Science.gov

Sample records for air flow regimes

  1. Flow regime classification in air magnetic fluid two-phase flow

    NASA Astrophysics Data System (ADS)

    Kuwahara, T.; DeVuyst, F.; Yamaguchi, H.

    2008-05-01

    A new experimental/numerical technique of classification of flow regimes (flow patterns) in air-magnetic fluid two-phase flow is proposed in the present paper. The proposed technique utilizes the electromagnetic induction to obtain time-series signals of the electromotive force, allowing us to make a non-contact measurement. Firstly, an experiment is carried out to obtain the time-series signals in a vertical upward air-magnetic fluid two-phase flow. The signals obtained are first treated using two kinds of wavelet transforms. The data sets treated are then used as input vectors for an artificial neural network (ANN) with supervised training. In the present study, flow regimes are classified into bubbly, slug, churn and annular flows, which are generally the main flow regimes. To validate the flow regimes, a visualization experiment is also performed with a glycerin solution that has roughly the same physical properties, i.e., kinetic viscosity and surface tension, as a magnetic fluid used in the present study. The flow regimes from the visualization are used as targets in an ANN and also used in the estimation of the accuracy of the present method. As a result, ANNs using radial basis functions are shown to be the most appropriate for the present classification of flow regimes, leading to small classification errors.

  2. Flow regime classification in air-magnetic fluid two-phase flow.

    PubMed

    Kuwahara, T; De Vuyst, F; Yamaguchi, H

    2008-05-21

    A new experimental/numerical technique of classification of flow regimes (flow patterns) in air-magnetic fluid two-phase flow is proposed in the present paper. The proposed technique utilizes the electromagnetic induction to obtain time-series signals of the electromotive force, allowing us to make a non-contact measurement. Firstly, an experiment is carried out to obtain the time-series signals in a vertical upward air-magnetic fluid two-phase flow. The signals obtained are first treated using two kinds of wavelet transforms. The data sets treated are then used as input vectors for an artificial neural network (ANN) with supervised training. In the present study, flow regimes are classified into bubbly, slug, churn and annular flows, which are generally the main flow regimes. To validate the flow regimes, a visualization experiment is also performed with a glycerin solution that has roughly the same physical properties, i.e., kinetic viscosity and surface tension, as a magnetic fluid used in the present study. The flow regimes from the visualization are used as targets in an ANN and also used in the estimation of the accuracy of the present method. As a result, ANNs using radial basis functions are shown to be the most appropriate for the present classification of flow regimes, leading to small classification errors. PMID:21694270

  3. Flow Regimes of Air-Water Counterflow Through Cross Corrugated Parallel Plates

    SciTech Connect

    de Almeida, V.F.

    2000-06-07

    Heretofore unknown flow regimes of air-water counterflow through a pair of transparent vertical parallel cross corrugated plates were observed via high-speed video. Air flows upward driven by pressure gradient and water, downward driven by gravity. The crimp geometry of the corrugations was drawn from typical corrugated sheets used as filling material in modern structured packed towers. Four regimes were featured, namely, rivulet, bicontinuous, flooding fronts, and flooding waves. It is conceivable that the regimes observed might constitute the basis for understanding how gas and liquid phases contend for available space in the interstices of structured packings in packed towers. Flow regime transitions were expressed in terms of liquid load (liquid superficial velocity) and gas flow factor parameters commonly used in pressure drop and capacity curves. We have carefully examined the range of parameters equivalent to the ill-understood high-liquid-flow operation in packed towers. More importantly, our findings should prove valuable in validating improved first-principles modeling of gas-liquid flows in these industrially important devices.

  4. Influence of local air flow regimes on the ozone content of two Pyrenean valleys

    NASA Astrophysics Data System (ADS)

    Ezcurra, A.; Benech, B.; Echelecou, A.; Santamaría, J. M.; Herrero, I.; Zulueta, E.

    2013-08-01

    The Pyrenees Mountains, the natural border between France and Spain, have experienced a large increase in road traffic in the last decade. Due to this fact, a research program named PAP (Pollution Atmospheric in the Pyrenees) was established in 2004 by several laboratories from Spain and France to address the influence of meteorological regimes on the pollution levels of two adjacent valleys, Aspe valley (France) and Canfranc valley (Spain), situated in the center of the Pyrenean range. Pollution measurements show that mean ozone concentrations increase with height. In Sarrance, the site placed at the bottom of the valleys at 335 m above sea level (ASL), the mean ozone value was 23 ppb, whereas at the Pic Midi observatory (2877 m ASL), the top of the PAP network, the value found for mean ozone values was 52 ppb. A linear trend fits this altitudinal variation with a vertical gradient of 17 ppb km-1. The data demonstrate that the observatories located over 1400 m ASL do not show the classical mean daily ozone cycle, and that mean ozone concentrations throughout the day are nearly constant. By contrast, below 1400 m ASL, the classical mean daily ozone cycle is clear, reaching a maximum around noon. These findings indicate that the photochemical reactions are almost inactive at the elevated observatories and, as a result, it can be concluded that ozone levels at those locations are mostly caused by advection of aged air masses. Consequently, we could find that the gradient inside the valleys follows a linear trend of 29 ppb km-1. Finally, it has been observed that in north Foehn situations, intrusions of polluted air coming from the Free Troposphere (FT) can be detected in the upper part of the Spanish valley of Canfranc, where the mean daily ozone cycle changes significantly and becomes similar to the ones measured at the stations situated above 1400 m ASL. However, the results also pointed out that, except for the Foehn situations, the different local air flow

  5. An experimental investigation on the effects of surface gravity waves on the water evaporation rate in different air flow regimes

    NASA Astrophysics Data System (ADS)

    Jodat, Amin; Moghiman, Mohammad; Shirkhani, Golshad

    2013-12-01

    Estimating rate of evaporation from undisturbed water surfaces to moving and quiet air has been the topic a vast number of research activities. The obvious presence of various shapes of gravity waves on the water body surfaces was the motivation of this experimental investigation. In this investigation experimental measurements have been done to quantify evaporation rate from wavy water surfaces in free, mixed and forced convection regimes. The effects of a wide range of surface gravity waves from low steepness, round shaped crest with slow celerity, to steep and very slight spilling crest waves, on the water evaporation rate have been investigated. A wide range of was achieved by applying different air flow velocities on a large heated wave flume equipped with a wind tunnel. Results reveal that wave motion on the water surface increase the rate of evaporation for all air flow regimes. For free convection, due to the effect of wave motion for pumping rotational airflows at the wave troughs and the dominant effect of natural convection for the air flow advection, the maximum evaporation increment percentage from wavy water surface is about 70 %. For mixed and forced convection, water evaporation rate increment is more sensitive to the air flow velocity for the appearance of very slight spilling on the steep wave crests and the leeward air flow structures.

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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. PMID:25976034

  12. 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.

  13. 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.

  14. Gas flow through rough microchannels in the transition flow regime.

    PubMed

    Deng, Zilong; Chen, Yongping; Shao, Chenxi

    2016-01-01

    A multiple-relaxation-time lattice Boltzmann model of Couette flow is developed to investigate the rarified gas flow through microchannels with roughness characterized by fractal geometry, especially to elucidate the coupled effects of roughness and rarefaction on microscale gas flow in the transition flow regime. The results indicate that the surface roughness effect on gas flow behavior becomes more significant in rarefied gas flow with the increase of Knudsen number. We find the gas flow behavior in the transition flow regime is more sensitive to roughness height than that in the slip flow regime. In particular, the influence of fractal dimension on rarefied gas flow behavior is less significant than roughness height. PMID:26871175

  15. 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.

  16. 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.

  17. Regimes of flow past a vortex generator

    NASA Astrophysics Data System (ADS)

    Velte, C. M.; Okulov, V. L.; Naumov, I. V.

    2012-04-01

    A complete parametric investigation of the development of multi-vortex regimes in a wake past simple vortex generator has been carried out. It is established that the vortex structure in the wake is much more complicated than a simple monopole tip vortex. The vortices were studied by stereoscopic particle image velocimetry (SPIV). Based on the obtained SPIV data, a map of the regimes of flow past the vortex generator has been constructed. One region with a developed stable multivortex system on this map reaches the vicinity of the optimum angle of attack of the vortex generator.

  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.

    2015-06-01

    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.

  19. 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.

  20. Cluster analysis of multiple planetary flow regimes

    NASA Technical Reports Server (NTRS)

    Mo, Kingtse; Ghil, Michael

    1988-01-01

    A modified cluster analysis method developed for the classification of quasi-stationary events into a few planetary flow regimes and for the examination of transitions between these regimes is described. The method was applied first to a simple deterministic model and then to a 500-mbar data set for Northern Hemisphere (NH), for which cluster analysis was carried out in the subspace of the first seven empirical orthogonal functions (EOFs). Stationary clusters were found in the low-frequency band of more than 10 days, while transient clusters were found in the band-pass frequency window between 2.5 and 6 days. In the low-frequency band, three pairs of clusters determined EOFs 1, 2, and 3, respectively; they exhibited well-known regional features, such as blocking, the Pacific/North American pattern, and wave trains. Both model and low-pass data exhibited strong bimodality.

  1. Zero-G two phase flow regime modeling in adiabatic flow

    NASA Astrophysics Data System (ADS)

    Reinarts, Thomas R.; Best, Frederick R.; Wheeler, Montgomery; Miller, Katheryn M.

    1993-01-01

    Two-phase flow, thermal management systems are currently being considered as an alternative to conventional, single phase systems for future space missions because of their potential to reduce overall system mass, size, and pumping power requirements. Knowledge of flow regime transitions, heat transfer characteristics, and pressure drop correlations is necessary to design and develop two-phase systems. This work is concerned with microgravity, two-phase flow regime analysis. The data come from a recent sets of experiments. The experiments were funded by NASA Johnson Space Center (JSC) and conducted by NASA JSC with Texas A&M University. The experiment was on loan to NASA JSC from Foster-Miller, Inc., who constructed it with funding from the Air Force Phillips Laboratory. The experiment used R12 as the working fluid. A Foster-Miller two phase pump was used to circulate the two phase mixture and allow separate measurements of the vapor and liquid flow streams. The experimental package was flown 19 times for 577 parabolas aboard the NASA KC-135 aircraft which simulates zero-G conditions by its parabolic flight trajectory. Test conditions included bubbly, slug and annular flow regimes in 0-G. The superficial velocities of liquid and vapor have been obtained from the measured flow rates and are presented along with the observed flow regimes and several flow regime transition predictions. None of the predictions completely describe the transitions as indicated by the data.

  2. Terminal Air Flow Planning

    NASA Technical Reports Server (NTRS)

    Denery, Dallas G.; Erzberger, Heinz; Edwards, Thomas A. (Technical Monitor)

    1998-01-01

    The Center TRACON Automation System (CTAS) will be the basis for air traffic planning and control in the terminal area. The system accepts arriving traffic within an extended terminal area and optimizes the flow based on current traffic and airport conditions. The operational use of CTAS will be presented together with results from current operations.

  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. Wavy regime of a viscoplastic film flow

    NASA Astrophysics Data System (ADS)

    Chakraborty, Symphony; Ruyer-Quil, Christian; Dandapat, Bhabani S.

    2010-11-01

    We consider a power-law fluid flowing down an inclined plane under the action of gravity. The divergence of the viscosity of a shear-thinning fluid at zero strain rate is taken care of by introducing a Newtonian plateau at small strain rate. Applying a weighted residual approach, a two-equations model is formulated in terms of two coupled evolution equations for the film thickness h and the local flow rate q within the framework of lubrication theory. The model accounts for the streamwise diffusion of momentum. Consistency of the model is achieved up to first order in the film parameter for inertia terms and up to second order for viscous terms. Comparison to Orr-Sommerfeld stability analysis and to DNS show convincing agreement in both linear and nonlinear regimes. In the case of shear-thinning fluids, lowering the power index has a non-trivial effect on the primary instability of the film: the threshold of the instability occurs at a smaller Reynolds number but the range of instable wavenumber is also reduced. In the nonlinear regime, we have evidenced a subcritical bifurcation of the traveling-wave solutions from marginal stability conditions.

  5. Constraints on flow regimes in wide-aperture fractures

    SciTech Connect

    Ghezzehei, Teamrat A.

    2004-02-28

    In recent years, significant advances have been made in our understanding of the complex flow processes in individual fractures, aided by flow visualization experiments and conceptual modeling efforts. These advances have led to the recognition of several flow regimes in individual fractures subjected to different initial and boundary conditions. Of these, the most important regimes are film flow, rivulet flow, and sliding of droplets. The existence of such significantly dissimilar flow regimes has been a major hindrance in the development of self-consistent conceptual models of flow for single fractures that encompass all the flow regimes. The objective of this study is to delineate the existence of the different flow regimes in individual fractures. For steady-state flow conditions, we developed physical constraints on the different flow regimes that satisfy minimum energy configurations, which enabled us to segregate the wide range of fracture transmissivity (volumetric flow rate per fracture width) into several flow regimes. These are, in increasing order of flow rate, flow of adsorbed films, flow of sliding drops, rivulet flow, stable film flow, and unstable (turbulent) film flow. The scope of this study is limited to wide-aperture fractures with the flow on the opposing sides of fracture being independent.

  6. 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.

  7. 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)

  8. 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.

  9. Flow regime study of a light material in an industrial scale cold flow circulating fluidized bed

    SciTech Connect

    Mei, J.S.; Monazam, E.R.; Shadle, L.J.

    2006-06-15

    A series of experiments was conducted in the 0.3 meter diameter circulating fluidized bed test facility at the National Energy Technology Laboratory (NETL) of the U. S. Department of Energy. The particle used in this study was a coarse, light material, cork, which has a particle density of 189 kg/m{sup 3} and a mean diameter of 812 {mu}m. Fluidizing this material in ambient air approximates the same gas-solids density ratio as coal and coal char in a pressurized gasifier. The purpose of this study is twofold. First, this study is to provide a better understanding on the fundamentals of flow regimes and their transitions. The second purpose of this study is to generate reliable data to validate the mathematical models, which are currently under development at NETL. This paper presents and discusses the data, which covered operating flow regime from dilute phase, fast fluidization, and to dense phase transport by varying the solid flux, G{sub s}. at a constant gas velocity, U{sub g}. Data are presented by mapping the flow regime for coarse cork particles in a {Delta}P/{Delta} L-G{sub s}-U{sub g} plot. A stable operation can be obtained at a fixed riser gas velocity higher than the transport velocity e.g., at U{sub g} = 3.2 m/s, even though the riser is operated within the fast fluidization flow regime. Depending upon the solids influx, the riser can also be operated at dilute phase or dense phase flow regimes. Experimental data were compared to empirical correlations in published literature for flow regime boundaries as well as solids, fractions in the upper dilute and the lower dense regions for fast fluidization flow regime. Comparisons of measured data with these empirical correlations show rather poor agreements. These discrepancies, however, are not surprising since the correlations for these transitions were derived from experimental data of comparative heavier materials such as sands, FCC, iron ore etc.

  10. 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.

  11. 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

  12. Flow regime shifts in the Little Piney creek (US)

    NASA Astrophysics Data System (ADS)

    Botter, G.

    2014-09-01

    Non-stationarity of climate drivers and soil-use strongly affects the hydrologic cycle, producing significant inter-annual and multi-decadal fluctuations of river flow regimes. Understanding the temporal trajectories of hydrologic regimes is a key issue for the management of freshwater ecosystems and the security of human water uses. Here, long-term changes in the seasonal flow regime of the Little Piney creek (US) are analyzed with the aid of a stochastic mechanistic approach that expresses analytically the streamflow distribution in terms of a few measurable hydroclimatic parameters, providing a basis for assessing the impact of climate and landscape modifications on water resources. Mean rainfall and streamflow rates exhibit a pronounced inter-annual variability across the last century, though in the absence of clear sustained drifts. Long-term modifications of streamflow regimes across different periods of 2 and 8 years are likewise significant. The stochastic model is able to reasonably reproduce the observed 2-years and 8-years regimes in the Little Piney creek, as well as the corresponding inter-annual variations of streamflow probability density. The study evidences that a flow regime shift occurred in the Little Piney creek during the last century, with erratic regimes typical of the 30s/40s that had been progressively replaced by persistent flow regimes featured by more dumped streamflow fluctuations. Causal drivers of regime shift are identified as the increase of the frequency of events (a byproduct of climate variability) and the decrease of recession rates (induced by a decrease of cultivated lands). The approach developed offers an objective basis for the analysis and prediction of the impact of climate/landscape change on water resources.

  13. Natural Flow Air Cooled Photovoltaics

    NASA Astrophysics Data System (ADS)

    Tanagnostopoulos, Y.; Themelis, P.

    2010-01-01

    Our experimental study aims to investigate the improvement in the electrical performance of a photovoltaic installation on buildings through cooling of the photovoltaic panels with natural air flow. Our experimental study aims to investigate the improvement in the electrical performance of a photovoltaic installation on buildings through cooling of the photovoltaic panels with natural air flow. We performed experiments using a prototype based on three silicon photovoltaic modules placed in series to simulate a typical sloping building roof with photovoltaic installation. In this system the air flows through a channel on the rear side of PV panels. The potential for increasing the heat exchange from the photovoltaic panel to the circulating air by the addition of a thin metal sheet (TMS) in the middle of air channel or metal fins (FIN) along the air duct was examined. The operation of the device was studied with the air duct closed tightly to avoid air circulation (CLOSED) and the air duct open (REF), with the thin metal sheet (TMS) and with metal fins (FIN). In each case the experiments were performed under sunlight and the operating parameters of the experimental device determining the electrical and thermal performance of the system were observed and recorded during a whole day and for several days. We collected the data and form PV panels from the comparative diagrams of the experimental results regarding the temperature of solar cells, the electrical efficiency of the installation, the temperature of the back wall of the air duct and the temperature difference in the entrance and exit of the air duct. The comparative results from the measurements determine the improvement in electrical performance of the photovoltaic cells because of the reduction of their temperature, which is achieved by the naturally circulating air.

  14. 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)

  15. 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

  16. 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.

  17. 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.

  18. Dynamic Modeling Strategy for Flow Regime Transition in Gas-Liquid Two-Phase Flows

    SciTech Connect

    Xia Wang; Xiaodong Sun; Benjamin Doup; Haihua Zhao

    2012-12-01

    In modeling gas-liquid two-phase flows, the concept of flow regimes has been widely 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 flow regime dependent. Current nuclear reactor safety analysis codes, such as RELAP5, classify flow regimes using flow regime maps or transition criteria that were developed for steady-state, fully-developed flows. As twophase flows are dynamic in nature, it is important to model the flow regime transitions dynamically to more accurately predict the two-phase flows. The present work aims to develop a dynamic modeling strategy to determine flow regimes in gas-liquid two-phase flows through 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 of the interfacial area, fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation, and the destruction of the interfacial area, fluid particle coalescence and condensation. For 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 shapes, namely group-1 and group-2 bubbles. A preliminary approach to dynamically identify the flow regimes is discussed, in which discriminator s are based on the predicted information, such as the void fraction and interfacial area concentration. The flow regime predicted with this method shows good agreement with the experimental observations.

  19. 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.

  20. Hydrodynamic flow regimes, gas holdup, and liquid circulation in airlift reactors

    SciTech Connect

    Abashar, M.E.; Narsingh, U.; Rouillard, A.E.; Judd, R.

    1998-04-01

    This study reports an experimental investigation into the hydrodynamic behavior of an external-loop airlift reactor (ALR) for the air-water system. Three distinct flow regimes are identified--namely homogeneous, transition, and heterogeneous regimes. The transition between homogeneous and heterogeneous flow is observed to occur over a wide range rather than being merely a single point as has been previously reported in the literature. A gas holdup correlation is developed for each flow regime. The correlations fit the experimental gas holdup data with very good accuracy (within {+-}5%). It would appear, therefore, that a deterministic equation to describe each flow regime is likely to exist in ALRs. This equation is a function of the reactor geometry and the system`s physical properties. New data concerning the axial variation of gas holdup is reported in which a minimum value is observed. This phenomenon is discussed and an explanation offered. Discrimination between two sound theoretical models--namely model 1 (Chisti et al., 1988) and model 2 (Garcia Calvo, 1989)--shows that model 1 predicts satisfactorily the liquid circulation velocity with an error of less than {+-} 10%. The good predictive features of model 1 may be due to the fact that it allows for a significant energy dissipation by wakes behind bubbles. Model 1 is now further improved by the new gas holdup correlations which are derived for the three different flow regimes.

  1. European river flow regimes: assessing space-time dynamics and links to large-scale climate

    NASA Astrophysics Data System (ADS)

    Hannah, D. M.; Kingston, D. G.; Laize, C.; Lavers, D. A.; Wilson, D.

    2011-12-01

    Given heightened concerns about climate change/ variability and human impacts on hydrology, there is a pressing need for research to quantify temporal variability and spatial structure in river flow regimes, and to establish hydroclimatological (climate-flow) associations as a basis for predicting future water stress. This paper draws together findings from studies undertaken at the UK and pan-European scale (using datasets of >100 stations with time series >25 years) and aims: (1) to demonstrate the utility of classification schemes for identifying space-time patterns in river flow regimes and (2) to explore the hydroclimatological relationships between large-scale atmospheric circulation and river flow response. Often, classification is undertaken prior to detailed analysis of large-scale patterns in river flow. In this paper, a suite of novel cluster analysis based methods are presented that identify hydrological regions as well as inter-annual river flow regime variation within regions. Statistical characteristics of the emergent classifications are analysed including geographical expression, teleconnections and presence of time-series trends. Results show that classification provides a useful general organising framework for large-scale hydrological research and facilitates systematic testing of hypotheses about drivers of hydrological variation across wide spatial domains. To investigate climate controls on space-time river flow variation, three methods for characterising atmospheric influences are considered: air-mass types, large-scale climate indices and gridded re-analyses (ECMWF ERA-40). A new air-mass classification for Europe (Spatial Synoptic Classification 2) is presented that classifies daily air-masses. Data are pooled by long-term flow regime regions to assess air-mass - flow regime (shape and magnitude) class associations across Europe; and multiple discriminant function analysis (MDFA) is used to model links between the categorical data. The

  2. Study of the Transition Flow Regime using Monte Carlo Methods

    NASA Technical Reports Server (NTRS)

    Hassan, H. A.

    1999-01-01

    This NASA Cooperative Agreement presents a study of the Transition Flow Regime Using Monte Carlo Methods. The topics included in this final report are: 1) New Direct Simulation Monte Carlo (DSMC) procedures; 2) The DS3W and DS2A Programs; 3) Papers presented; 4) Miscellaneous Applications and Program Modifications; 5) Solution of Transitional Wake Flows at Mach 10; and 6) Turbulence Modeling of Shock-Dominated Fows with a k-Enstrophy Formulation.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  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. 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.

  10. Predicting regime shifts in flow of the Colorado River

    NASA Astrophysics Data System (ADS)

    Gangopadhyay, S.; McCabe, G. J.; Brekke, L. D.

    2010-12-01

    The effects of continued global warming on water resources are a concern for water managers and stake holders. In the western United States, where the combined climatic demand and consumptive use of water is equal to or greater than the natural supply of water for some locations, there is growing concern regarding the sustainability of future water supplies. In addition to the adverse effects of warming on water supply, another issue for water managers is accounting for, and managing, the effects of natural climatic variability, particularly persistently dry and wet periods. Analyses of paleo-reconstructions of Upper Colorado River Basin (UCRB) flow demonstrate that severe sustained droughts, and persistent pluvial periods, are a recurring characteristic of hydroclimate in the Colorado River basin. Shifts between persistently dry and wet regimes (e.g. decadal to multi-decadal variability (D2M)) have important implications for water supply and water management. In this study paleo-reconstructions of UCRB flow are used to compute the risks of shifts between persistently wet and dry regimes given the length of time in a specific regime. Results indicate that low frequency variability of hydro-climatic conditions and the statistics that describe this low frequency variability can be useful to water managers by providing information about the risk of shifting from one hydrologic regime to another. Boxplot of risk outlooks in the Colorado River Basin from the nine flow reconstructions developed in Gangopadhyay et al. (2009). Gangopadhyay, S., B.L. Harding, B. Rajagopalan, J.J. Lukas, and T.J. Fulp, (2009) A non-parametric approach for paleohydrologic reconstruction of annual streamflow ensembles. Water Resour. Res., 45, W06417.

  11. Numerical Analysis of Granular Flows in a Silo Bed on Flow Regime Characterization

    PubMed Central

    Yang, Xingtuan; Gui, Nan; Tu, Jiyuan; Jiang, Shengyao

    2015-01-01

    The flow characteristics of a gravity-driven dense granular flow in a granular bed with a contracted drainage orifice are studied by using discrete element method and quantitative analysis. Three values of discharging rates, ranging from fast to slow dense flows, are investigated. Time variations and derivatives of mean forces and velocities, as well as their respective correlations, are analyzed to quantitatively depict the characteristics of granular flow as well as flow regime categorization. The auto-correlation functions, as well as their Fourier spectrums, are utilized to characterize the differences between the mechanisms of slow and fast granular flows. Finally, it is suggested that the flow regimes of slow and fast flows can be characterized by the kinetic and kinematic flow properties of particles. PMID:25793996

  12. Numerical analysis of granular flows in a silo bed on flow regime characterization.

    PubMed

    Yang, Xingtuan; Gui, Nan; Tu, Jiyuan; Jiang, Shengyao

    2015-01-01

    The flow characteristics of a gravity-driven dense granular flow in a granular bed with a contracted drainage orifice are studied by using discrete element method and quantitative analysis. Three values of discharging rates, ranging from fast to slow dense flows, are investigated. Time variations and derivatives of mean forces and velocities, as well as their respective correlations, are analyzed to quantitatively depict the characteristics of granular flow as well as flow regime categorization. The auto-correlation functions, as well as their Fourier spectrums, are utilized to characterize the differences between the mechanisms of slow and fast granular flows. Finally, it is suggested that the flow regimes of slow and fast flows can be characterized by the kinetic and kinematic flow properties of particles. PMID:25793996

  13. Predicting regime shifts in flow of the Colorado River

    NASA Astrophysics Data System (ADS)

    Gangopadhyay, Subhrendu; McCabe, Gregory J.

    2010-10-01

    The effects of continued global warming on water resources are a concern for water managers and stake holders. In the western United States, where the combined climatic demand and consumptive use of water is equal to or greater than the natural supply of water for some locations, there is growing concern regarding the sustainability of future water supplies. In addition to the adverse effects of warming on water supply, another issue for water managers is accounting for, and managing, the effects of natural climatic variability, particularly persistently dry and wet periods. Analyses of paleo-reconstructions of Upper Colorado River basin (UCRB) flow demonstrate that severe sustained droughts, and persistent pluvial periods, are a recurring characteristic of hydroclimate in the Colorado River basin. Shifts between persistently dry and wet regimes (e.g., decadal to multi-decadal variability (D2M)) have important implications for water supply and water management. In this study paleo-reconstructions of UCRB flow are used to compute the risks of shifts between persistently wet and dry regimes given the length of time in a specific regime. Results indicate that low frequency variability of hydro-climatic conditions and the statistics that describe this low frequency variability can be useful to water managers by providing information about the risk of shifting from one hydrologic regime to another. To manage water resources in the future water managers will have to understand the joint hydrologic effects of natural climate variability and global warming. These joint effects may produce future hydrologic conditions that are unprecedented in both the instrumental and paleoclimatic records.

  14. Space-charge-limited flow in quantum regime

    NASA Astrophysics Data System (ADS)

    Ang, Lay Kee

    2005-10-01

    Space-charge-limited (SCL) flow has been an area of active research in the development of non-neutral plasma physics, high current diodes, high power microwave sources, vacuum microelectronics and sheath physics. According to the classical Child-Langmuir (CL) law for the planar diodes, the current density scales as 3/2's power of gap voltage and to the inverse squared power of gap spacing. In the past decade, there have been renewed interests in extending the classical CL law to multi-dimensional models both numerically and analytically. The study of SCL flow in quantum regime has also attracted considerable interests in the past 3 years [1-3]. With the recent advances in nanotechnology, electron beam with very high current density may be transported in a nano-scale gap with a relatively low gap voltage. In this new operating regime, where the electron wavelength is comparable or larger than the gap spacing, the quantum effects become important. In this talk, the quantum theory of CL law will be introduced to reveal that the classical CL law is enhanced by a large factor due to electron tunneling and exchange-correlation effects, and there is a new quantum scaling for the current density, which is proportional to the 1/2's power of gap voltage, and to the inverse fourth-power of gap spacing [1-2]. Quasi-2D and 3D models with finite emission area will be shown [3]. We will also show that the classical properties of the SCL flow such as bipolar flow, beam-loaded capacitance, transit time and noise will require a complete revision in the quantum regime. The implications of the emission law of Fowler-Nordheim in the presence of intense space charge over the nanometer scale will be discussed.[1] L. K. Ang, T. J. T. Kwan, and Y. Y. Lau, ``New Scaling of Child-Langmuir Law in the Quantum Regime,'' Phys. Rev. Lett. 91, 208303 (2003). [2] L. K. Ang, Y. Y. Lau, and T. J. T. Kwan, ``Simple Derivation of Quantum Scaling in Child-Langmuir law,'' IEEE Trans Plasma Sci. 32, 410

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. Flow regime change in an Endorheic basin in Southern Ethiopia

    NASA Astrophysics Data System (ADS)

    Worku, F. F.; Werner, M.; Wright, N.; van der Zaag, P.; Demissie, S.

    2014-01-01

    Endorheic basins, often found in semi-arid and arid climates, are particularly sensitive to changes in climatological fluxes such as precipitation, evaporation and runoff, resulting in variability of river flows as well as of water levels in end-point lakes that are often present. In this paper we apply the Indicators of Hydrological Alteration (IHA) to characterise change to the natural flow regime of the Omo-Ghibe basin in Southern Ethiopia. This endorheic basin is considered relatively pristine, with the basin being the main source of flow to Lake Turkana, the end-point lake in the East-African rift valley. The water level in Lake Turkana shows significant fluctuation, but an increasing trend can be observed over the past 20 yr. The reasons are currently not well understood. Of the five groups of metrics in the IHA, only those related to magnitude were found to show significant trends, with the main trend being the increase of flow during the dry season. This trend was not reflected in climatological drivers such as rainfall, evaporation, and temperature (which shows an increasing trend), but rather is attributed to the substantial changes in Land Use and Land Cover (LULC) in the basin. The impact on the basin hydrology is apparent mainly in the more humid part of the basin. The significant shift from forest and woodland to grassland and cropland results in a decrease of actual evaporation and subsequent increase in (dry season) runoff. The long term trend of the increasing levels in lake Turkana are related to these trends in dry season flows, while shorter term fluctuations of the lake levels are attributed primarily to anomalies in consecutive wet and dry season rainfall.

  1. Flow regime change in an endorheic basin in southern Ethiopia

    NASA Astrophysics Data System (ADS)

    Worku, F. F.; Werner, M.; Wright, N.; van der Zaag, P.; Demissie, S. S.

    2014-09-01

    Endorheic basins, often found in semi-arid and arid climates, are particularly sensitive to variation in fluxes such as precipitation, evaporation and runoff, resulting in variability of river flows as well as of water levels in end-point lakes that are often present. In this paper we apply the indicators of hydrological alteration (IHA) to characterise change to the natural flow regime of the Omo-Ghibe Basin in southern Ethiopia. Little water resource infrastructure has been developed in the basin to date, and it is considered pristine. The basin is endorheic and is the main source of flow to Lake Turkana in the East African Rift Valley. The water level in Lake Turkana shows significant fluctuation, but increase of its level can be observed over the past 20 years. The reasons are currently not well understood. Of the five groups of hydrological characteristics in the IHA (magnitude, timing, duration, frequency and variability), only those related to magnitude were found to show significant trends, with the main trend being the increase of flow during the dry season. This trend was not reflected in climatological drivers such as rainfall, evaporation and temperature (which shows a positive trend), but rather is attributed to the substantial changes in land use and land cover in the basin. The change in the basin hydrology is apparent mainly in the more humid part of the basin. The significant shift from forest and woodland to grassland and cropland results in a decrease of actual evaporation and subsequent increase in (dry season) runoff. The long-term trend of the increasing levels in Lake Turkana are related to these trends in dry season flows, while shorter-term fluctuations of the lake levels are attributed primarily to anomalies in consecutive wet and dry season rainfall.

  2. 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.

  3. The development of effects-based air quality management regimes

    NASA Astrophysics Data System (ADS)

    Longhurst, J. W. S.; Irwin, J. G.; Chatterton, T. J.; Hayes, E. T.; Leksmono, N. S.; Symons, J. K.

    This paper considers the evolution of attempts to control and manage air pollution, principally but not exclusively focussing upon the challenge of managing air pollution in urban environments. The development and implementation of a range of air pollution control measures are considered. Initially the measures implemented primarily addressed point sources, a small number of fuel types and a limited number of pollutants. The adequacy of such a source-control approach is assessed within the context of a changing and challenging air pollution climate. An assessment of air quality management in the United Kingdom over a 50-year timeframe exemplifies the range of issues and challenges in contemporary air quality management. The need for new approaches is explored and the development and implementation of an effects-based, risk management system for air quality regulation is evaluated.

  4. The effect of solid particles on flow regime and implications for slug flow in high-crystallinity magmas

    NASA Astrophysics Data System (ADS)

    Belien, I. L.; Cashman, K. V.; Rempel, A. W.; Rust, A.; Phillips, J.

    2009-12-01

    Strombolian explosions are a common form of activity in small mafic systems. Strombolian eruptions are commonly attributed to a conduit-filling gas bubble rising and bursting at the magma free surface, and expelling magma as it bursts. This flow regime, called slug flow, has been identified for two-phase systems in which gas flows through a liquid. At many volcanoes exhibiting the Strombolian eruption style however, the crystallinity of the magma can be quite high (up to 50% at Stromboli). It is generally assumed that the primary effect of particles is to increase the bulk viscosity of the fluid; unknown is the effect of adding particles on two-phase flow regimes. To explore the role of particles on the slug flow regime, we have performed a set of analogue experiments in which air rises at different flow rates through a cylindrical tube filled with a mixture of corn syrup (magma) and varying proportions of solid particles (crystals). In previous studies, we have shown that bubbles a few times larger than the particles tend to split into smaller bubbles through interaction with particles in dense suspensions. Under these conditions it is unlikely that large conduit-filling bubbles will be able to form or maintain themselves. In this study we investigate the influence of particles on bubbles that are several orders of magnitude larger than the particles and approach the width of the conduit. Initial observations show that periodic bubbles are formed when a pressure gradient exists across the particle-liquid suspension. Bubbles tend to be conduit-filling when the particle concentration is low. When the concentration approaches 50%, smaller bubbles are formed. This shift in bubble size suggests that it may be difficult, or even impossible, for large (conduit-filling) bubbles to ascend through highly crystalline mafic magmas. Changing the flow rate of air changes the frequency with which bubbles form. Our results start to constrain the conditions of gas flux and magma

  5. Flow regime and deposition pattern of evaporating binary mixture droplet suspended with particles.

    PubMed

    Zhong, Xin; Duan, Fei

    2016-02-01

    The flow regimes and the deposition pattern have been investigated by changing the ethanol concentration in a water-based binary mixture droplet suspended with alumina nanoparticles. To visualize the flow patterns, Particle Image Velocimetry (PIV) has been applied in the binary liquid droplet containing the fluorescent microspheres. Three distinct flow regimes have been revealed in the evaporation. In Regime I, the vortices and chaotic flows are found to carry the particles to the liquid-vapor interface and to promote the formation of particle aggregation. The aggregates move inwards in Regime II as induced by the Marangoni flow along the droplet free surface. Regime III is dominated by the drying of the left water and the capillary flow driving particles radially outward is observed. The relative weightings of Regimes I and II, which are enhanced with an increasing load of ethanol, determine the motion of the nanoparticles and the formation of the final drying pattern. PMID:26920521

  6. 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

  7. 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.

  8. Two-phase interfacial area and flow regime modeling in FLOWTRAN-TF code

    SciTech Connect

    Smith, F.G. III; Lee, S.Y.; Flach, G.P.; Hamm, L.L.

    1992-01-01

    FLOWTRAN-TF is a new two-component, two-phase thermal-hydraulics code to capture the detailed assembly behavior associated with loss-of-coolant accident analyses in multichannel assemblies of the SRS reactors. The local interfacial area of the two-phase mixture is computed by summing the interfacial areas contributed by each of three flow regimes. For smooth flow regime transitions, the code uses an interpolation technique in terms of component void fraction for each basic flow regime.

  9. Two-phase interfacial area and flow regime modeling in FLOWTRAN-TF code

    SciTech Connect

    Smith, F.G. III; Lee, S.Y.; Flach, G.P.; Hamm, L.L.

    1992-12-31

    FLOWTRAN-TF is a new two-component, two-phase thermal-hydraulics code to capture the detailed assembly behavior associated with loss-of-coolant accident analyses in multichannel assemblies of the SRS reactors. The local interfacial area of the two-phase mixture is computed by summing the interfacial areas contributed by each of three flow regimes. For smooth flow regime transitions, the code uses an interpolation technique in terms of component void fraction for each basic flow regime.

  10. 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.

  11. 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.

  12. 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

  13. Meteorological regimes for the classification of aerospace air quality predictions for NASA-Kennedy Space Center

    NASA Technical Reports Server (NTRS)

    Stephens, J. B.; Sloan, J. C.

    1976-01-01

    A method is described for developing a statistical air quality assessment for the launch of an aerospace vehicle from the Kennedy Space Center in terms of existing climatological data sets. The procedure can be refined as developing meteorological conditions are identified for use with the NASA-Marshall Space Flight Center Rocket Exhaust Effluent Diffusion (REED) description. Classical climatological regimes for the long range analysis can be narrowed as the synoptic and mesoscale structure is identified. Only broad synoptic regimes are identified at this stage of analysis. As the statistical data matrix is developed, synoptic regimes will be refined in terms of the resulting eigenvectors as applicable to aerospace air quality predictions.

  14. 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.

  15. Development of an inflow controlled environmental flow regime for a Norwegian river

    NASA Astrophysics Data System (ADS)

    Alfredsen, Knut; Harby, Atle; Linnansaari, Tommi; Ugedal, Ola

    2010-05-01

    For most regulated rivers in Norway the common environmental flow regime is static and shows very little variation over the year. Recent research indicate that flow regimes that follow the natural inflow variation can meet the ecological and social demands for water in a better way. The implementation of a variable environmental flow regime provides many challenges both related to defining flow for various species and user groups in the river, but also due to practical implementation, legislation and control. A inflow controlled flow regime is developed for a Norwegian river regulated for hydro power as a pilot study. The regime should meet ecological demands from Atlantic salmon and brown trout, recreational use of water and visual impression of the river. This should be achieved preferably without altering the energy production in the hydro power system. The flow regime is developed for wet, dry and normal discharge conditions based on unregulated inflow to the catchment. The development of the seasonal flow requirements for various targets identified is done using a modification of the Building Block Method. Several options are tested regarding the integration of the flow regime into the operational strategy of the hydropower plant, both using real time prognosis of inflow and combinations with historical data. An important topic in selecting the release strategy is how it meets current Norwegian legislation and how well future documentation and environmental control can be carried out. An evaluation protocol is also proposed for the flow regime to test if the ecological targets are met.

  16. 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.

  17. Simulator Of Rain In Flowing Air

    NASA Technical Reports Server (NTRS)

    Clayton, Richard M.; Cho, Young I.; Shakkottai, Parthasarathy; Back, Lloyd H.

    1989-01-01

    Report describes relatively inexpensive apparatus that creates simulated precipitation from drizzle to heavy rain in flowing air. Small, positive-displacement pump and water-injecting device positioned at low-airspeed end of converging section of wind tunnel 10 in. in diameter. Drops injected by array entrained in flow of air as it accelerates toward narrower outlet, 15 in. downstream. Outlet 5 in. in diameter.

  18. 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.

  19. Computation of flow around a circular cylinder in a supercritical regime

    NASA Technical Reports Server (NTRS)

    Ishii, K.; Kuwahara, K.; Kawamura, T.; Ogawa, S.; Chyu, W. J.

    1985-01-01

    Compressible flows around a circular cylinder in a supercritical regime at Mach number 0.3 have been calculated by using the Beam-Warming-Steger scheme based on the full Navier-Stokes equations with improved accuracy. The flow patterns are visualized extensively to observe the characteristics in this regime. The computations show that the flow at certain Reynolds numbers in a supercritical regime becomes rather steady and irregular with small drag coefficients. This may correspond to the experimental observations that the Strouhal number can not be measured clearly at a certain Reynolds number range in the supercritical regime.

  20. Three-dimensional flow and vorticity transport in idealized airway model from laminar to turbulent regimes

    NASA Astrophysics Data System (ADS)

    Jalal, Sahar; van de Moortele, Tristan; Nemes, Andras; Eslam Panah, Azar; Coletti, Filippo

    2015-11-01

    The presence and intensity of secondary flows formed by the inhaled air during respiration has important consequences for gas exchange and particle transport in the lungs. Here we focus on the formation and persistence of such secondary flows by experimentally studying the steady inspiration in an idealized airway model. The geometry consists of a symmetric planar double bifurcation that respects the geometrical proportions of the human bronchial tree. Physiologically relevant Reynolds numbers from 100 to 5000 are investigated, ranging from laminar to turbulent regimes. The time-averaged, three-dimensional velocity fields are obtained from Magnetic Resonance Imaging (MRI), providing detailed distributions of vorticity, circulation, and secondary flow strength. Information on the velocity fluctuations are obtained by Particle Image Velocimetry (PIV). The measurements highlight the effect of the Reynolds number on the momentum transport, flow partitioning at the bifurcations, strength and sense of rotation of the longitudinal vortices. A marked change in topology is found at a specific Reynolds number, above which the influence of the upstream flow prevails over the effect of the local geometry. Finally, turbulence and its role in the mean vorticity transport are also discussed.

  1. Air flow cued spatial learning in mice.

    PubMed

    Bouchekioua, Youcef; Mimura, Masaru; Watanabe, Shigeru

    2015-01-01

    Spatial learning experiments in rodents typically employ visual cues that are associated with a goal place, even though it is now well established that they have poor visual acuity. We assessed here the possibility of spatial learning in mice based on an air flow cue in a dry version of the Morris water maze task. A miniature fan was placed at each of the four cardinal points of the circular maze, but only one blew air towards the centre of the maze. The three other fans were blowing towards their own box. The mice were able to learn the task only if the spatial relationship between the air flow cue and the position of the goal place was kept constant across trials. A change of this spatial relationship resulted in an increase in the time to find the goal place. We report here the first evidence of spatial learning relying on an air flow cue. PMID:25257773

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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).

  7. Air flow through poppet valves

    NASA Technical Reports Server (NTRS)

    Lewis, G W; Nutting, E M

    1920-01-01

    Report discusses the comparative continuous flow characteristics of single and double poppet valves. The experimental data presented affords a direct comparison of valves, single and in pairs of different sizes, tested in a cylinder designed in accordance with current practice in aviation engines.

  8. 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.

  9. 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. PMID:23660536

  10. 40 CFR 91.416 - Intake air flow measurement specifications.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Intake air flow measurement... Procedures § 91.416 Intake air flow measurement specifications. (a) If used, the engine intake air flow measurement method used must have a range large enough to accurately measure the air flow over the...

  11. 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

  12. 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

  13. On the different regimes of gas heating in air plasmas

    NASA Astrophysics Data System (ADS)

    Pintassilgo, Carlos D.; Guerra, Vasco

    2015-10-01

    Simulations of the gas temperature in air (N2-20%O2) plasma discharges are presented for different values of the reduced electric field, E/N g, electron density n e, pressure and tube radius. This study is based on the solutions to the time-dependent gas thermal balance in a cylindrical geometry coupled to the electron, vibrational and chemical kinetics, for E/{{N}\\text{g}}=50 and 100 Td (1 Td = 10-17 V cm2), 109  ⩽  n e  ⩽  1011 cm-3, pressure in the range 1-20 Torr, and also considering different tube radius, 0.5, 1 and 1.5 cm. The competing role of different gas heating mechanisms is discussed in detail within the time range 0.01-100 ms. For times below 1 ms, gas heating occurs from O2 dissociation by electron impact through pre-dissociative excited states, e + O2  →  e + \\text{O}2*   →  e + 2O(3P) and …  →  e + O(3P) + O(1D), as well as through the quenching of N2 electronically excited states by O2. For longer times, simulation results show that gas heating comes from processes N(4S) + NO(X)  →  N2(X, v ~ 3) + O, N2(A) + O  →  NO(X) + N(2D), V-T N2-O collisions and the recombination of oxygen atoms at the wall. Depending on the given E/N g and n e values, each one of these processes can be an important gas-heating channel. The contribution of V-T N2-O exchanges to gas heating is important in the analysis of the gas temperature for different pressures and values of the tube radius. A global picture of these effects is given by the study of the fraction of the discharge power spent on gas heating, which is always ~15%. The values for the fractional power transferred to gas heating from vibrational and electronic excitation are also presented and discussed.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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

  19. Nitric oxide flow tagging in unseeded air.

    PubMed

    Dam, N; Klein-Douwel, R J; Sijtsema, N M; Meulen, J J

    2001-01-01

    A scheme for molecular tagging velocimetry is presented that can be used in air flows without any kind of seeding. The method is based on the local and instantaneous creation of nitric oxide (NO) molecules from N(2) and O(2) in the waist region of a focused ArF excimer laser beam. This NO distribution is advected by the flow and can be visualized any time later by laser-induced fluorescence in the gamma bands. The creation of NO is confirmed by use of an excitation spectrum. Two examples of the application of the new scheme for air-flow velocimetry are given in which single laser pulses are used for creation and visualization of NO. PMID:18033499

  20. 40 CFR 89.414 - Air flow measurement specifications.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 20 2011-07-01 2011-07-01 false Air flow measurement specifications. 89.414 Section 89.414 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... Emission Test Procedures § 89.414 Air flow measurement specifications. (a) The air flow measurement...

  1. 40 CFR 89.414 - Air flow measurement specifications.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Air flow measurement specifications. 89.414 Section 89.414 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... Emission Test Procedures § 89.414 Air flow measurement specifications. (a) The air flow measurement...

  2. 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. PMID:24569271

  3. 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.

  4. Intermittent Flow Regimes in a Transonic Fan Airfoil Cascade

    NASA Technical Reports Server (NTRS)

    Lepicovsky, J.; McFarland, E. R.; Chima, R. V.; Capece, V. R.; Hayden, J.

    2002-01-01

    A study was conducted in the NASA Glenn Research Center linear cascade on the intermittent flow on the suction surface of an airfoil section from the tip region of a modern low aspect ratio fan blade. Experimental results revealed that, at a large incidence angle, a range of transonic inlet Mach numbers exist where the leading-edge shock-wave pattern was unstable. Flush mounted high frequency response pressure transducers indicated large local jumps in the pressure in the leading edge area, which generates large intermittent loading on the blade leading edge. These measurements suggest that for an inlet Mach number between 0.9 and 1.0 the flow is bi-stable, randomly switching between subsonic and supersonic flows. Hence, it appears that the change in overall flow conditions in the transonic region is based on the frequency of switching between two stable flow states rather than on the continuous increase of the flow velocity. To date, this flow behavior has only been observed in a linear transonic cascade. Further research is necessary to confirm this phenomenon occurs in actual transonic fans and is not the byproduct of an endwall restricted linear cascade.

  5. Surface-slip equations for multicomponent, nonequilibrium air flow

    NASA Technical Reports Server (NTRS)

    Gupta, Roop N.; Scott, Carl D.; Moss, James N.; Goglia, Gene

    1985-01-01

    Equations are presented for the surface slip (or jump) values of species concentration, pressure, velocity, and temperature in the low-Reynolds-number, high-altitude flight regime of a space vehicle. These are obtained from closed-form solutions of the mass, momentum, and energy flux equations using the Chapman-Enskog velocity distribution function. This function represents a solution of the Boltzmann equation in the Navier-Stokes approximation. The analysis, obtained for nonequilibrium multicomponent air flow, includes the finite-rate surface catalytic recombination and changes in the internal energy during reflection from the surface. Expressions for the various slip quantities have been obtained in a form which can readily be employed in flow-field computations. A consistent set of equations is provided for multicomponent, binary, and single species mixtures. Expression is also provided for the finite-rate species-concentration boundary condition for a multicomponent mixture in absence of slip.

  6. Structures in the Oscillatory regime of RLDCC flow

    NASA Astrophysics Data System (ADS)

    Panchapakesan, Nagangudy

    2015-11-01

    Rotating lid driven cubical cavity flow (RLDCC flow) is studied with a view to test structure eduction algorithms. OpenFoam software was used to simulate the RLDCC flow at Reynolds numbers higher than the critical Reynolds number for this geometry. Vortex bubble and other characteristic structures were observed in these simulations. The vector fields of the simulations were further analyzed with LCS and other methodologies to educe the structures. The structures were compared with level sets of different dynamical variables. The ability of these algorithms to present a coherent representation of the time evolution and unsteady dynamics of the bubble and other structures is evaluated. Funded by AR&DB India.

  7. 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

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

    NASA Astrophysics Data System (ADS)

    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.

  9. 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

  10. 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.

  11. Rheology of simple shear flows of dense granular assemblies in different regimes

    NASA Astrophysics Data System (ADS)

    Chialvo, Sebastian; Sun, Jin; Sundaresan, Sankaran

    2010-11-01

    Using the discrete element method, simulations of simple shear flow of dense assemblies of frictional particles have been carried out over a range of shear rates and volume fractions in order to characterize the transition from quasistatic or inertial flow to intermediate flow. In agreement with previous results for frictionless spheres [1], the pressure and shear stress in the intermediate regime are found to approach asymptotic power law relations with shear rate; curiously, these asymptotes appear to be common to all intermediate flows regardless of the value of the particle friction coefficient. The scaling relations for stress for the inertial and quasistatic regimes are consistent with a recent extension of kinetic theory to dense inertial flows [2] and a simple model for quasistatic flows [3], respectively. For the case of steady, simple shear flow, the different regimes can be bridged readily: a harmonic weighting function blends the inertial regime to the intermediate asymptote, while a simple additive rule combines the quasistatic and intermediate regimes. [4pt] [1] T. Hatano, et al., J. Phys. Soc. Japan 76, 023001 (2007). [0pt] [2] J. Jenkins, and D. Berzi, Granular Matter 12, 151 (2010). [0pt] [3] J. Sun, and S. Sundaresan, J. Fluid Mech. (under review).

  12. 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.

  13. 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. PMID:25554885

  14. 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.

  15. Natural laminar flow hits smoother air

    NASA Technical Reports Server (NTRS)

    Holmes, B. J.

    1985-01-01

    Natural laminar flow (NLF) may be attained in aircraft with lower cost, weight, and maintenance penalties than active flow laminarization by means of a slot suction system. A high performance general aviation jet aircraft possessing a moderate degree of NLF over wing, fuselage, empennage and engine nacelles will accrue a 24 percent reduction in total aircraft drag in the cruise regime. NASA-Langley has conducted NLF research centered on the use of novel airfoil profiles as well as composite and milled aluminum alloy construction methods which minimize three-dimensional aerodynamic surface roughness and waviness. It is noted that higher flight altitudes intrinsically reduce unit Reynolds numbers, thereby minimizing turbulence for a given cruise speed.

  16. 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

  17. 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.

  18. 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

  19. Experimental and analytical dynamic flow characteristics of an axial-flow fan from an air cushion landing system model

    NASA Technical Reports Server (NTRS)

    Thompson, W. C.; Boghani, A. B.; Leland, T. J. W.

    1977-01-01

    An investigation was conducted to compare the steady-state and dynamic flow characteristics of an axial-flow fan which had been used previously as the air supply fan for some model air cushion landing system studies. Steady-state flow characteristics were determined in the standard manner by using differential orifice pressures for the flow regime from free flow to zero flow. In this same regime, a correlative technique was established so that fan inlet and outlet pressures could be used to measure dynamic flow as created by a rotating damper. Dynamic tests at damper frequencies up to 5 Hz showed very different flow characteristics when compared with steady-state flow, particularly with respect to peak pressures and the pressure-flow relationship at fan stall and unstall. A generalized, rational mathematical fan model was developed based on physical fan parameters and a steady-state flow characteristic. The model showed good correlation with experimental tests at damper frequencies up to 5 Hz.

  20. Review of air flow measurement techniques

    SciTech Connect

    McWilliams, Jennifer

    2002-12-01

    Airflow measurement techniques are necessary to determine the most basic of indoor air quality questions: ''Is there enough fresh air to provide a healthy environment for the occupants of the building?'' This paper outlines airflow measurement techniques, but it does not make recommendations for techniques that should be used. The airflows that will be discussed are those within a room or zone, those between rooms or zones, such as through doorways (open or closed) or passive vents, those between the building and outdoors, and those through mechanical air distribution systems. Techniques that are highlighted include particle streak velocimetry, hot wire anemometry, fan pressurization (measuring flow at a given pressure), tracer gas, acoustic methods for leak size determination, the Delta Q test to determine duct leakage flows, and flow hood measurements. Because tracer gas techniques are widely used to measure airflow, this topic is broken down into sections as follows: decay, pulse injection, constant injection, constant concentration, passive sampling, and single and multiple gas measurements for multiple zones.

  1. Optical Air Flow Measurements for Flight Tests and Flight Testing Optical Air Flow Meters

    NASA Technical Reports Server (NTRS)

    Jentink, Henk W.; Bogue, Rodney K.

    2005-01-01

    Optical air flow measurements can support the testing of aircraft and can be instrumental to in-flight investigations of the atmosphere or atmospheric phenomena. Furthermore, optical air flow meters potentially contribute as avionics systems to flight safety and as air data systems. The qualification of these instruments for the flight environment is where we encounter the systems in flight testing. An overview is presented of different optical air flow measurement techniques applied in flight and what can be achieved with the techniques for flight test purposes is reviewed. All in-flight optical airflow velocity measurements use light scattering. Light is scattered on both air molecules and aerosols entrained in the air. Basic principles of making optical measurements in flight, some basic optical concepts, electronic concepts, optoelectronic interfaces, and some atmospheric processes associated with natural aerosols are reviewed. Safety aspects in applying the technique are shortly addressed. The different applications of the technique are listed and some typical examples are presented. Recently NASA acquired new data on mountain rotors, mountain induced turbulence, with the ACLAIM system. Rotor position was identified using the lidar system and the potentially hazardous air flow profile was monitored by the ACLAIM system.

  2. Infrared imaging and tufts studies of boundary layer flow regimes on a NACA 0012 airfoil

    NASA Technical Reports Server (NTRS)

    Gartenberg, Ehud; Roberts, A. Sidney, Jr.; Mcree, Griffith J.

    1989-01-01

    A study of boundary-layer flow regimes on a NACA 0012 airfoil from zero angle of attack up to separation is presented. The boundary-layer transition from the laminar to the turbulent regime and the onset of the separation were detected by surface thermography of the airfoil performed with an infrared imaging system. The findings were compared with observations of aluminum-foil tufts visible with the infrared imaging system. This arrangement allows the infrared imaging system to assume the dual role of flow regime detection through surface thermography and flow visualization through the observation of the aluminum-foil tufts. Ultimately the temperature history on an uncontaminated surface could provide an interpretation of the state of boundary-layer flow. Separation studies performed on the NACA 0012 airfoil showed that aluminum foil tufts can be observed with infrared imaging systems.

  3. Ontogenetic propulsive transitions from viscous to inertial flow regimes in the medusae Sarsia tubulosa

    NASA Astrophysics Data System (ADS)

    Katija, Kakani; Jiang, Houshuo; Colin, Sean; Costello, John

    2012-11-01

    Among marine organisms, the influences of flow regimes on swimming strategies are largely unknown. As an approach to examine this issue, we quantified how transitions from viscous to inertially dominated flow regimes, which commonly occur during the development of marine animals, relate to changes in swimming strategies. We used the hydromedusae Sarsia tubulosa as a model organism for this investigation because its morphology and propulsive actuation mechanism are radially symmetric. This feature allows for determination of three-dimensional fluid quantities from two-dimensional flow measurement techniques. Digital particle image velocimetry was used to quantify the flow fields created by free-swimming hydromedusae and calculate the impulse generated by their swimming pulses at different life stages. Swimming strategies were evaluated by quantifying the relationship between impulse production and hydrodynamic swimming efficiency. Utilizing these metrics enable us to generalize our findings to the swimming strategies of other aquatic animals that swim in similar fluid regimes.

  4. 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.

  5. 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

  6. 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

  7. 40 CFR 89.414 - Air flow measurement specifications.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 20 2014-07-01 2013-07-01 true Air flow measurement specifications. 89... Test Procedures § 89.414 Air flow measurement specifications. (a) The air flow measurement method used... during the test. Overall measurement accuracy must be ± 2 percent of the maximum engine value for...

  8. 40 CFR 89.414 - Air flow measurement specifications.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 21 2013-07-01 2013-07-01 false Air flow measurement specifications... Emission Test Procedures § 89.414 Air flow measurement specifications. (a) The air flow measurement method... during the test. Overall measurement accuracy must be ± 2 percent of the maximum engine value for...

  9. 40 CFR 89.414 - Air flow measurement specifications.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 21 2012-07-01 2012-07-01 false Air flow measurement specifications... Emission Test Procedures § 89.414 Air flow measurement specifications. (a) The air flow measurement method... during the test. Overall measurement accuracy must be ± 2 percent of the maximum engine value for...

  10. 40 CFR 90.416 - Intake air flow measurement specifications.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Intake air flow measurement... Gaseous Exhaust Test Procedures § 90.416 Intake air flow measurement specifications. (a) If used, the engine intake air flow measurement method used must have a range large enough to accurately measure...

  11. 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.

  12. 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.

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

    DOE PAGESBeta

    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

  14. Investigation of the motion and heat transfer of water droplets in the swirling air flow in weightlessness

    NASA Astrophysics Data System (ADS)

    Gubaidullin, D. A.; Fedyaev, V. L.; Morenko, I. V.; Snigerev, B. A.; Galimov, E. R.

    2016-06-01

    The motion and heat transfer of water droplets with a swirling air flow is investigated. Flow was considered in a cylindrical chamber in the absence of gravity. We created a mathematical model of this problem and made appropriate calculations. The features of the air flow at a tangential feeding it into the chamber, and the motion of the drops, their thermal behaviour are founded. We presented the recommendations for the rational choice of parameters of the apparatus and rational operation regime.

  15. Impact of subjacent rocks at the water and air regime of the depleted peat deposits

    NASA Astrophysics Data System (ADS)

    Rakovich, V. A.

    2009-04-01

    At the depleted peat deposits (after peat extraction), where the residual layer of peat with the thickness of about 0,5 meters is laid at the well water permeable rocks, vegetation typical for dry conditions is developed in case of good drainage conditions; birch trees, willow, alder-trees and buckthorn prevail in this vegetation. Water and air regime is characterized here by good aeration with prevailing of oxidative processes. If water regime is regulated, these depleted peat areas are suitable for agricultural and forest lands; however, necessity of transformation of these depleted lands into forest and agricultural lands must be ecologically and economically justified. If the residual layer of peat with the thickness of 0,05-0,3 m is based at the sapropel or peat sapropel, contrast amphibiotic water and air regime with strong fluctuation of oxidative and restoration process depending on the weather conditions is formed; this regime is formed without artificial increase of the ground waters level. This does not allow bog vegetation or vegetation typical for dry conditions to develop. Thus, within 20 and more years after completion of peat extraction, such areas are not covered by vegetation in spite of favorable agro-chemical qualities of peat layer and favorable for vegetation chemical composition of soil and ground waters. Depleted peat deposits, that are based at the sapropel, are not suitable for agricultural use, because agricultural vegetation requires stable water and air regime with good aeration and oxidative and restoration potential within 400-750 mV. Contrast amphibiotic water and air regime of the depleted peat deposits that are based at sapropel excludes possibility to use them as agricultural lands. Because of this reason, areas with residual peat layer that are based at sapropel are not suitable for forest planting. Due to periodic increase of ground waters level, rot systems of the plants can not penetrate into the required depth, and mechanical

  16. 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.

  17. 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.

  18. Flow regime patterns and their controlling factors in the Ebro basin (Spain)

    NASA Astrophysics Data System (ADS)

    Bejarano, M. Dolores; Marchamalo, Miguel; García de Jalón, Diego; González del Tánago, Marta

    2010-05-01

    SummaryNatural intra-annual flow fluctuations vary between rivers, being a determining factor for aquatic insects, fish and riparian communities which are adapted to the habitat conditions and different flows throughout the seasons. Moreover, restoration of seasonal flow patterns plays an important role in achieving good ecological status of rivers, through the preservation and/or recovery of components and processes of natural river ecosystems. In this work we: (a) classify fluvial segments in the Ebro basin (North-Eastern Spain) according to the intra-annual variability of flows under natural conditions using statistical cluster analysis of monthly mean flow data; (b) characterise the resulting flow typologies according to several ecologically important hydrological variables; (c) analyse the relationships between flow regimes of fluvial segments and physical variables from their catchments; and finally (d) predict the most probable natural flow regime using logistic models based on the most determinant physical characteristics. Fifteen natural flow typologies were described in the Ebro basin, which were characterised in terms of flow fluctuation through the year as well as timing, flow ratio and duration of the maximum and minimum flows. Precipitation, biogeography and geology of catchments showed the highest correlations with flow regimes. Basin size, mean elevation and slope were also correlated. The logistic model we developed had a prediction success of 72% in the Ebro basin. The definition of the natural hydrological conditions (to which the biological communities are tailored), even when flow data are not available, is an important support in the management of river ecosystems. It is especially suitable for setting goals in aquatic ecosystem conservation or restoration projects.

  19. 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

  20. Surface-slip equations for multicomponent nonequilibrium air flow

    NASA Technical Reports Server (NTRS)

    Gupta, R. N.; Scott, C. D.; Moss, J. N.

    1985-01-01

    Equations are presented for the surface-slip (or jump) values of species concentration, pressure, velocity, and temperature in the low-Reynolds number, high-altitude flight regime of a space vehicle. The equations are obtained from closed form solutions of the mass, momentum, and energy flux equations using the Chapman-Enskog velocity distribution function. This function represents a solution of the Boltzmann equation in the Navier-Stokes approximation. The analysis, obtained for nonequilibrium multicomponent air flow, includes the finite-rate surface catalytic recombination and changes in the internal energy during reflection from the surface. Expressions for the various slip quantities were obtained in a form which can be employed in flowfield computations. A consistent set of equations is provided for multicomponent, binary, and single species mixtures. Expression is also provided for the finite-rate, species-concentration boundary condition for a multicomponent mixture in absence of slip.

  1. Air temperature evolution during dry spells and its relation to prevailing soil moisture regimes

    NASA Astrophysics Data System (ADS)

    Schwingshackl, Clemens; Hirschi, Martin; Seneviratne, Sonia I.

    2015-04-01

    The complex interplay between land and atmosphere makes accurate climate predictions very challenging, in particular with respect to extreme events. More detailed investigations of the underlying dynamics, such as the identification of the drivers regulating the energy exchange at the land surface and the quantification of fluxes between soil and atmosphere over different land types, are thus necessary. The recently started DROUGHT-HEAT project (funded by the European Research Council) aims to provide better understanding of the processes governing the land-atmosphere exchange. In the first phase of the project, different datasets and methods are used to investigate major drivers of land-atmosphere dynamics leading to droughts and heatwaves. In the second phase, these findings will be used for reducing uncertainties and biases in earth system models. Finally, the third part of the project will focus on the application of the previous findings and use them for the attribution of extreme events to land processes and possible mitigation through land geoengineering. One of the major questions in land-atmosphere exchange is the relationship between air temperature and soil moisture. Different studies show that especially during dry spells soil moisture has a strong impact on air temperature and the amplification of hot extremes. Whereas in dry and wet soil moisture regimes variations in latent heat flux during rain-free periods are expected to be small, this is not the case in transitional soil moisture regimes: Due to decreasing soil moisture content latent heat flux reduces with time, which causes in turn an increase in sensible heat flux and, subsequently, higher air temperatures. The investigation of air temperature evolution during dry spells can thus help to detect different soil moisture regimes and to provide insights on the effect of different soil moisture levels on air temperature. Here we assess the underlying relationships using different observational and

  2. Stokes flow between eccentric rotating spheres with slip regime

    NASA Astrophysics Data System (ADS)

    Faltas, M. S.; Saad, E. I.

    2012-10-01

    The steady axisymmetric flow problem of a viscous fluid contained between two eccentric spheres that rotate about an axis joining their centers with different angular velocities is considered. A linear slip of Basset-type boundary condition at both surfaces of the spherical particle and the container is used. Under the Stokesian assumption, a general solution is constructed from the superposition of basic solutions in the spherical coordinate systems based on the inner solid particle and the spherical container. The boundary conditions on the particle's surface and spherical container are satisfied by a collocation technique. Numerical results for the coupling coefficient acting on the particle are obtained with good convergence for various values of the ratio of particle-to-container radii, the relative distance between the centers of the particle and container, the slip coefficients and the relative angular velocity. In the limiting cases, the numerical values of the coupling coefficient for the solid sphere in concentric position with the container and when the particle is near the inner surface of the container are obtained, and the results are in good agreement with the available values in the literature. The variation of the coupling coefficient with respect the parameters considered are tabulated and displayed graphically.

  3. 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.

  4. Lattice-Boltzmann simulation for pressure driven microscale gas flows in transition regime

    NASA Astrophysics Data System (ADS)

    Yue, Xiang-Ji; Wu, Ze-Huan; Ba, Yao-Shuai; Lu, Yan-Jun; Zhu, Zhi-Peng; Ba, De-Chun

    2015-09-01

    This paper carries out numerical simulation for pressure driven microscale gas flows in transition flow regime. The relaxation time of LBM model was modified with the application of near wall effective mean free path combined with a combination of Bounce-back and Specular Reflection (BSR) boundary condition. The results in this paper are more close to those of DSCM and IP-DSCM compared with the results obtained by other LBM models. The calculation results show that in transition regime, with the increase of Knudsen number, the dimensionless slip velocity at the wall significantly increases, but the maximum linear deviation of nonlinear pressure distribution gradually decreases.

  5. 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.

  6. 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.

  7. 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.

  8. Decentralized and Tactical Air Traffic Flow Management

    NASA Technical Reports Server (NTRS)

    Bertsimas, Dimitris; Odoni, Amedeo R.

    1997-01-01

    This project dealt with the following topics: 1. Review and description of the existing air traffic flow management system (ATFM) and identification of aspects with potential for improvement. 2. Identification and review of existing models and simulations dealing with all system segments (enroute, terminal area, ground) 3. Formulation of concepts for overall decentralization of the ATFM system, ranging from moderate decentralization to full decentralization 4. Specification of the modifications to the ATFM system required to accommodate each of the alternative concepts. 5. Identification of issues that need to be addressed with regard to: determination of the way the ATFM system would be operating; types of flow management strategies that would be used; and estimation of the effectiveness of ATFM with regard to reducing delay and re-routing costs. 6. Concept evaluation through identification of criteria and methodologies for accommodating the interests of stakeholders and of approaches to optimization of operational procedures for all segments of the ATFM system.

  9. Weathering of plagioclase across variable flow and solute transport regimes

    NASA Astrophysics Data System (ADS)

    Pacheco, Fernando A. L.; Van der Weijden, Cornelis H.

    2012-02-01

    SummaryThe study area is situated in a fault zone with fractured granites and metasediments. In a conceptual model, infiltrating water first passes the bedrock cover of soil and saprolite and then partly enters the fractures. Weathering reactions of minerals occur in small pores and fissures in the bedrock cover zone to continue in the larger fractures. Pumping tests were carried out in a number of boreholes to measure the drawdown as a function of pumping time. From the results, values of transmissivity ( T) could be derived. In combination with the storage coefficient ( S) for similar fault zones, the hydraulic diffusivity ( D = T/ S) could be computed. Water samples, collected from the boreholes, represent fluid packets with a history of weathering reactions in the bedrock cover and in the larger fractures. The major element composition of these samples was used by means of the SiB mass balance algorithm ( Pacheco and Van der Weijden, 1996) to calculate the moles L -1 of dissolved plagioclase (oligoclase with An ≈ 0.20) and the moles L -1 of secondary phases (gibbsite, halloysite, smectite) precipitated along the flow paths of the samples. These results were then used to calculate the net dissolved silica concentrations ( [HSiO40]) related to dissolution of plagioclase followed by precipitation of each of the secondary phases. An interpretation of a plot of each of these [HSiO40] 's versusD is that at D < 0.7 m 2 s -1, dissolution of plagioclase is followed by precipitation of halloysite in the large fractures of the fault zone (open system), whereas at D ⩾ 0.7 m 2 s -1 precipitation of both halloysite and smectite occurs in the rock matrix with small fissures and pores (semi-open system). Before being pumped, the percolating fluids travelled 0.01-13.7 years. During these periods, plagioclase weathered at rates ( W Pl) of 10 -(12.9±1.1) moles m -2 s -1, which are approximately 2.2 orders of magnitude higher than solid-state weathering rates reported in

  10. Operation of the ISL transonic shock tube in a high subsonic flow regime

    NASA Astrophysics Data System (ADS)

    Seiler, F.; Havermann, M.; Boller, F.; Mangold, P.; Takayama, K.

    The transonic flow regime plays an important role in experimental aerodynamic research. Modern civil aircraft fly up to a Mach number of M ≈ 0.9 in the high subsonic speed regime, as, for example, the Boeing or Airbus passenger aircraft. Nearly sonic Mach numbers are foreseen for innovative airplane concepts like the sonic cruiser by Boeing. In the military domain, guided missiles like the cruise missile also fly in the high subsonic flow regime. For testing purposes, transonic wind tunnels are mainly used for sub- as well as supersonic design applications. These wind tunnels have normally very large dimensions, which makes their operation quite expensive. If only small scale tests are required, a cheap working facility turns out to be more beneficial. For this purpose, a conventional shock tube operated at transonic flow conditions has been put into operation at the ISL. In the transonic flow regime, however, the reduction of the tube cross section by the model can produce severe distortions followed by a choking of the shock tube flow in the test section. Extensive experimental investigations were performed to determine the subsonic choking Mach number as a function of the model size. These results are compared with theoretical estimations and, more in detail, with CFD calculations.

  11. 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.

  12. Combustor air flow control method for fuel cell apparatus

    DOEpatents

    Clingerman, Bruce J.; Mowery, Kenneth D.; Ripley, Eugene V.

    2001-01-01

    A method for controlling the heat output of a combustor in a fuel cell apparatus to a fuel processor where the combustor has dual air inlet streams including atmospheric air and fuel cell cathode effluent containing oxygen depleted air. In all operating modes, an enthalpy balance is provided by regulating the quantity of the air flow stream to the combustor to support fuel cell processor heat requirements. A control provides a quick fast forward change in an air valve orifice cross section in response to a calculated predetermined air flow, the molar constituents of the air stream to the combustor, the pressure drop across the air valve, and a look up table of the orifice cross sectional area and valve steps. A feedback loop fine tunes any error between the measured air flow to the combustor and the predetermined air flow.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Dynamic Flow Management Problems in Air Transportation

    NASA Technical Reports Server (NTRS)

    Patterson, Sarah Stock

    1997-01-01

    In 1995, over six hundred thousand licensed pilots flew nearly thirty-five million flights into over eighteen thousand U.S. airports, logging more than 519 billion passenger miles. Since demand for air travel has increased by more than 50% in the last decade while capacity has stagnated, congestion is a problem of undeniable practical significance. In this thesis, we will develop optimization techniques that reduce the impact of congestion on the national airspace. We start by determining the optimal release times for flights into the airspace and the optimal speed adjustment while airborne taking into account the capacitated airspace. This is called the Air Traffic Flow Management Problem (TFMP). We address the complexity, showing that it is NP-hard. We build an integer programming formulation that is quite strong as some of the proposed inequalities are facet defining for the convex hull of solutions. For practical problems, the solutions of the LP relaxation of the TFMP are very often integral. In essence, we reduce the problem to efficiently solving large scale linear programming problems. Thus, the computation times are reasonably small for large scale, practical problems involving thousands of flights. Next, we address the problem of determining how to reroute aircraft in the airspace system when faced with dynamically changing weather conditions. This is called the Air Traffic Flow Management Rerouting Problem (TFMRP) We present an integrated mathematical programming approach for the TFMRP, which utilizes several methodologies, in order to minimize delay costs. In order to address the high dimensionality, we present an aggregate model, in which we formulate the TFMRP as a multicommodity, integer, dynamic network flow problem with certain side constraints. Using Lagrangian relaxation, we generate aggregate flows that are decomposed into a collection of flight paths using a randomized rounding heuristic. This collection of paths is used in a packing integer

  20. 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%.

  1. 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

  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 regimes in a T-mixer operating with a binary mixture

    NASA Astrophysics Data System (ADS)

    Camarri, Simone; Siconolfi, Lorenzo; Galletti, Chiara; Salvetti, Maria Vittoria

    2015-11-01

    Efficient mixing in small volumes is a key target in many processes. Among the most common micro-devices, passive T-shaped micro-mixers are widely used. For this reason, T-mixers have been studied in the literature and its working flow regimes have been identified. However, in most of the available theoretical studies it is assumed that only one working fluid is used, i.e. that the same fluid at the same thermodynamic conditions is entering the two inlet conduits of the mixer. Conversely, the practical use of micro-devices often involves the mixing of two different fluids or of the same fluid at different thermodynamic conditions. In this case flow regimes significantly different than those observed for a single working fluid may occur. The present work aims at investigating the flow regimes in a T-mixers when water at two different temperatures, i.e. having different viscosity and density, is entering the mixer. The effect of the temperature difference on the flow regimes in a 3D T-mixer is investigated by DNS and stability analysis and the results are compared to the case in which a single working fluid is employed.

  4. FLOW REGIME, JUVENILE ABUNDANCE, AND THE ASSEMBLAGE STRUCTURE OF STREAM FISHES

    EPA Science Inventory

    The assemblage of fishes in a second-order stream in east-central Illinois was compared through seine sampling for two years with distinctly different flow regimes. In both years adult (age 0) fish were most abundant in late spring and early summer while juvenile (age 0) abundanc...

  5. 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

  6. Changes in air flow patterns using surfactants and thickeners during air sparging: Bench-scale experiments

    NASA Astrophysics Data System (ADS)

    Kim, Juyoung; Kim, Heonki; Annable, Michael D.

    2015-01-01

    Air injected into an aquifer during air sparging normally flows upward according to the pressure gradients and buoyancy, and the direction of air flow depends on the natural hydrogeologic setting. In this study, a new method for controlling air flow paths in the saturated zone during air sparging processes is presented. Two hydrodynamic parameters, viscosity and surface tension of the aqueous phase in the aquifer, were altered using appropriate water-soluble reagents distributed before initiating air sparging. Increased viscosity retarded the travel velocity of the air front during air sparging by modifying the viscosity ratio. Using a one-dimensional column packed with water-saturated sand, the velocity of air intrusion into the saturated region under a constant pressure gradient was inversely proportional to the viscosity of the aqueous solution. The air flow direction, and thus the air flux distribution was measured using gaseous flux meters placed at the sand surface during air sparging experiments using both two-, and three-dimensional physical models. Air flow was found to be influenced by the presence of an aqueous patch of high viscosity or suppressed surface tension in the aquifer. Air flow was selective through the low-surface tension (46.5 dyn/cm) region, whereas an aqueous patch of high viscosity (2.77 cP) was as an effective air flow barrier. Formation of a low-surface tension region in the target contaminated zone in the aquifer, before the air sparging process is inaugurated, may induce air flow through the target zone maximizing the contaminant removal efficiency of the injected air. In contrast, a region with high viscosity in the air sparging influence zone may minimize air flow through the region prohibiting the region from de-saturating.

  7. Upper air teleconnections to Ob River flows and tree rings

    NASA Astrophysics Data System (ADS)

    Meko, David; Panyushkina, Irina; Agafonov, Leonid

    2015-04-01

    The Ob River, one of the world's greatest rivers, with a catchment basin about the size of Western Europe, contributes 12% or more of the annual freshwater inflow to the Arctic Ocean. The input of heat and fresh water is important to the global climate system through effects on sea ice, salinity, and the thermohaline circulation of the ocean. As part of a tree-ring project to obtain multi-century long information on variability of Ob River flows, a network of 18 sites of Pinus, Larix, Populus and Salix has been collected along the Ob in the summers of 2013 and 2014. Analysis of collections processed so far indicates a significant relationship of tree-growth to river discharge. Moderation of the floodplain air temperature regime by flooding appears to be an important driver of the tree-ring response. In unraveling the relationship of tree-growth to river flows, it is important to identify atmospheric circulation features directly linked to observed time series variations of flow and tree growth. In this study we examine statistical links between primary teleconnection modes of Northern Hemisphere upper-air (500 mb) circulation, Ob River flow, and tree-ring chronologies. Annual discharge at the mouth of the Ob River is found to be significantly positively related to the phase of the East Atlantic (EA) pattern, the second prominent mode of low-frequency variability over the North Atlantic. The EA pattern, consisting of a north-south dipole of pressure-anomaly centers spanning the North Atlantic from east to west, is associated with a low-pressure anomaly centered over the Ob River Basin, and with a pattern of positive precipitation anomaly of the same region. The positive correlation of discharge and EA is consistent with these know patterns, and is contrasted with generally negative (though smaller) correlations between EA and tree-ring chronologies. The signs of correlations are consistent with a conceptual model of river influence on tree growth through air

  8. Prediction of the multicellular flow regime of natural convection in fenestration glazing cavities

    SciTech Connect

    Zhao, Y.; Goss, W.P.; Curcija, D.

    1997-12-31

    In this work, gas-filled tall rectangular cavities, typically found in insulating glazing units (IGUs) of fenestration systems, with constant temperatures at the side walls and zero heat flux at the top and bottom, were investigated. Critical Rayleigh numbers, Ra{sub c}, at which multicellular flow begins to form were determined for aspect ratios from 10.7 to 80. Using a general-purpose fluid flow and heat transfer finite-element analysis computer program (FDI 1993), numerical calculations were performed over the range of aspect ratios, A, from 10 to 80 with Rayleigh numbers, Ra, varying within the laminar flow regime. The calculations revealed that for aspect ratios between 10.7 and 30, the multicellular flow pattern dies out before the flow enters the turbulent flow regime. In addition, the lowest aspect ratio at which multicellular flow patterns existed was 10.7, which is lower than the lowest limit (A = 12) published by other researchers. The resulting critical Rayleigh numbers are plotted on a graph as a function of the aspect ratio and the Rayleigh numbers. The overall heat transfer results in terms of the average, or integrated, Nusselt numbers, Nu, are compared with available numerical and experimental data on multicellular flow in rectangular cavities, and good agreement was found. Also, streamline contour plots and temperature profiles are plotted for selected cases.

  9. Nanosecond Repetitively Pulsed Discharges in Air at Atmospheric Pressure -- Experiment and Theory of Regime Transitions

    NASA Astrophysics Data System (ADS)

    Pai, David; Lacoste, Deanna; Laux, Christophe

    2009-10-01

    In atmospheric pressure air preheated from 300 to 1000 K, the Nanosecond Repetitively Pulsed (NRP) method has been used to generate corona, glow, and spark discharges. Experiments have been performed to determine the parameter space (applied voltage, pulse repetition frequency, ambient gas temperature, and inter-electrode gap distance) of each discharge regime. Notably, there is a minimum gap distance for the existence of the glow regime that increases with decreasing gas temperature. A theory is developed to describe the Corona-to-Glow (C-G) and Glow-to-Spark (G-S) transitions for NRP discharges. The C-G transition is shown to depend on the Avalanche-to-Streamer Transition (AST) as well as the electric field strength in the positive column. The G-S transition is due to the thermal ionization instability. The minimum gap distance for the existence of the glow regime can be understood by considering that the applied voltage of the AST must be lower than that of the thermal ionization instability. This is a previously unknown criterion for generating glow discharges, as it does not correspond to the Paschen minimum or to the Meek-Raether criterion.

  10. Effect of intermolecular potential on compressible Couette flow in slip and transitional regimes

    NASA Astrophysics Data System (ADS)

    Weaver, Andrew B.; Venkattraman, A.; Alexeenko, Alina A.

    2014-10-01

    The effect of intermolecular potentials on compressible, planar flow in slip and transitional regimes is investigated using the direct simulation Monte Carlo method. Two intermolecular interaction models, the variable hard sphere (VHS) and the Lennard-Jones (LJ) models, are first compared for subsonic and supersonic Couette flows of argon at temperatures of 40, 273, and 1,000 K, and then for Couette flows in the transitional regime ranging from Knudsen numbers (Kn) of 0.0051 to 1. The binary scattering model for elastic scattering using the Lennard-Jones (LJ) intermolecular potential proposed recently [A. Venkattraman and A. Alexeenko, "Binary scattering model for Lennard-Jones potential: Transport coefficients and collision integrals for non-equilibrium gas flow simulations," Phys. Fluids 24, 027101 (2012)] is shown to accurately reproduce both the theoretical collision frequency in an equilibrium gas as well as the theoretical viscosity variation with temperature. The use of a repulsive-attractive instead of a purely repulsive potential is found to be most important in the continuum and slip regimes as well as in flows with large temperature variations. Differences in shear stress of up to 28% between the VHS and LJ models is observed at Kn=0.0051 and is attributed to differences in collision frequencies, ultimately affecting velocity gradients at the wall. For Kn=1 where the Knudsen layer expands the entire domain, the effect of the larger collision frequency in the LJ model relative to VHS diminishes, and a 7% difference in shear stress is observed.

  11. Prediction of refrigerant void fraction in horizontal tubes using probabilistic flow regime maps

    SciTech Connect

    Jassim, E.W.; Newell, T.A.; Chato, J.C.

    2008-04-15

    A state of the art review of two-phase void fraction models in smooth horizontal tubes is provided and a probabilistic two-phase flow regime map void fraction model is developed for refrigerants under condensation, adiabatic, and evaporation conditions in smooth, horizontal tubes. Time fraction information from a generalized probabilistic two-phase flow map is used to provide a physically based weighting of void fraction models for different flow regimes. The present model and void fraction models in the literature are compared to data from multiple sources including R11, R12, R134a, R22, R410A refrigerants, 4.26-9.58 mm diameter tubes, mass fluxes from 70 to 900 kg/m{sup 2} s, and a full quality range. The present model has a mean absolute deviation of 3.5% when compared to the collected database. (author)

  12. 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.

  13. 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.

  14. Characterising temporary streams' regimes using qualitative "aquatic states" instead of quantitative flow measures.

    NASA Astrophysics Data System (ADS)

    Gallart, F.; Prat, N.

    2012-04-01

    The analysis of the biological communities found in stream reaches is currently used for the assessment of the quality of stream waters. Nevertheless, in temporary streams, these communities are largely varying in time, strongly depending on the occurrence of the sets of aquatic mesohabitats determined by the hydrological conditions (hereafter called Aquatic States). Particularly, the interruption of the flow in a stream, or even its total desiccation, plays a determinant role in their ecological communities so much so that temporary streams should be considered a distinct class of ecosystems instead of simply hydrologically challenged permanent streams. Within the EU MIRAGE project (grant FP7 n° 211732), two complementary tools have been developed to analyse and characterise the regime of temporary streams: the Aquatic States Frequency Graph (ASFG) that shows the monthly frequency of occurrence of the diverse Aquatic States throughout the year, and the Temporary Stream Regime Plot (TSRP) that maps the value of two metrics that describe respectively the relative number of months with flow per year (Mf) and the seasonal predictability of the zero-flow periods (Sd6). The ASFG allows a rapid appraisal of the stream regime relevant for the development of the aquatic life and is useful for anticipating the sampling calendars but is somewhat dependent of the subjective criteria of the observer. On the contrary, the TSRP manages much less information but allows the comparison and classification of the regimes and is based on the more objective criterion of the presence-absence of flow. In the case of lack of observations, rainfall-runoff models may be used to develop these analyses, although a threshold value for zero flow must be assessed as models usually do not simulate the absence of flow.

  15. Zonal flow regimes in rotating anelastic spherical shells: An application to giant planets

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    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. We use three-dimensional numerical models of compressible convection in rotating spherical shells to explore the properties of zonal flows in different regimes where either rotation or buoyancy dominates the force balance. We conduct a systematic parameter study to quantify the dependence of zonal flows on the background density stratification and the driving of convection. In our numerical models, we find that the direction of the equatorial zonal wind is controlled by the ratio of the global-scale buoyancy force and the Coriolis force. The prograde equatorial band maintained by Reynolds stresses is found in the rotation-dominated regime. In cases where buoyancy dominates Coriolis force, the angular momentum per unit mass is homogenized and the equatorial band is retrograde, reminiscent to those observed in the ice giants. In this regime, the amplitude of the zonal jets depends on the background density contrast with strongly stratified models producing stronger jets than comparable weakly stratified cases. Furthermore, our results can help to explain the transition between solar-like (i.e. prograde at the equator) and the "anti-solar" differential rotations (i.e. retrograde at the equator) found in anelastic models of stellar convection zones. In the strongly stratified cases, we find that the leading order force balance can significantly vary with depth. While the flow in the deep interior is dominated by rotation, buoyancy can indeed become larger than Coriolis force in a thin region close to the surface. This so-called "transitional regime" has a visible signature in the main equatorial jet which shows a pronounced dimple where flow amplitudes notably decay towards the equator. A similar dimple is observed on

  16. 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.

  17. Apparatus and method for generating large mass flow of high temperature air at hypersonic speeds

    NASA Technical Reports Server (NTRS)

    Sabol, A. P.; Stewart, R. B. (Inventor)

    1973-01-01

    High temperature, high mass air flow and a high Reynolds number test air flow in the Mach number 8-10 regime of adequate test flow duration is attained by pressurizing a ceramic-lined storage tank with air to a pressure of about 100 to 200 atmospheres. The air is heated to temperatures of 7,000 to 8,000 R prior to introduction into the tank by passing the air over an electric arc heater means. The air cools to 5,500 to 6,000 R while in the tank. A decomposable gas such as nitrous oxide or a combustible gas such as propane is injected into the tank after pressurization and the heated pressurized air in the tank is rapidly released through a Mach number 8-10 nozzle. The injected gas medium upon contact with the heated pressurized air effects an exothermic reaction which maintains the pressure and temperature of the pressurized air during the rapid release.

  18. Direct numerical simulation of a turbulent stably stratified air flow above a wavy water surface

    NASA Astrophysics Data System (ADS)

    Druzhinin, O. A.; Troitskaya, Yu. I.; Zilitinkevich, S. S.

    2016-01-01

    The influence of the roughness of the underlaying water surface on turbulence is studied in a stably stratified boundary layer (SSBL). Direct numerical simulation (DNS) is conducted at various Reynolds (Re) and Richardson (Ri) numbers and the wave steepness ka. It is shown that, at constant Re, the stationary turbulent regime is set in at Ri below the threshold value Ri c depending on Re. At Ri > Ri c , in the absence of turbulent fluctuations near the wave water surface, three-dimensional quasiperiodical structures are identified and their threshold of origin depends on the steepness of the surface wave on the water surface. This regime is called a wave pumping regime. The formation of three-dimensional structures is explained by the development of parametric instability of the disturbances induced by the surface water in the air flow. The DNS results are quite consistent with prediction of the theoretical model of the SSBL flow, in which solutions for the disturbances of the fields of velocity and temperature in the wave pumping regime are found to be a solution of a two-dimensional linearized system with the heterogeneous boundary condition, which is caused by the presence of the surface wave. In addition to the turbulent fluctuations, the three-dimensional structures in the wave pumping regime provide for the transfer of impulse and heat, i.e., the increase in the roughness of the water-air boundary caused by the presence of waves intensifies the exchange in the SSBL.

  19. 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.

  20. 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. PMID:18819012

  1. 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

  2. Femtosecond laser flow tagging in non-air flows

    NASA Astrophysics Data System (ADS)

    Zhang, Yibin; Calvert, Nathan

    2015-11-01

    The Femtosecond Laser Electronic Excitation Tagging (FLEET) [Michael, J. B. et al., Applied optics, 50(26), 2011] method is studied in nitrogen-containing gaseous flows. The underlying mechanism behind the FLEET process is the dissociation of molecular nitrogen into atomic nitrogen, which produces long-lived florescence as the nitrogen atoms recombine. Spectra and images of the resulting tagged line provide insight into the effects of different atmospheric gases on the FLEET process. The ionization cross-section, conductivity and energy states of the gaseous particles are each brought into consideration. These experiments demonstrate the feasibility for long-lived flow tagging on the order of hundreds of microseconds in non-air environments. Of particular interest are the enhancement of the FLEET signal with the addition of argon gas, and the non-monotonic quenching effect of oxygen on the length, duration and intensity of the resulting signal and spectra. FLEET is characterized in number of different atmospheric gases, including that simulating Mar's atmospheric composition.

  3. 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.

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

    SciTech Connect

    Carrigan, C. .; Schubert, G.; Eichelberger, J.C. California Univ., Los Angeles Alaska Univ., Fairbanks )

    1992-11-01

    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. 56 refs.

  5. A Study on the Air flow outside Ambient Vaporizer Fin

    NASA Astrophysics Data System (ADS)

    Oh, G.; Lee, T.; Jeong, H.; Chung, H.

    2015-09-01

    In this study, we interpreted Fog's Fluid that appear in the Ambient Vaporizer and predict the point of change Air to Fog. We interpreted using Analysis working fluid was applied to LNG and Air. We predict air flow when there is chill of LNG in the air Temperature and that makes fog. Also, we interpreted based on Summer and Winter criteria in the air temperature respectively. Finally, we can check the speed of the fog when fog excreted.

  6. Influence of air flow parameters on nanosecond repetitively pulsed discharges in a pin-annular electrode configuration

    NASA Astrophysics Data System (ADS)

    Heitz, Sylvain A.; Moeck, Jonas P.; Schuller, Thierry; Veynante, Denis; Lacoste, Deanna A.

    2016-04-01

    The effect of various air flow parameters on the plasma regimes of nanosecond repetitively pulsed (NRP) discharges is investigated at atmospheric pressure. The two electrodes are in a pin-annular configuration, transverse to the mean flow. The voltage pulses have amplitudes up to 15 kV, a duration of 10 ns and a repetition frequency ranging from 15 to 30 kHz. The NRP corona to NRP spark (C-S) regime transition and the NRP spark to NRP corona (S-C) regime transition are investigated for different steady and harmonically oscillating flows. First, the strong effect of a transverse flow on the C-S and S-C transitions, as reported in previous studies, is verified. Second, it is shown that the azimuthal flow imparted by a swirler does not affect the regime transition voltages. Finally, the influence of low frequency harmonic oscillations of the air flow, generated by a loudspeaker, is studied. A strong effect of frequency and amplitude of the incoming flow modulation on the NRP plasma regime is observed. Results are interpreted based on the cumulative effect of the NRP discharges and an analysis of the residence times of fluid particles in the inter-electrode region.

  7. 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.

  8. Sensitivity of atmospheric flow regimes to anthropogenic forcing: Insights from an intermediate atmospheric model

    NASA Astrophysics Data System (ADS)

    Khatiwala, S.

    2003-04-01

    Changes in the frequency of extreme events are of great societal importance. Recent work suggests that these changes can be surprisingly large for variables with ``fat-tailed'' probability density functions (PDFs) even for small mean changes in climate. Fat-tailed, and in particular exponential, PDFs imply a greater likelihood of occurrence of large fluctuations (``extreme events''). The exponentially distributed persistence time of anomalous atmospheric flow patterns known as weather regimes is a climatically important example. The notion of atmospheric weather regimes as persistent, quasi-stationary flow patterns controlled by intermittently attracting fixed points in the atmosphere's phase space led Palmer (1999) to explore the behavior of low-dimensional chaotic systems. Based on insight from these simpler systems, Palmer hypothesized that the response of climate to a small imposed forcing (such as the anthropogenic emission of greenhouse gases) would manifest itself primarily in terms of the PDFs associated with regimes, while the spatial patterns of these regimes would be relatively unchanged. Palmer focused on changes in the average frequency of occurrence of regimes. However, recent experiments (Khatiwala et al, 2001) with simple dynamical and stochastic systems suggest that a potentially more damaging way in which the atmosphere can respond to small perturbations is through changes in the frequency of occurrence of extremely persistent events. In common with the atmosphere, these systems too are characterized by both regime behavior and exponential PDFs of persistence time. Consequently, small perturbations in external parameters can change the probability of occurrence of persistent events by many orders of magnitude. This extreme sensitivity is directly related to the stability properties of the system. An immediate question then is whether more complex geophysical systems with multiple regimes such as the atmosphere, are similarly sensitive to small

  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. Modeling of cavitation phenomena in homogeneous flow in transitory regimes in pipes

    NASA Astrophysics Data System (ADS)

    Kessal, Mohand

    1987-12-01

    Cavitation in transitory regime of a homogeneous gas-liquid mixture in an elastic pipe was studied. For the case where the two components have the same velocity, it is shown that it is possible to model the flow while conserving the relations and the continuous character of the medium. The flow equations were solved using the standard MacCormack finite difference scheme and the method of characteristics. Measurements confirm model validity. A characteristic formulation for the case where the two components have different velocities was derived.

  12. 40 CFR 1065.225 - Intake-air flow meter.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 34 2013-07-01 2013-07-01 false Intake-air flow meter. 1065.225 Section 1065.225 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements § 1065.225...

  13. 40 CFR 1065.225 - Intake-air flow meter.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 33 2011-07-01 2011-07-01 false Intake-air flow meter. 1065.225 Section 1065.225 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements § 1065.225...

  14. 40 CFR 1065.225 - Intake-air flow meter.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 34 2012-07-01 2012-07-01 false Intake-air flow meter. 1065.225 Section 1065.225 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements § 1065.225...

  15. 40 CFR 1065.225 - Intake-air flow meter.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 33 2014-07-01 2014-07-01 false Intake-air flow meter. 1065.225 Section 1065.225 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements § 1065.225...

  16. 40 CFR 1065.225 - Intake-air flow meter.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 32 2010-07-01 2010-07-01 false Intake-air flow meter. 1065.225 Section 1065.225 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements § 1065.225...

  17. Particle displacement tracking applied to air flows

    NASA Technical Reports Server (NTRS)

    Wernet, Mark P.

    1991-01-01

    Electronic Particle Image Velocimeter (PIV) techniques offer many advantages over conventional photographic PIV methods such as fast turn around times and simplified data reduction. A new all electronic PIV technique was developed which can measure high speed gas velocities. The Particle Displacement Tracking (PDT) technique employs a single cw laser, small seed particles (1 micron), and a single intensified, gated CCD array frame camera to provide a simple and fast method of obtaining two-dimensional velocity vector maps with unambiguous direction determination. Use of a single CCD camera eliminates registration difficulties encountered when multiple cameras are used to obtain velocity magnitude and direction information. An 80386 PC equipped with a large memory buffer frame-grabber board provides all of the data acquisition and data reduction operations. No array processors of other numerical processing hardware are required. Full video resolution (640x480 pixel) is maintained in the acquired images, providing high resolution video frames of the recorded particle images. The time between data acquisition to display of the velocity vector map is less than 40 sec. The new electronic PDT technique is demonstrated on an air nozzle flow with velocities less than 150 m/s.

  18. Measurement of air distribution and void fraction of an upwards air-water flow using electrical resistance tomography and a wire-mesh sensor

    NASA Astrophysics Data System (ADS)

    Olerni, Claudio; Jia, Jiabin; Wang, Mi

    2013-03-01

    Measurements on an upwards air-water flow are reported that were obtained simultaneously with a dual-plane electrical resistance tomograph (ERT) and a wire-mesh sensor (WMS). The ultimate measurement target of both ERT and WMS is the same, the electrical conductivity of the medium. The ERT is a non-intrusive device whereas the WMS requires a net of wires that physically crosses the flow. This paper presents comparisons between the results obtained simultaneously from the ERT and the WMS for evaluation and calibration of the ERT. The length of the vertical testing pipeline section is 3 m with an internal diameter of 50 mm. Two distinct sets of air-water flow rate scenarios, bubble and slug regimes, were produced in the experiments. The fast impedance camera ERT recorded the data at an approximate time resolution of 896 frames per second (fps) per plane in contrast with the 1024 fps of the wire-mesh sensor WMS200. The set-up of the experiment was based on well established knowledge of air-water upwards flow, particularly the specific flow regimes and wall peak effects. The local air void fraction profiles and the overall air void fraction were produced from two systems to establish consistency for comparison of the data accuracy. Conventional bulk flow measurements in air mass and electromagnetic flow metering, as well as pressure and temperature, were employed, which brought the necessary calibration to the flow measurements. The results show that the profiles generated from the two systems have a certain level of inconsistency, particularly in a wall peak and a core peak from the ERT and WMS respectively, whereas the two tomography instruments achieve good agreement on the overall air void fraction for bubble flow. For slug flow, when the void fraction is over 30%, the ERT underestimates the void fraction, but a linear relation between ERT and WMS is still observed.

  19. Emulsification in turbulent flow 1. Mean and maximum drop diameters in inertial and viscous regimes.

    PubMed

    Vankova, Nina; Tcholakova, Slavka; Denkov, Nikolai D; Ivanov, Ivan B; Vulchev, Vassil D; Danner, Thomas

    2007-08-15

    Systematic experimental study of the effects of several factors on the mean and maximum drop sizes during emulsification in turbulent flow is performed. These factors include: (1) rate of energy dissipation, epsilon; (2) interfacial tension, sigma; (3) viscosity of the oil phase, eta(D); (4) viscosity of the aqueous phase, eta(C); and (5) oil volume fraction, Phi. The emulsions are prepared by using the so-called "narrow-gap homogenizer" working in turbulent regime of emulsification. The experiments are performed at high surfactant concentration to avoid the effect of drop-drop coalescence. For emulsions prepared in the inertial turbulent regime, the mean and the maximum drop sizes increase with the increase of eta(D) and sigma, and with the decrease of epsilon. In contrast, Phi and eta(C) affect only slightly the mean and the maximum drop sizes in this regime of emulsification. These results are described very well by a theoretical expression proposed by Davies [Chem. Eng. Sci. 40 (1985) 839], which accounts for the effects of the drop capillary pressure and the viscous dissipation inside the breaking drops. The polydispersity of the emulsions prepared in the inertial regime of emulsification does not depend significantly on sigma and epsilon. However, the emulsion polydispersity increases significantly with the increase of oil viscosity, eta(D). The experiments showed also that the inertial turbulent regime is inappropriate for emulsification of oils with viscosity above ca. 500 mPa s, if drops of micrometer size are to be obtained. The transition from inertial to viscous turbulent regime of emulsification was accomplished by a moderate increase of the viscosity of the aqueous phase (above 5 mPa s in the studied systems) and/or by increase of the oil volume fraction, Phi>0.6. Remarkably, emulsions with drops of micrometer size are easily formed in the viscous turbulent regime of emulsification, even for oils with viscosity as high as 10,000 mPa s. In this regime

  20. On the nonlinear characteristics of the axisymmetric flow regime: Cylindrical and spherical systems

    NASA Technical Reports Server (NTRS)

    Higgins, R. W.; Dutton, J. A.; Shirer, H. N.

    1985-01-01

    The physical relationship between steady axisymmetric flows that might be observed in the atmosphere and in laboratory vessels is investigated theoretically. This is accomplished by comparing both the nonlinear structure and the thermal forcing mechanisms in two truncated spectral models of flow in the atmosphere and the rotating laboratory cylinder, respectively. Under statically stable conditions, the response of the internally forced spherical model (which is developed here from a set of new orthonormal basis functions) exhibits steady behavior different from that in the externally forced cylindrical model. Two regions of multiple steady solutions occur in the cylindrical model, under stable conditions, that are not found in the spherical one. The possible physical relevance of these multiple solutions is investigated by determining their location in parameter space with respect to the classical Hadley-Rossby transition curve. The results suggest that the wave flow regime, in an annulus, might develop catastrophically when an upper symmetric flow ceases to exist.

  1. Integrated turbine-compressor provides air flow for cooling

    NASA Technical Reports Server (NTRS)

    Ferri, A.

    1970-01-01

    Modified supersonic turbine cycle provides cooling air to surrounding structures. Simplified mechanical design assures correct balance of air flow, allows direct issue of cool air to the structure, and assists in matching turbine work output to work input required by the compressor.

  2. Research on Air Flow Measurement and Optimization of Control Algorithm in Air Disinfection System

    NASA Astrophysics Data System (ADS)

    Bing-jie, Li; Jia-hong, Zhao; Xu, Wang; Amuer, Mohamode; Zhi-liang, Wang

    2013-01-01

    As the air flow control system has the characteristics of delay and uncertainty, this research designed and achieved a practical air flow control system by using the hydrodynamic theory and the modern control theory. Firstly, the mathematical model of the air flow distribution of the system is analyzed from the hydrodynamics perspective. Then the model of the system is transformed into a lumped parameter state space expression by using the Galerkin method. Finally, the air flow is distributed more evenly through the estimation of the system state and optimal control. The simulation results show that this algorithm has good robustness and anti-interference ability

  3. Flow Regime Study in a High Density Circulating Fluidized Bed Riser with an Abrupt Exit

    SciTech Connect

    Mei, J.S.; Shadle, L.J.; Yue, P.C.; Monazam, E.R.

    2007-01-01

    Flow regime study was conducted in a 0.3 m diameter, 15.5 m height circulating fluidized bed (CFB) riser with an abrupt exit at the National Energy Technology Laboratory of the U.S. Department of Energy. Local particle velocities were measured at various radial positions and riser heights using an optical fiber probe. On-line measurement of solid circulating rate was continuously recorded by the Spiral. Glass beads of mean diameter 61 μm and particle density of 2,500 kg/m3 were used as bed material. The CFB riser was operated at various superficial gas velocities ranging from 3 to 7.6 m/s and solid mass flux from 20 to 550 kg/m2-s. At a constant riser gas velocity, transition from fast fluidization to dense suspension upflow (DSU) regime started at the bottom of the riser with increasing solid flux. Except at comparatively low riser gas velocity and solid flux, the apparent solid holdup at the top exit region was higher than the middle section of the riser. The solid fraction at this top region could be much higher than 7% under high riser gas velocity and solid mass flux. The local particle velocity showed downward flow near the wall at the top of the riser due to its abrupt exit. This abrupt geometry reflected the solids and, therefore, caused solid particles traveling downward along the wall. However, at location below, but near, the top of the riser the local particle velocities were observed flowing upward at the wall. Therefore, DSU was identified in the upper region of the riser with an abrupt exit while the fully developed region, lower in the riser, was still exhibiting core-annular flow structure. Our data were compared with the flow regime boundaries proposed by Kim et al. [1] for distinguishing the dilute pneumatic transport, fast fluidization, and DSU.

  4. 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.

  5. Three-dimensional freezing of flowing water in a tube cooled by air flow

    NASA Astrophysics Data System (ADS)

    Sugawara, M.; Komatsu, Y.; Beer, H.

    2015-05-01

    The 3-D freezing of flowing water in a copper tube cooled by air flow is investigated by means of a numerical analysis. The air flows normal to the tube axis. Several parameters as inlet water mean velocity w m , inlet water temperature T iℓ t , air flow temperature T a and air flow velocity u a are selected in the calculations to adapt it to a winter season actually encountered. The numerical results present the development of the ice layer mean thickness and its 3-D morphologies as well as the critical ice layer thickness in the tube choked by the ice layer.

  6. Air-flow regulation system for a coal gasifier

    DOEpatents

    Fasching, George E.

    1984-01-01

    An improved air-flow regulator for a fixed-bed coal gasifier is provided which allows close air-flow regulation from a compressor source even though the pressure variations are too rapid for a single primary control loop to respond. The improved system includes a primary controller to control a valve in the main (large) air supply line to regulate large slow changes in flow. A secondary controller is used to control a smaller, faster acting valve in a secondary (small) air supply line parallel to the main line valve to regulate rapid cyclic deviations in air flow. A low-pass filter with a time constant of from 20 to 50 seconds couples the output of the secondary controller to the input of the primary controller so that the primary controller only responds to slow changes in the air-flow rate, the faster, cyclic deviations in flow rate sensed and corrected by the secondary controller loop do not reach the primary controller due to the high frequency rejection provided by the filter. This control arrangement provides at least a factor of 5 improvement in air-flow regulation for a coal gasifier in which air is supplied by a reciprocating compressor through a surge tank.

  7. 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

  8. Flow regimes, bed morphology, and flow resistance in self-formed step-pool channels

    NASA Astrophysics Data System (ADS)

    Comiti, F.; Cadol, D.; Wohl, E.

    2009-04-01

    We used a mobile bed flume with scaled grain size distribution, channel geometry, and flow to examine morphology and hydraulics of stepped channels. We hypothesized that (1) step geometry and flow resistance differs significantly as a function of the range of grain sizes present, (2) a transition from nappe to skimming flow occurs in stepped channels with mobile beds for conditions similar to stepped spillways, and (3) the partitioning of flow resistance changes significantly when flow passes from nappe to skimming conditions. Results support each of these hypotheses and help to illuminate the complexity of V-Q relationships in stepped channels, in which a dramatic decrease in flow resistance and increase in velocity accompany the transition from nappe to skimming flow near step-forming events. Therefore, a single flow resistance equation applicable to both ordinary and large floods may not be ideal in stepped channels. Nonetheless, models based on dimensionless velocity and unit discharge appear more robust compared to those based on the Darcy-Weisbach friction factor.

  9. Phase 2: HGM air flow tests in support of HEX vane investigation

    NASA Technical Reports Server (NTRS)

    Cox, G. B., Jr.; Steele, L. L.; Eisenhart, D. W.

    1993-01-01

    Following the start of SSME certification testing for the Pratt and Whitney Alternate Turbopump Development (ATD) High Pressure Oxidizer Turbopump (HPOTP), cracking of the leading edge of the inner HEX vane was experienced. The HEX vane, at the inlet of the oxidizer bowl in the Hot Gas Manifold (HGM), accepts the HPOTP turbine discharge flow and turns it toward the Gaseous Oxidizer Heat Exchanger (GOX HEX) coil. The cracking consistently initiated over a specific circumferential region of the hex vane, with other circumferential locations appearing with increased run time. Since cracking had not to date been seen with the baseline HPOTP, a fluid-structural interaction involving the ATD HPOTP turbine exit flowfield and the HEX inner vane was suspected. As part of NASA contract NAS8-36801, Pratt and Whitney conducted air flow tests of the ATD HPOTP turbine turnaround duct flowpath in the MSFC Phase 2 HGM air flow model. These tests included HEX vane strain gages and additional fluctuating pressure gages in the turnaround duct and HEX vane flowpath area. Three-dimensional flow probe measurements at two stations downstream of the turbine simulator exit plane were also made. Modifications to the HPOTP turbine simulator investigated the effects on turbine exit flow profile and velocity components, with the objective of reproducing flow conditions calculated for the actual ATD HPOTP hardware. Testing was done at the MSFC SSME Dynamic Fluid Air Flow (Dual-Leg) Facility, at air supply pressures between 50 and 250 psia. Combinations of turbine exit Mach number and pressure level were run to investigate the effect of flow regime. Information presented includes: (1) Descriptions of turbine simulator modifications to produce the desired flow environment; (2) Types and locations for instrumentation added to the flow model for improved diagnostic capability; (3) Evaluation of the effect of changes to the turbine simulator flowpath on the turbine exit flow environment; and (4

  10. Phase 2: HGM air flow tests in support of HEX vane investigation

    NASA Astrophysics Data System (ADS)

    Cox, G. B., Jr.; Steele, L. L.; Eisenhart, D. W.

    1993-07-01

    Following the start of SSME certification testing for the Pratt and Whitney Alternate Turbopump Development (ATD) High Pressure Oxidizer Turbopump (HPOTP), cracking of the leading edge of the inner HEX vane was experienced. The HEX vane, at the inlet of the oxidizer bowl in the Hot Gas Manifold (HGM), accepts the HPOTP turbine discharge flow and turns it toward the Gaseous Oxidizer Heat Exchanger (GOX HEX) coil. The cracking consistently initiated over a specific circumferential region of the hex vane, with other circumferential locations appearing with increased run time. Since cracking had not to date been seen with the baseline HPOTP, a fluid-structural interaction involving the ATD HPOTP turbine exit flowfield and the HEX inner vane was suspected. As part of NASA contract NAS8-36801, Pratt and Whitney conducted air flow tests of the ATD HPOTP turbine turnaround duct flowpath in the MSFC Phase 2 HGM air flow model. These tests included HEX vane strain gages and additional fluctuating pressure gages in the turnaround duct and HEX vane flowpath area. Three-dimensional flow probe measurements at two stations downstream of the turbine simulator exit plane were also made. Modifications to the HPOTP turbine simulator investigated the effects on turbine exit flow profile and velocity components, with the objective of reproducing flow conditions calculated for the actual ATD HPOTP hardware. Testing was done at the MSFC SSME Dynamic Fluid Air Flow (Dual-Leg) Facility, at air supply pressures between 50 and 250 psia. Combinations of turbine exit Mach number and pressure level were run to investigate the effect of flow regime. Information presented includes: (1) Descriptions of turbine simulator modifications to produce the desired flow environment; (2) Types and locations for instrumentation added to the flow model for improved diagnostic capability; (3) Evaluation of the effect of changes to the turbine simulator flowpath on the turbine exit flow environment; and (4

  11. 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.

  12. 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.

  13. Integrating Acoustic Imaging of Flow Regimes With Bathymetry: A Case Study, Main Endeavor Field

    NASA Astrophysics Data System (ADS)

    Bemis, K. G.; Rona, P. A.; Jackson, D. R.; Jones, C. D.

    2003-12-01

    A unified view of the seafloor and the hydrothermal flow regimes (plumes and diffuse flow) is constructed for three major vent clusters in the Main Endeavour Field (e.g., Grotto, S&M, and Salut) of the Endeavour Segment, Juan de Fuca Ridge. The Main Endeavour Field is one of RIDGE 2000's Integrated Study Sites. A variety of visualization techniques are used to reconstruct the plumes (3D) and the diffuse flow field (2D) based on our acoustic imaging data set (July 2000 cruise). Plumes are identified as volumes of high backscatter intensity (indicating high particulate content or sharp density contrasts due to temperature variations) that remained high intensity when successive acoustic pings were subtracted (indicating that the acoustic targets producing the backscatter were in motion). Areas of diffuse flow are detected using our acoustic scintillation technique (AST). For the Grotto vent region (where a new Doppler technique was used to estimate vertical velocities in the plume), we estimate the areal partitioning between black smoker and diffuse flow in terms of volume fluxes. The volumetric and areal regions, where plume and diffuse flow were imaged, are registered over the bathymetry and compared to geologic maps of each region. The resulting images provide a unified view of the seafloor by integrating hydrothermal flow with geology.

  14. A study of transient channel flow in a transitionally rough regime

    NASA Astrophysics Data System (ADS)

    Seddighi, Mehdi; He, Shuisheng; O'Donoghue, Tom; Pokrajac, Dubravka; Vardy, Alan

    2014-11-01

    DNS has been used to investigate the transient behaviour of turbulence following a rapid flow acceleration from an initially turbulent flow in a channel with a smooth top wall and a roughened bottom wall made of close-packed pyramids. Simulations have been performed at various flow conditions in the transitionally rough regime with equivalent roughness heights (ks+) ranging from 12 to 42. It is shown that the transient responses of the flow over the smooth and rough walls are practically independent of each other. Also, the nature of the process over the rough wall varies strongly as the influence of the roughness increases during the early stages of the acceleration. Whereas the transient flow over the smooth-wall undergoes a process strikingly similar to laminar-turbulent bypass transition, the corresponding behaviour over the rough wall depends on the wall condition. When the equivalent roughness height of the final flow condition is below ~30, bypass-like transition dominates, although the roughness induces early transition. When ks+ > 30 , however, the rough-wall flow undergoes a highly transient process resembling roughness induced transition.

  15. Impact of flow regulation and powerplant 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.

    1979-01-01

    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 estimate of natural temperature based on observed equilibrium temperatures were less than 0.5?C. Downstream of the powerplants, the combined thermal effects of flow regulation and powerplant effluents resulted in mean daily river temperatures about equal to or less than computed mean natural temperatures. Thus the thermal impact of heated effluents was offset by the cooling effects of structural regulation. An independent analysis of historical river- and air-temperature data, although considerably less accurate than model computations, provided substantially the same result. The range and rates of change of computed natural diurnal temperature fluctuations were considerably less than those in the river at the time of this study in 1976. The models also were used to simulate summer river temperatures using estimated year 2000 flow conditions and meteorologic data collected during 1976. Except during periods of peak water-supply demand, differences between computed year 2000 river temperatures and observed 1976 temperatures were less than 2?C.

  16. Modeling Food Delivery Dynamics For Juvenile Salmonids Under Variable Flow Regimes

    NASA Astrophysics Data System (ADS)

    Harrison, L.; Utz, R.; Anderson, K.; Nisbet, R.

    2010-12-01

    Traditional approaches for assessing instream flow needs for salmonids have typically focused on the importance of physical habitat in determining fish habitat selection. This somewhat simplistic approach does not account for differences in food delivery rates to salmonids that arise due to spatial variability in river morphology, hydraulics and temporal variations in the flow regime. Explicitly linking how changes in the flow regime influences food delivery dynamics is an important step in advancing process-based bioenergetic models that seek to predict growth rates of salmonids across various life-stages. Here we investigate how food delivery rates for juvenile salmonids vary both spatially and with flow magnitude in a meandering reach of the Merced River, CA. We utilize a two-dimensional (2D) hydrodynamic model and discrete particle tracking algorithm to simulate invertebrate drift transport rates at baseflow and a near-bankfull discharge. Modeling results indicate that at baseflow, the maximum drift density occurs in the channel thalweg, while drift densities decrease towards the channel margins due to the process of organisms settling out of the drift. During high-flow events, typical of spring dam-releases, the invertebrate drift transport pathway follows a similar trajectory along the high velocity core and the drift concentrations are greatest in the channel centerline, though the zone of invertebrate transport occupies a greater fraction of the channel width. Based on invertebrate supply rates alone, feeding juvenile salmonids would be expected to be distributed down the channel centerline where the maximum predicted food delivery rates are located in this reach. However, flow velocities in these channel sections are beyond maximum sustainable swimming speeds for most juvenile salmonids. Our preliminary findings suggest that a lack of low velocity refuge may prevent juvenile salmonids from deriving energy from the areas with maximum drift density in this

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

    DOE PAGESBeta

    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

  18. 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.

  19. Two-phase flow and transport in the air cathode of proton exchange membrane fuel cells

    SciTech Connect

    WANG,Z.H.; WANG,C.Y.; CHEN,KEN S.

    2000-03-20

    Two-phase flow and transport of reactants and products in the air cathode of proton exchange membrane (PEM) fuel cells is studied analytically and numerically. Four regimes of water distribution and transport are classified by defining three threshold current densities and a maximum current density. They correspond to first appearance of liquid water at the membrane/cathode interface, extension of the gas-liquid two-phase zone to the cathode/channel interface, saturated moist air exiting the gas channel, and complete consumption of oxygen by the electrochemical reaction. When the cell operates above the first threshold current density, liquid water appears and a two-phase zone forms within the porous cathode. A two-phase, multi-component mixture model in conjunction with a finite-volume-based computational fluid dynamics (CFD) technique is applied to simulate the cathode operation in this regime. The model is able to handle the situation where a single-phase region co-exists with a two-phase zone in the air cathode. For the first time, the polarization curve as well as water and oxygen concentration distributions encompassing both single- and two-phase regimes of the air cathode are presented. Capillary action is found to be the dominant mechanism for water transport inside the two-phase zone. The liquid water saturation within the cathode is predicted to reach 6.3% at 1.4 A/cm{sup 2}.

  20. 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

  1. Position paper -- Tank ventilation system design air flow rates

    SciTech Connect

    Goolsby, G.K.

    1995-01-04

    The purpose of this paper is to document a project position on required ventilation system design air flow rates for the waste storage tanks currently being designed by project W-236A, the Multi-Function Waste Tank Facility (MWTF). The Title 1 design primary tank heat removal system consists of two systems: a primary tank vapor space ventilation system; and an annulus ventilation system. At the conclusion of Title 1 design, air flow rates for the primary and annulus ventilation systems were 960 scfm and 4,400 scfm, respectively, per tank. These design flow rates were capable of removing 1,250,000 Btu/hr from each tank. However, recently completed and ongoing studies have resulted in a design change to reduce the extreme case heat load to 700,000 Btu/hr. This revision of the extreme case heat load, coupled with results of scale model evaporative testing performed by WHC Thermal Hydraulics, allow for a reduction of the design air flow rates for both primary and annulus ventilation systems. Based on the preceding discussion, ICF Kaiser Hanford Co. concludes that the design should incorporate the following design air flow rates: Primary ventilation system--500 scfm maximum and Annulus ventilation system--1,100 scfm maximum. In addition, the minimum air flow rates in the primary and annulus ventilation systems will be investigated during Title 2 design. The results of the Title 2 investigation will determine the range of available temperature control using variable air flows to both ventilation systems.

  2. The subtropical cloud regime transition: A 10-year view from AIRS, MODIS and ERA-Interim

    NASA Astrophysics Data System (ADS)

    Schreier, M. M.; Kahn, B. H.; Yue, Q.; Suselj, K.

    2012-12-01

    We describe a synergistic approach using multiple satellite observations to describe the statistical behavior of cloud and thermodynamic fields within the subtropical cloud regime transition. Cloud parameters obtained from the MODerate resolution Imaging Spectroradiometer (MODIS) are combined with atmospheric thermodynamic profile retrievals from the Atmospheric Infrared Sounder (AIRS) to quantify changes in the statistical moments over a decade of observations. The analysis is done across the transition of stratocumulus to trade cumulus in several areas around the globe. We analyze differences in the statistical behavior of cloud parameters, lower tropospheric stability, variations in temperature (T) and water vapor (q) profiles, and high-spectral-resolution infrared radiances, and demonstrate differences and similarities among the different cloud types. The statistics are compared to European Center for Medium Range Weather Forecasting Interim Re-analysis (ERA-Interim) data in the same region and time period for the same cloud types. This type of a statistical comparison of provides additional important constraints that are useful for the assessment of satellite retrievals and evaluating atmospheric variability in climate models.

  3. 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

  4. 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.

  5. 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. PMID:25196172

  6. Unsteady Flow of Radiating and Chemically Reacting MHD Micropolar Fluid in Slip-Flow Regime with Heat Generation

    NASA Astrophysics Data System (ADS)

    Abo-Dahab, S. M.; Mohamed, R. A.

    2013-11-01

    An analytical study of the problem of unsteady free convection with thermal radiation and heat generation on MHD micropolar fluid flow through a porous medium bounded by a semi-infinite vertical plate in a slip-flow regime has been presented. The Rosseland diffusion approximation is used to describe the radiation heat flux in the energy equation. The homogeneous chemical reaction of first order is accounted for in the mass diffusion equation. A uniform magnetic field acts perpendicular on the porous surface absorbing micropolar fluid with a suction velocity varying with time. A perturbation technique is applied to obtain the expressions for the velocity, microrotation, temperature, and concentration distributions. Expressions for the skin-friction, Nusselt number, and Sherwood number are also obtained. The results are discussed graphically for different values of the parameters entered into the equations of the problem.

  7. Effect of air flow on tubular solar still efficiency

    PubMed Central

    2013-01-01

    Background An experimental work was reported to estimate the increase in distillate yield for a compound parabolic concentrator-concentric tubular solar still (CPC-CTSS). The CPC dramatically increases the heating of the saline water. A novel idea was proposed to study the characteristic features of CPC for desalination to produce a large quantity of distillate yield. A rectangular basin of dimension 2 m × 0.025 m × 0.02 m was fabricated of copper and was placed at the focus of the CPC. This basin is covered by two cylindrical glass tubes of length 2 m with two different diameters of 0.02 m and 0.03 m. The experimental study was operated with two modes: without and with air flow between inner and outer tubes. The rate of air flow was fixed throughout the experiment at 4.5 m/s. On the basis of performance results, the water collection rate was 1445 ml/day without air flow and 2020 ml/day with air flow and the efficiencies were 16.2% and 18.9%, respectively. Findings The experimental study was operated with two modes: without and with air flow between inner and outer tubes. The rate of air flow was fixed throughout the experiment at 4.5 m/s. Conclusions On the basis of performance results, the water collection rate was 1445 ml/day without air flow and 2020 ml/day with air flow and the efficiencies were 16.2% and 18.9%, respectively. PMID:23587020

  8. Flow regimes in a vertical Taylor-Couette system with a radial thermal gradient

    NASA Astrophysics Data System (ADS)

    Guillerm, R.; Kang, C.; Savaro, C.; Lepiller, V.; Prigent, A.; Yang, K.-S.; Mutabazi, I.

    2015-09-01

    A rich variety of flow regimes in a Newtonian fluid inside a vertical large-aspect ratio and a wide-gap Taylor-Couette system with a radial temperature gradient has been determined in experiments and in direct numerical simulations (DNSs). Compared to previous experiments and numerical studies, a wider range of temperature differences (i.e., of the Grashof number Gr) and of the rotation rate (the Taylor number Ta) has been covered. The combined effect of rotation and of the radial temperature gradient is the occurrence of helicoidal vortices or modulated waves at the onset. Stationary axisymmetric vortices are found for very weak temperature differences. A good agreement was found for critical states between results from experiments, linear stability analysis, and DNS. Higher instability modes have been determined for a wide range of parameters and a state diagram of observable flow regimes has been established in the plane spanned by Gr and Ta. Some higher states observed in experiments were retrieved in DNS.

  9. 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.

  10. 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.

  11. Understanding multiple ecological responses to anthropogenic disturbance: rivers and potential flow regime change.

    PubMed

    Leigh, Catherine; Stewart-Koster, Ben; Sheldon, Fran; Burford, Michele A

    2012-01-01

    Human-induced alteration of the natural flow regime is a major threat to freshwater ecosystems and biodiversity. The effects of hydrological alteration on the structural and functional attributes of riverine communities are expected to be multiple and complex, and they may not be described easily by a single model. Based on existing knowledge of key hydrological and ecological attributes, we explored potential effects of a flow-regulation scenario on macroinvertebrate assemblage composition and diversity in two river systems in Australia's relatively undeveloped wet-dry tropics. We used a single Bayesian belief network (BBN) to model potential changes in multiple assemblage attributes within each river type during dry and wet seasons given two flow scenarios: the current, near-natural flow condition, and flow regulation. We then used multidimensional scaling (MDS) ordination to visually summarize and compare the most probable attributes of assemblages and their environment under the different scenarios. The flow-regulation scenario provided less certainty in the ecological responses of one river type during the dry season, which reduced the ability to make predictions from the BBN outputs directly. However, visualizing the BBN results in an ordination highlighted similarities and differences between the scenarios that may have been otherwise difficult to ascertain. In particular, the MDS showed that flow regulation would reduce the seasonal differentiation in hydrology and assemblage characteristics that is expected under the current low level of development. Our approach may have wider application in understanding ecosystem responses to different river management practices and should be transferred easily to other ecosystems or biotic assemblages to provide researchers, managers, and decision makers an enhanced understanding of ecological responses to potential anthropogenic disturbance. PMID:22471088

  12. Observation of flow regimes and transitions during a columnar solidification experiment

    NASA Astrophysics Data System (ADS)

    Stefan-Kharicha, M.; Kharicha, A.; Wu, M.; Ludwig, A.

    2014-08-01

    Experimental data for the validation of numerical models coupling solidification and hydrodynamics are very rare. Many experiments made in the field of solidifications are performed with pure metals or alloys (Al-Cu, Pb-Sn, etc) which are opaque and do not allow direct observation of the hydrodynamic. Only the results related to solidification such as grain size and orientation, or macro-segregation are usually used for the validation. The present paper is dedicated to the description of well-controlled experiments where both solidification and fluid dynamic can be simultaneously observed. The important point is the almost purely columnar nature of the solidified mushy region. To our knowledge this is the very first reported macro-scale experiment with almost purely columnar solidification where the flow was measured with a PIV technique. The experiments consist in studying the hydrodynamics during the columnar solidification of a H2O-NH4Cl hypereutectic alloy in a die cast cell. Particle image velocimetry was employed to measure the flow velocity in the liquid bulk. Different flow regimes generated by complex thermo-solutal double diffusive convection were observed. In the beginning of the solidification the solutal buoyancy generates a turbulent flow, which is progressively replaced by the development of stratification from the top of the cell. Later, the stratification leads to the development of a long lasting meandering flow, which filled almost all the liquid region. The kinetic energy of the flow was calculated and it was found out that it decreased with time. The solidification front was smooth and no freckles appeared in the mushy zone. The evolution of the thickness of the mushy zone was measured. As this experiment showed a good reproducibility it represents an excellent benchmark for validation of the numerical models that target the simultaneous prediction of flow dynamics and solidification.

  13. 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

  14. Study of flow regimes in two-phase pipeline flow using computer-based digital-image processing

    SciTech Connect

    Bowers, C.B.

    1986-01-01

    A new unobtrusive method for liquid-liquid two-phase flow data collection was proven reliable in this research. Drop-size distributions and concentration profiles were determined for a dilute water-in-kerosene system under horizontal straight pipe flow using this technique. The drop-size distributions were found to follow a Rosin-Rammler function for a limited droplet-diameter range, and the average value of the exponent in the Rosin-Rammler equation was determined to be 2.0. The velocity where the flow-regime transitions from stratified to adequately dispersed was found to be between 6.6 and 7.3 ft/s. Concentration profiles predicted by the Segev model were in general agreement with the profiles determined in this work. Using the experimentally determined Rosin-Rammler exponent value of 2.0 and using the proper choice of the dimensionless lateral diffusivity, the Segev model predicts very well the profiles found in this work. The new experimental method developed in this work will be useful to future researchers in two-phase flow. The data generated is useful both for theoretical modeling efforts and for application to industry sampling problems.

  15. Computational modelling of flow around a circular cylinder in sub-critical flow regime with various turbulence models

    NASA Astrophysics Data System (ADS)

    Tutar, M.; Holdø, A. E.

    2001-04-01

    The numerical simulation of transitional flow around a two-dimensional stationary circular cylinder is presented using two groups of turbulence models in a sub-critical flow regime. In the first group, enhanced two-equation turbulence models based on the eddy viscosity concept are used. They include the non-linear k- model with extended models, such as renormalization group (RNG) and the anisotropic model. In the second group, flow simulation is carried out using the large eddy simulation (LES) method, which is based on a standard sub-grid scale (SGS) model with a near-wall approach. This near-wall model, without using the law of wall, is achieved in a finite element code. The numerical results extracted from these simulations are compared with each other and with the experimental data in order to determine the relative performance of these turbulence models and to find the best model for the flow of interest. Although most of the LES simulations have been previously carried out using finite volume methods, results from using the present model show that the finite element method (FEM) can also be used with confidence. Copyright

  16. Supersonic Air Flow due to Solid-Liquid Impact

    NASA Astrophysics Data System (ADS)

    Gekle, Stephan; Peters, Ivo R.; Gordillo, José Manuel; van der Meer, Devaraj; Lohse, Detlef

    2010-01-01

    A solid object impacting on liquid creates a liquid jet due to the collapse of the impact cavity. Using visualization experiments with smoke particles and multiscale simulations, we show that in addition, a high-speed air jet is pushed out of the cavity. Despite an impact velocity of only 1m/s, this air jet attains supersonic speeds already when the cavity is slightly larger than 1 mm in diameter. The structure of the air flow closely resembles that of compressible flow through a nozzle—with the key difference that here the “nozzle” is a liquid cavity shrinking rapidly in time.

  17. Computational and experimental study of spin coater air flow

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaoguang; Liang, Faqiu; Haji-Sheikh, A.; Ghariban, N.

    1998-06-01

    An extensive 2- and 3-D analysis of air flow in a POLARISTM 2200 Microlithography Cluster spin coater was conducted using FLUENTTM Computational Fluid Dynamics (CFD) software. To supplement this analysis, direct measurement of air flow velocity was also performed using a DantecTM Hot Wire Anemometer. Velocity measurements were made along two major planes across the entire flow field in the spin coater at various operating conditions. It was found that the flow velocity at the spin coater inlet is much lower than previously assumed and quite nonuniform. Based on this observation, a pressure boundary condition rather than a velocity boundary condition was used for subsequent CFD analysis. A comparison between calculated results and experimental data shows that the 3D model accurately predicts the air flow field in the spin coater. An added advantage of this approach is that the CFD model can be easily generated from the mechanical design database and used to analyze the effect of design changes. The modeled and measured results show that the flow pattern in the spin bowl is affected by interactions between the spinning wafer, exhaust flow, and the gap between the spin head and surrounding baffle. Different operating conditions such as spin speed, inlet pressure, and exhaust pressure were found to generate substantially different flow patterns. It was also found that backflow of air could be generated under certain conditions.

  18. Low-noise flow valve for air ducts

    NASA Technical Reports Server (NTRS)

    Gallo, E. A.

    1970-01-01

    Valve assembly controls air flow from feeder into main duct, with minimum of turbulence, friction, pressure differential, and noise. Valve consists of damper, deflector, and spring. Streamlining of damper and deflector merges flow smoothly, while spring keeps damper and deflector in contact and eliminates valve chatter and damping vibrations.

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. 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

  4. Nanosecond repetitively pulsed discharges in air at atmospheric pressure—the spark regime

    NASA Astrophysics Data System (ADS)

    Pai, David Z.; Lacoste, Deanna A.; Laux, Christophe O.

    2010-12-01

    Nanosecond repetitively pulsed (NRP) spark discharges have been studied in atmospheric pressure air preheated to 1000 K. Measurements of spark initiation and stability, plasma dynamics, gas temperature and current-voltage characteristics of the spark regime are presented. Using 10 ns pulses applied repetitively at 30 kHz, we find that 2-400 pulses are required to initiate the spark, depending on the applied voltage. Furthermore, about 30-50 pulses are required for the spark discharge to reach steady state, following initiation. Based on space- and time-resolved optical emission spectroscopy, the spark discharge in steady state is found to ignite homogeneously in the discharge gap, without evidence of an initial streamer. Using measured emission from the N2 (C-B) 0-0 band, it is found that the gas temperature rises by several thousand Kelvin in the span of about 30 ns following the application of the high-voltage pulse. Current-voltage measurements show that up to 20-40 A of conduction current is generated, which corresponds to an electron number density of up to 1015 cm-3 towards the end of the high-voltage pulse. The discharge dynamics, gas temperature and electron number density are consistent with a streamer-less spark that develops homogeneously through avalanche ionization in volume. This occurs because the pre-ionization electron number density of about 1011 cm-3 produced by the high frequency train of pulses is above the critical density for streamer-less discharge development, which is shown to be about 108 cm-3.

  5. Low power, constant-flow air pump systems

    SciTech Connect

    Polito, M.D.; Albert, B.

    1994-01-01

    A rugged, yet small and lightweight constant-flow air pump system has been designed. Flow control is achieved using a novel approach which is three times more power efficient than previous designs. The resultant savings in battery size and weight makes these pumps ideal for sampling air on balloon platforms. The pump package includes meteorological sensors and an onboard computer that stores time and sensor data and turns the constant-flow pump circuit on/off. Some applications of these systems are also presented in this report.

  6. Visualization of the air flow behind the automotive benchmark vent

    NASA Astrophysics Data System (ADS)

    Pech, Ondrej; Jedelsky, Jan; Caletka, Petr; Jicha, Miroslav

    2015-05-01

    Passenger comfort in cars depends on appropriate function of the cabin HVAC system. A great attention is therefore paid to the effective function of automotive vents and proper formation of the flow behind the ventilation outlet. The article deals with the visualization of air flow from the automotive benchmark vent. The visualization was made for two different shapes of the inlet channel connected to the benchmark vent. The smoke visualization with the laser knife was used. The influence of the shape of the inlet channel to the airflow direction, its enlargement and position of air flow axis were investigated.

  7. 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. PMID:26207997

  8. 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

  9. Simulation of 3-D Nonequilibrium Seeded Air Flow in the NASA-Ames MHD Channel

    NASA Technical Reports Server (NTRS)

    Gupta, Sumeet; Tannehill, John C.; Mehta, Unmeel B.

    2004-01-01

    The 3-D nonequilibrium seeded air flow in the NASA-Ames experimental MHD channel has been numerically simulated. The channel contains a nozzle section, a center section, and an accelerator section where magnetic and electric fields can be imposed on the flow. In recent tests, velocity increases of up to 40% have been achieved in the accelerator section. The flow in the channel is numerically computed us ing a 3-D parabolized Navier-Stokes (PNS) algorithm that has been developed to efficiently compute MHD flows in the low magnetic Reynolds number regime: The MHD effects are modeled by introducing source terms into the PNS equations which can then be solved in a very efficient manner. The algorithm has been extended in the present study to account for nonequilibrium seeded air flows. The electrical conductivity of the flow is determined using the program of Park. The new algorithm has been used to compute two test cases that match the experimental conditions. In both cases, magnetic and electric fields are applied to the seeded flow. The computed results are in good agreement with the experimental data.

  10. Evaporation of stationary alcohol layer in minichannel under air flow

    NASA Astrophysics Data System (ADS)

    Afanasyev, Ilya; Orlova, Evgenija; Feoktistov, Dmitriy

    2015-01-01

    This paper presents experimental investigation of effect of the gas flow rate moving parallel to the stationary liquid layer on the evaporation rate under the conditions of formation of a stable plane "liquid-gas" interface. The average evaporation flow rate of liquid layer (ethanol) by the gas flow (air) has been calculated using two independent methods. Obtained results have been compared with previously published data.

  11. Annular fuel and air co-flow premixer

    SciTech Connect

    Stevenson, Christian Xavier; Melton, Patrick Benedict; York, William David

    2013-10-15

    Disclosed is a premixer for a combustor including an annular outer shell and an annular inner shell. The inner shell defines an inner flow channel inside of the inner shell and is located to define an outer flow channel between the outer shell and the inner shell. A fuel discharge annulus is located between the outer flow channel and the inner flow channel and is configured to inject a fuel flow into a mixing area in a direction substantially parallel to an outer airflow through the outer flow channel and an inner flow through the inner flow channel. Further disclosed are a combustor including a plurality of premixers and a method of premixing air and fuel in a combustor.

  12. Experimental study of sheet flow regime of sediment transport in a laboratory flume.

    NASA Astrophysics Data System (ADS)

    Revil-Baudard, Thibaud; Chauchat, Julien; Hurther, David; Barthélémy, Eric; Michallet, Hervé; Snabre, Patrick

    2014-05-01

    The sheet flow regime of sediment transport occurs when the shear stress exerted by the fluid flow on the sediment bed is high enough to set in motion a thick layer of particles. This phenomenon is very important for river and coastal morphodynamical evolution. However, the key mechanisms controlling this regime such as intergranular interactions or turbulent processes in dense fluid-sediment mixture are not well understood yet. For this purpose, an original laboratory experiment has been set up at LEGI in a tilted flume (10 meters long, 35 centimeters wide). 3mm plastic (PMMA) particles are stored in a 3m long tank located close to the channel outlet. The channel is tilted at 0.5 per cent slope and the fluid flow rate is 35 l/s. The instrumentation is composed of an acoustic profiler, ACVP, a high speed camera and a water level sensor. The acoustic profiler allows to get streamwise and vertical velocities profiles from the clear water flow down to the fixed bed with great spatial and temporal resolution (3mm and 0,013s respectively) permitting a good characterization of turbulence. The high speed camera together with a videotrajectography method allow to get sediment velocity profiles and qualitative concentration profiles close to the wall. To compensate the lack of sediment recirculation and the short duration of the experiment, it is repeated to carry out ensemble averaging. The statistical protocol for the treatment of the turbulent signal is presented. This initial treatment allows the estimation of the mean velocity, the turbulent shear and the normal stresses profiles. From these profiles, reproducibility and steadiness of the flow are verified and the main mechanisms of momentum transfer acting from the fixed bed to the dilute suspension are analyzed. The mean velocity profile close to the bed shows three different regions, from bottom to top, an exponential tail, a linear layer and a logarithmic layer. The exponential tail is characteristic of a Coulomb

  13. 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.

  14. Computation of flow and heat transfer in rotating cavities with peripheral flow of cooling air.

    PubMed

    Kiliç, M

    2001-05-01

    Numerical solutions of the Navier-Stokes equations have been used to model the flow and the heat transfer that occurs in the internal cooling-air systems of gas turbines. Computations are performed to study the effect of gap ratio, Reynolds number and the mass flow rate on the flow and the heat transfer structure inside isothermal and heated rotating cavities with peripheral flow of cooling air. Computations are compared with some of the recent experimental work on flow and heat transfer in rotating-cavities. The agreement between the computed and the available experimental data is reasonably good. PMID:11460668

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

    NASA Astrophysics Data System (ADS)

    Vigdorovich, I. I.

    2014-11-01

    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{/p -1/3} + O(Re{/p -2/3}), where Re p is the Reynolds number based on longitudinal pressure gradient. The theoretical results are in good agreement with experimental data.

  16. 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.

  17. 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.

  18. Flow regimes of micrometric ripples in a capillary channel in micro gravity.

    NASA Astrophysics Data System (ADS)

    Merlen, Alain; Zoueshtiagh, Farzam; Thomas, Peter

    Since the advent of nanotechnology microfluidic devices have become common in science and engineering. Examples are equipment for drug delivery, systems for the analysis of chemical substances or devices for the manipulation, transport or separation of suspended droplets, microparticles, cells, or macro-molecules in fluids. In these contexts observations of new patternformation phenomena in microfluidic two-phase flows is always of great interest. Here the oscillatory motion of a fluid carrying micron-sized particles inside a capillary tube is investigated experimentally in standard gravity condition. It is found that initially uniformly distributed particles can segregate and accumulate to form regularly spaced micron-sized particle clusters. The wavelength of the micro clusters is compared to data for macro-scale sand-ripple patterns and found to obey the same universal scaling as these. A physical and dimensional analysis is performed that confirms the universality of the experimentally observed scaling. From these theory, the effect of a low gravity can therefore be discussed on the basis of this universal scaling. The basis of the theory is the dominant importance of the interfacial velocity between the liquid and the grains layer. Of course this is only possible if the global flow variations in space are slow compared with the wave lengths observed. This allows a discussion about the flow regimes that can be present in space can therefore be forecasted and a few applications for bioscience or material sciences can be considered.

  19. 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

  20. Combustion wave propagation regimes in a channel equipped with an array of cross-flow cylindrical obstacles

    NASA Astrophysics Data System (ADS)

    Pinos, Thomas Arthur Richard

    Flame propagation through a channel equipped with obstacles was studied experimentally. Two types of obstacle geometries were investigated, i.e., wall-mounted cross-flow cylinders and fence-type obstacles mounted on the top and bottom channel surfaces. The motivation for this research is its applications to both high-speed propulsion and industrial explosion safety. The effect of obstacle distribution and blockage ratio on flame acceleration was investigated in a 2.54cm x 7.6cm "narrow" channel with wall-mounted cross-flow cylindrical obstacles. The cylinders were arranged in a "staggered" or "inline" pattern, with blockage ratios of 0.5 and 0.67. Schlieren images were used to study the flame shape and its leading edge velocity for a range of fuel-air mixtures compositions. It was determined that initial flame propagation occurs faster in higher blockage ratios due to the higher frequency perturbation to the flow. Flame acceleration led to different quasi-steady flame and detonation propagation regimes. In general, higher final steady flame velocities were reached in the lower blockage ratios, and detonation limits were found to be influenced by the geometry. The influence of channel width on flame acceleration was also determined using fence-type obstacles with a single blockage ratio. Experiments were performed in a 2.54cm x 7.6cm and 7.6cm x 7.6cm channel. Schlieren images were again used to study the flame shape and to obtain leading edge velocity. The flame tip was found to have a parabolic profile across the channel width for the narrower channel and flatter profile in the wider channel. It was determined that the channel width has a weak effect on the flame velocity down the channel length. As such, flame acceleration was initially only slightly more pronounced in the narrow channel before the reverse became true later in the wide channel.

  1. Spool Valve for Switching Air Flows Between Two Beds

    NASA Technical Reports Server (NTRS)

    Dean, W. Clark

    2005-01-01

    U.S. Patent 6,142,151 describes a dual-bed ventilation system for a space suit, with emphasis on a multiport spool valve that switches air flows between two chemical beds that adsorb carbon dioxide and water vapor. The valve is used to alternately make the air flow through one bed while exposing the other bed to the outer-space environment to regenerate that bed through vacuum desorption of CO2 and H2O. Oxygen flowing from a supply tank is routed through a pair of periodically switched solenoid valves to drive the spool valve in a reciprocating motion. The spool valve equalizes the pressures of air in the beds and the volumes of air flowing into and out of the beds during the alternations between the adsorption and desorption phases, in such a manner that the volume of air that must be vented to outer space is half of what it would be in the absence of pressure equalization. Oxygen that has been used to actuate the spool valve in its reciprocating motion is released into the ventilation loop to replenish air lost to vacuum during the previous desorption phase of the operating cycle.

  2. 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., Jr.

    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

  3. Equipment for Measuring Air Flow, Air Temperature, Relative Humidity, and Carbon Dioxide in Schools. Technical Bulletin.

    ERIC Educational Resources Information Center

    Jacobs, Bruce W.

    Information on equipment and techniques that school facility personnel may use to evaluate IAQ conditions are discussed. Focus is placed on the IAQ parameters of air flow, air temperature, relative humidity, as well as carbon dioxide and the equipment used to measure these factors. Reasons for measurement and for when the measurement of these…

  4. 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

  5. Cross-flow versus counterflow air-stripping towers

    SciTech Connect

    Little, J.C.; Marinas, B.J.

    1997-07-01

    Mass-transfer and pressure-drop packing performance correlations are used together with tower design equations and detailed cost models to compare the effectiveness of cross-flow and counterflow air stripping towers over a wide range of contaminant volatility. Cross-flow towers are shown to offer a significant economic advantage over counterflow towers when stripping low volatility organic contaminants primarily due to savings in energy costs. These savings increase as contaminant volatility decreases and as water flow rate increases. A further advantage of the cross-flow configuration is that it extends the feasible operating range for air stripping as cross-flow towers can accommodate higher air-to-water flow ratios than conventional counterflow towers. Finally it is shown that the optimized least-cost design for both counterflow and cross-flow towers varies with Henry`s law constant, water flow rate, and percent removal, but that the optimum is virtually insensitive to other cost and operating variables. This greatly simplifies the tower design procedure.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

    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), 10.1103/PhysRevE.69.027301], although a slight influence of the Reynolds number can be observed in our experiments.

  8. 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

  9. 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.

  10. Study of interfacial area transport and sensitivity analysis for air-water bubbly flow

    SciTech Connect

    Kim, S.; Sun, X.; Ishii, M.; Beus, S.G.

    2000-09-01

    The interfacial area transport equation applicable to the bubbly flow is presented. The model is evaluated against the data acquired by the state-of-the-art miniaturized double-sensor conductivity probe in an adiabatic air-water co-current vertical test loop under atmospheric pressure condition. In general, a good agreement, within the measurement error of plus/minus 10%, is observed for a wide range in the bubbly flow regime. The sensitivity analysis on the individual particle interaction mechanisms demonstrates the active interactions between the bubbles and highlights the mechanisms playing the dominant role in interfacial area transport. The analysis employing the drift flux model is also performed for the data acquired. Under the given flow conditions, the distribution parameter of 1.076 yields the best fit to the data.

  11. Optical Air Flow Measurements in Flight

    NASA Technical Reports Server (NTRS)

    Bogue, Rodney K.; Jentink, Henk W.

    2004-01-01

    This document has been written to assist the flight-test engineer and researcher in using optical flow measurements in flight applications. The emphasis is on describing tradeoffs in system design to provide desired measurement performance as currently understood. Optical system components are discussed with examples that illustrate the issues. The document concludes with descriptions of optical measurement systems designed for a variety of applications including aeronautics research, airspeed measurement, and turbulence hazard detection. Theoretical discussion is minimized, but numerous references are provided to supply ample opportunity for the reader to understand the theoretical underpinning of optical concepts.

  12. 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.

  13. 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.

  14. Air flow management in an internal combustion engine through the use of electronically controlled air jets

    SciTech Connect

    Swain, M.R.

    1988-12-27

    This patent describes a means for producing an air/fuel mixture in the valve pocket and means for directing the air/fuel mixture past the intake valve into the combustion chamber, the improvement comprising a device for generating a swirling flow of the air/fuel mixture in the combustion chamber to thereby obtain greater combustion stability. The device has a nozzle positioned within the valve pocket and directed at an acute angle toward the intake valve comprising at least one opening for receiving air, connected to a first pathway, and at least one opening for expelling air, connected, to a second pathway joined to the first pathway and extending to the expulsion opening. The device also includes a means for controlling the flow of air through the pathway and out the expulsion opening comprising: (i) a stopper having sides complementary in shape to the pair of opposed arcuate walls movable from an open position allowing air through the pathway to a closed position, wherein the sides of the stopper are in a sealed relationship with the opposed arcaute sides of the junction thereby preventing the flow of air through the second pathway and out of the expulsion opening; and (ii) an electronic computer which determines the size and duration of the pathway opening.

  15. How kelp produce blade shapes suited to different flow regimes: A new wrinkle.

    PubMed

    Koehl, M A R; Silk, W K; Liang, H; Mahadevan, L

    2008-12-01

    Many species of macroalgae have flat, strap-like blades in habitats exposed to rapidly flowing water, but have wide, ruffled "undulate" blades at protected sites. We used the giant bull kelp, Nereocystis luetkeana, to investigate how these ecomorphological differences are produced. The undulate blades of N. luetkeana from sites with low flow remain spread out and flutter erratically in moving water, thereby not only enhancing interception of light, but also increasing drag. In contrast, strap-like blades of kelp from habitats with rapid flow collapse into streamlined bundles and flutter at low amplitude in flowing water, thus reducing both drag and interception of light. Transplant experiments in the field revealed that shape of the blade in N. luetkeana is a plastic trait. Laboratory experiments in which growing blades from different sites were subjected to tensile forces that mimicked the hydrodynamic drag experienced by blades in different flow regimes showed that change in shape is induced by mechanical stress. During growth experiments in the field and laboratory, we mapped the spatial distribution of growth in both undulate and strap-like blades to determine how these different morphologies were produced. The highest growth rates occur near the proximal ends of N. luetkeana blades of both morphologies, but the rates of transverse growth of narrow, strap-like blades are lower than those of wide, undulate blades. If rates of longitudinal growth at the edges of a blade exceed the rate of longitudinal growth along the midline of the blade, ruffles along the edges of the blade are produced by elastic buckling. In contrast, flat blades are produced when rates of longitudinal growth are similar across the width of a blade. Because ruffles are the result of elastic buckling, a compliant undulate N. luetkeana blade can easily be pushed into different configurations (e.g., the wavelengths of the ruffles along the edges of the blade can change, and the whole blade can

  16. 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.

  17. Airway blood flow response to dry air hyperventilation in sheep

    SciTech Connect

    Parsons, G.H.; Baile, E.M.; Pare, P.D.

    1986-03-01

    Airway blood flow (Qaw) may be important in conditioning inspired air. To determine the effect of eucapneic dry air hyperventilation (hv) on Qaw in sheep the authors studied 7 anesthetized open-chest sheep after 25 min. of warm dry air hv. During each period of hv the authors have recorded vascular pressures, cardiac output (CO), and tracheal mucosal and inspired air temperature. Using a modification of the reference flow technique radiolabelled microspheres were injected into the left atrium to make separate measurements after humid air and dry air hv. In 4 animals a snare around the left main pulmonary artery was used following microsphere injection to prevent recirculation (entry into L lung of microspheres from the pulmonary artery). Qaw to the trachea and L lung as measured and Qaw for the R lung was estimated. After the final injection the sheep were killed and bronchi (Br) and lungs removed. Qaw (trachea plus L lung plus R lung) in 4 sheep increased from a mean of 30.8 to 67.0 ml/min. Airway mucosal temp. decreased from 39/sup 0/ to 33/sup 0/C. The authors conclude that dry air hv cools airway mucosa and increases Qaw in sheep.

  18. 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. PMID:26592146

  19. 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.

  20. 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.

  1. 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.

  2. Modeling the transition between upper plane bed regime and sheet flow without an active layer formulation. Preliminary results.

    NASA Astrophysics Data System (ADS)

    Viparelli, E.; Hernandez Moreira, R. R.; Blom, A.

    2015-12-01

    A perusal of the literature on bedload transport revealed that, notwithstanding the large number of studies on bedform morphology performed in the past decades, the upper plane bed regime has not been thoroughly investigated and the distinction between the upper plane bed and sheet flow transport regimes is still poorly defined. Previous experimental work demonstrated that the upper plane bed regime is characterized by long wavelength and small amplitude bedforms that migrate downstream. These bedforms, however, were not observed in experiments on sheet flow transport suggesting that the upper plane bed and the sheet flow are two different regimes. We thus designed and performed experiments in a sediment feed flume in the hydraulic laboratory of the Department of Civil and Environmental Engineering at the University of South Carolina at Columbia to study the transition from upper plane bed to sheet flow regime. Periodic measurements of water surface and bed elevation, bedform geometry and thicknesses of the bedload layer were performed by eyes, and with cameras, movies and a system of six ultrasonic probes that record the variations of bed elevation at a point over time. We used the time series of bed elevations to determine the probability functions of bed elevation. These probability functions are implemented in a continuous model of river morphodynamics, i.e. a model that does not use the active layer approximation to describe the sediment fluxes between the bedload and the deposit and that should thus be able to capture the details of the vertical and streamwise variation of the deposit grain size distribution. This model is validated against the experimental results for the case of uniform material. We then use the validated model in the attempt to study if and how the spatial distribution of grain sizes in the deposit changes from upper plane bed regime to sheet flow and if these results are influenced by the imposed rates of base level rise.

  3. 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).

  4. Transitions between corona, glow, and spark regimes of nanosecond repetitively pulsed discharges in air at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Pai, David Z.; Lacoste, Deanna A.; Laux, Christophe O.

    2010-05-01

    In atmospheric pressure air preheated from 300 to 1000 K, the nanosecond repetitively pulsed (NRP) method has been used to generate corona, glow, and spark discharges. Experiments have been performed to determine the parameter space (applied voltage, pulse repetition frequency, ambient gas temperature, and interelectrode gap distance) of each discharge regime. In particular, the experimental conditions necessary for the glow regime of NRP discharges have been determined, with the notable result that there exists a minimum and maximum gap distance for its existence at a given ambient gas temperature. The minimum gap distance increases with decreasing gas temperature, whereas the maximum does not vary appreciably. To explain the experimental results, an analytical model is developed to explain the corona-to-glow (C-G) and glow-to-spark (G-S) transitions. The C-G transition is analyzed in terms of the avalanche-to-streamer transition and the breakdown field during the conduction phase following the establishment of a conducting channel across the discharge gap. The G-S transition is determined by the thermal ionization instability, and we show analytically that this transition occurs at a certain reduced electric field for the NRP discharges studied here. This model shows that the electrode geometry plays an important role in the existence of the NRP glow regime at a given gas temperature. We derive a criterion for the existence of the NRP glow regime as a function of the ambient gas temperature, pulse repetition frequency, electrode radius of curvature, and interelectrode gap distance.

  5. Mixing of passive tracers in the decay Batchelor regime of a channel flow

    NASA Astrophysics Data System (ADS)

    Jun, Yonggun; Steinberg, Victor

    2010-12-01

    We report detailed quantitative studies of passive scalar mixing in a curvilinear channel flow, where elastic turbulence in a dilute polymer solution of high molecular weight polyacrylamide in a high viscosity water-sugar solvent was achieved. For quantitative investigation of mixing, a detailed study of the profiles of mean longitudinal and radial components of the velocity in the channel as a function of Wi was carried out. Besides, a maximum of the average value as well as a rms of the longitudinal velocity was used to determine the threshold of the elastic instability in the channel flow. The rms of the radial derivatives of the longitudinal and radial velocity components was utilized to define the control parameters of the problem, the Weissenberg Wiloc and the Péclet Pe numbers. The main result of these studies is the quantitative test of the theoretical prediction about the value of the mixing length in the decay Batchelor regime. The experiment shows large quantitative discrepancy, more than 200 times in the value of the coefficient C, which appears in the theoretical expression for the mixing length, but with the predicted scaling relation. There are two possible reasons to this discrepancy. First is the assumption made in the theory about the δ-correlated velocity field, which is in odds with the experimental observations. Second, and probably a more relevant suggestion for the significantly increased mixing length and thus reduced mixing efficiency, is the observed jets, the rare, localized, and vigorous ejection of the scalar trapped near the wall, which protrudes into the peripheral region as well as the bulk. They are first found in the recent numerical calculations and then observed in the experiment reported. The jets definitely strongly reduce the mixing efficiency in particular in the peripheral region and so can lead to considerable increase of the mixing length. We hope that this result will initiate further numerical calculations of the

  6. Evolutionary Concepts for Decentralized Air Traffic Flow Management

    NASA Technical Reports Server (NTRS)

    Adams, Milton; Kolitz, Stephan; Milner, Joseph; Odoni, Amedeo

    1997-01-01

    Alternative concepts for modifying the policies and procedures under which the air traffic flow management system operates are described, and an approach to the evaluation of those concepts is discussed. Here, air traffic flow management includes all activities related to the management of the flow of aircraft and related system resources from 'block to block.' The alternative concepts represent stages in the evolution from the current system, in which air traffic management decision making is largely centralized within the FAA, to a more decentralized approach wherein the airlines and other airspace users collaborate in air traffic management decision making with the FAA. The emphasis in the discussion is on a viable medium-term partially decentralized scenario representing a phase of this evolution that is consistent with the decision-making approaches embodied in proposed Free Flight concepts for air traffic management. System-level metrics for analyzing and evaluating the various alternatives are defined, and a simulation testbed developed to generate values for those metrics is described. The fundamental issue of modeling airline behavior in decentralized environments is also raised, and an example of such a model, which deals with the preservation of flight bank integrity in hub airports, is presented.

  7. Glow Discharge Characteristics in Transverse Supersonic Air Flow

    NASA Astrophysics Data System (ADS)

    Timerkaev, B. A.; Zalyaliev, B. R.; Saifutdinov, A. I.

    2014-11-01

    A low pressure glow discharge in a transverse supersonic gas flow of air at pressures of the order 1 torr has been experimentally studied for the case where the flow only partially fills the inter electrode gap. It is shown that the space region with supersonic gas flow has a higher concentration of gas particles and, therefore, works as a charged particle generator. The near electrode regions of glow discharge are concentrated specifically in this region. This structure of glow discharge is promising for plasma deposition of coatings under ultralow pressures

  8. Split-flow regeneration in absorptive air separation

    DOEpatents

    Weimer, Robert F.

    1987-01-01

    A chemical absorptive separation of air in multiple stage of absorption and desorption is performed with partial recycle of absorbent between stages of desorption necessary to match equilibrium conditions in the various stages of absorption. This allows reduced absorbent flow, reduced energy demand and reduced capital costs.

  9. The Wells turbine in an oscillating air flow

    SciTech Connect

    Raghunathan, S.; Ombaka,

    1984-08-01

    An experimental study of the performance of a 0.2 m diameter Wells self rectifying air turbine with NACA 0021 blades is presented. Experiments were conducted in an oscillating flowrig. The effects of Reynolds number and Strouhal number on the performance of the turbine were investigated. Finally comparison between the results with the predictions from uni-directional flow tests are made.

  10. Split-flow regeneration in absorptive air separation

    DOEpatents

    Weimer, R.F.

    1987-11-24

    A chemical absorptive separation of air in multiple stage of absorption and desorption is performed with partial recycle of absorbent between stages of desorption necessary to match equilibrium conditions in the various stages of absorption. This allows reduced absorbent flow, reduced energy demand and reduced capital costs. 4 figs.

  11. 30 CFR 57.22213 - Air flow (III mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Air flow (III mines). 57.22213 Section 57.22213 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  12. 30 CFR 57.22213 - Air flow (III mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Air flow (III mines). 57.22213 Section 57.22213 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  13. 30 CFR 57.22213 - Air flow (III mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Air flow (III mines). 57.22213 Section 57.22213 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  14. 30 CFR 57.22213 - Air flow (III mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Air flow (III mines). 57.22213 Section 57.22213 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  15. 30 CFR 57.22213 - Air flow (III mines).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Air flow (III mines). 57.22213 Section 57.22213 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  16. Optimization of various coal-conversion systems. Quarterly report No. 4 for the period February 1, 1982-April 30, 1982. [Dependence on flow regime

    SciTech Connect

    Wen, C Y

    1982-01-01

    It is well known that the identification of flow regimes is important in scale-ups and designs of multiphase reactors. Therefore, it is natural that the selections of parameter prediction methods for the reactor models should be based on flow regimes. Very few correlations, theories and models are capable of covering the whole spectrum of flow regimes. Often, accuracy is sacrificed for generality. By concentrating on each individual flow regime and its characteristics, the correlations and models selected can be expected to give better results. The evaluation of correlations for phase holdups and liquid dispersion coefficients has been evaluated for both the slurry reactors and the three-phase fluidized bed reactors.

  17. 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.

  18. A stagnation pressure probe for droplet-laden air flow

    NASA Technical Reports Server (NTRS)

    Murthy, S. N. B.; Leonardo, M.; Ehresman, C. M.

    1985-01-01

    It is often of interest in a droplet-laden gas flow to obtain the stagnation pressure of both the gas phase and the mixture. A flow-decelerating probe (TPF), with separate, purged ports for the gas phase and the mixture and with a bleed for accumulating liquid at the closed end, has been developed. Measurements obtained utilizing the TPF in a nearly isothermal air-water droplet mixture flow in a smooth circular pipe under various conditions of flow velocity, pressure, liquid concentration and droplet size are presented and compared with data obtained under identical conditions with a conventional, gas phase stagnation pressure probe (CSP). The data obtained with the CSP and TPF probes are analyzed to determine the applicability of the two probes in relation to the multi-phase characteristics of the flow and the geometry of the probe.

  19. Interfacial area measurement and transport modeling in air-water two-phase flow

    NASA Astrophysics Data System (ADS)

    Fu, Xinyu

    IAC evolution using the one-dimensional two-group transport equation and evaluation with experimental results are performed. The proposed model predicts a smooth transition across the bubbly-to-slug flow regime boundary and demonstrates mechanistic interactions for cap/slug bubble generation and developing processes. The finalized two-group interfacial area transport equation successfully covers a wide range from bubbly, slug, to churn turbulent flow regimes for adiabatic air-water upward flow in moderate diameter pipes.

  20. 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

  1. Mapping flood regime descriptors for flow-duration-frequency characterisation at ungauged location

    NASA Astrophysics Data System (ADS)

    Sauquet, E.; Leblois, E.; Galéa, G.

    2003-04-01

    Flood Frequency Analysis (FFA) is a commonly used tool for describing the flood regime. However, most often, FFA characterises a flood event only by its instantaneous peak or its maximum daily flow. This information is essential but insufficient for many purposes. Flood severity is not only defined by its peak value, but also by its volume and duration. The recommended method is the flow-duration-frequency (QdF) approach, that is similar to the intensity-duration-frequency analysis (IdF) applied to rainfall. QdF curves can be estimated at ungauged location using an analytical expression derived from regional analysis. To recover these curves where no streamflow data are available, two parameters need to be interpolated: D, a duration related to the flood dynamic behaviour and a flood index, i.e. Q10, the 10-year-return period instantaneous peak flood. It allows estimating any T-year-return period discharge averaged over different durations d. The main problem is the way to estimate these parameters related to an area - the drainage basin - and that are hierarchised by the river network. The presentation is focused on the regionalisation methods of the two parameters D and Q10. Two approaches for interpolation are considered. The first one is based on regression analysis: the two parameters are derived from catchment characteristics. The second one consists in an interpolation of the requested values taking the river network into account within an adapted geostatistical framework. Hypothesis and results are discussed on a case study, the French part of the Mosel basin.

  2. 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.

  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. PMID:25238401

  4. Filter feeders and plankton increase particle encounter rates through flow regime control.

    PubMed

    Humphries, Stuart

    2009-05-12

    Collisions between particles or between particles and other objects are fundamental to many processes that we take for granted. They drive the functioning of aquatic ecosystems, the onset of rain and snow precipitation, and the manufacture of pharmaceuticals, powders and crystals. Here, I show that the traditional assumption that viscosity dominates these situations leads to consistent and large-scale underestimation of encounter rates between particles and of deposition rates on surfaces. Numerical simulations reveal that the encounter rate is Reynolds number dependent and that encounter efficiencies are consistent with the sparse experimental data. This extension of aerosol theory has great implications for understanding of selection pressure on the physiology and ecology of organisms, for example filter feeders able to gather food at rates up to 5 times higher than expected. I provide evidence that filter feeders have been strongly selected to take advantage of this flow regime and show that both the predicted peak concentration and the steady-state concentrations of plankton during blooms are approximately 33% of that predicted by the current models of particle encounter. Many ecological and industrial processes may be operating at substantially greater rates than currently assumed. PMID:19416879

  5. 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.

  6. 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.

  7. Low-Frequency Variability in a GCM: Three-Dimensional Flow Regimes and Their Dynamics.

    NASA Astrophysics Data System (ADS)

    Hannachi, A.

    1997-06-01

    . They found, within the 500-mb EOF phase space, two local minima of area-averaged -tendency (based on barotropic vorticity dynamics), which were identified as ±Pacific-North America (PNA). In this work, the author demands that both the flow and its tendency be within the phase space spanned by the 3D EOFs. The streamfunction tendency is computed from the two-level quasigeostrophic potential vorticity equation and projected onto the EOF phase space. This projection produces a finite dynamical system whose singular points are identified as the quasi-stationary states. Two blocking solutions and one zonal solution are found over the Pacific. The first blocking solution is closer to the west coast of North America than the other blocking, which is shifted slightly westward and has a larger scale, rather similar to the +PNA pattern, indicating that blocking over the Pacific may have two phases in the model. Further investigation of the GCM trajectory within the EOF phase space using a mixture analysis shows the existence of realistic three-dimensional weather regimes similar to the singular points. The same solutions were found when the transient eddy contributions to the climatological quasigeostrophic potential vorticity budget were included. It is also shown that this extended technique allows a direct study of the stability of these quasi-stationary states and helps in drawing transition pictures and determining the transition times between them.

  8. Slab Geometry Control on Mantle Flow Regime: A case study from Central South America Subduction Zone

    NASA Astrophysics Data System (ADS)

    Biryol, C. B.; Beck, S. L.; Zandt, G.; Wagner, L. S.

    2013-12-01

    The subduction of oceanic lithosphere along convergent plate margins plays an important role in the dynamics of the upper mantle beneath convergent margins and major orogenic belts. Many studies of mantle dynamics show that the flow pattern of the mantle varies greatly between different subduction zones as well as within the same subduction zone. The factors that control such variations are poorly understood and need to be investigated further in order to develop a better understanding of various subduction zone processes such as the deformation of mantle beneath convergent plate margins and transport of melts and volatiles in the mantle wedge above subducting slabs. Earlier studies of mantle flow inferred from seismic anisotropy via shear-wave splitting analysis indicated that the dynamics and deformation of subducting and overriding plates as well as the slab geometry have important roles on mantle flow regime. In an effort to test the significance of these factors in constraining the mantle dynamics along the central South America subduction zone, we carried out a shear-wave splitting analysis. Our study area covers southern Peru and northwestern Bolivia encompassing the northernmost Altiplano plateau where subduction of the Nazca plate begins to gradually flatten towards the north. The major part of the data for our analysis comes from the CAUGHT temporary seismic deployment (2010 - 2012) with 49 three-component broadband seismometers. In our study we used SKS, SKKS and PKS arrivals from over 80 teleseismic earthquakes, located between the distance-range of 60 to 140 degrees. We determined polarization direction and delay-time of shear-wave arrivals that are polarized into fast and slow components and split in time. The resultant fast polarization directions indicate the direction of mantle flow beneath the study area and the delay-times show the strength and depth extend of the associated seismic anisotropy. The results of our analysis revealed a

  9. 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.

  10. Parametric Studies of Flow Separation using Air Injection

    NASA Technical Reports Server (NTRS)

    Zhang, Wei

    2004-01-01

    Boundary Layer separation causes the airfoil to stall and therefore imposes dramatic performance degradation on the airfoil. In recent years, flow separation control has been one of the active research areas in the field of aerodynamics due to its promising performance improvements on the lifting device. These active flow separation control techniques include steady and unsteady air injection as well as suction on the airfoil surface etc. This paper will be focusing on the steady and unsteady air injection on the airfoil. Although wind tunnel experiments revealed that the performance improvements on the airfoil using injection techniques, the details of how the key variables such as air injection slot geometry and air injection angle etc impact the effectiveness of flow separation control via air injection has not been studied. A parametric study of both steady and unsteady air injection active flow control will be the main objective for this summer. For steady injection, the key variables include the slot geometry, orientation, spacing, air injection velocity as well as the injection angle. For unsteady injection, the injection frequency will also be investigated. Key metrics such as lift coefficient, drag coefficient, total pressure loss and total injection mass will be used to measure the effectiveness of the control technique. A design of experiments using the Box-Behnken Design is set up in order to determine how each of the variables affects each of the key metrics. Design of experiment is used so that the number of experimental runs will be at minimum and still be able to predict which variables are the key contributors to the responses. The experiments will then be conducted in the 1ft by 1ft wind tunnel according to the design of experiment settings. The data obtained from the experiments will be imported into JMP, statistical software, to generate sets of response surface equations which represent the statistical empirical model for each of the metrics as

  11. Flow over a Modern Ram-Air Parachute Canopy

    NASA Astrophysics Data System (ADS)

    Mohammadi, Mohammad; Johari, Hamid

    2010-11-01

    The flow field on the central section of a modern ram-air parachute canopy was examined numerically using a finite-volume flow solver coupled with the one equation Spalart-Allmaras turbulence model. Ram-air parachutes are used for guided airdrop applications, and the canopy resembles a wing with an open leading edge for inflation. The canopy surfaces were assumed to be impermeable and rigid. The flow field consisted of a vortex inside the leading edge opening which effectively closed off the canopy and diverted the flow around the leading edge. The flow experienced a rather bluff leading edge in contrast to the smooth leading of an airfoil, leading to a separation bubble on the lower lip of the canopy. The flow inside the canopy was stagnant beyond the halfway point. The section lift coefficient increased linearly with the angle of attack up to 8.5 and the lift curve slope was about 8% smaller than the baseline airfoil. The leading edge opening had a major effect on the drag prior to stall; the drag is at least twice the baseline airfoil drag. The minimum drag of the section occurs over the angle of attack range of 3 -- 7 .

  12. Properties of a constricted-tube air-flow levitator

    NASA Technical Reports Server (NTRS)

    Rush, J. E.; Stephens, W. K.; Ethridge, E. C.

    1982-01-01

    The properties of a constricted-tube gas flow levitator first developed by Berge et al. (1981) have been investigated experimentally in order to predict its behavior in a gravity-free environment and at elevated temperatures. The levitator consists of a constricted (quartz) tube fed at one end by a source of heated air or gas. A spherical sample is positioned by the air stream on the downstream side of the constriction, where it can be melted and resolidified without touching the tube. It is shown experimentally that the kinematic viscosity is the important fluid parameter for operation in thermal equilibrium at high temperatures. If air is heated from room temperature to 1200 C, the kinematic viscosity increases by a factor of 14. To maintain a given value of the Reynolds number, the flow rate would have to be increased by the same factor for a specific geometry of tube and sample. Thus, to maintain stable equilibrium, the flow rate should be increased as the air or other gas is heated. The other stability problem discussed is associated with changes in the shape of a cylindrical sample as it melts.

  13. Annual regime of bedforms, roughness and flow resistance, Lillooet River, British Columbia, BC

    NASA Astrophysics Data System (ADS)

    Prent, Mariëtte T. H.; Hickin, Edward J.

    2001-12-01

    than critical, dunes appeared to wash out towards a plane bed as discharge increased due to a change from a bedload to suspended-load dominated sediment-transport regime. Flow resistance increased most rapidly during changes in base flow and at the beginning and end of the seasonal flood; resistance tended to be smaller in field A than B, reflecting local differences in energy gradient. Flow resistance increased until a dune steepness of 0.070 was attained and then decreased. The steepness value was considered to be coincident with kolk generation [Dyer, K.R., 1986. Coastal and Estuarine Sediment Dynamics. Wiley, NY, 342 pp.], suggesting that macroturbulent flow structures play an important role in defining the roughness of dunes on a channel bed.

  14. Air Flow and Pressure Drop Measurements Across Porous Oxides

    NASA Technical Reports Server (NTRS)

    Fox, Dennis S.; Cuy, Michael D.; Werner, Roger A.

    2008-01-01

    This report summarizes the results of air flow tests across eight porous, open cell ceramic oxide samples. During ceramic specimen processing, the porosity was formed using the sacrificial template technique, with two different sizes of polystyrene beads used for the template. The samples were initially supplied with thicknesses ranging from 0.14 to 0.20 in. (0.35 to 0.50 cm) and nonuniform backside morphology (some areas dense, some porous). Samples were therefore ground to a thickness of 0.12 to 0.14 in. (0.30 to 0.35 cm) using dry 120 grit SiC paper. Pressure drop versus air flow is reported. Comparisons of samples with thickness variations are made, as are pressure drop estimates. As the density of the ceramic material increases the maximum corrected flow decreases rapidly. Future sample sets should be supplied with samples of similar thickness and having uniform surface morphology. This would allow a more consistent determination of air flow versus processing parameters and the resulting porosity size and distribution.

  15. Oxidation rate of nuclear-grade graphite IG-110 in the kinetic regime for VHTR air ingress accident scenarios

    NASA Astrophysics Data System (ADS)

    Lee, Jo Jo; Ghosh, Tushar K.; Loyalka, Sudarshan K.

    2014-03-01

    The oxidation rates of nuclear-grade graphite IG-110 in the kinetically-controlled temperature regime of graphite oxidation were predicted and compared in Very High Temperature Reactor air ingress accident scenarios. The oxidative mass loss of graphite was measured thermogravimetrically from 873 to 1873 K in 100% air (21 mol%). The activation energy was found to be 222.07 kJ/mol, and the order of reaction with respect to oxygen concentration is 0.76. The surfaces of the samples were characterized by Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy before and after oxidation. These results are compared with those available in the literature, and our recently reported results for NBG-18 nuclear-grade graphite using the same technique.

  16. The influence of synoptic weather regimes on UK air quality: regional model studies of tropospheric column NO2

    NASA Astrophysics Data System (ADS)

    Pope, R. J.; Savage, N. H.; Chipperfield, M. P.; Ordóñez, C.; Neal, L. S.

    2015-07-01

    Synoptic meteorology can have a significant influence on UK air quality. Cyclonic (anticyclonic) conditions lead to the dispersion (accumulation) of air pollutants away from (over) source regions. Meteorology also modifies atmospheric chemistry processes such as photolysis and wet deposition. Previous studies have shown a relationship between observed satellite tropospheric column NO2 and synoptic meteorology in different seasons. Here, we test whether the UK Met Office Air Quality in the Unified Model (AQUM) can reproduce these observations and then use the model to determine the controlling factors. We show that AQUM successfully captures the observed relationships, when sampled under the Lamb Weather Types, an objective classification of midday UK circulation patterns. By using a range of idealised NOx-like tracers with different e-folding lifetimes, we show that under different synoptic regimes the NO2 lifetime in AQUM is approximately 6 h in summer and 12 h in winter. The longer lifetime can explain why synoptic spatial column NO2 variations are more significant in winter compared to summer, due to less NO2 photochemical loss. We also show that cyclonic conditions have more seasonality in column NO2 than anticyclonic conditions as they result in more extreme spatial departures from the wintertime seasonal average. Within a season (summer or winter) under different synoptic regimes, a large proportion of the spatial pattern in the UK column NO2 field can be explained by the idealised model tracers, showing that transport is an important factor in governing the variability of UK air quality on seasonal synoptic timescales.

  17. The influence of synoptic weather regimes on UK air quality: regional model studies of tropospheric column NO2

    NASA Astrophysics Data System (ADS)

    Pope, R. J.; Savage, N. H.; Chipperfield, M. P.; Ordóñez, C.; Neal, L. S.

    2015-10-01

    Synoptic meteorology can have a significant influence on UK air quality. Cyclonic conditions lead to the dispersion of air pollutants away from source regions, while anticyclonic conditions lead to their accumulation over source regions. Meteorology also modifies atmospheric chemistry processes such as photolysis and wet deposition. Previous studies have shown a relationship between observed satellite tropospheric column NO2 and synoptic meteorology in different seasons. Here, we test whether the UK Met Office Air Quality in the Unified Model (AQUM) can reproduce these observations and then use the model to explore the relative importance of various factors. We show that AQUM successfully captures the observed relationships when sampled under the Lamb weather types, an objective classification of midday UK circulation patterns. By using a range of idealized NOx-like tracers with different e-folding lifetimes, we show that under different synoptic regimes the NO2 lifetime in AQUM is approximately 6 h in summer and 12 h in winter. The longer lifetime can explain why synoptic spatial tropospheric column NO2 variations are more significant in winter compared to summer, due to less NO2 photochemical loss. We also show that cyclonic conditions have more seasonality in tropospheric column NO2 than anticyclonic conditions as they result in more extreme spatial departures from the wintertime seasonal average. Within a season (summer or winter) under different synoptic regimes, a large proportion of the spatial pattern in the UK tropospheric column NO2 field can be explained by the idealized model tracers, showing that transport is an important factor in governing the variability of UK air quality on seasonal synoptic timescales.

  18. Interrelationships of petiole air canal architecture, water depth and convective air flow in Nymphaea odorata (Nymphaeaceae)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Premise of the study--Nymphaea odorata grows in water up to 2 m deep, producing fewer, larger leaves in deeper water. This species has a convective flow system that moves gases from younger leaves through submerged parts to older leaves, aerating submerged parts. Petiole air canals are in the conv...

  19. Character of energy flow in air shower core

    NASA Technical Reports Server (NTRS)

    Mizushima, K.; Asakimori, K.; Maeda, T.; Kameda, T.; Misaki, Y.

    1985-01-01

    Energy per charged particle near the core of air showers was measured by 9 energy flow detectors, which were the combination of Cerenkov counters and scintillators. Energy per particle of each detector was normalized to energy at 2m from the core. The following results were obtained as to the energy flow: (1) integral frequency distribution of mean energy per particle (averaged over 9 detectors) is composed of two groups separated distinctly; and (2) showers contained in one group show an anisotropy of arrival direction.

  20. DEVELOPMENT OF A LOW PRESSURE, AIR ATOMIZED OIL BURNER WITH HIGH ATOMIZER AIR FLOW

    SciTech Connect

    BUTCHER,T.A.

    1998-01-01

    This report describes technical advances made to the concept of a low pressure, air atomized oil burner for home heating applications. Currently all oil burners on the market are of the pressure atomized, retention head type. These burners have a lower firing rate limit of about 0.5 gallons per hour of oil, due to reliability problems related to small flow passage sizes. High pressure air atomized burners have been shown to be one route to avoid this problem but air compressor cost and reliability have practically eliminated this approach. With the low pressure air atomized burner the air required for atomization can be provided by a fan at 5--8 inches of water pressure. A burner using this concept, termed the Fan-Atomized Burner or FAB has been developed and is currently being commercialized. In the head of the FAB, the combustion air is divided into three parts, much like a conventional retention head burner. This report describes development work on a new concept in which 100% of the air from the fan goes through the atomizer. The primary advantage of this approach is a great simplification of the head design. A nozzle specifically sized for this concept was built and is described in the report. Basic flow pressure tests, cold air velocity profiles, and atomization performance have been measured. A burner head/flame tube has been developed which promotes a torroidal recirculation zone near the nozzle for flame stability. The burner head has been tested in several furnace and boiler applications over the tiring rate range 0.2 to 0.28 gallons per hour. In all cases the burner can operate with very low excess air levels (under 10%) without producing smoke. Flue gas NO{sub x} concentration varied from 42 to 62 ppm at 3% 0{sub 2}. The concept is seen as having significant potential and planned development efforts are discussed.

  1. 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.

  2. 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.

  3. Vadose Zone Flow and Transport of Dissolved Organic Carbon at Multiple Scales in Humid Regimes

    SciTech Connect

    Jardine, Philip M; Mayes, Melanie; Mulholland, Patrick J; Hanson, Paul J; Phillips, Jana Randolph; Luxmoore, Robert J; McCarthy, John F

    2006-06-01

    Scientists must embrace the necessity to offset global CO{sub 2} emissions regardless of politics. Efforts to enhance terrestrial organic carbon sequestration have traditionally focused on aboveground biomass and surface soils. An unexplored potential exists in thick lower horizons of widespread, mature soils such as Alfisols, Ultisols, and Oxisols. We present a case study of fate and transport of dissolved organic carbon (DOC) in a highly weathered Ultisol, involving spatial scales from the laboratory to the landscape. Our objectives were to interpret processes observed at various scales and provide an improved understanding of coupled hydrogeochemical mechanisms that control DOC mobility and sequestration in deep subsoils within humid climatic regimes. Our approach is multiscale, using laboratory-scale batch and soil columns (0.2 by 1.0 m), an in situ pedon (2 by 2 by 3 m), a well-instrumented subsurface facility on a subwatershed (0.47 ha), and ephemeral and perennial stream discharge at the landscape scale (38.4 ha). Laboratory-scale experiments confirmed that lower horizons have the propensity to accumulate DOC, but that preferential fracture flow tends to limit sequestration. Intermediate-scale experiments demonstrated the beneficial effects of C diffusion into soil micropores. Field- and landscape-scale studies demonstrated coupled hydrological, geochemical, and microbiological mechanisms that limit DOC sequestration, and their sensitivity to local environmental conditions. Our results suggest a multi-scale approach is necessary to assess the propensity of deep subsoils to sequester organic C in situ. By unraveling fundamental organic C sequestration mechanisms, we improve the conceptual and quantitative understanding needed to predict and alter organic C budgets in soil systems.

  4. A New Parameter Regime for Dust in Plasma: the Case of Dense and Supersonic Plasma Flows

    NASA Astrophysics Data System (ADS)

    Ticoş, Cătălin M.; Wang, Zhehui; Wurden, Glen. A.

    2008-09-01

    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. ~1022 m-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 ~105-106 m/s2 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.

  5. Effects of air flow directions on composting process temperature profile

    SciTech Connect

    Kulcu, Recep; Yaldiz, Osman

    2008-07-01

    In this study, chicken manure mixed with carnation wastes was composted by using three different air flow directions: R1-sucking (downward), R2-blowing (upward) and R3-mixed. The aim was to find out the most appropriate air flow direction type for composting to provide more homogenous temperature distribution in the reactors. The efficiency of each aeration method was evaluated by monitoring the evolution of parameters such as temperature, moisture content, CO{sub 2} and O{sub 2} ratio in the material and dry material losses. Aeration of the reactors was managed by radial fans. The results showed that R3 resulted in a more homogenous temperature distribution and high dry material loss throughout the composting process. The most heterogeneous temperature distribution and the lowest dry material loss were obtained in R2.

  6. Vision and air flow combine to streamline flying honeybees

    PubMed Central

    Taylor, Gavin J.; Luu, Tien; Ball, David; Srinivasan, Mandyam V.

    2013-01-01

    Insects face the challenge of integrating multi-sensory information to control their flight. Here we study a ‘streamlining' response in honeybees, whereby honeybees raise their abdomen to reduce drag. We find that this response, which was recently reported to be mediated by optic flow, is also strongly modulated by the presence of air flow simulating a head wind. The Johnston's organs in the antennae were found to play a role in the measurement of the air speed that is used to control the streamlining response. The response to a combination of visual motion and wind is complex and can be explained by a model that incorporates a non-linear combination of the two stimuli. The use of visual and mechanosensory cues increases the strength of the streamlining response when the stimuli are present concurrently. We propose this multisensory integration will make the response more robust to transient disturbances in either modality. PMID:24019053

  7. Numerical characterization of the hydrodynamics and thermal behavior of air flow in flexible air distribution system

    NASA Astrophysics Data System (ADS)

    Gharehdaghi, Samad; Moujaes, Samir

    2013-10-01

    Flexible duct air distribution systems are used in a large percentage of residential and small commercial buildings in the United States . Very few empirical or predictive data are available though to help provide the HVAC design engineer with reliable information . Moreover, because of the ducts flexibility, the shapes of these ducts offer a different set of operating fluid flow and thermal conditions from traditional smooth metal ducts. Hence, both the flow field and heat transfer through this kind of ducts are much more complex and merit to be analyzed from a numerical predictive approach. The aim of this research paper is to compute some of the hydrodynamic and heat transfer characteristics of the air flow inside these ducts over a range of Re numbers commonly used in the flow conditions of these air distribution systems. The information resulting from this CFD simulation, where a κ-ɛ turbulent model is used to predict the flow conditions, provide pressure drop and average convective heat transfer coefficients that exist in these ducts and was compared to previously found data. Circulation zones in the depressions of these ducts are found to exist which are suspected of influencing the pressured drop and heat transfer coefficients as compared to smooth ducts. The results show that fully developed conditions exist much earlier with regard to the inlet for both hydrodynamic and thermal entrance regions than what would be expected in smooth ducts under the same turbulent conditions.

  8. Development of an air flow thermal balance calorimeter

    NASA Technical Reports Server (NTRS)

    Sherfey, J. M.

    1972-01-01

    An air flow calorimeter, based on the idea of balancing an unknown rate of heat evolution with a known rate of heat evolution, was developed. Under restricted conditions, the prototype system is capable of measuring thermal wattages from 10 milliwatts to 1 watt, with an error no greater than 1 percent. Data were obtained which reveal system weaknesses and point to modifications which would effect significant improvements.

  9. Electron concentration distribution in a glow discharge in air flow

    NASA Astrophysics Data System (ADS)

    Mukhamedzianov, R. B.; Gaisin, F. M.; Sabitov, R. A.

    1989-04-01

    Electron concentration distributions in a glow discharge in longitudinal and vortex air flows are determined from the attenuation of the electromagnetic wave passing through the plasma using microwave probes. An analysis of the distribution curves obtained indicates that electron concentration decreases in the direction of the anode. This can be explained by charge diffusion toward the chamber walls and electron recombination and sticking within the discharge.

  10. Methods of Visually Determining the Air Flow Around Airplanes

    NASA Technical Reports Server (NTRS)

    Gough, Melvin N; Johnson, Ernest

    1932-01-01

    This report describes methods used by the National Advisory Committee for Aeronautics to study visually the air flow around airplanes. The use of streamers, oil and exhaust gas streaks, lampblack and kerosene, powdered materials, and kerosene smoke is briefly described. The generation and distribution of smoke from candles and from titanium tetrachloride are described in greater detail because they appear most advantageous for general application. Examples are included showing results of the various methods.

  11. Dispersion of overdamped diffusing particles in channel flows coupled to transverse acoustophoretic potentials: Transport regimes and scaling anomalies

    NASA Astrophysics Data System (ADS)

    Giona, Massimiliano; Garofalo, Fabio

    2015-09-01

    We address the dispersion properties of overdamped Brownian particles migrating in a two-dimensional acoustophoretic microchannel, where a pressure-driven axial Stokes flow coexists with a transverse acoustophoretic potential. Depending on the number and symmetries of the stable nodal points of the acoustophoretic force with respect to the axial velocity profile, different convection-enhanced dispersion regimes can be observed. Among these regimes, an anomalous scaling, for which the axial dispersion increases exponentially with the particle Peclét number, is observed whenever two or more stable acoustophoretic nodes are associated with different axial velocities. A theoretical explanation of this regime is derived, based on exact moment homogenization. Attention is also focused on transient dispersion, which can exhibit superballistic behavior <(x- ) 2> ˜t3 ,x being the axial coordinate.

  12. On the impact of entrapped air in infiltration under ponding conditions. Part a: Preferential air flow path effects on infiltration

    NASA Astrophysics Data System (ADS)

    Mizrahi, Guy; Weisbrod, Noam; Furman, Alex

    2015-04-01

    Entrapped air effects on infiltration under ponding conditions could be important for massive infiltration of managed aquifer recharge (MAR) or soil aquifer treatment (SAT) of treated wastewater. Earlier studies found that under ponding conditions, air is being entrapped and compressed until it reaches a pressure which will enable the air to escape (unstable air flow). They also found that entrapped air could reduce infiltration by 70-90%. Most studies have dealt with entrapped air effects when soil surface topography is flat. The objective of this study is to investigate, under ponding conditions, the effects of: (1) irregular surface topography on preferential air flow path development (stable air flow); (2) preferential air flow path on infiltration; and (3) hydraulic head on infiltration when air is trapped. Column experiments were used to investigate these particular effects. A 140 cm deep and 30 cm wide column packed with silica sand was used under two boundary conditions: in the first, air can only escape vertically upward through the soil surface; in the second, air is free to escape through 20 ports installed along the column perimeter. The surface was flooded with 13 liters of water, with ponding depth decreasing with time. Two soil surface conditions were tested: flat surface and irregular surface (high and low surface zones). Additionally, Helle-show experiments were conducted in order to obtain a visual observation of preferential air flow path development. The measurements were carried out using a tension meter, air pressure transducers, TDR and video cameras. It was found that in irregular surfaces, stable air flow through preferential paths was developed in the high altitude zones. Flat surface topography caused unstable air flow through random paths. Comparison between irregular and flat surface topography showed that the entrapped air pressure was lower and the infiltration rate was about 40% higher in the irregular surface topography than in the

  13. 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

  14. Effects of flow regime and flooding on heavy metal availability in sediment and soil of a dynamic river system.

    PubMed

    Poot, A; Gillissen, F; Koelmans, A A

    2007-08-01

    The acid volatile sulphide (AVS) and simultaneously extracted metals (SigmaSEM) method is increasingly used for risk assessment of toxic metals. In this study, we assessed spatial and temporal variations of AVS and SigmaSEM in river sediments and floodplain soils, addressing influence of flow regime and flooding. Slow-flowing sites contained high organic matter and clay content, leading to anoxic conditions, and subsequent AVS formation and binding of metals. Seasonality affected these processes through temperature and oxygen concentration, leading to increased levels of AVS in summer at slow-flowing sites (max. 37micromolg(-1)). In contrast, fast-flowing sites hardly contained AVS, so that seasonality had no influence on these sites. Floodplain soils showed an opposite AVS seasonality because of preferential inundation and concomitant AVS formation in winter (max. 3-30micromolg(-1)). We conclude that in dynamic river systems, flow velocity is the key to understanding variability of AVS and SigmaSEM. PMID:17418923

  15. Time-resolved Fast Neutron Radiography of Air-water Two-phase Flows

    NASA Astrophysics Data System (ADS)

    Zboray, Robert; Dangendorf, Volker; Mor, Ilan; Tittelmeier, Kai; Bromberger, Benjamin; Prasser, Horst-Michael

    Neutron imaging, in general, is a useful technique for visualizing low-Z materials (such as water or plastics) obscured by high-Z materials. However, when significant amounts of both materials are present and full-bodied samples have to be examined, cold and thermal neutrons rapidly reach their applicability limit as the samples become opaque. In such cases one can benefit from the high penetrating power of fast neutrons. In this work we demonstrate the feasibility of time-resolved, fast neutron radiography of generic air-water two-phase flows in a 1.5 cm thick flow channel with Aluminum walls and rectangular cross section. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany. Exposure times down to 3.33 ms have been achieved at reasonable image quality and acceptable motion artifacts. Different two-phase flow regimes such as bubbly slug and churn flows have been examined. Two-phase flow parameters like the volumetric gas fraction, bubble size and bubble velocities have been measured.

  16. 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

  17. 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.

  18. 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.

  19. Flow modifying device

    NASA Technical Reports Server (NTRS)

    Kelm, J. S.; Vickers, E. C.; Williams, J. J.; Taylor, J. R. (Inventor)

    1985-01-01

    A swirler for a gas turbine engine combustor is disclosed for simultaneously controlling combustor flow rate, swirl angle, residence time and fuel-air ratio to provide three regimes of operation. A first regime is provided in which fuel-air ratio is less than stoichiometric, NOx is produced at one level, and combustor flow rate is high. In a second regime, fuel-air ratio is nearly stoichiometric, NOx production is less than that of the first regime, and combustor flow rate is low. In a third regime, used for example at highoff, fuel-air ratio is greater than stoichiometric and the combustor flow rate is less than in either of the other regimes.

  20. 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

  1. Flow over a Ram-Air Parachute Canopy

    NASA Astrophysics Data System (ADS)

    Eslambolchi, Ali; Johari, Hamid

    2012-11-01

    The flow field over a full-scale, ram-air personnel parachute canopy was investigated numerically using a finite-volume flow solver coupled with the Spalart-Allmaras turbulence model. Ram-air parachute canopies resemble wings with arc-anhedral, surface protuberances, and an open leading edge for inflation. The rectangular planform canopy had an aspect ratio of 2.2 and was assumed to be rigid and impermeable. The chord-based Reynolds number was 3.2 million. Results indicate that the oncoming flow barely penetrates the canopy opening, and creates a large separation bubble below the lower lip of canopy. A thick boundary layer exists over the entire lower surface of the canopy. The flow over the upper surface of the canopy remains attached for an extended fraction of the chord. Lift increases linearly with angle of attack up to about 12 degrees. To assess the capability of lifting-line theory in predicting the forces on the canopy, the lift and drag data from a two-dimensional simulation of the canopy profile were extended using finite-wing expressions and compared with the forces from the present simulations. The finite-wing predicted lift and drag trends compare poorly against the full-span simulation, and the maximum lift-to-drag ratio is over-predicted by 36%. Sponsored by the US Army NRDEC.

  2. Thermistor based, low velocity isothermal, air flow sensor

    NASA Astrophysics Data System (ADS)

    Cabrita, Admésio A. C. M.; Mendes, Ricardo; Quintela, Divo A.

    2016-03-01

    The semiconductor thermistor technology is applied as a flow sensor to measure low isothermal air velocities (<2 ms-1). The sensor is subjected to heating and cooling cycles controlled by a multifunctional timer. In the heating stage, the alternating current of a main AC power supply source guarantees a uniform thermistor temperature distribution. The conditioning circuit assures an adequate increase of the sensors temperature and avoids the thermal disturbance of the flow. The power supply interruption reduces the consumption from the source and extends the sensors life time. In the cooling stage, the resistance variation of the flow sensor is recorded by the measuring chain. The resistive sensor parameters proposed vary significantly and feature a high sensitivity to the flow velocity. With the aid of a computer, the data transfer, storage and analysis provides a great advantage over the traditional local anemometer readings. The data acquisition chain has a good repeatability and low standard uncertainties. The proposed method measures isothermal air mean velocities from 0.1 ms-1 to 2 ms-1 with a standard uncertainty error less than 4%.

  3. Stability of thermocapillary convection and regimes of a fluid flow acted upon by a standing surface wave

    NASA Astrophysics Data System (ADS)

    Feonychev, A. I.

    2007-09-01

    It has been established that, in the case where a standing surface wave acts on a thermocapillary-convection flow in a cylindrical volume, there arises an oscillating-convection zone between the laminar and turbulent regimes of flow. It is shown that the boundary between these regimes is determined by the amplitude δ and the number of periods n of the standing wave and is practically independent of the Marangoni number and the oscillation frequency of this wave. At n = 2, in the range 0.004 < δ < 0.006, the parameters of the fluid cease to oscillate. The mechanisms by which the thermocapillary convection in closed volumes loses its stability are discussed.

  4. Oxidation rate of graphitic matrix material in the kinetic regime for VHTR air ingress accident scenarios

    NASA Astrophysics Data System (ADS)

    Lee, Jo Jo; Ghosh, Tushar K.; Loyalka, Sudarshan K.

    2014-08-01

    Data on oxidation rates of matrix-grade graphite in the kinetically-controlled temperature regime of graphite oxidation are needed for safety analysis of High Temperature Gas Cooled Reactors and Very High Temperature Reactors. In this work, the oxidation rate of graphitic matrix material GKrS was measured thermogravimetrically for various oxygen concentrations and with temperatures from 873 to 1873 K. A semi-empirical Arrhenius rate equation was also developed for this temperature range. The activation energy of the graphitic material is found to be about 111.5 kJ/mol. The order of reaction was found to be about 0.89. The surface of oxidized GKrS was characterized by Scanning Electron Microscopy, Electron Dispersive Spectroscopy, Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy.

  5. SIMPLIFIED MODELING OF AIR FLOW DYNAMICS IN SSD RADON MITIGATION SYSTEMS FOR RESIDENCES WITH GRAVEL BEDS

    EPA Science Inventory

    In an attempt to better understand the dynamics of subslab air flow, the report suggests that subslab air flow induced by a central suction point be treated as radial air flow through a porous bed contained between two impermeable disks. (NOTE: Many subslab depressurization syste...

  6. 30 CFR 75.152 - Tests of air flow; qualified person.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Tests of air flow; qualified person. 75.152....152 Tests of air flow; qualified person. A person is a qualified person within the meaning of the provisions of Subpart D—Ventilation of this part requiring that tests of air flow be made by a...

  7. 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.

  8. Surfactant control of air-sea gas exchange across contrasting biogeochemical regimes

    NASA Astrophysics Data System (ADS)

    Pereira, Ryan; Schneider-Zapp, Klaus; Upstill-Goddard, Robert

    2014-05-01

    Air-sea gas exchange is important to the global partitioning of CO2.Exchange fluxes are products of an air-sea gas concentration difference, ΔC, and a gas transfer velocity, kw. The latter is controlled by the rate of turbulent diffusion at the air-sea interface but it cannot be directly measured and has a high uncertainty that is now considered one of the greatest challenges to quantifying net global air-sea CO2 exchange ...(Takahashi et al., 2009). One important control on kw is exerted by sea surface surfactants that arise both naturally from biological processes and through anthropogenic activity. They influence gas exchange in two fundamental ways: as a monolayer physical barrier and through modifying sea surface hydrodynamics and hence turbulent energy transfer. These effects have been demonstrated in the laboratory with artificial surfactants ...(Bock et al., 1999; Goldman et al., 1988) and through purposeful surfactant releases in coastal waters .(.).........().(Brockmann et al., 1982) and in the open ocean (Salter et al., 2011). Suppression of kwin these field experiments was ~5-55%. While changes in both total surfactant concentration and the composition of the natural surfactant pool might be expected to impact kw, the required in-situ studies are lacking. New data collected from the coastal North Sea in 2012-2013 shows significant spatio-temporal variability in the surfactant activity of organic matter within the sea surface microlayer that ranges from 0.07-0.94 mg/L T-X-100 (AC voltammetry). The surfactant activities show a strong winter/summer seasonal bias and general decrease in concentration with increasing distance from the coastline possibly associated with changing terrestrial vs. phytoplankton sources. Gas exchange experiments of this seawater using a novel laboratory tank and gas tracers (CH4 and SF6) demonstrate a 12-45% reduction in kw compared to surfactant-free water. Seasonally there is higher gas exchange suppression in the summer

  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. Air and groundwater flow at the interface between fractured host rock and a bentonite buffer

    NASA Astrophysics Data System (ADS)

    Dessirier, B.; Jarsjo, J.; Frampton, A.

    2014-12-01

    Designs of deep geological repositories for spent nuclear fuel include several levels of confinement. The Swedish and Finnish concept KBS-3 targets for example sparsely fractured crystalline bedrock as host formation and would have the waste canisters embedded in an engineered buffer of compacted MX-80 bentonite. The host rock is a highly heterogeneous dual porosity material containing fractures and a rock matrix. Bentonite is a complex expansive porous material. Its water content and mechanical properties are interdependent. Beyond the specific physics of unsaturated flow and transport in each medium, the interface between them is critical. Detailed knowledge of the transitory two-phase flow regime, induced by the insertion of the unsaturated buffer in a saturated rock environment, is necessary to assess the performance of planned KBS-3 deposition holes. A set of numerical simulations based on the equations of two-phase flow for water and air in porous media were conducted to investigate the dynamics of air and groundwater flow near the rock/bentonite interface in the period following installation of the unsaturated bentonite buffer. We assume state of the two-phase flow parameter values for bentonite from laboratory water uptake tests and typical fracture and rock properties from the Äspö Hard rock laboratory (Sweden) gathered under several field characterization campaigns. The results point to desaturation of the rock domain as far as 10 cm away from the interface into matrix-dominated regions for up to 160 days. Similar observations were made during the Bentonite Rock Interaction Experiment (BRIE) at the Äspö HRL, with a desaturation sustained for even longer times. More than the mere time to mechanical and hydraulic equilibrium, the occurrence of sustained unsaturated conditions opens the possibility for biogeochemical processes that could be critical in the safety assessment of the planned repository.

  11. Modelling impacts of present and future hydropower operations on flow regimes in data scarce mountain river ecosystems

    NASA Astrophysics Data System (ADS)

    Geris, Josie; Tetzlaff, Doerthe; Seibert, Jan; Vis, Marc; Soulsby, Chris

    2014-05-01

    Mountain river ecosystems in many parts of the world are increasingly exploited for hydropower production in order to meet pressing renewable energy targets. These systems also provide important ecosystem services, including the provision of high quality downstream water supplies and the maintenance of in-stream habitats. With future supply and demand of water resources both impacted by environmental change, a good understanding of the impacts and the resilience of hydropower regimes within the context of the wider ecosystem is important. However, quantifying these is often limited by inadequate pre-regulation data and information on current regimes. In such cases, where complex models with high data demands are inappropriate, there is a need for simple conceptual modelling approaches that can still capture the dominant natural runoff generation and artificial regulation processes. Here we present a new modelling tool that can be used in data sparse mountain river ecosystems to assess hydropower effects on natural flow regimes, predict water availability, and test system resilience for present and future hydropower production schemes. Model routines for simulation of runoff regulation (reservoirs and water transfers) were implemented into the HBV rainfall-runoff model, allowing for situations where regulation amounts are known and those where regulation amounts have to be estimated based on simple regulation rules. The new model was applied to the heavily regulated River Lyon (391 km2), Scotland, UK, which has a long history of hydropower generation that is supported by a complex network of inter- and intra-catchment water transfers and river impoundments. There are concerns that these are affecting high conservation freshwater populations of Atlantic Salmon (Salmo salar), highlighting the need for a good understanding of present impacts and the extent to which flow variables can be modified without major degradation to the river's ecosystem. The model was used to

  12. Air-structure coupling features analysis of mining contra-rotating axial flow fan cascade

    NASA Astrophysics Data System (ADS)

    Chen, Q. G.; Sun, W.; Li, F.; Zhang, Y. J.

    2013-12-01

    The interaction between contra-rotating axial flow fan blade and working gas has been studied by means of establishing air-structure coupling control equation and combining Computational Fluid Dynamics (CFD) and Computational solid mechanics (CSM). Based on the single flow channel model, the Finite Volume Method was used to make the field discrete. Additionally, the SIMPLE algorithm, the Standard k-ε model and the Arbitrary Lagrangian-Eulerian dynamic grids technology were utilized to get the airflow motion by solving the discrete governing equations. At the same time, the Finite Element Method was used to make the field discrete to solve dynamic response characteristics of blade. Based on weak coupling method, data exchange from the fluid solver and the solid solver was processed on the coupling interface. Then interpolation was used to obtain the coupling characteristics. The results showed that the blade's maximum amplitude was on the tip of the last-stage blade and aerodynamic force signal could reflect the blade working conditions to some extent. By analyzing the flow regime in contra-rotating axial flow fan, it could be found that the vortex core region was mainly in the blade surface, the hub and the blade clearance. In those regions, the turbulence intensity was very high. The last-stage blade's operating life is shorter than that of the pre-stage blade due to the fatigue fracture occurs much more easily on the last-stage blade which bears more stress.

  13. Impact pressures and flow regimes in dense snow avalanches observed at the Vallée de la Sionne test site

    NASA Astrophysics Data System (ADS)

    Sovilla, Betty; Schaer, M.; Kern, M.; Bartelt, P.

    2008-03-01

    A fundamental problem in avalanche engineering is to determine the impact pressures exerted on structures. This task is complicated because snow avalanches flow in a variety of regimes, primarily depending on snow temperature and moisture content. In this paper we address this problem by analyzing measured impact pressures, flow velocities, and flow depths of five Vallée de la Sionne avalanches. The measurements are made on a 20 m high tubular pylon instrumented with high-frequency pressure transducers and optoelectronic velocity sensors. In the observed avalanches, we find both subcritical and supercritical flow regimes. Typical Froude numbers were smaller than 6. The subcritical regime (Fr < 1) is characterized by a flow plug riding above a highly sheared basal layer. The measured pressures are large and velocity-independent in contradiction to calculation procedures. Pressure fluctuations increase with flow depth, indicating a kinematic stick-slip phenomena which is largest at the basal layer. Supercritical flow regimes (1 < Fr < 6) are characterized by a sheared flow all over the avalanche depth. In this regime the impact pressure is velocity-dependent. We derive relationships governing impact pressure as a function of the Froude number, and therefore flow regime, encompassing all the observed avalanches.

  14. 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.

  15. Optical observation of ultrafine droplets and air flows from newly designed supersonic air assist spray nozzles

    NASA Astrophysics Data System (ADS)

    Miyashiro, Seiji S.; Mori, H.; Takechi, H.

    2001-04-01

    One of the authors developed a new spray drying nozzle (special quadruplet fluid spray nozzle) for drug manufacturing and it has succeeded in manufacturing fine particles of 2 micrometer diameter of 1/15 ratios to those currently in use. The flow visualization results show that the two air jets become under-expanded on both edge sides of the nozzle, generate shock and expansion waves alternately on each side and reach the edge tip, where they collide, unite, and spout out while shock and expansion waves are again formed in the mixed jet. When the edge surfaces are supplied with water, the water is extended into thin film by the air jet and intensely disturbed. At the nozzle tip it is torn into droplets, which are further atomized afterwards in shock waves. At the spray tip, the friction with ambient air shears the droplets furthermore, and they decrease further in size.

  16. Interfacial area transport across vertical elbows in air-water two-phase flow

    NASA Astrophysics Data System (ADS)

    Yadav, Mohan Singh

    The accurate prediction of two-phase flow using the two-fluid model requires closure relations for the interfacial area concentration ( ai), which can be provided by the interfacial area transport equation (IATE). Models have been developed for the IATE in straight pipe geometries. However, to analyze practical systems, it is important that the IATE accounts for flows in pipes with varying orientation that are interconnected via different flow restrictions. In view of this, the current study performs experiments to investigate the geometric effects of 90- degree vertical elbows in air-water two-phase flows and develops a one-group IATE applicable to vertical-upward-to-horizontal two-phase flows. The experimental facility consists of both vertical and horizontal sections constructed from 50.8 mm inner diameter acrylic pipes that are interconnected via 90-degree glass elbows. The elbows have a radius of curvature of Rc/D = 3 and are installed at L/D = 63 and 244.7 from the inlet. Experiments are performed to characterize the elbow-effect on both global and local two-phase flow parameters. A four-sensor conductivity probe is used to acquire detailed measurements of local two-phase flow parameters at thirteen axial locations along the test section in eight flow conditions that are within the bubbly flow regime at inlet. The measurements show that in bubbly flow conditions, the vertical-upward elbow causes a characteristic bimodal-type bubble distribution and the change in this distribution farther downstream of the elbow corresponds to the dissipation of the elbow-effects. In view of developing the IATE for vertical-upward to horizontal two-phase flows, predictive models for the dissipation length of the elbow-effect and closure relations for advection of gas-phase, pressure loss, and covariance of bubble interactions are developed. The new models are evaluated against the current experimental database. Overall, the model predictions agree with the data within +/-7

  17. Non-equilibrium Flows of Reacting Air Components in Nozzles

    NASA Astrophysics Data System (ADS)

    Bazilevich, S. S.; Sinitsyn, K. A.; Nagnibeda, E. A.

    2008-12-01

    The paper presents the results of the investigation of non-equilibrium flows of reacting air mixtures in nozzles. State-to-state approach based on the solution of the equations for vibrational level populations of molecules and atomic concentrations coupled to the gas dynamics equations is used. For the 5-component air mixture (N2, O2, NO, N, O) non-equilibrium distributions and gasdynamical parameters are calculated for different conditions in a nozzle throat. The influence of various kinetic processes on distributions and gas dynamics parameters is studied. The paper presents the comparison of the results with ones obtained for binary mixtures of molecules and atoms and various models of elementary processes.

  18. 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

  19. Pareto-optimal solutions for environmental flow schemes incorporating the intra-annual and interannual variability of the natural flow regime

    NASA Astrophysics Data System (ADS)

    Shiau, Jenq-Tzong; Wu, Fu-Chun

    2007-06-01

    The temporal variations of natural flows are essential elements for preserving the ecological health of a river which are addressed in this paper by the environmental flow schemes that incorporate the intra-annual and interannual variability of the natural flow regime. We present an optimization framework to find the Pareto-optimal solutions for various flow schemes. The proposed framework integrates (1) the range of variability approach for evaluating the hydrologic alterations; (2) the standardized precipitation index approach for establishing the variation criteria for the wet, normal, and dry years; (3) a weir operation model for simulating the system of flows; and (4) a multiobjective optimization genetic algorithm for search of the Pareto-optimal solutions. The proposed framework is applied to the Kaoping diversion weir in Taiwan. The results reveal that the time-varying schemes incorporating the intra-annual variability in the environmental flow prescriptions promote the ecosystem and human needs fitness. Incorporation of the interannual flow variability using different criteria established for three types of water year further promotes both fitnesses. The merit of incorporating the interannual variability may be superimposed on that of incorporating only the intra-annual flow variability. The Pareto-optimal solutions searched with a limited range of flows replicate satisfactorily those obtained with a full search range. The limited-range Pareto front may be used as a surrogate of the full-range one if feasible prescriptions are to be found among the regular flows.

  20. Flow Analysis over Batten Reinforced Wings for Micro Air Vehicles

    NASA Astrophysics Data System (ADS)

    Townsend, Kurtis; Hicks, Travis; Hubner, James P.

    2008-11-01

    Flexible membrane wings modify the flow separation of low Reynolds number micro air vehicles (MAVs). A specific type of fixed-wing geometry is a batten-reinforced configuration in which the membrane is attached to a rigid frame with chordwise battens, allowing the vibration of the membrane at the trailing-edge. In this study, smoke-wire visualization and hot-wire anemometry, both near the trailing-edge and further downstream in the wake, are used to quantify the frequency and energy of these fluctuations for various cell geometries and flow angles-of-attack. Improvement in the wake momentum deficit will be analyzed to determine preferred membrane cell geometries for MAV flight conditions.

  1. Laboratory Evaluation of Air Flow Measurement Methods for Residential HVAC Returns

    SciTech Connect

    Walker, Iain; Stratton, Chris

    2015-07-01

    This project improved the accuracy of air flow measurements used in commissioning California heating and air conditioning systems in Title 24 (Building and Appliance Efficiency Standards), thereby improving system performance and efficiency of California residences. The research team at Lawrence Berkeley National Laboratory addressed the issue that typical tools used by contractors in the field to test air flows may not be accurate enough to measure return flows used in Title 24 applications. The team developed guidance on performance of current diagnostics as well as a draft test method for use in future evaluations. The series of tests performed measured air flow using a range of techniques and devices. The measured air flows were compared to reference air flow measurements using inline air flow meters built into the test apparatus. The experimental results showed that some devices had reasonable results (typical errors of 5 percent or less) but others had much bigger errors (up to 25 percent).

  2. Flow Regime Study in a Circulating Fluidized Bed Riser with an Abrupt Exit: [1] High Density Suspension

    SciTech Connect

    Mei, J.S.; Lee, G.T.; Seachman, S.M.; Ludlow, J.C.; Shadle, L.J.

    2008-05-13

    Flow regime study was conducted in a 0.3 m diameter, 15.5 m tall circulating fluidized bed (CFB) riser with an abrupt exit at the National Energy Technology Laboratory of the U. S. Department of Energy. A statistical designed test series was conducted including four (4) operating set points and a duplicated center point (therefore a total of 6 operating set points). Glass beads of mean diameter 200 μm and particle density of 2,430 kg/m3 were used as bed material. The CFB riser was operated at various superficial gas velocities ranging from 5.6 to 7.6 m/s and solid mass flux from a low of 86 to a high of 303 kg/m2-s. Results of the apparent solids fraction profile as well as the radial particle velocity profile were analyzed in order to identify the presence of Dense Suspension Upflow (DSU) conditions. DSU regime was found to exist at the bottom of the riser, while the middle section of the riser was still exhibiting core-annular flow structure. Due to the abrupt geometry of the exit, the DSU regime was also found at the top of the riser. In addition the effects of the azimuthal angle, riser gas velocity, and mass solids flux on the particle velocity were investigated and are discussed in this paper.

  3. 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...

  4. Ozone concentrations in air flowing into New York State

    NASA Astrophysics Data System (ADS)

    Aleksic, Nenad; Kent, John; Walcek, Chris

    2016-09-01

    Ozone (O3) concentrations measured at Pinnacle State Park (PSPNY), very close to the southern border of New York State, are used to estimate concentrations in air flowing into New York. On 20% of the ozone season (April-September) afternoons from 2004 to 2015, mid-afternoon 500-m back trajectories calculated from PSPNY cross New York border from the south and spend less than three hours in New York State, in this area of negligible local pollution emissions. One-hour (2p.m.-3p.m.) O3 concentrations during these inflowing conditions were 46 ± 13 ppb, and ranged from a minimum of 15 ppb to a maximum of 84 ppb. On average during 2004-2015, each year experienced 11.8 days with inflowing 1-hr O3 concentrations exceeding 50 ppb, 4.3 days with O3 > 60 ppb, and 1.5 days had O3 > 70 ppb. During the same period, 8-hr average concentrations (10a.m. to 6p.m.) exceeded 50 ppb on 10.0 days per season, while 3.9 days exceeded 60 ppb, and 70 ppb was exceeded 1.2 days per season. Two afternoons of minimal in-state emission influences with high ozone concentrations were analyzed in more detail. Synoptic and back trajectory analysis, including comparison with upwind ozone concentrations, indicated that the two periods were characterized as photo-chemically aged air containing high inflowing O3 concentrations most likely heavily influenced by pollution emissions from states upwind of New York including Pennsylvania, Tennessee, West Virginia, and Ohio. These results suggest that New York state-level attempts to comply with National Ambient Air Quality Standards by regulating in-state O3 precursor NOx and organic emissions would be very difficult, since air frequently enters New York State very close to or in excess of Federal Air Quality Standards.

  5. 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

  6. Drought-induced changes in flow regimes lead to long-term losses in mussel-provided ecosystem services.

    PubMed

    Vaughn, Caryn C; Atkinson, Carla L; Julian, Jason P

    2015-03-01

    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

  7. Experimental insights into flow impingement in cerebral aneurysm by stereoscopic particle image velocimetry: transition from a laminar regime

    PubMed Central

    Yagi, Takanobu; Sato, Ayaka; Shinke, Manabu; Takahashi, Sara; Tobe, Yasutaka; Takao, Hiroyuki; Murayama, Yuichi; Umezu, Mitsuo

    2013-01-01

    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. PMID:23427094

  8. Condensation of refrigerants in horizontal, spirally grooved microfin tubes: Numerical analysis of heat transfer in the annular flow regime

    SciTech Connect

    Nozu, S.; Honda, H.

    2000-02-01

    A method is presented for estimating the condensation heat transfer coefficient in a horizontal, spirally grooved microfin tube. Based on the flow observation study performed by the authors, a laminar film condensation model in the annular flow regime is proposed. The model assumes that all the condensate flow occurs through the grooves. The condensate film is segmented into thin and thick film regions. In the thin film region formed on the fin surface, the condensate is assumed to be drained by the combined surface tension and vapor shear forces. In the thick film region formed in the groove, on the other hand, the condensate is assumed to be driven by the vapor shear force. The present and previous local heat transfer data including four fluids (CFC11, HCFC22, HCFC123, and HFCl34a) and three microfin tubes are found to agree with the present predictions to a mean absolute deviation of 15.1%.

  9. 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

  10. 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.

  11. 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.

  12. 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

  13. Air-flow separation over unsteady breaking wind waves

    NASA Astrophysics Data System (ADS)

    Saxena, Gaurav

    2005-11-01

    In air-sea interaction processes, when considering wind stress over small-scale breaking waves, there are few direct quantitative experimental investigations into the role of air-flow separation on the interfacial momentum flux. Reul et. al, (1999), found multiple coherent patches of vorticity downwind of the crest that were strongly influenced by the geometric characteristics of the breaker. However, their breakers were generated by dispersive focusing techniques and, therefore, independent of the wind stress. We present experimental results obtained with particle image velocimetry (PIV) where moderate to strong winds directly generate unsteady small-scale breaking waves, a scenario commonly found in the open ocean. Particular attention has been devoted to capturing the spatio-temporal evolution of the air-water interface. Specifically, texture segmentation algorithms typically used for face recognition (Grey Level Co-occurrence Matrix (GLCM) and the Cross-Diagonal Texture Matrix (CDTM)) have been combined to yield robust and accurate estimates of the instantaneous breaker geometry.

  14. 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

  15. 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

  16. Numerical simulation of air flow in a model of lungs with mouth cavity

    NASA Astrophysics Data System (ADS)

    Elcner, Jakub; Lizal, Frantisek; Jedelsky, Jan; Jicha, Miroslav

    2012-04-01

    The air flow in a realistic geometry of human lung is simulated with computational flow dynamics approach as stationary inspiration. Geometry used for the simulation includes oral cavity, larynx, trachea and bronchial tree up to the seventh generation of branching. Unsteady RANS approach was used for the air flow simulation. Velocities corresponding to 15, 30 and 60 litres/min of flow rate were set as boundary conditions at the inlet to the model. These flow rates are frequently used as a representation of typical human activities. Character of air flow in the model for these different flow rates is discussed with respect to future investigation of particle deposition.

  17. Graphical User Interface Development for Representing Air Flow Patterns

    NASA Technical Reports Server (NTRS)

    Chaudhary, Nilika

    2004-01-01

    In the Turbine Branch, scientists carry out experimental and computational work to advance the efficiency and diminish the noise production of jet engine turbines. One way to do this is by decreasing the heat that the turbine blades receive. Most of the experimental work is carried out by taking a single turbine blade and analyzing the air flow patterns around it, because this data indicates the sections of the turbine blade that are getting too hot. Since the cost of doing turbine blade air flow experiments is very high, researchers try to do computational work that fits the experimental data. The goal of computational fluid dynamics is for scientists to find a numerical way to predict the complex flow patterns around different turbine blades without physically having to perform tests or costly experiments. When visualizing flow patterns, scientists need a way to represent the flow conditions around a turbine blade. A researcher will assign specific zones that surround the turbine blade. In a two-dimensional view, the zones are usually quadrilaterals. The next step is to assign boundary conditions which define how the flow enters or exits one side of a zone. way of setting up computational zones and grids, visualizing flow patterns, and storing all the flow conditions in a file on the computer for future computation. Such a program is necessary because the only method for creating flow pattern graphs is by hand, which is tedious and time-consuming. By using a computer program to create the zones and grids, the graph would be faster to make and easier to edit. Basically, the user would run a program that is an editable graph. The user could click and drag with the mouse to form various zones and grids, then edit the locations of these grids, add flow and boundary conditions, and finally save the graph for future use and analysis. My goal this summer is to create a graphical user interface (GUI) that incorporates all of these elements. I am writing the program in

  18. 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

  19. Assessment of temporal hydrologic anomalies coupled with drought impact for a transboundary river flow regime: The Diyala watershed case study

    NASA Astrophysics Data System (ADS)

    Al-Faraj, Furat A. M.; Scholz, Miklas

    2014-09-01

    Recent increases in human activities in shared river basins have unquestionably raised concerns about potential hydrological impacts, especially impacts of dams and large-scale water withdrawal schemes in the highlands. Anthropogenic pressures twinned with drought impacts have exacerbated water management challenges. This article assesses the cumulative consequences of upstream anthropogenic pressures and drought spells on temporal river flow regimes for the downstream country. The size and complexity of problems confronting transboundary river watersheds makes it necessary to use a representative example basin to study the problems and potential solutions. The Diyala (Sīrvān) river basin, which shares dozens of transboundary watersheds between Iraq and Iran, has been selected as a representative case study. A subset of the Indicators of Hydrologic Alteration (IHA) was utilised and climate variability was considered in assessing the combined effect of various forms of upstream human-river regulations and climatic conditions on natural flow regimes in the downstream state. Findings indicated that the anthropogenic river-regulation coupled with the impact of drought periods have noticeably modified the natural flow paradigm. The yearly average runoffs, which are no longer available for the downstream country, have soared to very high levels, particularly over the last fifteen years. More adverse impacts were detected in the non-rainy season. Findings reveal also that damming and considerable water diversion to large-scale irrigation projects in the upstream state are the main regulations affecting the management of shared water resources in the downstream country.

  20. Considerations of Air Flow in Combustion Chambers of High-Speed Compression-Ignition Engines

    NASA Technical Reports Server (NTRS)

    Spanogle, J A; Moore, C S

    1932-01-01

    The air flow in combustion chambers is divided into three fundamental classes - induced, forced, and residual. A generalized resume is given of the present status of air flow investigations and of the work done at this and other laboratories to determine the direction and velocity of air movement in auxiliary and integral combustion chambers. The effects of air flow on engine performance are mentioned to show that although air flow improves the combustion efficiency, considerable induction, friction, and thermal losses must be guarded against.

  1. 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...

  2. 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.

  3. Dry Flowing Abrasive Decontamination Technique for Pipe Systems with Swirling Air Flow

    SciTech Connect

    Kameo, Yutaka; Nakashima, Mikio; Hirabayashi, Takakuni

    2003-10-15

    A dry abrasive decontamination method was developed for removing radioactive corrosion products from surfaces of coolant pipe systems in decommissioning of a nuclear power plant. Erosion behavior of inside surfaces of stainless and carbon steel pipes by a swirling air flow containing alumina or cast-iron grit abrasive was studied. Erosion depths of the test pipes were approximately proportional to an abrasive concentration in air and an exponent of flow rate of airstream. The experimental results indicated that the present method could keep satisfactory erosion ability of abrasives even for a large-size pipe. The present method was successfully applied to {sup 60}Co-contaminated specimens sampled from a pipe of the water cleanup system of the Japan Power Demonstration Reactor.

  4. Simulation of air gap vibration on aerostatic bearing under flow/structure coupled conditions

    NASA Astrophysics Data System (ADS)

    Wang, Qian; Wu, Jianjin; Li, Dongsheng

    2008-10-01

    The vibration of aerostatic bearing air gap is one of the main factors, which restricts the precision of nano-processing and nano-measurement. Finite volume method was employed to obtain the air gap steady flow of different air gap thicknesses for the demonstration of vibrations under flow/structure coupled conditions. The unsteady flow of air gap was analyzed numerically by using the air gap flow & boundary movement control equations to get the pressure distribution on the slide surface and the amplitude of air gap for further study on the self-excited vibration of aerostatic bearings. Numerical analyses show that the highest aerostatic bearing amplitude is relative to the difference between load capacity and gravity at the initial moment as air gap rises, and the final air gap thickness has nothing to do with the initial air gap thickness. The results presented a new analytic demonstration for the research on the reduction of aerostatic bearing vibration.

  5. Flow regime in a restored wetland determines trophic links and species composition in the aquatic macroinvertebrate community.

    PubMed

    González-Ortegón, E; Walton, M E M; Moghaddam, B; Vilas, C; Prieto, A; Kennedy, H A; Pedro Cañavate, J; Le Vay, L

    2015-01-15

    In a restored wetland (South of Spain), where different flow regimes control water exchange with the adjacent Guadalquivir estuary, the native Palaemon varians coexists with an exotic counterpart species Palaemon macrodactylus. This controlled m\\acrocosm offers an excellent opportunity to investigate how the effects of water management, through different flow regimes, and the presence of a non-native species affect the aquatic community and the trophic niche (by gut contents and C-N isotopic composition) of the native shrimp Palaemon varians. We found that increased water exchange rate (5% day(-1) in mixed ponds vs. 0.1% day(-1) in extensive ponds) modified the aquatic community of this wetland; while extensive ponds are dominated by isopods and amphipods with low presence of P. macrodactylus, mixed ponds presented high biomass of mysids, corixids, copepods and both shrimp species. An estuarine origin of nutrients and primary production might explain seasonal and spatial differences found among ponds of this wetland. A combined analysis of gut contents and isotopic composition of the native and the exotic species showed that: (1) native P. varians is mainly omnivorous (2) while the non-native P. macrodactylus is more zooplanktivorous and (3) a dietary overlap occurred when both species coexist at mixed ponds where a higher water exchange and high abundance of mysids and copepods diversifies the native species' diet. Thus differences in the trophic ecology of both species are clearly explained by water management. This experimental study is a valuable tool for integrated management between river basin and wetlands since it allows quantification of wetland community changes in response to the flow regime. PMID:25242150

  6. 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.

  7. Laser ignition of hypersonic air-hydrogen flow

    NASA Astrophysics Data System (ADS)

    Brieschenk, S.; Kleine, H.; O'Byrne, S.

    2013-09-01

    An experimental investigation of the behaviour of laser-induced ignition in a hypersonic air-hydrogen flow is presented. A compression-ramp model with port-hole injection, fuelled with hydrogen gas, is used in the study. The experiments were conducted in the T-ADFA shock tunnel using a flow condition with a specific total enthalpy of 2.5 MJ/kg and a freestream velocity of 2 km/s. This study is the first comprehensive laser spark study in a hypersonic flow and demonstrates that laser-induced ignition at the fuel-injection site can be effective in terms of hydroxyl production. A semi-empirical method to estimate the conditions in the laser-heated gas kernel is presented in the paper. This method uses blast-wave theory together with an expansion-wave model to estimate the laser-heated gas conditions. The spatially averaged conditions found with this approach are matched to enthalpy curves generated using a standard chemical equilibrium code (NASA CEA). This allows us to account for differences that are introduced due to the idealised description of the blast wave, the isentropic expansion wave as well as thermochemical effects.

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

    NASA Astrophysics Data System (ADS)

    Lei, Wenwen; McKenzie, David R.

    2014-12-01

    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.

  9. Heat flows to the combustion chamber walls in detonation and turbulent combustion regimes

    NASA Astrophysics Data System (ADS)

    Bykovskii, F. A.

    1991-02-01

    Measuremens of heat flows to the walls of an annular combustion chamber under conditions of combustion and continuous detonation are reported for a propane-oxygen mixture. It is shown that specific heat flows to the chamber walls under conditions of detonation are significantly lower than those observed during ordinary combustion. The experimental equipment and details of the experimental procedure are described.

  10. 40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... meter, a thermal-mass meter, an averaging Pitot tube, or a hot-wire anemometer. (c) Flow conditioning... 40 Protection of Environment 33 2011-07-01 2011-07-01 false Dilution air and diluted exhaust flow...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related...

  11. 40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... meter, a thermal-mass meter, an averaging Pitot tube, or a hot-wire anemometer. (c) Flow conditioning... 40 Protection of Environment 32 2010-07-01 2010-07-01 false Dilution air and diluted exhaust flow...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related...

  12. 40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... meter, a thermal-mass meter, an averaging Pitot tube, or a hot-wire anemometer. (c) Flow conditioning... 40 Protection of Environment 34 2012-07-01 2012-07-01 false Dilution air and diluted exhaust flow...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related...

  13. 40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... meter, a thermal-mass meter, an averaging Pitot tube, or a hot-wire anemometer. (c) Flow conditioning... 40 Protection of Environment 34 2013-07-01 2013-07-01 false Dilution air and diluted exhaust flow...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related...

  14. 40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... meter, a thermal-mass meter, an averaging Pitot tube, or a hot-wire anemometer. (c) Flow conditioning... 40 Protection of Environment 33 2014-07-01 2014-07-01 false Dilution air and diluted exhaust flow...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related...

  15. On the impact of entrapped air in infiltration under ponding conditions: Part a: Preferential air flow path effects on infiltration

    NASA Astrophysics Data System (ADS)

    Weisbord, N.; Mizrahi, G.; Furman, A.

    2015-12-01

    Entrapped air effects on infiltration under ponding conditions could be important for massive infiltration of managed aquifer recharge or soil aquifer treatment. Earlier studies found that under ponding conditions air could reduce infiltration by 70-90%. Most studies have dealt with entrapped air effects when soil surface topography is flat. The objective of this study is to investigate the effects of: (1) irregular surface topography on preferential air flow path development; (2) preferential air flow path on infiltration; and (3) hydraulic head on infiltration when air is trapped. Column experiments were used to investigate these particular effects. A 140 cm deep and 30 cm wide column packed with silica sand was used under two boundary conditions: in the first, air can only escape vertically upward through the soil surface; in the second, air is free to escape. The surface was flooded with 13 liters of water, with ponding depth decreasing with time. Two soil surface conditions were tested: flat surface and irregular. It was found that in irregular surfaces, stable air flow through preferential paths was developed in the high altitude zones. Flat surface topography caused unstable air flow through random paths. Comparison between irregular and flat surface topography showed that the entrapped air pressure was lower and the infiltration rate was about 40% higher in the irregular surface topography than in the flat surface topography. No difference of infiltration rate between flat and irregular surface topography was observed when air was free to escape along the infiltration path. It was also found that at the first stage of infiltration, higher hydraulic heads caused higher entrapped air pressures and lower infiltration rates. In contrast, higher hydraulic head results in higher infiltration rate, when air was free to escape. Our results suggest that during ponding conditions: (1) preferential air flow paths develop at high surface zones of irregular topography

  16. 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)

  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. 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.

  20. Relief, nocturnal cold-air flow and air quality in Kigali, Rwanda

    NASA Astrophysics Data System (ADS)

    Henninger, Sascha

    2013-04-01

    , this result is not reassuringly, because all measured residential districts in Kigali exceeded the recommendations of the WHO, too. This suggests that the inhabitants of Kigali are exposed to enormous levels of PM10 during most of their time outdoors. So PM10 levels are increasing in areas with high rates of traffic due to the exhaust of the vehicles and the stirring up of dust from the ground, but also in fact of burning wood for cooking etc. within the residential districts. Hazardous measuring trips could be detected for nighttime measurements. Because of high temperatures, high solar radiation and a non-typical missing cloud cover the urban surface could heat up extremely, which produced a cold-air flow from the ridges and the slopes down to the "Marais" at night. This cold-air flow takes away the suspended particulate matters, which tends to accumulate within the "Marais" on the bottom of the hills, the places where most residential neighborhoods could be found and agricultural fields were used. The distinctive relief caused an accumulation within small valleys. Unfortunately, these are the favourite places of living and agriculture and this tends to high indoor-air pollution.

  1. New sensor for measurement of low air flow velocity. Phase I final report

    SciTech Connect

    Hashemian, H.M.; Hashemian, M.; Riggsbee, E.T.

    1995-08-01

    The project described here is the Phase I feasibility study of a two-phase program to integrate existing technologies to provide a system for determining air flow velocity and direction in radiation work areas. Basically, a low air flow sensor referred to as a thermocouple flow sensor has been developed. The sensor uses a thermocouple as its sensing element. The response time of the thermocouple is measured using an existing in-situ method called the Loop Current Step Response (LCSR) test. The response time results are then converted to a flow signal using a response time-versus-flow correlation. The Phase I effort has shown that a strong correlation exists between the response time of small diameter thermocouples and the ambient flow rate. As such, it has been demonstrated that thermocouple flow sensors can be used successfully to measure low air flow rates that can not be measured with conventional flow sensors. While the thermocouple flow sensor developed in this project was very successful in determining air flow velocity, determining air flow direction was beyond the scope of the Phase I project. Nevertheless, work was performed during Phase I to determine how the new flow sensor can be used to determine the direction, as well as the velocity, of ambient air movements. Basically, it is necessary to use either multiple flow sensors or move a single sensor in the monitoring area and make flow measurements at various locations sweeping the area from top to bottom and from left to right. The results can then be used with empirical or physical models, or in terms of directional vectors to estimate air flow patterns. The measurements can be made continuously or periodically to update the flow patterns as they change when people and objects are moved in the monitoring area. The potential for using multiple thermocouple flow sensors for determining air flow patterns will be examined in Phase II.

  2. 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. PMID:27136170

  3. Ecomorphological variation in shell shape of the freshwater turtle Pseudemys concinna inhabiting different aquatic flow regimes.

    PubMed

    Rivera, Gabriel

    2008-12-01

    Populations of species that inhabit a range of environments frequently display divergent morphologies that correlate with differences in ecological parameters. The velocity of water flow (i.e., flow velocity) is a critical feature of aquatic environments that has been shown to influence morphology in a broad range of taxa. The focus of this study was to evaluate the relationship between flow velocity and shell morphology for males and females of the semi-aquatic freshwater turtle Pseudemys concinna. For both sexes, the carapace and plastron show significant morphological differences between habitats characterized by slow-flowing (i.e., lentic) and fast-flowing (i.e., lotic) water. In general, the most prominent pattern for both sexes is that the shells of individuals from lotic habitats are more streamlined (small height-to-length ratio) than the shells of individuals from lentic habitats. Of the two shell components (carapace and plastron), the carapace shows greater divergence between habitats, particularly for males. These results are consistent with adaptations to flow velocity, and suggest that variation in shape may be more constrained in females. I also provide empirical evidence for an adaptive benefit of the observed shape change (i.e., drag reduction) and a brief comment on the relative roles of genetic divergence and phenotypic plasticity in generating shape differences observed in this species. PMID:21669831

  4. 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.

  5. 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.

  6. 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.

  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. Optimum design of bipolar plates for separate air flow cooling system of PEM fuel cells stacks

    NASA Astrophysics Data System (ADS)

    Franco, Alessandro

    2015-12-01

    The paper discusses about thermal management of PEM fuel cells. The objective is to define criteria and guidelines for the design of the air flow cooling system of fuel cells stacks for different combination of power density, bipolar plates material, air flow rate, operating temperature It is shown that the optimization of the geometry of the channel permits interesting margins for maintaining the use of separate air flow cooling systems for high power density PEM fuel cells.

  9. Balancing power production and instream flow regime for small scale hydropower

    NASA Astrophysics Data System (ADS)

    Perona, P.; Gorla, L.; Characklis, G. W.

    2013-12-01

    Flow diversion from river and torrent main stems is a common practice to feed water uses such run-of-river and mini-hydropower, irrigation, etc. Considering the worldwide increasing water demand, it becomes mandatory to take the importance of riparian ecosystems and related biodiversity into account before starting such practices. In this paper, we use a simple hydro-economic model (Perona et al., 2013, Gorla and Perona, 2013) to show that redistribution policies at diversion nodes allow for a clear bio-economic interpretation of residual flows. This model uses the Principle of Equal Marginal Utility (PEMU) as optimal water allocation rule for generating natural-like flow releases while maximizing the aggregated economic benefits of both the riparian environment and the traditional use (e.g., hydropower). We show that both static and dynamic release polices such Minimal Flow, and Proportional/Non-proportional Repartitions, respectively, can all be represented in terms of PEMU, making explicit the value of the ecosystem health underlying each policy. The related ecological and economical performances are evaluated by means of hydrological/ecological indicators. We recommend taking this method into account as a helpful tool guiding political, economical and ecological decisions when replacing the inadequate concept of Minimum Flow Requirement (MFR) with dynamic ones. References Perona, P., D. Dürrenmatt and G. Characklis (2013) Obtaining natural-like flow releases in diverted river reaches from simple riparian benefit economic models. Journal of Environmental Management, 118: 161-169, http://dx.doi.org/10.1016/j.jenvman.2013.01.010 Gorla, L. and P. Perona (2013) On quantifying ecologically sustainable flow releases in a diverted river reach. Journal of Hydrology, 489: 98- 107, http://dx.doi.org/10.1016/j.jhydrol.2013.02.043

  10. Two lighter than air systems in opposing flight regimes: An unmanned short haul, heavy load transport balloon and a manned, light payload airship

    NASA Technical Reports Server (NTRS)

    Pohl, R. A.

    1975-01-01

    Lighter Than Air vehicles are generally defined or categorized by the shape of the balloon, payload capacity and operational flight regime. Two balloon systems that are classed as being in opposite categories are described. One is a cable guided, helium filled, short haul, heavy load transport Lighter Than Air system with a natural shaped envelope. The other is a manned, aerodynamic shaped airship which utilizes hot air as the buoyancy medium and is in the light payload class. While the airship is in the design/fabrication phase with flight tests scheduled for the latter part of 1974, the transport balloon system has been operational for some eight years.

  11. Gas and liquid measurements in air-water bubbly flows

    SciTech Connect

    Zhou, X.; Doup, B.; Sun, X.

    2012-07-01

    Local measurements of gas- and liquid-phase flow parameters are conducted in an air-water two-phase flow loop. The test section is a vertical pipe with an inner diameter of 50 mm and a height of 3.2 m. The measurements are performed at z/D = 10. The gas-phase measurements are performed using a four-sensor conductivity probe. The data taken from this probe are processed using a signal processing program to yield radial profiles of the void fraction, bubble velocity, and interfacial area concentration. The velocity measurements of the liquid-phase are performed using a state-of-the-art Particle Image Velocimetry (PIV) system. The raw PIV images are acquired using fluorescent particles and an optical filtration device. Image processing is used to remove noise in the raw PIV images. The statistical cross correlation is introduced to determine the axial velocity field and turbulence intensity of the liquid-phase. Measurements are currently being performed at z/D = 32 to provide a more complete data set. These data can be used for computational fluid dynamic model development and validation. (authors)

  12. Flow development over low aspect ratio cantilevered circular cylinders in the laminar shedding regime

    NASA Astrophysics Data System (ADS)

    Morton, Chris; Saeedi, Mohammad; Martinuzzi, Robert

    2015-11-01

    The flow development over a cantilevered circular cylinder of aspect ratio 4 at Re = 300 has been investigated numerically by employing a laminar flow solution to the Navier-Stokes equations. The results show that two distinct wake modulation frequencies are detectable downstream of the cylinder, differing from higher Reynolds number turbulent flow cases where only one dominant frequency is present. In particular, there is a low frequency modulation with a well-defined narrow-band peak (fm) , and a high frequency contribution from the shedding of vortices (fv) . The fluctuating loading on the cylinder in the streamwise direction is tightly coupled with the low frequency modulation, while the transverse direction forces show only a weak correlation with the vortex shedding frequency. Coherent flow structures have been analyzed using proper orthogonal decomposition (POD) to provide insight into the nature of vortex formation and associated coupling with the detected low frequency modulation. The temporal coefficients obtained from the POD analysis have been used to construct a low order model for the investigation of the overall flow development. While the high frequency component is known to be related to the formation and shedding of vortices, the low frequency component is shown to be associated with a modulation in upwash and downwash intensity.

  13. 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.

  14. Some Effects of Air Flow on the Penetration and Distribution of Oil Sprays

    NASA Technical Reports Server (NTRS)

    Rothrock, A M; Beardsley, E G

    1929-01-01

    Tests were made to determine the effects of air flow on the characteristics of fuel sprays from fuel injection valves. Curves and photographs are presented showing the airflow throughout the chamber and the effects of the air flow on the fuel spray characteristics. It was found that the moving air had little effect on the spray penetration except with the 0.006 inch orifice. The moving air did, however, affect the oil particles on the outside of the spray cone. After spray cut-off, the air flow rapidly distributed the atomized fuel throughout the spray chamber.

  15. Real-Time Aerodynamic Parameter Estimation without Air Flow Angle Measurements

    NASA Technical Reports Server (NTRS)

    Morelli, Eugene A.

    2010-01-01

    A technique for estimating aerodynamic parameters in real time from flight data without air flow angle measurements is described and demonstrated. The method is applied to simulated F-16 data, and to flight data from a subscale jet transport aircraft. Modeling results obtained with the new approach using flight data without air flow angle measurements were compared to modeling results computed conventionally using flight data that included air flow angle measurements. Comparisons demonstrated that the new technique can provide accurate aerodynamic modeling results without air flow angle measurements, which are often difficult and expensive to obtain. Implications for efficient flight testing and flight safety are discussed.

  16. Flow regimes in model viscoelastic fluids in a circular couette system with independently rotating cylinders

    NASA Astrophysics Data System (ADS)

    Baumert, Brandon Max; Muller, Susan J.

    1997-03-01

    Flow visualization of two highly elastic, nonshear-thinning polyisobutylene/polybutene fluids in the gap between concentric cylinders was performed over a range of shear rates and choices of relative cylinder rotations. The observed secondary flows are discussed in terms of destabilizing elastic and centrifugal forces. In the more viscous, more elastic fluid, instabilities are found to be independent of the choice of rotating cylinder and due entirely to elasticity. At the lowest shear rates examined, the first detectable secondary flows are steady counter-rotating vortices forming after a shearing time more than five orders of magnitude greater than the characteristic relaxation time of the fluid. At somewhat higher shear rates, a much more rapidly appearing oscillatory flow is observed to evolve into the steady vortex structure. In the less elastic fluid, the structure first detectable at the lowest shear rates is again steady vortices regardless of the choice of driving cylinder. At all shear rates examined, only elastic stationary vortices are observed in the absence of centrifugal destabilization (outer cylinder rotating). Secondary flows are significantly stronger in the presence of the centrifugal destabilization due to a rotating inner cylinder. Interaction of elasticity and centrifugal forces is found to generate a number of axially translating vortex structures, many of which are described here for the first time. At a shear rate more than five times the critical, another family of instability is observed which closely resembles a purely elastic instability observed by Baumert and Muller (1995). These experimental results are expected to provide a challenging test of numerical simulations of these viscoelastic flows.

  17. Flow regimes in model viscoelastic fluids in a circular couette system with independently rotating cylinders

    SciTech Connect

    Baumert, B.M.; Muller, S.J.

    1997-03-01

    Flow visualization of two highly elastic, nonshear-thinning polyisobutylene/polybutene fluids in the gap between concentric cylinders was performed over a range of shear rates and choices of relative cylinder rotations. The observed secondary flows are discussed in terms of destabilizing elastic and centrifugal forces. In the more viscous, more elastic fluid, instabilities are found to be independent of the choice of rotating cylinder and due entirely to elasticity. At the lowest shear rates examined, the first detectable secondary flows are steady counter-rotating vortices forming after a shearing time more than five orders of magnitude greater than the characteristic relaxation time of the fluid. At somewhat higher shear rates, a much more rapidly appearing oscillatory flow is observed to evolve into the steady vortex structure. In the less elastic fluid, the structure first detectable at the lowest shear rates is again steady vortices regardless of the choice of driving cylinder. At all shear rates examined, only elastic stationary vortices are observed in the absence of centrifugal destabilization (outer cylinder rotating). Secondary flows are significantly stronger in the presence of the centrifugal destabilization due to a rotating inner cylinder. Interaction of elasticity and centrifugal forces is found to generate a number of axially translating vortex structures, many of which are described here for the first time. At a shear rate more than five times the critical, another family of instability is observed which closely resembles a purely elastic instability observed by Baumert and Muller (1995). These experimental results are expected to provide a challenging test of numerical simulations of these viscoelastic flows. {copyright} {ital 1997 American Institute of Physics.}

  18. Numerical Analysis of Flow Evolution in a Helium Jet Injected into Ambient Air

    NASA Technical Reports Server (NTRS)

    Satti, Rajani P.; Agrawal, Ajay K.

    2005-01-01

    A computational model to study the stability characteristics of an evolving buoyant helium gas jet in ambient air environment is presented. Numerical formulation incorporates a segregated approach to solve for the transport equations of helium mass fraction coupled with the conservation equations of mixture mass and momentum using a staggered grid method. The operating parameters correspond to the Reynolds number varying from 30 to 300 to demarcate the flow dynamics in oscillating and non-oscillating regimes. Computed velocity and concentration fields were used to analyze the flow structure in the evolving jet. For Re=300 case, results showed that an instability mode that sets in during the evolution process in Earth gravity is absent in zero gravity, signifying the importance of buoyancy. Though buoyancy initiates the instability, below a certain jet exit velocity, diffusion dominates the entrainment process to make the jet non-oscillatory as observed for the Re=30 case. Initiation of the instability was found to be dependent on the interaction of buoyancy and momentum forces along the jet shear layer.

  19. 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.

  20. 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...

  1. 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.

  2. 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.

  3. Quantifying the transition of blood flow to the non-continuum regime

    NASA Astrophysics Data System (ADS)

    Lei, Huan; Fedosov, Dmitry; Caswell, Bruce; Karniadakis, George

    2013-11-01

    Blood flow is usually treated as a Newtonian fluid down to diameters of about 200 μ m. We employ the dissipative particle dynamics to simulate the flow of red blood cell suspensions driven through small tubes (diameters 10-150 μ m) in the range marking the transition from venules to the large capillaries. Simulation results show that for diameters less than about 100 μ m the suspension's stress cannot be described as a continuum, even a heterogeneous one. In tube flow the cross-stream stress gradient induces an inhomogeneous distribution of RBCs featuring a centerline cell density peak, and a cell-free layer next to the wall. The local viscosity across the section as a function of the strain rate is found to be essentially independent of tube size for the larger diameters and is determined by the local hematocrit (H) and shear rate. As the tube diameter decreases below about 100 μ m, the viscosity in the central region departs from the large-tube similarity function of the shear rate, since H increases significantly towards the centerline. The dependence of shear stress on tube size, in addition to the expected local shear rate and local hematocrit, implies that blood flow in small tubes cannot be described as a heterogeneous continuum.

  4. Direct simulation of open-channel flow in the fully rough regime: focus on fluid-roughness interaction

    NASA Astrophysics Data System (ADS)

    Mazzuoli, Marco; Uhlmann, Markus

    2015-04-01

    The interaction between an incompressible open-channel flow at Reb = 6900 and rigid spheres of size k+ = 120 mounted in square arrangement on the bottom, has been investigated by means of Direct Numerical Simulation (DNS) for the purpose of contributing to the knowledge of the basic mechanism of sediment transport. The shift generated by the roughness on mean velocity profile in the log-region is in the range of values characterizing the Fully-Rough Regime (FRR). First, average quantities (i.e. flow velocity, shear-stress distribution on the sphere surface, force and torque acting on the spheres) are analyzed exploiting the spatial periodicity of the arrangement of roughness elements. Then, spatial and temporal fluctuations of the quantities are studied. Results are compared with those obtained for a similar DNS at Reb = 2900, which is in the Transitionally-Rough Regime (TRR). Although the largest fluctuations of the velocity components are observed ~ 8 wall units below the crest of the spheres in the FRR, their effect on the drag and lift fluctuations acting on individual spheres is weaker than in the TRR. Nonetheless, the lift coefficient in the FRR case was found the 24% larger than in the TRR case. The characteristics of vortex structures in the vicinity of roughness elements are also investigated. Differences in the flow structure between the two simulations in the TRR and in the FRR reflect on the stress distribution on the surface of the spheres. Finally, the arrangement of the roughness elements might play a key role in the modulation of turbulence.

  5. 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

  6. Simulation and classification of the impacts of projected climate change on flow regimes in the arid Hexi Corridor of Northwest China

    NASA Astrophysics Data System (ADS)

    Zhang, Yongyong; Fu, Guobin; Sun, Boyang; Zhang, Shifeng; Men, Baohui

    2015-08-01

    Traditional assessment approaches of climate change on flow regimes usually focus on flow magnitude and cannot capture the overall variation of flow regimes (e.g., variability, frequency, duration, timing, and rating). The Hexi Corridor, which is a typical arid and semiarid region in Northwest China, was selected as the study area. Streamflows were simulated by an integrated water system model in a historical period (1985-2005) and three future periods (2030s, 2050s, and 2070s). Twenty-nine global climate models were picked from the Coupled Model Intercomparison Project Phase 5 based on projection performance, and the high (RCP85) and intermediate (RCP45) ranges of Representative Concentration Pathways were selected for future scenario analysis. All the streamflows were characterized in detail by flow regime metrics, including the magnitude, variability, and frequency of the overall flow events. The regional impacts of climate change were assessed and clustered into several similar spatial patterns. Results showed that the projected climate change would sensibly increase the magnitudes of average and low flows (75th percentile), as well as the frequencies of low and high flows (25th percentile), but decrease the flow variability. By contrast, it would not sensibly change the magnitude of high-flow events. The flow regime variations of all scenarios and periods were clustered into three robust classes (highly, moderately, and slightly impacted classes) in the entire region. The flow regimes would be highly and moderately impacted in the middle stream and downstream with large-sized and semidesert catchments but slightly impacted in the upper and middle streams with small-sized and montane vegetation catchments. The impacted classes will sensibly vary at most stations in different future periods because of the spatial differences of climate change. This study would provide scientific support to implement the integrated adaptive water resource management for climate

  7. Blood flow in small tubes: quantifying the transition to the non-continuum regime

    PubMed Central

    Lei, Huan; Fedosov, Dmitry A.; Caswell, Bruce; Karniadakis, George Em

    2013-01-01

    In small vessels blood is usually treated as a Newtonian fluid down to diameters of ~200 μm. We investigate the flow of red blood cell (RBC) suspensions driven through small tubes (diameters 10–150 μm) in the range marking the transition from arterioles and venules to the largest capillary vessels. The results of the simulations combined with previous simulations of uniform shear flow and experimental data show that for diameters less than ~100 μm the suspension’s stress cannot be described as a continuum, even a heterogeneous one. We employ the dissipative particle dynamics (DPD) model, which has been successfully used to predict human blood bulk viscosity in homogeneous shear flow. In tube flow the cross-stream stress gradient induces an inhomogeneous distribution of RBCs featuring a centreline cell density peak, and a cell-free layer (CFL) next to the wall. For a neutrally buoyant suspension the imposed linear shear-stress distribution together with the differentiable velocity distribution allow the calculation of the local viscosity across the tube section. The viscosity across the section as a function of the strain rate is found to be essentially independent of tube size for the larger diameters and is determined by the local haematocrit (H) and shear rate. Other RBC properties such as asphericity, deformation, and cell-flow orientation exhibit similar dependence for the larger tube diameters. As the tube size decreases below ~100 μm in diameter, the viscosity in the central region departs from the large-tube similarity function of the shear rate, since H increases significantly towards the centreline. The dependence of shear stress on tube size, in addition to the expected local shear rate and local haematocrit, implies that blood flow in small tubes cannot be described as a heterogeneous continuum. Based on the analysis of the DPD simulations and on available experimental results, we propose a simple velocity-slip model that can be used in

  8. Investigation of Countercurrent Helium-Air Flows in Air-ingress Accidents for VHTRs

    SciTech Connect

    Sun, Xiaodong; Christensen, Richard; Oh, Chang

    2013-10-03

    The primary objective of this research is to develop an extensive experimental database for the air- ingress phenomenon for the validation of computational fluid dynamics (CFD) analyses. This research is intended to be a separate-effects experimental study. However, the project team will perform a careful scaling analysis prior to designing a scaled-down test facility in order to closely tie this research with the real application. As a reference design in this study, the team will use the 600 MWth gas turbine modular helium reactor (GT-MHR) developed by General Atomic. In the test matrix of the experiments, researchers will vary the temperature and pressure of the helium— along with break size, location, shape, and orientation—to simulate deferent scenarios and to identify potential mitigation strategies. Under support of the Department of Energy, a high-temperature helium test facility has been designed and is currently being constructed at Ohio State University, primarily for high- temperature compact heat exchanger testing for the VHTR program. Once the facility is in operation (expected April 2009), this study will utilize high-temperature helium up to 900°C and 3 MPa for loss-of-coolant accident (LOCA) depressurization and air-ingress experiments. The project team will first conduct a scaling study and then design an air-ingress test facility. The major parameter to be measured in the experiments is oxygen (or nitrogen) concentration history at various locations following a LOCA scenario. The team will use two measurement techniques: 1) oxygen (or similar type) sensors employed in the flow field, which will introduce some undesirable intrusiveness, disturbing the flow, and 2) a planar laser-induced fluorescence (PLIF) imaging technique, which has no physical intrusiveness to the flow but requires a transparent window or test section that the laser beam can penetrate. The team will construct two test facilities, one for high-temperature helium tests with

  9. Modeling the Effect of Changing Sediment Load on the Flow Regime of the Lower Mississippi River

    NASA Astrophysics Data System (ADS)

    Parker, G.; Yeh, T.

    2012-12-01

    The effect of hundreds of dams on the lower Mississippi River system has been to reduce sediment supply to about half its pre-settlement value. This decline appears to be continuing today. The lower Mississippi River undergoes a transition from a purely alluvial river to a mixed alluvial-bedrock river at a point upstream of Baton Rouge. Here attention is focused upon the alluvial reach. A model that treats a) both bedload and suspended load transport of mixed sizes of sand and mud, b) the effect of flow self-stratification due to suspended sediment and c) the effect of flow-dependent bedform resistance is used to study the long-term effect of varying sediment supply on river depth and slope under a variety of scenarios.

  10. Geostatistical prediction of stream-flow regime in southeastern United States

    NASA Astrophysics Data System (ADS)

    Pugliese, Alessio; Castellarin, Attilio; Archfield, Stacey; Farmer, William

    2015-04-01

    A Flow-Duration Curve (FDC) represents the percentage of time (duration) during which a given stream-flow is equalled or exceeded over a given period of time. In many water-engineering applications FDCs need to be predicted for ungauged sites (Prediction in Ungauged Basins, PUB problem) using the information collected in donor neighboring gauged basins. We present an application of kriging procedures which makes the procedures capable of predicting FDCs in ungauged catchments. As many of the techniques proposed in the recent literature, the curve is predicted at the target site as a weighted average of empirical dimensionless FDCs that are constructed for neighboring streamgauges and standardized by discharge Q*. Geostatistical weights are obtained by applying two different interpolation techniques, i.e. Top-kriging (TK, see e.g. Pugliese et al., 2014) and Ordinary-kriging (OK, see e.g. Castiglioni et al., 2009), for interpolating a point streamflow-index computed as the overall negative deviation of each empirical curve from Q*, which we term Total Negative Deviation (TND). Empirical TND values can be used to assess the hydrological similarity between catchments and can be interpolated using TK or OK procedures along the stream-network. We consider period-of-record/annual, and complete/seasonal FDCs standardized by two different Q* values, i.e. Mean Annual Flow (MAF) and Mean Annual Precipitation at catchment scale times the drainage area (MAP*), and we apply TK and OK in a wide study area in the Southeastern United States including 182 unregulated gauged catchments. The accuracy of the predicted FDCs is assessed comprehensively under different operational conditions through the (1) leave-one-out and (2) three-fold cross-validation procedures. The results are compared with six different methods for predicting FDCs from synthetically generated daily stream-flow series, which were recently analysed by U.S. Geological Survey. The application of OK and TK reveal

  11. A Monte Carlo model for seeded atomic flows in the transition regime

    SciTech Connect

    Longo, S. Diomede, P.

    2009-06-01

    A simple model for the numerical determination of separation effects in seeded atomic gas flows is presented. The model is based on the known possibility to provide a statistically convergent estimate of the exact solution for a linear transport equation using the test particle Monte Carlo method. Accordingly, the flow field of the main gas is preliminary calculated and as a second step the linear transport equations obtained by fixing the target distribution in the collision term of the Boltzmann equation for both main and minority components are solved. Both solutions are based on appropriately devised test particle Monte Carlo methods. The second step, the critical one in evaluating the separation effects, is exact and thereby completely free of numerical diffusion. The model is described in details and illustrated by 2D test cases of atomic separation in shock fronts.

  12. Chemical fingerprinting of stratigraphic surfaces to refine reservoir architecture and differentiate fluid flow regimes

    SciTech Connect

    Eisenberg, R.A.; Harris, P.M.

    1995-08-01

    The variable development of depositional cycles within hydrocarbon reservoirs, especially reservoirs contained within platform carbonates, can have a profound influence on fluid flow. These cycles can be recognized in core and logs and should form the basis of subsurface geologic models. When placed into a sequence stratigraphic framework, cycle variability can be predicted. We herein investigate the use of chemostratigraphy to refine a reservoir-scale stratigraphic framework and demonstrate the influence of this framework on fluid flow. Using cores and outcrops of the Permian San Andres Formation in the Guadalupe Mountains of southeastern New Mexico, permeability distribution and waterflood response was modeled for a small-scale carbonate sequence (105 no thick) containing variably developed depositional cycles that formed in a carbonate ramp setting. Cross-sectional fractal permeability fields, used in simulated waterfloods, demonstrate sensitivities of oil recovery and overall injection rare to the stratigraphic framework. Major, minor and trace element variation measured on 44 interval composites from core, using a combination of techniques including inductively coupled plasma (ICP) and mass spectrometry, characterize and fingerprint important stratigraphic surfaces (sequence boundaries, cycle boundaries, and flooding surfaces). Less distinct cycles below this surface we characterized by compartmentalized flow and poor vertical sweep efficiency, whereas well-developed cycles above are characterized in our analog by a potential for early water breakthrough and relatively high vertical sweep efficiencies.

  13. Dynamic stochastic optimization models for air traffic flow management

    NASA Astrophysics Data System (ADS)

    Mukherjee, Avijit

    This dissertation presents dynamic stochastic optimization models for Air Traffic Flow Management (ATFM) that enables decisions to adapt to new information on evolving capacities of National Airspace System (NAS) resources. Uncertainty is represented by a set of capacity scenarios, each depicting a particular time-varying capacity profile of NAS resources. We use the concept of a scenario tree in which multiple scenarios are possible initially. Scenarios are eliminated as possibilities in a succession of branching points, until the specific scenario that will be realized on a particular day is known. Thus the scenario tree branching provides updated information on evolving scenarios, and allows ATFM decisions to be re-addressed and revised. First, we propose a dynamic stochastic model for a single airport ground holding problem (SAGHP) that can be used for planning Ground Delay Programs (GDPs) when there is uncertainty about future airport arrival capacities. Ground delays of non-departed flights can be revised based on updated information from scenario tree branching. The problem is formulated so that a wide range of objective functions, including non-linear delay cost functions and functions that reflect equity concerns can be optimized. Furthermore, the model improves on existing practice by ensuring efficient use of available capacity without necessarily exempting long-haul flights. Following this, we present a methodology and optimization models that can be used for decentralized decision making by individual airlines in the GDP planning process, using the solutions from the stochastic dynamic SAGHP. Airlines are allowed to perform cancellations, and re-allocate slots to remaining flights by substitutions. We also present an optimization model that can be used by the FAA, after the airlines perform cancellation and substitutions, to re-utilize vacant arrival slots that are created due to cancellations. Finally, we present three stochastic integer programming

  14. On the physical processes ruling an atmospheric pressure air glow discharge operating in an intermediate current regime

    SciTech Connect

    Prevosto, L. Mancinelli, B.; Chamorro, J. C.; Cejas, E.; Kelly, H.

    2015-02-15

    Low-frequency (100 Hz), intermediate-current (50 to 200 mA) glow discharges were experimentally investigated in atmospheric pressure air between blunt copper electrodes. Voltage–current characteristics and images of the discharge for different inter-electrode distances are reported. A cathode-fall voltage close to 360 V and a current density at the cathode surface of about 11 A/cm{sup 2}, both independent of the discharge current, were found. The visible emissive structure of the discharge resembles to that of a typical low-pressure glow, thus suggesting a glow-like electric field distribution in the discharge. A kinetic model for the discharge ionization processes is also presented with the aim of identifying the main physical processes ruling the discharge behavior. The numerical results indicate the presence of a non-equilibrium plasma with rather high gas temperature (above 4000 K) leading to the production of components such as NO, O, and N which are usually absent in low-current glows. Hence, the ionization by electron-impact is replaced by associative ionization, which is independent of the reduced electric field. This leads to a negative current-voltage characteristic curve, in spite of the glow-like features of the discharge. On the other hand, several estimations show that the discharge seems to be stabilized by heat conduction; being thermally stable due to its reduced size. All the quoted results indicate that although this discharge regime might be considered to be close to an arc, it is still a glow discharge as demonstrated by its overall properties, supported also by the presence of thermal non-equilibrium.

  15. A method for characterizing late-season low-flow regime in the upper Grand Ronde River Basin, Oregon

    USGS Publications Warehouse

    Kelly, Valerie J.; White, Seth

    2016-01-01

    This report describes a method for estimating ecologically relevant low-flow metrics that quantify late‑season streamflow regime for ungaged sites in the upper Grande Ronde River Basin, Oregon. The analysis presented here focuses on sites sampled by the Columbia River Inter‑Tribal Fish Commission as part of their efforts to monitor habitat restoration to benefit spring Chinook salmon recovery in the basin. Streamflow data were provided by the U.S. Geological Survey and the Oregon Water Resources Department. Specific guidance was provided for selection of streamgages, development of probabilistic frequency distributions for annual 7-day low-flow events, and regionalization of the frequency curves based on multivariate analysis of watershed characteristics. Evaluation of the uncertainty associated with the various components of this protocol indicates that the results are reliable for the intended purpose of hydrologic classification to support ecological analysis of factors contributing to juvenile salmon success. They should not be considered suitable for more standard water-resource evaluations that require greater precision, especially those focused on management and forecasting of extreme low-flow conditions.

  16. The study of the effect of the surface wave on turbulent stably-stratified boundary layer air-flow by direct numerical simulation

    NASA Astrophysics Data System (ADS)

    Druzhinin, Oleg; Troitskaya, Yliya; Zilitinkevich, Sergej

    2015-04-01

    Detailed knowledge of the interaction of surface water waves with the wind flow is of primary importance for correct parameterization of turbulent momentum and heat fluxes which define the energy and momentum transfer between the atmosphere and hydrosphere. The objective of the present study is to investigate the properties of the stably stratified turbulent boundary-layer (BL) air-flow over waved water surface by direct numerical simulation (DNS) at a bulk Reynolds number varying from 15000 to 80000 and the surface-wave slope up to ka = 0.2. The DNS results show that the BL-flow remains in the statistically stationary, turbulent regime if the Reynolds number (ReL) based on the Obukhov length scale and friction velocity is sufficiently large (ReL > 100). In this case, mean velocity and temperature vertical profiles are well predicted by log-linear asymptotic solutions following from the Monin-Obukhov similarity theory provided the velocity and temperature roughness parameters, z0U and z0T, are appropriately prescribed. Both z0U and z0T increase for larger surface-wave slope. DNS results also show that turbulent momentum and heat fluxes and turbulent velocity and temperature fluctuations are increased for larger wave slope (ka) whereas the mean velocity and temperature derivatives remain practically the same for different ka. Thus, we conclude that the source of turbulence enhancement in BL-flow are perturbations induced by the surface wave, and not the shear instability of the bulk flow. On the other hand, if stratification is sufficiently strong, and the surface-wave slope is sufficiently small, the BL-flow over waved surface relaminarizes in the bulk of the domain. However, if the surface-wave slope exceeds a threshold value, the velocity and temperature fluctuations remain finite in the vicinity of the critical-layer level, where the surface-wave phase velocity coincides with the mean flow velocity. We call this new stably-stratified BL-flow regime observed in

  17. Seasonal Dynamics of Trace Elements in Tidal Salt Marsh Soils as Affected by the Flow-Sediment Regulation Regime

    PubMed Central

    Bai, Junhong; Xiao, Rong; Zhao, Qingqing; Lu, Qiongqiong; Wang, Junjing; Reddy, K. Ramesh

    2014-01-01

    Soil profiles were collected in three salt marshes with different plant species (i.e. Phragmites australis, Tamarix chinensis and Suaeda salsa) in the Yellow River Delta (YRD) of China during three seasons (summer and fall of 2007 and the following spring of 2008) after the flow-sediment regulation regime. Total elemental contents of As, Cd, Cu, Pb and Zn were determined using inductively coupled plasma atomic absorption spectrometry to investigate temporal variations in trace elements in soil profiles of the three salt marshes, assess the enrichment levels and ecological risks of these trace elements in three sampling seasons and identify their influencing factors. Trace elements did not change significantly along soil profiles at each site in each sampling season. The highest value for each sampling site was observed in summer and the lowest one in fall. Soils in both P. australis and S. salsa wetlands tended to have higher trace element levels than those in T. chinensis wetland. Compared to other elements, both Cd and As had higher enrichment factors exceeding moderate enrichment levels. However, the toxic unit (TU) values of these trace elements did not exceed probable effect levels. Correlation analysis showed that these trace elements were closely linked to soil properties such as moisture, sulfur, salinity, soil organic matter, soil texture and pH values. Principal component analysis showed that the sampling season affected by the flow-sediment regulation regime was the dominant factor influencing the distribution patterns of these trace elements in soils, and plant community type was another important factor. The findings of this study could contribute to wetland conservation and management in coastal regions affected by the hydrological engineering. PMID:25216278

  18. MODELING AIR FLOW DYNAMICS IN RADON MITIGATION SYSTEMS: A SIMPLIFIED APPROACH

    EPA Science Inventory

    The paper refines and extends an earlier study--relating to the design of optimal radon mitigation systems based on subslab depressurization-- that suggested that subslab air flow induced by a central suction point be treated as radial air flow through a porous bed contained betw...

  19. Use of exhaust gas as sweep flow to enhance air separation membrane performance

    DOEpatents

    Dutart, Charles H.; Choi, Cathy Y.

    2003-01-01

    An intake air separation system for an internal combustion engine is provided with purge gas or sweep flow on the permeate side of separation membranes in the air separation device. Exhaust gas from the engine is used as a purge gas flow, to increase oxygen flux in the separation device without increasing the nitrogen flux.

  20. Ignition of hydrocarbon-air supersonic flow by volumetric ionization

    NASA Astrophysics Data System (ADS)

    Goldfeld, Marat A.; Pozdnyakov, George A.

    2015-11-01

    The paper describes the results of the electron-beam initiation of the combustion in the mixtures of hydrogen, natural gas or kerosene vapors with air. Electron beam characteristics were studied in closed volume with immobile gas. The researches included definition of an integrated current of an electronic beam, distribution of a current density and an estimation of average energy of electrons. Possibility of fuel mixtures ignition by means of this approach in the combustor at high velocity at the entrance was demonstrated. Experiments were carried out at Mach numbers of 4 and 5. Process of ignition and combustion under electron beam action was researched. It was revealed that ignition of mixture occurs after completion of electron gun operation. Data obtained have confirmed effectiveness of electron beam application for ignition of hydrogen and natural gas. The numerical simulation of the combustion of mixture in channel was carried out by means of ANSYS CFD 12.0 instrumentation on the basis of Reynolds averaged Navier-Stokes equation using SST/k-ω turbulence model. For combustion modeling, a detailed kinetic scheme with 38 reactions of 8 species was implemented taking into account finite rate chemistry. Computations have shown that the developed model allow to predict ignition of a mixture and flame propagation even at low flow temperatures.

  1. Some free boundary problems in potential flow regime usinga based level set method

    SciTech Connect

    Garzon, M.; Bobillo-Ares, N.; Sethian, J.A.

    2008-12-09

    Recent advances in the field of fluid mechanics with moving fronts are linked to the use of Level Set Methods, a versatile mathematical technique to follow free boundaries which undergo topological changes. A challenging class of problems in this context are those related to the solution of a partial differential equation posed on a moving domain, in which the boundary condition for the PDE solver has to be obtained from a partial differential equation defined on the front. This is the case of potential flow models with moving boundaries. Moreover the fluid front will possibly be carrying some material substance which will diffuse in the front and be advected by the front velocity, as for example the use of surfactants to lower surface tension. We present a Level Set based methodology to embed this partial differential equations defined on the front in a complete Eulerian framework, fully avoiding the tracking of fluid particles and its known limitations. To show the advantages of this approach in the field of Fluid Mechanics we present in this work one particular application: the numerical approximation of a potential flow model to simulate the evolution and breaking of a solitary wave propagating over a slopping bottom and compare the level set based algorithm with previous front tracking models.

  2. Exact solutions to the interfacial surfactant transport equation on a droplet in a Stokes flow regime

    NASA Astrophysics Data System (ADS)

    Kallendorf, Christina; Fath, Anja; Oberlack, Martin; Wang, Yongqi

    2015-08-01

    In the research literature there exist very rare analytical solutions of the surfactant transport equation on an interface. In the present article, we derive sets of exact solutions to interfacial convection-diffusion equations which describe the interfacial transport of insoluble surfactants in a two-phase flow. The investigated model is based on a Stokes flow setting where a spherical shaped inner phase is dispersed in an outer phase. Under the assumption of the small capillary number, the deformation of the spherical phase interface is not taken into account. Neglecting the dependence of the surface tension on the interfacial surfactant concentration, hence neglecting the Marangoni effect, general exact solutions to the surfactant conservation law on the spherical surface with both convective and diffusive terms are provided by means of Heun's confluent function. For the steady case, it is shown that these solutions collapse to a simple exponential form. Furthermore, for the purely diffusive problem, exact solutions are constructed using Legendre polynomials. Such analytical solutions are very valuable as benchmark problems in numerical investigations.

  3. Modelling ecological flow regime: an example from the Tennessee and Cumberland River basins

    USGS Publications Warehouse

    Knight, Rodney R.; Gain, W. Scott; Wolfe, William J.

    2012-01-01

    Predictive equations were developed for 19 ecologically relevant streamflow characteristics within five major groups of flow variables (magnitude, ratio, frequency, variability, and date) for use in the Tennessee and Cumberland River basins using stepbackward regression. Basin characteristics explain 50% or more of the variation for 12 of the 19 equations. Independent variables identified through stepbackward regression were statistically significant in 78 of 304 cases (α > 0.0001) and represent four major groups: climate, physical landscape features, regional indicators, and land use. Of these groups, the regional and climate variables were the most influential for determining hydrologic response. Daily temperature range, geologic factor, and rock depth were major factors explaining the variability in 17, 15, and 13 equations, respectively. The equations and independent datasets were used to explore the broad relation between basin properties and streamflow and the implication of streamflow to the study of ecological flow requirements. Key results include a high degree of hydrologic variability among least disturbed Blue Ridge streams, similar hydrologic behaviour for watersheds with widely varying degrees of forest cover, and distinct hydrologic profiles for streams in different geographic regions. Published in 2011. This article is a US Government work and is in the public domain in the USA.

  4. Numerical investigation of a two-phase swirl flow in the post-CHF regime

    NASA Astrophysics Data System (ADS)

    Yang, Wen-Tzao

    A numerical simulation was developed for a swirl-flow boiling fluid to predict heat transfer coefficients and hydrodynamic parameters. The simulation included the modeling of multiple sizes and number densities of liquid drops in the flow. Governing equations are derived using the principles of conservation of mass, momentum, and energy, and are based on an Eulerian-Lagrangian hybrid method. Due to the complexity of the phase distributions, the velocity fields, and the intramedium heat transfer, several assumptions and simplifications had to be made. The predictions of the model were compared with the experimental data from a vertical tube with twisted-tape inserts in a high pressure (16.0 MPa) water-steam heat exchanger. The mass flux range of the data was 910-1878 kg/msp2s, and the tape-twist ratios were 2.51, 5.02, and 7.53. Computational results indicate that the number of drop-size groups and the total number of drops have a significant influence on the wall temperature predictions.

  5. Hydrologic Partitioning of Evapotranspiration, Flows and Storage Across Landscapes and Climate Regimes in the Congo Basin

    NASA Astrophysics Data System (ADS)

    Aloysius, N. R.; Saiers, J. E.

    2011-12-01

    We use a distributed hydrological modeling framework to simulate the spatial and temporal variability of water-balance components in the Congo River basin (CRB) in Central Africa. In particular, our goal is to develop a predictive framework suitable for describing surface-water runoff, evapotranspiration (ET), and terrestrial-water storage and the responses of these processes to changes in climate and land cover. Information on the region's climate, soil properties, land cover, and topography are used to develop the model. The CRB is divided into 1,600 sub basins. The model computes the partitioning of precipitation (P) into quick flow (Qs), and soil wetting (W = P - Qs) at the sub basin level. The soil wetting component is further partitioned into ET, base flow (Qb), and storage. We calibrate the model by minimizing an objective function defined as the sum-of-squared differences between calculated and measured monthly average total flows, base flows and water yield at 27 stream-gage locations within the CRB. Annual precipitation within the basin varies between 1,000 to over 1,800 mm. The central parts of the basin, where the tropical evergreen forests are located, receive the highest amount of precipitation, whereas the northern and southern headwater regions are dryer. The model calculations of the fraction of annual precipitation returned to the atmosphere as ET from the land surface, lakes and wetlands varies from 0.30 to 0.90 across the CRB. The Aridity Index (AI), defined as the ratio of annual precipitation to potential ET, varies from 0.50 to 1.20. Nearly ten percent of the CRB area, mostly the southeastern headwater region, falls under semi-arid to dry sub-humid category (AI <= 0.65). The mean value of the runoff fraction, defined as the ratio of annual runoff to precipitation, is 0.17 (±0.10). The highest runoff-producing areas lie mostly within the forest land cover types in the central and northwestern part of the CRB, which also receive high

  6. Quantifying flow regimes in a Greenland glacial fjord using iceberg drifters

    NASA Astrophysics Data System (ADS)

    Sutherland, David A.; Roth, George E.; Hamilton, Gordon S.; Mernild, Sebastian H.; Stearns, Leigh A.; Straneo, Fiammetta

    2014-12-01

    Large, deep-keeled icebergs are ubiquitous in Greenland's outlet glacial fjords. Here we use the movement of these icebergs to quantify flow variability in Sermilik Fjord, southeast Greenland, from the ice mélange through the fjord to the shelf. In the ice mélange, a proglacial mixture of sea ice and icebergs, we find that icebergs consistently track the glacier speed, with slightly faster speeds near terminus and episodic increases due to calving events. In the fjord, icebergs accurately capture synoptic circulation driven by both along-fjord and along-shelf winds. Recirculation and in-/out-fjord variations occur throughout the fjord more frequently than previously reported, suggesting that across-fjord velocity gradients cannot be ignored. Once on the shelf, icebergs move southeastward in the East Greenland Coastal Current, providing wintertime observations of this freshwater pathway.

  7. Evaluation of generalized habitat criteria for assessing impacts of altered flow regimes on warmwater fishes

    USGS Publications Warehouse

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

    1998-01-01

    Assessing potential effects of flow regulation on southeastern warmwater fish assemblages is problematic because of high species richness and our poor knowledge of habitat requirements for most species. A previous attempt to reduce the complexity of describing habitat requirements for diverse assemblages defined five 'key habitat' types based on quantitative descriptions of depth, velocity, substrate, and cover for assessing the effects of streamflow alteration on fish communities. Our study investigated relationships between availability and temporal stability of key habitats and fish abundances at regulated and unregulated sites in the Tallapoosa River system. Fish assemblage characteristics at seven sites were quantified based on 1,400 electrofishing samples collected during 1994 and 1995. Simulations were used to model availability and temporal stability of key habitats at regulated and unregulated sites, Associations between fish assemblages and availability or stability of key habitats were identified using correlation analysis. We found that hydropeaking dam operation reduced the average length of time that shallow-water habitats were stable during the spring and summer and also reduced year-to-year variation in the stability of shallow-water habitats compared to unregulated sites. Within-site comparisons of fish and habitat variables indicated that differences in fish abundances correlated with differences in the availability and temporal stability of shallow-water habitats. Additionally, groups of stream fishes defined by taxonomy or differences in orientation to the substrate and feeding mode responded similarly to changes in key habitat availability. These findings demonstrate that the temporal and spatial availability of key habitats could serve as a useful measure of the potential effects of flow alteration on lotic fish assemblages, and suggest that both short-term temporal stability of key habitats as well as annual variation in key habitat

  8. Incorporating Climate Change in Flow Regime Alteration Studies in Hydropower Licensing

    NASA Astrophysics Data System (ADS)

    Rheinheimer, D. E.; Akhbari, M.; Peek, R.; Yarnell, S. M.; Null, S. E.; Viers, J. H.

    2013-12-01

    The U.S. Federal Energy Regulatory Commission has yet to mandate incorporation of anticipated climate change effects on hydropower system operations when assessing environmental impacts from the renewal of hydropower licenses. One stated reason is the lack of specific project-level specificity in future impacts. We demonstrate how a hydropower system operations model, incorporating the latest climatological realizations (3 GCMs x RCPs 4.5 and 8.5), can be used to assess environmental impacts generally, and hydrological flow alterations in particular, during the hydropower licensing process. We demonstrate that we can, in fact, quantify project-level impacts from climate change, albeit within the context of quantified uncertainty about non-stationary future conditions. The systems operations model analysis encompasses the combined effects of the Yuba River Development Project and Yuba-Bear Drum-Spaulding Projects, an interconnected series of complex hydropower systems located in the Sierra Nevada, California. Daily water system operations are simulated using a monthly-scale optimization model for hydropower decisions. Though there is inherent uncertainty generated by the modeling process and operational assumptions (e.g., static energy demand), there are sufficient data, modeling techniques, and analytical approaches to assess the how management decisions made today may be confounded by non-stationary hydroclimates in 30-50 years, which is the duration of most hydropower licenses. Such decisions need to include adaptive management approaches to address not only non-stationary hydroclimates, but also cumulative impacts to ecological functions and processes caused by serial flow manipulation. This study can help provide the scientific guidance needed to improve climate change policy in hydropower system planning.

  9. Agricultural practices influence flow regimes of headwater streams in western Iowa.

    PubMed

    Tomer, M D; Meek, D W; Kramer, L A

    2005-01-01

    Agricultural tillage influences runoff and infiltration, but consequent effects on watershed hydrology are poorly documented. This study evaluated 25 yr (1971-1995) hydrologic records from four first-order watersheds in Iowa's loess hills. Two watersheds were under conventional tillage and two were under conservation (ridge) tillage, one of which was terraced. All four watersheds grew corn (Zea mays L.) every year. Flow-frequency statistics and autoregressive modeling were used to determine how conservation treatments influenced stream hydrology. The autoregressive modeling characterized variations in discharge, baseflow, and runoff at multi-year, annual, and shorter time scales. The ridge-tilled watershed (nonterraced) had 47% less runoff and 36% more baseflow than the conventional watershed of similar landform and slope. Recovery of baseflow after drought was quicker in the conservation watersheds, as evidenced by 365-d moving average plots, and 67% greater baseflow during the driest 2 yr. The two conventional watersheds were similar, except the steeper watershed discharged more runoff and baseflow during short (<30 d), wet periods. Significant multi-year and annual cycles occurred in all variables. Under ridge-till, seasonal (annual-cycle) variations in baseflow had greater amplitude, showing the seasonality of subsurface contaminant movement could increase under conservation practices. However, deviations from the modeled cycles of baseflow were also more persistent under conservation practices, indicating baseflow was more stable. Indeed, flow-frequency curves showed wet-weather discharge decreased and dry-weather discharge increased under conservation practices. Although mean discharge increased in the conservation watersheds, variance and skewness of daily values were smaller. Ridge tillage with or without terraces increased stream discharge but reduced its variability. PMID:16091607

  10. Flow measurement in base cooling air passages of a rotating turbine blade

    NASA Technical Reports Server (NTRS)

    Liebert, C. H.; Pollack, F. G.

    1974-01-01

    The operational performance is decribed of a shaft-mounted system for measuring the air mass flow rate in the base cooling passages of a rotating turbine blade. Shaft speeds of 0 to 9000 rpm, air mass flow rates of 0.0035 to 0.039 kg/sec (0.0077 to 0.085 lbm/sec), and blade air temperatures of 300 to 385 K (80 to 233 F) were measured. Comparisons of individual rotating blade flows and corresponding stationary supply orifice flows agreed to within 10 percent.

  11. Flow-focusing regimes for accelerated production of monodisperse drug-loadable microbubbles toward clinical-scale applications

    PubMed Central

    Shih, Roger; Bardin, David; Martz, Thomas D.; Sheeran, Paul S.; Dayton, Paul A.

    2013-01-01

    Ultrasound imaging often calls for the injection of contrast agents, micron-sized bubbles which echo strongly in blood and help distinguish vascularized tissue. Such microbubbles are also being augmented for targeted drug delivery and gene therapy, by the addition of surface receptors and therapeutic payloads. Unfortunately, conventional production methods yield a polydisperse population, whose nonuniform resonance and drug-loading are less than ideal. An alternative technique, microfluidic flow-focusing, is able to produce highly monodisperse microbubbles with stabilizing lipid membranes and drug-carrying oil layers. However, the published 1 kHz production rate for these uniform drug bubbles is very low compared to conventional methods, and must be improved before clinical use can be practical. In this study, flow-focusing production of oil-layered lipid microbubbles was tested up to 300 kHz, with coalescence suppressed by high lipid concentrations or inclusion of Pluronic F68 surfactant in the lipid solution. The transition between geometry-controlled and dripping production regimes was analysed, and production scaling was found to be continuous, with a power trend of exponent ~5/12 similar to literature. Unlike prior studies with this trend, however, scaling curves here were found to be pressure-dependent, particularly at lower pressure-flow equilibria (e.g. <15 psi). Adjustments in oil flow rate were observed to have a similar effect, akin to a pressure change of 1–3 psi. This analysis and characterization of high-speed dual-layer bubble generation will enable more-predictive production control, at rates practical for in vivo or clinical use. PMID:24162868

  12. Effects of honeycomb shaped walls on the flow regime between a rotating disk and a stationary wall

    NASA Astrophysics Data System (ADS)

    Uzkan, T.; Lipstein, N. J.

    1986-06-01

    In order to cool a gas turbine disk with a limited supply of coolant air, the radial inflow of hot gases between rotor disk and housing must be reduced. Attention is presently given to the use of different surface shapes on the stationary housing to inhibit disk pumping capacity and hence to reduce the radial influx of hot gases into the clearance. The basic geometry that was experimentally investigated was the flow field between a smooth cylindrical rotating disk parallel to a plain circular coaxial wall open to the free space at the disk periphery. The results obtained are presented in terms of the tangential and radial velocity profiles in the gap, the static pressure measurements, and the disk torque coefficients. A honeycombed stationary wall surface had a profound effect on the ingestion of external flow into the gap from the disk periphery.

  13. Influence of the sputtering flow regime on the structural properties and magnetic behavior of Fe-Ga thin films (Ga ˜ 30 at.%)

    NASA Astrophysics Data System (ADS)

    Muñoz-Noval, A.; Ordóñez-Fontes, A.; Ranchal, R.

    2016-06-01

    In this paper we analyze the structure of Fe-Ga layers with a Ga content of ˜30 at.% deposited by the sputtering technique under two different regimes. We also studied the correlation between the structure and magnetic behavior of the samples. Keeping the Ar pressure fixed, we modified the flow regime from ballistic to diffusive by increasing the distance between the target and the substrate. X-ray diffraction measurements have shown a lower structural quality when growing in the diffusive flow. We investigated the impact of the growth regime by means of x-ray absorption fine structure (XAFS) measurements and obtained signs of its influence on the local atomic order. Full multiple scattering and finite difference calculations based on XAFS measurements point to a more relevant presence of a disordered A 2 phase and of orthorhombic Ga clusters on the Fe-Ga alloy deposited under a diffusive regime; however, in the ballistic sample, a higher presence of D 03/B 2 phases is evidenced. Structural characteristics, from local to long range, seem to determine the magnetic behavior of the layers. Whereas a clear in-plane magnetic anisotropy is observed in the film deposited under ballistic flow, the diffusive sample is magnetically isotropic. Therefore, our experimental results provide evidence of a correlation between flow regime and structural properties and its impact on the magnetic behavior of a rather unexplored compositional region of Fe-Ga compounds.

  14. LJUBLJANICA CONNECTS - Restoration of the Ljubljanica River corridor and improvement of the river's flow regime

    NASA Astrophysics Data System (ADS)

    Zabret, Katarina; Sapač, Klaudija; Šraj, Mojca; Bezak, Nejc; Sečnik, Matej; Vidmar, Andrej; Brilly, Mitja

    2016-04-01

    The project Ljubljanica connects is focused on improving connectivity and living conditions in Ljubljanica River which flows through capital city of Slovenia, Ljubljana. It represents living environment for endangered and Natura 2000 targeted fish species Danube Salmon (Hucho hucho), Danube Roach (Rutilus pigus) and Striped Chub (Leuciscus souffia). The project consists of four sets of activities: concrete restoration actions including improvement of two fish passes, monitoring of fish migration, monitoring of eco-hydrological parameters, and raising of public awareness. To improve living conditions the concrete restoration measures were performed. The reconstructions of sill and two fish passes on the Ljubljanica River have been implemented and barrier's lifting system on the weir was modernized. Above the sill in Zalog there is an oxbow which was disconnected with main river channel during the low flows. Interrupted inflow of fresh water caused very poor living conditions for animals in the oxbow. The raise of the sill helped to improve this situation. One of the fish passes included in the project is more than 100 years old whereas both are protected as cultural and technical heritage. None was working properly and due to the protection no visible nor drastic measures were allowed. With smaller improvements we managed to re-establish their operation. A lifting system of the barrier at the Ambrožev trg gate was outdated and did not allow precise regulation of the water level. Too fast raising of the barrier instantly caused deterioration of eco-hydrological conditions downstream. With modernization of the electromechanical equipment the situation is improved. The fish monitoring helps us to evaluate success of concrete restoration actions. The fish population status is monitored with marking the fish with Visible Implant Elastomer (VIE) tags. Regarding the location of catch we implant tags beneath transparent or translucent tissue combining different tag

  15. An objective and parsimonious approach for classifying natural flow regimes at a continental scale

    USGS Publications Warehouse

    Archfield, Stacey A.; Kennen, Jonathan G.; Carlisle, Daren M.; Wolock, David M.

    2014-01-01

    Hydro-ecological stream classification-the process of grouping streams by similar hydrologic responses and, by extension, similar aquatic habitat-has been widely accepted and is considered by some to be one of the first steps towards developing ecological flow targets. A new classification of 1543 streamgauges in the contiguous USA is presented by use of a novel and parsimonious approach to understand similarity in ecological streamflow response. This novel classification approach uses seven fundamental daily streamflow statistics (FDSS) rather than winnowing down an uncorrelated subset from 200 or more ecologically relevant streamflow statistics (ERSS) commonly used in hydro-ecological classification studies. The results of this investigation demonstrate that the distributions of 33 tested ERSS are consistently different among the classification groups derived from the seven FDSS. It is further shown that classification based solely on the 33 ERSS generally does a poorer job in grouping similar streamgauges than the classification based on the seven FDSS. This new classification approach has the additional advantages of overcoming some of the subjectivity associated with the selection of the classification variables and provides a set of robust continental-scale classes of US streamgauges. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

  16. Slow flows of a vapor-gas mixture with large density and temperature variations in the near-continuum regime

    NASA Astrophysics Data System (ADS)

    Laneryd, Carl-Johan Tor; Aoki, Kazuo; Takata, Shigeru

    2007-10-01

    A binary mixture of a vapor and a noncondensable gas in contact with the boundary made of the condensed phase (liquid or solid) of the vapor is considered in the following situation: the amount of the noncondensable gas contained in the system is of the same order of magnitude as that of the vapor; the temperature variation along the boundary may be large; the boundary is at rest, and there is no flow at infinity when an infinite domain is considered; and the Knudsen number is small (i.e., near-continuum regime). Slow steady flows (with Mach number of the order of Knudsen number, or equivalently, with Reynolds number of the order of unity) of the mixture, mainly caused by evaporation and condensation of the vapor on the boundary, are investigated on the basis of kinetic theory. The basic system used in this work is the fluid-dynamic-type system that was derived systematically from the Boltzmann system in a previous paper [S. Takata and K. Aoki, Transp. Theor. Stat. Phys. 30, 205 (2001); erratum, Transp. Theor. Stat. Phys. 31, 289 (2002)] in connection with the ghost effect, and it is solved numerically by a finite-volume method. Some additional computation using the direct simulation Monte Carlo method, based on the original Boltzmann system, is also performed for comparison. The behavior of the mixture in the continuum limit in which the Knudsen number vanishes is discussed with special interest in the ghost effect.

  17. Experimental verification of the four-sensor probe model for flow diagnosis in air water flow in vertical pipe

    NASA Astrophysics Data System (ADS)

    Pradhan, S.; Mishra, R.

    2012-05-01

    Measuring the volumetric flow rate of each of the flowing components is required to be monitored in production logging applications. Hence it is necessary to measure the flow rates of gas, oil and water in vertical and inclined oil wells. An increasing level of interest has been shown by the researchers in developing system for the flow rate measurement in multiphase flows. This paper describes the experimental methodology using a miniature, local four-sensor probe for the measurement of dispersed flow parameters in bubbly two-phase flow for spherical bubbles. To establish interdependent among different parameters corresponding to dispersed flow, the available model has been used to experimentally obtain different parameters such as volume fraction, velocity and bubble shape of the dispersed phase in the bubbly air-water flow.

  18. Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime.

    PubMed

    Speyer, K; Pastorino, C

    2015-07-21

    We performed molecular dynamics simulations to study the equilibrium and flow properties of a liquid in a nano-channel with confining surfaces coated with a layer of grafted semiflexible polymers. The coverage spans a wide range of grafting densities from essentially isolated chains to dense brushes. The end-grafted polymers were described by a bead spring model with a harmonic potential to include the bond stiffness of the chains. We varied the rigidity of the chains, from fully flexible polymers to rigid rods, in which the configurational entropy of the chains is negligible. The brush-liquid interaction was tuned to obtain a super-hydrophobic channel, in which the liquid did not penetrate the polymer brush, giving rise to a Cassie-Baxter state. Equilibrium properties such as brush height and bending energy were measured, varying the grafting density and the stiffness of the polymers. We also studied the characteristics of the brush-liquid interface and the morphology of the polymer chains supporting the liquid for different bending rigidities. Non-equilibrium simulations were performed, moving the walls of the channel in opposite directions at constant speed, obtaining a Couette velocity profile in the bulk liquid. The molecular degrees of freedom of the polymers were studied as a function of the Weissenberg number. Also, the violation of the no-slip boundary condition and the slip properties were analyzed as a function of the shear rate, grafting density and bending stiffness. At high grafting densities, a finite slip length independent of the shear rate or bending constant was found, while at low grafting densities a very interesting non-monotonic dependence on the bending constant is observed. PMID:26061866

  19. Operation of a full-scale pumped flow biofilm reactor (PFBR) under two aeration regimes.

    PubMed

    O'Reilly, E; Rodgers, M; Clifford, E

    2011-01-01

    A novel technology suitable for centralised and decentralised wastewater treatment has been developed, extensively tested at laboratory-scale, and trialled at a number of sites for populations ranging from 15 to 400 population equivalents (PE). The two-reactor-tank pumped flow biofilm reactor (PFBR) is characterised by: (i) its simple construction; (ii) its ease of operation and maintenance; (iii) low operating costs; (iv) low sludge production; and (v) comprising no moving parts or compressors, other than hydraulic pumps. By operating the system in a sequencing batch biofilm reactor (SBBR) mode, the following treatment can be achieved: 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD) and total suspended solids (TSS) reduction; nitrification and denitrification. During a 100-day full-scale plant study treating municipal wastewater and operating at 165 PE and 200 PE (Experiments 1 and 2, respectively), maximum average removals of 94% BOD5, 86% TSS and 80% ammonium-nitrogen (NH4-N) were achieved. During the latter part of Experiment 2, effluent concentrations averaged: 14 mg BOD5/l; 32 mg COD(filtered)/l; 14 mg TSS/l; 4.4 mg NH4-N/l; and 4.0 mg NO3-N/l (nitrate-nitrogen). The average energy consumption was 0.46-0.63 kWh/m3(treated) or 1.25-1.76 kWh/kg BOD5 removed. No maintenance was required during these experiments. The PFBR technology offers a low energy, minimal maintenance technology for the treatment of municipal wastewater. PMID:22214073

  20. The changing flow regime and sediment load of the Red River, Viet Nam

    NASA Astrophysics Data System (ADS)

    Le, Thi Phuong Quynh; Garnier, Josette; Gilles, Billen; Sylvain, Théry; Van Minh, Chau

    2007-02-01

    SummarySouth-East Asian Rivers contribute very significantly to the global sediment load to the ocean, hence to global biogeochemical cycles, and are subject to rapid changes owing to recent population and economic growth. The Red River system (Viet Nam and China) offers a good example of these changes. Previous estimates (before the year 1980) of the suspended matter loading of the Red River ranged from 100 to 170 × 10 6 t yr -1, i.e. from 640 to 1060 t km -2 yr -1. The strong dependence of suspended solid transport on hydrology results in a large year-to-year variability. Based on the available hydrological data from the period 1997-2004, and on a one-year survey of daily suspended matter of the three main tributaries of the Red River system in 2003, a simplified modeling approach, distinguishing between surface runoff and base flow, is established to estimate the mean suspended loading of the Red River under present conditions. The obtained value is 40 × 10 6 t yr -1, corresponding to a specific load of 280 t km -2 yr -1. It reflects a 70% decrease of the total suspended load since the impoundment of the Hoa Binh and Thac Ba reservoirs in the 1980s. Following the planned construction of two additional reservoirs, the model predicts a further reduction by 20% of the suspended load of the Red River, which might be compensated by an expected increase in suspended loading due to enhanced rainfall induced by climate change. Using measurements of the total phosphorus content of the suspended material in the different Red River tributaries, the present phosphorus delivery by the Red River can be estimated as 36 × 10 6 kgP yr -1.

  1. Managing the Drivers of Air Flow and Water Vapor Transport in Existing Single Family Homes (Revised)

    SciTech Connect

    Cummings, J.; Withers, C.; Martin, E.; Moyer, N.

    2012-10-01

    This document focuses on managing the driving forces which move air and moisture across the building envelope. While other previously published Measure Guidelines focus on elimination of air pathways, the ultimate goal of this Measure Guideline is to manage drivers which cause air flow and water vapor transport across the building envelope (and also within the home), control air infiltration, keep relative humidity (RH) within acceptable limits, avoid combustion safety problems, improve occupant comfort, and reduce house energy use.

  2. Combined Influence of Hall Current and Soret Effect on Chemically Reacting Magnetomicropolar Fluid Flow from Radiative Rotating Vertical Surface with Variable Suction in Slip-Flow Regime

    PubMed Central

    Jain, Preeti

    2014-01-01

    An analysis study is presented to study the effects of Hall current and Soret effect on unsteady hydromagnetic natural convection of a micropolar fluid in a rotating frame of reference with slip-flow regime. A uniform magnetic field acts perpendicularly to the porous surface which absorbs the micropolar fluid with variable suction velocity. The effects of heat absorption, chemical reaction, and thermal radiation are discussed and for this Rosseland approximation is used to describe the radiative heat flux in energy equation. The entire system rotates with uniform angular velocity Ω about an axis normal to the plate. The nonlinear coupled partial differential equations are solved by perturbation techniques. In order to get physical insight, the numerical results of translational velocity, microrotation, fluid temperature, and species concentration for different physical parameters entering into the analysis are discussed and explained graphically. Also, the results of the skin-friction coefficient, the couple stress coefficient, Nusselt number, and Sherwood number are discussed with the help of figures for various values of flow pertinent flow parameters. PMID:27350957

  3. Two-phase air-water stratified flow measurement using ultrasonic techniques

    SciTech Connect

    Fan, Shiwei; Yan, Tinghu; Yeung, Hoi

    2014-04-11

    In this paper, a time resolved ultrasound system was developed for investigating two-phase air-water stratified flow. The hardware of the system includes a pulsed wave transducer, a pulser/receiver, and a digital oscilloscope. The time domain cross correlation method is used to calculate the velocity profile along ultrasonic beam. The system is able to provide velocities with spatial resolution of around 1mm and the temporal resolution of 200μs. Experiments were carried out on single phase water flow and two-phase air-water stratified flow. For single phase water flow, the flow rates from ultrasound system were compared with those from electromagnetic flow (EM) meter, which showed good agreement. Then, the experiments were conducted on two-phase air-water stratified flow and the results were given. Compared with liquid height measurement from conductance probe, it indicated that the measured velocities were explainable.

  4. Flow properties in expansion tube with helium, argon, air, and CO2

    NASA Technical Reports Server (NTRS)

    Miller, C. G.

    1974-01-01

    Test flow velocities from 5 to 7 km/sec were generated in a 6-in. expansion tube using helium, argon, air, and CO2 test gases. Pitot pressure profiles across the flow at the test section are presented for the four test gases, and measured flow quantities are compared to computer predicted values. Comparison of predicted and measured flow quantities suggests the expansion to be near thermochemical equilibrium for all test gases and implies the existence of a totally reflected shock at the secondary diaphragm. Argon, air, and CO2 flows were observed to attenuate while traversing the acceleration section, whereas no attenuation was observed for helium.

  5. Laboratory Evaluation of Air Flow Measurement Methods for Residential HVAC Returns for New Instrument Standards

    SciTech Connect

    Walker, Iain; Stratton, Chris

    2015-08-01

    This project improved the accuracy of air flow measurements used in commissioning California heating and air conditioning systems in Title 24 (Building and Appliance Efficiency Standards), thereby improving system performance and efficiency of California residences. The research team at Lawrence Berkeley National Laboratory addressed the issue that typical tools used by contractors in the field to test air flows may not be accurate enough to measure return flows used in Title 24 applications. The team developed guidance on performance of current diagnostics as well as a draft test method for use in future evaluations. The study team prepared a draft test method through ASTM International to determine the uncertainty of air flow measurements at residential heating ventilation and air conditioning returns and other terminals. This test method, when finalized, can be used by the Energy Commission and other entities to specify required accuracy of measurement devices used to show compliance with standards.

  6. Numerical Simulation of Two-phase Flow in a Microchannel with Air Gap

    NASA Astrophysics Data System (ADS)

    Liu, Xiaojun; Meinhart, Carl D.

    2001-11-01

    Fluid transport in nano- and micro-scale devices becomes more and more important. The potential advantages of micro-channel with air gap are studied. A simple one-dimensional model of air-water two-phase flow is investigated theoretically. The flow of water is driven by pressure drop. The air in the gap is driven by surface tension and friction forces that exist at the interface between the water and air. With the limitation that air flow rate is zero, the theoretical results are obtained based on continuity and Navier-Stokes equations. Because the viscosity of air is much less than that of water, under same pressure drop, the flow rate of water can be increased to as 4.76 times as that of normal channel without air gap. The theoretical results are tested by numerical simulation with three different software package (CFD2000, FEMLab and CFDRC) using a two-dimensional model. The interface shape, interface velocity, water flow rate and optimum height ratio are studied. Thenumerical results for different package match each other very well. The numerical results show that increasing water flow rate by adding air gap in the micro channel is practicable.

  7. Plant pneumatics: stem air flow is related to embolism - new perspectives on methods in plant hydraulics.

    PubMed

    Pereira, Luciano; Bittencourt, Paulo R L; Oliveira, Rafael S; Junior, Mauro B M; Barros, Fernanda V; Ribeiro, Rafael V; Mazzafera, Paulo

    2016-07-01

    Wood contains a large amount of air, even in functional xylem. Air embolisms in the xylem affect water transport and can determine plant growth and survival. Embolisms are usually estimated with laborious hydraulic methods, which can be prone to several artefacts. Here, we describe a new method for estimating embolisms that is based on air flow measurements of entire branches. To calculate the amount of air flowing out of the branch, a vacuum was applied to the cut bases of branches under different water potentials. We first investigated the source of air by determining whether it came from inside or outside the branch. Second, we compared embolism curves according to air flow or hydraulic measurements in 15 vessel- and tracheid-bearing species to test the hypothesis that the air flow is related to embolism. Air flow came almost exclusively from air inside the branch during the 2.5-min measurements and was strongly related to embolism. We propose a new embolism measurement method that is simple, effective, rapid and inexpensive, and that allows several measurements on the same branch, thus opening up new possibilities for studying plant hydraulics. PMID:26918522

  8. Indoor air flow and pollutant removal in a room with desk-top ventilation

    SciTech Connect

    Faulkner, D.; Fisk, W.J.; Sullivan, D.P.

    1993-04-01

    In a furnished experimental facility with three workstations separated by partitions, we studied indoor air flow patterns and tobacco smoke removal efficiency of a desk-top task ventilation system. The task ventilation system permits occupant control of the temperature, flow rate and direction of air supplied through two desk-mounted supply nozzles. In the configuration evaluated, air exited the ventilated space through a ceiling-mounted return grill. To study indoor air flow patterns, we measured the age of air at multiple indoor locations using the tracer gas step-up procedure. To study the intra-room transport of tobacco smoke particles and the efficiency of panicle removal by ventilation, a cigarette was smoked mechanically in one workstation and particle concentrations were measured at multiple indoor locations including the exhaust airstream. Test variables included the direction of air supply from the nozzles, supply nozzle area, supply flow rate and temperature, percent recirculation of chamber air, and internal heatloads. With nozzles pointed toward the occupants, 100% outside air supplied at the desk-top, and air supply rates of approximately 40 L/s per workstation, the age of air at the breathing level of ventilated workstations was approximately 30% less than the age of air that would occur throughout the test space with perfectly mixed indoor air. With smaller air supply rates and/or air supplied parallel to the edges of the desk, ages of air at breathing locations were not significantly lower than the age with perfect mixing. Indoor tobacco smoke particle concentrations at specific locations were generally within 12% of the average measured indoor concentration and concentrations of particles in the exhaust airstream were not significantly different from concentration of particles at breathing locations.

  9. Cold air performance of a 12.766-centimeter-tip-diameter axial-flow cooled turbine. 2: Effect of air ejection on turbine performance

    NASA Technical Reports Server (NTRS)

    Haas, J. E.; Kofskey, M. G.

    1977-01-01

    An air cooled version of a single-stage, axial-flow turbine was investigated to determine aerodynamic performance with and without air ejection from the stator and rotor blades surfaces to simulate the effect of cooling air discharge. Air ejection rate was varied from 0 to 10 percent of turbine mass flow for both the stator and the rotor. A primary-to-air ejection temperature ratio of about 1 was maintained.

  10. Using Flow Regime Lightning and Sounding Climatologies to Initialize Gridded Lightning Threat Forecasts for East Central Florida

    NASA Technical Reports Server (NTRS)

    Lambert, Winifred; Short, David; Wolkmer, Matthew; Sharp, David; Spratt, Scott

    2006-01-01

    Each morning, the forecasters at the National Weather Service in Melbourne, FL (NWS MLB) produce an experimental cloud-to-ground (CG) lightning threat index map for their county warning area (CWA) that is posted to their web site (http://www.srh.weather.gov/mlb/ghwo/lightning.shtml) . Given the hazardous nature of lightning in East Central Florida, especially during the warm season months of May September, these maps help users factor the threat of lightning, relative to their location, into their daily plans. The maps are color-coded in five levels from Very Low to Extreme, with threat level definitions based on the probability of lightning occurrence and the expected amount of CG activity. On a day in which thunderstorms are expected, there are typically two or more threat levels depicted spatially across the CWA. The locations of relative lightning threat maxima and minima often depend on the position and orientation of the low-level ridge axis, forecast propagation and interaction of sea/lake/outflow boundaries, expected evolution of moisture and stability fields, and other factors that can influence the spatial distribution of thunderstorms over the CWA. The lightning threat index maps are issued for the 24-hour period beginning at 1200 UTC each day with a grid resolution of 5 km x 5 km. Product preparation is performed on the AWIPS Graphical Forecast Editor (GFE), which is the standard NWS platform for graphical editing. Currently, the forecasters create each map manually, starting with a blank map. To improve efficiency of the forecast process, NWS MLB requested that the Applied Meteorology Unit (AMU) create gridded warm season lightning climatologies that could be used as first-guess inputs to initialize lightning threat index maps. The gridded values requested included CG strike densities and frequency of occurrence stratified by synoptic-scale flow regime. The intent is to improve consistency between forecasters while allowing them to focus on the

  11. Using Flow Regime Lightning and Sounding Climatologies to Initialize Gridded Lightning Threat Forecasts for East Central Florida

    NASA Technical Reports Server (NTRS)

    Lambert, Winifred; Short, David; Volkmer, Matthew; Sharp, David; Spratt, Scott

    2007-01-01

    Each morning, the forecasters at the National Weather Service in Melbourne, FL (NWS MLB) produce an experimental cloud-to-ground (CG) lightning threat index map for their county warning area (CWA) that is posted to their web site (httl://www.srh.weather.gov/mlb/ghwo/lightning.shtml) . Given the hazardous nature of lightning in East Central Florida, especially during the warm season months of May September, these maps help users factor the threat of lightning, relative to their location, into their daily plans. The maps are color-coded in five levels from Very Low to Extreme, with threat level definitions based on the probability of lightning occurrence and the expected amount of CG activity. On a day in which thunderstorms are expected, there are typically two or more threat levels depicted spatially across the CWA. The locations of relative lightning threat maxima and minima often depend on the position and orientation of the low-level ridge axis, forecast propagation and interaction of sea/lake/outflow boundaries, expected evolution of moisture and stability fields, and other factors that can influence the spatial distribution of thunderstorms over the CWA. The lightning threat index maps are issued for the 24-hour period beginning at 1200 UTC each day with a grid resolution of 5 km x 5 km. Product preparation is performed on the AWIPS Graphical Forecast Editor (GFE), which is the standard NWS platform for graphical editing. Until recently, the forecasters created each map manually, starting with a blank map. To improve efficiency of the forecast process, NWS MLB requested that the Applied Meteorology Unit (AMU) create gridded warm season lightning climatologies that could be used as first-guess inputs to initialize lightning threat index maps. The gridded values requested included CG strike densities and frequency of occurrence stratified by synoptic-scale flow regime. The intent was to improve consistency between forecasters while allowing them to focus on the

  12. A compressible two-phase model for dispersed particle flows with application from dense to dilute regimes

    NASA Astrophysics Data System (ADS)

    McGrath, Thomas P.; St. Clair, Jeffrey G.; Balachandar, S.

    2016-05-01

    Multiphase flows are present in many important fields ranging from multiphase explosions to chemical processing. An important subset of multiphase flow applications involves dispersed materials, such as particles, droplets, and bubbles. This work presents an Eulerian-Eulerian model for multiphase flows containing dispersed particles surrounded by a continuous media such as air or water. Following a large body of multiphase literature, the driving force for particle acceleration is modeled as a direct function of both the continuous-phase pressure gradient and the gradient of intergranular stress existing within the particle phase. While the application of these two components of driving force is well accepted in much of the literature, other models exist in which the particle-phase pressure gradient itself drives particle motion. The multiphase model treats all phases as compressible and is derived to ensure adherence to the 2nd Law of Thermodynamics. The governing equations are presented and discussed, and a characteristic analysis shows the model to be hyperbolic, with a degeneracy in the case that the intergranular stress, which is modeled as a configuration pressure, is zero. Finally, results from a two sample problems involving shock-induced particle dispersion are presented. The results agree well with experimental measurements, providing initial confidence in the proposed model.

  13. On the '-1' scaling of air temperature spectra in atmospheric surface layer flows

    NASA Astrophysics Data System (ADS)

    Li, D.; Katul, G. G.; Gentine, P.

    2015-12-01

    The spectral properties of scalar turbulence at high wavenumbers have been extensively studied in turbulent flows, and existing theories explaining the k-5/3 scaling within the inertial subrange appear satisfactory at high Reynolds numbers. Equivalent theories for the low wavenumber range have been comparatively lacking because boundary conditions prohibit attainment of such universal behavior. A number of atmospheric surface layer (ASL) experiments reported a k-1 scaling in air temperature spectra ETT(k) at low wavenumbers but other experiments did not. Here, the occurrence of a k-1 scaling in ETT(k) in an idealized ASL flow across a wide range of atmospheric stability regimes is investigated theoretically and experimentally. Experiments reveal a k-1 scaling persisted across different atmospheric stability parameter values (ζ) ranging from mildly unstable to mildly stable conditions (-0.1< ζ < 0.2). As instability increases, the k-1 scaling vanishes. Based on a combined spectral and co-spectral budget models and upon using a Heisenberg eddy viscosity as a closure to the spectral flux transfer term, conditions promoting a k-1 scaling are identified. Existence of a k-1 scaling is shown to be primarily linked to an imbalance between the production and dissipation rates of half the temperature variance. The role of the imbalance between the production and dissipation rates of half the temperature variance in controlling the existence of a '-1' scaling suggests that the '-1' scaling in ETT(k) does not necessarily concur with the '-1' scaling in the spectra of longitudinal velocity Euu(k). This finding explains why some ASL experiments reported k-1 in Euu(k) but not ETT(k). It also differs from prior arguments derived from directional-dimensional analysis that lead to simultaneous k-1 scaling in Euu(k) and ETT(k) at low wavenumbers in a neutral ASL.

  14. Computational modeling of air-breathing microfluidic fuel cells with flow-ov