcing functions, which were considered in the model, are temperature, pH and dissolved oxygen. Stella II software was used to simulate the nitrogen processes influencing the removal of nitrogen in the constructed wetland. One of the two-wetland units was used for model calibration and the second unit for model validation. The model results indicated that 0.872 gN/m 2 d was settled at the bottom of the wetland and on gravel bed and roots of the plants. However, 0.752 gN/m 2 d (86.2%) of the settled nitrogen was regenerated back to the water body, which means that

  14. Nitrogen transformation in horizontal subsurface flow constructed wetlands II: Effect of biofilm

    NASA Astrophysics Data System (ADS)

    Bigambo, T.; Mayo, A. W.

    In this paper the significance of the biofilm biomass present in horizontal subsurface flow constructed wetland in removal of nitrogen was demonstrated. The model was developed and optimised using data obtained in a horizontal subsurface flow constructed wetland planted with Phragmites mauritianus and filled with 6-25 mm diameter gravel pack. The effects of biofilm biomass activities were studied by removing the effects of plant and gravel bed biofilm in an already calibrated model and re-run the same. Research results indicate that total nitrogen removal was largely influenced by growth of biofilm on plants than on aggregates. When plant biofilm and suspended biomasses were considered total nitrogen removal of 38.1% was observed compared with 25.1% when aggregate-biofilm and suspended biomasses were considered because plants have more surface areas, which are active sites for the effective biofilm activities than aggregates. However, in a natural wetland where the soil grain size is smaller, the effect of biofilm on plants may be smaller than biofilm on soil particles. There was no significant difference in organic-nitrogen effluent concentrations when biofilm biomass was considered or rejected. The averages in organic-nitrogen effluent concentrations were 0.39, 0.41 and 0.53 gN/m 2 for suspended alone, aggregate-biofilm and suspended; and suspended and plant-biofilm, respectively. This indicates that the removal of organic-nitrogen in wastewater is not significantly influenced by biofilm activities. Sedimentation and mineralization processes are the major factors influencing the concentration of organic-nitrogen in the effluent. On the other hand, biofilm activities had significant influence on ammonia-nitrogen and nitrate-nitrogen transformation. The developed model output indicates that the effluent ammonia concentration was 2 gN/m 2, but in absence of biofilm the effluent ammonia concentration increases to 3.5 gN/m 2. Statistical analysis indicates that the

  15. Microbubble generation in a co-flow device operated in a new regime.

    PubMed

    Castro-Hernández, Elena; van Hoeve, Wim; Lohse, Detlef; Gordillo, José M

    2011-06-21

    A new regime of operation of PDMS-based flow-focusing microfluidic devices is presented. We show that monodisperse microbubbles with diameters below one-tenth of the channel width (here w = 50 μm) can be produced in low viscosity liquids thanks to a strong pressure gradient in the entrance region of the channel. In this new regime bubbles are generated at the tip of a long and stable gas ligament whose diameter, which can be varied by tuning appropriately the gas and liquid flow rates, is substantially smaller than the channel width. Through this procedure the volume of the bubbles formed at the tip of the gas ligament can be varied by more than two orders of magnitude. The experimental results for the bubble diameter d(b) as function of the control parameters are accounted for by a scaling theory, which predicts d(b)/w ∝ (μ(g)/μ(l))(1/12)(Q(g)/Q(l))(5/12), where μ(g) and μ(l) indicate, respectively, the gas and liquid viscosities and Q(g) and Q(l) are the gas and liquid flow rates. As a particularly important application of our results we produce monodisperse bubbles with the appropriate diameter for therapeutic applications (d(b) ≃ 5 μm) and a production rate exceeding 10(5) Hz. PMID:21431188

  16. Microbubble generation in a co-flow device operated in a new regime.

    PubMed

    Castro-Hernández, Elena; van Hoeve, Wim; Lohse, Detlef; Gordillo, José M

    2011-06-21

    A new regime of operation of PDMS-based flow-focusing microfluidic devices is presented. We show that monodisperse microbubbles with diameters below one-tenth of the channel width (here w = 50 μm) can be produced in low viscosity liquids thanks to a strong pressure gradient in the entrance region of the channel. In this new regime bubbles are generated at the tip of a long and stable gas ligament whose diameter, which can be varied by tuning appropriately the gas and liquid flow rates, is substantially smaller than the channel width. Through this procedure the volume of the bubbles formed at the tip of the gas ligament can be varied by more than two orders of magnitude. The experimental results for the bubble diameter d(b) as function of the control parameters are accounted for by a scaling theory, which predicts d(b)/w ∝ (μ(g)/μ(l))(1/12)(Q(g)/Q(l))(5/12), where μ(g) and μ(l) indicate, respectively, the gas and liquid viscosities and Q(g) and Q(l) are the gas and liquid flow rates. As a particularly important application of our results we produce monodisperse bubbles with the appropriate diameter for therapeutic applications (d(b) ≃ 5 μm) and a production rate exceeding 10(5) Hz.

  17. Calibration of Mineralization Degree for Dynamic Pure-water Measurement in Horizontal Oil-water Two-phase Flow

    NASA Astrophysics Data System (ADS)

    Kong, Weihang; Li, Lei; Kong, Lingfu; Liu, Xingbin

    2016-08-01

    In order to solve the problem of dynamic pure-water electrical conductivity measurement in the process of calculating water content of oil-water two-phase flow of production profile logging in horizontal wells, a six-group local-conductance probe (SGLCP) is proposed to measure dynamic pure-water electrical conductivity in horizontal oil-water two-phase flow. The structures of conductance sensors which include the SGLCP and ring-shaped conductance probe (RSCP) are analyzed by using the finite-element method (FEM). In the process of simulation, the electric field distribution generated by the SGLCP and RSCP are investigated, and the responses of the measuring electrodes are calculated under the different values of the water resistivity. The static experiments of the SGLCP and RSCP under different mineralization degrees in horizontal oil-water two-phase flow are carried out. Results of simulation and experiments demonstrate a nice linearity between the SGLCP and RSCP under different mineralization degrees. The SGLCP has also a good adaptability to stratified flow, stratified flow with mixing at the interface and dispersion of oil in water and water flow. The validity and feasibility of pure-water electrical conductivity measurement with the designed SGLCP under different mineralization degrees are verified by experimental results.

  18. Anomalous flow deflection at planetary bow shocks in the low Alfven Mach number regime

    NASA Astrophysics Data System (ADS)

    Nishino, Masaki N.; Fujimoto, Masaki; Tai, Phan-Duc; Mukai, Toshifumi; Saito, Yoshifumi; Kuznetsova, Masha M.; Rastaetter, Lutz

    A planetary magnetosphere is an obstacle to the super-sonic solar wind and the bow shock is formed in the front-side of it. In ordinary hydro-dynamics, the flow decelerated at the shock is diverted around the obstacle symmetrically about the planet-Sun line, which is indeed observed in the magnetosheath most of the time. Here we show a case under a very low density solar wind in which duskward flow was observed in the dawnside magnetosheath of the Earth's magnetosphere. A Rankine-Hugoniot test across the bow shock shows that the magnetic effect is crucial for this "wrong flow" to appear. A full three-dimensional Magneto- Hydro-Dynamics (MHD) simulation of the situation in this previously unexplored parameter regime is also performed. It is illustrated that in addition to the "wrong flow" feature, various peculiar characteristics appear in the global picture of the MHD flow interaction with the obstacle. The magnetic effect at the bow shock should become more conspicuously around the Mercury's magnetosphere, because stronger interplanetary magnetic field and slower solar wind around the Mercury let the Alfven Mach number low. Resultant strong deformation of the magnetosphere induced by the "wrong flow" will cause more complex interaction between the solar wind and the Mercury.

  19. Exact solutions of incompressible potential flows induced by a horizontal flat plate near a plane wall

    NASA Astrophysics Data System (ADS)

    Wang, Qianxi; Zhuang, Lixian; Tong, Binggang

    1992-12-01

    Yih (1974) obtained the first-order analytical solution to the problem of a falling plate in extreme ground effect. Tuck (1980) gave a similar approximate solution for the failing plate still having horizontal velocity. In this paper, both the exact solution of the complex velocity induced by a horizontal flat plate moving vertically near a plane wall and the pseudosteady approximate solution to the same problem for the plate still having horizontal velocity are obtained together using the theory of elliptical functions.

  20. Characterizing Sub-Daily Flow Regimes: Implications of Hydrologic Resolution on Ecohydrology Studies

    DOE PAGES

    Bevelhimer, Mark S.; McManamay, Ryan A.; O'Connor, B.

    2014-05-26

    Natural variability in flow is a primary factor controlling geomorphic and ecological processes in riverine ecosystems. Within the hydropower industry, there is growing pressure from environmental groups and natural resource managers to change reservoir releases from daily peaking to run-of-river operations on the basis of the assumption that downstream biological communities will improve under a more natural flow regime. In this paper, we discuss the importance of assessing sub-daily flows for understanding the physical and ecological dynamics within river systems. We present a variety of metrics for characterizing sub-daily flow variation and use these metrics to evaluate general trends amongmore » streams affected by peaking hydroelectric projects, run-of-river projects and streams that are largely unaffected by flow altering activities. Univariate and multivariate techniques were used to assess similarity among different stream types on the basis of these sub-daily metrics. For comparison, similar analyses were performed using analogous metrics calculated with mean daily flow values. Our results confirm that sub-daily flow metrics reveal variation among and within streams that are not captured by daily flow statistics. Using sub-daily flow statistics, we were able to quantify the degree of difference between unaltered and peaking streams and the amount of similarity between unaltered and run-of-river streams. The sub-daily statistics were largely uncorrelated with daily statistics of similar scope. Furthermore, on short temporal scales, sub-daily statistics reveal the relatively constant nature of unaltered streamreaches and the highly variable nature of hydropower-affected streams, whereas daily statistics show just the opposite over longer temporal scales.« less

  1. Characterizing Sub-Daily Flow Regimes: Implications of Hydrologic Resolution on Ecohydrology Studies

    SciTech Connect

    Bevelhimer, Mark S.; McManamay, Ryan A.; O'Connor, B.

    2014-05-26

    Natural variability in flow is a primary factor controlling geomorphic and ecological processes in riverine ecosystems. Within the hydropower industry, there is growing pressure from environmental groups and natural resource managers to change reservoir releases from daily peaking to run-of-river operations on the basis of the assumption that downstream biological communities will improve under a more natural flow regime. In this paper, we discuss the importance of assessing sub-daily flows for understanding the physical and ecological dynamics within river systems. We present a variety of metrics for characterizing sub-daily flow variation and use these metrics to evaluate general trends among streams affected by peaking hydroelectric projects, run-of-river projects and streams that are largely unaffected by flow altering activities. Univariate and multivariate techniques were used to assess similarity among different stream types on the basis of these sub-daily metrics. For comparison, similar analyses were performed using analogous metrics calculated with mean daily flow values. Our results confirm that sub-daily flow metrics reveal variation among and within streams that are not captured by daily flow statistics. Using sub-daily flow statistics, we were able to quantify the degree of difference between unaltered and peaking streams and the amount of similarity between unaltered and run-of-river streams. The sub-daily statistics were largely uncorrelated with daily statistics of similar scope. Furthermore, on short temporal scales, sub-daily statistics reveal the relatively constant nature of unaltered streamreaches and the highly variable nature of hydropower-affected streams, whereas daily statistics show just the opposite over longer temporal scales.

  2. Flow Regime Based Climatologies of Lightning Probabilities for Spaceports and Airports

    NASA Technical Reports Server (NTRS)

    Bauman, William H., III; Volmer, Matthew; Sharp, David; Spratt, Scott; Lafosse, Richard A.

    2007-01-01

    Objective: provide forecasters with a "first guess" climatological lightning probability tool (1) Focus on Space Shuttle landings and NWS T AFs (2) Four circles around sites: 5-, 10-, 20- and 30 n mi (4) Three time intervals: hourly, every 3 hr and every 6 hr It is based on: (1) NLDN gridded data (2) Flow regime (3) Warm season months of May-Sep for years 1989-2004 Gridded data and available code yields squares, not circles Over 850 spread sheets converted into manageable user-friendly web-based GUI

  3. Sulfamethoxazole and ciprofloxacin removal using a horizontal-flow anaerobic immobilized biomass reactor.

    PubMed

    Chatila, Sami; Amparo, Maura R; Carvalho, Lucas S; Penteado, Eduardo D; Tomita, Inês N; Santos-Neto, Álvaro J; Lima Gomes, Paulo C F; Zaiat, Marcelo

    2016-01-01

    The antibiotics sulfamethoxazole (SMTX) and ciprofloxacin (CIP) are commonly used in human and veterinary medicine, which explains their occurrence in wastewater. Anaerobic reactors are low-cost, simple and suitable technology to wastewater treatment, but there is a lack of studies related to the removal efficiency of antibiotics. To overcome this knowledge gap, the objective of this study was to evaluate the removal kinetics of SMTX and CIP using a horizontal-flow anaerobic immobilized biomass reactor. Two different concentrations were evaluated, for SMTX 20 and 40 μg L(-1); for CIP 2.0 and 5.0 μg L(-1). The affluent and effluent analysis was carried out in liquid chromatography/tandem mass spectrometry (LC-MS/MS) with the sample preparation procedure using an off-line solid-phase extraction. This method was developed, validated and successfully applied for monitoring the affluent and effluent samples. The removal efficiency found for both antibiotics at the two concentrations studied was 97%. Chemical oxygen demand (COD) exhibited kinetic constants that were different from that observed for the antibiotics, indicating the absence of co-metabolism. Also, though the antibiotic concentration was increased, there was no inhibitory effect in the removal of COD and antibiotics.

  4. Removal of total suspended solids from wastewater in constructed horizontal flow subsurface wetlands.

    PubMed

    Manios, T; Stentiford, E I; Millner, P

    2003-06-01

    Subsurface horizontal flow experimental wetlands (reed beds), were designed and built based on a combination of two design methodologies, that of the WRc and Severn Trent Water plc (1996) and that of the USA, EPA (1988). Four different growing media were used with a combination of top soil, gravel, river sand, and mature sewage sludge compost, to determine the best substrate for total suspended solids (TSS) removal. Eight units were constructed, two for each growing media. One bed for each pair was planted with Typha latifolia plants commonly known as cattails. Primary treated domestic wastewater, was continuously fed to the beds for more than six months. All eight beds performed very well. The best performance was achieved by the gravel reed beds with an almost constant removal rate above 95% and an average effluent concentration of less than 10 mg/L. Soil based beds containing top soil and sand, managed to reach values of removal around 90%. The wetlands containing compost in their substrate, produced an effluent with average concentration of less than 30 mg/L and a percentage removal between 80% and 90%. As expected, there was no significant difference in the performance of planted and unplanted wetlands.

  5. Alternative filter media for phosphorous removal in a horizontal subsurface flow constructed wetland.

    PubMed

    Vohla, Christina; Põldvere, Elar; Noorvee, Alar; Kuusemets, Valdo; Mander, Ulo

    2005-01-01

    During the study period from 1997 to 2002 the purification efficiency of phosphorus in the horizontal subsurface flow (HSSF) constructed wetland (CW) in Kodijärve, has been quite high (63-95%). However, slowly increasing trend in outlet P concentrations and decreasing annual P removal rate are obviously the indicators that show possible saturation processes in filter media. To search for potential filter media with high phosphorus sorption capacity, sorption characteristics and particle size distribution of several local sands, gravels, glauconite-sandstone, LWA, and calcareous waste products from oil-shale industry were investigated. The average P sorption capacity for best materials (crashed ash block, oil, shale fly ash and the sediment from oil shale ash plateau) was higher than 96% and estimated design capacity was around 4-5 g P kg(-1). According to results, sediment from oil shale ash plateau was considered as perspective filter media for P retention. In Summer 2002 experimental sedimentation filter, filled with the sediment from oil shale ash plateau, was installed in the outlet from the Kodijärve HSSF CW. According to preliminary results the average P removal in the sedimentation filter was 52%. PMID:15921280

  6. Sub-grid drag models for horizontal cylinder arrays immersed in gas-particle multiphase flows

    SciTech Connect

    Sarkar, Avik; Sun, Xin; Sundaresan, Sankaran

    2013-09-08

    Immersed cylindrical tube arrays often are used as heat exchangers in gas-particle fluidized beds. In multiphase computational fluid dynamics (CFD) simulations of large fluidized beds, explicit resolution of small cylinders is computationally infeasible. Instead, the cylinder array may be viewed as an effective porous medium in coarse-grid simulations. The cylinders' influence on the suspension as a whole, manifested as an effective drag force, and on the relative motion between gas and particles, manifested as a correction to the gas-particle drag, must be modeled via suitable sub-grid constitutive relationships. In this work, highly resolved unit-cell simulations of flow around an array of horizontal cylinders, arranged in a staggered configuration, are filtered to construct sub-grid, or `filtered', drag models, which can be implemented in coarse-grid simulations. The force on the suspension exerted by the cylinders is comprised of, as expected, a buoyancy contribution, and a kinetic component analogous to fluid drag on a single cylinder. Furthermore, the introduction of tubes also is found to enhance segregation at the scale of the cylinder size, which, in turn, leads to a reduction in the filtered gas-particle drag.

  7. Effects of intermittent loading on nitrogen removal in horizontal subsurface flow wetlands.

    PubMed

    Forbes, Margaret G; Yelderman, Joe C; Potterton, Tina; Doyle, Robert D

    2010-01-01

    Removal of CBOD(5) and nitrogen from septic tank effluent was evaluated in four horizontal subsurface flow (HSSF) wetlands. An intermittently loaded cell was compared to a continuously loaded control cell, with both treatments receiving the same weekly volume. The intermittent cell was rapidly drained and "rested" for 24-hr, then refilled in steps, twice weekly. Two media with different particle sizes but similar porosities were also compared. The two media, light weight expanded shale and gravel, were both continuously loaded. As hypothesized, the wetland cell that was intermittently loaded had higher dissolved oxygen, greater ammonia removal, and greater nitrate production than the continuously loaded cells. Areal NH(3)-N removal for the intermittently loaded cell was 0.90 g m(-2) d(-1) compared to 0.47 g m(-2) d(-1) for the control. Ammonia removal was also higher in continuously loaded gravel cells than in cells with expanded shale. Ammonia-N removal was an order of magnitude lower in a similar SSF wetland that had been in operation for 3 years. However, CBOD(5), total suspended solids, and total nitrogen did not vary substantially among the treatments.

  8. Experimental Studies on Carbon Dioxide Flow Boiling Heat Transfer Coefficient in Horizontal Smooth Tube

    NASA Astrophysics Data System (ADS)

    Hashimoto, Katsumi; Kiyotani, Akihiro; Sasaki, Naoe

    The CO2 heat pump water heater ”ECO CUTE” which was commercialized in 2001 has a high potential for energy conservation and greenhouse abatement. The most important element apparatus is always the evaporator in order to develop smaller and higher performance equipment. In this paper, an experimental study has been conducted to measure the pure CO2 flow boiling heat transfer coefficient (99.999 % purity, without oil) in a horizontal smooth tube (outer diameter 6 mm, thickness 0.4 mm). The measured mean heat transfer coefficients are compared with calculated value with using previous experimental heat transfer correlation equations. These two values are different from each other. Mean heat transfer coefficients are measured with varying mass velocity, pressure and heat transfer lengths. The tube length is varied to 3.0 m, 4.0 m and 5.0 m, to distinguish the influence of mass velocity and that of heat flux to the heat transfer coefficient. The test conditions were: CO2 mass velocity from about 150 to about 700 kg⁄(m2s) (heat flux from about 10 to about 40 kW⁄m2), quality at inlet of test section is 0.17, CO2 super heat at outlet of test section is 5 K and saturation temperature of CO2 ranges from 0 to 10 °C. As a result, it has been understood that heat flux has a greater influence on the heat transfer coefficient.

  9. Application of horizontal-flow anaerobic immobilized biomass reactor for bioremediation of acid mine drainage.

    PubMed

    Rodriguez, R P; Vich, D V; Garcia, M L; Varesche, M B A; Zaiat, M

    2016-06-01

    The production of low-pH effluent with sulfate and metals is one of the biggest environmental concerns in the mining industry. The biological process for sulfate reduction has the potential to become a low-cost solution that enables the recovery of interesting compounds. The present study analyzed such a process in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor, employing ethanol as the carbon and energy source. Results showed that a maximal efficiency in the removal of sulfate and ethanol could only be obtained by reducing the applied sulfate load (225.1 ± 38 g m(-3) d(-1)). This strategy led to over 75% of chemical oxygen demand (COD) and sulfate removal. Among the COD/SO4(2-) studied ratios, 0.67 showed the most promising performance. The effluent's pH has naturally remained between 6.8 and 7.0 and the complete oxidation of the organic matter has been observed. Corrections of the influent pH or effluent recirculation did not show any significant effect on the COD and sulfate removal efficiency. Species closely related to strains of Clostridium sp. and species of Acidaminobacter hydrogenomorfans and Fusibacter paucivorans that can be related to the process of sulfate reduction were found in the HAIB reactors when the initial pH was 5 and the COD/SO4(2-) ratio increased to 1.0. PMID:27280606

  10. Influence of chlorothalonil on the removal of organic matter in horizontal subsurface flow constructed wetlands.

    PubMed

    Casas-Zapata, Juan C; Ríos, Karina; Florville-Alejandre, Tomás R; Morató, Jordi; Peñuela, Gustavo

    2013-01-01

    This study investigates the effects of chlorothalonil (CLT) on chemical oxygen demand (COD) and dissolved organic carbon (DOC) in pilot-scale horizontal subsurface flow constructed wetlands (HSSFCW) planted with Phragmites australis. Physicochemical parameters of influent and effluent water samples, microbial population counting methods and statistical analysis were used to evaluate the influence of CLT on organic matter removal efficiency. The experiments were conducted on four planted replicate wetlands (HSSFCW-Pa) and one unplanted control wetland (HSSFCW-NPa). The wetlands exhibited high average organic matter removal efficiencies (HSSFCW-Pa: 80.6% DOC, 98.0% COD; HSSFCW-NPa: 93.2% DOC, 98.4% COD). The addition of CLT did not influence organic removal parameters. In all cases CLT concentrations in the effluent occurred in concentrations lower than the detection limit of the analytical method. Microbial population counts from HSSFCW-Pa showed significant correlations among different microbial groups and with different physicochemical variables. The apparent independence of organic matter removal and CLT inputs, along with the CLT depletion observed in effluent samples demonstrated that HSSFCW are a viable technology for the treatment of agricultural effluents contaminated with organo-chloride pesticides like CLT.

  11. Effects of intermittent loading on nitrogen removal in horizontal subsurface flow wetlands.

    PubMed

    Forbes, Margaret G; Yelderman, Joe C; Potterton, Tina; Doyle, Robert D

    2010-01-01

    Removal of CBOD(5) and nitrogen from septic tank effluent was evaluated in four horizontal subsurface flow (HSSF) wetlands. An intermittently loaded cell was compared to a continuously loaded control cell, with both treatments receiving the same weekly volume. The intermittent cell was rapidly drained and "rested" for 24-hr, then refilled in steps, twice weekly. Two media with different particle sizes but similar porosities were also compared. The two media, light weight expanded shale and gravel, were both continuously loaded. As hypothesized, the wetland cell that was intermittently loaded had higher dissolved oxygen, greater ammonia removal, and greater nitrate production than the continuously loaded cells. Areal NH(3)-N removal for the intermittently loaded cell was 0.90 g m(-2) d(-1) compared to 0.47 g m(-2) d(-1) for the control. Ammonia removal was also higher in continuously loaded gravel cells than in cells with expanded shale. Ammonia-N removal was an order of magnitude lower in a similar SSF wetland that had been in operation for 3 years. However, CBOD(5), total suspended solids, and total nitrogen did not vary substantially among the treatments. PMID:20962402

  12. Influence of chlorothalonil on the removal of organic matter in horizontal subsurface flow constructed wetlands.

    PubMed

    Casas-Zapata, Juan C; Ríos, Karina; Florville-Alejandre, Tomás R; Morató, Jordi; Peñuela, Gustavo

    2013-01-01

    This study investigates the effects of chlorothalonil (CLT) on chemical oxygen demand (COD) and dissolved organic carbon (DOC) in pilot-scale horizontal subsurface flow constructed wetlands (HSSFCW) planted with Phragmites australis. Physicochemical parameters of influent and effluent water samples, microbial population counting methods and statistical analysis were used to evaluate the influence of CLT on organic matter removal efficiency. The experiments were conducted on four planted replicate wetlands (HSSFCW-Pa) and one unplanted control wetland (HSSFCW-NPa). The wetlands exhibited high average organic matter removal efficiencies (HSSFCW-Pa: 80.6% DOC, 98.0% COD; HSSFCW-NPa: 93.2% DOC, 98.4% COD). The addition of CLT did not influence organic removal parameters. In all cases CLT concentrations in the effluent occurred in concentrations lower than the detection limit of the analytical method. Microbial population counts from HSSFCW-Pa showed significant correlations among different microbial groups and with different physicochemical variables. The apparent independence of organic matter removal and CLT inputs, along with the CLT depletion observed in effluent samples demonstrated that HSSFCW are a viable technology for the treatment of agricultural effluents contaminated with organo-chloride pesticides like CLT. PMID:23305280

  13. Application of horizontal-flow anaerobic immobilized biomass reactor for bioremediation of acid mine drainage.

    PubMed

    Rodriguez, R P; Vich, D V; Garcia, M L; Varesche, M B A; Zaiat, M

    2016-06-01

    The production of low-pH effluent with sulfate and metals is one of the biggest environmental concerns in the mining industry. The biological process for sulfate reduction has the potential to become a low-cost solution that enables the recovery of interesting compounds. The present study analyzed such a process in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor, employing ethanol as the carbon and energy source. Results showed that a maximal efficiency in the removal of sulfate and ethanol could only be obtained by reducing the applied sulfate load (225.1 ± 38 g m(-3) d(-1)). This strategy led to over 75% of chemical oxygen demand (COD) and sulfate removal. Among the COD/SO4(2-) studied ratios, 0.67 showed the most promising performance. The effluent's pH has naturally remained between 6.8 and 7.0 and the complete oxidation of the organic matter has been observed. Corrections of the influent pH or effluent recirculation did not show any significant effect on the COD and sulfate removal efficiency. Species closely related to strains of Clostridium sp. and species of Acidaminobacter hydrogenomorfans and Fusibacter paucivorans that can be related to the process of sulfate reduction were found in the HAIB reactors when the initial pH was 5 and the COD/SO4(2-) ratio increased to 1.0.

  14. Generalized linear stability of non-inertial rimming flow in a rotating horizontal cylinder.

    PubMed

    Aggarwal, Himanshu; Tiwari, Naveen

    2015-10-01

    The stability of a thin film of viscous liquid inside a horizontally rotating cylinder is studied using modal and non-modal analysis. The equation governing the film thickness is derived within lubrication approximation and up to first order in aspect ratio (average film thickness to radius of the cylinder). Effect of gravity, viscous stress and capillary pressure are considered in the model. Steady base profiles are computed in the parameter space of interest that are uniform in the axial direction. A linear stability analysis is performed on these base profiles to study their stability to axial perturbations. The destabilizing behavior of aspect ratio and surface tension is demonstrated which is attributed to capillary instability. The transient growth that gives maximum amplification of any initial disturbance and the pseudospectra of the stability operator are computed. These computations reveal weak effect of non-normality of the operator and the results of eigenvalue analysis are recovered after a brief transient period. Results from nonlinear simulations are also presented which also confirm the validity of the modal analysis for the flow considered in this study. PMID:26496740

  15. An experimental investigation of flow patterns and liquid entrainment in a horizontal-tube evaporator

    NASA Astrophysics Data System (ADS)

    Barnhart, John Steven

    An experimental study of two-phase flow patterns and droplet entrainment in a horizontal-tube evaporator was conducted. Measurements were made with serpentine aluminum and glass evaporators with geometries typical of those used for domestic refrigeration. The refrigerant in the majority of tests was R134a, which will replace R12 for refrigeration and automotive air-conditioning in 1995. The phenomenon of primary interest was the nonequilibrium transport of droplets within superheated vapor at the evaporator exit. Of particular concern were substantial variations in the liquid rate with time, and corresponding fluctuations in exit temperature. These variations are due to the formation of slugs which rapidly transport a surplus of liquid toward the exit. A flow loop was constructed to circulate oil-free refrigerant through the evaporator under widely varying conditions. Liquid carry over (expressed as a dimensionless entrained mass fraction, EMF) was measured as a function of inlet quality, heat flux, mass flux, and exit superheat. A laser-based phase/Doppler particle analyzer was used to measure droplet diameters and velocities at the evaporator exit. Tests with three refrigerants over wide ranges of operating conditions revealed time-averaged EMF's of no more than 0.1 percent. Analysis of variance showed exit superheat to have the strongest effect, followed by mass flux, inlet quality, and heat flux. Time-averaged EMF's varied with operating conditions by several orders of magnitude, decreasing with increasing superheat level (due to lower entrainment rates near the exit and more rapid droplet vaporization) and mass flux and inlet quality (due to reduced slug formation). The incidence of slug flow and its effect on evaporator exit conditions were documented in time-resolved experiments, using techniques such as auto- and cross-correlation and Fourier transform. Time-resolved EMF's as high as one percent were observed, as well as sharp reductions in exit superheat

  16. Dual-permeability model for flow in shrinking soil with dominant horizontal deformation

    NASA Astrophysics Data System (ADS)

    Coppola, Antonio; Gerke, Horst H.; Comegna, Alessandro; Basile, Angelo; Comegna, Vincenzo

    2012-08-01

    In this study, a dual-permeability approach is discussed for modeling preferential flow in shrinking soils by accounting for shrinking effects on macropore and matrix domain hydraulic properties. Conceptually, the soil is treated as a dual-permeability bulk porous medium consisting of two dynamic interacting pore domains: (1) the fracture (from shrinkage) pore domain and (2) the aggregate (interparticles plus structural) or matrix pore domain. The model assumes that the swell-shrink dynamics is represented by the inversely proportional volume changes of the fracture and matrix domains, while the overall porosity of the total soil, and hence the layer thickness, remains constant. This assumption can be justified for soils with dominant horizontal soil deformation in the swelling-shrinkage process (shrinkage geometry factor,rs> 3). The swell-shrink dynamics was included in a one-dimensional dual-permeability model in which water flow in both domains was described with the Richards' equation. Swell-shrink dynamics was incorporated in the model partly by changing the coupled domain-specific hydraulic properties according to the shrinkage characteristics of the matrix and partly by allowing the fractional contribution of the two domains to change with the pressure head. As a first step, the hysteresis in the swell-shrink dynamics was not included. We also assumed that the aggregate behavior and its hydraulic properties depend only on the average aggregate water content and not on its internal real distribution. The model proved, describing successfully effects of shrinkage on the spatial and temporal evolution of water contents measured in a silty loam soil in the field.

  17. Statistical analysis of the horizontal divergent flow in emerging solar active regions

    SciTech Connect

    Toriumi, Shin; Hayashi, Keiji; Yokoyama, Takaaki

    2014-10-10

    Solar active regions (ARs) are thought to be formed by magnetic fields from the convection zone. Our flux emergence simulations revealed that a strong horizontal divergent flow (HDF) of unmagnetized plasma appears at the photosphere before the flux begins to emerge. In our earlier study, we analyzed HMI data for a single AR and confirmed presence of this precursor plasma flow in the actual Sun. In this paper, as an extension of our earlier study, we conducted a statistical analysis of the HDFs to further investigate their characteristics and better determine the properties. From SDO/HMI data, we picked up 23 flux emergence events over a period of 14 months, the total flux of which ranges from 10{sup 20} to 10{sup 22} Mx. Out of 23 selected events, 6 clear HDFs were detected by the method we developed in our earlier study, and 7 HDFs detected by visual inspection were added to this statistic analysis. We found that the duration of the HDF is on average 61 minutes and the maximum HDF speed is on average 3.1 km s{sup –1}. We also estimated the rising speed of the subsurface magnetic flux to be 0.6-1.4 km s{sup –1}. These values are highly consistent with our previous one-event analysis as well as our simulation results. The observation results lead us to the conclusion that the HDF is a rather common feature in the earliest phase of AR emergence. Moreover, our HDF analysis has the capability of determining the subsurface properties of emerging fields that cannot be directly measured.

  18. Assessment of future variability in extreme precipitation and the potential effects on the wadi flow regime.

    PubMed

    Gunawardhana, Luminda Niroshana; Al-Rawas, Ghazi A; Kazama, So; Al-Najar, Khalid A

    2015-10-01

    The objective of this study is to investigate how the magnitude and occurrence of extreme precipitation events are affected by climate change and to predict the subsequent impacts on the wadi flow regime in the Al-Khod catchment area, Muscat, Oman. The tank model, a lumped-parameter rainfall-runoff model, was used to simulate the wadi flow. Precipitation extremes and their potential future changes were predicted using six-member ensembles of general circulation models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Yearly maxima of the daily precipitation and wadi flow for varying return periods were compared for observed and projected data by fitting the generalized extreme value (GEV) distribution function. Flow duration curves (FDC) were developed and compared for the observed and projected wadi flows. The results indicate that extreme precipitation events consistently increase by the middle of the twenty-first century for all return periods (49-52%), but changes may become more profound by the end of the twenty-first century (81-101%). Consequently, the relative change in extreme wadi flow is greater than twofolds for all of the return periods in the late twenty-first century compared to the relative changes that occur in the mid-century period. Precipitation analysis further suggests that greater than 50% of the precipitation may be associated with extreme events in the future. The FDC analysis reveals that changes in low-to-moderate flows (Q60-Q90) may not be statistically significant, whereas increases in high flows (Q5) are statistically robust (20 and 25% for the mid- and late-century periods, respectively). PMID:26370197

  19. Flow regime effects on mature Populus fremontii (Fremont cottonwood) productivity on two contrasting dryland river floodplains

    USGS Publications Warehouse

    Andersen, Douglas C.

    2016-01-01

    I compared riparian cottonwood (Populus fremontii) productivity-discharge relationships in a relictual stand along the highly regulated Green River and in a naturally functioning stand along the unregulated Yampa River in semiarid northwest Colorado. I used multiple regression to model flow effects on annual basal area increment (BAI) from 1982 to 2011, after removing any autocorrelation present. Each BAI series was developed from 20 trees whose mean size (67 cm diameter at breast height [DBH]) was equivalent in the two stands. BAI was larger in the Yampa River stand except in 2 y when defoliating leaf beetles were present there. I found no evidence for a Yampa flood-magnitude threshold above which BAI declined. Flow variables explained ∼45% of residual BAI variability, with most explained by current-year maximum 90-d discharge (QM90) in the Yampa River stand and by a measure of the year-to-year change in QM90 in the Green River stand. The latter reflects a management-imposed ceiling on flood magnitude—Flaming Gorge Dam power plant capacity—infrequently exceeded during the study period. BAI in the relictual stand began to trend upward in 1992 when flows started to mimic a natural flow regime. Mature Fremont cottonwoods appear to be ecologically resilient. Their productivity along regulated rivers might be optimized using multiyear environmental flow designs.

  20. Shifting chemical equilibria in flow--efficient decarbonylation driven by annular flow regimes.

    PubMed

    Gutmann, Bernhard; Elsner, Petteri; Glasnov, Toma; Roberge, Dominique M; Kappe, C Oliver

    2014-10-20

    To efficiently drive chemical reactions, it is often necessary to influence an equilibrium by removing one or more components from the reaction space. Such manipulation is straightforward in open systems, for example, by distillation of a volatile product from the reaction mixture. Herein we describe a unique high-temperature/high-pressure gas/liquid continuous-flow process for the rhodium-catalyzed decarbonylation of aldehydes. The carbon monoxide released during the reaction is carried with a stream of an inert gas through the center of the tubing, whereas the liquid feed travels as an annular film along the wall of the channel. As a consequence, carbon monoxide is effectively vaporized from the liquid phase into the gas phase and stripped from the reaction mixture, thus driving the equilibrium to the product and preventing poisoning of the catalyst. This approach enables the catalytic decarbonylation of a variety of aldehydes with unprecedented efficiency with a standard coil-based flow device.

  1. Integrated model for the natural flow regime in the Cerro Prieto hydrothermal system, B. C. , Mexico, based upon petrological and isotope geochemical criteria

    SciTech Connect

    Elders, W.A.; Williams, A.E.; Hoagland, J.R.

    1981-01-01

    Studies of cuttings and core at Cerro Prieto have now been extended to more than 50 boreholes. The aims of this petrological and isotopic work are to determine the shape of the reservoir, its physical properties, and its temperature distribution and flow regime before the steam field was produced. A map showing the first occurrence of hydrothermal epidote shows a dome-shaped top to the steam-producing zone. The hottest of the mapped mineral zones - the biotite vermiculite zone - shows a dome displaced to the northeast relative to the epidote zone. Patterns of mineral zones observed in wells are consistent with patterns of oxygen isotopic ratios in calcite and quartz. Using both criteria all of the boreholes so far studied were classified as belonging to one of four different regimes. These are: (a) the thermal plume of upward flowing water close to boiling, marked by a regular sequence of prograde mineral zones and large isotopic shifts; (b) the discharge system where fluid leaks to the surface, as indicated by the occurrence of only a few low temperature mineral zones, which extend over large depth intervals with little isotope exchange; (c) the horizontal flow zone, in which boreholes penetrate reversals of both mineral zones and isotope shifts with increasing depth; and (d) the recharge zone where cold water is descending. Plotting these four types of boreholes on a map reveals a simple, consistent, pattern. This is interpreted to have been produced by a thermal plume dipping at 45/sup 0/ to the northeast.

  2. Effective discharge for sediment transport: the sorting role of river flow regimes

    NASA Astrophysics Data System (ADS)

    Basso, Stefano; Sprocati, Riccardo; Frascati, Alessandro; Marani, Marco; Schirmer, Mario; Botter, Gianluca

    2016-04-01

    The effective discharge is a key concept in geomorphology, river engineering and restoration. It is used to design the most stable channel configuration, to estimate sedimentation rate and lifespan of reservoirs and to characterize the hydrologic forcing in models studying long-term evolution of rivers. Previous empirical, theoretical and numerical studies found the effective discharge to be affected by climate, landscape and river morphology, type of transport (dissolved, suspended or bedload), and by streamflow variability. However, the heterogeneity of values observed for the effective discharge challenges a clear understanding of its pivotal drivers, and a consistent framework which explains observations carried out in different catchments and geographic areas is still lacking. This work relates the observed diversity of effective discharge values to the underlying heterogeneity of river flow regimes. The effective ratio (i.e. the ratio between effective discharge and mean streamflow) is derived as a function of the empirical exponent of the sediment rating curve and the streamflow variability, resulting from climatic and landscape drivers. The proposed analytic expression helps to disentangle hydrologic and landscape controls on the effective discharge, and highlights distinct effective ratios of persistent and erratic hydrologic regimes (respectively characterized by low and high flow variability), attributable to intrinsically different streamflow dynamics. The framework captures observed values of effective discharge for suspended sediment transport in a set of catchments of the continental United States, and may allow for first-order estimates of effective discharge in rivers belonging to different climatic regions.

  3. Effects of hydrologic infrastructure on flow regimes of California's Central Valley rivers: Implications for fish populations

    USGS Publications Warehouse

    Brown, Larry R.; Bauer, Marissa L.

    2010-01-01

    Alteration of natural flow regimes is generally acknowledged to have negative effects on native biota; however, methods for defining ecologically appropriate flow regimes in managed river systems are only beginning to be developed. Understanding how past and present water management has affected rivers is an important part of developing such tools. In this paper, we evaluate how existing hydrologic infrastructure and management affect streamflow characteristics of rivers in the Central Valley, California and discuss those characteristics in the context of habitat requirements of native and alien fishes. We evaluated the effects of water management by comparing observed discharges with estimated discharges assuming no water management ("full natural runoff"). Rivers in the Sacramento River drainage were characterized by reduced winter–spring discharges and augmented discharges in other months. Rivers in the San Joaquin River drainage were characterized by reduced discharges in all months but particularly in winter and spring. Two largely unaltered streams had hydrographs similar to those based on full natural runoff of the regulated rivers. The reduced discharges in the San Joaquin River drainage streams are favourable for spawning of many alien species, which is consistent with observed patterns of fish distribution and abundance in the Central Valley. However, other factors, such as water temperature, are also important to the relative success of native and alien resident fishes. As water management changes in response to climate change and societal demands, interdisciplinary programs of research and monitoring will be essential for anticipating effects on fishes and to avoid unanticipated ecological outcomes.

  4. Watershed flow paths and stream water nitrogen-to-phosphorus ratios under simulated precipitation regimes

    NASA Astrophysics Data System (ADS)

    Green, Mark B.; Wang, Dong

    2008-12-01

    Stream water nitrogen-to-phosphorus (N:P) ratios influence algal community composition and nutrient limitation in lotic ecosystems. N:P ratios trend across climates, with low stream water N:P ratios more common in arid climates, yet little is known about mechanisms that cause this spatial and temporal variation. This study evaluates the relationship between precipitation regime (mean annual precipitation and its frequency), watershed flow pathways, and stream water total N-to-total P (TN:TP) ratios, using a model based on a central Minnesota watershed. The purpose of the study was to examine hydrologic mechanisms that control stream water TN:TP ratios. We constructed a model that accounted for hydrological and biogeochemical processes, followed by 161 simulations under a wide range of precipitation frequency and intensity scenarios. Precipitation regime controlled total runoff and subsurface hydrologic connectivity, which had implications for TN and TP concentrations and TN:TP ratios. Results supported the hypothesis that watershed hydrology is an important control on stream water TN:TP ratios and suggested that variation of flow pathways can lead to fundamental changes of N:P ratios.

  5. Optical vortex tracking studies of a horizontal axis wind turbine in yaw using laser-sheet, flow visualisation

    NASA Astrophysics Data System (ADS)

    Grant, I.; Parkin, P.; Wang, X.

    Experimental studies have been conducted on a 0.9 m diameter, horizontal axis wind turbine (HAWT) placed in the open jet of a closed return wind tunnel. The turbine was tested in a three blade and a two blade configuration. The power coefficient of the turbine was measured and wake flow studies conducted for a range of yawed flows by tilting the rotor plane at various angles up to 30° to the incident wind direction. The motion of the shed vorticity was followed using laser-sheet flow visualisation with the overall wake deflection being measured. The results were compared with theoretical predictions and with studies conducted elsewhere.

  6. Invasive riparian vegetation response to flow regimes and flood pulses in a braided river floodplain.

    PubMed

    Caruso, Brian S; Pithie, Callum; Edmondson, Laura

    2013-08-15

    This study evaluated flow regimes and flood pulse characteristics, and their influences on invasive riparian vegetation, in a free-flowing braided river in the Southern Alps, South Island, New Zealand. A 46-year gauged flow record was used to evaluate 67 flow metrics for the Ahuriri River, and five sets of colour aerial photographs over 20 years (1991-2011) were analysed to quantify temporal and spatial changes in vegetation (crack willow, Russell lupin, and grassland). The correlation between flow metrics and vegetation class cover for each aerial photo interval was analysed, and multiple regression models were developed. Significant changes in different invasive vegetation classes were found, including cover, number and sizes of patches, and distances from patches to primary channels. In addition to infrequent large floods, specific characteristics of small floods, high flows, low/baseflows, and extreme low flows had influences on different vegetation classes. Key metrics that appear to drive changes in cover and provide a useful multiple regression model include the largest flood peak, frequency of floods, and the time since the last flood for each air photo interval. Up to 25% of invasive vegetation cover was removed and bare substrate increased after the largest flood on record (approximately 50-year flood), and the amount of vegetation cover is highly variable over time and space. Within approximately six years, however, the proportion of vegetation recovered to pre-flood levels. The study reach appears to demonstrate the "shifting-mosaic steady state" conceptual model of riverine floodplains, where the total proportion of substrate, vegetation and water remain relatively constant over long time periods.

  7. Detailled AMS analysis of recent dykes. Inferences about the flow regime and progression magnetic trends.

    NASA Astrophysics Data System (ADS)

    Pueyo Anchuela, Ó.; Gil Imaz, A.; Lago Sanjosé, M.; França, Z.; Forjaz, V. H.

    2009-04-01

    Anisotropy of Magnetic Susceptibility (AMS) has been applied to characterize the flow and emplacement conditions in tabular intrusions. The results in dykes have shown different models of relationship between the AMS ellipsoids and rock-fabric. These models include: a) imbrications during the flow observed in the margins of the intrusion (in the proximity of the dyke walls), b) magnetic lineation parallel to the flow, c) magnetic lineation normal to the flow (rolling of particles) or d) not evident relations between the flow and the magnetic axis. This complexity makes that, even when no mineralogical complexities exist, a contrast with outcrop evidences, shear indicators, orientation of grain, bubbles or vacuoles are needed. This complexity can be increased when this methodology is applied to old dykes, where not only the flow has influenced the AMS. In cases where the emplacement is syn-tectonic, or where deformational processes after the emplacement exist, the relation between flow regime and AMS can be more complex. To understand the changes and the model of emplacement in dykes, 12 recent dykes in sub-vertical position have been chosen to analyze the changes in orientation and the magnetic parameters along profiles border-center-border. The usual methodology recommends the sampling preferentially in the margin of the dykes. In this sense, the sampling has been focused in the margins but sampling also the whole extension. The average of cores for dyke is 54 (98 samples). The emplacement conditions of these dykes are related with a fracturation net parallel to the MAR in a passive manner. The dykes come from the Corvo and Flores islands, situated over North American Plate in the Western Azores (Portugal). Ten of the sampled dykes show clusters of axes and not significant variations in orientation of the magnetic ellipsoid between the sampling along the cross-sections border-center-border and the samples from both sides. Only two of the sampled dykes show

  8. Palladium Catalysis in Horizontal-Flow Treatment Wells: Field-Scale Design and Laboratory Study

    SciTech Connect

    Munakata, N; Cunningham, J A; Reinhard, M; Ruiz, R; Lebron, C

    2002-03-01

    This paper discusses the field-scale design and associated laboratory experiments for a new groundwater remediation system that combines palladium-catalyzed hydrodehalogenation with the use of dual horizontal-flow treatment wells (HFTWs). Palladium (Pd) catalysts can treat a wide range of halogenated compounds, often completely and rapidly dehalogenating them. The HFTW system recirculates water within the treatment zone and provides the opportunity for multiple treatment passes, thereby enhancing contaminant removal. The combined Pd/HFTW system is scheduled to go on line in mid-2002 at Edwards Air Force Base in southeastern California, with groundwater contaminated with 0.5 to 1.5 mg/L of trichloroethylene (TCE). Laboratory work, performed in conjunction with the field-scale design, provided reaction rates for field-scale design and information on long-term catalyst behavior. The apparent first-order reaction rate constant for TCE was 0.43/min, corresponding to a half-life of 1.6 min. Over the long term (1 to 2 months), the reaction rate decreased, indicating catalyst deactivation. The data show three distinct deactivation rates: a slow rate of 0.03/day over approximately the first month, followed by faster deactivation at 0.16 to 0.19/day. The final, fastest deactivation (0.55/day) was attributed to an artifact of the laboratory setup, which caused unnaturally high sulfide concentrations through bacterial reduction of sulfate to sulfide, a known catalyst poison. Sodium hypochlorite recovered the catalyst activity, and is expected to maintain activity in the field with periodic pulses to regenerate the catalyst and control growth of sulfate-reducing bacteria.

  9. Ibuprofen removal in horizontal subsurface flow constructed wetlands: treatment performance and fungal community dynamics.

    PubMed

    Zhang, Dongqing; Luo, Jinxue; Lee, Zarraz May Ping; Gersberg, Richard M; Liu, Yu; Tan, Soon Keat; Ng, Wun Jern

    2016-01-01

    The treatment performance of ibuprofen (IBP)-enriched wastewater by horizontal subsurface flow constructed wetlands planted with cattail (Typha angustifolia) and unplanted control mesocosms was investigated. Removal efficiencies of IBP were significantly (p < .05) enhanced in the planted mesocosms (78.5%) compared to those in the unplanted beds (57.9%). An 18S rRNA gene high-throughput pyrosequencing approach was used to investigate the effects of IBP on the structure of the fungal community in these wetland systems. The overall diversity of the fungal community was reduced under the IBP exposure. Taxonomic analysis revealed that 62.2% of the fungal sequences were affiliated with Basidiomycota, followed by Ascomycota (37.4%) at the phylum level. Uncultured fungus (48.2%), Chaetomium sp. (14.2%), Aspergillus sp. (12.4%), Trichoderma sp. (5.7%), Cladosporium sp. (5.4%), and Emericellopsis sp. (5.2%) were identified as dominant genera. At the genus level, a distinct profile of the fungal community in the IBP-enriched mesocosms was observed as compared to the control beds, and as well specific fungal genera were enhanced in the planted beds, regardless of IBP enrichment. However, despite these differences, the composition of the fungal community (as measured by Bray-Curtis similarity) was mostly unaffected by the significant IBP enrichment. On the other hand, a consistent similarity pattern of fungal community structure in the planted mesocosms suggests that the presence of higher macrophytes in the wetland systems may well help shape the fungal community structure.

  10. Biological mechanisms associated with triazophos (TAP) removal by horizontal subsurface flow constructed wetlands (HSFCW).

    PubMed

    Wu, Juan; Feng, Yuqin; Dai, Yanran; Cui, Naxin; Anderson, Bruce; Cheng, Shuiping

    2016-05-15

    Triazophos (TAP) is a widely used pesticide that is easily accumulated in the environment due to its relatively high stability: this accumulation from agricultural runoff results in potential hazards to aquatic ecosystems. Constructed wetlands are generally considered to be an effective technology for treating TAP polluted surface water. However, knowledge about the biological mechanisms of TAP removal is still lacking. This study investigates the responses of a wetland plant (Canna indica), substrate enzymes and microbial communities in bench-scale horizontal subsurface-flow constructed wetlands (HSCWs) loaded with different TAP concentrations (0, 0.1, 0.5 and 5 mg · L(-1)). The results indicate that TAP stimulated the activities of superoxide dismutase (SOD) and peroxidase (POD) in the roots of C. indica. The highest TAP concentrations significantly inhibited photosynthetic activities, as shown by a reduced effective quantum yield of PS II (ΦPS II) and lower electron transport rates (ETR). However, interestingly, the lower TAP loadings exhibited some favorable effects on these two variables, suggesting that C. indica is a suitable species for use in wetlands designed for treatment of low TAP concentrations. Urease and alkaline phosphatase (ALP) in the wetland substrate were activated by TAP. Two-way ANOVA demonstrated that urease activity was influenced by both the TAP concentrations and season, while acidphosphatase (ACP) only responded to seasonal variations. Analysis of high throughput sequencing of 16S rRNA revealed seasonal variations in the microbial community structure of the wetland substrate at the phylum and family levels. In addition, urease activity had a greater correlation with the relative abundance of some functional microbial groups, such as the Bacillaceae family, and the ALP and ACP may be influenced by the plant more than substrate microbial communities.

  11. Effect of dosing regime on nitrification in a subsurface vertical flow treatment wetland system.

    PubMed

    Kantawanichkul, Suwasa; Boontakhum, Walaya

    2012-01-01

    In this study, the effect of dosing regime on nitrification in a subsurface vertical flow treatment wetland system was investigated. The experimental unit was composed of four circular concrete tanks (1 m diameter and 80 cm deep), filled with gravel (1-2 cm) and planted with Cyperus alternifolius L. Synthetic wastewater with average chemical oxygen demand (COD) and ammonia nitrogen of 1,151 and 339 mg/L was fed into each tank. Different feeding and resting periods were applied: continuous flow (tank 1), 4 hrs on and 4 hrs off (tank 2), 1 hr on and 3 hrs off (tank 3) and 15 minutes on and 3 hrs 45 minutes off (tank 4). All four tanks were under the same hydraulic loading rate of 5 cm/day. After 165 days the reduction of total Kjeldahl nitrogen and ammonia nitrogen and the increase of nitrate nitrogen were greatest in tank 4, which had the shortest feeding period, while the continuous flow produced the lowest results. Effluent tanks 2 and 3 experienced similar levels of nitrification, both higher than that of tank 1. Thus supporting the idea that rapid dosing periods provide better aerobic conditions resulting in enhanced nitrification within the bed. Tank 4 had the highest removal rates for COD, and the continuous flow had the lowest. Tank 2 also exhibited a higher COD removal rate than tank 3, demonstrating that short dosing periods provide better within-bed oxidation and therefore offer higher removal efficiency.

  12. Effect of dosing regime on nitrification in a subsurface vertical flow treatment wetland system.

    PubMed

    Kantawanichkul, Suwasa; Boontakhum, Walaya

    2012-01-01

    In this study, the effect of dosing regime on nitrification in a subsurface vertical flow treatment wetland system was investigated. The experimental unit was composed of four circular concrete tanks (1 m diameter and 80 cm deep), filled with gravel (1-2 cm) and planted with Cyperus alternifolius L. Synthetic wastewater with average chemical oxygen demand (COD) and ammonia nitrogen of 1,151 and 339 mg/L was fed into each tank. Different feeding and resting periods were applied: continuous flow (tank 1), 4 hrs on and 4 hrs off (tank 2), 1 hr on and 3 hrs off (tank 3) and 15 minutes on and 3 hrs 45 minutes off (tank 4). All four tanks were under the same hydraulic loading rate of 5 cm/day. After 165 days the reduction of total Kjeldahl nitrogen and ammonia nitrogen and the increase of nitrate nitrogen were greatest in tank 4, which had the shortest feeding period, while the continuous flow produced the lowest results. Effluent tanks 2 and 3 experienced similar levels of nitrification, both higher than that of tank 1. Thus supporting the idea that rapid dosing periods provide better aerobic conditions resulting in enhanced nitrification within the bed. Tank 4 had the highest removal rates for COD, and the continuous flow had the lowest. Tank 2 also exhibited a higher COD removal rate than tank 3, demonstrating that short dosing periods provide better within-bed oxidation and therefore offer higher removal efficiency. PMID:22828298

  13. Increasing power generation in horizontal axis wind turbines using optimized flow control

    NASA Astrophysics Data System (ADS)

    Cooney, John A., Jr.

    In order to effectively realize future goals for wind energy, the efficiency of wind turbines must increase beyond existing technology. One direct method for achieving increased efficiency is by improving the individual power generation characteristics of horizontal axis wind turbines. The potential for additional improvement by traditional approaches is diminishing rapidly however. As a result, a research program was undertaken to assess the potential of using distributed flow control to increase power generation. The overall objective was the development of validated aerodynamic simulations and flow control approaches to improve wind turbine power generation characteristics. BEM analysis was conducted for a general set of wind turbine models encompassing last, current, and next generation designs. This analysis indicated that rotor lift control applied in Region II of the turbine power curve would produce a notable increase in annual power generated. This was achieved by optimizing induction factors along the rotor blade for maximum power generation. In order to demonstrate this approach and other advanced concepts, the University of Notre Dame established the Laboratory for Enhanced Wind Energy Design (eWiND). This initiative includes a fully instrumented meteorological tower and two pitch-controlled wind turbines. The wind turbines are representative in their design and operation to larger multi-megawatt turbines, but of a scale that allows rotors to be easily instrumented and replaced to explore new design concepts. Baseline data detailing typical site conditions and turbine operation is presented. To realize optimized performance, lift control systems were designed and evaluated in CFD simulations coupled with shape optimization tools. These were integrated into a systematic design methodology involving BEM simulations, CFD simulations and shape optimization, and selected experimental validation. To refine and illustrate the proposed design methodology, a

  14. Effectiveness of a regional model calibrated to different parts of a flow regime in regionalisation

    NASA Astrophysics Data System (ADS)

    Kim, H. S.

    2015-07-01

    The objective of this study was to reduce the parameter uncertainty which has an effect on the identification of the relationship between the catchment characteristics and the catchment response dynamics in ungauged catchments. A water balance model calibrated to represent the rainfall runoff characteristics over long time scales had a potential limitation in the modelling capacity to accurately predict the hydrological effects of non-stationary catchment response dynamics under different climate conditions (distinct wet and dry periods). The accuracy and precision of hydrological modelling predictions was assessed to yield a better understanding for the potential improvement of the model's predictability. In the assessment of model structure suitability to represent the non-stationary catchment response characteristics, there was a flow-dependent bias in the runoff simulations. In particular, over-prediction of the streamflow was dominant for the dry period. The poor model performance during the dry period was associated with the largely different impulse response estimates for the entire period and the dry period. The refined calibration approach was established based on assessment of model deficiencies. The rainfall-runoff models were separately calibrated to different parts of the flow regime, and the calibrated models for the separated time series were used to establish the regional models of relevant parts of the flow regime (i.e. wet and dry periods). The effectiveness of the parameter values for the refined approach in regionalisation was evaluated through investigating the accuracy of predictions of the regional models. The predictability was demonstrated using only the dry period to highlight the improvement in model performance easily veiled by the performance of the model for the whole period. The regional models from the refined calibration approach clearly enhanced the hydrological behaviour by improving the identification of the relationships between

  15. Monitoring strategies of stream phosphorus under contrasting climate-driven flow regimes

    NASA Astrophysics Data System (ADS)

    Goyenola, G.; Meerhoff, M.; Teixeira-de Mello, F.; González-Bergonzoni, I.; Graeber, D.; Fosalba, C.; Vidal, N.; Mazzeo, N.; Ovesen, N. B.; Jeppesen, E.; Kronvang, B.

    2015-10-01

    Climate and hydrology are relevant control factors determining the timing and amount of nutrient losses from land to downstream aquatic systems, in particular of phosphorus (P) from agricultural lands. The main objective of the study was to evaluate the differences in P export patterns and the performance of alternative monitoring strategies in streams under contrasting climate-driven flow regimes. We compared a set of paired streams draining lowland micro-catchments under temperate climate and stable discharge conditions (Denmark) and under sub-tropical climate and flashy conditions (Uruguay). We applied two alternative nutrient sampling programs (high-frequency composite sampling and low-frequency instantaneous-grab sampling) and estimated the contribution derived from point and diffuse sources fitting a source apportionment model. We expected to detect a pattern of higher total and particulate phosphorus export from diffuse sources in streams in Uruguay streams, mostly as a consequence of higher variability in flow regime (higher flashiness). Contrarily, we found a higher contribution of dissolved P in flashy streams. We did not find a notably poorer performance of the low-frequency sampling program to estimate P exports in flashy streams compared to the less variable streams. We also found signs of interaction between climate/hydrology and land use intensity, in particular in the presence of point sources of P, leading to a bias towards underestimation of P in hydrologically stable streams and overestimation of P in flashy streams. Based on our findings, we suggest that the evaluation and use of more accurate monitoring methods, such as automatized flow-proportional water samplers and automatized bankside analyzers, should be prioritized whenever logistically possible. However, it seems particularly relevant in currently flashy systems and also in systems where climate change predictions suggest an increase in stream flashiness.

  16. Flow regime, temperature, and biotic interactions drive differential declines of trout species under climate change

    PubMed Central

    Wenger, Seth J.; Isaak, Daniel J.; Luce, Charles H.; Neville, Helen M.; Fausch, Kurt D.; Dunham, Jason B.; Dauwalter, Daniel C.; Young, Michael K.; Elsner, Marketa M.; Rieman, Bruce E.; Hamlet, Alan F.; Williams, Jack E.

    2011-01-01

    Broad-scale studies of climate change effects on freshwater species have focused mainly on temperature, ignoring critical drivers such as flow regime and biotic interactions. We use downscaled outputs from general circulation models coupled with a hydrologic model to forecast the effects of altered flows and increased temperatures on four interacting species of trout across the interior western United States (1.01 million km2), based on empirical statistical models built from fish surveys at 9,890 sites. Projections under the 2080s A1B emissions scenario forecast a mean 47% decline in total suitable habitat for all trout, a group of fishes of major socioeconomic and ecological significance. We project that native cutthroat trout Oncorhynchus clarkii, already excluded from much of its potential range by nonnative species, will lose a further 58% of habitat due to an increase in temperatures beyond the species’ physiological optima and continued negative biotic interactions. Habitat for nonnative brook trout Salvelinus fontinalis and brown trout Salmo trutta is predicted to decline by 77% and 48%, respectively, driven by increases in temperature and winter flood frequency caused by warmer, rainier winters. Habitat for rainbow trout, Oncorhynchus mykiss, is projected to decline the least (35%) because negative temperature effects are partly offset by flow regime shifts that benefit the species. These results illustrate how drivers other than temperature influence species response to climate change. Despite some uncertainty, large declines in trout habitat are likely, but our findings point to opportunities for strategic targeting of mitigation efforts to appropriate stressors and locations. PMID:21844354

  17. Flow regime, temperature, and biotic interactions drive differential declines of trout species under climate change

    USGS Publications Warehouse

    Wenger, S.J.; Isaak, D.J.; Luce, C.H.; Neville, H.M.; Fausch, K.D.; Dunham, J.B.; Dauwalter, D.C.; Young, M.K.; Elsner, M.M.; Rieman, B.E.; Hamlet, A.F.; Williams, J.E.

    2011-01-01

    Broad-scale studies of climate change effects on freshwater species have focused mainly on temperature, ignoring critical drivers such as flow regime and biotic interactions. We use downscaled outputs from general circulation models coupled with a hydrologic model to forecast the effects of altered flows and increased temperatures on four interacting species of trout across the interior western United States (1.01 million km2), based on empirical statistical models built from fish surveys at 9,890 sites. Projections under the 2080s A1B emissions scenario forecast a mean 47% decline in total suitable habitat for all trout, a group of fishes of major socioeconomic and ecological significance. We project that native cutthroat trout Oncorhynchus clarkii, already excluded from much of its potential range by nonnative species, will lose a further 58% of habitat due to an increase in temperatures beyond the species' physiological optima and continued negative biotic interactions. Habitat for nonnative brook trout Salvelinus fontinalis and brown trout Salmo trutta is predicted to decline by 77% and 48%, respectively, driven by increases in temperature and winter flood frequency caused by warmer, rainier winters. Habitat for rainbow trout, Oncorhynchus mykiss, is projected to decline the least (35%) because negative temperature effects are partly offset by flow regime shifts that benefit the species. These results illustrate how drivers other than temperature influence species response to climate change. Despite some uncertainty, large declines in trout habitat are likely, but our findings point to opportunities for strategic targeting of mitigation efforts to appropriate stressors and locations.

  18. Modeling the Evolution of Riparian Woodlands Facing Climate Change in Three European Rivers with Contrasting Flow Regimes

    PubMed Central

    Rivaes, Rui P.; Rodríguez-González, Patricia M.; Ferreira, Maria Teresa; Pinheiro, António N.; Politti, Emilio; Egger, Gregory; García-Arias, Alicia; Francés, Felix

    2014-01-01

    Global circulation models forecasts indicate a future temperature and rainfall pattern modification worldwide. Such phenomena will become particularly evident in Europe where climate modifications could be more severe than the average change at the global level. As such, river flow regimes are expected to change, with resultant impacts on aquatic and riparian ecosystems. Riparian woodlands are among the most endangered ecosystems on earth and provide vital services to interconnected ecosystems and human societies. However, they have not been the object of many studies designed to spatially and temporally quantify how these ecosystems will react to climate change-induced flow regimes. Our goal was to assess the effects of climate-changed flow regimes on the existing riparian vegetation of three different European flow regimes. Cases studies were selected in the light of the most common watershed alimentation modes occurring across European regions, with the objective of appraising expected alterations in the riparian elements of fluvial systems due to climate change. Riparian vegetation modeling was performed using the CASiMiR-vegetation model, which bases its computation on the fluvial disturbance of the riparian patch mosaic. Modeling results show that riparian woodlands may undergo not only at least moderate changes for all flow regimes, but also some dramatic adjustments in specific areas of particular vegetation development stages. There are circumstances in which complete annihilation is feasible. Pluvial flow regimes, like the ones in southern European rivers, are those likely to experience more pronounced changes. Furthermore, regardless of the flow regime, younger and more water-dependent individuals are expected to be the most affected by climate change. PMID:25330151

  19. Projected impacts of climate change on the flow regime from Bârlad River Basin, Romania

    NASA Astrophysics Data System (ADS)

    Mic, Rodica Paula; Corbus, Ciprian; Matreata, Marius

    2015-04-01

    The paper presents the partial results, obtained within the CLIMHYDEX project (www.climhydex.meteoromania.ro), regarding the assessment of the climate change impact on flow regime from Bârlad River Basin by long term hydrological simulation. To estimate the impact of variability and climate change on monthly mean, seasonal and annual flow regime, in the Bârlad River Basin, the long-term simulations were performed, by means of CONSUL hydrological model, using as input data series of precipitation and temperature resulted from the data processing obtained from simulations of climate evolution by means of regional climate model REMO having spatial resolution of 10 km. The CONSUL model is a deterministic hydrological mathematical model which allows the simulation of flow in small as well as in large and complex basins, divided into homogeneous units (sub-basins). The model enables the computing of discharge hydrographs on sub-basins, their routing and composition on the main river and tributaries. Using of CONSUL model assumed the calibration of model parameters, an operation that was performed by the simulation of flow from the period 1975 - 2010 in the analysed river basin. Calibration of model parameters was performed in two stages: based on events and global. Calibration based on events was made considering 25 rainfall-runoff events, chosen to cover a wide range of possible situations in the case of floods formation. Global calibration of rainfall-runoff model parameters was done by simulating the flow on considered calibration period. Flow simulations using the CONSUL model, having optimal parameters derived from the calibration process, were conducted for two periods: the reference period 1971 - 2000 and the future period 2021 - 2050 respectively, at 9 hydrometric stations from the river basin analysed. For the input data in the CONSUL model, i.e. precipitation and temperature series, averaged on the sub-basins corresponding to the gauge stations, a comparative

  20. Evaluation of Spatial Pattern of Altered Flow Regimes on a River Network Using a Distributed Hydrological Model.

    PubMed

    Ryo, Masahiro; Iwasaki, Yuichi; Yoshimura, Chihiro; Saavedra V, Oliver C

    2015-01-01

    Alteration of the spatial variability of natural flow regimes has been less studied than that of the temporal variability, despite its ecological importance for river ecosystems. Here, we aimed to quantify the spatial patterns of flow regime alterations along a river network in the Sagami River, Japan, by estimating river discharge under natural and altered flow conditions. We used a distributed hydrological model, which simulates hydrological processes spatiotemporally, to estimate 20-year daily river discharge along the river network. Then, 33 hydrologic indices (i.e., Indicators of Hydrologic Alteration) were calculated from the simulated discharge to estimate the spatial patterns of their alterations. Some hydrologic indices were relatively well estimated such as the magnitude and timing of maximum flows, monthly median flows, and the frequency of low and high flow pulses. The accuracy was evaluated with correlation analysis (r > 0.4) and the Kolmogorov-Smirnov test (α = 0.05) by comparing these indices calculated from both observed and simulated discharge. The spatial patterns of the flow regime alterations varied depending on the hydrologic indices. For example, both the median flow in August and the frequency of high flow pulses were reduced by the maximum of approximately 70%, but these strongest alterations were detected at different locations (i.e., on the mainstream and the tributary, respectively). These results are likely caused by different operational purposes of multiple water control facilities. The results imply that the evaluation only at discharge gauges is insufficient to capture the alteration of the flow regime. Our findings clearly emphasize the importance of evaluating the spatial pattern of flow regime alteration on a river network where its discharge is affected by multiple water control facilities.

  1. Evaluation of Spatial Pattern of Altered Flow Regimes on a River Network Using a Distributed Hydrological Model

    PubMed Central

    Ryo, Masahiro; Iwasaki, Yuichi; Yoshimura, Chihiro; Saavedra V., Oliver C.

    2015-01-01

    Alteration of the spatial variability of natural flow regimes has been less studied than that of the temporal variability, despite its ecological importance for river ecosystems. Here, we aimed to quantify the spatial patterns of flow regime alterations along a river network in the Sagami River, Japan, by estimating river discharge under natural and altered flow conditions. We used a distributed hydrological model, which simulates hydrological processes spatiotemporally, to estimate 20-year daily river discharge along the river network. Then, 33 hydrologic indices (i.e., Indicators of Hydrologic Alteration) were calculated from the simulated discharge to estimate the spatial patterns of their alterations. Some hydrologic indices were relatively well estimated such as the magnitude and timing of maximum flows, monthly median flows, and the frequency of low and high flow pulses. The accuracy was evaluated with correlation analysis (r > 0.4) and the Kolmogorov–Smirnov test (α = 0.05) by comparing these indices calculated from both observed and simulated discharge. The spatial patterns of the flow regime alterations varied depending on the hydrologic indices. For example, both the median flow in August and the frequency of high flow pulses were reduced by the maximum of approximately 70%, but these strongest alterations were detected at different locations (i.e., on the mainstream and the tributary, respectively). These results are likely caused by different operational purposes of multiple water control facilities. The results imply that the evaluation only at discharge gauges is insufficient to capture the alteration of the flow regime. Our findings clearly emphasize the importance of evaluating the spatial pattern of flow regime alteration on a river network where its discharge is affected by multiple water control facilities. PMID:26207997

  2. Stagnation point flow and heat transfer behavior of Cu-water nanofluid towards horizontal and exponentially stretching/shrinking cylinders

    NASA Astrophysics Data System (ADS)

    Sulochana, C.; Sandeep, N.

    2016-03-01

    In this study we analyzed the stagnation point flow and heat transfer behavior of Cu-water nanofluid towards horizontal and exponentially permeable stretching/shrinking cylinders in presence of suction/injection, heat source and shape of nanoparticles. The governing boundary layer equations are transformed to nonlinear ordinary differential equations using similarity transformation which are then solved numerically using bvp4c Matlab package. The influence of non-dimensional governing parameters on the flow field and heat transfer characteristics are discussed and presented through graphs and tables. The study indicates that the solutions for the horizontal and exponential cylinders are non-unique and shape of nanoparticles also influences the rate of heat transfer. Comparisons of the present results with existed studies are presented. Present study has an excellent agreement with the existed studies under some special conditions.

  3. Maximum density effects on vortex instability of horizontal and inclined buoyancy-induced flows in porous media

    SciTech Connect

    Jang, Jiinyuh; Chang, Wenjeng )

    1989-05-01

    Buoyancy-induced flows in a porous medium saturated with cold water are strongly affected by the occurrence of the density extremum associated with the temperature of 4C in pure water at 1 atm. Such conditions occur commonly in a porous medium, such as the moist ground trapped under a layer of ice in winter, permeable soils flooded by cold lake or seawater, water-ice slurries. The present investigation uses equation to re-examine conditions marking the onset of stationary longitudinal vortices in horizontal and inclined buoyancy-induced boundary layer flow in porous media with maximum density effect. Both the streamwise and normal components of the buoyancy force are retained in the momentum equations. This is in contrast to the authors previous analyses. Thus the present study is applicable for angles ranging from 0 to close to 90 deg from the horizontal.

  4. Porous anodes with helical flow pathways in bioelectrochemical systems: The effects of fluid dynamics and operating regimes

    NASA Astrophysics Data System (ADS)

    Kim, Jung Rae; Boghani, Hitesh C.; Amini, Negar; Aguey-Zinsou, Kondo-François; Michie, Iain; Dinsdale, Richard M.; Guwy, Alan J.; Guo, Zheng Xiao; Premier, Giuliano C.

    2012-09-01

    Bioelectrochemical systems (BES) and/or microbial fuel cell (MFC) mass transport and associated over-potential limitations are affected by flow regimes, which may simultaneously increase the power and pollution treatment capacities. Two electrodes with helical flow channels were compared in the same tubular MFC reactor. 1). A machined monolithic microporous conductive carbon (MMCC). 2). A layered carbon veil with spoked ABS former (LVSF); both presented helical flow channel. Anode performances were compared when subject to temperature, substrate concentration and flow rate variations. The MMCC maximum power increased from 2.9 ± 0.3 to 7.6 ± 0.7 mW with influent acetate concentration, from 1 to 10 mM (with 2 mL min-1), but decreased power to 5.5 ± 0.5 mW at 40 mM, implicated localized pH/buffering. Flow rate (0.1 to 7.5 mL min-1) effects were relatively small but an increase was evident from batch to continuous operation at 0.1 mL min-1. The LVSF configuration showed improved performance in power as the flow rate increased, indicating that flow pattern affects BES performance. Computational fluid dynamics (CFD) modelling showed less uniform flow with the LVSF. Thus flow regime driven mass transfer improves the power output in continuously fed system operation. These results indicate that electrode configuration, flow regime and operating condition need consideration to optimize the bioelectrochemical reaction.

  5. Assessing the flow regime in a contaminated fractured and karstic dolostone aquifer supplying municipal water

    NASA Astrophysics Data System (ADS)

    Perrin, Jérôme; Parker, Beth L.; Cherry, John A.

    2011-04-01

    SummaryThe Silurian dolostone bedrock in Ontario, Canada, is a broad 400 km long swath northward from Niagara Falls through the Bruce Peninsula that represents an important water source for municipal, industrial, and agricultural uses. Where the Quaternary overburden is thin or absent, karst is common. This study concerns an urban area where the dolostone aquifer is 100 m thick beneath up to 50 m thick Quaternary deposits and where karst features identified by borehole information are common. Hydraulic tests show moderate to large bulk rock hydraulic conductivity and rock core tests indicate much smaller matrix hydraulic conductivity than the bulk rock values. Therefore, the aquifer is essentially a dual permeability, fully saturated system in which conduits occur within a network of ubiquitous extensive, horizontally- and vertically-interconnected fractures. Karst features are concentrated in a thin zone at the top-of-rock, likely representing former epikarst, and also in a thicker zone in the middle of the aquifer. Some pumping test results and large yields of some municipal wells are consistent with conduit occurrences. However, atmospheric tritium, distributed-source contamination (Cl -, NO3-), and a point-source pesticide plume (metolachlor) show detailed concentration distributions lacking influence of flow in conduits. Detailed hydraulic head profiles also show no influence of conduit flow. This study shows that when designing monitoring networks for groundwater quality and source water protection in similar contexts, locating conduits is not necessary because contaminant distributions are governed by the combined influences of the rock matrix, fractures and conduits, the hydraulic boundary conditions, and the interconnected fracture network with only minimal conduit effects. Prior to glaciations, an integrated karstic aquifer could develop with flow controlled by conduits; however, this original, converging flow system became non-functional when the

  6. Theory for modeling the equatorial evening ionosphere and the origin of the shear in the horizontal plasma flow

    SciTech Connect

    Haerendel, G.; Eccles, J.V.; Cakir, S. )

    1992-02-01

    Companion papers in this series present (1) the role of equatorial E region postsunset ionosphere, (2) the origin of horizontal plasma shear flow in the postsunset equatorial ionosphere (this paper), (3) the Colored Bubbles experiments results, and (4) computer simulations of artificial initiation of plasma density depletions (bubbles) in the equatorial ionosphere. Within this paper, equations describing the time evolution of the equatorial ionosphere are developed using flux tube integrated and flux tube weighted quantities which model the chemistry, dynamics, and electrodynamics of the equatorial ionosphere. The resulting two-dimensional set of equations can be used to investigate equatorial ionosphere. The resulting two-dimensional set of equations can be used to investigate equatorial electric fields neglecting small-scale phenomena ({lambda} < 1 km). An immediate result derived from the integrated current equations is an equation describing the physics of the shear in the horizontal flow of the equatorial plasma during the evening hours. The profile of the horizontal flow has three important contributing terms relating to the neutral wind dynamo, Hall conduction, and the equatorial electrojet current divergence. Using a one-dimensional model of the velocity shear equation and the integrated ionosphere transport equations, a time history of the development of the shear feature during postsunset hours is presented. The one-dimensional model results are compared to the velocity shear measurements from the Colored Bubbles experiments.

  7. Solution breakdown due to natural convection of the boundary-layer radial flow on a constant temperature horizontal plate

    NASA Astrophysics Data System (ADS)

    Fernandez-Feria, Ramon; Del Pino, Carlos; Fernández-Gutiérrez, Alberto

    2013-11-01

    The boundary-layer flow of a cold horizontal current exiting radially from a cylindrical vertical surface with a constant velocity over a hotter horizontal wall with constant temperature is analyzed. The temperature and velocity fields are coupled by buoyancy through the pressure gradients, so that the boundary-layer equations are made dimensionless with a radial characteristic length in which natural and forced convection become of the same order of magnitude, being the Prandtl number the only nondimensional parameter governing the problem. A similarity solution valid for the leading edge boundary-layer flow is obtained, yielding as a first order correction the effect of natural convection on Blasius' thermal boundary layer. This solution is also used to start the numerical integration of the equations to find out the location where the boundary-layer flow blows up due to the termination of the solution in a singularity. The physical nature of this singularity is analyzed and its position is characterized numerically. The heat flux from the horizontal wall up to this singularity is also characterized and qualitatively compared with previous experimental results from a related experimental setup.

  8. Scaling of two-phase flow regimes in a rod bundle with freon

    SciTech Connect

    Symolon, P.D.

    1990-07-01

    Fluid to fluid modeling of the thermal-hydraulics of steam/water systems using Freon has been the subject of research for the past 25 years. However, there is as yet no universally accepted set of scaling laws to define the geometry and velocity scaling requirements of an equivalent Freon test of the full scale steam/water system being simulated. This paper describes a scaling concept where the Weber and Froud numbers of the Freon model are matched to that of the prototype being simulated, thus creating a comparable balance among inertia, surface tension and buoyancy forces. In this test it was demonstrated that similar flow regime transitions are observed in a half scale Freon simulation of a full scale steam/water test run at Dynatech. It is also shown using a two fluid analytical model and existing correlations for friction and interfacial momentum exchange from the open literature, that a half scale simulation leads to nearly the same slip ratio as for full scale steam/water, while the slip ratio for a full scale Freon simulation is too high. A comparison of the predicted flow distribution in the 4-rod bundle is made using the COBRA-IV code for a full scale simulation using Freon, a half scale simulation using Freon and full scale test with water. The COBRA results demonstrated that a half scale test section model using Freon yields a subchannel flow distribution similar to the steam/water case, while a full scale Freon simulation results in a distorted subchannel flow distribution. It is concluded that the appropriate geometric scale factor for Freon simulation of two-phase steam/water flow in tube bundles is one-half for a broad range of thermal-hydraulic conditions. 24 refs., 12 figs., 4 tabs.

  9. Climate change impact assessment on flow regime by incorporating spatial correlation and scenario uncertainty

    NASA Astrophysics Data System (ADS)

    Vallam, P.; Qin, X. S.

    2016-04-01

    Flooding risk is increasing in many parts of the world and may worsen under climate change conditions. The accuracy of predicting flooding risk relies on reasonable projection of meteorological data (especially rainfall) at the local scale. The current statistical downscaling approaches face the difficulty of projecting multi-site climate information for future conditions while conserving spatial information. This study presents a combined Long Ashton Research Station Weather Generator (LARS-WG) stochastic weather generator and multi-site rainfall simulator RainSim (CLWRS) approach to investigate flow regimes under future conditions in the Kootenay Watershed, Canada. To understand the uncertainty effect stemming from different scenarios, the climate output is fed into a hydrologic model. The results showed different variation trends of annual peak flows (in 2080-2099) based on different climate change scenarios and demonstrated that the hydrological impact would be driven by the interaction between snowmelt and peak flows. The proposed CLWRS approach is useful where there is a need for projection of potential climate change scenarios.

  10. Self-similar turbulent boundary layer with imposed pressure gradient. Four flow regimes

    SciTech Connect

    Vigdorovich, I. I.

    2014-11-15

    Self-similar flows of an incompressible fluid in a turbulent boundary layer, when the free-stream velocity is a power function (with the exponent m) of the longitudinal coordinate, have been studied. It has been shown that there are four different self-similar flow regimes corresponding to four individual similarity parameters one of which is the known Clauser parameter and the three other parameters have been established for the first time. At adverse pressure gradient, when the exponent m lies in a certain range depending on Reynolds number, the problem has two solutions with different values of the boundary-layer thickness and skin friction; consequently, hysteresis in a pre-separation flow is possible. Separation occurs not at the minimal value of m that corresponds to the strongest adverse pressure gradient, but at m = −0.216 −0.4 Re{sub p}{sup −1/3} + O(Re{sub p}{sup −2/3}), where Re{sub p} is the Reynolds number based on longitudinal pressure gradient. The theoretical results are in good agreement with experimental data.

  11. Multidimensional flow modeling of the compression test of a Gaede pump stage in the viscous regime

    NASA Astrophysics Data System (ADS)

    Giors, S.; Subba, F.

    2004-07-01

    Two-dimensional and three-dimensional models for a Gaede pump, based on the Navier-Stokes equations, are developed and a commercial Computational Fluid Dynamics code is used to solve them. We simulate a compression test in an outlet pressure range (30-2500 Pa) corresponding to the viscous laminar regime for an experimental pump. Experimental data are collected in order to validate the developed model. The pump tested is the high pressure stage of a commercial hybrid turbomolecular vacuum pump and can work in both transition and viscous regime, according to the operating pressure. The data show that the standard Couette-Poiseuille one-dimensional analytic model, developed by Helmer and Levi to describe the Gaede pump behavior and operating principle, has a limited accuracy when it is used as a design tool and not just as a physical model. The two-dimensional and the three-dimensional model results are compared with the experimental data showing an increasing level of agreement, with only a 10% maximum difference for the three-dimensional model in terms of compression ratio. The different flow structures shown by the models are critically analyzed to explain the different level of agreement. .

  12. Can water sensitive urban design systems help to preserve natural channel-forming flow regimes in an urbanised catchment?

    PubMed

    Wella-Hewage, Chathurika Subhashini; Alankarage Hewa, Guna; Pezzaniti, David

    2016-01-01

    Increased stormwater runoff and pollutant loads due to catchment urbanisation bring inevitable impacts on the physical and ecological conditions of environmentally sensitive urban streams. Water sensitive urban design (WSUD) has been recognised as a possible means to minimise these negative impacts. This paper reports on a study that investigated the ability of infiltration-based WSUD systems to replicate the predevelopment channel-forming flow (CFF) regime in urban catchments. Catchment models were developed for the 'pre-urban', 'urban' and 'managed' conditions of a case study catchment and the hydrological effect on CFF regime was investigated using a number of flow indices. The results clearly show that changes to flow regime are apparent under urban catchment conditions and are even more severe under highly urbanised conditions. The use of WSUD systems was found to result in the replication of predevelopment flow regimes, particularly at low levels of urbanisation. Under highly urbanised conditions (of managed catchments) overcontrol of the CFF indices was observed as indicated by flow statistics below their pre-urban values. The overall results suggest that WSUD systems are highly effective in replicating the predevelopment CFF regime in urban streams and could be used as a means to protect environmentally sensitive urban streams.

  13. Can water sensitive urban design systems help to preserve natural channel-forming flow regimes in an urbanised catchment?

    PubMed

    Wella-Hewage, Chathurika Subhashini; Alankarage Hewa, Guna; Pezzaniti, David

    2016-01-01

    Increased stormwater runoff and pollutant loads due to catchment urbanisation bring inevitable impacts on the physical and ecological conditions of environmentally sensitive urban streams. Water sensitive urban design (WSUD) has been recognised as a possible means to minimise these negative impacts. This paper reports on a study that investigated the ability of infiltration-based WSUD systems to replicate the predevelopment channel-forming flow (CFF) regime in urban catchments. Catchment models were developed for the 'pre-urban', 'urban' and 'managed' conditions of a case study catchment and the hydrological effect on CFF regime was investigated using a number of flow indices. The results clearly show that changes to flow regime are apparent under urban catchment conditions and are even more severe under highly urbanised conditions. The use of WSUD systems was found to result in the replication of predevelopment flow regimes, particularly at low levels of urbanisation. Under highly urbanised conditions (of managed catchments) overcontrol of the CFF indices was observed as indicated by flow statistics below their pre-urban values. The overall results suggest that WSUD systems are highly effective in replicating the predevelopment CFF regime in urban streams and could be used as a means to protect environmentally sensitive urban streams. PMID:26744937

  14. Permafrost, heat flow, and the geothermal regime at Prudhoe Bay, Alaska.

    USGS Publications Warehouse

    Lachenbruch, A.H.; Sass, J.H.; Marshall, B.V.; Moses, T.H.

    1982-01-01

    Temperature measurements through permafrost in the oil field at Prudhoe Bay, Alaska, combined with laboratory measurements of the thermal conductivity of drill cutting permit an evaluation of in situ thermal properties and an understanding of the general factors that control the geothermal regime. A sharp contrast in temperatire gradient at c600m represents a contrast in thermal conductivity caused by the downward change from interstitial ice to interstitial water at the base of permafrost under near steady state conditions. These results yield a heat flow of c1.3HFU, which is similar to other values on the Alaskan Arctic Coast: the anomalously deep permafrost is a result of the anomalously high conductivity of the siliceous ice-rich sediments. With confirmation of the permafrost configuration by offshore drilling, heat conduction models can yield reliable new information on the chronology of arctic shoreline. -from Authors

  15. Suspended particulate composition: evolution along a river linear and influence of regime flow

    NASA Astrophysics Data System (ADS)

    Le Meur, Mathieu; Montargès-Pelletier, Emmanuelle; Bauer, Allan; Gley, Renaud; Migot, Sylvie; Mansuy-Huault, Laurence; Lorgeoux, Catherine; Razafitianamaharavo, Angelina; Villièras, Frédéric

    2015-04-01

    Suspended Particulate Matters are recognized to play a crucial role in the transport and fate of chemicals like trace metal elements. The affinity of trace metals with natural SPM is influenced by (i) the nature of metal (ii) physical-chemical conditions of the water column (iii) SPM physical characteristics (grain size, surface area) (iiii) SPM chemical characteristics (elemental composition, mineralogy, organic composition). Some authors observed that the SPM composition was the predominant factor controlling the affinity of trace metals with natural SPM. One purpose of this work is to follow the physical and chemical characteristics of SPM along the river linear in order to better understand the affinity between SPM and heavy metals. One other purpose is to study the influence of regime flow on SPM physical and chemical composition in order to detect any variation of SPM composition with regime flow. SPM were sampled along Moselle river (North East of France) following an urbanization gradient. Two tributaries were also sampled, the Madon river which drains an agricultural catchment and the Fensch stream which flows through an ancient steel-making basin. SPM were sampled several times during high flow and low flow. Particulate matter was extracted on field using continuous flow field centrifuge. Frozen-dried samples were then characterized in terms of size distribution, elemental composition (ICP - AES, ICP - MS), mineralogy (XRD, FTIR, SEM, TEM), surface properties (gas adsorption techniques) and organic composition (Py-GC-MS and GC-MS). Grain size distribution evidenced the presence of coarser particles during high flow but no difference in the grain size distribution could be evidenced between the different stations. The grain size distribution of collected SPM appeared globally identical, although the increase of conductivity due to the junction of Meurthe river . In terms of composition, major element contents in SPM are characterized by the predominance of

  16. Production of microbubbles from axisymmetric flow focusing in the jetting regime for moderate Reynolds numbers.

    PubMed

    Vega, E J; Acero, A J; Montanero, J M; Herrada, M A; Gañán-Calvo, A M

    2014-06-01

    We analyze both experimentally and numerically the formation of microbubbles in the jetting regime reached when a moderately viscous liquid stream focuses a gaseous meniscus inside a converging micronozzle. If the total (stagnation) pressure of the injected gas current is fixed upstream, then there are certain conditions on which a quasisteady gas meniscus forms. The meniscus tip is sharpened by the liquid stream down to the gas molecular scale. On the other side, monodisperse collections of microbubbles can be steadily produced in the jetting regime if the feeding capillary is appropriately located inside the nozzle. In this case, the microbubble size depends on the feeding capillary position. The numerical simulations for an imposed gas flow rate show that a recirculation cell appears in the gaseous meniscus for low enough values of that parameter. The experiments allow one to conclude that the bubble pinch-off comprises two phases: (i) a stretching motion of the precursor jet where the neck radius versus the time before the pinch essentially follows a potential law, and (ii) a final stage where a very thin and slender gaseous thread forms and eventually breaks apart into a number of micron-sized bubbles. Because of the difference between the free surface and core velocities, the gaseous jet breakage differs substantially from that of liquid capillary jets and gives rise to bubbles with diameters much larger than those expected from the Rayleigh-type capillary instability. The dependency of the bubble diameter upon the flow-rate ratio agrees with the scaling law derived by A. M. Gañán-Calvo [Phys. Rev. E 69, 027301 (2004)], although a slight influence of the Reynolds number can be observed in our experiments. PMID:25019884

  17. Production of microbubbles from axisymmetric flow focusing in the jetting regime for moderate Reynolds numbers.

    PubMed

    Vega, E J; Acero, A J; Montanero, J M; Herrada, M A; Gañán-Calvo, A M

    2014-06-01

    We analyze both experimentally and numerically the formation of microbubbles in the jetting regime reached when a moderately viscous liquid stream focuses a gaseous meniscus inside a converging micronozzle. If the total (stagnation) pressure of the injected gas current is fixed upstream, then there are certain conditions on which a quasisteady gas meniscus forms. The meniscus tip is sharpened by the liquid stream down to the gas molecular scale. On the other side, monodisperse collections of microbubbles can be steadily produced in the jetting regime if the feeding capillary is appropriately located inside the nozzle. In this case, the microbubble size depends on the feeding capillary position. The numerical simulations for an imposed gas flow rate show that a recirculation cell appears in the gaseous meniscus for low enough values of that parameter. The experiments allow one to conclude that the bubble pinch-off comprises two phases: (i) a stretching motion of the precursor jet where the neck radius versus the time before the pinch essentially follows a potential law, and (ii) a final stage where a very thin and slender gaseous thread forms and eventually breaks apart into a number of micron-sized bubbles. Because of the difference between the free surface and core velocities, the gaseous jet breakage differs substantially from that of liquid capillary jets and gives rise to bubbles with diameters much larger than those expected from the Rayleigh-type capillary instability. The dependency of the bubble diameter upon the flow-rate ratio agrees with the scaling law derived by A. M. Gañán-Calvo [Phys. Rev. E 69, 027301 (2004)], although a slight influence of the Reynolds number can be observed in our experiments.

  18. Modeling the Relations Between Flow Regime Components, Species Traits, and Spawning Success of Fishes in Warmwater Streams

    NASA Astrophysics Data System (ADS)

    Craven, Scott W.; Peterson, James T.; Freeman, Mary C.; Kwak, Thomas J.; Irwin, Elise

    2010-08-01

    Modifications to stream hydrologic regimes can have a profound influence on the dynamics of their fish populations. Using hierarchical linear models, we examined the relations between flow regime and young-of-year fish density using fish sampling and discharge data from three different warmwater streams in Illinois, Alabama, and Georgia. We used an information theoretic approach to evaluate the relative support for models describing hypothesized influences of five flow regime components representing: short-term high and low flows; short-term flow stability; and long-term mean flows and flow stability on fish reproductive success during fish spawning and rearing periods. We also evaluated the influence of ten fish species traits on fish reproductive success. Species traits included spawning duration, reproductive strategy, egg incubation rate, swimming locomotion morphology, general habitat preference, and food habits. Model selection results indicated that young-of-year fish density was positively related to short-term high flows during the spawning period and negatively related to flow variability during the rearing period. However, the effect of the flow regime components varied substantially among species, but was related to species traits. The effect of short-term high flows on the reproductive success was lower for species that broadcast their eggs during spawning. Species with cruiser swimming locomotion morphologies (e.g., Micropterus) also were more vulnerable to variable flows during the rearing period. Our models provide insight into the conditions and timing of flows that influence the reproductive success of warmwater stream fishes and may guide decisions related to stream regulation and management.

  19. Modeling the relations between flow regime components, species traits, and spawning success of fishes in warmwater streams

    USGS Publications Warehouse

    Craven, S.W.; Peterson, J.T.; Freeman, Mary C.; Kwak, T.J.; Irwin, E.

    2010-01-01

    Modifications to stream hydrologic regimes can have a profound influence on the dynamics of their fish populations. Using hierarchical linear models, we examined the relations between flow regime and young-of-year fish density using fish sampling and discharge data from three different warmwater streams in Illinois, Alabama, and Georgia. We used an information theoretic approach to evaluate the relative support for models describing hypothesized influences of five flow regime components representing: short-term high and low flows; short-term flow stability; and long-term mean flows and flow stability on fish reproductive success during fish spawning and rearing periods. We also evaluated the influence of ten fish species traits on fish reproductive success. Species traits included spawning duration, reproductive strategy, egg incubation rate, swimming locomotion morphology, general habitat preference, and food habits. Model selection results indicated that young-of-year fish density was positively related to short-term high flows during the spawning period and negatively related to flow variability during the rearing period. However, the effect of the flow regime components varied substantially among species, but was related to species traits. The effect of short-term high flows on the reproductive success was lower for species that broadcast their eggs during spawning. Species with cruiser swimming locomotion morphologies (e.g., Micropterus) also were more vulnerable to variable flows during the rearing period. Our models provide insight into the conditions and timing of flows that influence the reproductive success of warmwater stream fishes and may guide decisions related to stream regulation and management. ?? 2010 US Government.

  20. Experimental investigation on the interfacial characteristics of stratified air-water two-phase flow in a horizontal pipe

    NASA Astrophysics Data System (ADS)

    Hudaya, Akhmad Zidni; Kuntoro, Hadiyan Yusuf; Dinaryanto, Okto; Deendarlianto, Indarto

    2016-06-01

    The interfacial wave characteristics of stratified air-water two-phase flow in a horizontal pipe were experimentally investigated by using the flush-mounted constant electric current method (CECM) sensors. The experiments were conducted in a horizontal two-phase flow loop 9.5 m long (L) consisting of transparent acrylic pipe of 26 mm i.d. (D). To obtain the stratified flow pattern, the superficial gas and liquid velocities were set to 1.02 - 3.77 m/s and 0.016 - 0.92 m/s, respectively. Several interfacial wave patterns as described by several investigators were identified. The common parameters such as liquid hold-up, probability distribution function, wave velocity and wave frequency were investigated as the function of the liquid and gas flow rates. The interfacial curvature was calculated on the basis of the liquid hold-up data from the CECM sensors and the liquid film thickness data from the image processing technique in the previous work. As a result, it was found that the mean liquid hold-up decreases with the increase of the superficial gas velocity. In the same sub flow pattern, the wave velocity increases as the superficial gas velocity increases. On the other hand, in the two-dimensional wave region, the dominant frequency decreases with the increase of the superficial liquid velocity.

  1. An evaluation of borehole flowmeters used to measure horizontal ground-water flow in limestones of Indiana, Kentucky, and Tennessee, 1999

    USGS Publications Warehouse

    Wilson, John T.; Mandell, Wayne A.; Paillet, Frederick L.; Bayless, E. Randall; Hanson, Randall T.; Kearl, Peter M.; Kerfoot, William B.; Newhouse, Mark W.; Pedler, William H.

    2001-01-01

    Three borehole flowmeters and hydrophysical logging were used to measure ground-water flow in carbonate bedrock at sites in southeastern Indiana and on the westcentral border of Kentucky and Tennessee. The three flowmeters make point measurements of the direction and magnitude of horizontal flow, and hydrophysical logging measures the magnitude of horizontal flowover an interval. The directional flowmeters evaluated include a horizontal heat-pulse flowmeter, an acoustic Doppler velocimeter, and a colloidal borescope flowmeter. Each method was used to measure flow in selected zones where previous geophysical logging had indicated water-producing beds, bedding planes, or other permeable features that made conditions favorable for horizontal-flow measurements. Background geophysical logging indicated that ground-water production from the Indiana test wells was characterized by inflow from a single, 20-foot-thick limestone bed. The Kentucky/Tennessee test wells produced water from one or more bedding planes where geophysical logs indicated the bedding planes had been enlarged by dissolution. Two of the three test wells at the latter site contained measurable vertical flow between two or more bedding planes under ambient hydraulic head conditions. Field measurements and data analyses for each flow-measurement technique were completed by a developer of the technology or by a contractor with extensive experience in the application of that specific technology. Comparison of the horizontal-flow measurements indicated that the three point-measurement techniques rarely measured the same velocities and flow directions at the same measurement stations. Repeat measurements at selected depth stations also failed to consistently reproduce either flow direction, flow magnitude, or both. At a few test stations, two of the techniques provided similar flow magnitude or direction but usually not both. Some of this variability may be attributed to naturally occurring changes in

  2. Investigations on the turbulent wake of a generic space launcher geometry in the hypersonic flow regime

    NASA Astrophysics Data System (ADS)

    Saile, D.; Gülhan, A.; Henckels, A.; Glatzer, C.; Statnikov, V.; Meinke, M.

    2013-06-01

    The turbulent wake flow of generic rocket configurations is investigated experimentally and numerically at a freestream Mach number of 6.0 and a unit Reynolds number of 10·106 m-1. The flow condition is based on the trajectory of Ariane V-like launcher at an altitude of 50 km, which is used as the baseline to address the overarching tasks of wake flows in the hypersonic regime like fluid-structural coupling, reverse hot jets and base heating. Experimental results using pressure transducers and the high-speed Schlieren measurement technique are shown to gain insight into the local pressure fluctuations on the base and the oscillations of the recompression shock. This experimental configuration features a wedgeprofiled strut orthogonally mounted to the main body. Additionally, the influence of cylindrical dummy nozzles attached to the base of the rocket is investigated, which is the link to the numerical investigations. Here, the axisymmetric model possesses a cylindrical sting support of the same diameter as the dummy nozzles. The sting support allows investigations for an undisturbed wake flow. A time-accurate zonal Reynolds-Averaged Navier-Stokes/Large Eddy Simulation (RANS/LES) approach is applied to identify shocks, expansion waves, and the highly unsteady recompression region numerically. Subsequently, experimental and numerical results in the strut-averted region are compared with regard to the wall pressure and recompression shock frequency spectra. For the compared configurations, experimental pressure spectra exhibit dominant Strouhal numbers at about SrD = 0.03 and 0.27, and the recompression shock oscillates at 0.2. In general, the pressure and recompression shock fluctuations numerically calculated agree reasonably with the experimental results. The experiments with a blunt base reveal base-pressure spectra with dominant Strouhal numbers at 0.08 at the center position and 0.145, 0.21-0.22, and 0.31-0.33 at the outskirts of the base.

  3. Transient heat flow due to tectonic processes in the deep geothermal regime between the Nord Eifel-Venn Massif, Brabant Massif and adjacent Graben (Central Europe)

    NASA Astrophysics Data System (ADS)

    Dijkshoorn, L.; Clauser, C.

    2005-12-01

    A 3D model for flow and heat transport is build, based on vitrinite reflectance measurements, fission track data, geophysical logging as well as core data from deep boreholes, geological maps and, balanced profiles. The model will be used to study the regional heat flow: key parameter for energy and cost efficiency of geothermal energy use of a deep borehole heat exchanger. The model is 40 by 40 square km with a depth of 5 km. It includes parts of Germany, Belgium and The Netherlands. The importance of the different tectonic processes for the thermal regime is demonstrated: extension, erosion & sedimentation, heat production, water flow (forced and free convection) and deep magmatic processes (Eifel Plume). These processes are investigated with respect to their thermal response time and there influence on present heat flow. Where appropriated, Greens response functions where used to study these processes. The tectonic events manifested in the studied area gives a heat flow diversity of 20 mW/m2. The hanging walls of the fault systems have an increased heat flow due to uplift, erosion and the large river valley, while the foot walls have a decreased heat flow due to down warp and sedimentation. These results in horizontal heat flow at the normal faults or the over thrust faults. The diversity is more pronounced for transient conduction. Long period temperature changes at to top or bottom of the model caused by deep plume or climatic changes at the surface yield a faster and deeper response in the hanging wall than in foot wall. These responses are caused by the higher thermal diffusivities of the older geologic rocks in the hanging wall.

  4. New regimes of plastic flow at very high pressures and strain rates

    NASA Astrophysics Data System (ADS)

    Remington, Bruce

    2015-06-01

    Recent progress in understanding solid-state plastic flow at very high pressures and strain rates for high energy density (HED) science will be described. These results are relevant to hypervelocity impacts, space hardware durability, planetary formation dynamics, advanced designs for inertial confinement fusion, and basic HED science. We use high power lasers to study the Rayleigh-Taylor and Richtmyer-Meshkov hydrodynamic instability evolution in the solid state plastic flow regime on the Janus, Omega, and NIF lasers, spanning peak pressures from 10 - 500 GPa (0.1 - 5 Mbar). We are pursuing time resolved diffraction experiments to understand the lattice level dynamics resulting from high rate compression of samples. EXAFS experiments probe the atomic level structure and phase, and provide a volume-averaged temperature. We use the very bright, high time resolution x-ray probe at LCLS to examine the detailed lattice response and time evolution right behind the shock front. And finally, shock driven samples are recovered so that the residual microstructure caused by the shock can be examined by SEM, TEM, and other characterization techniques. An overview of these recent results, with comparisons to theory and simulations, will be given. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  5. Hydrothermal flow regime and magmatic heat source of the Cerro Prieto geothermal system, Baja California, Mexico

    SciTech Connect

    Elders, W.A.; Bird, D.K.; Schiffman, P.; Williams, A.E.

    1984-01-01

    This detailed three-dimensional model of the natural flow regime of the Cerro Prieto geothermal field, before steam production began, is based on patterns of hydrothermal mineral zones and light stable isotopic ratios observed in rock samples from more than 50 deep wells, together with temperature gradients, wireline logs and other data. At the level so far penetrated by drilling, this hydrothermal system was heated by a thermal plume of water close to boiling, inclined at 45/sup 0/, rising from the northeast and discharging to the west. To the east a zone of cold water recharge overlies the inclined thermal plume. Fission track annealing studies show the reservoir reached 170/sup 0/C only 10/sup 4/ years ago. Oxygen isotope exchange data indicate that a 12 km/sup 3/ volume of rock subsequently reacted with three times its volume of water hotter than 200/sup 0/C. Averaged over the duration of the heating event this would require a flow velocity through a typical cross-section of the reservoir of about 6 m/year. The heat in storage in that part of the reservoir hotter than 200/sup 0/C and shallower than 3 km depth is equivalent to that which would be released by the cooling of about 1 or 2 km/sup 3/ of basalt or gabbro magma.

  6. The Impact of Surface Friction on Boundary Layer Separation for Different Mountain Flow Regimes: An Analysis Based on Large-Eddy-Simulations

    NASA Astrophysics Data System (ADS)

    Sachsperger, Johannes; Serafin, Stefano; Grubišić, Vanda

    2014-05-01

    expected; rather we find those in moderately non-linear flows. A possible explanation for that is that for flows in the strongest non-linear regime, the BLS is associated with low-level mountain-wave breaking which leads to the formation of a lee wave train underneath a self-induced critical level and an attendant train of smaller rotors underneath the lee wave crests. It appears also that the trapped flow over this train of rotors excites an upward propagating gravity wave (similar to a terrain generated internal gravity wave) which partially passes through the critical level and changes the structure of the larger-scale flow above. The sensitivity tests for the strength of surface friction show that with increasing surface drag the rotor interior structure changes from a single coherent horizontal vortex to a more complex interior filled with sub-vortices that impact the overall shape of the rotor.

  7. Creep and Flow Regimes of Magnetic Domain-Wall Motion in Ultrathin Pt/Co/Pt Films with Perpendicular Anisotropy

    NASA Astrophysics Data System (ADS)

    Metaxas, P. J.; Jamet, J. P.; Mougin, A.; Cormier, M.; Ferré, J.; Baltz, V.; Rodmacq, B.; Dieny, B.; Stamps, R. L.

    2007-11-01

    We report on magnetic domain-wall velocity measurements in ultrathin Pt/Co(0.5 0.8nm)/Pt films with perpendicular anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain-wall motion, analysis of which yields values for the damping parameter, α.

  8. Fabrication of cm scale buckypapers of horizontally aligned multiwalled carbon nanotubes highly filled with Fe3C: the key roles of Cl and Ar-flow rates.

    PubMed

    Boi, Filippo S; Guo, Jian; Wang, Shanling; He, Yi; Xiang, Gang; Zhang, Xi; Baxendale, Mark

    2016-03-18

    A key challenge in the fabrication of ferromagnetically filled carbon-nanotube buckypapers in the presence of Cl-radicals is the achievement of a preferential horizontal nanotube-alignment. We show that a horizontal-alignment can be achieved by tuning two main CVD parameters for a fixed dichlorobenzene concentration: the precursor-evaporation temperature and the flow rate. PMID:26905009

  9. Arrays of horizontally-oriented mini-reservoirs generate steady microfluidic flows for continuous perfusion cell culture and gradient generation.

    PubMed

    Zhu, Xiaoyue; Yi Chu, Leonard; Chueh, Bor-han; Shen, Mingwu; Hazarika, Bhaskar; Phadke, Nandita; Takayama, Shuichi

    2004-11-01

    This paper describes the use of arrays of horizontally-oriented reservoirs to deliver liquids through microchannels at a constant flow rate over extended periods of time (hours to days). The horizontal orientation maintains a constant hydraulic pressure drop across microfluidic channels even as the volumes of liquids within the reservoirs change over time. For a given channel-reservoir system, the magnitude of the flow velocity depends linearly on the height difference between reservoirs. The simple structure and operation mechanism make this pumping system versatile. A one-inlet-one-outlet system was used to continuously deliver media for perfusion cell culture, and an array of inlet reservoirs coupled to an outlet reservoir via microchannels was used to drive flows of multiple laminar streams. The parallel pumping scheme conveniently generated various smooth and step concentration gradients, and allowed evaluation of the effect of colchicine on myoblasts. Since the reservoir arrays are configured to be compatible with commercialized multichannel pipettors designed for 96 well plate handling, this simple pumping scheme is envisioned to be broadly useful for medium to high throughput microfluidic perfusion cell culture assays, cell migration assays, multiple laminar flow drug tests, and any other applications needing multiple microfluidic streams.

  10. Experimental study on the void fraction of air-water two-phase flow in a horizontal circular minichannel

    NASA Astrophysics Data System (ADS)

    Sudarja, Indarto, Deendarlianto, Haq, Aqli

    2016-06-01

    Void fraction is an important parameter in two-phase flow. In the present work, the adiabatic two-phase air-water flow void fraction in a horizontal minichannel has been studied experimentally. A transparent circular channel with 1.6 mm inner diameter was employed as the test section. Superficial gas and liquid velocities were varied in the range of 1.25 - 66.3 m/s and 0.033 - 4.935 m/s, respectively. Void fraction data were obtained by analyzing the flow images being captured by using a high-speed camera. Here, the homogeneous (β) and the measured void fractions (ɛ), respectively, were compared to the existing correlations. It was found that: (1) for the bubbly and slug flows, the void fractions increases with the increase of JG, (2) for churn, slug-annular, and annular flow patterns, there is no specific correlation between JG and void fraction was observed due to effect of the slip between gas and liquid, and (3) whilst for bubbly and slug flows the void fractions are close to homogeneous line, for churn, annular, and slug-annular flows are far below the homogeneous line. It indicates that the slip ratios for the second group of flow patterns are higher than unity.

  11. Basal ice flow regime influenced by glacial lake formation in Rhonegletscher, Switzerland

    NASA Astrophysics Data System (ADS)

    Nishimura, D.; Tsutaki, S.; Sugiyama, S.

    2010-12-01

    After the retreat of glacier terminus over a bedrock bump, a glacial lake has formed in front of Rhonegletscher, Switzerland. It is suspected that ice flow regime is now significantly influenced by the lake water. To investigate the impact of lake formation on glacier dynamics, we carried out surface and borehole observations in the terminus region of Rhonegletscher. In 2008 and 2009 summer seasons, we drilled more than 20 boreholes to measure borehole deformation by repeated inclinometry. Ice surface speed was measured by surveying stakes installed nearby the boreholes. We used a borehole televiewer to measure basal sliding speed by tracking stones and markers at the bottom of the boreholes. We also measured basal sediment layer thickness by hammering a penetrometer at the bottom of the boreholes. Our measurements showed clear decrease in the ice deformation rate near the lake (Fig. 1). Ice deformation accounted for 60-80% in the upper part of our study site (e.g. boreholes 1 and 5), whereas it is less than 10% near the lake (e.g. boreholes 7, 10 and 11). This result suggests that the basal ice flow near the lake is enhanced by the lake water. According to the basal sliding speed measurement in borehole 2, sliding accounted for less than 10% of basal flow speed from 2 to 31 August 2009. Deformation of a subglacial sediment layer is thus important in this region. The penetrometer measurement confirmed that the study site is underlain by a subglacial sediment layer whose thickness was in a range of 0-70 m. Fig.1 Terminus of Rhonegletscher and proglacial lakes indicated by the shaded areas. The columns show ice surface and deformation speeds measured at each borehole site from 9 July to 5 September in 2009. Ice deformation speed was negligibly small at boreholes 7, 10, and 11. Surface contour spacing is 20 m.

  12. The mantle wedge's transient 3-D flow regime and thermal structure

    NASA Astrophysics Data System (ADS)

    Davies, D. R.; Le Voci, G.; Goes, S.; Kramer, S. C.; Wilson, C. R.

    2016-01-01

    Arc volcanism, volatile cycling, mineralization, and continental crust formation are likely regulated by the mantle wedge's flow regime and thermal structure. Wedge flow is often assumed to follow a regular corner-flow pattern. However, studies that incorporate a hydrated rheology and thermal buoyancy predict internal small-scale-convection (SSC). Here, we systematically explore mantle-wedge dynamics in 3-D simulations. We find that longitudinal "Richter-rolls" of SSC (with trench-perpendicular axes) commonly occur if wedge hydration reduces viscosities to Pa s, although transient transverse rolls (with trench-parallel axes) can dominate at viscosities of Pa s. Rolls below the arc and back arc differ. Subarc rolls have similar trench-parallel and trench-perpendicular dimensions of 100-150 km and evolve on a 1-5 Myr time-scale. Subback-arc instabilities, on the other hand, coalesce into elongated sheets, usually with a preferential trench-perpendicular alignment, display a wavelength of 150-400 km and vary on a 5-10 Myr time scale. The modulating influence of subback-arc ridges on the subarc system increases with stronger wedge hydration, higher subduction velocity, and thicker upper plates. We find that trench-parallel averages of wedge velocities and temperature are consistent with those predicted in 2-D models. However, lithospheric thinning through SSC is somewhat enhanced in 3-D, thus expanding hydrous melting regions and shifting dehydration boundaries. Subarc Richter-rolls generate time-dependent trench-parallel temperature variations of up to K, which exceed the transient 50-100 K variations predicted in 2-D and may contribute to arc-volcano spacing and the variable seismic velocity structures imaged beneath some arcs.

  13. Expansion of bubbles under a pulsatile flow regime in decompressed ovine blood vessels.

    PubMed

    Arieli, Ran; Marmur, Abraham

    2016-02-01

    After decompression of ovine large blood vessels, bubbles nucleate and expand at active hydrophobic spots on their luminal aspect. These bubbles will be in the path of the blood flow within the vessel, which might replenish the supply of gas-supersaturated plasma in their vicinity and thus, in contrast with our previous estimations, enhance their growth. We used the data from our previous study on the effect of pulsatile flow in ovine blood vessels stretched on microscope slides and photographed after decompression from hyperbaric exposure. We measured the diameter of 46 bubbles in 4 samples taken from 3 blood vessels (pulmonary artery, pulmonary vein, and aorta) in which both a "multi-bubble active spot" (MBAS)--which produces several bubbles at a time, and at least one "single-bubble active spot" (SBAS)--which produces a single bubble at a time, were seen together. The linear expansion rate for diameter in SBAS ranged from 0.077 to 0.498 mm/min and in MBAS from 0.001 to 0.332 mm/min. There was a trend toward a reduced expansion rate for bubbles in MBAS compared with SBAS. The expansion rate for bubbles in an MBAS when it was surrounded by others was very low. Bubble growth is related to gas tension, and under a flow regime, bubbles expand from a diameter of 0.1 to 1mm in 2-24 min at a gas supersaturation of 620 kPa and lower. There are two phases of bubble development. The slow and disperse initiation of active spots (from nanobubbles to gas micronuclei) continues for more than 1h, whereas the fast increase in size (2-24 min) is governed by diffusion. Bubble-based decompression models should not artificially reduce diffusion constants, but rather take both phases of bubble development into consideration.

  14. Investigating the flow and stress regime at the front of a tidewater outlet glacier

    NASA Astrophysics Data System (ADS)

    Mercenier, Rémy; Luethi, Martin; Vieli, Andreas; Rohner, Christoph; Small, David

    2016-04-01

    Dynamic changes in ocean-terminating glaciers are responsible for approximately half of the current high rate of mass loss of the Greenland ice sheet. The related calving process, which occurs when the stresses at the calving front exceed the fracture toughness of ice, is still not well understood and poorly represented in current generation ice-sheet models, but is a crucial requisite to understand and model dynamics and future mass loss of the ice sheet. Here, we use a two-dimensional finite-element model to compute the stress and flow fields near the front of a tidewater outlet glacier. First, we perform a sensitivity analysis for an idealized glacier exploring the effects of variable calving front slope, water depth and basal sliding. We then apply the model to two flowlines of Eqip Sermia, an ocean terminating outlet glacier in West Greenland. Detailed velocity and geometry measurements obtained from terrestrial radar interferometry serve as constraints to the model. These flowline geometries and velocities strongly differ. One flowline ends with a ˜ 50 meter vertical cliff, close to floatation, while the other has a 150-200 meter high grounded front with a ˜ 45° slope and for which extrusion flow is observed. These different geometry settings lead to substantial difference in stress and flow regimes. This stress analysis improves our understanding of how and where the ice is susceptible to failure and crevasse formation for different idealized as well as real conditions. In further work, we aim to use this information as a constraint to investigate the short-term and long-term processes related to outlet glacier calving.

  15. Prediction of strong and weak ignition regimes in turbulent reacting flows with temperature fluctuations: A direct numerical simulation study

    NASA Astrophysics Data System (ADS)

    Pal, Pinaki; Valorani, Mauro; Im, Hong; Wooldridge, Margaret

    2015-11-01

    The present work investigates the auto-ignition characteristics of compositionally homogeneous reactant mixtures in the presence of thermal non-uniformities and turbulent velocity fluctuations. An auto-ignition regime diagram is briefly discussed, that provides the framework for predicting the expected ignition behavior based on the thermo-chemical properties of the reactant mixture and flow/scalar field conditions. The regime diagram classifies the ignition regimes mainly into three categories: weak (deflagration dominant), reaction-controlled strong and mixing-controlled strong (volumetric ignition/spontaneous propagation dominant) regimes. Two-dimensional direct numerical simulations (DNS) of auto-ignition in a lean thermally-stratified syngas/air turbulent mixture at high-pressure, low-temperature conditions are performed to assess the validity of the regime diagram. Various parametric cases are considered corresponding to different locations on the regime diagram, by varying the characteristic turbulent Damköhler and Reynolds numbers. Detailed analysis of the reaction front propagation and heat release indicates that the observed ignition behaviors agree very well with the corresponding predictions by the regime diagram. U.S. DOE NETL award number DE-FE0007465; King Abdullah University of Science and Technology (KAUST).

  16. The analysis of two-dimensional two-phase flow in horizontal heated tube bundles using drift flux model

    NASA Astrophysics Data System (ADS)

    Yang, Ruichang; Zheng, Rongchuan; Wang, Yanwu

    This paper presents the experimental study and numerical simulation of two-dimensional two-phase flow in horizontal heated tube bundles. In the experiments, two advanced measuring systems with a single-fibre optical probe and a tri-fibre-optical-probe were developed to measure respectively the local void fraction and vapor bubble velocities among the heated tube bundles. In accordance with the internal circulation characteristics of two-phase flow in the tube bundles, a mathematical model of two-dimensional two-phase low Reynolds number turbulent flow based on the modified drift flux model and the numerical simulation method to analyze the two-phase flow structures have been developed. The modified drift flux model in which both the acceleration by gravity and the acceleration of the average volumetric flow are taken into account for the calculation of the drift velocities enables its application to the analysis of multi-dimensional two-phase flow. In the analysis the distributions of the vapor-phase velocity, liquid-phase velocity and void fraction were numerically obtained by using the modified drift flux model and conventional drift flux model respectively and compared with the experimental results. The numerical analysis results by using the modified drift flux model agree reasonably well with the experimental investigation. It is confirmed that the modified drift flux model has the capability of correctly simulating the two-dimensional two-phase flow.

  17. Horizontal density-gradient effects on simulation of flow and transport in the Potomac Estuary

    USGS Publications Warehouse

    Schaffranek, Raymond W.; Baltzer, Robert A.; ,

    1990-01-01

    A two-dimensional, depth-integrated, hydrodynamic/transport model of the Potomac Estuary between Indian Head and Morgantown, Md., has been extended to include treatment of baroclinic forcing due to horizontal density gradients. The finite-difference model numerically integrates equations of mass and momentum conservation in conjunction with a transport equation for heat, salt, and constituent fluxes. Lateral and longitudinal density gradients are determined from salinity distributions computed from the convection-diffusion equation and an equation of state that expresses density as a function of temperature and salinity; thus, the hydrodynamic and transport computations are directly coupled. Horizontal density variations are shown to contribute significantly to momentum fluxes determined in the hydrodynamic computation. These fluxes lead to enchanced tidal pumping, and consequently greater dispersion, as is evidenced by numerical simulations. Density gradient effects on tidal propagation and transport behavior are discussed and demonstrated.

  18. Determination of flow-regime boundaries for cohesive particles. Quarterly report, December 20, 1990--March 19, 1991

    SciTech Connect

    Knowlton, T.M.; Findlay, J.G.

    1992-01-01

    The overall objective of this program is the development of a hydrodynamic model to predict the choking/non-choking flow regime boundary of fine, cohesive (i.e., Geldart Group C) powders. Specific objectives are to: (1) Develop a two-dimensional hydrodynamic model that can be applied to cohesive solids. (2) Generate large-scale solids-flows data that will be used to verify the model.

  19. Situational Lightning Climatologies for Central Florida: Phase IV: Central Florida Flow Regime Based Climatologies of Lightning Probabilities

    NASA Technical Reports Server (NTRS)

    Bauman, William H., III

    2009-01-01

    The threat of lightning is a daily concern during the warm season in Florida. Research has revealed distinct spatial and temporal distributions of lightning occurrence that are strongly influenced by large-scale atmospheric flow regimes. Previously, the Applied Meteorology Unit (AMU) calculated the gridded lightning climatologies based on seven flow regimes over Florida for 1-, 3- and 6-hr intervals in 5-, 10-, 20-, and 30-NM diameter range rings around the Shuttle Landing Facility (SLF) and eight other airfields in the National Weather Service in Melbourne (NWS MLB) county warning area (CWA). In this update to the work, the AMU recalculated the lightning climatologies for using individual lightning strike data to improve the accuracy of the climatologies. The AMU included all data regardless of flow regime as one of the stratifications, added monthly stratifications, added three years of data to the period of record and used modified flow regimes based work from the AMU's Objective Lightning Probability Forecast Tool, Phase II. The AMU made changes so the 5- and 10-NM radius range rings are consistent with the aviation forecast requirements at NWS MLB, while the 20- and 30-NM radius range rings at the SLF assist the Spaceflight Meteorology Group in making forecasts for weather Flight Rule violations during Shuttle landings. The AMU also updated the graphical user interface with the new data.

  20. Adapting of the Background-Oriented Schlieren (BOS) Technique in the Characterization of the Flow Regimes in Thermal Spraying Processes

    NASA Astrophysics Data System (ADS)

    Tillmann, W.; Abdulgader, M.; Rademacher, H. G.; Anjami, N.; Hagen, L.

    2014-01-01

    In thermal spraying technique, the changes in the in-flight particle velocities are considered to be only a function of the drag forces caused by the dominating flow regimes in the spray jet. Therefore, the correct understanding of the aerodynamic phenomena occurred at nozzle out let and at the substrate interface is an important task in the targeted improvement in the nozzle and air-cap design as well as in the spraying process in total. The presented work deals with the adapting of an innovative technique for the flow characterization called background-oriented Schlieren. The flow regimes in twin wire arc spraying (TWAS) and high velocity oxygen fuel (HVOF) were analyzed with this technique. The interfering of the atomization gas flow with the intersected wires causes in case of TWAS process a deformation of the jet shape. It leads also to areas with different aero dynamic forces. The configurations of the outlet air-caps in TWAS effect predominantly the outlet flow characteristics. The ratio between fuel and oxygen determine the dominating flow regimes in the HVOF spraying jet. Enhanced understanding of the aerodynamics at outlet and at the substrate interface could lead to a targeted improvement in thermal spraying processes.

  1. Predicting the natural flow regime: Models for assessing hydrological alteration in streams

    USGS Publications Warehouse

    Carlisle, D.M.; Falcone, J.; Wolock, D.M.; Meador, M.R.; Norris, R.H.

    2010-01-01

    Understanding the extent to which natural streamflow characteristics have been altered is an important consideration for ecological assessments of streams. Assessing hydrologic condition requires that we quantify the attributes of the flow regime that would be expected in the absence of anthropogenic modifications. The objective of this study was to evaluate whether selected streamflow characteristics could be predicted at regional and national scales using geospatial data. Long-term, gaged river basins distributed throughout the contiguous US that had streamflow characteristics representing least disturbed or near pristine conditions were identified. Thirteen metrics of the magnitude, frequency, duration, timing and rate of change of streamflow were calculated using a 20-50 year period of record for each site. We used random forests (RF), a robust statistical modelling approach, to develop models that predicted the value for each streamflow metric using natural watershed characteristics. We compared the performance (i.e. bias and precision) of national- and regional-scale predictive models to that of models based on landscape classifications, including major river basins, ecoregions and hydrologic landscape regions (HLR). For all hydrologic metrics, landscape stratification models produced estimates that were less biased and more precise than a null model that accounted for no natural variability. Predictive models at the national and regional scale performed equally well, and substantially improved predictions of all hydrologic metrics relative to landscape stratification models. Prediction error rates ranged from 15 to 40%, but were 25% for most metrics. We selected three gaged, non-reference sites to illustrate how predictive models could be used to assess hydrologic condition. These examples show how the models accurately estimate predisturbance conditions and are sensitive to changes in streamflow variability associated with long-term land-use change. We also

  2. Catalytic oxygen production mediated by smart capsules to modulate elastic turbulence under a laminar flow regime.

    PubMed

    Zizzari, A; Bianco, M; Miglietta, R; del Mercato, L L; Carraro, M; Sorarù, A; Bonchio, M; Gigli, G; Rinaldi, R; Viola, I; Arima, V

    2014-11-21

    Liquid flow in microchannels is completely laminar and uniaxial, with a very low Reynolds number regime and long mixing lengths. To increase fluid mixing and solubility of reactants, as well as to reduce reaction time, complex three-dimensional networks inducing chaotic advection have to be designed. Alternatively, turbulence in the liquid can be generated by active mixing methods (magnetic, acoustic waves, etc.) or adding small quantities of elastic materials to the working liquid. Here, polyelectrolyte multilayer capsules embodying a catalytic polyoxometalate complex have been suspended in an aqueous solution and used to create elastic turbulence and to propel fluids inside microchannels as an alternative to viscoelastic polymers. The overall effect is enhanced and controlled by feeding the polyoxometalate-modified capsules with hydrogen peroxide, H2O2, thus triggering an on-demand propulsion due to oxygen evolution resulting from H2O2 decomposition. The quantification of the process is done by analysing some structural parameters of motion such as speed, pressure, viscosity, and Reynolds and Weissenberg numbers, directly obtained from the capillary dynamics of the aqueous mixtures with different concentrations of H2O2. The increases in fluid speed as well as the capsule-induced turbulence effects are proportional to the H2O2 added and therefore dependent on the kinetics of H2O2 dismutation. PMID:25238401

  3. Catalytic oxygen production mediated by smart capsules to modulate elastic turbulence under a laminar flow regime.

    PubMed

    Zizzari, A; Bianco, M; Miglietta, R; del Mercato, L L; Carraro, M; Sorarù, A; Bonchio, M; Gigli, G; Rinaldi, R; Viola, I; Arima, V

    2014-11-21

    Liquid flow in microchannels is completely laminar and uniaxial, with a very low Reynolds number regime and long mixing lengths. To increase fluid mixing and solubility of reactants, as well as to reduce reaction time, complex three-dimensional networks inducing chaotic advection have to be designed. Alternatively, turbulence in the liquid can be generated by active mixing methods (magnetic, acoustic waves, etc.) or adding small quantities of elastic materials to the working liquid. Here, polyelectrolyte multilayer capsules embodying a catalytic polyoxometalate complex have been suspended in an aqueous solution and used to create elastic turbulence and to propel fluids inside microchannels as an alternative to viscoelastic polymers. The overall effect is enhanced and controlled by feeding the polyoxometalate-modified capsules with hydrogen peroxide, H2O2, thus triggering an on-demand propulsion due to oxygen evolution resulting from H2O2 decomposition. The quantification of the process is done by analysing some structural parameters of motion such as speed, pressure, viscosity, and Reynolds and Weissenberg numbers, directly obtained from the capillary dynamics of the aqueous mixtures with different concentrations of H2O2. The increases in fluid speed as well as the capsule-induced turbulence effects are proportional to the H2O2 added and therefore dependent on the kinetics of H2O2 dismutation.

  4. Gas Flux and Density Surrounding a Cylindrical Aperture in the Free Molecular Flow Regime

    NASA Technical Reports Server (NTRS)

    Soulas, George C.

    2011-01-01

    The equations for rigorously calculating the particle flux and density surrounding a cylindrical aperture in the free molecular flow regime are developed and presented. The fundamental equations for particle flux and density from a reservoir and a diffusely reflecting surface will initially be developed. Assumptions will include a Maxwell-Boltzmann speed distribution, equal particle and wall temperatures, and a linear flux distribution along the cylindrical aperture walls. With this information, the equations for axial flux and density surrounding a cylindrical aperture will be developed. The cylindrical aperture will be divided into multiple volumes and regions to rigorously determine the surrounding axial flux and density, and appropriate limits of integration will be determined. The results of these equations will then be evaluated. The linear wall flux distribution assumption will be assessed. The axial flux and density surrounding a cylindrical aperture with a thickness-to-radius ratio of 1.25 will be presented. Finally, the equations determined in this study will be verified using multiple methods.

  5. Conduction in Low Mach Number Flows. I. Linear and Weakly Nonlinear Regimes

    NASA Astrophysics Data System (ADS)

    Lecoanet, Daniel; Brown, Benjamin P.; Zweibel, Ellen G.; Burns, Keaton J.; Oishi, Jeffrey S.; Vasil, Geoffrey M.

    2014-12-01

    Thermal conduction is an important energy transfer and damping mechanism in astrophysical flows. Fourier's law, in which the heat flux is proportional to the negative temperature gradient, leading to temperature diffusion, is a well-known empirical model of thermal conduction. However, entropy diffusion has emerged as an alternative thermal conduction model, despite not ensuring the monotonicity of entropy. This paper investigates the differences between temperature and entropy diffusion for both linear internal gravity waves and weakly nonlinear convection. In addition to simulating the two thermal conduction models with the fully compressible Navier-Stokes equations, we also study their effects in the reduced "soundproof" anelastic and pseudoincompressible (PI) equations. We find that in the linear and weakly nonlinear regime, temperature and entropy diffusion give quantitatively similar results, although there are some larger errors in the PI equations with temperature diffusion due to inaccuracies in the equation of state. Extrapolating our weakly nonlinear results, we speculate that differences between temperature and entropy diffusion might become more important for strongly turbulent convection.

  6. CONDUCTION IN LOW MACH NUMBER FLOWS. I. LINEAR AND WEAKLY NONLINEAR REGIMES

    SciTech Connect

    Lecoanet, Daniel; Brown, Benjamin P.; Zweibel, Ellen G.; Burns, Keaton J.; Oishi, Jeffrey S.; Vasil, Geoffrey M.

    2014-12-20

    Thermal conduction is an important energy transfer and damping mechanism in astrophysical flows. Fourier's law, in which the heat flux is proportional to the negative temperature gradient, leading to temperature diffusion, is a well-known empirical model of thermal conduction. However, entropy diffusion has emerged as an alternative thermal conduction model, despite not ensuring the monotonicity of entropy. This paper investigates the differences between temperature and entropy diffusion for both linear internal gravity waves and weakly nonlinear convection. In addition to simulating the two thermal conduction models with the fully compressible Navier-Stokes equations, we also study their effects in the reduced ''soundproof'' anelastic and pseudoincompressible (PI) equations. We find that in the linear and weakly nonlinear regime, temperature and entropy diffusion give quantitatively similar results, although there are some larger errors in the PI equations with temperature diffusion due to inaccuracies in the equation of state. Extrapolating our weakly nonlinear results, we speculate that differences between temperature and entropy diffusion might become more important for strongly turbulent convection.

  7. A two-phase flow regime map for a MAPLE-type nuclear research reactor fuel channel: Effect of hexagonal finned bundle

    SciTech Connect

    Harvel, G.D.; Chang, J.S.; Krishnan, V.S.

    1997-05-01

    A two-phase flow regime map is developed experimentally and theoretically for a vertical hexagonal flow channel with and without a 36-finned rod hexagonal bundle. This type of flow channel is of interest to MAPLE-type nuclear research reactors. The flow regime maps are determined by visual observations and observation of waveforms shown by a capacitance-type void fraction meter. The experimental results show that the inclusion of the finned hexagonal bundle shifts the flow regime transition boundaries toward higher water flow rates. Existing flow regime maps based on pipe flow require slight modifications when applied to the hexagonal flow channel with and without a MAPLE-type finned hexagonal bundle. The proposed theoretical model agrees well with experimental results.

  8. Experimental investigation of buoyancy effects on convection heat transfer of supercritical CO2 flow in a horizontal tube

    NASA Astrophysics Data System (ADS)

    Tanimizu, Katsuyoshi; Sadr, Reza

    2016-04-01

    The heat transfer characteristics of supercritical carbon dioxide (S-CO2) turbulent flow were investigated experimentally in a horizontal circular pipe with an inner diameter of 8.7 mm. Local convection coefficients and Nusselt numbers of the flow were obtained at different locations along the pipe with a constant heat flux ranging from 16 to 64 kW/m2. Experiments were performed for fluid mass flow rate ranging from 0.011 to 0.017 kg/s, an inlet fluid temperature ranging from 24 to 28 °C, and a flow pressure ranging from 7.5 to 9.0 MPa to investigate their effects on the convection heat transfer in the pipe. Both enhancement as well as deterioration in the heat transfer coefficient was observed for the flow conditions examined in this work. Experimental results were then compared with the widely used empirical correlation for pipe flow. Three commonly used buoyancy parameters were utilized to investigate their applicability in the present test conditions. Results indicate that all the parameters show a strong presence of buoyancy effects in the present test conditions. The trend and magnitude of these parameters, however, do not agree with the trend and magnitude of heat transfer enhancement and deterioration along the pipe.

  9. Experimental study on the flow patterns and the two-phase pressure drops in a horizontal impacting T-Junction

    NASA Astrophysics Data System (ADS)

    Bertani, C.; Malandrone, M.; Panella, B.

    2014-04-01

    The present paper analyzes the experimental results concerning the flow patterns and pressure drops in two-phase flow through a horizontal impacting T-junction, whose outlet pipes are aligned and perpendicular to the inlet pipe. The test section consists of plexiglass pipes with inner diameter of 10 mm. A mixture of water and air at ambient temperature and pressures up to 2.4 bar flows through the T-junction, with different splitting of flow rates in the two outlet branches; superficial velocities of air and water in the inlet pipe have been varied up to a maximum of 35 m/s and 3.5 m/s respectively. The flow patterns occurring in the inlet and branch pipes are compared with the predictions of the Baker and Taitel - Dukler maps. The pressure drops along the branches have been measured relatively to different splitting of the flow rate through the two branches and the pressure loss coefficients in the junction have been evaluated. Friction pressure drops have allowed us to evaluate two-phase friction multipliers, which have then been compared to the predictions of Lockhart-Martinelli, and Friedel correlations. Local pressure drops have been extrapolated at the junction centre and analyzed; the two-phase multiplier has been evaluated and compared with the predictions of Chisholm correlation; the value of the empirical coefficient that minimizes the discrepancy has also been evaluated.

  10. Bubble Size Control to Improve Oxygen-Based Bleaching: Characterization of Flow Regimes in Pulp-Water-Gas Three-Phase Flows

    SciTech Connect

    S.M. Ghiaasiaan and Seppo Karrila

    2006-03-20

    Flow characteristics of fibrous paper pulp-water-air slurries were investigated in a vertical circular column 1.8 m long, with 5.08 cm diameter. Flow structures, gas holdup (void fraction), and the geometric and population characteristics of gas bubbles were experimentally investigated, using visual observation, Gamma-ray densitometry, and flash X-ray photography. Five distinct flow regimes could be visually identified: dispersed bubbly, layered bubbly, plug, churn-turbulent, and slug. Flow regime maps were constructed, and the regime transition lines were found to be sensitive to consistency. The feasibility of using artificial neural networks (ANNs) for the identification of the flow regimes, using the statistical characteristics of pressure fluctuations measured by a single pressure sensor, was demonstrated. Local pressure fluctuations at a station were recorded with a minimally-intrusive transducer. Three-layer, feed-forward ANNs were designed that could identify the four major flow patterns (bubbly, plug, churn, and slug) well. The feasibility of a transportable artificial neural network (ANN) - based technique for the classification of flow regimes was also examined. Local pressures were recorded at three different locations using three independent but similar transducers. An ANN was designed, trained and successfully tested for the classification of the flow regimes using one of the normalized pressure signals (from Sensor 1). The ANN trained and tested for Sensor 1 predicted the flow regimes reasonably well when applied directly to the other two sensors, indicating a good deal of transportability. An ANN-based method was also developed, whereby the power spectrum density characteristics of other sensors were adjusted before they were used as input to the ANN that was based on Sensor 1 alone. The method improved the predictions. The gas-liquid interfacial surface area concentration was also measured in the study. The gas absorption technique was applied

  11. Experimental investigation on thermo-physical properties and overall performance of MWCNT-water nanofluid flow inside horizontal coiled wire inserted tubes

    NASA Astrophysics Data System (ADS)

    Akhavan-Behabadi, M. A.; Shahidi, Mohamad; Aligoodarz, M. R.; Ghazvini, Mohammad

    2016-04-01

    The present study is aimed to measure and analyze the thermo-physical properties and overall performance of MWCNT-water nanofluid in turbulent flow regimes under constant heat flux conditions inside horizontal coiled wire inserted tubes. For this purpose, stable MWCNT-water nanofluids with different particle weight fractions of 0.05, 0.1 and 0.2 % as well as deionized water were utilized as the working fluids. It was found that the existing theoretical models could not predict the thermo-physical property values accurately, especially in case of specific heat capacity. Therefore, new empirical correlations are presented based on the obtained experimental results to predict such properties for the nanofluids. In addition, the overall performance of heat transfer techniques considered in this paper was evaluated based on thermal performance factor. The results revealed that thermal performance factor for all cases are greater than unity which indicate that simultaneous usage of nanofluids and wire coil inserts enhances the heat transfer without huge penalty in pumping power. Hence, using nanofluids as the working fluid in combination with coiled wire inserted tubes can be considered for some practical applications.

  12. An ecological economic assessment of flow regimes in a hydropower dominated river basin: the case of the lower Zambezi River, Mozambique.

    PubMed

    Fanaian, Safa; Graas, Susan; Jiang, Yong; van der Zaag, Pieter

    2015-02-01

    The flow regime of rivers, being an integral part of aquatic ecosystems, provides many important services benefiting humans in catchments. Past water resource developments characterized by river embankments and dams, however, were often dominated by one (or few) economic use(s) of water. This results in a dramatically changed flow regime negatively affecting the provision of other ecosystem services sustained by the river flow. This study is intended to demonstrate the value of alternative flow regimes in a river that is highly modified by the presence of large hydropower dams and reservoirs, explicitly accounting for a broad range of flow-dependent ecosystem services. In this study, we propose a holistic approach for conducting an ecological economic assessment of a river's flow regime. This integrates recent advances in the conceptualization and classification of ecosystem services (UK NEA, 2011) with the flow regime evaluation technique developed by Korsgaard (2006). This integrated approach allows for a systematic comparison of the economic values of alternative flow regimes, including those that are considered beneficial for aquatic ecosystems. As an illustration, we applied this combined approach to the Lower Zambezi Basin, Mozambique. Empirical analysis shows that even though re-operating dams to create environmentally friendly flow regimes reduces hydropower benefits, the gains to goods derived from the aquatic ecosystem may offset the forgone hydropower benefits, thereby increasing the total economic value of river flow to society. The proposed integrated flow assessment approach can be a useful tool for welfare-improving decision-making in managing river basins.

  13. Forced convection and flow boiling with and without enhancement devices for top-side-heated horizontal channels

    NASA Technical Reports Server (NTRS)

    Boyd, Ronald D., Sr.; Turknett, Jerry C.

    1989-01-01

    The effect of enhancement devices on flow boiling heat transfer in coolant channels, which are heated either from the top side or uniformly was studied. Studies are completed of the variations in the local (axial and circumferential) and mean heat transfer coefficients in horizontal, top-heated coolant channels with smooth walls and internal heat transfer enhancement devices. The working fluid is freon-11. The objectives are to: (1) examine the variations in both the mean and local (axial and circumferential) heat transfer coefficients for a circular coolant channel with either smooth walls or with both a twisted tape and spiral finned walls; (2) examine the effect of channel diameter (and the length-to-diameter aspect ratio) variations for the smooth wall channel; and (3) develop and improved data reduction analysis. The case of the top-heated, horizontal flow channel with smooth wall (1.37 cm inside diameter, and 122 cm heated length) was completed. The data were reduced using a preliminary analysis based on the heated hydraulic diameter. Preliminary examination of the local heat transfer coefficient variations indicated that there are significant axial and circumferential variations. However, it appears that the circumferential variation is more significant than the axial ones. In some cases, the circumferential variations were as much as a factor of ten. The axial variations rarely exceeded a factor of three.

  14. Effect of diffusional mass transfer on the performance of horizontal subsurface flow constructed wetlands in tropical climate conditions.

    PubMed

    Njau, K N; Gastory, L; Eshton, B; Katima, J H Y; Minja, R J A; Kimwaga, R; Shaaban, M

    2011-01-01

    The effect of mass transfer on the removal rate constants of BOD5, NH3, NO3 and TKN has been investigated in a Horizontal Subsurface Flow Constructed Wetland (HSSFCW) planted with Phragmites mauritianus. The plug flow model was assumed and the inlet and outlet concentrations were used to determine the observed removal rate constants. Mass transfer effects were studied by assessing the influence of interstitial velocity on pollutant removal rates in CW cells of different widths. The flow velocities varied between 3-46 m/d. Results indicate that the observed removal rate constants are highly influenced by the flow velocity. Correlation of dimensionless groups namely Reynolds Number (Re), Sherwood Number (Sh) and Schmidt Number (Sc) were applied and log-log plots of rate constants against velocity yielded straight lines with values beta = 0.87 for BOD5, 1.88 for NH3, 1.20 for NO3 and 0.94 for TKN. The correlation matched the expected for packed beds although the constant beta was higher than expected for low Reynolds numbers. These results indicate that the design values of rate constants used to size wetlands are influenced by flow velocity. This paper suggests the incorporation of mass transfer into CW design procedures in order to improve the performance of CW systems and reduce land requirements.

  15. Evaluation of correlations of flow boiling heat transfer of R22 in horizontal channels.

    PubMed

    Zhou, Zhanru; Fang, Xiande; Li, Dingkun

    2013-01-01

    The calculation of two-phase flow boiling heat transfer of R22 in channels is required in a variety of applications, such as chemical process cooling systems, refrigeration, and air conditioning. A number of correlations for flow boiling heat transfer in channels have been proposed. This work evaluates the existing correlations for flow boiling heat transfer coefficient with 1669 experimental data points of flow boiling heat transfer of R22 collected from 18 published papers. The top two correlations for R22 are those of Liu and Winterton (1991) and Fang (2013), with the mean absolute deviation of 32.7% and 32.8%, respectively. More studies should be carried out to develop better ones. Effects of channel dimension and vapor quality on heat transfer are analyzed, and the results provide valuable information for further research in the correlation of two-phase flow boiling heat transfer of R22 in channels.

  16. Evaluation of correlations of flow boiling heat transfer of R22 in horizontal channels.

    PubMed

    Zhou, Zhanru; Fang, Xiande; Li, Dingkun

    2013-01-01

    The calculation of two-phase flow boiling heat transfer of R22 in channels is required in a variety of applications, such as chemical process cooling systems, refrigeration, and air conditioning. A number of correlations for flow boiling heat transfer in channels have been proposed. This work evaluates the existing correlations for flow boiling heat transfer coefficient with 1669 experimental data points of flow boiling heat transfer of R22 collected from 18 published papers. The top two correlations for R22 are those of Liu and Winterton (1991) and Fang (2013), with the mean absolute deviation of 32.7% and 32.8%, respectively. More studies should be carried out to develop better ones. Effects of channel dimension and vapor quality on heat transfer are analyzed, and the results provide valuable information for further research in the correlation of two-phase flow boiling heat transfer of R22 in channels. PMID:23956695

  17. A contrast between nocturnal flow regimes: Observations and modeling simulations of katabatic intrusions in the Laramie Valley

    NASA Astrophysics Data System (ADS)

    Juliano, Timothy W.

    Katabatic winds commonly occur in mountainous regions under statically stable conditions when a sufficient deficit exists in the net radiation budget. Observations of these stable boundary layer (SBL) downslope flows have extended back to the 1930s. Their interactions with other SBL processes, including cold air pools (CAPs) and mountain waves, are quite complex, however, and have only more recently been deeply investigated. The University of Wyoming (UW) wind tower (WT) and flux tower (WT), situated in the Laramie Valley, were utilized in examining a dataset spanning from 14 December 2011 to 12 September 2013. A set of criteria were developed to determine katabatic intrusion events, and establish a climatology of these events, at the WT. The 21-22 December 2012 nighttime period was then studied in detail using data from the aforementioned towers in addition to weather stations throughout the Laramie Valley and the Weather Research and Forecasting (WRF) model. Both observations and modeling results indicated a competition between two strongly contrasting flow regimes: synoptic and katabatic. The synoptic regime was characterized by strong, southwesterly winds, warm temperatures, and turbulent flow, while the katabatic regime featured weaker, southeasterly winds, cooler temperatures, and intermittently turbulent flow. Sonic and propeller anemometers on the WT elucidated the chaotic transition between the regimes. At the WT, it was found that between regimes the wind speed decreased by up to 60%, wind direction often shifted over 120°, and potential temperature usually decreased more than 2°C. The katabatic wind depth was postulated to be variable in time and space, with its head sloping towards the trailing CAP. Topographically generated mountain waves and local terrain forcing are suspected to play an integral role in the development and evolution of the katabatic wind in the Laramie Valley. Results from this research yield promising insight into the intricate

  18. Fluctuating zonal flows in the I-mode regime in Alcator C-Moda)

    NASA Astrophysics Data System (ADS)

    Cziegler, I.; Diamond, P. H.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M.; Churchill, R. M.; Hubbard, A. E.; Lipschultz, B.; Sierchio, J. M.; Terry, J. L.; Theiler, C.

    2013-05-01

    Velocity fields and density fluctuations of edge turbulence are studied in I-mode [F. Ryter et al., Plasma Phys. Controlled Fusion 40, 725 (1998)] plasmas of the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] tokamak, which are characterized by a strong thermal transport barrier in the edge while providing little or no barrier to the transport of both bulk and impurity particles. Although previous work showed no clear geodesic-acoustic modes (GAM) on C-Mod, using a newly implemented, gas-puff-imaging based time-delay-estimate velocity inference algorithm, GAM are now shown to be ubiquitous in all I-mode discharges examined to date, with the time histories of the GAM and the I-mode specific [D. Whyte et al., Nucl. Fusion 50, 105005 (2010)] Weakly Coherent Mode (WCM, f = 100-300 kHz, Δf/f≈0.5, and kθ≈1.3 cm-1) closely following each other through the entire duration of the regime. Thus, the I-mode presents an example of a plasma state in which zero frequency zonal flows and GAM continuously coexist. Using two-field (density-velocity and radial-poloidal velocity) bispectral methods, the GAM are shown to be coupled to the WCM and to be responsible for its broad frequency structure. The effective nonlinear growth rate of the GAM is estimated, and its comparison to the collisional damping rate seems to suggest a new view on I-mode threshold physics.

  19. A New Parameter Regime for Dust in Plasma: the Case of Dense and Supersonic Plasma Flows

    SciTech Connect

    Ticos, Catalin M.; Wang Zhehui; Wurden, Glen A.

    2008-09-07

    The co-existence between charged micron-size particulates of matter and plasma electrons and ions can lead to interesting physics phenomena. Some of the most spectacular observations in laboratory low ionized gases include the formation of aligned dust structures, the propagation of dust waves or self-organization leading to dust voids. Here, the dust dynamics is established by the forces of gravity, of electrostatic interaction with electric fields within the plasma, of friction with the neutral gas, and by the Coulomb repulsion between grains. Measurements of dust trajectories have been carried out in situ when the plasma density is about 6-7 orders of magnitude higher than in typical laboratory dusty plasmas, i.e. {approx}10{sup 22} m{sup -3}, and the ion temperature is a few eV. The plasma flows at speeds of the order of 20-60 km/s. Two observed features characterize dust in this new plasma regime: the plasma drag force dominates over all other forces acting on the grains and the microparticles are heated to temperatures sufficiently high, to become self-illuminated. Simultaneous observation at different moments in time of up to a few hundred flying dust grains has been possible due to the timing capabilities of a high-speed camera equipped with a telephoto lens. Dust speed of a few km/s and accelerations of {approx}10{sup 5}-10{sup 6} m/s{sup 2} have been inferred using the time-of-flight technique. Among the applications of hypervelocity dust are local diagnostics performed on hot plasmas, interstellar propulsion or simulation of meteorite impacts.

  20. Geothermal regimes at Clearlake California: A preliminary review

    SciTech Connect

    Burns, K.L.; Potter, R.M.; Zyvoloski, G.

    1992-01-01

    Three distinct geothermal regimes are inferred in the vicinity of the city of Clearlake, California. The first is a conductive heat flow regime, the second is a fault-controlled hot spring flow of magmatic'' fluids, and the third is a resurgent flow of meteoric warm water. The conductive heat flow results in flat, horizontal isotherms. The hot spring generates a localized spike in the isotherms. The advective disturbance carries heat laterally to a fault-line resurgence, lowering the apparent heat flow at the surface.

  1. Geothermal regimes at Clearlake California: A preliminary review

    SciTech Connect

    Burns, K.L.; Potter, R.M.; Zyvoloski, G.

    1992-08-01

    Three distinct geothermal regimes are inferred in the vicinity of the city of Clearlake, California. The first is a conductive heat flow regime, the second is a fault-controlled hot spring flow of ``magmatic`` fluids, and the third is a resurgent flow of meteoric warm water. The conductive heat flow results in flat, horizontal isotherms. The hot spring generates a localized spike in the isotherms. The advective disturbance carries heat laterally to a fault-line resurgence, lowering the apparent heat flow at the surface.

  2. Invertebrates associated with a horizontal-flow, subsurface constructed wetland in a northern climate.

    PubMed

    Giordano, Rosanna; Weber, Everett; Darby, Brian J; Soto-Adames, Felipe N; Murray, Robert E; Drizo, Aleksandra

    2014-04-01

    Wetlands function as buffers between terrestrial and aquatic ecosystems, filtering pollutants generated by human activity. Constructed wetlands were developed to mimic the physical and biological filtering functions of natural systems for the treatment of human and animal waste under controlled conditions. Previous studies on the effect of constructed wetlands on native invertebrate populations have concentrated almost exclusively on mosquitoes. Here, we present the first study investigating the relationship between vegetation cover and aeration regime, and the diversity and abundance of nematodes and springtails (Collembola) in a constructed wetland designed to treat dairy farm wastewater in northwestern Vermont. We investigated four treatment cells differing in aeration regime and vegetation cover, but equally overlaid by a layer of compost to provide insulation. Analysis showed that nematodes were most abundant in the nonplanted and nonaerated cells, and that bacterivorous nematodes dominated the community in all cells. Springtails were found to be most numerous in the planted and nonaerated cells. We hypothesize that the vegetation provided differing environmental niches that supported a more diverse system of bacteria and fungi, as well as offering protection from predators and inclement weather. Nematodes were likely imported with the original compost material, while springtails migrated into the cells either via air, water, or direct locomotion. PMID:24534015

  3. Invertebrates associated with a horizontal-flow, subsurface constructed wetland in a northern climate.

    PubMed

    Giordano, Rosanna; Weber, Everett; Darby, Brian J; Soto-Adames, Felipe N; Murray, Robert E; Drizo, Aleksandra

    2014-04-01

    Wetlands function as buffers between terrestrial and aquatic ecosystems, filtering pollutants generated by human activity. Constructed wetlands were developed to mimic the physical and biological filtering functions of natural systems for the treatment of human and animal waste under controlled conditions. Previous studies on the effect of constructed wetlands on native invertebrate populations have concentrated almost exclusively on mosquitoes. Here, we present the first study investigating the relationship between vegetation cover and aeration regime, and the diversity and abundance of nematodes and springtails (Collembola) in a constructed wetland designed to treat dairy farm wastewater in northwestern Vermont. We investigated four treatment cells differing in aeration regime and vegetation cover, but equally overlaid by a layer of compost to provide insulation. Analysis showed that nematodes were most abundant in the nonplanted and nonaerated cells, and that bacterivorous nematodes dominated the community in all cells. Springtails were found to be most numerous in the planted and nonaerated cells. We hypothesize that the vegetation provided differing environmental niches that supported a more diverse system of bacteria and fungi, as well as offering protection from predators and inclement weather. Nematodes were likely imported with the original compost material, while springtails migrated into the cells either via air, water, or direct locomotion.

  4. Flow structure of natural dehumidification over a horizontal finned-tube

    NASA Astrophysics Data System (ADS)

    Hirbodi, Kamran; Yaghoubi, Mahmood

    2016-08-01

    In the present study, structure of water drops formation, growth, coalescence and departure over a horizontal finned-tube during natural dehumidification is investigated experimentally. Starting time of repelling the drops as well as heat transfer rate and the rate of dripping condensates in quasi-steady-state conditions are presented. Furthermore, cold airflow pattern around the horizontal finned-tube is visualized by using smoke generation scheme during natural dehumidification process. The finned-tube has a length of 300 mm, and inner and outer fin diameters, fin thickness and fin spacing are 25.4, 56, 0.4 and 2 mm, respectively. The tests are conducted in an insulated control room with dimensions of 5.8 m × 3 m × 4 m. Ambient air temperature, relative humidity and fin base temperature are selected from 25 to 35 °C, from 40 to 70 % and from 4 to 8 °C, respectively. Observations show that natural condensation from humid air over the test case is completely dropwise. Droplets only form on the edge of the fin and lateral fin surfaces remain almost dry. Dehumidification process over the tested finned-tube is divided into four stages; nucleation, formation, growth and departure of drops. It is also observed that the condensate inundation leaves the tube bottom in the form of droplets. Smoke visualization depicts that humid airflows downward around the cold finned-tube surface without noticeable turbulence and separation in the initial stages of dehumidification process. But the airflow has some disturbances in the intermediate stage and especially during drop departure on the edge of the fins.

  5. Seepage flow behaviors of multi-stage fractured horizontal wells in arbitrary shaped shale gas reservoirs

    NASA Astrophysics Data System (ADS)

    Zhao, Yu-Long; Shan, Bao-Chao; Zhang, Lie-Hui; Liu, Qi-Guo

    2016-10-01

    The horizontal well incorporated with massive hydraulic fracturing has become a key and necessary technology to develop shale gas reservoirs efficiently, and transient pressure analysis is a practical method to evaluate the effectiveness of the fracturing. Until now, however, the related studies on the pressure of such wells have mainly focused on regular outer-boundaries, such as infinite, circular and rectangular boundary shapes, which do not always fulfill the practical conditions and, of course, could cause errors. By extending the boundary element method (BEM) into the application of multi-staged fractured horizontal wells, this paper presents a way of analyzing the transient pressure in arbitrary shaped shale gas reservoirs considering ad-/de-sorption and diffusion of the shale gas with the ‘tri-porosity’ mechanism model. The boundary integral equation can be obtained by coupling the fundamental solution of the Helmholtz equation with the dimensionless diffusivity equation. After discretizing the outer-boundaries and the fractures, the boundary integral equations are linearized and the coefficient matrix of the pressure on the boundaries is assembled, after which bottom-hole pressure can be calculated conveniently. Comparing the BEM solution with semi-analytical solution cases, the accuracy of the new solution can be validated. Then, the characteristic curves of the dimensionless pseudo pressure, as well as its derivative for a well in shale gas reservoirs, are drawn, based on which the parameters’ sensitivity analyses are also conducted. This paper not only enriches the well testing theory and method in shale gas reservoirs, but also provides an effective method to solve problems with complex inner- and outer-boundaries.

  6. Performance of system consisting of vertical flow trickling filter and horizontal flow multi-soil-layering reactor for treatment of rural wastewater.

    PubMed

    Zhang, Yi; Cheng, Yan; Yang, Chunping; Luo, Wei; Zeng, Guangming; Lu, Li

    2015-10-01

    In order to improve nitrogen removal for rural wastewater, a novel two-stage hybrid system, consisting of a vertical flow trickling filter (VFTF) and a horizontal flow multi-soil-layering (HFMSL) bioreactor was developed. The performance of the apparatus was observed under various carbon-nitrogen ratios and water spraying frequencies separately. The maximum removal efficiency of total nitrogen (TN) for the hybrid system was 92.8% while the removal rates of CODCr, ammonium (NH4(+)-N), and total phosphorus (TP) were 94.1%, 96.1%, 92.0% respectively, and the corresponding effluent concentrations were 3.61, 21.20, 1.91, and 0.33 mg L(-1). The horizontal flow mode for MSL led the system to denitrifying satisfactorily as it ensured relatively long hydraulic retention time (HRT), ideal anoxic condition and adequate organic substrates supply. Also, higher water spraying frequency benefited intermittent feeding system for pollutants removal. Shock loading test indicated that the hybrid system could operate well even at hydraulic shock loadings. PMID:26151854

  7. Performance of system consisting of vertical flow trickling filter and horizontal flow multi-soil-layering reactor for treatment of rural wastewater.

    PubMed

    Zhang, Yi; Cheng, Yan; Yang, Chunping; Luo, Wei; Zeng, Guangming; Lu, Li

    2015-10-01

    In order to improve nitrogen removal for rural wastewater, a novel two-stage hybrid system, consisting of a vertical flow trickling filter (VFTF) and a horizontal flow multi-soil-layering (HFMSL) bioreactor was developed. The performance of the apparatus was observed under various carbon-nitrogen ratios and water spraying frequencies separately. The maximum removal efficiency of total nitrogen (TN) for the hybrid system was 92.8% while the removal rates of CODCr, ammonium (NH4(+)-N), and total phosphorus (TP) were 94.1%, 96.1%, 92.0% respectively, and the corresponding effluent concentrations were 3.61, 21.20, 1.91, and 0.33 mg L(-1). The horizontal flow mode for MSL led the system to denitrifying satisfactorily as it ensured relatively long hydraulic retention time (HRT), ideal anoxic condition and adequate organic substrates supply. Also, higher water spraying frequency benefited intermittent feeding system for pollutants removal. Shock loading test indicated that the hybrid system could operate well even at hydraulic shock loadings.

  8. Electrospray characteristic curves: in pursuit of improved performance in the nano-flow regime

    PubMed Central

    Marginean, Ioan; Kelly, Ryan T.; Page, Jason S.; Tang, Keqi

    2008-01-01

    Depending on its coordinates in the parameter space, an electrospray can manifest in one of several known regimes – stable, quasi-stable, transitional-chaotic, and non-axial – that ultimately impact measurement sensitivity and precision. An electrospray operating in cone-jet regime provides large and stable spray current, as well as smaller initial droplets that are prerequisites for higher sensitivity and quality mass spectrometric analyses. However, the dynamic conditions encountered in gradient elution-based liquid separations create difficulties for continuous operation in this regime throughout the analysis. We present a preliminary study aimed at stabilizing the electrospray in the cone-jet regime. On the basis of spray current measurements obtained using solvent conditions typically found in liquid chromatography-mass spectrometry, an improved description of the cone-jet stability island is provided by including transitions to and from the recently described astable regime. Additionally, the experimental conditions in which the astable regime marks the transition between pulsating and cone-jet regimes are further clarified. PMID:17896826

  9. Limitation of parallel flow in double diffusive convection: Two- and three-dimensional transitions in a horizontal porous domain

    SciTech Connect

    Mimouni, N.; Chikh, S.; Rahli, O.; Bennacer, R.

    2014-07-15

    Two-dimensional (2D) and three-dimensional (3D) numerical simulations of double diffusion natural convection in an elongated enclosure filled with a binary fluid saturating a porous medium are carried out in the present work. The Boussinesq approximation is made in the formulation of the problem, and Neumann boundary conditions for temperature and concentration are adopted, respectively, on vertical and horizontal walls of the cavity. The used numerical method is based on the control volume approach, with the third order quadratic upstream interpolation scheme in approximating the advection terms. A semi implicit method algorithm is used to handle the velocity-pressure coupling. To avoid the excessively high computer time inherent to the solution of 3D natural convection problems, full approximation storage with full multigrid method is used to solve the problem. A wide range of the controlling parameters (Rayleigh-Darcy number Ra, lateral aspect ratio Ay, Lewis number Le, and the buoyancy ration N) is investigated. We clearly show that increasing the depth of the cavity (i.e., the lateral aspect ratio) has an important effect on the flow patterns. The 2D perfect parallel flows obtained for small lateral aspect ratio are drastically destabilized by increasing the cavity lateral dimension. This yields a 3D fluid motion with a much more complex flow pattern and the usually considered 2D parallel flow model cannot be applied.

  10. Numerical Modeling of One-Dimensional Steady-State Flow and Contaminant Transport in a Horizontally Heterogeneous Unconfined Aquifer with an Uneven Base

    EPA Science Inventory

    Algorithms and a short description of the D1_Flow program for numerical modeling of one-dimensional steady-state flow in horizontally heterogeneous aquifers with uneven sloping bases are presented. The algorithms are based on the Dupuit-Forchheimer approximations. The program per...

  11. Influence of intra-event-based flood regime on sediment flow behavior from a typical agro-catchment of the Chinese Loess Plateau

    NASA Astrophysics Data System (ADS)

    Zhang, Le-Tao; Li, Zhan-Bin; Wang, He; Xiao, Jun-Bo

    2016-07-01

    The pluvial erosion process is significantly affected by tempo-spatial patterns of flood flows. However, despite their importance, only a few studies have investigated the sediment flow behavior that is driven by different flood regimes. The study aims to investigate the effect of intra-event-based flood regimes on the dynamics of sediment exports at Tuanshangou catchment, a typical agricultural catchment (unmanaged) in the hilly loess region on the Chinese Loess Plateau. Measurements of 193 flood events and 158 sediment-producing events were collected from Tuanshangou station between 1961 and 1969. The combined methods of hierarchical clustering approach, discriminant analysis and One-Way ANOVA were used to classify the flood events in terms of their event-based flood characteristics, including flood duration, peak discharge, and event flood runoff depth. The 193 flood events were classified into five regimes, and the mean statistical features of each regime significantly differed. Regime A includes flood events with the shortest duration (76 min), minimum flood crest (0.045 m s-1), least runoff depth (0.2 mm), and highest frequency. Regime B includes flood events with a medium duration (274 min), medium flood crest (0.206 m s-1), and minor runoff depth (0.7 mm). Regime C includes flood events with the longest duration (822 min), medium flood crest (0.236 m s-1), and medium runoff depth (1.7 mm). Regime D includes flood events with a medium duration (239 min), large flood crest (4.21 m s-1), and large runoff depth (10 mm). Regime E includes flood events with a medium duration (304 min), maximum flood crest (8.62 m s-1), and largest runoff depth (25.9 mm). The sediment yield by different flood regimes is ranked as follows: Regime E > Regime D > Regime B > Regime C > Regime A. In terms of event-based average and maximum suspended sediment concentration, these regimes are ordered as follows: Regime E > Regime D > Regime C > Regime B > Regime A. Regimes D and E

  12. Implication for horizontally-elongated fluid flow inferred from heat flow measurements in the Iheya-North hydrothermal field, Okinawa Trough back-arc basin

    NASA Astrophysics Data System (ADS)

    Masaki, Yuka; Kinoshita, Masataka; Kawada, Yoshifumi

    2010-05-01

    The Okinawa Trough is a back-arc basin located in the southwestern part of Japan. It is considered to be in the initial stage of rifting of continental crust, and the activity generates volcanic edifices in this area, accompanied by hydrothermal circulation. The Iheya-North is one of the most active hydrothermal fields among them. As a proposed drilling site for the Integrated ocean Drilling Program, extensive geophysical surveys have been carried out including single-channel seismic imaging, and precise side-scan sonar imaging by using autonomous underwater vehicle 'Urashima' of Japan Agency for Marine-Science and Technology. In the recent few years, we have measured heat flow in and around the Iheya-North hydrothermal field to understand the spatial of hydrothermal circulation in detail. 78 measurements show that heat flow is higher than 10 W/m2 with in 0.5 km of the hydrothermal vent complex, that it gradually decrease eastward to < 1 W/m2, and that very low heat flow around 0.01 W/m2 is observed at 1.5 km east from the hydrothermal field. The average heat flow outside of Iheya-North is ~0.1 W/m2. The low heat flow to the east is most likely caused by an inward flow of seawater into the formation. Seismic and side-scan sonar images as well as piston core samples suggest an impermeable sediment layer to a few hundreds meters below the seafloor in this area. This sediment layer should work as a hydrological barrier to suppress flow through the seafloor, whereas seawater can penetrate into the formation at 1.5 km east of the hydrothermal field, where sidescan images suggest coars sediments on the seafloor. We infer that the hydrothermal circulation within the Iheya-North involves one with a horizontally-elongated scale (~1.5 km horizontal vs. ~a few hundreds meters vertical). We performed numerical calculations of fluid flow and heat transportation to give constraints on the depth of hydrothermal circulation, the magnitude of darcy velocity, and the permeability at

  13. Letter Report: Borehole Flow and Horizontal Hydraulic Conductivity with Depth at Well ER-12-3

    SciTech Connect

    P. Oberlander; C. Russell

    2005-09-01

    Borehole flow and fluid temperature during pumping were measured at well ER-12-3 at the Nevada Test Site in Nye County, Nevada. This well was constructed to characterize the carbonate aquifer. The well is cased from land surface to the total depth at 1,487 m (4,880 ft) below ground surface (bgs). Slotted screen is placed in an upper screened section from 1,095 to 1,160 m bgs (3,591 to 3,805 ft bgs) and in the lower screened section from 1,278 to 1,474 m bgs (4,191 to 4,834 ft bgs). Borehole flow velocity (LT-1) with depth was measured with an impeller flowmeter from the top of the screened section to the maximum accessible depth while the well was pumped and under ambient conditions. A complicating factor to data interpretation is that the well was not filter packed and there is significant upward and downward vertical flow in the open annulus under ambient and pumping conditions. The open annulus and large vertical flow velocities in the well casing result in the measured borehole flow rates being potentially highly nonrepresentative of conditions in the aquifer. Hydraulic conductivities calculated under these conditions would require unsupportable assumptions and would be subject to very large uncertainties. Borehole hydraulic conductivities are not presented under these conditions.

  14. Effect of the inlet outlet positions on the hydraulic performance of horizontal subsurface-flow wetlands constructed with heterogeneous porous media

    NASA Astrophysics Data System (ADS)

    Suliman, F.; Futsaether, C.; Oxaal, U.; Haugen, L. E.; Jenssen, P.

    2006-09-01

    Effects of the inlet and outlet position on flow patterns of saturated fluids in a horizontal subsurface-flow constructed wetland were investigated experimentally using a quasi two-dimensional flow cell representing a vertical cross-section in the longitudinal direction of the wetland. The filter medium consisted of glass beads that were either uniformly sized or a mixture of sizes with a distribution corresponding to wetland filter media. Flow through the filter bed was visualized by injecting dyed fluid into the water-saturated model. Next, breakthrough curves were obtained using chloride tracer. Flow through the homogeneous filter formed by uniformly sized beads displayed a clear density-driven component. Using mixed sizes, finer and coarser beads tended to separate into alternating and incomplete layers. Flow occurred preferentially along roughly horizontal high-conductivity paths of coarser filter material. Density-driven vertical flow was much slower than the horizontal flow. Nevertheless, appropriate positioning of the inlet and less importantly the outlet could to some extent mitigate the dominant effect of the medium stratification on the flow patterns. Using inlet-outlet configurations that forced the flow through larger portions of the filter bed by injecting into low-conductivity layers and opposing the gravity-driven flow increased the treatment efficiency.

  15. Circumventing Imprecise Geometric Information and Development of a Unified Modeling Technique for Various Flow Regimes in Capillary Tubes

    NASA Astrophysics Data System (ADS)

    Abbasi, Bahman

    2012-11-01

    Owing to their manufacturability and reliability, capillary tubes are the most common expansion devices in household refrigerators. Therefore, investigating flow properties in the capillary tubes is of immense appeal in the said business. The models to predict pressure drop in two-phase internal flows invariably rely upon highly precise geometric information. The manner in which capillary tubes are manufactured makes them highly susceptible to geometric imprecisions, which renders geometry-based models unreliable to the point of obsoleteness. Aware of the issue, manufacturers categorize capillary tubes based on Nitrogen flow rate through them. This categorization method presents an opportunity to substitute geometric details with Nitrogen flow data as the basis for customized models. The simulation tools developed by implementation of this technique have the singular advantage of being applicable across flow regimes. Thus the error-prone process of identifying compatible correlations is eliminated. Equally importantly, compressibility and chocking effects can be incorporated in the same model. The outcome is a standalone correlation that provides accurate predictions, regardless of any particular fluid or flow regime. Thereby, exploratory investigations for capillary tube design and optimization are greatly simplified. Bahman Abbasi, Ph.D., is Lead Advanced Systems Engineer at General Electric Appliances in Louisville, KY. He conducts research projects across disciplines in the household refrigeration industry.

  16. Restoring a flow regime through the coordinated operation of a multireservoir system: The case of the Zambezi River basin

    NASA Astrophysics Data System (ADS)

    Tilmant, A.; Beevers, L.; Muyunda, B.

    2010-07-01

    Large storage facilities in hydropower-dominated river basins have traditionally been designed and managed to maximize revenues from energy generation. In an attempt to mitigate the externalities downstream due to a reduction in flow fluctuation, minimum flow requirements have been imposed to reservoir operators. However, it is now recognized that a varying flow regime including flow pulses provides the best conditions for many aquatic ecosystems. This paper presents a methodology to derive a trade-off relationship between hydropower generation and ecological preservation in a system with multiple reservoirs and stochastic inflows. Instead of imposing minimum flow requirements, the method brings more flexibility to the allocation process by building upon environmental valuation studies to derive simple demand curves for environmental goods and services, which are then used in a reservoir optimization model together with the demand for energy. The objective here is not to put precise monetary values on environmental flows but to see the marginal changes in release policies should those values be considered. After selecting appropriate risk indicators for hydropower generation and ecological preservation, the trade-off curve provides a concise way of exploring the extent to which one of the objectives must be sacrificed in order to achieve more of the other. The methodology is illustrated with the Zambezi River basin where large man-made reservoirs have disrupted the hydrological regime.

  17. Classification of Unsteady Flow Patterns in a Rotodynamic Blood Pump: Introduction of Non-Dimensional Regime Map.

    PubMed

    Shu, Fangjun; Vandenberghe, Stijn; Brackett, Jaclyn; Antaki, James F

    2015-09-01

    Rotodynamic blood pumps (also known as rotary or continuous flow blood pumps) are commonly evaluated in vitro under steady flow conditions. However, when these devices are used clinically as ventricular assist devices (VADs), the flow is pulsatile due to the contribution of the native heart. This study investigated the influence of this unsteady flow upon the internal hemodynamics of a centrifugal blood pump. The flow field within the median axial plane of the flow path was visualized with particle image velocimetry (PIV) using a transparent replica of the Levacor VAD. The replica was inserted in a dynamic cardiovascular simulator that synchronized the image acquisition to the cardiac cycle. As compared to steady flow, pulsatile conditions produced periodic, transient recirculation regions within the impeller and separation in the outlet diffuser. Dimensional analysis revealed that the flow characteristics could be uniquely described by the non-dimensional flow coefficient (Φ) and its time derivative ([Formula: see text]), thereby eliminating impeller speed from the experimental matrix. Four regimes within the Φ-[Formula: see text] plane were found to classify the flow patterns, well-attached or disturbed. These results and methods can be generalized to provide insights for both design and operation of rotodynamic blood pumps for safety and efficacy. PMID:26577357

  18. Determination of cooling air mass flow for a horizontally-opposed aircraft engine installation

    NASA Technical Reports Server (NTRS)

    Miley, S. J.; Cross, E. J., Jr.; Ghomi, N. A.; Bridges, P. D.

    1979-01-01

    The relationship between the amount of cooling air flow and the corresponding flow pressure difference across an aircraft engine was investigated in flight and on the ground. The flight test results were consistent with theory, but indicated a significant installation leakage problem. A ground test blower system was used to identify and reduce the leakage. The correlation between ground test cell determined engine orifice characteristics and flight measurements showed good agreement if the engine pressure difference was based on total pressure rather than static pressure.

  19. Prediction of horizontal gas-solid flows under different gravitational fields

    NASA Astrophysics Data System (ADS)

    Laín, Santiago; Sommerfeld, Martin

    2014-11-01

    In this paper the performance of horizontal pneumatic conveying under different gravity environments is evaluated. An Euler-Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux, mean conveying and fluctuating velocities in terrestrial, lunar and micro-gravity conditions. Gravity reduced computations predict a reduction in the global particle-wall collision frequency. Also, in the case of low wall roughness and small particle mass loading, reduction of gravity acceleration implies an increase of particle-wall collision frequency with the upper wall of the channel affecting greatly the particle mass flux profile. In the case of high wall roughness and/or high particle-to-fluid mass loading (i.e., around 1.0) particle conveying characteristics are similar in the three gravity conditions evaluated. This is due to the fact that both, wall roughness and inter-particle collisions reduce gravitational settling. However, the influence of gravity on the additional pressure loss along the channel due to the conveying of the particles is much reduced.

  20. Cuttings-liquid frictional pressure loss model for horizontal narrow annular flow with rotating drillpipe

    NASA Astrophysics Data System (ADS)

    Ofei, T. N.; Irawan, S.; Pao, W.

    2015-04-01

    During oil and gas drilling operations, frictional pressure loss is experienced as the drilling fluid transports the drilled cuttings from the bottom-hole, through the annulus, to the surface. Estimation of these pressure losses is critical when designing the drilling hydraulic program. Two-phase frictional pressure loss in the annulus is very difficult to predict, and even more complex when there is drillpipe rotation. Accurate prediction will ensure that the correct equivalent circulating density (ECD) is applied in the wellbore to prevent formation fracture, especially in formations with narrow window between the pore pressure and fracture gradient. Few researchers have attempted to propose cuttings-liquid frictional pressure loss models, nevertheless, these models fail when they are applied to narrow wellbores such as in casing- while-drilling and slimhole applications. This study proposes improved cuttings-liquid frictional pressure loss models for narrow horizontal annuli with drillpipe rotation using Dimensional Analysis. Both Newtonian and non-Newtonian fluids were considered. The proposed model constants were fitted by generated data from a full-scale simulation study using ANSYS-CFX. The models showed improvement over existing cuttings-liquid pressure loss correlations in literature.

  1. Free-surface flow in horizontally rotating cylinder: experiment and simulation

    NASA Astrophysics Data System (ADS)

    Bohacek, J.; Kharicha, A.; Ludwig, A.; Wu, M.; Paar, A.; Brandner, M.; Elizondo, L.; Trickl, T.

    2016-07-01

    The horizontal centrifugal casting process targets on a liquid layer with a uniform thickness. To achieve this, the rotations of the mold have to be large enough so that the liquid can pick up the speed of the mold. In the present paper, an experiment was conducted using a laboratory plexi-glass mold with water as a working fluid. Starting with an initial volume fraction of liquid resting in the bottom of the mold, the mold rotations were gradually increased from 0 rpm to max rpm and a new position of the contact line was recorded. In addition, first critical rpm was recorded, at which the transition from the liquid pool to a uniform liquid layer occurred. While gradually going back from max rpm to 0 rpm, second critical rpm was recorded, at which the uniform liquid layer collapsed. The experiment was compared with the numerical simulation solving the modified shallow water equations using the Newton-Raphson method with the Wallington filter.

  2. Flow in horizontally anisotropic multilayered aquifer systems with leaky wells and aquitards

    EPA Science Inventory

    Flow problems in an anisotropic domain can be transformed into ones in an equivalent isotropic domain by coordinate transformations. Once analytical solutions are obtained for the equivalent isotropic domain, they can be back transformed to the original anisotropic domain. The ex...

  3. Letter Report: Borehole Flow and Horizontal Hydraulic Conductivity with Depth at Well ER-12-4

    SciTech Connect

    Phil L. Oberlander; Charles E. Russell

    2005-12-31

    Borehole flow and fluid temperature during pumping were measured at well ER-12-4 at the Nevada Test Site in Nye County, Nevada. This well was constructed to characterize the carbonate aquifer. The well is cased from land surface to the total depth at 1,132 m (3,713 ft bgs) below ground surface (bgs). The screened section of the well consists of alternating sections of slotted well screen and blank casing from 948 to 1,132 m bgs (3,111 to 3,713 ft bgs). Borehole flow velocity (LT-1) with depth was measured with an impeller flowmeter from the top of the screened section to the maximum accessible depth while the well was pumped and under ambient conditions. A complicating factor to data interpretation is that the well was not filter packed and there is upward and downward vertical flow in the open annulus under ambient and pumping conditions. The open annulus in the well casing likely causes the calculated borehole flow rates being highly nonrepresentative of inflow from the formation. Hydraulic conductivities calculated under these conditions would require unsupportable assumptions and would be subject to very large uncertainties. Borehole hydraulic conductivities are not presented under these conditions.

  4. Tracing Nitrate Contributions to Streams During Varying Flow Regimes at the Sleepers River Research Watershed, Vermont, USA

    NASA Astrophysics Data System (ADS)

    Sebestyen, S. D.; Shanley, J. B.; Boyer, E. W.; Ohte, N.; Doctor, D. H.; Kendall, C.

    2003-12-01

    Quantifying sources and transformations of nitrate in headwater catchments is fundamental to understanding the movement of nitrogen to streams. At the Sleepers River Research Watershed in northeastern Vermont (USA), we are using multiple chemical tracer and mixing model approaches to quantify sources and transport of nitrate to streams under varying flow regimes. We sampled streams, lysimeters, and wells at nested locations from the headwaters to the outlet of the 41 ha W-9 watershed under the entire range of flow regimes observed throughout 2002-2003, including baseflow and multiple events (stormflow and snowmelt). Our results suggest that nitrogen sources, and consequently stream nitrate concentrations, are rapidly regenerated during several weeks of baseflow and nitrogen is flushed from the watershed by stormflow events that follow baseflow periods. Both basic chemistry data (anions, cations, & dissolved organic carbon) and isotopic data (nitrate, dissolved organic carbon, and dissolved inorganic carbon) indicate that nitrogen source contributions vary depending upon the extent of saturation in the watershed, the initiation of shallow subsurface water inputs, and other hydrological processes. Stream nitrate concentrations typically peak with discharge and are higher on the falling than the rising limb of the hydrograph. Our data also indicate the importance of terrestrial and aquatic biogeochemical processes, in addition to hydrological connectivity in controlling how nitrate moves from the terrestrial landscape to streams. Our detailed sampling data from multiple flow regimes are helping to identify and quantify the "hot spots" and "hot moments" of biogeochemical and hydrological processes that control nitrogen fluxes in streams.

  5. Image processing analysis on the air-water slug two-phase flow in a horizontal pipe

    NASA Astrophysics Data System (ADS)

    Dinaryanto, Okto; Widyatama, Arif; Majid, Akmal Irfan; Deendarlianto, Indarto

    2016-06-01

    Slug flow is a part of intermittent flow which is avoided in industrial application because of its irregularity and high pressure fluctuation. Those characteristics cause some problems such as internal corrosion and the damage of the pipeline construction. In order to understand the slug characteristics, some of the measurement techniques can be applied such as wire-mesh sensors, CECM, and high speed camera. The present study was aimed to determine slug characteristics by using image processing techniques. Experiment has been carried out in 26 mm i.d. acrylic horizontal pipe with 9 m long. Air-water flow was recorded 5 m from the air-water mixer using high speed video camera. Each of image sequence was processed using MATLAB. There are some steps including image complement, background subtraction, and image filtering that used in this algorithm to produce binary images. Special treatments also were applied to reduce the disturbance effect of dispersed bubble around the bubble. Furthermore, binary images were used to describe bubble contour and calculate slug parameter such as gas slug length, gas slug velocity, and slug frequency. As a result the effect of superficial gas velocity and superficial liquid velocity on the fundamental parameters can be understood. After comparing the results to the previous experimental results, the image processing techniques is a useful and potential technique to explain the slug characteristics.

  6. Flow structure in the near wake of a horizontal axis marine current turbine under steady and unsteady inflow conditions

    NASA Astrophysics Data System (ADS)

    Luznik, Luksa; Lust, Ethan; Flack, Karen

    2015-11-01

    Near wake flow field results are presented for a 1/25 scale, 0.8 m diameter (D) two bladed horizontal axis tidal turbine. The 2D PIV measurements were obtained in the USNA 380 ft tow tank for two inflow conditions. The first case had steady inflow conditions, i.e. the turbine was towed at a constant carriage speed (Utow = 1.68 m/s) and the second case had a constant carriage speed and incoming regular waves with a period of 2.3 seconds and 0.18 m wave height. The underwater PIV system is comprised of two submersible housings with forward looking submersible containing laser sheet forming optics, and the side looking submersible includes a camera and remote focus/aperture electronics. The resulting individual field of view for this experiment was nominally 30x30 cm2. Near wake mapping is accomplished by ``tiling'' individual fields of view with approximately 5 cm overlap. All measurements were performed at the nominal tip speed ratio (TSR) of 7. The mapping is accomplished in a vertical streamwise plane (x-z plane) centered on the turbine nacelle and the image pair captures were phase locked to two phases: reference blade horizontal and reference blade vertical. Results presented include distribution of mean velocities, Reynolds stresses, 2D turbulent kinetic energy. The discussion will focus on comparisons between steady and unsteady case. Further discussion will include comparisons between the current high resolution PIV measurements and the previous point measurements with the same turbine at different lateral planes in the same flow conditions.

  7. Some spectral and pulsation characteristics of the horizontal flow of a gas-liquid suspension

    NASA Astrophysics Data System (ADS)

    Krokovnyi, P. M.

    1980-02-01

    In the experiments described, the turbulence characteristics of a two-phase gas-liquid pipe flow were studied, using a 6 m long, 19-mm-diam tube. The inlet temperature of the suspension was maintained at 25 C. The friction energy spectra and the relative intensity of the friction pulsations were measured. The spectral and pulsation characteristics were obtained by an electrodiffusion technique which provided reliable data on the pulsations of the wall shear stress.

  8. The Numerical Simulation of Liquid-Vapor Stratified Flow in Horizontal Metal-Foam Tubes.

    PubMed

    Wang, Jingxuan; Wang, Yueshe; Chen, Zhengwei; Chen, Kaituo; Li, Bing

    2015-04-01

    In this paper, a boiling stratified flow model in a metal-foam tube is proposed. First, based on Branuer non-equilibrium gas-liquid interface model, a force balance on the gas-liquid interface in metal-foam is calculated. The shape of the interface of upper gas phase and lower liquid phase in metal foam tube is obtained. As for the lower liquid phase, the energy conservation equations of liquid and metal foam are formulated, which account for porosity and fiber diameter of foam on the basis of non-local thermal equilibrium model (NTEM), respectively. Therefore, a profile of temperature difference between liquid and metal foam can be obtained. For the upper gas phase, an empirical correlation developed by other researchers is utilized to obtain temperature difference between gas phase and solid wall. In addition, the variation of the Reynolds number with increasing mass quality along the flow direction is acquired. Ultimately, an average circumference heat transfer coefficient is calculated. The results of circumference heat transfer coefficient agree well with available experimental data, showing the prediction of the proposed stratified flow model is feasible. The reason resulting in discrepancies between the prediction and experiment data is also illustrated. PMID:26353555

  9. Effects of climate change on three flow regime-related ecosystem services in a highly-regulated Alpine river

    NASA Astrophysics Data System (ADS)

    Carolli, Mauro; Zolezzi, Guido; Geneletti, Davide; Majone, Bruno; Bellin, Alberto

    2016-04-01

    River systems provide several flow regime-related ecosystem services (ES) to society. The flow regime of several Alpine rivers is often regulated by hydropower production, which represents one of the most relevant ES in the area. Climate change is expected to modify the flow regime of rivers, with possible relevant consequences on the suitability of related ES. In this work we applied an approach aimed at evaluating the variations of ES under different flow regime conditions and consequently, the possibility to quantify the effects of different climate change scenarios on river ecosystem services. The case-study is the Noce River, a gravel-bed river in the Italian Alps (Trentino, North East Italy) which hydrological regime is subject to daily alterations of flow regime (hydropeaking) induced by the management of large hydropower plants. Here we considered three ES indicators: habitat for adult marble trout as representative for habitat provisioning service, rafting for recreational services, and small hydropower production as provisioning service. In particular, we evaluated the daily variations of these indicators under three different operating scenarios: a reference scenarios (REF, from 1970 to 2000) and two future scenarios (from 2040 to 2070), with (FUT) and without (FUT CC) the inclusion of the required minimum environmental flow (minimum vital flow) recently implemented in the regional water resources policy. For each scenario, four climate models have been applied (see Majone et al., 2016). Future scenarios indicate a modification of the flow regime, with a direct effect on the suitability of related ES. The effects on ES differ according with climate models and management scenarios: as a general result and considering the comparison with respect to the reference period, the applied models predict a temporal shift from late to early summer in the rafting suitability, a decrease of the suitability for trout in spring months and an increase of the suitability

  10. Horizontal drilling developments

    SciTech Connect

    Gust, D.

    1997-05-01

    The advantages of horizontal drilling are discussed. Use of horizontal drilling has climbed in the past half decade as technology and familiarity offset higher costs with higher production rates and greater recoveries from new and existing wells. In essence, all types of horizontal wells expose a larger section of the reservoir to the wellbore with a resulting increase in flow rates. (A horizontal well may also be drilled to provide coning control or to intersect vertical fractures.) Thus, drilling horizontally, both onshore and offshore, reduces the number of wells necessary to develop a field.

  11. Numerical modeling of the conditions for realization of flow regimes in supersonic axisymmetric conical inlets of internal compression

    NASA Astrophysics Data System (ADS)

    Gounko, Yu. P.; Mazhul, I. I.

    2015-09-01

    The results of the numerical investigation of flow regimes in the axisymmetric inlets of internal compression at a supersonic flow around them are presented in the work. The main attention is paid to the determination of the ranges of the duct geometric convergence, in which a supersonic inflow in the inlet realizes. The investigation has been carried out at high supersonic freestream velocities corresponding to the Mach numbers M = 2-8 by the example of the frontal conical (funnel-shaped) inlets with the angles of the internal cone wall inclination δ w = 7.5-15° under the variation of the relative area of the throat cross section. The flow structure alteration was studied and the critical relative areas of the inlet throat were determined, at which either there is no starting of the inlet in the process of flow steadying at the initial subsonic flow in it or a flow breakdown occurs in the process of flow steadying at an initial supersonic inflow. Numerical computations of the axisymmetric flow were done on the basis of the solution of the Navier-Stokes equations and the k-ω SST turbulence model.

  12. The removal of nutrients from plant nursery irrigation runoff in subsurface horizontal-flow wetlands.

    PubMed

    Headley, T R; Huett, D O; Davison, L

    2001-01-01

    In New South Wales (NSW) Australia, the recent introduction of legislation to control runoff and charge for water used in agricultural production has encouraged commercial plant nurseries to collect and recycle their irrigation drainage. Runoff from a nursery typically contains around 6 mg/L TN (> 70% as NO3), 0.5 mg/L TP (> 50% as P04), and virtually no organic matter (BOD < 5 mg/L; DOC < 20 mg/L). As a result, algal blooms frequently occur in storage dams. This paper describes a study evaluating the effectiveness of subsurface flow wetlands in the removal of nutrients from nursery runoff on the sub-tropical northern coast of NSW, Australia. Four experimental subsurface flow wetlands (1 m x 4 m x 0.5 m water depth) were planted with Phragmites australis in April 1999. TN and TP load removals were > 84% and > 65% respectively at HRTs of between 5 and 2 days, with the majority of out-flowing TN and TP being organic in form. Internal generation of organic N and P resulted in persistent background levels of 0.45 mg/L TN and 0.15 mg/L TP in the reed bed effluent. TN, NH4 and TP removal was affected by HRT (P < 0.05). Greater than 90% load removal of NH4, NO2, NO3 and Ortho-P was achieved at all HRTs, with outlet concentrations generally < 0.01 mg/L for all. For TN, a strong relationship existed between removal rate (g/m2/day) and loading rate (r2 = 0.995), while a weaker relationship existed for TP (r2 = 0.47). It is estimated that a 1 ha nursery would require a reed bed area of 200 m2 for a 2 day HRT. PMID:11804161

  13. New flow boiling heat transfer model for hydrocarbons evaporating inside horizontal tubes

    SciTech Connect

    Chen, G. F.; Gong, M. Q.; Wu, J. F.; Zou, X.; Wang, S.

    2014-01-29

    Hydrocarbons have high thermodynamic performances, belong to the group of natural refrigerants, and they are the main components in mixture Joule-Thomson low temperature refrigerators (MJTR). New evaluations of nucleate boiling contribution and nucleate boiling suppression factor in flow boiling heat transfer have been proposed for hydrocarbons. A forced convection heat transfer enhancement factor correlation incorporating liquid velocity has also been proposed. In addition, the comparisons of the new model and other classic models were made to evaluate its accuracy in heat transfer prediction.

  14. Prediction of light aircraft horizontal tail onset flows: A review and analysis

    NASA Technical Reports Server (NTRS)

    Summey, D. C.; Smetana, F. O.

    1977-01-01

    The theoretical basis of the two computer programs (WASH and WAKE) are developed. WASH calculates the location of wake-sheet streamlines behind the wing, and upwash and downwash angles ahead of and behind the wing, respectively. WAKE computes two-dimensional velocity profiles along the wake streamlines given the upper and lower surface velocity profiles at the wing trailing edge. Comparisons with experiment indicate good agreement for wake location, downwash angles, and two-dimensional velocity profiles at low to moderate angles of attack. The adaptation of the results of the two programs to predict the total onset flow at the tail is discussed.

  15. Detailed predictions of climate induced changes in the thermal and flow regimes in mountain streams of the Iberian Peninsula

    NASA Astrophysics Data System (ADS)

    Santiago, José M.; Muñoz-Mas, Rafael; García de Jalón, Diego; Solana, Joaquín; Alonso, Carlos; Martínez-Capel, Francisco; Ribalaygua, Jaime; Pórtoles, Javier; Monjo, Robert

    2016-04-01

    Streamflow and temperature regimes are well-known to influence on the availability of suitable physical habitat for instream biological communities. General Circulation Models (GCMs) have predicted significant changes in timing and geographic distribution of precipitation and atmospheric temperature for the ongoing century. However, differences in these predictions may arise when focusing on different spatial and temporal scales. Therefore, to perform substantiated mitigation and management actions detailed scales are necessary to adequately forecast the consequent thermal and flow regimes. Regional predictions are relatively abundant but detailed ones, both spatially and temporally, are still scarce. The present study aimed at predicting the effects of climate change on the thermal and flow regime in the Iberian Peninsula, refining the resolution of previous studies. For this purpose, the study encompassed 28 sites at eight different mountain rivers and streams in the central part of the Iberian Peninsula (Spain). The daily flow was modelled using different daily, monthly and quarterly lags of the historical precipitation and temperature time series. These precipitation-runoff models were developed by means of M5 model trees. On the other hand water temperature was modelled at similar time scale by means of nonlinear regression from dedicated site-specific data. The developed models were used to simulate the temperature and flow regime under two Representative Concentration Pathway (RCPs) climate change scenarios (RCP 4.5 and RCP 8.5) until the end of the present century by considering nine different GCMs, which were pertinently downscaled. The precipitation-runoff models achieved high accuracy (NSE>0.7), especially in regards of the low flows of the historical series. Results concomitantly forecasted flow reductions between 7 and 17 % (RCP4.5) and between 8 and 49% (RCP8.5) of the annual average in the most cases, being variable the magnitude and timing at each

  16. Subcooled flow film boiling across a horizontal cylinder. Part II. Comparison to experimental data

    SciTech Connect

    Chou, X.S.; Sankaran, S.; Witte, L.C. )

    1995-02-01

    In this paper, the results of a rigorous heat transfer analysis of subcooled flow film boiling over a heated cylinder are compared to experimental data. The analysis includes both the influence of the front part of the heater and the wake region behind the heater. Experiments using Freon-113 were conducted at subcooling levels up to 58[degree]C and at velocities up to 3.81 m/s. The configuration was upflowing Freon-113 in crossflow over a 0.635-cm electric heater. A comparison of these data as well as other available experimental data to the analysis of Chou and Witte showed good agreement as long as the subcooling level of the liquid was substantial - that is, for liquid Jakob numbers above about 0.04. This represents a considerable improvement over other models that have been developed to predict subcooled flow boiling heat transfer. A method using a temperature correction to a constant-property heat transfer solution that corresponds to the full variable-property solution is also presented, and applied to water and Freon-113. 11 refs., 5 figs., 2 tabs.

  17. Cluster Regime—The New Regime Of Flowing Of Gas-Liquid Mixture In Vertical Columns (Based On Experimental Data)

    NASA Astrophysics Data System (ADS)

    Ozerov, A. Yu.

    2010-03-01

    For the revealing of the reasons of occurrence of discrete volcanic explosions of basalt magma the Complex Apparatus for Modeling Basaltic Eruptions (CAMBE) has been developed. It consists of two major systems—modeling and recording. The device is 18 meters high. During experiments gas-saturated model liquid acts from the saturator to the vertical transparent hose in which arising two-phase structures and its kinetics are studied. The experiments resulted in detecting and describing a new, never before known, mode of gas-liquid two-phase flow in a vertical column—defined here as cluster regime, which is characterized by regular alteration of dense gas bubble clusters separated from each other by the liquid not containing free gas phase. The mechanism of the cluster regime formation is conditioned by the processes of blocking of the hose working section by one big bubble or several smaller ones. It has been demonstrated that liquid, bubble, cluster and slug regime are regularly sequential and present polymorphic modifications of gas-saturated liquids migrating within vertically oriented conduits. Analysis of data on explosions at volcanoes, given the obtained experimental data on the mechanism of this process, allows concluding that realization of cluster or slug regimes in volcanic crater produces basaltic explosions.

  18. Data acquisition and interpretation of horizontal well pressure-transient tests

    SciTech Connect

    Lichtenberger, G.J. )

    1994-02-01

    For both vertical and horizontal wells, pressure-transient testing is a powerful tool for evaluating in-situ reservoir and wellbore parameters that describe the production characteristics of a well. Although many operators use horizontal well technology, many engineers consider pressure-transient testing of horizontal wells impractical and too complex. Experience has shown, however, that with adequate test planning, based on the concept of low regimes and focused on optimizing test conditions, horizontal well testing can be as successful as vertical well testing. Using the concept of flow regimes and drawing on analogies with vertical wells, this paper reviews the pressure-transient behavior of horizontal wells. Practical guidelines are given for planning, executing, and interpreting horizontal well tests. The application of various interpretation techniques is illustrated with field examples.

  19. Influence of channel morphology and flow regime on larval drift of pallid sturgeon in the Lower Missouri River

    USGS Publications Warehouse

    Erwin, Susannah O.; Jacobson, Robert B.

    2015-01-01

    The transition from drifting free embryo to exogenously feeding larvae has been identified as a potential life-stage bottleneck for the endangered Missouri River pallid sturgeon. Previous studies have indicated that river regulation and fragmentation may contribute to the mortality of larval pallid sturgeon by reducing the extent of free-flowing river available to free embryos to complete ontogenetic development. Calculations of total drift distance based on mean velocity, however, do not address the potential for complex channels and flow patterns to increase retention or longitudinal dispersion of free embryos. We use a one-dimensional advection–dispersion model to estimate total drift distance and employ the longitudinal dispersion coefficient as a metric to quantify the tendency towards dispersion or retention of passively drifting larvae. We describe the effects of different styles of channel morphology on larval dispersion and consider the implications of flow regime modifications on retention of free embryos within the Lower Missouri River. The results illustrate the complex interactions of local morphology, engineered structures, and hydraulics that determine patterns of dispersion in riverine environments and inform how changes to channel morphology and flow regime may alter dispersion of drifting organisms.

  20. RELATIONSHIP OF STREAM FLOW REGIME IN THE WESTERN LAKE SUPERIOR BASIN TO WATERSHED TYPE CHARACTERISTICS

    EPA Science Inventory

    To test a conceptual model of nonlinear response of hydrologic regimes to watershed characteristics, we selected 48 second- and third-order study sites on the North and South Shores of western Lake Superior, MN (USA) using a random-stratified design based on hydrogeomorphic regio...

  1. Inspiration of slip effects on electromagnetohydrodynamics (EMHD) nanofluid flow through a horizontal Riga plate

    NASA Astrophysics Data System (ADS)

    Ayub, M.; Abbas, T.; Bhatti, M. M.

    2016-06-01

    The boundary layer flow of nanofluid that is electrically conducting over a Riga plate is considered. The Riga plate is an electromagnetic actuator which comprises a spanwise adjusted cluster of substituting terminal and lasting magnets mounted on a plane surface. The numerical model fuses the Brownian motion and the thermophoresis impacts because of the nanofluid and the Grinberg term for the wall parallel Lorentz force due to the Riga plate in the presence of slip effects. The numerical solution of the problem is presented using the shooting method. The novelties of all the physical parameters such as modified Hartmann number, Richardson number, nanoparticle concentration flux parameter, Prandtl number, Lewis number, thermophoresis parameter, Brownian motion parameter and slip parameter are demonstrated graphically. Numerical values of reduced Nusselt number, Sherwood number are discussed in detail.

  2. Drought-induced changes in flow regimes lead to long-term losses in mussel-provided ecosystem services

    PubMed Central

    Vaughn, Caryn C; Atkinson, Carla L; Julian, Jason P

    2015-01-01

    Extreme hydro-meteorological events such as droughts are becoming more frequent, intense, and persistent. This is particularly true in the south central USA, where rapidly growing urban areas are running out of water and human-engineered water storage and management are leading to broad-scale changes in flow regimes. The Kiamichi River in southeastern Oklahoma, USA, has high fish and freshwater mussel biodiversity. However, water from this rural river is desired by multiple urban areas and other entities. Freshwater mussels are large, long-lived filter feeders that provide important ecosystem services. We ask how observed changes in mussel biomass and community composition resulting from drought-induced changes in flow regimes might lead to changes in river ecosystem services. We sampled mussel communities in this river over a 20-year period that included two severe droughts. We then used laboratory-derived physiological rates and river-wide estimates of species-specific mussel biomass to estimate three aggregate ecosystem services provided by mussels over this time period: biofiltration, nutrient recycling (nitrogen and phosphorus), and nutrient storage (nitrogen, phosphorus, and carbon). Mussel populations declined over 60%, and declines were directly linked to drought-induced changes in flow regimes. All ecosystem services declined over time and mirrored biomass losses. Mussel declines were exacerbated by human water management, which has increased the magnitude and frequency of hydrologic drought in downstream reaches of the river. Freshwater mussels are globally imperiled and declining around the world. Summed across multiple streams and rivers, mussel losses similar to those we document here could have considerable consequences for downstream water quality although lost biofiltration and nutrient retention. While we cannot control the frequency and severity of climatological droughts, water releases from reservoirs could be used to augment stream flows and

  3. Life cycle assessment of vertical and horizontal flow constructed wetlands for wastewater treatment considering nitrogen and carbon greenhouse gas emissions.

    PubMed

    Fuchs, Valerie J; Mihelcic, James R; Gierke, John S

    2011-02-01

    Life cycle assessment (LCA) is used to compare the environmental impacts of vertical flow constructed wetlands (VFCW) and horizontal flow constructed wetlands (HFCW). The LCAs include greenhouse gas (N(2)O, CO(2) and CH(4)) emissions. Baseline constructed wetland designs are compared to different treatment performance scenarios and to conventional wastewater treatment at the materials acquisition, assembly and operation life stages. The LCAs suggest that constructed wetlands have less environmental impact, in terms of resource consumption and greenhouse gas emissions. The VFCW is a less impactful configuration for removing total nitrogen from domestic wastewater. Both wetland designs have negligible impacts on respiratory organics, radiation and ozone. Gaseous emissions, often not included in wastewater LCAs because of lack of data or lack of agreement on impacts, have the largest impact on climate change. Nitrous oxide accounts for the increase in impact on respiratory inorganic, and the combined acidification/eutrophication category. The LCAs were used to assess the importance of nitrogen removal and recycling, and the potential for optimizing nitrogen removal in constructed wetlands.

  4. Evaluation of clogging in planted and unplanted horizontal subsurface flow constructed wetlands: solids accumulation and hydraulic conductivity reduction.

    PubMed

    De Paoli, André Cordeiro; von Sperling, Marcos

    2013-01-01

    This study aimed to evaluate the behaviour of two horizontal subsurface flow constructed wetland units regarding solids build up and clogging of the filter medium. In order to analyse the causes of this process, which is considered the major operational problem of constructed wetlands, studies were carried out to characterize accumulated solids and hydraulic conductivity at specific points of the beds of two wetlands (planted with Typha latifolia and unplanted units) receiving effluent from an upflow anaerobic sludge blanket reactor treating sanitary sewage (population equivalent of 50 inhabitants each unit). The experiments were performed after the units were operating for 2 years and 4 months. This study presents comparative results related to the quantification and characterization of accumulated solids and hydraulic conductivity along the length and width of the filter beds. Approximately 80% of the solids found were inorganic (fixed). Near the inlet end, the rate interstitial solids/attached solids was 5.0, while in the outlet end it was reduced to 1.5. Hydraulic conductivity was lower near the inlet of the units (as expected) and, by comparing the planted wetland with the unplanted, the hydraulic conductivity was lower in the former, resulting in larger undesired surface flow.

  5. Modeling total phosphorus removal in an aquatic environment restoring horizontal subsurface flow constructed wetland based on artificial neural networks.

    PubMed

    Li, Wei; Zhang, Yan; Cui, Lijuan; Zhang, Manyin; Wang, Yifei

    2015-08-01

    A horizontal subsurface flow constructed wetland (HSSF-CW) was designed to improve the water quality of an artificial lake in Beijing Wildlife Rescue and Rehabilitation Center, Beijing, China. Artificial neural networks (ANNs), including multilayer perceptron (MLP) and radial basis function (RBF), were used to model the removal of total phosphorus (TP). Four variables were selected as the input parameters based on the principal component analysis: the influent TP concentration, water temperature, flow rate, and porosity. In order to improve model accuracy, alternative ANNs were developed by incorporating meteorological variables, including precipitation, air humidity, evapotranspiration, solar heat flux, and barometric pressure. A genetic algorithm and cross-validation were used to find the optimal network architectures for the ANNs. Comparison of the observed data and the model predictions indicated that, with careful variable selection, ANNs appeared to be an efficient and robust tool for predicting TP removal in the HSSF-CW. Comparison of the accuracy and efficiency of MLP and RBF for predicting TP removal showed that the RBF with additional meteorological variables produced the most accurate results, indicating a high potentiality for modeling TP removal in the HSSF-CW.

  6. Enhancement of azo dye Acid Orange 7 removal in newly developed horizontal subsurface-flow constructed wetland.

    PubMed

    Tee, Heng-Chong; Lim, Poh-Eng; Seng, Chye-Eng; Mohd Nawi, Mohd Asri; Adnan, Rohana

    2015-01-01

    Horizontal subsurface-flow (HSF) constructed wetland incorporating baffles was developed to facilitate upflow and downflow conditions so that the treatment of pollutants could be achieved under multiple aerobic, anoxic and anaerobic conditions sequentially in the same wetland bed. The performances of the baffled and conventional HSF constructed wetlands, planted and unplanted, in the removal of azo dye Acid Orange 7 (AO7) were compared at the hydraulic retention times (HRT) of 5, 3 and 2 days when treating domestic wastewater spiked with AO7 concentration of 300 mg/L. The planted baffled unit was found to achieve 100%, 83% and 69% AO7 removal against 73%, 46% and 30% for the conventional unit at HRT of 5, 3 and 2 days, respectively. Longer flow path provided by baffled wetland units allowed more contact of the wastewater with the rhizomes, microbes and micro-aerobic zones resulting in relatively higher oxidation reduction potential (ORP) and enhanced performance as kinetic studies revealed faster AO7 biodegradation rate under aerobic condition. In addition, complete mineralization of AO7 was achieved in planted baffled wetland unit due to the availability of a combination of aerobic, anoxic and anaerobic conditions.

  7. Microbial communities from different types of natural wastewater treatment systems: vertical and horizontal flow constructed wetlands and biofilters.

    PubMed

    Adrados, B; Sánchez, O; Arias, C A; Becares, E; Garrido, L; Mas, J; Brix, H; Morató, J

    2014-05-15

    The prokaryotic microbial communities (Bacteria and Archaea) of three different systems operating in Denmark for the treatment of domestic wastewater (horizontal flow constructed wetlands (HFCW), vertical flow constructed wetlands (VFCW) and biofilters (BF)) was analysed using endpoint PCR followed by Denaturing Gradient Gel Electrophoresis (DGGE). Further sequencing of the most representative bacterial bands revealed that diverse and distinct bacterial communities were found in each system unit, being γ-Proteobacteria and Bacteroidetes present mainly in all of them, while Firmicutes was observed in HFCW and BF. Members of the Actinobacteria group, although found in HFCW and VFCW, seemed to be more abundant in BF units. Finally, some representatives of α, β and δ-Proteobacteria, Acidobacteria and Chloroflexi were also retrieved from some samples. On the other hand, a lower archaeal diversity was found in comparison with the bacterial population. Cluster analysis of the DGGE bacterial band patterns showed that community structure was related to the design of the treatment system and the organic matter load, while no clear relation was established between the microbial assemblage and the wastewater influent.

  8. Modeling total phosphorus removal in an aquatic environment restoring horizontal subsurface flow constructed wetland based on artificial neural networks.

    PubMed

    Li, Wei; Zhang, Yan; Cui, Lijuan; Zhang, Manyin; Wang, Yifei

    2015-08-01

    A horizontal subsurface flow constructed wetland (HSSF-CW) was designed to improve the water quality of an artificial lake in Beijing Wildlife Rescue and Rehabilitation Center, Beijing, China. Artificial neural networks (ANNs), including multilayer perceptron (MLP) and radial basis function (RBF), were used to model the removal of total phosphorus (TP). Four variables were selected as the input parameters based on the principal component analysis: the influent TP concentration, water temperature, flow rate, and porosity. In order to improve model accuracy, alternative ANNs were developed by incorporating meteorological variables, including precipitation, air humidity, evapotranspiration, solar heat flux, and barometric pressure. A genetic algorithm and cross-validation were used to find the optimal network architectures for the ANNs. Comparison of the observed data and the model predictions indicated that, with careful variable selection, ANNs appeared to be an efficient and robust tool for predicting TP removal in the HSSF-CW. Comparison of the accuracy and efficiency of MLP and RBF for predicting TP removal showed that the RBF with additional meteorological variables produced the most accurate results, indicating a high potentiality for modeling TP removal in the HSSF-CW. PMID:25903184

  9. Experimental insights into flow impingement in cerebral aneurysm by stereoscopic particle image velocimetry: transition from a laminar regime.

    PubMed

    Yagi, Takanobu; Sato, Ayaka; Shinke, Manabu; Takahashi, Sara; Tobe, Yasutaka; Takao, Hiroyuki; Murayama, Yuichi; Umezu, Mitsuo

    2013-05-01

    This study experimentally investigated the instability of flow impingement in a cerebral aneurysm, which was speculated to promote the degradation of aneurysmal wall. A patient-specific, full-scale and elastic-wall replica of cerebral artery was fabricated from transparent silicone rubber. The geometry of the aneurysm corresponded to that found at 9 days before rupture. The flow in a replica was analysed by quantitative flow visualization (stereoscopic particle image velocimetry) in a three-dimensional, high-resolution and time-resolved manner. The mid-systolic and late-diastolic flows with a Reynolds number of 450 and 230 were compared. The temporal and spatial variations of near-wall velocity at flow impingement delineated its inherent instability at a low Reynolds number. Wall shear stress (WSS) at that site exhibited a combination of temporal fluctuation and spatial divergence. The frequency range of fluctuation was found to exceed significantly that of the heart rate. The high-frequency-fluctuating WSS appeared only during mid-systole and disappeared during late diastole. These results suggested that the flow impingement induced a transition from a laminar regime. This study demonstrated that the hydrodynamic instability of shear layer could not be neglected even at a low Reynolds number. No assumption was found to justify treating the aneurysmal haemodynamics as a fully viscous laminar flow.

  10. Effects of the spring snowmelt recession on abiotic and biotic conditions in northern Sierra Nevada CA rivers with varying flow regimes

    NASA Astrophysics Data System (ADS)

    Yarnell, S. M.; Peek, R.; Viers, J. H.

    2012-12-01

    Recent research has discussed the importance of the spring snowmelt recession in montane environments for driving physical and biological stream processes and supporting the success of native riverine species adapted to its predictability, yet there have been no field-based studies that directly address the relationship between the snowmelt recession and stream ecology. There are a variety of studies that explore the relationship between the flow regime and an individual species, the flow regime and riparian habitat, and flow and sediment movement. However, there are few, if any, studies that attempt to delineate the relationship between recession flows and stream ecology or quantify key characteristics of the flow regime beyond determinations of minimum instream flows or peak magnitudes of geomorphic flows. Regulated flow management issues such as suitable ramping rates to transition from peak flows to baseflow or a suitable duration of flooding that provides the greatest habitat heterogeneity during the ecologically-sensitive spring season have not previously been addressed. In this study, we examined the geomorphic, hydraulic and riparian habitat in relation to aquatic biological diversity at six stream study sites across two basins with varying flow regime types: unimpaired, semi-impaired (regulated-bypass reaches), and fully impaired (regulated-peaking or regulated-augmented reaches). In two very different water year types (2011-wet, 2012-dry), we quantified the variability in the spring flow regime using flow metrics (e.g. daily recession rate, timing) and compared it to variability in abiotic stream conditions (e.g. diversity of hydraulic habitat, diversity of riparian habitat) and diversity of biotic conditions (e.g. algal abundance, EPT index). In addition, we analyzed the relationship between habitat heterogeneity and species diversity across flow regime types in both water years. Results indicate both flow regime and water year type contribute to the

  11. Treatment of landfill leachate using an aerated, horizontal subsurface-flow constructed wetland.

    PubMed

    Nivala, J; Hoos, M B; Cross, C; Wallace, S; Parkin, G

    2007-07-15

    A pilot-scale subsurface-flow constructed wetland was installed at the Jones County Municipal Landfill, near Anamosa, Iowa, in August 1999 to demonstrate the use of constructed wetlands as a viable low-cost treatment option for leachate generated at small landfills. The system was equipped with a patented wetland aeration process to aid in removal of organic matter and ammonia nitrogen. The high iron content of the leachate caused the aeration system to cease 2 years into operation. Upon the installation of a pretreatment chamber for iron removal and a new aeration system, treatment efficiencies dramatically improved. Seasonal performance with and without aeration is reported for 5-day biochemical oxygen demand (BOD(5)), chemical oxygen demand (COD), ammonia nitrogen (NH(4)-N), and nitrate nitrogen (NO(3)-N). Since winter air temperatures in Iowa can be very cold, a layer of mulch insulation was installed on top of the wetland bed to keep the system from freezing. When the insulation layer was properly maintained (either through sufficient litterfall or replenishing the mulch layer), the wetland sustained air temperatures of as low as -26 degrees C without freezing problems.

  12. Visco-elastic effects with simultaneous thermal and mass diffusion in MHD free convection flow near an oscillating plate in the slip flow regime

    NASA Astrophysics Data System (ADS)

    Das, Bandita; Choudhury, Rita

    2016-06-01

    The present study analyzes the influence of visco-elastic flow of fluid through a porous medium bounded by an oscillating porous plate with heat source in the slip flow regime. Effects of heat transfer, mass transfer and chemical reaction are also taken into account. The porous plate is subjected to a transverse suction velocity. The dimensionless governing equations of the problem are solved by regular perturbation technique. The analytical expressions for the velocity, temperature, concentration, and Shearing stress have been obtained and illustrated graphically for different values of physical parameters involved in the problem. The investigation reveals that the visco-elastic fluid has significant effects on the considered flow field in comparison with Newtonian fluid flow phenomenon.

  13. Changes in Bedform Shape at the Transition Between Upper Plane-Bed and Sheet-Flow Bedload Transport Regimes

    NASA Astrophysics Data System (ADS)

    Hernandez Moreira, R. R.; Huffman, B.; Vautin, D.; Viparelli, E.

    2015-12-01

    The interactions between flow hydrodynamics and bedform characteristics at the transition between upper plane-bed bedload transport regime and sheet-flow have not yet been thoroughly described and still remain poorly understood. The present study focuses on the experimental study of this transition in open channel mode. The experiments were performed in the hydraulic laboratory of the Department of Civil and Environmental Engineering of the University of South Carolina in a sediment-feed flume, 9-m long by 19-cm wide with uniform material sediment of geometric mean grain size diameter of 1.11 mm. Sediment feed rates ranged between 0.5 kg/min and 20 kg/min with two different flow rates of 20 l/s and 30 l/s. We recorded periodic measurements of water surface and bed elevation to estimate the global flow parameters, e.g. mean flow velocity and bed shear stress, and to determine when the flow and the sediment transport reached conditions of mobile bed equilibrium. We define mobile bed equilibrium as a condition in which the mean bed elevation does not change in time. At equilibrium, measurements of bed elevation fluctuations were taken with an ultrasonic transducer system at six discrete locations. In the runs with low and medium feed rates, i.e. smaller than ~12 kg/min, the long wavelength and small amplitude bedforms typical of the upper plane bed regime, which were observed in previous experimental work, formed and migrated downstream. In particular, with increasing feed rates, the amplitude of the bedforms decreases and their geometry changes, from well-defined triangular shapes, to rounded shapes to flat bed with very small amplitude, long wavelength undulations. The decrease in amplitude corresponds to a decrease in form drag and an increase in the thickness of the bedload layer. The ultrasonic measurements are analyzed to statistically describe the observed transition in terms of probability distribution functions of the bed elevation fluctuations.

  14. Influence of flow regime and channel morphology on larval drift and dispersion in a large regulated river

    NASA Astrophysics Data System (ADS)

    Erwin, S.; Jacobson, R. B.

    2013-12-01

    Larval drift is a critical phase of ontogenetic development for many species of lotic fishes. Downstream advection and dispersion of passively drifting larvae or eggs is controlled by the complex interaction of flow regime, channel planform, local channel morphology, and the resulting hydraulic gradients. In many regulated rivers, channel engineering and perturbations to the flow regime may disrupt natural drift processes and impact successful recruitment of native fishes. Here we explore the influence of flow regime and channel morphology on the downstream transport, dispersion, and retention of Pallid Sturgeon larvae, an endangered species endemic to the Mississippi River basin and the focus of significant conservation effort on the Missouri River. The transition from drifting free embryo to exogenously feeding larvae has been identified as a potential life stage bottleneck for the Pallid Sturgeon. Previous studies have indicated that river regulation and fragmentation may contribute to mortality of larval Pallid Sturgeon by reducing the extent of free-flowing river required by free embryos to complete the transition to exogenous feeding. Additionally, channelization may have increased the rate at which larvae are advected downstream out of the Missouri River basin. We describe the complex interactions and influence of morphologic and hydraulic factors on larval drift using an extensive library of hydroacoustic data collected along more than 1300 km of the Lower Missouri River. We use a one-dimensional advection-dispersion model to estimate total drift distance and employ the longitudinal dispersion coefficient as a measure to quantify the tendency towards dispersion or retention of passively drifting larvae in geomorphically distinct segments of river. We use a two-dimensional hydrodynamic model to evaluate the sensitivity of drift and dispersion to in-channel navigation structures and flood hydrology. Based on insights gained from the analysis of field data and

  15. Determining the flow regime in a biofilm carrier by means of magnetic resonance imaging.

    PubMed

    Herrling, Maria P; Guthausen, Gisela; Wagner, Michael; Lackner, Susanne; Horn, Harald

    2015-05-01

    Biofilms on cylindrical carrier material originating from a lab-scale moving bed biofilm reactor (MBBR) were investigated by means of Magnetic Resonance Imaging (MRI). The aim of this study was to determine the local flow velocities at the inner face of the biofilm carrier. To get an insight into the mass transport processes, flow velocity maps of blank and with biofilm cultivated carriers were measured. A single carrier was placed in a tube in three different orientations and exposed to flow velocities of 0.21, 0.42, and 0.64 mm/s. The interplay of the biofilm morphology and the local flow pattern was then analyzed including the effect of the orientation of the carrier in relation to the upstream flow angle. Within this study, the biofilm carrier can be understood as an interconnected system of four sections in which the incoming fluid volume will be distributed depending on the biomass occupation and morphology. In sections with high biofilm occupation, the flow resistance is increased. Depending on the orientation of the carrier in the flow field, this effect leads to flow evasion through less covered sections showing higher flow velocities and consequently the risk of biofilm detachment. However, there was no clear correlation between biofilm coverage and flow ratio. PMID:25425488

  16. Determining the flow regime in a biofilm carrier by means of magnetic resonance imaging.

    PubMed

    Herrling, Maria P; Guthausen, Gisela; Wagner, Michael; Lackner, Susanne; Horn, Harald

    2015-05-01

    Biofilms on cylindrical carrier material originating from a lab-scale moving bed biofilm reactor (MBBR) were investigated by means of Magnetic Resonance Imaging (MRI). The aim of this study was to determine the local flow velocities at the inner face of the biofilm carrier. To get an insight into the mass transport processes, flow velocity maps of blank and with biofilm cultivated carriers were measured. A single carrier was placed in a tube in three different orientations and exposed to flow velocities of 0.21, 0.42, and 0.64 mm/s. The interplay of the biofilm morphology and the local flow pattern was then analyzed including the effect of the orientation of the carrier in relation to the upstream flow angle. Within this study, the biofilm carrier can be understood as an interconnected system of four sections in which the incoming fluid volume will be distributed depending on the biomass occupation and morphology. In sections with high biofilm occupation, the flow resistance is increased. Depending on the orientation of the carrier in the flow field, this effect leads to flow evasion through less covered sections showing higher flow velocities and consequently the risk of biofilm detachment. However, there was no clear correlation between biofilm coverage and flow ratio.

  17. An ecological economic assessment of flow regimes in a hydropower dominated river basin: the case of the lower Zambezi River, Mozambique.

    PubMed

    Fanaian, Safa; Graas, Susan; Jiang, Yong; van der Zaag, Pieter

    2015-02-01

    The flow regime of rivers, being an integral part of aquatic ecosystems, provides many important services benefiting humans in catchments. Past water resource developments characterized by river embankments and dams, however, were often dominated by one (or few) economic use(s) of water. This results in a dramatically changed flow regime negatively affecting the provision of other ecosystem services sustained by the river flow. This study is intended to demonstrate the value of alternative flow regimes in a river that is highly modified by the presence of large hydropower dams and reservoirs, explicitly accounting for a broad range of flow-dependent ecosystem services. In this study, we propose a holistic approach for conducting an ecological economic assessment of a river's flow regime. This integrates recent advances in the conceptualization and classification of ecosystem services (UK NEA, 2011) with the flow regime evaluation technique developed by Korsgaard (2006). This integrated approach allows for a systematic comparison of the economic values of alternative flow regimes, including those that are considered beneficial for aquatic ecosystems. As an illustration, we applied this combined approach to the Lower Zambezi Basin, Mozambique. Empirical analysis shows that even though re-operating dams to create environmentally friendly flow regimes reduces hydropower benefits, the gains to goods derived from the aquatic ecosystem may offset the forgone hydropower benefits, thereby increasing the total economic value of river flow to society. The proposed integrated flow assessment approach can be a useful tool for welfare-improving decision-making in managing river basins. PMID:25461048

  18. Mixed convection laminar flow and heat transfer of liquids in horizontal internally finned tubes

    SciTech Connect

    Shome, B.

    1998-01-01

    Energy and material savings, as well as economic incentives, have led to concentrated efforts over the past several decades in the field of heat transfer enhancement to produce more efficient and compact heat exchangers. Internally finned tubes are widely used for heat transfer enhancement, particularly in chemical process and petroleum industries. A finned tube heat exchanger with optimum geometry could offer 35--40% increase in heat duty for equal pumping power and size over a smooth tube heat exchanger or a comparable decrease in the heat exchanger size for a given heat duty. Developing mixed convection flow in internally finned tubes with variable viscosity was numerically investigated for a fin geometry range of 8 {le} N {le} 24, 0.1 {le} H {le} 0.3 and an operating condition range of 50 {le} Pr{sub in} {le} 1,250, 0 {le} Ra{sub in} {le} 10{sup 7}, and 0 {le} q{sub w}d/k{sub in} {le} 2,000. The numerical model was validated by comparison with existing numerical and experimental data. Internal finning was found to produce a complex two-cell, buoyancy-induced vortex structure. The results show that coring (retarded velocity in the interfin region) leads to poor heat transfer performance of tubes with large numbers of fins or with tall fins. The overall results indicated that large enhancement in the heat transfer can be obtained in the entrance region. Furthermore, variable viscosity effects are seen to have a pronounced effect on the friction factor and Nusselt number predictions.

  19. Application of acoustic tomography to reconstruct the horizontal flow velocity field in a shallow river

    NASA Astrophysics Data System (ADS)

    Razaz, Mahdi; Kawanisi, Kiyosi; Kaneko, Arata; Nistor, Ioan

    2015-12-01

    A novel acoustic tomographic measurement system capable of resolving sound travel time in extremely shallow rivers is introduced and the results of an extensive field measurements campaign are presented and further discussed. Acoustic pulses were transmitted over a wide frequency band of 20-35 kHz between eight transducers for about a week in a meandering reach of theBāsen River, Hiroshima, Japan. The purpose of the field experiment was validating the concept of acoustic tomography in rivers for visualizing current fields. The particular novelty of the experiment resides in its unusual tomographic features: subbasin scale (100 m × 270 m) and shallowness (0.5-3.0 m) of the physical domain, frequency of the transmitted acoustic signals (central frequency of 30 kHz), and the use of small sampling intervals (105 s). Inverse techniques with no a priori statistical information were used to estimate the depth-average current velocity components from differential travel times. Zeroth-order Tikhonov regularization, in conjunction with L-curve method deployed to stabilize the solution and to determine the weighting factor appearing in the inverse analysis. Concurrent direct environmental measurements were provided in the form of ADCP readings close to the right and left bank. Very good agreement found between along-channel velocities larger than 0.2 m/s obtained from the two techniques. Inverted quantities were, however, underestimated, perhaps due to vicinity of the ADCPs to the banks and strong effect of river geometry on the readings. In general, comparing the visualized currents with direct nodal measurements illustrate the plausibility of the tomographically reconstructed flow structures.

  20. Analysis of pressure drop characteristics and methods for calculating gas and gas-solid flow in horizontal pipes for dilute coal conveying system

    SciTech Connect

    Weiguo Pan; Zuohe Chi; Yongjing Liao

    1997-07-01

    This article reported pressure drop characteristics and methods for calculating friction factors {lambda} 0 and {lambda}{sub {mu}} for gas and gas-solids flows, respectively, in straight horizontal pipes are summarized advantages seed. The and disadvantages of calculating friction factor {lambda}{sub {mu}} through dimensional analysis in comparison with model simulation are analyzed. It is pointed out that model simulation is more suitable to engineering use than dimensional analysis. According to experimental results of dilute gas-coal powder flow in straight horizontal pipes of the coal pulverization system in a power plant; an empirical formula and a theoretical formula for calculating friction factor {lambda}{sub {mu}} in straight horizontal pipes transporting dilute coal powder are obtained.

  1. Sedimentary structures formed by upper-regime flows on a Pleistocene carbonate ramp (Favignana Calcarenite, Sicily, Italy)

    NASA Astrophysics Data System (ADS)

    Slootman, Arnoud; Moscariello, Andrea; Cartigny, Matthieu; de Boer, Poppe

    2015-04-01

    Antidune, chute-and-pool and cyclic step deposits are found in the outcrops of the Pleistocene calcarenite wedge of Favignana Island. These deposits were formed on a prograding carbonate ramp. Three zones are identified: inner-mid ramp (shoreface), ramp slope, and outer ramp (offshore). The ramp slope dips 3° to 10° and drops 30-40 m over 400-600 m. The ramp slope and outer ramp show a succession of bioturbated dune cross beds with up to 10 m-thick, intercalated event beds containing supercritical-flow structures. Grain sizes range from coarse sand to granules, with large rhodoliths (algal balls) and shells as gravel-sized clasts. It is our aim to provide insight into the processes that create upper-regime flow structures and the hydraulic parameters of their generating flows. During normal storms, wind-driven currents generated submarine dunes that migrated across the sea floor. During exceptional high-energy events (megastorms, tsunamis), large amounts of skeletal debris from the carbonate factory were transported towards the top of the ramp slope, where under the effect of gravity sustained supercritical sediment gravity flows were generated. In a case study of bedform evolution, we present the formation of a large downstream-asymmetric bedform with two antidunes superimposed on its upstream flank. A stepwise flow reconstruction reveals the progressive steepening of the antidunes until critical steepness is reached, and the first and, shortly after, the second antidune wave breaks. The two hydraulic jumps thus formed, developed a temporary cyclic step morphology (i.e. hydraulic jump, accelerating subcritical flow, supercritical chute, hydraulic jump etc.). The bedform geometries are used to reconstruct the nature of the catastrophic events that were active on the ramp slope. The wave length of the antidunes is measured from outcrop, which, through hydraulic equations, allows for estimation of mean flow velocity as a function of sediment concentration in the

  2. Occurrence of phthalate esters in sediments in Qiantang River, China and inference with urbanization and river flow regime.

    PubMed

    Sun, Jianqiang; Huang, Jing; Zhang, Anping; Liu, Weiping; Cheng, Wenwei

    2013-03-15

    Phthalate esters (PAEs), a group of emerging organic contaminants, have become a serious issue arousing much attention for their ubiquitous presence and hazardous impact on the environment. This study provides the first data on distribution of PAEs in the sediments in the Qiantang River, Zhejiang Province, China, and the inference with urbanization and river flow regime. PAEs were detected in all 23 sediment samples analyzed, and the total concentrations of their 16 congeners in sediments ranged from 0.59 to 6.74μg/g dry weight (dw), with the geometric mean value of 2.03μg/g dw. Of the 16 PAE congeners, di-n-butyl phthalate (DnBP), diisobutyl phthalate (DiBP), and di(2-ethylhexyl) phthalate (DEHP) were present in all sediment samples. The PAEs concentrations in urban regions were higher than those in rural regions because of higher discharge of PAEs from plastic materials in urbanized areas. Concentrations of PAEs were positively correlated with sediment organic matter (fOM) and negatively correlated with logistic value of annual average flow volume at sample sites. River flow regime modified by man-made dams significantly affected the distribution of PAEs. Analysis of congener composition of PAEs indicated that the DEHP was predominant congener in the Qiantang River. The normalized concentration of DEHP exceeded recommended environmental risk limit (ERL).

  3. Can Horizontal Hydraulic Fracturing Lead to Less Expensive Achievement of More Natural River Flows?

    NASA Astrophysics Data System (ADS)

    Kern, J.; Characklis, G. W.

    2014-12-01

    order to reduce this financial uncertainty, we propose the use of "collar" agreements between a downstream stakeholder and a third party insurer that would provide a stable price for parties "buying" more natural flows.

  4. THE HYDROLOGIC SYSTEM: GEOMORPHIC AND HYDROGEOLOGIC CONTROLS ON SURFACE AND SUBSURFACE FLOW REGIMES IN RIPARIAN MEADOW ECOSYSTEMS IN THE CENTRAL GREAT BASIN

    EPA Science Inventory

    Riparian corridors in upland watersheds in the Great Basin of central Nevada contain the majority of the region's biodiversity. Water, in both surface and subsurface flow regimes, is an important resource sustaining these sensitive ecosystems and other similar riparian ecosystem...

  5. The use of habitat structure preferenda for establishing flow regimes necessary for maintenance of fish habitat

    USGS Publications Warehouse

    Stalnaker, Clair B.

    1979-01-01

    The pursuit of simplicity in the complex management of instream and out-of-stream water uses very early led to the minimum, or “base,” flow concept and the myth that a consistent methodology could be used to establish the desired minimum flow. Such a single flow value has not proven to be practical. As water becomes fully appropriated to upstream use and storage, the minimum flow, if not violated, tends to become the average condition. This situation is manifest in a flat or stepped but fixed hydrograph throughout the stream reach of concern for much of the year.

  6. Mathematical Analysis of Hall Effect on Transient Hartman Flow about a Rotating Horizontal Permeable Surface in a Porous Medium under Inclined Magnetic Field.

    PubMed

    Suresh, M; Manglik, A

    2014-01-01

    This paper proposes the exact solution for unsteady flow of a viscous incompressible electrically conducting fluid past a impulsively started infinite horizontal surface which is rotating with an angular velocity embedded in a saturated porous medium under the influence of strong magnetic field with hall effect. Our study focuses on the change of direction of the external magnetic field on the flow system which leads to change in the flow behavior and skin frictional forces at the boundary. Systems of flow equations are solved using Laplace transform technique. The impacts of control parameters Hartman number, rotation of the system, hall effect, inclination of the magnetic field, and Darcy number on primary and secondary velocities are shown graphically, skin friction at horizontal boundary in tabular form. For validating our results, in the absence of permeability of the porous medium and inclination of the magnetic field the results are in good agreement with the published results.

  7. Emerging organic contaminant removal depending on primary treatment and operational strategy in horizontal subsurface flow constructed wetlands: influence of redox.

    PubMed

    Avila, Cristina; Reyes, Carolina; Bayona, Josep María; García, Joan

    2013-01-01

    This study aimed at assessing the influence of primary treatment (hydrolytic upflow sludge blanket (HUSB) reactor vs. conventional settling) and operational strategy (alternation of saturated/unsaturated phases vs. permanently saturated) on the removal of various emerging organic contaminants (i.e. ibuprofen, diclofenac, acetaminophen, tonalide, oxybenzone, bisphenol A) in horizontal subsurface flow constructed wetlands. For that purpose, a continuous injection experiment was carried out in an experimental treatment plant for 26 days. The plant had 3 treatment lines: a control line (settler-wetland permanently saturated), a batch line (settler-wetland operated with saturate/unsaturated phases) and an anaerobic line (HUSB reactor-wetland permanently saturated). In each line, wetlands had a surface area of 2.95 m(2), a water depth of 25 cm and a granular medium D(60) = 7.3 mm, and were planted with common reed. During the study period the wetlands were operated at a hydraulic and organic load of 25 mm/d and about 4.7 g BOD/m(2)d, respectively. The injection experiment delivered very robust results that show how the occurrence of higher redox potentials within the wetland bed promotes the elimination of conventional quality parameters as well as emerging microcontaminants. Overall, removal efficiencies were always greater for the batch line than for the control and anaerobic lines, and to this respect statistically significantly differences were found for ibuprofen, diclofenac, oxybenzone and bisphenol A. As an example, ibuprofen, whose major removal mechanism has been reported to be biodegradation under aerobic conditions, showed a higher removal in the batch line (85%) than in the control (63%) and anaerobic (52%) lines. Bisphenol A showed also a great dependence on the redox status of the wetlands, finding an 89% removal rate for the batch line, as opposed to the control and anaerobic lines (79 and 65%, respectively). Furthermore, diclofenac showed a greater

  8. The effect of different flow regimes on the growth and metabolic rates of the scleractinian coral Galaxea fascicularis

    NASA Astrophysics Data System (ADS)

    Schutter, M.; Crocker, J.; Paijmans, A.; Janse, M.; Osinga, R.; Verreth, A. J.; Wijffels, R. H.

    2010-09-01

    To study the effect of water flow on coral growth, four series of ten coral nubbins of Galaxea fascicularis were exposed to four different flow regimes (0, 10, 20, and 25 cm s-1, bidirectional flow) for 42 weeks. Buoyant weight, surface area, and polyp number were measured at regular intervals. Net photosynthesis and dark respiration were measured at the corresponding flow speeds, and daily amount of photosynthetic carbon left for coral growth was calculated. Finally, skeletal density and CN content, chlorophyll concentration and dry weight of coral tissue were determined for each coral. Specific growth rate (in day-1) decreased with time in each flow treatment. Absence of flow resulted in significantly lower growth rates. Average specific growth rate calculated over the entire experiment was not significantly different between 10 and 20 cm s-1, while it was significantly higher at 25 cm s-1. From 10 to 25 cm s-1, average net photosynthetic rate decreased and average dark respiration rate did not change significantly. Scope for growth based on phototrophic carbon decreased with increasing flow. Growth was not positively correlated with either photosynthesis or respiration, or scope for growth. It is suggested that higher flow rates reduce the chance of disturbance of coral growth by competing algae or cyanobacteria, allowing corals to grow more readily with the maximum specific growth rate possible under the given environmental conditions. Notably, other effects of increased flow, such as increased respiratory rates and increased (in)organic nutrient uptake, might have been equally responsible for the increased growth of the corals in 25 cm s-1.

  9. Convection of tin in a Bridgman system. II - An electrochemical method for detecting flow regimes

    NASA Technical Reports Server (NTRS)

    Sears, B.; Fripp, A. L.; Debnam, W. J., Jr.; Woodell, G. A.; Anderson, T. J.; Narayanan, R.

    1992-01-01

    An ampoule was designed in order to obtain local flow behavior of the flow fields for convection of tin in a vertical Bridgman configuration. Multiple electrochemical cells were located along the periphery of the ampoule. Oxygen was titrated into the ampoule at one of the cell locations using a potentiostat and the concentration of oxygen was monitored at the other cell locations by operating the cells in a galvanic mode. Onset of oscillations were detected by means of thermocouples. We conclude that the flows are generally three dimensional for an aspect ratio of 5. Results on oscillations concurred with those of earlier workers. Suggestions for improved designs were made.

  10. Phytoextraction, phytotransformation and rhizodegradation of ibuprofen associated with Typha angustifolia in a horizontal subsurface flow constructed wetland.

    PubMed

    Li, Yifei; Zhang, Jiefeng; Zhu, Guibing; Liu, Yu; Wu, Bing; Ng, Wun Jern; Appan, Adhityan; Tan, Soon Keat

    2016-10-01

    Widespread occurrence of trace pharmaceutical residues in aquatic environments is of great concerns due to the potential chronic toxicity of certain pharmaceuticals including ibuprofen on aquatic organisms even at environmental levels. In this study, the phytoextraction, phytotransformation and rhizodegradation of ibuprofen associated with Typha angustifolia were investigated in a horizontal subsurface flow constructed wetland system. The experimental wetland system consisted of a planted bed with Typha angustifolia and an unplanted bed (control) to treat ibuprofen-loaded wastewater (∼107.2 μg L(-1)). Over a period of 342 days, ibuprofen was accumulated in leaf sheath and lamina tissues at a mean concentration of 160.7 ng g(-1), indicating the occurrence of the phytoextraction of ibuprofen. Root-uptake ibuprofen was partially transformed to ibuprofen carboxylic acid, 2-hydroxy ibuprofen and 1-hydroxy ibuprofen which were found to be 1374.9, 235.6 and 301.5 ng g(-1) in the sheath, respectively, while they were 1051.1, 693.6 and 178.7 ng g(-1) in the lamina. The findings from pyrosequencing analysis of the rhizosphere bacteria suggest that the Dechloromonas sp., the Clostridium sp. (e.g. Clostridium saccharobutylicum), the order Sphingobacteriales, and the Cytophaga sp. in the order Cytophagales were most probably responsible for the rhizodegradation of ibuprofen. PMID:27372652

  11. Pathways of nitrobenzene degradation in horizontal subsurface flow constructed wetlands: Effect of intermittent aeration and glucose addition.

    PubMed

    Kirui, Wesley K; Wu, Shubiao; Kizito, Simon; Carvalho, Pedro N; Dong, Renjie

    2016-01-15

    Intermittent aeration and addition of glucose were applied to horizontal subsurface flow constructed wetlands in order to investigate the effect on pathways of nitrobenzene (NB) degradation and interactions with microbial nitrogen and sulphur transformations. The experiment was carried out in three phases A, B and C consisting of different NB loading and glucose dosing. For each phase, the effect of aeration was assessed by intermittently aerating one wetland and leaving one unaerated. Regardless of whether or not the wetland was aerated, at an influent NB concentration of 140 mg/L, both wetlands significantly reduced NB to less than 2 mg/L, a reduction efficiency of 98%. However, once the influent NB concentration was increased to 280 mg/L, the aerated wetland had a higher removal performance 82% compared to that of the unaerated wetland 71%. Addition of glucose further intensified the NB removal to 95% in the aerated wetlands and 92% in the unaerated. Aeration of wetlands enhanced NB degradation, but also resulted in higher NB volatilization of 6 mg m(-2) d(-1). The detected high concentration of sulphide 20-60 mg/L in the unaerated wetland gave a strong indication that NB may act as an electron donor to sulphate-reducing bacteria, but this should be further investigated. Aeration positively improved NB removal in constructed wetlands, but resulted in higher NB volatilization. Glucose addition induced co-metabolism to enhance NB degradation. PMID:26468606

  12. Ammonia oxidizing bacteria and archaea in horizontal flow biofilm reactors treating ammonia-contaminated air at 10 °C.

    PubMed

    Gerrity, Seán; Clifford, Eoghan; Kennelly, Colm; Collins, Gavin

    2016-05-01

    The objective of this study was to demonstrate the feasibility of novel, Horizontal Flow Biofilm Reactor (HFBR) technology for the treatment of ammonia (NH3)-contaminated airstreams. Three laboratory-scale HFBRs were used for remediation of an NH3-containing airstream at 10 °C during a 90-d trial to test the efficacy of low-temperature treatment. Average ammonia removal efficiencies of 99.7 % were achieved at maximum loading rates of 4.8 g NH3 m(3) h(-1). Biological nitrification of ammonia to nitrite (NO2 (-)) and nitrate (NO3 (-)) was mediated by nitrifying bacterial and archaeal biofilm populations. Ammonia-oxidising bacteria (AOB) were significantly more abundant than ammonia-oxidising archaea (AOA) vertically at each of seven sampling zones along the vertical HFBRs. Nitrosomonas and Nitrosospira, were the two most dominant bacterial genera detected in the HFBRs, while an uncultured archaeal clone dominated the AOA community. The bacterial community composition across the three HFBRs was highly conserved, although variations occurred between HFBR zones and were driven by physicochemical variables. The study demonstrates the feasibility of HFBRs for the treatment of ammonia-contaminated airstreams at low temperatures; identifies key nitrifying microorganisms driving the removal process; and provides insights for process optimisation and control. The findings are significant for industrial applications of gas oxidation technology in temperate climates. PMID:26879980

  13. Pathways of nitrobenzene degradation in horizontal subsurface flow constructed wetlands: Effect of intermittent aeration and glucose addition.

    PubMed

    Kirui, Wesley K; Wu, Shubiao; Kizito, Simon; Carvalho, Pedro N; Dong, Renjie

    2016-01-15

    Intermittent aeration and addition of glucose were applied to horizontal subsurface flow constructed wetlands in order to investigate the effect on pathways of nitrobenzene (NB) degradation and interactions with microbial nitrogen and sulphur transformations. The experiment was carried out in three phases A, B and C consisting of different NB loading and glucose dosing. For each phase, the effect of aeration was assessed by intermittently aerating one wetland and leaving one unaerated. Regardless of whether or not the wetland was aerated, at an influent NB concentration of 140 mg/L, both wetlands significantly reduced NB to less than 2 mg/L, a reduction efficiency of 98%. However, once the influent NB concentration was increased to 280 mg/L, the aerated wetland had a higher removal performance 82% compared to that of the unaerated wetland 71%. Addition of glucose further intensified the NB removal to 95% in the aerated wetlands and 92% in the unaerated. Aeration of wetlands enhanced NB degradation, but also resulted in higher NB volatilization of 6 mg m(-2) d(-1). The detected high concentration of sulphide 20-60 mg/L in the unaerated wetland gave a strong indication that NB may act as an electron donor to sulphate-reducing bacteria, but this should be further investigated. Aeration positively improved NB removal in constructed wetlands, but resulted in higher NB volatilization. Glucose addition induced co-metabolism to enhance NB degradation.

  14. High-resolution digital movies of emerging flux and horizontal flows in active regions on the sun

    NASA Technical Reports Server (NTRS)

    Topka, K.; Ferguson, S.; Frank, Z.; Tarbell, T.; Title, A.

    1988-01-01

    High-resolution observations of active regions in many wavelength bands obtained at the Vacuum Tower Telescope of NSO/Sunspot (Sacramento Peak) are presented. The SOUP tunable filter, HRSO 1024 x 1024 CCD camera, and a sunspot tracker for image stabilization were used. Subarrays of 512 x 512 pixels were processed digitally and recorded on videodisk in movie format. The movies with 0.5 to 1 arcsecond resolution of the following simultaneous observations were shown: green continuum, longitudinal magnetogram, Doppler velocity, Fe I 5576 A line center, H alpha wings, and H alpha line center. The best set of movies show a 90 x 90 arcsecond field-of-view of an active region at S29, W11. When viewed at speeds of a few thousand times real-time, the photospheric movies clearly show the active region fields being distorted by a remarkable combination of systematic flows and small eruptions of new flux. Flux emergence is most easily discovered in line center movies: an elongated dark feature appears first, followed soon after by bright points at one or both ends. A brief, strong upflow is seen when the dark feature first appears; downflow in the bright points persists much longer. The magnetic flux appears to increase gradually over this extended period. Some of the flux emergence events were studied in detail, with measurements of horizontal and vertical velocities and magnetic flux versus time within one footpoint of the loop.

  15. Effect of different plant species on nutrient removal and rhizospheric microorganisms distribution in horizontal-flow constructed wetlands.

    PubMed

    Meng, Panpan; Hu, Wenrong; Pei, Haiyan; Hou, Qingjie; Ji, Yan

    2014-01-01

    Three macrophyte species, Phragmites australis, Arundo donax L., and Typha latifolia L. have been separately grown in a horizontal-flow (HF) constructed wetland (CW) fed with domestic wastewater to investigate effects of plant species on nutrient removal and rhizospheric microorganisms. All the three mesocosms have been in operation for eight months under the loading rates of 1.14 g Nm(-2) d(-1) and 0.014gP m(-2) d(-1). Appropriately 34-43% phosphorus (P) was removed in HF CWs, and no distinct difference was found among the plants. In the growing season, A. donax L. removed 31.19 gm(-2) of nitrogen (N), followed by P. australis (29.96 g m(-2)), both of which were significantly higher than T. latifolia L. (7.21 g m(-2). Depending on the species, plants absorbed 1.73-7.15% of the overall N, and 0.06-0.56% of the P input. At least 10 common dominant microorganisms were found in the rhizosphere of all the three plants, and 6 of the 10 kinds of bacteria had close relationship with denitrifying bacteria, implying that denitrifiers were dominant microorganism distributed in rhizosphere of wetland plants.

  16. Nitrogen removal performance in planted and unplanted horizontal subsurface flow constructed wetlands treating different influent COD/N ratios.

    PubMed

    Wang, Wei; Ding, Yi; Ullman, Jeffrey L; Ambrose, Richard F; Wang, Yuhui; Song, Xinshan; Zhao, Zhimiao

    2016-05-01

    Microcosm horizontal subsurface flow constructed wetlands (HSSFCWs) were used to examine the impacts of vegetation on nitrogen dynamics treating different influent COD/N ratios (1:1, 4:1, and 8:1). An increase in the COD/N ratio led to increased reductions in NO3 and total inorganic nitrogen (TIN) in planted and unplanted wetlands, but diminished removal of NH4. The HSSFCW planted with Canna indica L. exhibited a significant reduction in NH4 compared to the unplanted system, particularly in the active root zone where NH4 removal performance increased by up to 26 % at the COD/N ratio of 8:1. There was no significant difference in NO3 removal between the planted and unplanted wetlands. TIN removal efficiency in the planted wetland increased with COD/N ratios, which was likely influenced by plant uptake. NH4 reductions were greater in planted wetland at the 20- and 40-cm depths while NO3 reductions were uniformly greater with depth in all cases, but no statistical difference was impacted by depth on TIN removal. These findings show that planting a HSSFCW can provide some benefit in reducing nitrogen loads in effluents, but only when a sufficient carbon source is present.

  17. Boundary condition for lattice Boltzmann modeling of microscale gas flows with curved walls in the slip regime.

    PubMed

    Tao, Shi; Guo, Zhaoli

    2015-04-01

    The lattice Boltzmann method (LBM) has been widely used to simulate microgaseous flows in recent years. However, it is still a challenging task for LBM to model that kind of microscale flow involving complex geometries, owing to the use of uniform Cartesian lattices in space. In this work, a boundary condition for microflows in the slip regime is developed for LBM in which the shape of a solid wall is well considered. The proposed treatment is a combination of the Maxwellian diffuse reflection scheme and the simple bounce-back method. A portion of each part is determined by the relative position between the boundary node and curved walls, which is the key point that distinguishes this method from some previous schemes where the smooth curved surface was assumed to be zigzag lines. The present curved boundary condition is implemented with the multiple-relaxation-times model and verified for several established cases, including the plane microchannel flow (aligned and inclined), microcylindrical Couette flow, and the flow over an inclined microscale airfoil. The numerical results agree well with those predicted by the direct simulation Monte Carlo method. PMID:25974610

  18. Boundary condition for lattice Boltzmann modeling of microscale gas flows with curved walls in the slip regime

    NASA Astrophysics Data System (ADS)

    Tao, Shi; Guo, Zhaoli

    2015-04-01

    The lattice Boltzmann method (LBM) has been widely used to simulate microgaseous flows in recent years. However, it is still a challenging task for LBM to model that kind of microscale flow involving complex geometries, owing to the use of uniform Cartesian lattices in space. In this work, a boundary condition for microflows in the slip regime is developed for LBM in which the shape of a solid wall is well considered. The proposed treatment is a combination of the Maxwellian diffuse reflection scheme and the simple bounce-back method. A portion of each part is determined by the relative position between the boundary node and curved walls, which is the key point that distinguishes this method from some previous schemes where the smooth curved surface was assumed to be zigzag lines. The present curved boundary condition is implemented with the multiple-relaxation-times model and verified for several established cases, including the plane microchannel flow (aligned and inclined), microcylindrical Couette flow, and the flow over an inclined microscale airfoil. The numerical results agree well with those predicted by the direct simulation Monte Carlo method.

  19. Boundary condition for lattice Boltzmann modeling of microscale gas flows with curved walls in the slip regime.

    PubMed

    Tao, Shi; Guo, Zhaoli

    2015-04-01

    The lattice Boltzmann method (LBM) has been widely used to simulate microgaseous flows in recent years. However, it is still a challenging task for LBM to model that kind of microscale flow involving complex geometries, owing to the use of uniform Cartesian lattices in space. In this work, a boundary condition for microflows in the slip regime is developed for LBM in which the shape of a solid wall is well considered. The proposed treatment is a combination of the Maxwellian diffuse reflection scheme and the simple bounce-back method. A portion of each part is determined by the relative position between the boundary node and curved walls, which is the key point that distinguishes this method from some previous schemes where the smooth curved surface was assumed to be zigzag lines. The present curved boundary condition is implemented with the multiple-relaxation-times model and verified for several established cases, including the plane microchannel flow (aligned and inclined), microcylindrical Couette flow, and the flow over an inclined microscale airfoil. The numerical results agree well with those predicted by the direct simulation Monte Carlo method.

  20. Thin-film deposition with high pressure capillary micro-discharges under different supersonic flow and shock regimes

    NASA Astrophysics Data System (ADS)

    Koh, T. L.; Gordon, M. J.

    2013-12-01

    Hollow cathode microplasma jets operating under different supersonic flow regimes were investigated for spray deposition of nanostructured CuO thin films. A variety of supersonic flow phenomena (e.g., shock fronts, stagnation regions, flow instabilities, and turbulent mixing) were studied using fluorescence imaging of the jet afterglow, and were seen to have a dramatic effect on film deposition. Material growth with under-expanded flows was dominated by flux inhomogeneities related to standoff shocks and stagnation regions due to complex fluid interactions between the jet and substrate, resulting in dense, polycrystalline films with variable thickness. For a pressure-matched jet, film thickness was more uniform and morphology evolved from dense polycrystalline films to crystalline nanowires oriented perpendicularly to the substrate as source-substrate distance was increased. Overall, this work demonstrates that microplasma jet-based deposition is a scientifically rich and promising approach for nanostructured thin-film growth, which involves a unique combination of supersonic flow phenomena, plasma physics at high pressure, and mass transport processes.

  1. Impact of flow regulation and power plant effluents on the flow and temperature regimes of the Chattahoochee River; Atlanta to Whitesburg, Georgia

    USGS Publications Warehouse

    Faye, Robert E.; Jobson, Harvey E.; Land, Larry F.

    1978-01-01

    A calibrated and verified transient-flow temperature model was used to evaluate the effects of flow regulation and powerplant loadings on the natural temperature regime of the Chattahoochee River in northeast Georgia. Estimates were made of both instantaneous and average natural temperatures in the river during an 8-day period in August 1976. Differences between the computed average natural temperature and an independent estimateof natural temperature based on observed equilibrium temperatures were less than 0.5C. The combined thermal effects of flow regulation and powerplant effluents resulted in mean daily river temperatures downstreams of the powerplants about equal to or less than computed mean natural temperatures. The range and rates of change of computed natural diurnal temperature fluctuations were considerably less than those presently observed (1976) in the river. Except during periods of peak water-supply demand, differences between computed year 2000 river temperatures and observed present-day temperatures were less than 2C. (Woodard-USGS)

  2. Numerical simulation for horizontal subsurface flow constructed wetlands: A short review including geothermal effects and solution bounding in biodegradation procedures

    NASA Astrophysics Data System (ADS)

    Liolios, K.; Tsihrintzis, V.; Angelidis, P.; Georgiev, K.; Georgiev, I.

    2016-10-01

    Current developments on modeling of groundwater flow and contaminant transport and removal in the porous media of Horizontal Subsurface Flow Constructed Wetlands (HSF CWs) are first reviewed in a short way. The two usual environmental engineering approaches, the black-box and the process-based one, are briefly presented. Next, recent research results obtained by using these two approaches are briefly discussed as application examples, where emphasis is given to the evaluation of the optimal design and operation parameters concerning HSF CWs. For the black-box approach, the use of Artificial Neural Networks is discussed for the formulation of models, which predict the removal performance of HSF CWs. A novel mathematical prove is presented, which concerns the dependence of the first-order removal coefficient on the Temperature and the Hydraulic Residence Time. For the process-based approach, an application example is first discussed which concerns procedures to evaluate the optimal range of values for the removal coefficient, dependent on either the Temperature or the Hydraulic Residence Time. This evaluation is based on simulating available experimental results of pilot-scale units operated in Democritus University of Thrace, Xanthi, Greece. Further, in a second example, a novel enlargement of the system of Partial Differential Equations is presented, in order to include geothermal effects. Finally, in a third example, the case of parameters uncertainty concerning biodegradation procedures is considered and the use of upper and a novel approach is presented, which concerns the upper and the lower solution bound for the practical draft design of HSF CWs.

  3. Influence of substrate heterogeneity on the hydraulic residence time and removal efficiency of horizontal subsurface flow constructed wetlands

    NASA Astrophysics Data System (ADS)

    Carranza-Diaz, O.; Brovelli, A.; Rossi, L.; Barry, D. A.

    2009-04-01

    Horizontal, subsurface flow constructed wetlands are wastewater treatment devices. The influent polluted water flows through a porous substrate where the contaminants are removed, for example by microbial oxidation, surface adsorption and mineral precipitation. These systems are widely used with varying degrees of success to treat municipal and agricultural contaminated waters and remove the organic carbon and nutrient load. Constructed wetlands are an appealing and promising technology, because they (i) are potentially very efficient in removing the pollutants, (ii) require only a small external energy input and (iii) require low maintenance. However, practical experience has shown that the observed purification rate is highly variable and is often much smaller than expected. One of the numerous reasons proposed to explain the variable efficiency of constructed wetlands is the existence of highly conductive zones within the porous substrate, which produce a dramatic reduction of the hydraulic residence time and therefore directly decreases the overall water purification rate. This work aims to understand quantitatively the relationship between the spatial variability in the hydraulic properties of the substrate and the effective residence time in constructed wetlands. We conducted two suites of stochastic numerical simulations, modelling the transport of a conservative tracer in a three-dimensional simulated constructed wetland in one case, and the microbial oxidation of a carbon source in the other. Within each group of simulations, different hydraulic conductivity fields were tested. These were based on a log-normal, spatially correlated random field (with exponential spatial correlation). The amount of heterogeneity was varied by changing the variance correlation length in the three directions. For each set of parameters, different realizations are considered to deduce both the expected residence time for a certain amount of heterogeneity, and its range of

  4. Three-dimensional flow simulation about the AFE vehicle in the transitional regime. [Aeroassist Flight Experiment

    NASA Technical Reports Server (NTRS)

    Celenligil, M. Cevdet; Moss, James N.; Blanchard, Robert C.

    1989-01-01

    The direct-simulation Monte Carlo technique is used to analyze the hypersonic rarefied flow about the three-dimensional NASA Aeroassist Flight Experiment vehicle. Results are given for typical transitional flows encountered during the vehicle's atmospheric entry from altitudes of 200-100 km with an entry velocity of 9.9 km/s. It is found that dissociation is important at altitudes of 110 km and below, and that transitional effects are significant even at an altitude of 200 km.

  5. Evaluating Key Watershed Components of Low Flow Regimes in New England Streams.

    PubMed

    Morrison, Alisa C; Gold, Arthur J; Pelletier, Marguerite C

    2016-05-01

    Water resource managers seeking to optimize stream ecosystem services and abstractions of water from watersheds need an understanding of the importance of land use, physical and climatic characteristics, and hydrography on different low flow components of stream hydrographs. Within 33 USGS gaged watersheds of southern New England, we assessed relationships between watershed variables and a set of low flow parameters by using an information-theoretical approach. The key variables identified by the Akaike Information Criteria (AIC) weighting factors as generating positive relationships with low flow events included percent stratified drift, mean elevation, drainage area, and mean August precipitation. The extent of wetlands in the watershed was negatively related to low flow magnitudes. Of the various land use variables, the percentage of developed land was found to have the highest importance and a negative relationship on low flow magnitudes, but was less important than wetlands and physical and climatic features. Our results suggest that management practices aimed to sustain low flows in fluvial systems can benefit from attention to specific watershed features. We draw attention to the finding that streams located in watersheds with high proportions of wetlands may require more stringent approaches to withdrawals to sustain fluvial ecosystems during drought periods, particularly in watersheds with extensive development and limited deposits of stratified drift.

  6. 3D crustal-scale heat-flow regimes at a developing active margin (Taranaki Basin, New Zealand)

    NASA Astrophysics Data System (ADS)

    Kroeger, K. F.; Funnell, R. H.; Nicol, A.; Fohrmann, M.; Bland, K. J.; King, P. R.

    2013-04-01

    The Taranaki Basin in the west of New Zealand's North Island has evolved from a rifted Mesozoic Gondwana margin to a basin straddling the Neogene convergent Australian-Pacific plate margin. However, given its proximity to the modern subduction front, Taranaki Basin is surprisingly cold when compared to other convergent margins. To investigate the effects of active margin evolution on the thermal regime of the Taranaki Basin we developed a 3D crustal-scale forward model using the petroleum industry-standard basin-modelling software Petromod™. The crustal structure inherited from Mesozoic Gondwana margin breakup and processes related to modern Hikurangi convergent margin initiation are identified to be the main controls on the thermal regime of the Taranaki Basin. Present-day surface heat flow across Taranaki on average is 59 mW/m2, but varies by as much as 30 mW/m2 due to the difference in crustal heat generation between mafic and felsic basement terranes alone. In addition, changes in mantle heat advection, tectonic subsidence, crustal thickening and basin inversion, together with related sedimentary processes result in variability of up to 10 mW/m2. Modelling suggests that increased heating of the upper crust due to additional mantle heat advection following the onset of subduction is an ongoing process and heating has only recently begun to reach the surface, explaining the relatively low surface heat flow. We propose that the depth of the subducted slab and related mantle convection processes control the thermal and structural regimes in the Taranaki Basin. The thermal effects of the subduction initiation process are modified and overprinted by the thickness, structure and composition of the lithosphere.

  7. The influence of water depth and flow regime on phytoplankton biomass and community structure in a shallow, lowland river

    USGS Publications Warehouse

    Leland, H.V.

    2003-01-01

    The taxonomic composition and biomass of phytoplankton in the San Joaquin River, California, were examined in relation to water depth, flow regime, and water chemistry. Without substantial tributary inflow, maintenance demands exceeded algal production during summer and autumn in this eutrophic, 'lowland type' river due to light-limiting conditions for algal growth. Streamflow from tributaries that drain the Sierra Nevada contributed to a substantial net gain in algal production during the spring and summer by increasing water transparency and the extent of turbulence. Abundances of the major taxa (centric diatoms, pennate diatoms and chlorophytes) indicated differing responses to the longitudinal variation in water depth and flow regime, with the areal extent of pools and other geomorphic features that influence time-for-development being a major contributing factor to the selection of species. Tychoplanktonic species were most abundant upstream and in tributaries that drain the San Joaquin Valley. Seasonally-varying factors such as water temperature that influence algal growth rates also contributed significantly to the selection of species. Nutrient limitation appears not to be a primary constraint on species selection in the phytoplankton of this river.

  8. Land use and flow regime effects on phosphorus chemical dynamics in the fluvial sediment of the Winooski River, Vermont

    USGS Publications Warehouse

    McDowell, R.W.; Sharpley, A.N.; Chalmers, A.T.

    2002-01-01

    In the last century, fourfold increase in phosphorus (P) loadings to Lake Champlain, Vermont (VT), USA, have led to nuisance levels of algal growth occurring more often. To better understand the transport, storage, and cycling of P within the lake's catchment, we examined the chemistry, bioavailability and processes controlling sediment P release to waters of the Winooski River, VT, the largest tributary to Lake Champlain. Iron-oxide strip P (algal-bioavailable P) of the river sediments adjacent to agricultural land (3.6 mg kg-1) was greater (P < 0.05) than adjacent to forested land (2.4 mg kg-1). When compared among flow regimes, impoundment (731 mg kg-1) and reservoir sediments (803 mg kg-1) had greater total P concentrations than river sediment (462 mg kg-1). This was attributed to more fines (< 63 ??m) in impoundments and reservoirs (64%) than in river sediments (33%), which also decreased the ability of impoundment sediments to release P to solution and thereby be a sink for P. Although land use and flow regime influenced whether Winooski River sediments acted as a sink or source of P to Lake Champlain, long-term remedial strategies for the catchment should continue to focus on decreasing P losses in agricultural and urban runoff. ?? 2002 Elsevier Science B.V. All rights reserved.

  9. Testing the limits of quasi-geostrophic theory: application to observed laboratory flows outside the quasi-geostrophic regime

    NASA Astrophysics Data System (ADS)

    Williams, Paul; Read, Peter; Haine, Thomas

    2010-05-01

    We compare laboratory observations of equilibrated baroclinic waves in the rotating two-layer annulus, with numerical simulations from a quasi-geostrophic model. The laboratory experiments lie well outside the quasi-geostrophic regime: the Rossby number reaches unity; the depth-to-width aspect ratio is large; and the fluid contains ageostrophic inertia-gravity waves. Despite being formally inapplicable, the quasi-geostrophic model captures the laboratory flows reasonably well. The model displays several systematic biases, which are consequences of its treatment of boundary layers and neglect of interfacial surface tension, and which may be explained without invoking the dynamical effects of the moderate Rossby number, large aspect ratio or inertia-gravity waves. We conclude that quasi-geostrophic theory appears to continue to apply well outside its formal bounds. This is an unexpected and intriguing result that could not have been predicted from the existing literature. It is also potentially useful, for example by permitting the use of a low-order quasi-geostrophic model to easily map out the bifurcation structure - which would be very difficult with a primitive equations model - followed by the use of a primitive equations model for more quantitative agreement in specific cases. Reference Williams, PD, PL Read and TWN Haine (2010) Testing the limits of quasi-geostrophic theory: application to observed laboratory flows outside the quasi-geostrophic regime. Journal of Fluid Mechanics, in press.

  10. Managing flow, sediment, and hydropower regimes in the Sre Pok, Se San, and Se Kong Rivers of the Mekong basin

    NASA Astrophysics Data System (ADS)

    Wild, Thomas B.; Loucks, Daniel P.

    2014-06-01

    The Lancang/Mekong River Basin is presently undergoing a period of rapid hydropower development. In its natural undeveloped state, the river transports about 160 million metric tons of sediment per year, maintaining the geomorphologic features of the basin, sustaining habitats, and transporting the nutrients that support ecosystem productivity. Despite the importance of sediment in the river, currently little attention is being paid to reservoir sediment trapping. This study is devoted to assessing the potential for managing sediment and its impact on energy production in the Se San, Sre Pok, and Se Kong tributaries of the Mekong River. These tributaries drain a set of adjacent watersheds that are important with respect to biodiversity and ecological productivity, and serve as a significant source of flow and sediment to the mainstream Mekong River. A daily sediment transport model is used to assess tradeoffs among energy production and sediment and flow regime alteration in multiple reservoir systems. This study finds that eventually about 40%-80% of the annual suspended sediment load may be trapped in reservoirs. Clearly, these reservoirs will affect the rivers' sediment regimes. However, even after 100 years of simulated sedimentation, reservoir storage capacities and hydropower production at most reservoir sites are not significantly reduced. This suggests that the strongest motivation for implementing measures to reduce trapped sediment is their impact not on hydropower production but on fish migration and survival and on sediment-dependent ecosystems such as the Vietnam Delta and Cambodia's Tonle Sap Lake.

  11. Theory of matrix and fracture flow regimes in unsaturated, fractured porous media

    SciTech Connect

    Nitao, J.J.

    1991-01-01

    The flow behavior of a two-dimensional, unsaturated fracture-matrix system is characterized by a critical flux q*{sub f} = {phi}(S{sub s} {minus} S{sub i})D{sub m} where {phi} is matrix porosity, S{sub s} maximum matrix saturation, S{sub i} initial saturation, and D{sub m} matrix imbibition diffusivity constant. If the flux q{sub f} into the fracture satisfies q{sub f} {much_gt} q*{sub f}, the flow field is fracture-dominated; whereas, if q{sub f} {much_lt} q*{sub f}, the flow is matrix-dominated, and the system behaves as a single equivalent medium with capillary equilibrium between fracture and matrix. If the fracture entrance is ponded, the critical fracture hydraulic conductivity K*{sub f}, or corresponding critical aperture 2b* from the ``cubic law,`` controls the flow behavior instead of the critical flux. Rocks with fracture apertures 2b that are sufficiently large, b{sup 3} {much_gt} b*{sup 3}, have flow that is fracture-dominated while rocks with small aperture fractures, b{sup 3} {much_lt} b*{sup 3}, will be matrix-dominated. Numerical modeling verifies the theory and tests approximate analytical solutions predicting fracture front movement. 15 refs., 7 figs., 4 tabs.

  12. Flow Processes in the Dry Regime: The Effect on Capillary Barrier Performance

    SciTech Connect

    Jansik, Danielle P.; Wildenschild, Dorthe; Rosenberg, Nina D.

    2011-11-01

    Engineered capillary barriers typically consist of two layers of granular materials designed so that the contrast in material hydraulic properties and sloping interface retains infiltrating water in the upper layer. We report here on the results of two bench-top capillary barrier experiments, interpretation, and numerical modeling. We measured hydraulic parameters for two coarse materials using standard methods and found that the materials had similar hydraulic properties despite being morphologically different (round vs. angular). The round sand provided a better functioning capillary barrier than the angular sand, but neither experiment could be characterized as a perfectly working capillary barrier. In both cases, more than 93% of the infiltrating water was successfully diverted from the lower layer, however, infiltration into the underlying layer was observed in both systems. Based on this work, we believe that non-continuum processes such as vapor diffusion and film flow contribute to the observed phenomena and are important aspects to consider with respect to capillary barrier design, as well as dry vadose zone processes in general. Using a theoretical film flow equation that incorporates the surface geometry of the porous material we found that infiltration into the coarse underlying sand layer appeared to be dominated by water film flow. The NUFT (Non-isothermal Unsaturated-saturated Flow and Transport) model was used for qualitative comparison simulations. We were able to reproduce the barrier breach observed in the experiments using targeted parameter adjustment, by which pseudo-film flow was successfully simulated.

  13. Spatial sap flow and xylem anatomical characteristics in olive trees under different irrigation regimes.

    PubMed

    López-Bernal, Álvaro; Alcántara, Esteban; Testi, Luca; Villalobos, Francisco J

    2010-12-01

    The compensation heat pulse (CHP) method is widely used to estimate sap flow and transpiration in conducting organs of woody plants. Previous studies have reported a natural azimuthal variability in sap flow, which could have practical implications in locating the CHP probes and integrating their output. Sap flow of several olive trees (Olea europaea L. cv. 'Arbequina') previously grown under different irrigation treatments were monitored by the CHP method, and their xylem anatomical characteristics were analyzed from wood samples taken at the same location in which the probes were installed. A significant azimuthal variability in the sap flow was found in a well-irrigated olive tree monitored by eight CHP probes. The azimuthal variability was well related to crown architecture, but poorly to azimuthal differences in the xylem anatomical characteristics. Well-irrigated and deficit-irrigated olive trees showed similar xylem anatomical characteristics, but they differed in xylem growth and in the ratio of nocturnal-to-diurnal sap flow (N/D index). The results of this work indicate that transpiration cannot be accurately estimated by the CHP method in olive trees if a small number of sensors are employed and that the N/D index could be used as a sensitive water status indicator.

  14. Dimensional Analysis of Taylor-Couette Flow with Hourglass Geometry in both Laminar and Turbulent Regimes

    NASA Astrophysics Data System (ADS)

    Kowalski, Adam; Olsen, Thomas; Wiener, Richard

    2006-11-01

    Previously we have presented preliminary measurements indicating that the irregular generation of new Taylor Vortex Pairs in laminar Taylor-Couette flow with hourglass geometry could be characterized as low dimensional chaos and in the corresponding case of turbulent flow the chaotic dimension was higher. We now present data from far more extended time series of the periods between vortex formation, confirming and extending our original results. We present confirmation of our computational methodology in other systems. T. Olsen, R. Bjorge, & R. Wiener, Bull. Am. Phys. Soc. 47-10, 76 (2002). T. Olsen, B. Tomlin, R. Bjorge, & R. Wiener, Bull. Am. Phys. Soc. 48-10, 111 (2003)

  15. On salinity regimes and the vertical structure of residual flows in narrow tidal estuaries

    NASA Astrophysics Data System (ADS)

    Prandle, D.

    1985-05-01

    An examination is made of the circulation in narrow estuaries subject to a predominant tidal forcing. Velocity structures are derived separately for residual flow components associated with (a) river flow, (b) wind stress, (c) a well-mixed longitudinal density gradient and (d) a fully stratified saline wedge. Dimensionless parameters are introduced to indicate the magnitude of each component and these parameters are evaluated for 9 major estuaries, thereby revealing their sensitivity to each component. For a channel of constant breadth and depth, formulae are deduced for the length of saline intrusion, L. Comparisons with observed data show that such formulae may be used with confidence to predict changes in L arising from variations in river flow, tidal range or channel depths. The level of stratification is shown to be related to a product of two parameters, one associated with velocity structure and a second involving the square of the 'flow ratio' overlineu/û (i.e. residual velocity/amplitude of the tidal velocity). This relationship provides a simple classification system for estuarine stratification which can be used to indicate the sensitivity of any particular estuary to changing conditions.

  16. Experimental analysis on the effects of DC arc discharges at various flow regimes

    NASA Astrophysics Data System (ADS)

    Bianchi, G.; Saracoglu, B. H.; Paniagua, G.; Regert, T.

    2015-03-01

    This paper addresses the control of the boundary layer on a compression ramp by means of DC electrical arc discharges. The development and realization of the control system are first described and then assessed in the wind tunnel. The objective of the research was to control the supersonic flow using the minimum amount of energy. The array of electrodes was located at the base of a ramp, where a low momentum flow develops. The electrical discharge was generated by a custom designed electronic facility based on high-voltage ignition coils. The slanted tungsten electrodes were insulated by mounting them in a ceramic support. The discharge evolution was studied through high-speed flow visualizations, while electrical measurements at the high-voltage section of the circuitry allowed to estimate the energy release. The development of a high-speed short exposure Schlieren imaging technique, based on a very short duration laser pulse illumination and a double shot CCD camera, allowed to observe the macroscopic effects associated with the arc establishment between the electrodes (glow, sound wave and heat release). Due to the long residence time, the thermal perturbation spread along the streamwise direction. Cross correlation of Schlieren images with short time separation revealed that in supersonic conditions, the discharges led to an overall acceleration of the flow field underneath the oblique shock wave.

  17. Ecosystem Consequences of Contrasting Flow Regimes in an Urban Effects Stream Mesocosm Study

    EPA Science Inventory

    A stream mesocosm experiment was conducted to study the ecosystem-wide effects of two replicated flow hydrograph treatments programmed in an attempt to compare a simulated predevelopment condition to the theoretical changes that new development brings, while accounting for engine...

  18. Unified gas-kinetic scheme for diatomic molecular simulations in all flow regimes

    NASA Astrophysics Data System (ADS)

    Liu, Sha; Yu, Pubing; Xu, Kun; Zhong, Chengwen

    2014-02-01

    A unified gas-kinetic scheme (UGKS) is constructed for both continuum and rarefied flow computations. The underlying principle for the development of UGKS is the direct modeling for the gas evolution process from the kinetic to the hydrodynamic scale, which is used in the flux construction across a cell interface. More specifically, the physical process from the kinetic particle free transport to the hydrodynamic pressure wave propagation is recovered in the flux function. In the previous study, the UGKS has been developed mainly for monatomic gas with particle translational motion only. The construction of time evolution solution is based on the BGK, Shakhov, and ES-BGK models. The UGKS has been validated through extensive numerical tests. In this paper, a UGKS for diatomic gas will be constructed, where the gas-kinetic Rykov model with a Landau-Teller-Jeans-type rotational energy relaxation is used in the numerical scheme. The new scheme will be tested in many cases, such as homogeneous flow relaxation, shock structure calculations, hypersonic flow passing a flat plate, and the flow around a blunt circular cylinder. The analytic, DSMC, and experimental measurements will be used for validating the solutions of UGKS.

  19. Experimental analysis on the effects of DC arc discharges at various flow regimes

    SciTech Connect

    Bianchi, G.; Saracoglu, B. H. Regert, T.; Paniagua, G.

    2015-03-15

    This paper addresses the control of the boundary layer on a compression ramp by means of DC electrical arc discharges. The development and realization of the control system are first described and then assessed in the wind tunnel. The objective of the research was to control the supersonic flow using the minimum amount of energy. The array of electrodes was located at the base of a ramp, where a low momentum flow develops. The electrical discharge was generated by a custom designed electronic facility based on high-voltage ignition coils. The slanted tungsten electrodes were insulated by mounting them in a ceramic support. The discharge evolution was studied through high-speed flow visualizations, while electrical measurements at the high-voltage section of the circuitry allowed to estimate the energy release. The development of a high-speed short exposure Schlieren imaging technique, based on a very short duration laser pulse illumination and a double shot CCD camera, allowed to observe the macroscopic effects associated with the arc establishment between the electrodes (glow, sound wave and heat release). Due to the long residence time, the thermal perturbation spread along the streamwise direction. Cross correlation of Schlieren images with short time separation revealed that in supersonic conditions, the discharges led to an overall acceleration of the flow field underneath the oblique shock wave.

  20. Potential impacts of climate change on flow regime and fish habitat in mountain rivers of the south-western Balkans.

    PubMed

    Papadaki, Christina; Soulis, Konstantinos; Muñoz-Mas, Rafael; Martinez-Capel, Francisco; Zogaris, Stamatis; Ntoanidis, Lazaros; Dimitriou, Elias

    2016-01-01

    The climate change in the Mediterranean area is expected to have significant impacts on the aquatic ecosystems and particular in the mountain rivers and streams that often host important species such as the Salmo farioides, Karaman 1938. These impacts will most possibly affect the habitat availability for various aquatic species resulting to an essential alteration of the water requirements, either for dams or other water abstractions, in order to maintain the essential levels of ecological flow for the rivers. The main scope of this study was to assess potential climate change impacts on the hydrological patterns and typical biota for a south-western Balkan mountain river, the Acheloos. The altered flow regimes under different emission scenarios of the Intergovernmental Panel on Climate Change (IPCC) were estimated using a hydrological model and based on regional climate simulations over the study area. The Indicators of Hydrologic Alteration (IHA) methodology was then used to assess the potential streamflow alterations in the studied river due to predicted climate change conditions. A fish habitat simulation method integrating univariate habitat suitability curves and hydraulic modeling techniques were used to assess the impacts on the relationships between the aquatic biota and hydrological status utilizing a sentinel species, the West Balkan trout. The most prominent effects of the climate change scenarios depict severe flow reductions that are likely to occur especially during the summer flows, changing the duration and depressing the magnitude of the natural low flow conditions. Weighted Usable Area-flow curves indicated the limitation of suitable habitat for the native trout. Finally, this preliminary application highlighted the potential of science-based hydrological and habitat simulation approaches that are relevant to both biological quality elements (fish) and current EU Water policy to serve as efficient tools for the estimation of possible climate

  1. A two layer model of permeability in the unsaturated flow regime for a woven RTM preform

    SciTech Connect

    Pillai, K.M.; Advani, S.G.

    1994-12-31

    In Resin Transfer molding (RTM) with woven fiber preforms, the preforms are placed in a closed mold and are impregnated by a resin. This process of permeation is modeled as the flow of resin through porous media formed by the preform. Woven preforms are tows of fibers knitted together. This architecture introduces dual length scales in the porous media which causes the resistance to the flow of resin to be much higher inside the tows than outside the tow regions. Numerical simulations of mold filling in RTM assign a permeability value to each location before the start of the simulation which does not account for the ``sink`` effect. In this paper, the concept of dynamic permeability is developed. This will permit us to incorporate the ``sink`` effect in the unsaturated region close to the resin front. The model is constructed by considering a woven preform as an equivalent tow layered preform such that one layer corresponds to the more permeable inter-tow region in the woven preform and the other corresponds to the less permeable intra-tow region. Cross flow of resin from more permeable region to the low permeable region reproduces the ``sink`` effect. Numerical simulation of 1-D flow through this two layered preform yields information about the gradation of permeability close to the front which can later be used to assign permeability dynamically during the simulation of an RTM part. Results of this model reproduces the trend of the experiments conducted in 1-D flow of resin through a woven preform qualitatively.

  2. Capacity of a horizontal subsurface flow constructed wetland system for the removal of emerging pollutants: an injection experiment.

    PubMed

    Avila, Cristina; Pedescoll, Anna; Matamoros, Víctor; Bayona, Josep María; García, Joan

    2010-11-01

    A continuous injection experiment was implemented in a pilot-scale horizontal subsurface flow constructed wetland system to evaluate the behavior of four pharmaceuticals and personal care products (i.e. ibuprofen, naproxen, diclofenac and tonalide) and a phenolic estrogenic compound (i.e. bisphenol A). The treatment system consisted of an anaerobic reactor as a primary treatment, followed by two 0.65 m² wetlands (B1 and B2) working in parallel and connected to a 1.65 m² wetland (B3) operating in series. Overall removal efficiencies for the selected compounds ranged from 97% to 99%. The response curves of the injected pollutants show that the behavior of these compounds strongly depends on their sorption and biodegradation characteristics. While about 50% of ibuprofen was removed in B1 and B2, 99% was achieved at B3, where the dissolved oxygen concentration was significantly higher (B1-B2=0.5 mg L⁻¹ and B3=5.4 mg L⁻¹). Naproxen and diclofenac were efficiently removed (93%) in B1 and B2, revealing anaerobic degradation as a probable removal mechanism. Moreover, tonalide and bisphenol A were readily removed in the small wetlands (94% and 83%, respectively), where the removal of total suspended solids was 93%. Therefore, given their high hydrophobicity, sorption onto the particulate matter stands for the major removal mechanism. However, the tentative identification of carboxy-bisphenol A as an intermediate degradation product in B3 suggested biodegradation as a relevant bisphenol A removal pathway under aerobic prevailing conditions.

  3. Dynamics of sulphur compounds in horizontal sub-surface flow laboratory-scale constructed wetlands treating artificial sewage.

    PubMed

    Wiessner, A; Rahman, K Z; Kuschk, P; Kästner, M; Jechorek, M

    2010-12-01

    The knowledge regarding the dynamics of sulphur compounds inside constructed wetlands is still insufficient. Experiments in planted (Juncus effusus) and unplanted horizontal sub-surface-flow laboratory-scale constructed wetlands fed with artificial wastewater were carried out to evaluate the sulphate reduction, the composition and dynamics of generated sulphur compounds, as well as the influence of carbon load and plants on processes of sulphur transformation. In planted and unplanted wetlands, the addition of organic carbon (TOC of about 120 mg L(-1)) immediately affected the transformation of up to 90% of the incoming sulphate (150 mg L(-1)), directing it mainly towards elemental sulphur (30%) and sulphide (8%). During this experimental period, nearly 52% of the transformed sulphate-sulphur was calculated to be immobilized inside the planted wetland and 66% inside the unplanted one. In subsequent experiments, the deficiency of organic carbon inside the planted wetlands favoured the decrease of elemental sulphur in the pore water coupled to retransformation of depot-sulphur to dissolved sulphate. Nearly 90% of the deposited and reduced sulphur was found to be reoxidized. In principle, the results indicate a substantial improvement of this reoxidation of sulphur by oxygen released by the helophytes. Surplus of organic carbon promotes the ongoing sulphate reduction and the stability of deposed and dissolved reduced sulphur compounds. In contrast, inside the unplanted control wetland, a relative stability of the formed sulphur depots and the generated amount of dissolved sulphur compounds including elemental sulphur could be observed independently of the different loading conditions.

  4. Evaluation of the giant reed (Arundo donax) in horizontal subsurface flow wetlands for the treatment of dairy processing factory wastewater.

    PubMed

    Idris, Shaharah Mohd; Jones, Paul L; Salzman, Scott A; Croatto, George; Allinson, Graeme

    2012-09-01

    Two emergent macrophytes, Arundo donax and Phragmites australis, were established in experimental horizontal subsurface flow (HSSF), gravel-based constructed wetlands (CWs) and challenged by treated dairy processing factory wastewater with a median electrical conductivity of 8.9 mS cm(-1). The hydraulic loading rate was tested at 3.75 cm day(-1). In general, the plants grew well during the 7-month study period, with no obvious signs of salt stress. The major water quality parameters monitored (biological oxygen demand (BOD), suspended solids (SS) and total nitrogen (TN) but not total phosphorus) were generally improved after the effluent had passed through the CWs. There was no significance different in removal efficiencies between the planted beds and unplanted gravel beds (p > 0.007), nor was there any significant difference in removal efficiencies between the A. donax and P. australis beds for most parameters. BOD, SS and TN removal in the A. donax and P. australis CWs was 69, 95 and 26 % and 62, 97 and 26 %, respectively. Bacterial removal was observed but only to levels that would allow reuse of the effluent for use on non-food crops under Victorian state regulations. As expected, the A. donax CWs produced considerably more biomass (37 ± 7.2 kg wet weight) than the P. australis CWs (11 ± 1.4 kg wet weight). This standing crop equates to approximately 179 and 68 tonnes ha(-1) year(-1) biomass (dry weight) for A. donax and P. australis, respectively (assuming a 250-day growing season and single-cut harvest). The performance similarity of the A. donax and P. australis planted CWs indicates that either may be used in HSSF wetlands treating dairy factory wastewater, although the planting of A. donax provides additional opportunities