Localised boundary air layer and clothing evaporative resistances for individual body segments.

PubMed

Wang, Faming; del Ferraro, Simona; Lin, Li-Yen; Sotto Mayor, Tiago; Molinaro, Vincenzo; Ribeiro, Miguel; Gao, Chuansi; Kuklane, Kalev; Holmér, Ingvar

2012-01-01

Evaporative resistance is an important parameter to characterise clothing thermal comfort. However, previous work has focused mainly on either total static or dynamic evaporative resistance. There is a lack of investigation of localised clothing evaporative resistance. The objective of this study was to study localised evaporative resistance using sweating thermal manikins. The individual and interaction effects of air and body movements on localised resultant evaporative resistance were examined in a strict protocol. The boundary air layer's localised evaporative resistance was investigated on nude sweating manikins at three different air velocity levels (0.18, 0.48 and 0.78 m/s) and three different walking speeds (0, 0.96 and 1.17 m/s). Similarly, localised clothing evaporative resistance was measured on sweating manikins at three different air velocities (0.13, 0.48 and 0.70 m/s) and three walking speeds (0, 0.96 and 1.17 m/s). Results showed that the wind speed has distinct effects on local body segments. In contrast, walking speed brought much more effect on the limbs, such as thigh and forearm, than on body torso, such as back and waist. In addition, the combined effect of body and air movement on localised evaporative resistance demonstrated that the walking effect has more influence on the extremities than on the torso. Therefore, localised evaporative resistance values should be provided when reporting test results in order to clearly describe clothing local moisture transfer characteristics. Localised boundary air layer and clothing evaporative resistances are essential data for clothing design and assessment of thermal comfort. A comprehensive understanding of the effects of air and body movement on localised evaporative resistance is also necessary by both textile and apparel researchers and industry.

Design of an air ejector for boundary-layer bleed of an acoustically treated turbofan engine inlet during ground testing

NASA Technical Reports Server (NTRS)

Stakolich, E. G.

1978-01-01

An air ejector was designed and built to remove the boundary-layer air from the inlet a turbofan engine during an acoustic ground test program. This report describes; (1) how the ejector was sized; (2) how the ejector performed; and (3) the performance of a scale model ejector built and tested to verify the design. With proper acoustic insulation, the ejector was effective in reducing boundary layer thickness in the inlet of the turbofan engine while obtaining the desired acoustic test conditions.

Boundary Layer Control on Airfoils.

ERIC Educational Resources Information Center

Gerhab, George; Eastlake, Charles

1991-01-01

A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)

The Role of Wave Cyclones in Transporting Boundary Layer Air to the Free Troposphere During the Spring 2001 NASA / TRACE-P Experiment

NASA Technical Reports Server (NTRS)

Fuelberg, Henry E.; Hannan, J. R.; Crawford, J. H.; Sachse, G. W.; Blake, D. R.

2003-01-01

Transport of boundary layer air to the free troposphere by cyclones during NASA's Transport and Chemical Evolution over the Pacific (TRACE-P) experiment is investigated. Airstreams responsible for boundary layer venting are diagnosed using results from a high-resolution meteorological model (MM5) together with in situ and remotely sensed chemical data. Hourly wind data from the MM5 are used to calculate three-dimensional grids of backward air trajectories. A reverse domain filling (RDF) technique then is employed to examine the characteristics of airstreams over the computational domain, and to isolate airstreams ascending from the boundary layer to the free troposphere during the previous 36 hours. Two cases are examined in detail. Results show that airstreams responsible for venting the boundary layer differ considerably from those described by classic conceptual models and in the recent literature. In addition, airstreams sampled by the TRACE-P aircraft are found to exhibit large variability in chemical concentrations. This variability is due to differences in the boundary layer histories of individual airstreams with respect to anthropogenic sources over continental Asia and Japan. Complex interactions between successive wave cyclones also are found to be important in determining the chemical composition of the airstreams. Particularly important is the process of post-cold frontal boundary layer air being rapidly transported offshore and recirculated into ascending airstreams of upstream cyclones.

Boundary Layer Flow Over a Moving Wavy Surface

NASA Astrophysics Data System (ADS)

Hendin, Gali; Toledo, Yaron

2016-04-01

Boundary Layer Flow Over a Moving Wavy Surface Gali Hendin(1), Yaron Toledo(1) January 13, 2016 (1)School of Mechanical Engineering, Tel-Aviv University, Israel Understanding the boundary layer flow over surface gravity waves is of great importance as various atmosphere-ocean processes are essentially coupled through these waves. Nevertheless, there are still significant gaps in our understanding of this complex flow behaviour. The present work investigates the fundamentals of the boundary layer air flow over progressive, small-amplitude waves. It aims to extend the well-known Blasius solution for a boundary layer over a flat plate to one over a moving wavy surface. The current analysis pro- claims the importance of the small curvature and the time-dependency as second order effects, with a meaningful impact on the similarity pattern in the first order. The air flow over the ocean surface is modelled using an outer, inviscid half-infinite flow, overlaying the viscous boundary layer above the wavy surface. The assumption of a uniform flow in the outer layer, used in former studies, is now replaced with a precise analytical solution of the potential flow over a moving wavy surface with a known celerity, wavelength and amplitude. This results in a conceptual change from former models as it shows that the pressure variations within the boundary layer cannot be neglected. In the boundary layer, time-dependent Navier-Stokes equations are formulated in a curvilinear, orthogonal coordinate system. The formulation is done in an elaborate way that presents additional, formerly neglected first-order effects, resulting from the time-varying coordinate system. The suggested time-dependent curvilinear orthogonal coordinate system introduces a platform that can also support the formulation of turbulent problems for any surface shape. In order to produce a self-similar Blasius-type solution, a small wave-steepness is assumed and a perturbation method is applied. Consequently, a

Effects of air pollution on thermal structure and dispersion in an urban planetary boundary layer

NASA Technical Reports Server (NTRS)

Viskanta, R.; Johnson, R. O.; Bergstrom, R. W.

1977-01-01

The short-term effects of urbanization and air pollution on the transport processes in the urban planetary boundary layer (PBL) are studied. The investigation makes use of an unsteady two-dimensional transport model which has been developed by Viskanta et al., (1976). The model predicts pollutant concentrations and temperature in the PBL. The potential effects of urbanization and air pollution on the thermal structure in the urban PBL are considered, taking into account the results of numerical simulations modeling the St. Louis, Missouri metropolitan area.

Enthalpy effects on hypervelocity boundary layers

NASA Astrophysics Data System (ADS)

Adam, Philippe H.

Shots with air and carbon dioxide were carried out in the T5 shock tunnel at GALCIT to study enthalpy effects on hypervelocity boundary layers. The model tested was a 1-meter long, 5-deg half-angle cone. It was instrumented with 51 chromel-constantan coaxial thermocouples and the surface heat transfer rate was computed to deduce the state of the boundary layer. Transitional boundary layers obtained confirm the stabilizing effect of enthalpy. As the reservoir enthalpy is increased, the transition Reynolds number evaluated at the reference conditions increases. This stabilizing effect is more rapid in gases with lower dissociation energy and it seems to level off when no further dissociation can be achieved. Normalizing the reservoir enthalpy with the edge enthalpy appears to collapse the data for all gases onto a single curve. A similar collapse is obtained when normalizing both the transition location and the reservoir enthalpy with the maximum temperature conditions obtained with BLIMPK, a nonequilibrium boundary layer code. The observation that reference conditions are more appropriate to normalize high enthalpy transition data was taken a step further by comparing the tunnel data with results from a reentry experiment. When the edge conditions are used, the tunnel and flight data are around an order of magnitude apart. This is commonly attributed to high disturbance levels in tunnels that cause the boundary layer to transition early. However, when the reference conditions are used instead, the tunnel and flight data come within striking distance of one another although the trends with enthalpy are reversed. This difference could be due to the cone bending and nose blunting. Experimental laminar heat transfer levels were compared to numerical results obtained with BLIMPK. Results for air indicate that the reactions are probably in nonequilibrium and that the wall is catalytic. The catalycity is seen to yield higher surface heat transfer rates than the

Lidar observations of the planetary boundary layer during FASINEX

NASA Technical Reports Server (NTRS)

Melfi, S. H.; Boers, R.; Palm, S. P.

1988-01-01

Data are presented on the planetary boundary layer (PBL) over the ocean acquired with an airborne downward-looking lidar during the Frontal Air-Sea Interaction Experiment (FASINEX) with the purpose of studying the impact of an ocean front on air-sea interactions. No changes in the PBL structure were detected by lidar. Lidar data were then used along with other readily available remotely-sensed data and a one-dimensional boundary-layer-growth model to infer the mean PBL moisture and temperature structure and to estimate the surface fluxes of heat and moisture.

High-Reynolds-number turbulent-boundary-layer wall pressure fluctuations with skin-friction reduction by air injection.

PubMed

Winkel, Eric S; Elbing, Brian R; Ceccio, Steven L; Perlin, Marc; Dowling, David R

2008-05-01

The hydrodynamic pressure fluctuations that occur on the solid surface beneath a turbulent boundary layer are a common source of flow noise. This paper reports multipoint surface pressure fluctuation measurements in water beneath a high-Reynolds-number turbulent boundary layer with wall injection of air to reduce skin-friction drag. The experiments were conducted in the U.S. Navy's Large Cavitation Channel on a 12.9-m-long, 3.05-m-wide hydrodynamically smooth flat plate at freestream speeds up to 20 ms and downstream-distance-based Reynolds numbers exceeding 200 x 10(6). Air was injected from one of two spanwise slots through flush-mounted porous stainless steel frits (approximately 40 microm mean pore diameter) at volume flow rates from 17.8 to 142.5 l/s per meter span. The two injectors were located 1.32 and 9.78 m from the model's leading edge and spanned the center 87% of the test model. Surface pressure measurements were made with 16 flush-mounted transducers in an "L-shaped" array located 10.7 m from the plate's leading edge. When compared to no-injection conditions, the observed wall-pressure variance was reduced by as much as 87% with air injection. In addition, air injection altered the inferred convection speed of pressure fluctuation sources and the streamwise coherence of pressure fluctuations.

Measurements in the near-wall region of a relaxing three-dimensional low speed turbulent air boundary layer

NASA Technical Reports Server (NTRS)

Hebbar, K. S.; Melnik, W. L.

1976-01-01

An experimental investigation was conducted at selected locations of the near-wall region of a three dimensional turbulent air boundary layer relaxing in a nominally zero external pressure gradient behind a transverse hump (in the form of a 30 deg swept, 5-foot chord wing-type model) faired into the side wall of a low speed wind tunnel. Wall shear stresses measured with a flush-mounted hot-film gage and a sublayer fence were in very good agreement with experimental data obtained with two Preston probes. With the upstream unit Reynolds number held constant at 325,000/ft. approximately one-fourth of the boundary layer thickness adjacent to the wall was surveyed with a single rotated hot-wire probe mounted on a specially designed minimum interference traverse mechanism. The boundary layer (approximately 3.5 in thick near the first survey station where the length Reynolds number was 5.5 million) had a maximum crossflow velocity ratio of 0.145 and a maximum crossflow angle of 21.875 deg close to the wall.

Possibilities for drag reduction by boundary layer control

NASA Technical Reports Server (NTRS)

Naiman, I.

1946-01-01

The mechanics of laminar boundary layer transition are reviewed. Drag possibilities for boundary layer control are analyzed using assumed conditions of transition Reynolds number, inlet loss, number of slots, blower efficiency, and duct losses. Although the results of such analysis are highly favorable, those obtained by experimental investigations yield conflicting results, showing only small gains, and sometimes losses. Reduction of this data indicates that there is a lower limit to the quantity of air which must be removed at the slot in order to stabilize the laminar flow. The removal of insufficient air permits transition to occur while the removal of excessive amounts of air results in high power costs, with a net drag increases. With the estimated value of flow coefficient and duct losses equal to half the dynamic pressure, drag reductions of 50% may be obtained; with twice this flow coefficient, the drag saving is reduced to 25%.

Planetary Boundary Layer from AERI and MPL

DOE Data Explorer

Sawyer, Virginia

2014-02-13

The distribution and transport of aerosol emitted to the lower troposphere is governed by the height of the planetary boundary layer (PBL), which limits the dilution of pollutants and influences boundary-layer convection. Because radiative heating and cooling of the surface strongly affect the PBL top height, it follows diurnal and seasonal cycles and may vary by hundreds of meters over a 24-hour period. The cap the PBL imposes on low-level aerosol transport makes aerosol concentration an effective proxy for PBL height: the top of the PBL is marked by a rapid transition from polluted, well-mixed boundary-layer air to the cleaner, more stratified free troposphere. Micropulse lidar (MPL) can provide much higher temporal resolution than radiosonde and better vertical resolution than infrared spectrometer (AERI), but PBL heights from all three instruments at the ARM SGP site are compared to one another for validation. If there is agreement among them, the higher-resolution remote sensing-derived PBL heights can accurately fill in the gaps left by the low frequency of radiosonde launches, and thus improve model parameterizations and our understanding of boundary-layer processes.

Outer layer effects in wind-farm boundary layers: Coriolis forces and boundary layer height

NASA Astrophysics Data System (ADS)

Allaerts, Dries; Meyers, Johan

2015-11-01

In LES studies of wind-farm boundary layers, scale separation between the inner and outer region of the atmospheric boundary layer (ABL) is frequently assumed, i.e., wind turbines are presumed to fall within the inner layer and are not affected by outer layer effects. However, modern wind turbine and wind farm design tends towards larger rotor diameters and farm sizes, which means that outer layer effects will become more important. In a prior study, it was already shown for fully-developed wind farms that the ABL height influences the power performance. In this study, we use the in-house LES code SP-Wind to investigate the importance of outer layer effects on wind-farm boundary layers. In a suite of LES cases, the ABL height is varied by imposing a capping inversion with varying inversion strengths. Results indicate the growth of an internal boundary layer (IBL), which is limited in cases with low inversion layers. We further find that flow deceleration combined with Coriolis effects causes a change in wind direction throughout the farm. This effect increases with decreasing boundary layer height, and can result in considerable turbine wake deflection near the end of the farm. The authors are supported by the ERC (ActiveWindFarms, grant no: 306471). Computations were performed on VSC infrastructiure (Flemish Supercomputer Center), funded by the Hercules Foundation and the Flemish Government-department EWI.

Boundary-Layer & health

NASA Astrophysics Data System (ADS)

Costigliola, V.

2010-09-01

It has long been known that specific atmospheric processes, such as weather and longer-term climatic fluctuations, affect human health. The biometeorological literature refers to this relationship as meteorotropism, defined as a change in an organism that is correlated with a change in atmospheric conditions. Plenty of (patho)physiological functions are affected by those conditions - like the respiratory diseases - and currently it is difficult to put any limits for pathologies developed in reply. Nowadays the importance of atmospheric boundary layer and health is increasingly recognised. A number of epidemiologic studies have reported associations between ambient concentrations of air pollution, specifically particulate pollution, and adverse health effects, even at the relatively low concentrations of pollution found. Since 1995 there have been over twenty-one studies from four continents that have explicitly examined the association between ambient air pollutant mixes and daily mortality. Statistically significant and positive associations have been reported in data from various locations around the world, all with varying air pollutant concentrations, weather conditions, population characteristics and public health policies. Particular role has been given to atmospheric boundary layer processes, the impact of which for specific patient-cohort is, however, not well understood till now. Assessing and monitoring air quality are thus fundamental to improve Europe's welfare. One of current projects run by the "European Medical Association" - PASODOBLE will develop and demonstrate user-driven downstream information services for the regional and local air quality sectors by combining space-based and in-situ data with models in 4 thematic service lines: - Health community support for hospitals, pharmacies, doctors and people at risk - Public information for regions, cities, tourist industry and sporting event organizers - Compliance monitoring support on particulate

Impact of the Loess Plateau on the atmospheric boundary layer structure and air quality in the North China Plain: a case study.

PubMed

Hu, Xiao-Ming; Ma, ZhiQiang; Lin, Weili; Zhang, Hongliang; Hu, Jianlin; Wang, Ying; Xu, Xiaobin; Fuentes, Jose D; Xue, Ming

2014-11-15

The North China Plain (NCP), to the east of the Loess Plateau, experiences severe regional air pollution. During the daytime in the summer, the Loess Plateau acts as an elevated heat source. The impacts of such a thermal effect on meteorological phenomena (e.g., waves, precipitation) in this region have been discussed. However, its impacts on the atmospheric boundary layer structure and air quality have not been reported. It is hypothesized that the thermal effect of the Plateau likely modulates the boundary layer structure and ambient concentrations of pollutants over the NCP under certain meteorological conditions. Thus, this study investigates such effect and its impacts using measurements and three-dimensional model simulations. It is found that in the presence of daytime westerly wind in the lower troposphere (~1 km above the NCP), warmer air above the Loess Plateau was transported over the NCP and imposed a thermal inversion above the mixed boundary layer, which acted as a lid and suppressed the mixed layer growth. As a result, pollutants accumulated in the shallow mixed layer and ozone was efficiently produced. The downward branch of the thermally-induced Mountain-Plains Solenoid circulation over the NCP contributed to enhancing the capping inversion and exacerbating air pollution. Previous studies have reported that low mixed layer, a factor for elevated pollution in the NCP, may be caused by aerosol scattering and absorption of solar radiation, frontal inversion, and large scale subsidence. The present study revealed a different mechanism (i.e., westerly warm advection) for the suppression of the mixed layer in summer NCP, which caused severe O3 pollution. This study has important implications for understanding the essential meteorological factors for pollution episodes in this region and forecasting these severe events. Copyright © 2014 Elsevier B.V. All rights reserved.

Finite-Difference Solution for Laminar or Turbulent Boundary Layer Flow over Axisymmetric Bodies with Ideal Gas, CF4, or Equilibrium Air Chemistry

NASA Technical Reports Server (NTRS)

Hamilton, H. Harris, II; Millman, Daniel R.; Greendyke, Robert B.

1992-01-01

A computer code was developed that uses an implicit finite-difference technique to solve nonsimilar, axisymmetric boundary layer equations for both laminar and turbulent flow. The code can treat ideal gases, air in chemical equilibrium, and carbon tetrafluoride (CF4), which is a useful gas for hypersonic blunt-body simulations. This is the only known boundary layer code that can treat CF4. Comparisons with experimental data have demonstrated that accurate solutions are obtained. The method should prove useful as an analysis tool for comparing calculations with wind tunnel experiments and for making calculations about flight vehicles where equilibrium air chemistry assumptions are valid.

Finite-difference solution for laminar or turbulent boundary layer flow over axisymmetric bodies with ideal gas, CF4, or equilibrium air chemistry

NASA Astrophysics Data System (ADS)

Hamilton, H. Harris, II; Millman, Daniel R.; Greendyke, Robert B.

1992-12-01

A computer code was developed that uses an implicit finite-difference technique to solve nonsimilar, axisymmetric boundary layer equations for both laminar and turbulent flow. The code can treat ideal gases, air in chemical equilibrium, and carbon tetrafluoride (CF4), which is a useful gas for hypersonic blunt-body simulations. This is the only known boundary layer code that can treat CF4. Comparisons with experimental data have demonstrated that accurate solutions are obtained. The method should prove useful as an analysis tool for comparing calculations with wind tunnel experiments and for making calculations about flight vehicles where equilibrium air chemistry assumptions are valid.

Boundary layer analysis in turbulent Rayleigh-Bénard convection in air: experiment versus simulation.

PubMed

Li, Ling; Shi, Nan; du Puits, Ronald; Resagk, Christian; Schumacher, Jörg; Thess, André

2012-08-01

We report measurements and numerical simulations of the three-dimensional velocity and temperature fields in turbulent Rayleigh-Bénard convection in air. Highly resolved velocity and temperature measurements inside and outside the boundary layers have been directly compared with equivalent data obtained in direct numerical simulations (DNSs). This comparison comprises a set of two Rayleigh numbers at Ra=3×10(9) and 3×10(10) and a fixed aspect ratio; this is the ratio between the diameter and the height of the Rayleigh-Bénard cell of Γ=1. We find that the measured velocity data are in excellent agreement with the DNS results while the temperature data slightly differ. In particular, the measured mean temperature profile does not show the linear trend as seen in the DNS data, and the measured gradients at the wall are significantly higher than those obtained from the DNS. Both viscous and thermal boundary layer thickness scale with respect to the Rayleigh number as δ(v)~Ra(-0.24) and δ(θ)~Ra(-0.24), respectively.

Comparison of Methods for Determining Boundary Layer Edge Conditions for Transition Correlations

NASA Technical Reports Server (NTRS)

Liechty, Derek S.; Berry, Scott A.; Hollis, Brian R.; Horvath, Thomas J.

2003-01-01

Data previously obtained for the X-33 in the NASA Langley Research Center 20-Inch Mach 6 Air Tunnel have been reanalyzed to compare methods for determining boundary layer edge conditions for use in transition correlations. The experimental results were previously obtained utilizing the phosphor thermography technique to monitor the status of the boundary layer downstream of discrete roughness elements via global heat transfer images of the X-33 windward surface. A boundary layer transition correlation was previously developed for this data set using boundary layer edge conditions calculated using an inviscid/integral boundary layer approach. An algorithm was written in the present study to extract boundary layer edge quantities from higher fidelity viscous computational fluid dynamic solutions to develop transition correlations that account for viscous effects on vehicles of arbitrary complexity. The boundary layer transition correlation developed for the X-33 from the viscous solutions are compared to the previous boundary layer transition correlations. It is shown that the boundary layer edge conditions calculated using an inviscid/integral boundary layer approach are significantly different than those extracted from viscous computational fluid dynamic solutions. The present results demonstrate the differences obtained in correlating transition data using different computational methods.

Acoustic explorations of the upper ocean boundary layer

NASA Astrophysics Data System (ADS)

Vagle, Svein

2005-04-01

The upper ocean boundary layer is an important but difficult to probe part of the ocean. A better understanding of small scale processes at the air-sea interface, including the vertical transfer of gases, heat, mass and momentum, are crucial to improving our understanding of the coupling between atmosphere and ocean. Also, this part of the ocean contains a significant part of the total biomass at all trophic levels and is therefore of great interest to researchers in a range of different fields. Innovative measurement plays a critical role in developing our understanding of the processes involved in the boundary layer, and the availability of low-cost, compact, digital signal processors and sonar technology in self-contained and cabled configurations has led to a number of exciting developments. This talk summarizes some recent explorations of this dynamic boundary layer using both active and passive acoustics. The resonant behavior of upper ocean bubbles combined with single and multi-frequency broad band active and passive devices are now giving us invaluable information on air-sea gas transfer, estimation of biological production, marine mammal behavior, wind speed and precipitation, surface and internal waves, turbulence, and acoustic communication in the surf zone.

Studies of acoustic effects on a flow boundary layer in air

NASA Technical Reports Server (NTRS)

Mechel, F.; Schilz, W.

1986-01-01

Effects of sound fields on the flow boundary layer on a flat plate subjected to a parallel flow are studied. The boundary layer is influenced by controlling the stagnation point flow at the front edge of the plate. Depending on the Reynolds number and sound frequency, excitation or suppression of turbulent is observed. Measurements were taken at wind velocities between 10 and 30 m/sec and sound frequencies between 0.2 and 3.0 kHz.

Convective Cold Pool Structure and Boundary Layer Recovery in DYNAMO

NASA Astrophysics Data System (ADS)

Savarin, A.; Chen, S. S.; Kerns, B. W.; Lee, C.; Jorgensen, D. P.

2012-12-01

One of the key factors controlling convective cloud systems in the Madden-Julian Oscillation (MJO) over the tropical Indian Ocean is the property of the atmospheric boundary layer. Convective downdrafts and precipitation from the cloud systems produce cold pools in the boundary layer, which can inhibit subsequent development of convection. The recovery time is the time it takes for the boundary layer to return to pre convective conditions. It may affect the variability of the convection on various time scales during the initiation of MJO. This study examines the convective cold pool structure and boundary layer recovery using the NOAA WP-3D aircraft observations, include the flight-level, Doppler radar, and GPS dropsonde data, collected during the Dynamics of MJO (DYNAMO) field campaign from November-December 2011. The depth and strength of convective cold pools are defined by the negative buoyancy, which can be computed from the dropsonde data. Convective downdraft can be affected by environmental water vapor due to entrainment. Mid-level dry air observed during the convectively suppressed phase of MJO seems to enhance convective downdraft, making the cold pools stronger and deeper. Recovery of the cold pools in the boundary layer is determined by the strength and depth of the cold pools and also the air-sea heat and moisture fluxes. Given that the water vapor and surface winds are distinct for the convectively active and suppressed phases of MJO over the Indian Ocean, the aircraft data are stratified by the two different large-scale regimes of MJO. Preliminary results show that the strength and depth of the cold pools are inversely correlated with the surrounding mid-level moisture. During the convectively suppressed phase, the recovery time is ~5-20 hours in relative weak wind condition with small air-sea fluxes. The recovery time is generally less than 6 hours during the active phase of MJO with moist mid-levels and stronger surface wind and air-sea fluxes.

The Interactions of a Flame and Its Self-Induced Boundary Layer

NASA Technical Reports Server (NTRS)

Ott, James D.; Oran, Elaine S.; Anderson, John D.

1999-01-01

The interaction of a laminar flame with its self-generated boundary layer in a rectangular channel was numerically simulated using the two-dimensional, reacting, Navier-Stokes equations. A two species chemistry model was implemented which simulates the stoichiometric reaction of acetylene and air. Calculations were performed to investigate the effects of altering the boundary condition of the wall temperature, the Lewis number, the dynamic viscosity, and the ignition method. The purpose of this study was to examine the fundamental physics of the formation of the boundary layer and the interaction of the flame as it propagates into the boundary layer that its own motion has created.

Transport of contaminants in the planetary boundary layer

NASA Technical Reports Server (NTRS)

Lee, I. Y.; Swan, P. R.

1978-01-01

A planetary boundary layer model is described and used to simulate PBL phenomena including cloud formation and pollution transport in the San Francisco Bay Area. The effect of events in the PBL on air pollution is considered, and governing equations for the average momentum, potential temperature, water vapor mixing ratio, and air contaminants are presented. These equations are derived by integrating the basic equations vertically through the mixed layer. Characteristics of the day selected for simulation are reported, and the results suggest that the diurnally cyclic features of the mesoscale motion, including clouds and air pollution, can be simulated in a readily interpretable way with the model.

Boundary Layer Control for Hypersonic Airbreathing Vehicles

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Nowak, Robert J.; Horvath, Thomas J.

2004-01-01

Active and passive methods for tripping hypersonic boundary layers have been examined in NASA Langley Research Center wind tunnels using a Hyper-X model. This investigation assessed several concepts for forcing transition, including passive discrete roughness elements and active mass addition (or blowing), in the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air Tunnels. Heat transfer distributions obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the Hyper-X nominal Mach 7 flight test-point of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For passive roughness, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The passive roughness study resulted in a swept ramp configuration, scaled to be roughly 0.6 of the calculated boundary layer thickness, being selected for the Mach 7 flight vehicle. For the active blowing study, the manifold pressure was systematically varied (while monitoring the mass flow) for each configuration to determine the jet penetration height, with schlieren, and transition movement, with the phosphor system, for comparison to the passive results. All the blowing concepts tested, which included various rows of sonic orifices (holes), two- and three-dimensional slots, and random porosity, provided transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model surface static pressure, which is adequate to ensure sonic jets. The present results indicate that the jet penetration height for blowing was roughly half the height required with passive roughness elements for an equivalent amount of transition movement.

Combined effect of boundary layer recirculation factor and stable energy on local air quality in the Pearl River Delta over southern China.

PubMed

Li, Haowen; Wang, Baomin; Fang, Xingqin; Zhu, Wei; Fan, Qi; Liao, Zhiheng; Liu, Jian; Zhang, Asi; Fan, Shaojia

2018-03-01

Atmospheric boundary layer (ABL) has a significant impact on the spatial and temporal distribution of air pollutants. In order to gain a better understanding of how ABL affects the variation of air pollutants, atmospheric boundary layer observations were performed at Sanshui in the Pearl River Delta (PRD) region over southern China during the winter of 2013. Two types of typical ABL status that could lead to air pollution were analyzed comparatively: weak vertical diffusion ability type (WVDAT) and weak horizontal transportation ability type (WHTAT). Results show that (1) WVDAT was featured by moderate wind speed, consistent wind direction, and thick inversion layer at 600~1000 m above ground level (AGL), and air pollutants were restricted in the low altitudes due to the stable atmospheric structure; (2) WHTAT was characterized by calm wind, varied wind direction, and shallow intense ground inversion layer, and air pollutants accumulated in locally because of strong recirculation in the low ABL; (3) recirculation factor (RF) and stable energy (SE) were proved to be good indicators for horizontal transportation ability and vertical diffusion ability of the atmosphere, respectively. Combined utilization of RF and SE can be very helpful in the evaluation of air pollution potential of the ABL. Air quality data from ground and meteorological data collected from radio sounding in Sanshui in the Pearl River Delta showed that local air quality was poor when wind reversal was pronounced or temperature stratification state was stable. The combination of horizontal and vertical transportation ability of the local atmosphere should be taken into consideration when evaluating local environmental bearing capacity for air pollution.

Effects of future land use and ecosystem changes on boundary-layer meteorology and air quality

NASA Astrophysics Data System (ADS)

Tai, A. P. K.; Wang, L.; Sadeke, M.

2017-12-01

Land vegetation plays key roles shaping boundary-layer meteorology and air quality via various pathways. Vegetation can directly affect surface ozone via dry deposition and biogenic emissions of volatile organic compounds (VOCs). Transpiration from land plants can also influence surface temperature, soil moisture and boundary-layer mixing depth, thereby indirectly affecting surface ozone. Future changes in the distribution, density and physiology of vegetation are therefore expected to have major ramifications for surface ozone air quality. In our study, we examine two aspects of potential vegetation changes using the Community Earth System Model (CESM) in the fully coupled land-atmosphere configuration, and evaluate their implications on meteorology and air quality: 1) land use change, which alters the distribution of plant functional types and total leaf density; and 2) ozone damage on vegetation, which alters leaf density and physiology (e.g., stomatal resistance). We find that, following the RCP8.5 scenario for 2050, global cropland expansion induces only minor changes in surface ozone in tropical and subtropical regions, but statistically significant changes by up to +4 ppbv in midlatitude North America and East Asia, mostly due to higher surface temperature that enhances biogenic VOC emissions, and reduced dry deposition to a lesser degree. These changes are in turn to driven mostly by meteorological changes that include a shift from latent to sensible heat in the surface energy balance and reduced soil moisture, reflecting not only local responses but also a northward expansion of the Hadley Cell. On the other hand, ozone damage on vegetation driven by rising anthropogenic emissions is shown to induce a further enhancement of ozone by up to +6 ppbv in midlatitude regions by 2050. This reflects a strong localized positive feedback, with severe ozone damage in polluted regions generally inducing stomatal closure, which in turn reduces transpiration, increases

The inner core thermodynamics of the tropical cyclone boundary layer

NASA Astrophysics Data System (ADS)

Williams, Gabriel J.

2016-10-01

Although considerable progress has been made in understanding the inner-core dynamics of the tropical cyclone boundary layer (TCBL), our knowledge of the inner-core thermodynamics of the TCBL remains limited. In this study, the inner-core budgets of potential temperature (θ), specific humidity ( q), and reversible equivalent potential temperature (θ _e) are examined using a high-resolution multilevel boundary layer model. The potential temperature budgets show that the heat energy is dominated by latent heat release in the eyewall, evaporative cooling along the outer edge of the eyewall, and upward surface fluxes of sensible and latent heat from the underlying warm ocean. It is shown that the vertical θ advection overcompensates the sum of radial advective warming from the boundary layer outflow jet and latent heating for the development of cooling in the eyewall within the TCBL. The moisture budgets show the dominant upward transport of moisture in the eyewall updrafts, partly by the boundary-layer outflow jet from the bottom eye region, so that the eyewall remains nearly saturated. The θ _e budgets reveal that the TCBL is maintained thermodynamically by the upward surface flux of higher-θ _e air from the underlying warm ocean, the radial transport of low-θ _e air from the outer regions of the TCBL, and the dry adiabatic cooling associated by eyewall updrafts. These results underscore the significance of vertical motion and the location of the boundary layer outflow jet in maintaining the inner core thermal structure of the TCBL.

Boundary layers in centrifugal compressors. [application of boundary layer theory to compressor design

NASA Technical Reports Server (NTRS)

Dean, R. C., Jr.

1974-01-01

The utility of boundary-layer theory in the design of centrifugal compressors is demonstrated. Boundary-layer development in the diffuser entry region is shown to be important to stage efficiency. The result of an earnest attempt to analyze this boundary layer with the best tools available is displayed. Acceptable prediction accuracy was not achieved. The inaccuracy of boundary-layer analysis in this case would result in stage efficiency prediction as much as four points low. Fluid dynamic reasons for analysis failure are discussed with support from flow data. Empirical correlations used today to circumnavigate the weakness of the theory are illustrated.

Studying the Afternoon Transition of the Planetary Boundary Layer

NASA Astrophysics Data System (ADS)

Lothon, Marie; Lenschow, Donald H.

2010-07-01

The planetary boundary layer is the part of the atmosphere that interacts directly with the Earth's surface on a time scale of a few hours or less. In daytime, solar heating of the surface can generate buoyant turbulent eddies that efficiently mix the air through a depth of more than a kilometer. This convective boundary layer (CBL) is a conduit for trace gases such as water vapor and carbon dioxide that are emitted or absorbed by the surface (and surface vegetation) to be transported into or out of the layer nearest the surface. The CBL has been extensively observed and relatively successfully modeled. But the early morning transition—when the CBL emerges from the nocturnal boundary layer—and the late afternoon transition—when the CBL decays to an intermittently turbulent “residual layer” overlying a shallower, stably stratified boundary layer—are difficult to observe and model due to turbulence intermittency and anisotropy, horizontal heterogeneity, and rapid time changes. Even the definition of the boundary layer during these transitional periods is fuzzy; there is no consensus on what criteria to use and no simple scaling laws, as there are for the CBL, that apply during these transitions.

Wall Boundary Layer Measurements for the NASA Langley Transonic Dynamics Tunnel

NASA Technical Reports Server (NTRS)

Wieseman, Carol D.; Bennett, Robert M.

2007-01-01

Measurements of the boundary layer parameters in the NASA Langley Transonic Dynamics tunnel were conducted during extensive calibration activities following the facility conversion from a Freon-12 heavy-gas test medium to R-134a. Boundary-layer rakes were mounted on the wind-tunnel walls, ceiling, and floor. Measurements were made over the range of tunnel operation envelope in both heavy gas and air and without a model in the test section at three tunnel stations. Configuration variables included open and closed east sidewall wall slots, for air and R134a test media, reentry flap settings, and stagnation pressures over the full range of tunnel operation. The boundary layer thickness varied considerably for the six rakes. The thickness for the east wall was considerably larger that the other rakes and was also larger than previously reported. There generally was some reduction in thickness at supersonic Mach numbers, but the effect of stagnation pressure, and test medium were not extensive.

Variation of turbulence in a coastal thermal internal boundary layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

SethuRaman, S.; Raynor, G.S.; Brown, R.M.

1981-01-01

Internal boundary layers (IBL) form when an air mass encounters a change in surface characteristics. There are essentially two types of internal boundary layers - one caused by the change in surface roughness and the other by the variation in surface heating. The former is known as the aerodynamic internal boundary layer (AIBL) and the latter the thermal internal boundary layer (TIBL). Change in shear stress generally characterizes the AIBL and change in turbulence the TIBL. Results of some observations of the vertical component of turbulence made in a coastal TIBL over Long Island, New York from 1974 to 1978more » are reported. Vertical turbulence measured by a simple sail plane variometer in a thermal internal boundary layer over Long Island with onshore flows indicates the structure to depend significantly on the land-water temperature difference. The position of the vertical velocity fluctuation maximum seems to vary from one test to another but its variation could not be correlated to other parameters due to lack of a sufficient number of tests. The structure of vertical turbulence was found to be different for sea breeze flows as compared to gradient winds.« less

Comparison of secondary flows and boundary-layer accumulations in several turbine nozzles

NASA Technical Reports Server (NTRS)

Kofskey, Milton G; Allen, Hubert W; Herzig, Howard Z

1953-01-01

An investigation was made of losses and secondary flows in three different turbine nozzle configurations in annular cascade. Appreciable outer shroud loss cores (passage vortices) were found to exist at the discharge of blades which had thickened suction surface boundary layers near the outer shroud. Blade designs having thinner boundary layers did not show such outer shroud loss cores, but indicated greater inward radial flow of low momentum air, in the wake loss is to this extent an indication of the presence or absence of radial flow. The blade wake was a combination of profile loss and low momentum air from the outer shroud, and the magnitude of the wake loss is to this extent an indication of the presence or absence of radial flow. At a high Mach number, shock-boundary-layer thickening on the blade suction surfaces provided an additional radial flow path for low momentum air, which resulted in large inner shroud loss regions accompanied by large deviations from design values of discharge angle. (author)

Computational Study of Surface Tension and Wall Adhesion Effects on an Oil Film Flow Underneath an Air Boundary Layer

NASA Technical Reports Server (NTRS)

Celic, Alan; Zilliac, Gregory G.

1998-01-01

The fringe-imaging skin friction (FISF) technique, which was originally developed by D. J. Monson and G. G. Mateer at Ames Research Center and recently extended to 3-D flows, is the most accurate skin friction measurement technique currently available. The principle of this technique is that the skin friction at a point on an aerodynamic surface can be determined by measuring the time-rate-of-change of the thickness of an oil drop placed on the surface under the influence of the external air boundary layer. Lubrication theory is used to relate the oil-patch thickness variation to shear stress. The uncertainty of FISF measurements is estimated to be as low as 4 percent, yet little is known about the effects of surface tension and wall adhesion forces on the measured results. A modified version of the free-surface Navier-Stokes solver RIPPLE, developed at Los Alamos National Laboratories, was used to compute the time development of an oil drop on a surface under a simulated air boundary layer. RIPPLE uses the volume of fluid method to track the surface and the continuum surface force approach to model surface tension and wall adhesion effects. The development of an oil drop, over a time period of approximately 4 seconds, was studied. Under the influence of shear imposed by an air boundary layer, the computed profile of the drop rapidly changes from its initial circular-arc shape to a wedge-like shape. Comparison of the time-varying oil-thickness distributions computed using RIPPLE and also computed using a greatly simplified numerical model of an oil drop equation which does not include surface tension and wall adhesion effects) was used to evaluate the effects of surface tension on FISF measurement results. The effects of surface tension were found to be small but not necessarily negligible in some cases.

Fluorescence Visualization of Hypersonic Flow Past Triangular and Rectangular Boundary-layer Trips

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; Garcia, A. P.; Borg, Stephen E.; Dyakonov, Artem A.; Berry, Scott A.; Inman, Jennifer A.; Alderfer, David W.

2007-01-01

Planar laser-induced fluorescence (PLIF) flow visualization has been used to investigate the hypersonic flow of air over surface protrusions that are sized to force laminar-to-turbulent boundary layer transition. These trips were selected to simulate protruding Space Shuttle Orbiter heat shield gap-filler material. Experiments were performed in the NASA Langley Research Center 31-Inch Mach 10 Air Wind Tunnel, which is an electrically-heated, blowdown facility. Two-mm high by 8-mm wide triangular and rectangular trips were attached to a flat plate and were oriented at an angle of 45 degrees with respect to the oncoming flow. Upstream of these trips, nitric oxide (NO) was seeded into the boundary layer. PLIF visualization of this NO allowed observation of both laminar and turbulent boundary layer flow downstream of the trips for varying flow conditions as the flat plate angle of attack was varied. By varying the angle of attack, the Mach number above the boundary layer was varied between 4.2 and 9.8, according to analytical oblique-shock calculations. Computational Fluid Dynamics (CFD) simulations of the flowfield with a laminar boundary layer were also performed to better understand the flow environment. The PLIF images of the tripped boundary layer flow were compared to a case with no trip for which the flow remained laminar over the entire angle-of-attack range studied. Qualitative agreement is found between the present observed transition measurements and a previous experimental roughness-induced transition database determined by other means, which is used by the shuttle return-to-flight program.

Delay in convection in nocturnal boundary layer due to aerosol-induced cooling

NASA Astrophysics Data System (ADS)

Singh, Dhiraj Kumar; Ponnulakshmi, V. K.; Subramanian, G.; Sreenivas, K. R.

2012-11-01

Heat transfer processes in the nocturnal boundary layer (NBL) influence the surface energy budget, and play an important role in many micro-meteorological processes including the formation of inversion layers, radiation fog, and in the control of air-quality near the ground. Under calm clear-sky conditions, radiation dominates over other transport processes, and as a result, the air layers just above ground cool the fastest after sunset. This leads to an anomalous post-sunset temperature profile characterized by a minimum a few decimeters above ground (Lifted temperature minimum). We have designed a laboratory experimental setup to simulate LTM, involving an enclosed layer of ambient air, and wherein the boundary condition for radiation is decoupled from those for conduction and convection. The results from experiments involving both ambient and filtered air indicate that the high cooling rates observed are due to the presence of aerosols. Calculated Rayleigh number of LTM-type profiles is of the order 105-107 in the field and of order 103-105 in the laboratory. In the LTM region, there is convective motion when the Rayleigh number is greater than 104 rather than the critical Rayleigh number (Rac = 1709). The diameter of convection rolls is a function of height of minimum of LTM-type profiles. The results obtained should help in the parameterization of transport process in the nocturnal boundary layer, and highlight the need to accounting the effects of aerosols and ground emissivity in climate models.

Air flow in the boundary layer near a plate

NASA Technical Reports Server (NTRS)

Dryden, Hugh L

1937-01-01

The published data on the distribution of speed near a thin flat plate with sharp leading edge placed parallel to the flow (skin friction plate) are reviewed and the results of some additional measurements are described. The purpose of the experiments was to study the basic phenomena of boundary-layer flow under simple conditions.

Atmospheric boundary layer modification in the marginal ice zone

NASA Technical Reports Server (NTRS)

Bennett, Theodore J., Jr.; Hunkins, Kenneth

1986-01-01

A case study of the Andreas et al. (1984) data on atmospheric boundary layer modification in the marginal ice zone is made. The model is a two-dimensional, multilevel, linear model with turbulence, lateral and vertical advection, and radiation. Good agreement between observed and modeled temperature cross sections is obtained. In contrast to the hypothesis of Andreas et al., the air flow is found to be stable to secondary circulations. Adiabatic lifting and, at long fetches, cloud top longwave cooling, not an air-to-surface heat flux, dominate the cooling of the boundary layer. The accumulation with fetch over the ice of changes in the surface wind field is shown to have a large effect on estimates of the surface wind stress. It is speculated that the Andreas et al. estimates of the drag coefficient over the compact sea ice are too high.

Turbulence measurements in high Reynolds number boundary layers

NASA Astrophysics Data System (ADS)

Vallikivi, Margit; Smits, Alexander

2013-11-01

Measurements are conducted in zero pressure gradient turbulent boundary layers for Reynolds numbers from Reθ = 9,000 to 225,000. The experiments were performed in the High Reynolds number Test Facility (HRTF) at Princeton University, which uses compressed air as the working fluid. Nano-Scale Thermal Anemometry Probes (NSTAPs) are used to acquire data with very high spatial and temporal precision. These new data are used to study the scaling behavior of the streamwise velocity fluctuations in the boundary layer and make comparisons with the scaling of other wall-bounded turbulent flows. Supported under ONR Grant N00014-09-1-0263 (program manager Ron Joslin) and NSF Grant CBET-1064257 (program manager Henning Winter).

X-33 Hypersonic Boundary Layer Transition

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Horvath, Thomas J.; Hollis, Brian R.; Thompson, Richard A.; Hamilton, H. Harris, II

1999-01-01

Boundary layer and aeroheating characteristics of several X-33 configurations have been experimentally examined in the Langley 20-Inch Mach 6 Air Tunnel. Global surface heat transfer distributions, surface streamline patterns, and shock shapes were measured on 0.013-scale models at Mach 6 in air. Parametric variations include angles-of-attack of 20-deg, 30-deg, and 40-deg; Reynolds numbers based on model length of 0.9 to 6.6 million; and body-flap deflections of 0, 10 and 20-deg. The effects of discrete and distributed roughness elements on boundary layer transition, which included trip height, size, location, and distribution, both on and off the windward centerline, were investigated. The discrete roughness results on centerline were used to provide a transition correlation for the X-33 flight vehicle that was applicable across the range of reentry angles of attack. The attachment line discrete roughness results were shown to be consistent with the centerline results, as no increased sensitivity to roughness along the attachment line was identified. The effect of bowed panels was qualitatively shown to be less effective than the discrete trips; however, the distributed nature of the bowed panels affected a larger percent of the aft-body windward surface than a single discrete trip.

Forced Boundary-Layer Transition on X-43 (Hyper-X) in NASA LaRC 20-Inch Mach 6 Air Tunnel

NASA Technical Reports Server (NTRS)

Berry, Scott A.; DiFulvio, Michael; Kowalkowski, Matthew K.

2000-01-01

Aeroheating and boundary layer transition characteristics for the X-43 (Hyper-X) configuration have been experimentally examined in the Langley 20-Inch Mach 6 Air Tunnel. Global surface heat transfer distributions, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. Parametric variations include angles-of-attack of 0-deg, 2-deg, and 4-deg; Reynolds numbers based on model length of 1.2 to 15.4 million; and inlet cowl door both open and closed. The effects of discrete roughness elements on the forebody boundary layer, which included variations in trip configuration and height, were investigated. This document is intended to serve as a release of preliminary data to the Hyper-X program; analysis is limited to observations of the experimental trends in order to expedite dissemination.

Vortex/boundary layer interactions

NASA Technical Reports Server (NTRS)

Cutler, A. D.; Bradshaw, P.

1989-01-01

Detailed and high quality measurements with hot-wires and pressure probes are presented for two different interactions between a vortex pair with common flow down and a turbulent boundary layer. The interactions studied have larger values of the vortex circulation parameter than those studied previously. The results indicate that the boundary layer under the vortex pair is thinned by lateral divergence and that boundary layer fluid is entrained into the vortex. The effect of the interaction on the vortex core (other than the inviscid effect of the image vortices behind the surface) is small.

Boundary layers at a dynamic interface: air-sea exchange of heat and mass

NASA Astrophysics Data System (ADS)

Szeri, Andrew

2017-11-01

Exchange of mass or heat across a turbulent liquid-gas interface is a problem of critical interest, especially in air-sea transfer of natural and man-made gases involved in climate change. The goal in this research area is to determine the gas flux from air to sea or vice versa. For sparingly soluble non-reactive gases, this is controlled by liquid phase turbulent velocity fluctuations that act on the thin species concentration boundary layer on the liquid side of the interface. If the fluctuations in surface-normal velocity and gas concentration differences are known, then it is possible to determine the turbulent contribution to the gas flux. However, there is no suitable fundamental direct approach in the general case where neither of these quantities can be easily measured. A new approach is presented to deduce key aspects about the near-surface turbulent motions from remote measurements, which allows one to determine the gas transfer velocity, or gas flux per unit area if overall concentration differences are known. The approach is illustrated with conceptual examples.

A model of the planetary boundary layer over a snow surface

NASA Technical Reports Server (NTRS)

Halberstam, I.; Melendez, R.

1979-01-01

A model of the planetary boundary layer over a snow surface has been developed. It contains the vertical heat exchange processes due to radiation, conduction, and atmospheric turbulence. Parametrization of the boundary layer is based on similarity functions developed by Hoffert and Sud (1976), which involve a dimensionless variable, dependent on boundary-layer height and a localized Monin-Obukhov length. The model also contains the atmospheric surface layer and the snowpack itself, where snowmelt and snow evaporation are calculated. The results indicate a strong dependence of surface temperatures, especially at night, on the bursts of turbulence which result from the frictional damping of surface-layer winds during periods of high stability, as described by Businger (1973). The model also shows the cooling and drying effect of the snow on the atmosphere, which may be the mechanism for air mass transformation in sub-Arctic regions.

Predictions and Verification of an Isotope Marine Boundary Layer Model

NASA Astrophysics Data System (ADS)

Feng, X.; Posmentier, E. S.; Sonder, L. J.; Fan, N.

2017-12-01

A one-dimensional (1D), steady state isotope marine boundary layer (IMBL) model is constructed. The model includes meteorologically important features absent in Craig and Gordon type models, namely height-dependent diffusion/mixing and convergence of subsiding external air. Kinetic isotopic fractionation results from this height-dependent diffusion which starts as pure molecular diffusion at the air-water interface and increases linearly with height due to turbulent mixing. The convergence permits dry, isotopically depleted air subsiding adjacent to the model column to mix into ambient air. In δD-δ18O space, the model results fill a quadrilateral, of which three sides represent 1) vapor in equilibrium with various sea surface temperatures (SSTs) (high d18O boundary of quadrilateral); 2) mixture of vapor in equilibrium with seawater and vapor in the subsiding air (lower boundary depleted in both D and 18O); and 3) vapor that has experienced the maximum possible kinetic fractionation (high δD upper boundary). The results can be plotted in d-excess vs. δ18O space, indicating that these processes all cause variations in d-excess of MBL vapor. In particular, due to relatively high d-excess in the descending air, mixing of this air into the MBL causes an increase in d-excess, even without kinetic isotope fractionation. The model is tested by comparison with seven datasets of marine vapor isotopic ratios, with excellent correspondence; >95% of observational data fall within the quadrilateral area predicted by the model. The distribution of observations also highlights the significant influence of vapor from the nearby converging descending air on isotopic variations in the MBL. At least three factors may explain the <5% of observations that fall slightly outside of the predicted region in both δD-δ18O and d-excess - δ18O space: 1) variations in seawater isotopic ratios, 2) variations in isotopic composition of subsiding air, and 3) influence of sea spray. The model

Fifty Years of Boundary-Layer Theory and Experiment

NASA Technical Reports Server (NTRS)

Dryden, Hugh L.

1955-01-01

The year 1954 marked the 50th anniversary of the Prandtl boundary-layer theory from which we may date the beginning of man's understanding of the dynamics of real fluids. A backward look at this aspect of the history of the last 50 years may be instructive. This paper (1) attempts to compress the events of those 50 years into a few thousand words, to tell in this brief space the interesting story of the development of a new concept, its slow acceptance and growth, its spread from group to group within its country of origin, and its diffusion to other countries of the world. The original brief paper of Prandtl (2) was presented at the Third International Mathematical Congress at Heidelberg in 1904 and published in the following year. It was an attempt to explain the d'Alembert paradox, namely, that the neglect of the small friction of air in the theory resulted in the prediction of zero resistance to motion. Prandtl set himself the task of computing the motion of a fluid of small friction, so small that its effect could be neglected everywhere except where large velocity differences were present or a cumulative effect of friction occurred This led to the concept of boundary layer, or transition layer, near the wall of a body immersed in a fluid stream in which the velocity rises from zero to the free-stream value. It is interesting that Prandtl used the term Grenzsehicht (boundary layer) only once and the term Ubergangsschicht (transition layer) seven times in the brief article. Later writers also used Reibungsschicht (friction layer), but most writers today use Grenzschicht (boundary layer).

Planetary Boundary Layer Dynamics over Reno, Nevada in Summer

NASA Astrophysics Data System (ADS)

Liming, A.; Sumlin, B.; Loria Salazar, S. M.; Holmes, H.; Arnott, W. P.

2014-12-01

Quantifying the height of the planetary boundary layer (PBL) is important to understand the transport behavior, mixing, and surface concentrations of air pollutants. In Reno, NV, located in complex, mountainous terrain with high desert climate, the daytime boundary layer can rise to an estimated 3km or more on a summer day due to surface heating and convection. The nocturnal boundary layer, conversely, tends to be much lower and highly stable due to radiative cooling from the surface at night and downslope flow of cool air from nearby mountains. With limited availability of radiosonde data, current estimates of the PBL height at any given time or location are potentially over or underestimated. To better quantify the height and characterize the PBL physics, we developed portable, lightweight sensors that measure CO2 concentrations, temperature, pressure, and humidity every 5 seconds. Four of these sensors are used on a tethered balloon system to monitor CO2 concentrations from the surface up to 300m. We will combine this data with Radio Acoustic Sounding System (RASS) data that measures vertical profiles of wind speed, temperature, and humidity from 40m to 400m. This experiment will characterize the diurnal evolution of CO2 concentrations at multiple heights in the PBL, provide insight into PBL physics during stability transition periods at sunrise and sunset, and estimate the nighttime PBL depth during August in Reno. Further, we expect to gain a better understanding of the impact of mixing volume changes (i.e., PBL height) on air quality and pollution concentrations in Reno. The custom portable sensor design will also be presented. It is expected that these instruments can be used for indoor or outdoor air quality studies, where lightness, small size, and battery operation can be of benefit.

Extreme Vertical Gusts in the Atmospheric Boundary Layer

DTIC Science & Technology

2015-07-01

significant effect on the statistics of the rare, extreme gusts. In the lowest 5,000 ft, boundary layer effects make small to moderate vertical...4 2.4 Effects of Gust Shape ............................................................................................... 5... Definitions Adiabatic Lapse Rate The rate of change of temperature with altitude that would occur if a parcel of air was transported sufficiently

Wind and boundary layers in Rayleigh-Bénard convection. II. Boundary layer character and scaling.

PubMed

van Reeuwijk, Maarten; Jonker, Harm J J; Hanjalić, Kemo

2008-03-01

The scaling of the kinematic boundary layer thickness lambda(u) and the friction factor C(f) at the top and bottom walls of Rayleigh-Bénard convection is studied by direct numerical simulation (DNS). By a detailed analysis of the friction factor, a new parameterisation for C(f) and lambda(u) is proposed. The simulations were made of an L/H=4 aspect-ratio domain with periodic lateral boundary conditions at Ra=(10(5), 10(6), 10(7), 10(8)) and Pr=1. The continuous spectrum, as well as significant forcing due to Reynolds stresses, clearly indicates a turbulent character of the boundary layer, while viscous effects cannot be neglected, judging from the scaling of classical integral boundary layer parameters with Reynolds number. Using a conceptual wind model, we find that the friction factor C(f) should scale proportionally to the thermal boundary layer thickness as C(f) proportional variant lambda(Theta)/H, while the kinetic boundary layer thickness lambda(u) scales inversely proportionally to the thermal boundary layer thickness and wind Reynolds number lambda(u)/H proportional variant (lambda(Theta)/H)(-1)Re(-1). The predicted trends for C(f) and lambda(u) are in agreement with DNS results.

PLIF Visualization of Active Control of Hypersonic Boundary Layers Using Blowing

NASA Technical Reports Server (NTRS)

Bathel, Brett F.; Danehy, Paul M.; Inman, Jennifer A.; Alderfer, David W.; Berry, Scott A.

2008-01-01

Planar laser-induced fluorescence (PLIF) imaging was used to visualize the boundary layer flow on a 1/3-scale Hyper-X forebody model. The boundary layer was perturbed by blowing out of orifices normal to the model surface. Two blowing orifice configurations were used: a spanwise row of 17-holes spaced at 1/8 inch, with diameters of 0.020 inches and a single-hole orifice with a diameter of 0.010 inches. The purpose of the study was to visualize and identify laminar and turbulent structures in the boundary layer and to make comparisons with previous phosphor thermography measurements of surface heating. Jet penetration and its influence on the boundary layer development was also examined as was the effect of a compression corner on downstream boundary layer transition. Based upon the acquired PLIF images, it was determined that global surface heating measurements obtained using the phosphor thermography technique provide an incomplete indicator of transitional and turbulent behavior of the corresponding boundary layer flow. Additionally, the PLIF images show a significant contribution towards transition from instabilities originating from the underexpanded jets. For this experiment, a nitric oxide/nitrogen mixture was seeded through the orifices, with nitric oxide (NO) serving as the fluorescing gas. The experiment was performed in the 31-inch Mach 10 Air Tunnel at NASA Langley Research Center.

Forced Boundary-Layer Transition on X-43 (Hyper-X) in NASA LaRC 31-Inch Mach 10 Air Tunnel

NASA Technical Reports Server (NTRS)

Berry, Scott A.; DiFulvio, Michael; Kowalkowski, Matthew K.

2000-01-01

Aeroheating and boundary layer transition characteristics for the X-43 (Hyper-X) configuration have been experimentally examined in the Langley 31-Inch Mach 10 Air Tunnel. Global surface heat transfer distributions, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. Parametric variations include angles-of-attack of 0-deg, 2-deg, 3-deg, and 4-deg; Reynolds numbers based on model length of 1.2 to 5.1 million; and inlet cowl door both open and closed. The effects of discrete roughness elements on the forebody boundary layer, which included variations in trip configuration and height, were investigated. This document is intended to serve as a release of preliminary data to the Hyper-X program; analysis is limited to observations of the experimental trends in order to expedite dissemination.

Air Layer Drag Reduction

NASA Astrophysics Data System (ADS)

Ceccio, Steven; Elbing, Brian; Winkel, Eric; Dowling, David; Perlin, Marc

2008-11-01

A set of experiments have been conducted at the US Navy's Large Cavitation Channel to investigate skin-friction drag reduction with the injection of air into a high Reynolds number turbulent boundary layer. Testing was performed on a 12.9 m long flat-plate test model with the surface hydraulically smooth and fully rough at downstream-distance-based Reynolds numbers to 220 million and at speeds to 20 m/s. Local skin-friction, near-wall bulk void fraction, and near-wall bubble imaging were monitored along the length of the model. The instrument suite was used to access the requirements necessary to achieve air layer drag reduction (ALDR). Injection of air over a wide range of air fluxes showed that three drag reduction regimes exist when injecting air; (1) bubble drag reduction that has poor downstream persistence, (2) a transitional regime with a steep rise in drag reduction, and (3) ALDR regime where the drag reduction plateaus at 90% ± 10% over the entire model length with large void fractions in the near-wall region. These investigations revealed several requirements for ALDR including; sufficient volumetric air fluxes that increase approximately with the square of the free-stream speed, slightly higher air fluxes are needed when the surface tension is reduced, higher air fluxes are required for rough surfaces, and the formation of ALDR is sensitive to the inlet condition.

Effect of an isolated semi-arid pine forest on the boundary layer height

NASA Astrophysics Data System (ADS)

Brugger, Peter; Banerjee, Tirtha; Kröniger, Konstantin; Preisler, Yakir; Rotenberg, Eyal; Tatarinov, Fedor; Yakir, Dan; Mauder, Matthias

2017-04-01

Forests play an important role for earth's climate by influencing the surface energy balance and CO2 concentrations in the atmosphere. Semi-arid forests and their effects on the local and regional climate are studied within the CliFF project (Climate Feedbacks and benefits of semi-arid Forests). This requires understanding of the atmospheric boundary layer over semi-arid forests, because it links the surface and the free atmosphere and determines the exchange of momentum, heat and trace gases. Our study site, Yatir, is a semi-arid isolated pine forest in the Negev desert in Israel. Higher roughness and lower albedo compared to the surrounding shrubland make it interesting to study the influences of the semi-arid Yatir forest on the boundary layer. Previous studies of the forest focused on the energy balance and secondary circulations. This study focuses on the boundary layer structure above the forest, in particular the boundary layer height. The boundary layer height is an essential parameter for many applications (e.g. construction of convective scaling parameters or air pollution modeling). We measured the boundary layer height upwind, over and downwind of the forest. In addition we measured at two sites wind profiles within the boundary layer and turbulent fluxes at the surface. This allows us to quantify the effects of the forest on boundary layer compared to the surrounding shrubland. Results show that the forest increases the boundary layer height in absence of a strong boundary layer top inversion. A model of the boundary layer height based on eddy-covariance data shows some agreement to the measurements, but fails during anticyclonic conditions and the transition to the nocturnal boundary layer. More complex models accounting for large scale influences are investigated. Further influences of the forest and surrounding shrubland on the turbulent transport of energy are discussed in a companion presentation (EGU2017-2219).

Dry intrusions: Lagrangian climatology and impact on the boundary layer

NASA Astrophysics Data System (ADS)

Raveh-Rubin, Shira; Wernli, Heini

2017-04-01

Dry air intrusions (DIs) are large-scale descending airstreams. A DI is typically referred to as a coherent airstream in the cold sector of an extratropical cyclone. Emerging evidence suggests that DIs are linked to severe surface wind gusts. However, there is yet no strict Lagrangian definition of DIs, and so their climatological frequency, dynamical characteristics as well as their seasonal and spatial distributions are unknown. Furthermore, the dynamical interaction between DIs and the planetary boundary layer is not fully understood. Here, we suggest a Lagrangian definition for DI air parcels, namely a minimum pressure increase along a trajectory of 400 hPa in 48 hours. Based on this criterion, the open questions are addressed by: (i) a novel global Lagrangian climatology for the ECMWF ERA-Interim reanalysis dataset for the years 1979-2014; (ii) a case study illustrating the interaction between DIs and the boundary layer. We find that DIs occur predominantly in winter. DIs coherently descend from the upper troposphere (their stratospheric origin is small), to the mid- and low levels, where they mix with their environment and diverge. Different physical characteristics typify DIs in the different regions and seasons. Finally, we demonstrate the different mechanisms by which DIs can destabilize the boundary layer and facilitate the formation of strong surface winds.

Stability of hypersonic boundary-layer flows with chemistry

NASA Technical Reports Server (NTRS)

Reed, Helen L.; Stuckert, Gregory K.; Haynes, Timothy S.

1993-01-01

The effects of nonequilibrium chemistry and three dimensionality on the stability characteristics of hypersonic flows are discussed. In two-dimensional (2-D) and axisymmetric flows, the inclusion of chemistry causes a shift of the second mode of Mack to lower frequencies. This is found to be due to the increase in size of the region of relative supersonic flow because of the lower speeds of sound in the relatively cooler boundary layers. Although this shift in frequency is present in both the equilibrium and nonequilibrium air results, the equilibrium approximation predicts modes which are not observed in the nonequilibrium calculations (for the flight conditions considered). These modes are superpositions of incoming and outgoing unstable disturbances which travel supersonically relative to the boundary-layer edge velocity. Such solutions are possible because of the finite shock stand-off distance. Their corresponding wall-normal profiles exhibit an oscillatory behavior in the inviscid region between the boundary-layer edge and the bow shock. For the examination of three-dimensional (3-D) effects, a rotating cone is used as a model of a swept wing. An increase of stagnation temperature is found to be only slightly stabilizing. The correlation of transition location (N = 9) with parameters describing the crossflow profile is discussed. Transition location does not correlate with the traditional crossflow Reynolds number. A new parameter that appears to correlate for boundary-layer flow was found. A verification with experiments on a yawed cone is provided.

Vertical ozone characteristics in urban boundary layer in Beijing.

PubMed

Ma, Zhiqiang; Xu, Honghui; Meng, Wei; Zhang, Xiaoling; Xu, Jing; Liu, Quan; Wang, Yuesi

2013-07-01

Vertical ozone and meteorological parameters were measured by tethered balloon in the boundary layer in the summer of 2009 in Beijing, China. A total of 77 tethersonde soundings were taken during the 27-day campaign. The surface ozone concentrations measured by ozonesondes and TEI 49C showed good agreement, albeit with temporal difference between the two instruments. Two case studies of nocturnal secondary ozone maxima are discussed in detail. The development of the low-level jet played a critical role leading to the observed ozone peak concentrations in nocturnal boundary layer (NBL). The maximum of surface ozone was 161.7 ppbv during the campaign, which could be attributed to abundant precursors storage near surface layer at nighttime. Vertical distribution of ozone was also measured utilizing conventional continuous analyzers on 325-m meteorological observation tower. The results showed the NBL height was between 47 and 280 m, which were consistent with the balloon data. Southerly air flow could bring ozone-rich air to Beijing, and the ozone concentrations exceeded the China's hourly ozone standard (approximately 100 ppb) above 600 m for more than 12 h.

Finite-element numerical modeling of atmospheric turbulent boundary layer

NASA Technical Reports Server (NTRS)

Lee, H. N.; Kao, S. K.

1979-01-01

A dynamic turbulent boundary-layer model in the neutral atmosphere is constructed, using a dynamic turbulent equation of the eddy viscosity coefficient for momentum derived from the relationship among the turbulent dissipation rate, the turbulent kinetic energy and the eddy viscosity coefficient, with aid of the turbulent second-order closure scheme. A finite-element technique was used for the numerical integration. In preliminary results, the behavior of the neutral planetary boundary layer agrees well with the available data and with the existing elaborate turbulent models, using a finite-difference scheme. The proposed dynamic formulation of the eddy viscosity coefficient for momentum is particularly attractive and can provide a viable alternative approach to study atmospheric turbulence, diffusion and air pollution.

Sublayer of Prandtl Boundary Layers

NASA Astrophysics Data System (ADS)

Grenier, Emmanuel; Nguyen, Toan T.

2018-03-01

The aim of this paper is to investigate the stability of Prandtl boundary layers in the vanishing viscosity limit {ν \\to 0} . In Grenier (Commun Pure Appl Math 53(9):1067-1091, 2000), one of the authors proved that there exists no asymptotic expansion involving one of Prandtl's boundary layer, with thickness of order {√{ν}} , which describes the inviscid limit of Navier-Stokes equations. The instability gives rise to a viscous boundary sublayer whose thickness is of order {ν^{3/4}} . In this paper, we point out how the stability of the classical Prandtl's layer is linked to the stability of this sublayer. In particular, we prove that the two layers cannot both be nonlinearly stable in L^∞. That is, either the Prandtl's layer or the boundary sublayer is nonlinearly unstable in the sup norm.

Boundary layers in turbulent convection for air, liquid gallium and liquid sodium

NASA Astrophysics Data System (ADS)

Scheel, Janet; Schumacher, Joerg

2017-11-01

The scaling of physical quantities that characterize the shape and dynamics of the viscous and thermal boundary layers with respect to the Rayleigh number will be presented for three series of three-dimensional high-resolution direct numerical simulations of Rayleigh-Benard convection (RBC) in a closed cylindrical cell of aspect ratio one. The simulations have been conducted for convection in air at a Prandtl number Pr = 0.7, in liquid gallium at Pr = 0.021 and in liquid sodium at Pr = 0.005. Then we discuss three statistical analysis methods which have been developed to predict the transition of turbulent RBC into the ultimate regime. The methods are based on the large-scale properties of the velocity profile. All three methods indicate that the range of critical Rayleigh numbers is shifted to smaller magnitudes as the Prandtl number becomes smaller. This work is supported by the Priority Programme SPP 1881 of the Deutsche Forschungsgemeinschaft.

TURBULENCE PARAMETERS IMPACTING DISPERSION IN AN URBAN CONVECTIVE BOUNDARY LAYER

EPA Science Inventory

Turbulence measurements of the three dimensional wind components were collected by an instrumented research aircraft on 7 days in August 1976. These aircraft flights were conducted as part of the Regional Air Pollution Study (RAPS) urban boundary layer field program in St. Louis,...

The Coupled Boundary Layers and Air-Sea Transfer (CBLAST) Experiments at the Martha's Vineyard Coastal Observatory

NASA Astrophysics Data System (ADS)

Edson, J. B.

2001-12-01

The Woods Hole Oceanographic Institution (WHOI) completed the initial phase of the Martha's Vineyard Coastal Observatory (MVCO) in July of 2001. The MVCO is being using to monitor coastal atmospheric and oceanic processes. Specifically, the observatory is expected to: - Provide continuous long-term observations for climate studies. - Provide a reliable system and rugged sensors that allow opportunistic sampling of extreme events. - Provide a local climatology for intensive, short duration field campaigns. - Further facilitate regional studies of coastal processes by providing infrastructure that supports easy access to power and data. This talk provides an example of the last two objectives using the low wind component of the Office of Naval Research's (ONR) Coupled Boundary Layers and Air-Sea Transfer (CBLAST) program. CBLAST-LOW has been designed to investigate air-sea interaction and coupled atmospheric and oceanic boundary layer dynamics at low wind speeds where the dynamic processes are driven and/or strongly modulated by thermal forcing. This effort is being carried out by scientists at WHOI, NPS, NOAA, NRL, Rutgers, UW/APL, JH/APL, OSU, NCAR, and other institutions, and includes observational and modeling components. The MVCO is providing observations and infrastructure in support of several intensive operating periods in the summers of 2001, 2002, and possibly 2003. During these periods, the observational network around the observatory was and will be greatly expanded using traditional oceanographic moorings and bottom mounted instrumentation, innovative 2- and 3-D moored and drifting arrays, survey ships, AUVs, satellite remote sensing, and heavily instrumented aircraft. In addition, the MVCO cabled components will be extended out to the 20-m isobath where we plan to deploy a 35-m tower. The tower will be instrumented from 15-m above the ocean surface to the ocean bottom with instruments capable of directly measuring the momentum, heat, and radiative

The China Clipper - Fast advective transport of radon-rich air from the Asian boundary layer to the upper troposphere near California

NASA Technical Reports Server (NTRS)

Kritz, Mark A.; Le Roulley, Jean-Claude; Danielsen, Edwin F.

1990-01-01

A series of upper tropospheric radon concentration measurements made over the eastern Pacific and west coast of the U.S. during the summers of 1983 and 1984 has revealed the occurrence of unexpectedly high radon concentrations for 9 of the 61 measurements. A frequency distribution plot of the set of 61 observations shows a distinct bimodal distribution, with approximately 2/5 of the observations falling close to 1 pCi/SCM, and 3/5 falling in a high concentration mode centered at about 11 pCi/SCM. Trajectory and synoptic analyses for two of the flights on which such high radon concentrations were observed indicate that this radon-rich air originated in the Asian boundary layer, ascended in cumulus updrafts, and was carried eastward in the fast moving air on the anticyclonic side of the upper tropospheric jet. The results suggest that the combination of rapid vertical transport from the surface boundary layer to the upper troposphere, followed by rapid horizontal transport eastward represents an efficient mode of long-transport for other, chemically reactive atmospheric trace constituents.

The China Clipper - Fast advective transport of radon-rich air from the Asian boundary layer to the upper troposphere near California

NASA Astrophysics Data System (ADS)

Kritz, Mark A.; Le Roulley, Jean-Claude; Danielsen, Edwin F.

1990-02-01

A series of upper tropospheric radon concentration measurements made over the eastern Pacific and west coast of the U.S. during the summers of 1983 and 1984 has revealed the occurrence of unexpectedly high radon concentrations for 9 of the 61 measurements. A frequency distribution plot of the set of 61 observations shows a distinct bimodal distribution, with approximately 2/5 of the observations falling close to 1 pCi/SCM, and 3/5 falling in a high concentration mode centered at about 11 pCi/SCM. Trajectory and synoptic analyses for two of the flights on which such high radon concentrations were observed indicate that this radon-rich air originated in the Asian boundary layer, ascended in cumulus updrafts, and was carried eastward in the fast moving air on the anticyclonic side of the upper tropospheric jet. The results suggest that the combination of rapid vertical transport from the surface boundary layer to the upper troposphere, followed by rapid horizontal transport eastward represents an efficient mode of long-transport for other, chemically reactive atmospheric trace constituents.

Version 2 of the Protuberance Correlations for the Shuttle-Orbiter Boundary Layer Transition Tool

NASA Technical Reports Server (NTRS)

King, Rudolph A.; Kegerise, Michael A.; Berry, Scott A.

2009-01-01

Orbiter-specific transition data, acquired in four ground-based facilities (LaRC 20-Inch Mach 6 Air Tunnel, LaRC 31-Inch Mach 10 Air Tunnel, LaRC 20-Inch Mach 6 CF4 Tunnel, and CUBRC LENS-I Shock Tunnel) with three wind tunnel model scales (0.75, 0.90, and 1.8%) and from Orbiter historical flight data, have been analyzed to improve a pre-existing engineering tool for reentry transition prediction on the windward side of the Orbiter. Boundary layer transition (BLT) engineering correlations for transition induced by isolated protuberances are presented using a laminar Navier-Stokes (N-S) database to provide the relevant boundary-layer properties. It is demonstrated that the earlier version of the BLT correlation that had been developed using parameters derived from an engineering boundary-layer code has improved data collapse when developed with the N-S database. Of the new correlations examined, the proposed correlation 5, based on boundary-layer edge and wall properties, was found to provide the best overall correlation metrics when the entire database is employed. The second independent correlation (proposed correlation 7) selected is based on properties within the boundary layer at the protuberance height. The Aeroheating Panel selected a process to derive the recommended coefficients for Version 2 of the BLT Tool. The assumptions and limitations of the recommended protuberance BLT Tool V.2 are presented.

Boundary layer height determination from Lidar for improving air pollution episode modelling: development of new algorithm and evaluation

NASA Astrophysics Data System (ADS)

Yang, T.; Wang, Z.; Zhang, W.; Gbaguidi, A.; Sugimoto, N.; Matsui, I.; Wang, X.; Yele, S.

2017-12-01

Predicting air pollution events in low atmosphere over megacities requires thorough understanding of the tropospheric dynamic and chemical processes, involving notably, continuous and accurate determination of the boundary layer height (BLH). Through intensive observations experimented over Beijing (China), and an exhaustive evaluation existing algorithms applied to the BLH determination, persistent critical limitations are noticed, in particular over polluted episodes. Basically, under weak thermal convection with high aerosol loading, none of the retrieval algorithms is able to fully capture the diurnal cycle of the BLH due to pollutant insufficient vertical mixing in the boundary layer associated with the impact of gravity waves on the tropospheric structure. Subsequently, a new approach based on gravity wave theory (the cubic root gradient method: CRGM), is developed to overcome such weakness and accurately reproduce the fluctuations of the BLH under various atmospheric pollution conditions. Comprehensive evaluation of CRGM highlights its high performance in determining BLH from Lidar. In comparison with the existing retrieval algorithms, the CRGM potentially reduces related computational uncertainties and errors from BLH determination (strong increase of correlation coefficient from 0.44 to 0.91 and significant decreases of the root mean square error from 643 m to 142 m). Such newly developed technique is undoubtedly expected to contribute to improve the accuracy of air quality modelling and forecasting systems.

F-16XL ship #1 - CAWAP boundary layer hot film, left wing

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the boundary layer hot film on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. Hot film is used to measure temperature changes on a surface. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Boundary-Layer Effects on Acoustic Transmission Through Narrow Slit Cavities.

PubMed

Ward, G P; Lovelock, R K; Murray, A R J; Hibbins, A P; Sambles, J R; Smith, J D

2015-07-24

We explore the slit-width dependence of the resonant transmission of sound in air through both a slit array formed of aluminum slats and a single open-ended slit cavity in an aluminum plate. Our experimental results accord well with Lord Rayleigh's theory concerning how thin viscous and thermal boundary layers at a slit's walls affect the acoustic wave across the whole slit cavity. By measuring accurately the frequencies of the Fabry-Perot-like cavity resonances, we find a significant 5% reduction in the effective speed of sound through the slits when an individual viscous boundary layer occupies only 5% of the total slit width. Importantly, this effect is true for any airborne slit cavity, with the reduction being achieved despite the slit width being on a far larger scale than an individual boundary layer's thickness. This work demonstrates that the recent prevalent loss-free treatment of narrow slit cavities within acoustic metamaterials is unrealistic.

F-16XL ship #1 wing close-up showing boundary layer detection Preston tubes

NASA Technical Reports Server (NTRS)

1995-01-01

This photo shows the boundary layer Preston tubes mounted on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

F-16XL ship #1 - CAWAP boundary layer rakes and hot film on left wing

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the boundary layer hot film and the boundary layer rakes on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Wintertime Boundary Layer Structure in the Grand Canyon.

NASA Astrophysics Data System (ADS)

Whiteman, C. David; Zhong, Shiyuan; Bian, Xindi

1999-08-01

Wintertime temperature profiles in the Grand Canyon exhibit a neutral to isothermal stratification during both daytime and nighttime, with only rare instances of actual temperature inversions. The canyon warms during daytime and cools during nighttime more or less uniformly through the canyon's entire depth. This weak stability and temperature structure evolution differ from other Rocky Mountain valleys, which develop strong nocturnal inversions and exhibit convective and stable boundary layers that grow upward from the valley floor. Mechanisms that may be responsible for the different behavior of the Grand Canyon are discussed, including the possibility that the canyon atmosphere is frequently mixed to near-neutral stratification when cold air drains into the top of the canyon from the nearby snow-covered Kaibab Plateau. Another feature of canyon temperature profiles is the sharp inversions that often form near the canyon rims. These are generally produced when warm air is advected over the canyon in advance of passing synoptic-scale ridges.Wintertime winds in the main canyon are not classical diurnal along-valley wind systems. Rather, they are driven along the canyon axis by the horizontal synoptic-scale pressure gradient that is superimposed along the canyon's axis by passing synoptic-scale weather disturbances. They may thus bring winds into the canyon from either end at any time of day.The implications of the observed canyon boundary layer structure for air pollution dispersion are discussed.

Lear jet boundary layer/shear layer laser propagation experiments

NASA Technical Reports Server (NTRS)

Gilbert, K.

1980-01-01

Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.

Transition within a Hypervelocity Boundary Layer on a 5-degree Half-Angle Cone in Freestream Air/CO2 Mixtures

DTIC Science & Technology

2013-01-01

Pasadena, CA, 91125 Nomenclature A = amplitude of oscillation f = frequency hres = reservoir enthalpy Me = boundary layer edge Mach number Pres...showed an increase in the reference Reynolds number Re* at the point of transition as reservoir enthalpy hres increased. Germain and Adam also observed...that flows of CO2 transitioned at higher values of Re* than flows of air for the same hres and Pres. Johnson et al. (1998) studied this effect with a

The Bottom Boundary Layer.

PubMed

Trowbridge, John H; Lentz, Steven J

2018-01-03

The oceanic bottom boundary layer extracts energy and momentum from the overlying flow, mediates the fate of near-bottom substances, and generates bedforms that retard the flow and affect benthic processes. The bottom boundary layer is forced by winds, waves, tides, and buoyancy and is influenced by surface waves, internal waves, and stratification by heat, salt, and suspended sediments. This review focuses on the coastal ocean. The main points are that (a) classical turbulence concepts and modern turbulence parameterizations provide accurate representations of the structure and turbulent fluxes under conditions in which the underlying assumptions hold, (b) modern sensors and analyses enable high-quality direct or near-direct measurements of the turbulent fluxes and dissipation rates, and (c) the remaining challenges include the interaction of waves and currents with the erodible seabed, the impact of layer-scale two- and three-dimensional instabilities, and the role of the bottom boundary layer in shelf-slope exchange.

The Bottom Boundary Layer

NASA Astrophysics Data System (ADS)

Trowbridge, John H.; Lentz, Steven J.

2018-01-01

The oceanic bottom boundary layer extracts energy and momentum from the overlying flow, mediates the fate of near-bottom substances, and generates bedforms that retard the flow and affect benthic processes. The bottom boundary layer is forced by winds, waves, tides, and buoyancy and is influenced by surface waves, internal waves, and stratification by heat, salt, and suspended sediments. This review focuses on the coastal ocean. The main points are that (a) classical turbulence concepts and modern turbulence parameterizations provide accurate representations of the structure and turbulent fluxes under conditions in which the underlying assumptions hold, (b) modern sensors and analyses enable high-quality direct or near-direct measurements of the turbulent fluxes and dissipation rates, and (c) the remaining challenges include the interaction of waves and currents with the erodible seabed, the impact of layer-scale two- and three-dimensional instabilities, and the role of the bottom boundary layer in shelf-slope exchange.

F-16XL ship #1 - CAWAP boundary layer rakes and hot film on left wing

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the boundary layer hot film and the boundary layer rakes on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Mechanics of Boundary Layer Transition. Part 5: Boundary Layer Stability theory in incompressible and compressible flow

NASA Technical Reports Server (NTRS)

Mack, L. M.

1967-01-01

The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the boundary layer which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.

Modeling the urban boundary layer

NASA Technical Reports Server (NTRS)

Bergstrom, R. W., Jr.

1976-01-01

A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and boundary problems, (5) nocturnal boundary layer, and (6) verification of models.

Turbulent dusty boundary layer in an ANFO surface-burst explosion

NASA Astrophysics Data System (ADS)

Kuhl, A. L.; Ferguson, R. E.; Chien, K. Y.; Collins, J. P.

1992-01-01

This paper describes the results of numerical simulations of the dusty, turbulent boundary layer created by a surface burst explosion. The blast wave was generated by the detonation of a 600-T hemisphere of ANFO, similar to those used in large-scale field tests. The surface was assumed to be ideally noncratering but contained an initial loose layer of dust. The dust-air mixture in this fluidized bed was modeled as a dense gas (i.e., an equilibrium model, valid for very small-diameter dust particles). The evolution of the flow was calculated by a high-order Godunov code that solves the nonsteady conservation laws. Shock interactions with dense layer generated vorticity near the wall, a result that is similar to viscous, no-slip effects found in clean flows. The resulting wall shear layer was unstable, and rolled up into large-scale rotational structures. These structures entrained dense material from the wall layer and created a chaotically striated flow. The boundary layer grew due to merging of the large-scale structures and due to local entrainment of the dense material from the fluidized bed. The chaotic flow was averaged along similarity lines (i.e., lines of constant values of x = r/Rs and y = z/Rs where R(sub s) = ct(exp alpha)) to establish the mean-flow profiles and the r.m.s. fluctuating-flow profiles of the boundary layer.

Airborne Measurement of Insolation Impact on the Atmospheric Surface Boundary Layer

NASA Astrophysics Data System (ADS)

Jacob, Jamey; Chilson, Phil; Houston, Adam; Detweiler, Carrick; Bailey, Sean; Cloud-Map Team

2017-11-01

Atmospheric surface boundary layer measurements of wind and thermodynamic parameters are conducted during variable insolation conditions, including the 2017 eclipse, using an unmanned aircraft system. It is well known that the air temperatures can drop significantly during a total solar eclipse as has been previously observed. In past eclipses, these observations have primarily been made on the ground. We present results from airborne measurements of the near surface boundary layer using a small unmanned aircraft with high temporal resolution wind and thermodynamic observations. Questions that motivate the study include: How does the temperature within the lower atmospheric boundary vary during an eclipse? What impact does the immediate removal of radiative heating on the ground have on the lower ABL? Do local wind patterns change during an eclipse event and if so why? Will there be a manifestation of the nocturnal boundary layer wind maximum? Comparisons are made with the DOE ARM SGP site that experiences a lower but still significant insolation. Supported by the National Science Foundation under Award Number 1539070.

Grain Boundary Engineering and Air Oxidation Behavior of Alloy 690

NASA Astrophysics Data System (ADS)

Xu, Peng; Zhao, Liang Y.; Sridharan, Kumar; Allen, Todd R.

Grain boundary engineering (GBE) was performed on nickel-based alloy 690 by thermomechanical processing (TMP) to alter the grain boundary character distribution (GBCD). It was found that 5% and 35% thickness reduction in single and multiple steps followed by solution annealing and water quench yielded a high fraction of special boundaries. The total length fraction of the low ∑ CSL (coincidence site lattice) was as high as 87.2%. The grain boundary network was disrupted after the TMP treatment, and the average grain size calculated after exclusion of special twin boundaries can be as much as 5 times larger than the as-received (AR) sample. The GBE sample showed better oxidation resistance compared to the AR sample during the long term air oxidation. In the cyclic oxidation test, both AR and GBE samples showed a mass gain at the beginning of the test which was then followed by a mass loss. The mass change of GBE samples oscillated after the first couple cycles, while the AR sample became relatively stable. The oxide film most likely consists of duplex structures with one stable layer that was formed inside and one unstable layer that was formed outside. The stable inner layer was the protective layer and prevented alloy 690 from further oxidation.

Progress in modeling hypersonic turbulent boundary layers

NASA Technical Reports Server (NTRS)

Zeman, Otto

1993-01-01

A good knowledge of the turbulence structure, wall heat transfer, and friction in turbulent boundary layers (TBL) at high speeds is required for the design of hypersonic air breathing airplanes and reentry space vehicles. This work reports on recent progress in the modeling of high speed TBL flows. The specific research goal described here is the development of a second order closure model for zero pressure gradient TBL's for the range of Mach numbers up to hypersonic speeds with arbitrary wall cooling requirements.

Senstitivity analysis of horizontal heat and vapor transfer coefficients for a cloud-topped marine boundary layer during cold-air outbreaks. M.S. Thesis

NASA Technical Reports Server (NTRS)

Chang, Y. V.

1986-01-01

The effects of external parameters on the surface heat and vapor fluxes into the marine atmospheric boundary layer (MABL) during cold-air outbreaks are investigated using the numerical model of Stage and Businger (1981a). These fluxes are nondimensionalized using the horizontal heat (g1) and vapor (g2) transfer coefficient method first suggested by Chou and Atlas (1982) and further formulated by Stage (1983a). In order to simplify the problem, the boundary layer is assumed to be well mixed and horizontally homogeneous, and to have linear shoreline soundings of equivalent potential temperature and mixing ratio. Modifications of initial surface flux estimates, time step limitation, and termination conditions are made to the MABL model to obtain accurate computations. The dependence of g1 and g2 in the cloud topped boundary layer on the external parameters (wind speed, divergence, sea surface temperature, radiative sky temperature, cloud top radiation cooling, and initial shoreline soundings of temperature, and mixing ratio) is studied by a sensitivity analysis, which shows that the uncertainties of horizontal transfer coefficients caused by changes in the parameters are reasonably small.

Measuring Plume Meander in the Nighttime Stable Boundary Layer with Lidar

NASA Astrophysics Data System (ADS)

Hiscox, A.; Miller, D. R.; Nappo, C. J.

2009-12-01

Complex dynamics of the stable planetary boundary layer (PBL), such as the effects of density currents, intermittent turbulence, surface-layer decoupling, internal gravity waves, cold air pooling, and katabatic flows affect plume transport and diffusion. A better understanding of these effects is needed for nighttime transport model development. The JORNADA (Joint Observational Research on Nocturnal Atmospheric Dispersion of Aerosols) field campaign, conducted in the New Mexico desert during April 2005, sought to address some of these issues The JORNADA data set includes simultaneous micrometeorological measurements of the boundary layer structure, turbulence, and wave activity along with continuous lidar measurement of aerosol plume releases. What makes JORNADA unique is the real-time monitoring of an elevated plume with a lidar. The quantification of plume meander will be presented in this paper. The application of these techniques to the JORNADA data allows for a more complete understanding of the nocturnal boundary layer (NBL). We will present an in-depth analysis of lidar measurements of plume meander and dispersion and their relationship to the complexities of NBL structure.

Turbulent boundary layers with secondary flow

NASA Technical Reports Server (NTRS)

Grushwitz, E.

1984-01-01

An experimental analysis of the boundary layer on a plane wall, along which the flow occurs, whose potential flow lines are curved in plane parallel to the wall is discussed. According to the equation frequently applied to boundary layers in a plane flow, which is usually obtained by using the pulse law, a generalization is derived which is valid for boundary layers with spatial flow. The wall shear stresses were calculated with this equation.

Three-dimensional boundary layers approaching separation

NASA Technical Reports Server (NTRS)

Williams, J. C., III

1976-01-01

The theory of semi-similar solutions of the laminar boundary layer equations is applied to several flows in which the boundary layer approaches a three-dimensional separation line. The solutions obtained are used to deduce the nature of three-dimensional separation. It is shown that in these cases separation is of the "ordinary" type. A solution is also presented for a case in which a vortex is embedded within the three-dimensional boundary layer.

Turbulence measurements in hypersonic boundary layers using constant-temperature anemometry and Reynolds stress measurements in hypersonic boundary layers

NASA Technical Reports Server (NTRS)

Spina, Eric F.

1995-01-01

The primary objective in the two research investigations performed under NASA Langley sponsorship (Turbulence measurements in hypersonic boundary layers using constant temperature anemometry and Reynolds stress measurements in hypersonic boundary layers) has been to increase the understanding of the physics of hypersonic turbulent boundary layers. The study began with an extension of constant-temperature thermal anemometry techniques to a Mach 11 helium flow, including careful examinations of hot-wire construction techniques, system response, and system calibration. This was followed by the application of these techniques to the exploration of a Mach 11 helium turbulent boundary layer (To approximately 290 K). The data that was acquired over the course of more than two years consists of instantaneous streamwise mass flux measurements at a frequency response of about 500 kHz. The data are of exceptional quality in both the time and frequency domain and possess a high degree of repeatability. The data analysis that has been performed to date has added significantly to the body of knowledge on hypersonic turbulence, and the data reduction is continuing. An attempt was then made to extend these thermal anemometry techniques to higher enthalpy flows, starting with a Mach 6 air flow with a stagnation temperature just above that needed to prevent liquefaction (To approximately 475 F). Conventional hot-wire anemometry proved to be inadequate for the selected high-temperature, high dynamic pressure flow, with frequent wire breakage and poor system frequency response. The use of hot-film anemometry has since been investigated for these higher-enthalpy, severe environment flows. The difficulty with using hot-film probes for dynamic (turbulence) measurements is associated with construction limitations and conduction of heat into the film substrate. Work continues under a NASA GSRP grant on the development of a hot film probe that overcomes these shortcomings for hypersonic

Validation of High-Speed Turbulent Boundary Layer and Shock-Boundary Layer Interaction Computations with the OVERFLOW Code

NASA Technical Reports Server (NTRS)

Oliver, A. B.; Lillard, R. P.; Blaisdell, G. A.; Lyrintizis, A. S.

2006-01-01

The capability of the OVERFLOW code to accurately compute high-speed turbulent boundary layers and turbulent shock-boundary layer interactions is being evaluated. Configurations being investigated include a Mach 2.87 flat plate to compare experimental velocity profiles and boundary layer growth, a Mach 6 flat plate to compare experimental surface heat transfer,a direct numerical simulation (DNS) at Mach 2.25 for turbulent quantities, and several Mach 3 compression ramps to compare computations of shock-boundary layer interactions to experimental laser doppler velocimetry (LDV) data and hot-wire data. The present paper describes outlines the study and presents preliminary results for two of the flat plate cases and two small-angle compression corner test cases.

Boundary Layer Transition Correlations and Aeroheating Predictions for Mars Smart Lander

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Liechty, Derek S.

2002-01-01

Laminar and turbulent perfect-gas air, Navier-Stokes computations have been performed for a proposed Mars Smart Lander entry vehicle at Mach 6 over a free stream Reynolds number range of 6.9 x 10(exp 6)/m to 2.4 x 10(exp 7)/m (2.1 x 10(exp 6)/ft to 7.3 x 10(exp 6)/ft) for angles-of-attack of 0-deg, 11-deg, 16-deg, and 20-deg, and comparisons were made to wind tunnel heating data obtained a t the same conditions. Boundary layer edge properties were extracted from the solutions and used to correlate experimental data on the effects of heat-shield penetrations (bolt-holes where the entry vehicle would be attached to the propulsion module during transit to Mars) on boundary-layer transition. A non-equilibrium Martian-atmosphere computation was performed for the peak heating point on the entry trajectory in order to determine if the penetrations would produce boundary-layer transition by using this correlation.

Boundary Layer Transition Correlations and Aeroheating Predictions for Mars Smart Lander

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Liechty, Derek S.

2002-01-01

Laminar and turbulent perfect-gas air, Navier-Stokes computations have been performed for a proposed Mars Smart Lander entry vehicle at Mach 6 over a free stream Reynolds number range of 6.9 x 10(exp 6/m to 2.4 x 10(exp 7)m(2.1 x 10(exp 6)/ft to 7.3 x 10(exp 6)ft) for angles-of-attack of 0-deg, 11-deg, 16-deg, and 20-deg, and comparisons were made to wind tunnel heating data obtained at the same conditions. Boundary layer edge properties were extracted from the solutions and used to correlate experimental data on the effects of heat-shield penetrations (bolt-holes where the entry vehicle would be attached to the propulsion module during transit to Mars) on boundary-layer transition. A non-equilibrium Martian-atmosphere computation was performed for the peak heating point on the entry trajectory in order to determine if the penetrations would produce boundary-layer transition by using this correlation.

Boundary-layer effects on cold fronts at a coastline

NASA Astrophysics Data System (ADS)

Garratt, J. R.

1986-07-01

The present note discusses one physical mechanism which may contribute to cold air channelling, manifest as a frontal bulge on a surface-analysis chart, in the coastal region of Victoria in southeast Australia. This involves the modification of boundary-layer air in both offshore (prefrontal) and onshore (postfrontal) flow, and the effect on cross-frontal thermal contrast. The problem is discussed in terms of a north-south-oriented cold front behaving as an atmospheric gravity current, propagating along an east-west-oriented coastline, in the presence of a prefrontal offshore stream.

The turbulent plasmasphere boundary layer and the outer radiation belt boundary

NASA Astrophysics Data System (ADS)

Mishin, Evgeny; Sotnikov, Vladimir

2017-12-01

We report on observations of enhanced plasma turbulence and hot particle distributions in the plasmasphere boundary layer formed by reconnection-injected hot plasma jets entering the plasmasphere. The data confirm that the electron pressure peak is formed just outward of the plasmapause in the premidnight sector. Free energy for plasma wave excitation comes from diamagnetic ion currents near the inner edge of the boundary layer due to the ion pressure gradient, electron diamagnetic currents in the entry layer near the electron plasma sheet boundary, and anisotropic (sometimes ring-like) ion distributions revealed inside, and further inward of, the inner boundary. We also show that nonlinear parametric coupling between lower oblique resonance and fast magnetosonic waves significantly contributes to the VLF whistler wave spectrum in the plasmasphere boundary layer. These emissions represent a distinctive subset of substorm/storm-related VLF activity in the region devoid of substorm injected tens keV electrons and could be responsible for the alteration of the outer radiation belt boundary during (sub)storms.

Boundary layer relaminarization device

NASA Technical Reports Server (NTRS)

Creel, Theodore R. (Inventor)

1992-01-01

Relamination of a boundary layer formed in supersonic flow over the leading edge of a swept airfoil is accomplished by means of at least one band, especially a quadrangular band, and most preferably a square band. Each band conforms to the leading edge and the upper and lower surfaces of the airfoil as an integral part thereof and extends perpendicularly from the leading edge. Each band has a height of about two times the thickness of the maximum expected boundary layer.

Physics of magnetospheric boundary layers

NASA Technical Reports Server (NTRS)

Cairns, I. H.

1993-01-01

The central ideas of this grant are that the magnetospheric boundary layers link disparate regions of the magnetosphere together, and the global behavior of the magnetosphere can be understood only by understanding the linking mechanisms. Accordingly the present grant includes simultaneous research on the global, meso-, and micro-scale physics of the magnetosphere and its boundary layers. These boundary layers include the bow shock, magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical and simulation projects have been performed on these subjects, as well as comparison of theoretical results with observational data. Very good progress has been made, with four papers published or in press and two additional papers submitted for publication during the six month period 1 June - 30 November 1993. At least two projects are currently being written up. In addition, members of the group have given papers at scientific meetings. The further structure of this report is as follows: section two contains brief accounts of research completed during the last six months, while section three describes the research projects intended for the grant's final period.

Calculation methods for compressible turbulent boundary layers, 1976

NASA Technical Reports Server (NTRS)

Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.

1977-01-01

Equations and closure methods for compressible turbulent boundary layers are discussed. Flow phenomena peculiar to calculation of these boundary layers were considered, along with calculations of three dimensional compressible turbulent boundary layers. Procedures for ascertaining nonsimilar two and three dimensional compressible turbulent boundary layers were appended, including finite difference, finite element, and mass-weighted residual methods.

Boundary layer control for airships

NASA Technical Reports Server (NTRS)

Pake, F. A.; Pipitone, S. J.

1975-01-01

An investigation is summarized of the aerodynamic principle of boundary layer control for nonrigid LTA craft. The project included a wind tunnel test on a BLC body of revolution at zero angle of attack. Theoretical analysis is shown to be in excellent agreement with the test data. Methods are evolved for predicting the boundary layer development on a body of revolution and the suction pumping and propulsive power requirements. These methods are used to predict the performance characteristics of a full-scale airship. The analysis indicates that propulsive power reductions of 15 to 25 percent and endurance improvements of 20 to 40 percent may be realized in employing boundary-layer control to nonrigid airships.

Genesis of Atlantic Lows Experiment NASA Electra Boundary Layer Flights Data Report

NASA Technical Reports Server (NTRS)

Palm, Stephen P.; Melfi, S. H.; Boers, Reinout

1988-01-01

The objective of this research was to obtain high resolution measurements of the height of the Marine Atmospheric Boundary Layer (MABL) during cold air outbreaks using an Airborne Lidar System. The research was coordinated with other investigators participating in the Genesis of Atlantic Lows Experiment (GALE). An objective computerized scheme was developed to obtain the Boundary Layer Height from the Lidar Data. The algorithm was used on each of the four flight days producing a high resolution data set of the MABL height over the GALE experiment area. Plots of the retrieved MABL height as well as tabular data summaries are presented.

Analytic prediction of unconfined boundary layer flashback limits in premixed hydrogen-air flames

NASA Astrophysics Data System (ADS)

Hoferichter, Vera; Hirsch, Christoph; Sattelmayer, Thomas

2017-05-01

Flame flashback is a major challenge in premixed combustion. Hence, the prediction of the minimum flow velocity to prevent boundary layer flashback is of high technical interest. This paper presents an analytic approach to predicting boundary layer flashback limits for channel and tube burners. The model reflects the experimentally observed flashback mechanism and consists of a local and global analysis. Based on the local analysis, the flow velocity at flashback initiation is obtained depending on flame angle and local turbulent burning velocity. The local turbulent burning velocity is calculated in accordance with a predictive model for boundary layer flashback limits of duct-confined flames presented by the authors in an earlier publication. This ensures consistency of both models. The flame angle of the stable flame near flashback conditions can be obtained by various methods. In this study, an approach based on global mass conservation is applied and is validated using Mie-scattering images from a channel burner test rig at ambient conditions. The predicted flashback limits are compared to experimental results and to literature data from preheated tube burner experiments. Finally, a method for including the effect of burner exit temperature is demonstrated and used to explain the discrepancies in flashback limits obtained from different burner configurations reported in the literature.

Hairpin vortices in turbulent boundary layers

NASA Astrophysics Data System (ADS)

Eitel-Amor, G.; Örlü, R.; Schlatter, P.; Flores, O.

2015-02-01

The present work presents a number of parallel and spatially developing simulations of boundary layers to address the question of whether hairpin vortices are a dominant feature of near-wall turbulence, and which role they play during transition. In the first part, the parent-offspring regeneration mechanism is investigated in parallel (temporal) simulations of a single hairpin vortex introduced in a mean shear flow corresponding to either turbulent channels or boundary layers (Reτ ≲ 590). The effect of a turbulent background superimposed on the mean flow is considered by using an eddy viscosity computed from resolved simulations. Tracking the vortical structure downstream, it is found that secondary hairpins are only created shortly after initialization, with all rotational structures decaying for later times. For hairpins in a clean (laminar) environment, the decay is relatively slow, while hairpins in weak turbulent environments (10% of νt) dissipate after a couple of eddy turnover times. In the second part, the role of hairpin vortices in laminar-turbulent transition is studied using simulations of spatial boundary layers tripped by hairpin vortices. These vortices are generated by means of specific volumetric forces representing an ejection event, creating a synthetic turbulent boundary layer initially dominated by hairpin-like vortices. These hairpins are advected towards the wake region of the boundary layer, while a sinusoidal instability of the streaks near the wall results in rapid development of a turbulent boundary layer. For Reθ > 400, the boundary layer is fully developed, with no evidence of hairpin vortices reaching into the wall region. The results from both the parallel and spatial simulations strongly suggest that the regeneration process is rather short-lived and may not sustain once a turbulent background is developed. From the transitional flow simulations, it is conjectured that the forest of hairpins reported in former direct numerical

Boundary layer simulator improvement

NASA Technical Reports Server (NTRS)

Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.

1989-01-01

Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.

Boundary-layer effects in droplet splashing

NASA Astrophysics Data System (ADS)

Riboux, Guillaume; Gordillo, Jose Manuel

2017-11-01

A drop falling onto a solid substrate will disintegrate into smaller parts when its impact velocity exceeds the so called critical velocity for splashing. Under these circumstances, the very thin liquid sheet ejected tangentially to the solid after the drop touches the substrate, lifts off as a consequence of the aerodynamic forces exerted on it and finally breaks into smaller droplets, violently ejected radially outwards, provoking the splash. Here, the tangential deceleration experienced by the fluid entering the thin liquid sheet is investigated making use of boundary layer theory. The velocity component tangent to the solid, computed using potential flow theory provides the far field boundary condition as well as the pressure gradient for the boundary layer equations. The structure of the flow permits to find a self similar solution of the boundary layer equations. This solution is then used to calculate the boundary layer thickness at the root of the lamella as well as the shear stress at the wall. The splash model presented in, which is slightly modified to account for the results obtained from the boundary layer analysis, provides a very good agreement between the measurements and the predicted values of the critical velocity for the splash.

DESIGN OF TWO-DIMENSIONAL SUPERSONIC TURBINE ROTOR BLADES WITH BOUNDARY-LAYER CORRECTION

NASA Technical Reports Server (NTRS)

Goldman, L. J.

1994-01-01

A computer program has been developed for the design of supersonic rotor blades where losses are accounted for by correcting the ideal blade geometry for boundary layer displacement thickness. The ideal blade passage is designed by the method of characteristics and is based on establishing vortex flow within the passage. Boundary-layer parameters (displacement and momentum thicknesses) are calculated for the ideal passage, and the final blade geometry is obtained by adding the displacement thicknesses to the ideal nozzle coordinates. The boundary-layer parameters are also used to calculate the aftermixing conditions downstream of the rotor blades assuming the flow mixes to a uniform state. The computer program input consists essentially of the rotor inlet and outlet Mach numbers, upper- and lower-surface Mach numbers, inlet flow angle, specific heat ratio, and total flow conditions. The program gas properties are set up for air. Additional gases require changes to be made to the program. The computer output consists of the corrected rotor blade coordinates, the principal boundary-layer parameters, and the aftermixing conditions. This program is written in FORTRAN IV for batch execution and has been implemented on an IBM 7094. This program was developed in 1971.

Spatial Linear Instability of Confluent Wake/Boundary Layers

NASA Technical Reports Server (NTRS)

Liou, William W.; Liu, Feng-Jun; Rumsey, C. L. (Technical Monitor)

2001-01-01

The spatial linear instability of incompressible confluent wake/boundary layers is analyzed. The flow model adopted is a superposition of the Blasius boundary layer and a wake located above the boundary layer. The Orr-Sommerfeld equation is solved using a global numerical method for the resulting eigenvalue problem. The numerical procedure is validated by comparing the present solutions for the instability of the Blasius boundary layer and for the instability of a wake with published results. For the confluent wake/boundary layers, modes associated with the boundary layer and the wake, respectively, are identified. The boundary layer mode is found amplified as the wake approaches the wall. On the other hand, the modes associated with the wake, including a symmetric mode and an antisymmetric mode, are stabilized by the reduced distance between the wall and the wake. An unstable mode switching at low frequency is observed where the antisymmetric mode becomes more unstable than the symmetric mode when the wake velocity defect is high.

Aerothermodynamic Testing and Boundary Layer Trip Sizing of the HIFiRE Flight 1 Vehicle

NASA Technical Reports Server (NTRS)

Berger, Karen T.; Greene, Frank A.; Kimmel, Roger

2008-01-01

An experimental wind tunnel test was conducted in the NASA Langley Research Center s 20-Inch Mach 6 Air Tunnel in support of the Hypersonic International Flight Research Experimentation Program. The information in this report is focused on the Flight 1 configuration, the first in a series of flight experiments. This report documents experimental measurements made over a range of Reynolds numbers and angles of attack on several scaled ceramic heat transfer models of the Flight 1 payload. Global heat transfer was measured using phosphor thermography and the resulting images and heat transfer distributions were used to infer the state of the boundary layer on the vehicle windside and leeside surfaces. Boundary layer trips were used to force the boundary layer turbulent, and a brief study was conducted to determine the effectiveness of the trips with various heights. The experimental data highlighted in this test report were used to size and place the boundary layer trip for the flight test vehicle.

Boundary-Layer Characteristics Over a Coastal Megacity

NASA Astrophysics Data System (ADS)

Melecio-Vazquez, D.; Ramamurthy, P.; Arend, M.; Moshary, F.; Gonzalez, J.

2017-12-01

Boundary-layer characteristics over New York City are analyzed for various local and synoptic conditions over several seasons. An array of vertical profilers, including a Doppler LiDAR, a micro-pulse LiDAR and a microwave radiometer are used to observe the structure and evolution of the boundary-layer. Additionally, an urbanized Weather Research and Forecasting (uWRF) model coupled to a high resolution landcover/land-use database is used to study the spatial variability in boundary layer characteristics. The summer daytime averaged potential temperature profile from the microwave radiometer shows the presence of a thermal internal boundary layer wherein a superadiabatic layer lies underneath a stable layer instead of a mixed-layer. Both the winter daytime and nighttime seasonal averages show that the atmosphere remains unstable near the surface and does not reach stable conditions during the nighttime. The mixing ratio seasonal averages show peaks in humidity near 200-m and 1100-m, above instrument level, which could result from sea breeze and anthropogenic sources. Ceilometer measurements show a high degree of variability in boundary layer height depending on wind direction. Comparison with uWRF results show that the model tends to overestimate convective efficiency for selected summer and winter cases and therefore shows a much deeper thermal boundary layer than the observed profiles. The model estimates a less humid atmosphere than seen in observations.

Nonequilibrium chemistry boundary layer integral matrix procedure

NASA Technical Reports Server (NTRS)

Tong, H.; Buckingham, A. C.; Morse, H. L.

1973-01-01

The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the boundary layer.

Modification of the Atmospheric Boundary Layer by a Small Island: Observations from Nauru

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matthews, Stuart; Hacker, Jorg M.; Cole, Jason N.

2007-03-01

Nauru, a small island in the tropical pacific, generates plumes of clouds that may grow to several hundred km length. This study uses observations to examine the mesoscale disturbance of the marine atmospheric boundary layer by the island that produces these cloud streets. Observations of the surface layer were made from two ships in the vicinity of Nauru and from instruments on the island. The structure of the atmospheric boundary layer over the island was investigated using aircraft flights. Cloud production over Nauru was examined using remote sensing instruments. During the day the island surface layer was warmer than themore » marine surface layer and wind speed was lower than over the ocean. Surface heating forced the growth of a thermal internal boundary layer, above which a street of cumulus clouds formed. The production of clouds resulted in reduced downwelling shortwave irradiance at the island surface. A plume of warm-dry air was observed over the island which extended 15 – 20 km downwind.« less

Sound-turbulence interaction in transonic boundary layers

NASA Astrophysics Data System (ADS)

Lelostec, Ludovic; Scalo, Carlo; Lele, Sanjiva

2014-11-01

Acoustic wave scattering in a transonic boundary layer is investigated through a novel approach. Instead of simulating directly the interaction of an incoming oblique acoustic wave with a turbulent boundary layer, suitable Dirichlet conditions are imposed at the wall to reproduce only the reflected wave resulting from the interaction of the incident wave with the boundary layer. The method is first validated using the laminar boundary layer profiles in a parallel flow approximation. For this scattering problem an exact inviscid solution can be found in the frequency domain which requires numerical solution of an ODE. The Dirichlet conditions are imposed in a high-fidelity unstructured compressible flow solver for Large Eddy Simulation (LES), CharLESx. The acoustic field of the reflected wave is then solved and the interaction between the boundary layer and sound scattering can be studied.

Hypersonic Boundary Layer Transition Measurements Using NO2 approaches NO Photo-dissociation Tagging Velocimetry

NASA Technical Reports Server (NTRS)

Bathel, Brett F.; Johansen, Craig T.; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Goyne, Christopher P.

2011-01-01

Measurements of instantaneous and mean streamwise velocity profiles in a hypersonic laminar boundary layer as well as a boundary layer undergoing laminar-to-turbulent transition were obtained over a 10-degree half-angle wedge model. A molecular tagging velocimetry technique consisting of a NO2 approaches?NO photo-dissociation reaction and two subsequent excitations of NO was used. The measurement of the transitional boundary layer velocity profiles was made downstream of a 1-mm tall, 4-mm diameter cylindrical trip along several lines lying within a streamwise measurement plane normal to the model surface and offset 6-mm from the model centerline. For laminar and transitional boundary layer measurements, the magnitudes of streamwise velocity fluctuations are compared. In the transitional boundary layer the fluctuations were, in general, 2-4 times larger than those in the laminar boundary layer. Of particular interest were fluctuations corresponding to a height of approximately 50% of the laminar boundary layer thickness having a magnitude of nearly 30% of the mean measured velocity. For comparison, the measured fluctuations in the laminar boundary layer were approximately 5% of the mean measured velocity at the same location. For the highest 10% signal-to-noise ratio data, average single-shot uncertainties using a 1 ?Es and 50 ?Es interframe delay were 115 m/s and 3 m/s, respectively. By averaging single-shot measurements of the transitional boundary layer, uncertainties in mean velocity as low as 39 m/s were obtained in the wind tunnel. The wall-normal and streamwise spatial resolutions were 0.14-mm (2 pixel) and 0.82-mm (11 pixels), respectively. These measurements were performed in the 31-inch Mach 10 Air Wind Tunnel at the NASA Langley Research Center.

High enthalpy hypersonic boundary layer flow

NASA Technical Reports Server (NTRS)

Yanow, G.

1972-01-01

A theoretical and experimental study of an ionizing laminar boundary layer formed by a very high enthalpy flow (in excess of 12 eV per atom or 7000 cal/gm) with allowance for the presence of helium driver gas is described. The theoretical investigation has shown that the use of variable transport properties and their respective derivatives is very important in the solution of equilibrium boundary layer equations of high enthalpy flow. The effect of low level helium contamination on the surface heat transfer rate is minimal. The variation of ionization is much smaller in a chemically frozen boundary layer solution than in an equilibrium boundary layer calculation and consequently, the variation of the transport properties in the case of the former was not essential in the integration. The experiments have been conducted in a free piston shock tunnel, and a detailed study of its nozzle operation, including the effects of low levels of helium driver gas contamination has been made. Neither the extreme solutions of an equilibrium nor of a frozen boundary layer will adequately predict surface heat transfer rate in very high enthalpy flows.

Summary of experimentally determined facts concerning the behavior of the boundary layer and performance of boundary layer measurements. [considering sailing flight

NASA Technical Reports Server (NTRS)

Vanness, W.

1978-01-01

A summary report of boundary layer studies is presented. Preliminary results of experimental measurements show that: (1) A very thin layer (approximately 0.4 mm) of the boundary layer seems to be accelerated; (2) the static pressure of the outer flow does not remain exactly constant through the boundary layer; and (3) an oncoming boundary layer which is already turbulent at the suction point can again become laminar behind this point without being completely sucked off.

Diagnosis of boundary-layer circulations.

PubMed

Beare, Robert J; Cullen, Michael J P

2013-05-28

Diagnoses of circulations in the vertical plane provide valuable insights into aspects of the dynamics of the climate system. Dynamical theories based on geostrophic balance have proved useful in deriving diagnostic equations for these circulations. For example, semi-geostrophic theory gives rise to the Sawyer-Eliassen equation (SEE) that predicts, among other things, circulations around mid-latitude fronts. A limitation of the SEE is the absence of a realistic boundary layer. However, the coupling provided by the boundary layer between the atmosphere and the surface is fundamental to the climate system. Here, we use a theory based on Ekman momentum balance to derive an SEE that includes a boundary layer (SEEBL). We consider a case study of a baroclinic low-level jet. The SEEBL solution shows significant benefits over Ekman pumping, including accommodating a boundary-layer depth that varies in space and structure, which accounts for buoyancy and momentum advection. The diagnosed low-level jet is stronger than that determined by Ekman balance. This is due to the inclusion of momentum advection. Momentum advection provides an additional mechanism for enhancement of the low-level jet that is distinct from inertial oscillations.

Numerical investigation of implementation of air-earth boundary by acoustic-elastic boundary approach

USGS Publications Warehouse

Xu, Y.; Xia, J.; Miller, R.D.

2007-01-01

The need for incorporating the traction-free condition at the air-earth boundary for finite-difference modeling of seismic wave propagation has been discussed widely. A new implementation has been developed for simulating elastic wave propagation in which the free-surface condition is replaced by an explicit acoustic-elastic boundary. Detailed comparisons of seismograms with different implementations for the air-earth boundary were undertaken using the (2,2) (the finite-difference operators are second order in time and space) and the (2,6) (second order in time and sixth order in space) standard staggered-grid (SSG) schemes. Methods used in these comparisons to define the air-earth boundary included the stress image method (SIM), the heterogeneous approach, the scheme of modifying material properties based on transversely isotropic medium approach, the acoustic-elastic boundary approach, and an analytical approach. The method proposed achieves the same or higher accuracy of modeled body waves relative to the SIM. Rayleigh waves calculated using the explicit acoustic-elastic boundary approach differ slightly from those calculated using the SIM. Numerical results indicate that when using the (2,2) SSG scheme for SIM and our new method, a spatial step of 16 points per minimum wavelength is sufficient to achieve 90% accuracy; 32 points per minimum wavelength achieves 95% accuracy in modeled Rayleigh waves. When using the (2,6) SSG scheme for the two methods, a spatial step of eight points per minimum wavelength achieves 95% accuracy in modeled Rayleigh waves. Our proposed method is physically reasonable and, based on dispersive analysis of simulated seismographs from a layered half-space model, is highly accurate. As a bonus, our proposed method is easy to program and slightly faster than the SIM. ?? 2007 Society of Exploration Geophysicists.

Convection Cells in the Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Fodor, Katherine; Mellado, Juan-Pedro

2017-04-01

In dry, shear-free convective boundary layers (CBLs), the turbulent flow of air is known to organise itself on large scales into coherent, cellular patterns, or superstructures, consisting of fast, narrow updraughts and slow, wide downdraughts which together form circulations. Superstructures act as transport mechanisms from the surface to the top of the boundary layer and vice-versa, as opposed to small-scale turbulence, which only modifies conditions locally. This suggests that a thorough investigation into superstructure properties may help us better understand transport across the atmospheric boundary layer as a whole. Whilst their existence has been noted, detailed studies into superstructures in the CBL have been scarce. By applying methods which are known to successfully isolate similar large-scale patterns in turbulent Rayleigh-Bénard convection, we can assess the efficacy of those detection techniques in the CBL. In addition, through non-dimensional analysis, we can systematically compare superstructures in various convective regimes. We use direct numerical simulation of four different cases for intercomparison: Rayleigh-Bénard convection (steady), Rayleigh-Bénard convection with an adiabatic top lid (quasi-steady), a stably-stratified CBL (quasi-steady) and a neutrally-stratified CBL (unsteady). The first two are non-penetrative and the latter two penetrative. We find that although superstructures clearly emerge from the time-mean flow in the non-penetrative cases, they become obscured by temporal averaging in the CBL. This is because a rigid lid acts to direct the flow into counter-rotating circulation cells whose axis of rotation remains stationary, whereas a boundary layer that grows in time and is able to entrain fluid from above causes the circulations to not only grow in vertical extent, but also to move horizontally and merge with neighbouring circulations. Spatial filtering is a useful comparative technique as it can be performed on boundary

Shuttle Damage/Repair from the Perspective of Hypersonic Boundary Layer Transition - Experimental Results

NASA Technical Reports Server (NTRS)

Horvath, Thomas J.; Berry, Scott A.; Merski, N. Ronald; Berger, Karen T.; Buck, Gregory M.; Liechty, Derek S.; Schneider, Steven P.

2006-01-01

state of the boundary layer (laminar, transitional, or turbulent). Test parametrics include angles-of-attack of 30 deg and 40 deg, sideslip angle of 0 deg, freestream Reynolds numbers from 0.02x106 to 7.3x106 per foot, edge-to-wall temperature ratio from 0.4 to 0.8, and normal shock density ratios of approximately 5.3, 6.0, and 12 in Mach 6 air, Mach 10 air, and Mach 6 CF4, respectively. Testing to simulate the effects of ablation from a proposed tile repair concept indicated that transition was not a concern. The experimental protuberance and cavity databases highlighted in this report were used to formulate boundary layer transition correlations that were an integral part of an analytical process to disposition observed Orbiter TPS damage during STS- 114.

Self-organized classification of boundary layer meteorology and associated characteristics of air quality in Beijing

NASA Astrophysics Data System (ADS)

Liao, Zhiheng; Sun, Jiaren; Yao, Jialin; Liu, Li; Li, Haowen; Liu, Jian; Xie, Jielan; Wu, Dui; Fan, Shaojia

2018-05-01

Self-organizing maps (SOMs; a feature-extracting technique based on an unsupervised machine learning algorithm) are used to classify atmospheric boundary layer (ABL) meteorology over Beijing through detecting topological relationships among the 5-year (2013-2017) radiosonde-based virtual potential temperature profiles. The classified ABL types are then examined in relation to near-surface pollutant concentrations to understand the modulation effects of the changing ABL meteorology on Beijing's air quality. Nine ABL types (i.e., SOM nodes) are obtained through the SOM classification technique, and each is characterized by distinct dynamic and thermodynamic conditions. In general, the self-organized ABL types are able to distinguish between high and low loadings of near-surface pollutants. The average concentrations of PM2.5, NO2 and CO dramatically increased from the near neutral (i.e., Node 1) to strong stable conditions (i.e., Node 9) during all seasons except for summer. Since extremely strong stability can isolate the near-surface observations from the influence of elevated SO2 pollution layers, the highest average SO2 concentrations are typically observed in Node 3 (a layer with strong stability in the upper ABL) rather than Node 9. In contrast, near-surface O3 shows an opposite dependence on atmospheric stability, with the lowest average concentration in Node 9. Analysis of three typical pollution months (i.e., January 2013, December 2015 and December 2016) suggests that the ABL types are the primary drivers of day-to-day variations in Beijing's air quality. Assuming a fixed relationship between ABL type and PM2.5 loading for different years, the relative (absolute) contributions of the ABL anomaly to elevated PM2.5 levels are estimated to be 58.3 % (44.4 µg m-3) in January 2013, 46.4 % (22.2 µg m-3) in December 2015 and 73.3 % (34.6 µg m-3) in December 2016.

An operational large-scale marine planetary boundary layer model

NASA Technical Reports Server (NTRS)

Brown, R. A.; Liu, W. T.

1982-01-01

A marine planetary boundary layer (PBL) model is presented and compared with data from sea-based experiments. The PBL model comprises two layers, the outer an Ekman-Taylor layer with stratification-dependent secondary flow, and the logarithmic surface layer corrected for stratification and humidity effects and variable surface roughness. Corrections are noted for air much warmer than water in stable conditions and for low wind speeds. The layers are analytically defined along with similarity relations and a resistance law for inclusion in a program. An additional interfacial layer correction is developed and shown to be significant for heat flux calculations. Experimental data from GOASEX were used to predict the windfield in the Gulf of Alaska, and JASIN data was used for windfields SE of Iceland. The JASIN-derived wind field predictions were accurate to within 1 m/sec and 10 deg in a 200 km triangle.

Boundary-Layer Bypass Transition Over Large-Scale Bodies

DTIC Science & Technology

2016-12-16

shape of the streamwise velocity profile compared to the flat- plate boundary layer. The research showed that the streamwise wavenumber plays a key role...many works on the suppression of the transitional boundary layer. Most of the results in the literature are for the flat- plate boundary layer but the...behaviour of the velocity and pressure changes with the curvature. This work aims to extend the results of the flat- plate boundary layer to a Rankine

Ozone Laminae and Their Entrainment Into a Valley Boundary Layer, as Observed From a Mountaintop Monitoring Station, Ozonesondes, and Aircraft Over California's San Joaquin Valley

NASA Astrophysics Data System (ADS)

Faloona, I. C.; Conley, S. A.; Caputi, D.; Trousdell, J.; Chiao, S.; Eiserloh, A. J., Jr.; Clark, J.; Iraci, L. T.; Yates, E. L.; Marrero, J. E.; Ryoo, J. M.; McNamara, M. E.

2016-12-01

The San Joaquin Valley of California is wide ( 75 km) and long ( 400 km), and is situated under strong atmospheric subsidence due, in part, to the proximity of the midlatitude anticyclone of the Pacific High. The capping effect of this subsidence is especially prominent during the warm season when ground level ozone is a serious air quality concern across the region. While relatively clean marine boundary layer air is primarily funneled into the valley below the strong subsidence inversion at significant gaps in the upwind Coast Range mountains, airflow aloft also spills over these barriers and mixes into the valley from above. Because this transmountain flow occurs under the influence of synoptic subsidence it tends to present discrete, laminar sheets of differing air composition above the valley boundary layer. Meanwhile, although the boundary layers tend to remain shallow due to the prevailing subsidence, orographic and anabatic venting of valley boundary layer air around the basin whips up a complex admixture of regional air masses into a "buffer layer" just above the boundary layer (zi) and below the lower free troposphere. We present scalar data of widely varying lifetimes including ozone, methane, NOx, and thermodynamic observations from upwind and within the San Joaquin Valley to better explain this layering and its subsequent erosion into the valley boundary layer via entrainment. Data collected at a mountaintop monitoring station on Chews Ridge in the Coast Range, by coastal ozonesondes, and aircraft are analyzed to document the dynamic layering processes around the complex terrain surrounding the valley. Particular emphasis will be made on observational methods whereby distal ozone can be distinguished from the regional ozone to better understand the influence of exogenous sources on air quality in the valley.

Towards Natural Transition in Compressible Boundary Layers

DTIC Science & Technology

2016-06-29

AFRL-AFOSR-CL-TR-2016-0011 Towards natural transition in compressible boundary layers Marcello Faraco de Medeiros FUNDACAO PARA O INCREMENTO DA...to 29-03-2016 Towards natural transition in compressible boundary layers FA9550-11-1-0354 Marcello A. Faraco de Medeiros Germán Andrés Gaviria...unlimited. 109 Final report Towards natural transition in compressible boundary layers Principal Investigator: Marcello Augusto Faraco de Medeiros

Differential analysis for the turbulent boundary layer on a compressor blade element (including boundary-layer separation)

NASA Technical Reports Server (NTRS)

Schmidt, J. F.; Todd, C. A.

1974-01-01

A two-dimensional differential analysis is developed to approximate the turbulent boundary layer on a compressor blade element with strong adverse pressure gradients, including the separated region with reverse flow. The predicted turbulent boundary layer thicknesses and velocity profiles are in good agreement with experimental data for a cascade blade, even in the separated region.

Separation behavior of boundary layers on three-dimensional wings

NASA Technical Reports Server (NTRS)

Stock, H. W.

1981-01-01

An inverse boundary layer procedure for calculating separated, turbulent boundary layers at infinitely long, crabbing wing was developed. The procedure was developed for calculating three dimensional, incompressible turbulent boundary layers was expanded to adiabatic, compressible flows. Example calculations with transsonic wings were made including viscose effects. In this case an approximated calculation method described for areas of separated, turbulent boundary layers, permitting calculation of this displacement thickness. The laminar boundary layer development was calculated with inclined ellipsoids.

A Study Of The Atmospheric Boundary Layer Using Radon And Air Pollutants As Tracers

NASA Astrophysics Data System (ADS)

Kataoka, Toshio; Yunoki, Eiji; Shimizu, Mitsuo; Mori, Tadashige; Tsukamoto, Osamu; Ohashi, Yukitaka, Sahashi, Ken; Maitani, Toshihiko; Miyashita, Koh'ichi; Iwata, Toru; Fujikawa, Yoko; Kudo, Akira; Shaw, Roger H.

Concentrations of radon 222Rn andair pollutants, meteorological parametersnear the surface and vertical profiles of meteorological elements were measured atUchio (Okayama City, Okayama Prefecture, Japan) 12 km north from the coast ofthe Inland Sea of Japan. In the nighttime, the 222Rn concentration increased in the case of weak winds, but did not increase as much in the case of moderate or strong winds, as had been expected. In the daytime, the 222Rn concentrationheld at a slightly higher than average level for the period from sunrise to about 1100 JST. It is considered that this phenomenon is due to a period of morning calm, that is, a transition period from land breeze to sea breeze.NO, which is sensitive to traffic volume,brought information concerning advection.Oxidant concentrations,which reflect the availability of sunlight,acted in the reverse manner to 222Rnconcentrations. Thus, a set of 222Rn and air pollutants could provide useful information regarding the local conditions of the atmospheric boundary layer.

Investigations on entropy layer along hypersonic hyperboloids using a defect boundary layer

NASA Technical Reports Server (NTRS)

Brazier, J. P.; Aupoix, B.; Cousteix, J.

1992-01-01

A defect approach coupled with matched asymptotic expansions is used to derive a new set of boundary layer equations. This method ensures a smooth matching of the boundary layer with the inviscid solution. These equations are solved to calculate boundary layers over hypersonic blunt bodies involving the entropy gradient effect. Systematic comparisons are made for both axisymmetric and plane flows in several cases with different Mach and Reynolds numbers. After a brief survey of the entropy layer characteristics, the defect boundary layer results are compared with standard boundary layer and full Navier-Stokes solutions. The entropy gradient effects are found to be more important in the axisymmetric case than in the plane one. The wall temperature has a great influence on the results through the displacement effect. Good predictions can be obtained with the defect approach over a cold wall in the nose region, with a first order solution. However, the defect approach gives less accurate results far from the nose on axisymmetric bodies because of the thinning of the entropy layer.

Shock-Wave Boundary Layer Interactions

DTIC Science & Technology

1986-02-01

Security Classification of Document UNCLASSIFIED 6. Title TURBULENT SHOCK-WAVE/BOUNDARY-LAYER INTERACTION 7. Presented at 8. Author(s)/Editor(s...contrary effects. The above demonstration puts an emphasis on inertia forces in the sense that the "fullness" for the Incoming boundary-layer profile is...expression "quasi-normal" means that in most transonic streams, the shocks are strong oblique shock, in the sense of the strong solution of the oblique shock

Characteristics of early winter high Arctic atmospheric boundary layer profiles

NASA Astrophysics Data System (ADS)

Wickström, Siiri; Vihma, Timo; Nygård, Tiina; Kramer, Daniel; Palo, Timo; Jonassen, Marius

2017-04-01

For a large part of the year, the Arctic climate system is characterised by a stably stratified atmospheric boundary layer, with strong temperature inversions isolating the surface from the air aloft. These nversions are typically driven by longwave radiative cooling, warm-air advection aloft, or subsidence. All these mechanisms are affected by the synoptic sate of the atmosphere in the high Arctic. In this study we present data from an intensive measurement campaign in Svalbard in October 2014, when atmospheric profiles were measured with a tethered balloon in Adventdalen and Hornsund. In addition radiosonde soundings from Ny-Ålesund were analysed. A total of 115 individual profiles were analysed, almost all of them showing a surface-based temperature inversion. Our preliminary results show that the strongest and deepest inversions are observed at the beginning of a warm-air advection event, but as the temperature, wind and cloudiness increase the inversion strength and depth decrease rapidly. The inversion curvature parameter seems to be strongly dependent on the longwave radiative balance with the highest curvatures (strongest vertical temperature gradient close to the surface) associated with strong longwave radiative heat loss from the surface. The different processes affecting the stable atmospheric boundary layer during a low-pressure passage are determined, and the effects of the synoptic scale changes are isolated from those caused by local topographic forcing.

Sensitivity of boundary-layer stability to base-state distortions at high Mach numbers

NASA Astrophysics Data System (ADS)

Park, Junho; Zaki, Tamer

2017-11-01

The stability diagram of high-speed boundary layers has been established by evaluating the linear instability modes of the similarity profile, over wide ranges of Reynolds and Mach numbers. In real flows, however, the base state can deviate from the similarity profile. Both the base velocity and temperature can be distorted, for example due to roughness and thermal wall treatments. We review the stability problem of high-speed boundary layer, and derive a new formulation of the sensitivity to base-state distortion using forward and adjoint parabolized stability equations. The new formulation provides qualitative and quantitative interpretations on change in growth rate due to modifications of mean-flow and mean-temperature in heated high-speed boundary layers, and establishes the foundation for future control strategies. This work has been funded by the Air Force Office of Scientific Research (AFOSR) Grant: FA9550-16-1-0103.

Turbulence in a convective marine atmospheric boundary layer

NASA Technical Reports Server (NTRS)

Chou, S.-H.; Atlas, D.; Yeh, E.-N.

1986-01-01

The structure and kinetic energy budget of turbulence in the convective marine atmospheric boundary layer as observed by aircraft during a cold air outbreak have been studied using mixed layer scaling. The results are significantly different from those of previous studies under conditions closer to free convection. The normalized turbulent kinetic energy and turbulent transport are about twice those found during the Air Mass Transformation Experiment (AMTEX). This implies that for a given surface heating the present case is dynamically more active. The difference is mainly due to the greater importance of wind shear in the present case. This case is closer to the roll vortex regime, whereas AMTEX observed mesoscale cellular convection which is closer to free convection. Shear generation is found to provide a significant energy source, in addition to buoyancy production, to maintain a larger normalized turbulent kinetic energy and to balance a larger normalized dissipation. The interaction between turbulent pressure and divergence (i.e., pressure scrambling) is also found to transfer energy from the vertical to the horizontal components, and is expected to be stronger in roll vortices than in m esoscale cells. The sensible heat flux is found to fit well with a linear vertical profile in a clear or subcloud planetary boundary layer (PBL), in good agreement with the results of Lenschow et al., (1980). The heat flux ratio between the PBL top and the surface, derived from the linear fitted curve, is approximately -0.14, in good agreement with that derived from the lidar data for the same case. Near the PBL top, the heat flux profiles are consistent with those of Deardoff (1979) and Deardorff et al. (1980).

Tracking atmospheric boundary layer in tehran using combined lidar remote sensing and ground base measurements

NASA Astrophysics Data System (ADS)

Panahifar, Hossein; Khalesifard, Hamid

2018-04-01

The vertical structure of the atmospheric boundary layer (ABL) has been studied by use of a depolarized LiDAR over Tehran, Iran. The boundary layer height (BLH) remains under 1km, and its retrieval from LiDAR have been compared with sonding measurements and meteorological model outputs. It is also shown that the wind speed and direction as well as topography lead to the persistence of air pollution in Tehran. The situation aggravate in fall and winter due to temperature inversion.

Boundary-Layer-Ingesting Inlet Flow Control

NASA Technical Reports Server (NTRS)

Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.

2008-01-01

An experimental study was conducted to provide the first demonstration of an active flow control system for a flush-mounted inlet with significant boundary-layer-ingestion in transonic flow conditions. The effectiveness of the flow control in reducing the circumferential distortion at the engine fan-face location was assessed using a 2.5%-scale model of a boundary-layer-ingesting offset diffusing inlet. The inlet was flush mounted to the tunnel wall and ingested a large boundary layer with a boundary-layer-to-inlet height ratio of 35%. Different jet distribution patterns and jet mass flow rates were used in the inlet to control distortion. A vane configuration was also tested. Finally a hybrid vane/jet configuration was tested leveraging strengths of both types of devices. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow rates through the duct and the flow control actuators. The distortion and pressure recovery were measured at the aerodynamic interface plane. The data show that control jets and vanes reduce circumferential distortion to acceptable levels. The point-design vane configuration produced higher distortion levels at off-design settings. The hybrid vane/jet flow control configuration reduced the off-design distortion levels to acceptable ones and used less than 0.5% of the inlet mass flow to supply the jets.

Planetary Boundary Layer Simulation Using TASS

NASA Technical Reports Server (NTRS)

Schowalter, David G.; DeCroix, David S.; Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael

1996-01-01

Boundary conditions to an existing large-eddy simulation model have been changed in order to simulate turbulence in the atmospheric boundary layer. Several options are now available, including the use of a surface energy balance. In addition, we compare convective boundary layer simulations with the Wangara and Minnesota field experiments as well as with other model results. We find excellent agreement of modelled mean profiles of wind and temperature with observations and good agreement for velocity variances. Neutral boundary simulation results are compared with theory and with previously used models. Agreement with theory is reasonable, while agreement with previous models is excellent.

Atmospheric tides on Venus. III - The planetary boundary layer

NASA Technical Reports Server (NTRS)

Dobrovolskis, A. R.

1983-01-01

Diurnal solar heating of Venus' surface produces variable temperatures, winds, and pressure gradients within a shallow layer at the bottom of the atmosphere. The corresponding asymmetric mass distribution experiences a tidal torque tending to maintain Venus' slow retrograde rotation. It is shown that including viscosity in the boundary layer does not materially affect the balance of torques. On the other hand, friction between the air and ground can reduce the predicted wind speeds from about 5 to about 1 m/sec in the lower atmosphere, more consistent with the observations from Venus landers and descent probes. Implications for aeolian activity on Venus' surface and for future missions are discussed.

Influence of trans-boundary air pollution from China on multi-day high PM10 episodes in Seoul, Korea

NASA Astrophysics Data System (ADS)

Oh, H. R.; Ho, C. H.; Kim, J.; Chen, D.; Lee, S.; Choi, Y. S.; Chang, L. S.; Song, C. K.

2014-12-01

Air quality problems have become a serious global issue as it causes over 3 million deaths per year all over the world. With generations of massive air pollutants in China, the effects of trans-boundary transports of air pollutants on human health have become a serious international concern in East Asia. However, only a limited number of studies are available for providing scientific evidences for quantifying the sources and transports of air pollutants over major countries in East Asia. Here, it is shown that particulate matters originated from China played major role in the occurrence of multi-day (≥ 4 days) severe air pollution episodes in Seoul, Korea, in which the concentration of particulate matter of diameters ≤ 10 μm exceeds 100 μg m-3. Observations show that these multi-day severe air quality episodes occur when a strong high-pressure system resides over the eastern China - Korea region. Such a weather condition confines air pollutants within the atmospheric boundary layer and spread them by slow westerlies within the boundary layer from China into the neighboring countries. Understanding such dynamical processes is a key for advancing the predictability of trans-boundary air pollutants and their health impacts in East Asia as well as developing international measures to improve air quality for the region.

Further results related to the turbulent boundary layer with slot injection of helium

NASA Technical Reports Server (NTRS)

Larue, J. C.; Libby, P. A.

1978-01-01

Data from an experiment involving the slot injection of helium into a turbulent boundary layer in air are analyzed in terms of unconditioned and conditioned Favre-averages. The conditioning is based on two levels of helium concentration so that the contributions to the unconditioned statistics from air, helium, and mixture of these two gases can be determined. The distributions of intermittency associated with the two helium levels establish the domains of influence of air, helium, and mixture.

Removing Boundary Layer by Suction

NASA Technical Reports Server (NTRS)

Ackeret, J

1927-01-01

Through the utilization of the "Magnus effect" on the Flettner rotor ship, the attention of the public has been directed to the underlying physical principle. It has been found that the Prandtl boundary-layer theory furnishes a satisfactory explanation of the observed phenomena. The present article deals with the prevention of this separation or detachment of the flow by drawing the boundary layer into the inside of a body through a slot or slots in its surface.

Stability of spatially developing boundary layers

NASA Astrophysics Data System (ADS)

Govindarajan, Rama

1993-07-01

A new formulation of the stability of boundary-layer flows in pressure gradients is presented, taking into account the spatial development of the flow. The formulation assumes that disturbance wavelength and eigenfunction vary downstream no more rapidly than the boundary-layer thickness, and includes all terms of O(1) and O(R(exp -1)) in the boundary-layer Reynolds number R. Although containing the Orr-Sommerfeld operator, the present approach does not yield the Orr-Sommerfeld equation in any rational limit. In Blasius flow, the present stability equation is consistent with that of Bertolotti et al. (1992) to terms of O(R(exp -1)). For the Falkner-Skan similarity solutions neutral boundaries are computed without the necessity of having to march in space. Results show that the effects of spatial growth are striking in flows subjected to adverse pressure gradients.

Role of the boundary layer dynamics effects on an extreme air pollution event in Paris

NASA Astrophysics Data System (ADS)

Dupont, J.-C.; Haeffelin, M.; Badosa, J.; Elias, T.; Favez, O.; Petit, J. E.; Meleux, F.; Sciare, J.; Crenn, V.; Bonne, J. L.

2016-09-01

The physical and chemical aerosol properties are explored here based on ground-based observations in the Paris region to better understand the role of clouds, radiative fluxes and dynamics on aerosol loading during a heavy regional air pollution that occurred in March 2014 over North-Western Europe. This event is primarily characterized by a fine particle mass (PM2.5) increase from 10 to more than 120 μg m-3 and a simultaneous decrease of the horizontal visibility from 40 to 1 km, mainly due to significant formation of ammonium nitrate particles. The aerosol optical depth (AOD) at 550 nm increased steadily from about 0.06 on March 6 to more than 0.9 five days later. The scattering of the solar radiation by polluted particles induced, at the peak of the heavy pollution event, an instantaneous shortwave flux decrease of about 300 W m-2 for direct irradiance and an increase of about 150 W m-2 for diffuse irradiance (only scattering). The mean surface aerosol effect efficiency (effect per unit optical depth) is of about -80 W m-2 with a mean aerosol direct radiative effect of -23 W m-2. The dynamical and radiative processes that can be responsible for the diurnal cycle of PM2.5 in terms of amplitude and timing are investigated. A comparative analysis is performed for 4 consecutive days (between March 11 and 14), showing that the PM2.5 diurnal cycle can be modulated in time and amplitude by local processes such as the boundary layer depth development (ranging from 100 m to 1350 m), surface relative humidity (100%-35%), thermal structure (10 °C-16 °C for day/night amplitude), dynamics (wind speed ranging from 4 m s-1 to 1.5 m s-1) and turbulence (turbulent kinetic energy reaching 2 m2 s-2) near the surface and wind shear along the vertical. Finally, modeled and measured surface PM2.5 loadings are also compared here, notably illustrating the need of accurate boundary layer depth data for efficient air quality forecasts.

Flow unsteadiness effects on boundary layers

NASA Technical Reports Server (NTRS)

Murthy, Sreedhara V.

1989-01-01

The development of boundary layers at high subsonic speeds in the presence of either mass flux fluctuations or acoustic disturbances (the two most important parameters in the unsteadiness environment affecting the aerodynamics of a flight vehicle) was investigated. A high quality database for generating detailed information concerning free-stream flow unsteadiness effects on boundary layer growth and transition in high subsonic and transonic speeds is described. The database will be generated with a two-pronged approach: (1) from a detailed review of existing literature on research and wind tunnel calibration database, and (2) from detailed tests in the Boundary Layer Apparatus for Subsonic and Transonic flow Affected by Noise Environment (BLASTANE). Special instrumentation, including hot wire anemometry, the buried wire gage technique, and laser velocimetry were used to obtain skin friction and turbulent shear stress data along the entire boundary layer for various free stream noise levels, turbulence content, and pressure gradients. This database will be useful for improving the correction methodology of applying wind tunnel test data to flight predictions and will be helpful for making improvements in turbulence modeling laws.

Experiments on aerosol-induced cooling in the nocturnal boundary layer

NASA Astrophysics Data System (ADS)

Sreenivas, K.; Singh, D. K.; Vk, P.; Mukund, V.; Subramanian, G.

2012-12-01

In the nocturnal boundary layer (NBL), under calm & clear-sky conditions, radiation is the principal mode of heat transfer & it determines the temperature distribution close to the ground. Radiative processes thus influence the surface energy budget, & play a decisive role in many micro-meteorological processes including the formation of radiation-fog & inversion layer. Here, we report hyper-cooling of air layers close to the ground that has a radiative origin. Resulting vertical temperature distribution has an anomalous profile with an elevated minimum few decimetres above the ground (known as Lifted Temperature Minimum; LTM). Even though the first observation of this type of profile dates back to 1930s, its origin has not been explained till recently. We report field experiments to elucidate effects of emissivity and other physical properties of the ground on the LTM profile. Field observations clearly indicate that LTM-profiles are observed as a rule in the lowest meter of the NBL. We also demonstrate that the air-layer near the ground, rather than the ground itself, leads the post sunset cooling. This fact changes the very nature of the sensible heat-flux boundary condition. A laboratory experimental setup has been developed that can reproduce LTM. Lab-experiments demonstrate that the high cooling rates observed in the field experiments arise from the presence of aerosols & the intensity of cooling is proportional to aerosol concentration (Fig-1). We have also captured penetrative convection cells in the field experiments (Fig-2). Results presented here thus help in parameterizing transport processes in the NBL.

Effect of real-time boundary wind conditions on the air flow and pollutant dispersion in an urban street canyon—Large eddy simulations

NASA Astrophysics Data System (ADS)

Zhang, Yun-Wei; Gu, Zhao-Lin; Cheng, Yan; Lee, Shun-Cheng

2011-07-01

Air flow and pollutant dispersion characteristics in an urban street canyon are studied under the real-time boundary conditions. A new scheme for realizing real-time boundary conditions in simulations is proposed, to keep the upper boundary wind conditions consistent with the measured time series of wind data. The air flow structure and its evolution under real-time boundary wind conditions are simulated by using this new scheme. The induced effect of time series of ambient wind conditions on the flow structures inside and above the street canyon is investigated. The flow shows an obvious intermittent feature in the street canyon and the flapping of the shear layer forms near the roof layer under real-time wind conditions, resulting in the expansion or compression of the air mass in the canyon. The simulations of pollutant dispersion show that the pollutants inside and above the street canyon are transported by different dispersion mechanisms, relying on the time series of air flow structures. Large scale air movements in the processes of the air mass expansion or compression in the canyon exhibit obvious effects on pollutant dispersion. The simulations of pollutant dispersion also show that the transport of pollutants from the canyon to the upper air flow is dominated by the shear layer turbulence near the roof level and the expansion or compression of the air mass in street canyon under real-time boundary wind conditions. Especially, the expansion of the air mass, which features the large scale air movement of the air mass, makes more contribution to the pollutant dispersion in this study. Comparisons of simulated results under different boundary wind conditions indicate that real-time boundary wind conditions produces better condition for pollutant dispersion than the artificially-designed steady boundary wind conditions.

Exact solutions of laminar-boundary-layer equations with constant property values for porous wall with variable temperature

NASA Technical Reports Server (NTRS)

Donoughe, Patrick L; Livingood, John N B

1955-01-01

Exact solution of the laminar-boundary-layer equations for wedge-type flow with constant property values are presented for transpiration-cooled surfaces with variable wall temperatures. The difference between wall and stream temperature is assumed proportional to a power of the distance from the leading edge. Solutions are given for a Prandtl number of 0.7 and ranges of pressure-gradient, cooling-air-flow, and wall-temperature-gradient parameters. Boundary-layer profiles, dimensionless boundary-layer thicknesses, and convective heat-transfer coefficients are given in both tabular and graphical form. Corresponding results for constant wall temperature and for impermeable surfaces are included for comparison purposes.

Shear-induced surface alignment of polymer dispersed liquid crystal microdroplets on the boundary layer

NASA Technical Reports Server (NTRS)

Parmar, D. S.; Singh, J. J.

1993-01-01

Polymer dispersed liquid crystal thin films have been deposited on a glass substrate, utilizing the processes of polymerization and solvent evaporation induced phase separation. Liquid crystal microdroplets trapped on the upper surface of the thin film respond to the shear stress due to air or gas flow on the surface layer. Response to an applied step shear stress input on the surface layer has been measured by measuring the time response of the transmitted light intensity. Initial results on the measurements of the light transmission as a function of the air flow differential pressure indicate that these systems offer features suitable for boundary layer and gas flow sensors.

Characterizing the structure of the atmospheric boundary layer under heavy pollution over urban area, Beijing, China

NASA Astrophysics Data System (ADS)

WANG, L.; Gao, Z.; Huang, M.; Fan, S.; Miao, S.

2017-12-01

A better understanding of the interactions between the occurrence of air pollution and the structure of the atmospheric boundary layer (ABL) is very important for the air-pollution-relevant investigations. In this study, the ABL structure was studied by using a Doppler lidar, a Depolarization lidar and the 325-m meteorological tower in Beijing during the winter 2016-2017, in particular during heavy polluted episodes. The planetary boundary layer (PBL) depth was estimated by using lidar data. The characteristics of wind, temperature and relative humidity at 15 levels, turbulence transport and radiation balance at three levels (47, 140 and 280 m) were analyzed by using the observational data collected on the 325-m meteorological tower.

Measurements in a synthetic turbulent boundary layer

NASA Astrophysics Data System (ADS)

Arakeri, J. H.; Coles, D. E.

Some measurements in a synthetic turbulent boundary layer (SBL) are reported. The main diagnostic tool is an X-wire probe. The velocity of the large eddies is determined to be 0.842 times the freestream velocity. The mean properties of the SBL are reasonably close to those of a natural turbulent boundary layer. The large eddy in the SBL appears to be a pair of counterrotating eddies in the stream direction, inclined at a shallow angle and occupying much of the boundary-layer thickness.

Physics of magnetospheric boundary layers

NASA Technical Reports Server (NTRS)

Cairns, Iver H.

1995-01-01

This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.

Turbulence structure of the marine stable boundary layer over the Baltic Sea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smedman, A.S.; Hoegstroem, U.

For more than half of the year the land surfaces surrounding the Baltic Sea is warmer than the sea surface, and the marine boundary layer over the Baltic is stable. Observations, at various sites in the Baltic Sea area during the last decade. also indicate frequent occurrence of low-level jets at the top of the stable boundary layer. In many cases the marine jet can be considered as an analogy in space to the evolution of the nocturnal jet with time. The frictional decoupling occurs when warm air over the land is flowing out over the sea. Data from twomore » areas together with model simulations are used in this study to characterize turbulence structure in the marine boundary layer. The measurements include profiles of wind and temperature on towers situated at two isolated islands, together with turbulence recordings and aircraft measurements. Also wave height and water surface temperature have been measured. The model simulations are performed with a second-order closure model.« less

Unsteady boundary-layer injection

NASA Technical Reports Server (NTRS)

Telionis, D. P.; Jones, G. S.

1981-01-01

The boundary-layer equations for two-dimensional incompressible flow are integrated numerically for the flow over a flat plate and a Howarth body. Injection is introduced either impulsively or periodically along a narrow strip. Results indicate that injection perpendicular to the wall is transmitted instantly across the boundary layer and has little effect on the velocity profile parallel to the wall. The effect is a little more noticeable for flows with adverse pressure gradients. Injection parallel to the wall results in fuller velocity profiles. Parallel and oscillatory injection appears to influence the mean. The amplitude of oscillation decreases with distance from the injection strip but further downstream it increases again in a manner reminiscent of an unstable process.

Swept Impinging Oblique Shock/Boundary-Layer Interactions

NASA Astrophysics Data System (ADS)

Little, Jesse; Threadgill, James; Stab, Ilona

2016-11-01

Oblique shock waves impinging on boundary layers are common flow features associated with high-speed flows around complex body geometries and through internal channel flows. The increasingly three-dimensional surface geometries of modern vehicles has led to a prevalence of complex shock/boundary-layer interactions. Sweep has been observed to vary the interaction structure, unsteadinesses, and similarity scalings. Sharp-fins and highly-swept ramps have been noted to induce a quasi-conical development of the interaction, in contrast to a quasi-cylindrical scaling observed in low-sweep interactions. However, swept impinging oblique shock cases have largely been overlooked, with evidence of only cylindrical similarities observed in hypersonic conditions. Flow deflection beyond the maximum turning angle has been proposed as the mechanism for conical interaction development but such behavior has not been established for the present configuration. This study examines the effect of sweep on the interaction induced by a 12.5° generator in Mach 2.3 flow using oil-flow, Schlieren and PIV. Results document the development of similarity scalings at various angles of sweep, and highlight the difficulty in replicating a quasi-infinite span conditions in a moderately sized wind tun Supported by the Air Force Office of Scientific Research (FA9550-15-1-0430) and Raytheon Missile Systems.

Molecular Diagnostics of Diffusive Boundary Layers

NASA Astrophysics Data System (ADS)

Rawlings, J. M. C.; Hartquist, T. W.

1997-10-01

We have examined the chemistry in thin (<~0.01 pc) boundary layers between dark star-forming cores and warm, shocked T Tauri winds on the assumption that turbulence-driven diffusion occurs within them. The results indicate that emissions from C+, CH, OH, H2O and the J = 6 --> 5 transition of CO, among others, may serve as diagnostics of the boundary layers.

Aerothermodynamic Testing and Boundary Layer Trip Sizing of the HIFiRE Flight 1 Vehicle

NASA Technical Reports Server (NTRS)

Berger, Karen T.; Greene, Frank A.; Kimmel, Roger; Alba, Christopher; Johnson, Heath

2008-01-01

An experimental wind tunnel test was conducted in the NASA Langley Research Center s 20-Inch Mach 6 Air Tunnel in support of the Hypersonic International Flight Research Experimentation Program. The information in this article is focused on the Flight 1 configuration, the first in a series of flight experiments. The article documents experimental measurements made over a Reynolds numbers range of 2.1x10(exp 6)/ft to 5.6x10(exp 6)/ft and angles of attack of -5 to +5 deg on several scaled ceramic heat transfer models of the Flight 1 configuration. Global heat transfer was measured using phosphor thermography and the resulting images and heat transfer distributions were used to infer the state of the boundary layer on the vehicle windside and leeside surfaces. Boundary layer trips were used to force the boundary layer turbulent and the experimental data highlighted in this article were used to size and place the boundary layer trip for the flight vehicle. The required height of the flight boundary layer trip was determined to be 0.079 in and the trip was moved from the design location of 7.87 in to 20.47 in to ensure that augmented heating would not impact the laminar side of the vehicle. Allowable roughness was selected to be 3.2x10(exp -3) in.

On optical imaging through aircraft turbulent boundary layers

NASA Technical Reports Server (NTRS)

Sutton, G. W.

1980-01-01

Optical resolution quality as affected by aircraft turbulent boundary layers is analyzed. Wind-tunnel data was analyzed to obtained the variation of boundary layer turbulence scale length and mass density rms fluctuations with Mach number. The data gave good agreement with a mass density fluctuation turbulence spectrum that is either isotropic of orthogonally anisotropic. The data did not match an isotropic turbulence velocity spectrum which causes an anisotropic non-orthogonal mass density fluctuation spectrum. The results indicate that the average mass density rms fluctuation is about 10% of the maximum mass density across the boundary layer and that the transverse turbulence scale size is about 10% of the boundary layer thickness. The results indicate that the effect of the turbulent boundary layer is large angle scattering which decreases contrast but not resolution. Using extinction as a criteria the range of acceptable aircraft operating conditions are given.

Experimental Investigation of Soil and Atmospheric Conditions on the Momentum, Mass, and Thermal Boundary Layers Above the Land Atmosphere Interface

NASA Astrophysics Data System (ADS)

Trautz, A.; Smits, K. M.; Illangasekare, T. H.; Schulte, P.

2014-12-01

The purpose of this study is to investigate the impacts of soil conditions (i.e. soil type, saturation) and atmospheric forcings (i.e. velocity, temperature, relative humidity) on the momentum, mass, and temperature boundary layers. The atmospheric conditions tested represent those typically found in semi-arid and arid climates and the soil conditions simulate the three stages of evaporation. The data generated will help identify the importance of different soil conditions and atmospheric forcings with respect to land-atmospheric interactions which will have direct implications on future numerical studies investigating the effects of turbulent air flow on evaporation. The experimental datasets generated for this study were performed using a unique climate controlled closed-circuit wind tunnel/porous media facility located at the Center for Experimental Study of Subsurface Environmental Processes (CESEP) at the Colorado School of Mines. The test apparatus consisting of a 7.3 m long porous media tank and wind tunnel, were outfitted with a sensor network to carefully measure wind velocity, air and soil temperature, relative humidity, soil moisture, and soil air pressure. Boundary layer measurements were made between the heights of 2 and 500 mm above the soil tank under constant conditions (i.e. wind velocity, temperature, relative humidity). The soil conditions (e.g. soil type, soil moisture) were varied between datasets to analyze their impact on the boundary layers. Experimental results show that the momentum boundary layer is very sensitive to the applied atmospheric conditions and soil conditions to a much less extent. Increases in velocity above porous media leads to momentum boundary layer thinning and closely reflect classical flat plate theory. The mass and thermal boundary layers are directly dependent on both atmospheric and soil conditions. Air pressure within the soil is independent of atmospheric temperature and relative humidity - wind velocity and soil

Laser transit anemometer and Pitot probe comparative measurements in a sharp cone boundary layer at Mach 4

NASA Technical Reports Server (NTRS)

Hunter, W. W., Jr.; Ocheltree, S. L.; Russ, C. E., Jr.

1991-01-01

Laser transit anemometer (LTA) measurements of a 7 degree sharp cone boundary layer were conducted in the Air Force/AEDC Supersonic Tunnel A Mach 4 flow field. These measurements are compared with Pitot probe measurements and tricone theory provided by AEDC staff. Measurements were made both in laminar and turbulent boundary layers of the model. Comparison of LTA measurements with theory showed agreement to better than 1 percent for the laminar boundary layer cases. This level of agreement was obtained after small position corrections, 0.01 to 0.6 mm, were applied to the experimental data sets. Pitot probe data when compared with theory also showed small positioning errors. The Pitot data value was also limited due to probe interference with the flow near the model. The LTA turbulent boundary layer data indicated a power law dependence of 6.3 to 6.9. The LTA data was analyzed in the time (Tau) domain in which it was obtained and in the velocity domain. No significant differences were noted between Tau and velocity domain results except in one turbulent boundary layer case.

Re-Innovating Recycling for Turbulent Boundary Layer Simulations

NASA Astrophysics Data System (ADS)

Ruan, Joseph; Blanquart, Guillaume

2017-11-01

Historically, turbulent boundary layers along a flat plate have been expensive to simulate numerically, in part due to the difficulty of initializing the inflow with ``realistic'' turbulence, but also due to boundary layer growth. The former has been resolved in several ways, primarily dedicating a region of at least 10 boundary layer thicknesses in width to rescale and recycle flow or by extending the region far enough downstream to allow a laminar flow to develop into turbulence. Both of these methods are relatively costly. We propose a new method to remove the need for an inflow region, thus reducing computational costs significantly. Leveraging the scale similarity of the mean flow profiles, we introduce a coordinate transformation so that the boundary layer problem can be solved as a parallel flow problem with additional source terms. The solutions in the new coordinate system are statistically homogeneous in the downstream direction and so the problem can be solved with periodic boundary conditions. The present study shows the stability of this method, its implementation and its validation for a few laminar and turbulent boundary layer cases.

Cloud-Scale Numerical Modeling of the Arctic Boundary Layer

NASA Technical Reports Server (NTRS)

Krueger, Steven K.

1998-01-01

The interactions between sea ice, open ocean, atmospheric radiation, and clouds over the Arctic Ocean exert a strong influence on global climate. Uncertainties in the formulation of interactive air-sea-ice processes in global climate models (GCMs) result in large differences between the Arctic, and global, climates simulated by different models. Arctic stratus clouds are not well-simulated by GCMs, yet exert a strong influence on the surface energy budget of the Arctic. Leads (channels of open water in sea ice) have significant impacts on the large-scale budgets during the Arctic winter, when they contribute about 50 percent of the surface fluxes over the Arctic Ocean, but cover only 1 to 2 percent of its area. Convective plumes generated by wide leads may penetrate the surface inversion and produce condensate that spreads up to 250 km downwind of the lead, and may significantly affect the longwave radiative fluxes at the surface and thereby the sea ice thickness. The effects of leads and boundary layer clouds must be accurately represented in climate models to allow possible feedbacks between them and the sea ice thickness. The FIRE III Arctic boundary layer clouds field program, in conjunction with the SHEBA ice camp and the ARM North Slope of Alaska and Adjacent Arctic Ocean site, will offer an unprecedented opportunity to greatly improve our ability to parameterize the important effects of leads and boundary layer clouds in GCMs.

Boundary Layer Flow of Air Over Water on a Flat Plate

DTIC Science & Technology

1993-08-01

similar (or coupled self -similar) solution appears to be a global attractor for all initial conditions. 2 Governing Equations A water film of height y...assumptions are self -consistent. The reader may verify that the solution (13) with c(x) given by (16) is self -similar (satisfies (24) without the the...attractor for all solutions of this non-similar family. Self similar boundary layers depend only on q and not on 4. The ý derivatives of u, v and y* may

Blended Wing Body Systems Studies: Boundary Layer Ingestion Inlets With Active Flow Control

NASA Technical Reports Server (NTRS)

Geiselhart, Karl A. (Technical Monitor); Daggett, David L.; Kawai, Ron; Friedman, Doug

2003-01-01

A CFD analysis was performed on a Blended Wing Body (BWB) aircraft with advanced, turbofan engines analyzing various inlet configurations atop the aft end of the aircraft. The results are presented showing that the optimal design for best aircraft fuel efficiency would be a configuration with a partially buried engine, short offset diffuser using active flow control, and a D-shaped inlet duct that partially ingests the boundary layer air in flight. The CFD models showed that if active flow control technology can be satisfactorily developed, it might be able to control the inlet flow distortion to the engine fan face and reduce the powerplant performance losses to an acceptable level. The weight and surface area drag benefits of a partially submerged engine shows that it might offset the penalties of ingesting the low energy boundary layer air. The combined airplane performance of such a design might deliver approximately 5.5% better aircraft fuel efficiency over a conventionally designed, pod-mounted engine.

Relaxation of the accelerating-gas boundary layer to the test-gas boundary layer on a flat plate in an expansion tube

NASA Technical Reports Server (NTRS)

Gupta, R. N.; Trimpi, R. L.

1973-01-01

An analytic investigation of the relaxation of the accelerating-gas boundary layer to the test-gas boundary layer over a flat plate mounted in an expansion tube has been conducted. In this treatment, nitrogen has been considered as the test gas and helium as the accelerating gas. The problem is analyzed in two conically similar limits: (1) when the time lag between the arrival of the shock and the interface at the leading edge of the plate is very large, and (2) when this time lag is negligible. The transient laminar boundary-layer equations of a perfect binary-gas mixture are taken as the flow governing equations. These coupled equations have been solved numerically by Gauss-Seidel line-relaxation method. The results predict the transient behavior as well as the time required for an all-helium accelerating-gas boundary layer to relax to an all-nitrogen boundary layer.

Dynamic behavior of an unsteady trubulent boundary layer

NASA Technical Reports Server (NTRS)

Parikh, P. G.; Reynolds, W. C.; Jayaramen, R.; Carr, L. W.

1981-01-01

Experiments on an unsteady turbulent boundary layer are reported in which the upstream portion of the flow is steady (in the mean) and in the downstream region, the boundary layer sees a linearly decreasing free stream velocity. This velocity gradient oscillates in time, at frequencies ranging from zero to approximately the bursting frequency. For the small amplitude, the mean velocity and mean turbulence intensity profiles are unaffected by the oscillations. The amplitude of the periodic velocity component, although as much as 70% greater than that in the free stream for very low frequencies, becomes equal to that in the free stream at higher frequencies. At high frequencies, both the boundary layer thickness and the Reynolds stress distribution across the boundary layer become frozen. The behavior at higher amplitude is quite similar. At sufficiently high frequencies, the boundary layer thickness remains frozen at the mean value over the oscillation cycle, even though flow reverses near the wall during a part of the cycle.

The boundary layer moist static energy budget: Convection picks up moisture and leaves footprints in the marine boundary layer

NASA Astrophysics Data System (ADS)

de Szoeke, S. P.

2017-12-01

Averaged over the tropical marine boundary layer (BL), 130 W m-2 turbulent surface moist static energy (MSE) flux, 120 W m-2 of which is evaporation, is balanced by upward MSE flux at the BL top due to 1) incorporation of cold air by downdrafts from deep convective clouds, and 2) turbulent entrainment of dry air into the BL. Cold saturated downdraft air, and warm clear air entrained into the BL have distinct thermodynamic properties. This work observationally quantifies their respective MSE fluxes in the central Indian Ocean in 2011, under different convective conditions of the intraseasonal (40-90 day) Madden Julian oscillation (MJO). Under convectively suppressed conditions, entrainment and downdraft fluxes export equal shares (60 W m-2) of MSE from the BL. Downdraft fluxes are more variable, increasing for stronger convection. In the convectively active phase of the MJO, downdrafts export 90 W m-2 from the BL, compared to 40 W m-2 by entrainment. These processes that control the internal, latent (condensation), and MSE of the tropical marine atmospheric BL determine the parcel buoyancy and strength of tropical deep convection.

Vertical distribution of ozone and VOCs in the low boundary layer of Mexico City

NASA Astrophysics Data System (ADS)

Velasco, E.; Márquez, C.; Bueno, E.; Bernabé, R. M.; Sánchez, A.; Fentanes, O.; Wöhrnschimmel, H.; Cárdenas, B.; Kamilla, A.; Wakamatsu, S.; Molina, L. T.

2007-08-01

The evolution of ozone and 13 volatile organic compounds (VOCs) in the boundary layer of Mexico City was investigated during 2000-2004 to improve our understanding of the complex interactions between those trace gases and meteorological variables, and their influence on the air quality of a polluted megacity. A tethered balloon, fitted with electrochemical and meteorological sondes, was used to obtain detailed vertical profiles of ozone and meteorological parameters up to 1000 m above ground during part of the diurnal cycle (02:00-18:00 h). VOCs samples were collected up to 200 m by pumping air to canisters with a Teflon tube attached to the tether line. Overall, features of these profiles were found to be consistent with a simple picture of nighttime trapping of ozone in an upper residual layer and of VOCs in a shallow unstable layer above the ground. After sunrise an ozone balance is determined by photochemical production, entrainment from the upper residual layer and destruction by titration with NO, delaying the ground-level ozone rise by 2 h. The subsequent evolution of the conductive boundary layer and vertical distribution of pollutants are discussed in terms of the energy balance, the presence of turbulence and the atmospheric stability.

Characteristics of nocturnal coastal boundary layer in Ahtopol based on averaged SODAR profiles

NASA Astrophysics Data System (ADS)

Barantiev, Damyan; Batchvarova, Ekaterina; Novitzky, Mikhail

2014-05-01

The ground-based remote sensing instruments allow studying the wind regime and the turbulent characteristics of the atmosphere with height, achieving new knowledge and solving practical problems, such as air quality assessments, mesoscale models evaluation with high resolution data, characterization of the exchange processes between the surface and the atmosphere, the climate comfort conditions and the risk for extreme events, etc. Very important parameter in such studies is the height of the atmospheric boundary layer. Acoustic remote sensing data of the coastal atmospheric boundary layer were explored based on over 4-years continuous measurements at the meteorological observatory of Ahtopol (Bulgarian Southern Black Sea Coast) under Bulgarian - Russian scientific agreement. Profiles of 12 parameters from a mid-range acoustic sounding instrument type SCINTEC MFAS are derived and averaged up to about 600 m according filtering based on wind direction (land or sea type of night fowls). From the whole investigated period of 1454 days with 10-minute resolution SODAR data 2296 profiles represented night marine air masses and 1975 profiles represented the night flow from land during the months May to September. Graphics of averaged profiles of 12 SODAR output parameters with different availability of data in height are analyzed for both cases. A marine boundary-layer height of about 300 m is identified in the profiles of standard deviation of vertical wind speed (σw), Turbulent Kinetic Energy (TKE) and eddy dissipation rate (EDR). A nocturnal boundary-layer height of about 420 m was identified from the profiles of the same parameters under flows from land condition. In addition, the Buoyancy Production (BP= σw3/z) profiles were calculated from the standard deviation of the vertical wind speed and the height z above ground.

Subsidence in the Nocturnal Boundary Layer.

NASA Astrophysics Data System (ADS)

Carlson, Merrilee A.; Stull, Roland B.

1986-08-01

Nights with clear skies and strong radiative cooling that favor the formation of statically stable nocturnal boundary layers (NBL) are also those nights most likely to have subsidence, because of the presence of synoptic high-pressure regions. The divergence associated with subsidence laterally removes some of the chilled nocturnal boundary layer air causing the NBL to not grow as rapidly as would otherwise be expected. An equivalent interpretation is that subsidence-induced heating partially counteracts the radiative and turbulent cooling.A new form of nocturnal integral depth scale, HT, is introduced that incorporates the heating and cooling contributions at night. This scale can be used with a variety of idealized temperature profile shapes, including slab, linear, and exponential. It is shown that observed values of subsidence for two case studies can reduce the NBL growth rate, as measured by HT/t, by 5 to 50% and can cause corresponding errors in the estimation of accumulated cooling unless there is a proper accounting of subsidence.Subsidence plays a very minor role close to the ground, but for the case studies presented here its heating rate increases with height and becomes of comparable magnitude to the cooling rates of turbulence and radiation within the top third of the NBL. Although no adequate measurements of horizontal advective effects were available for the case studies used here, it appears from an energy balance that advection must not be neglected because its magnitude can be as large as turbulence and radiation.

Modeling large wind farms in conventionally neutral atmospheric boundary layers under varying initial conditions

NASA Astrophysics Data System (ADS)

Allaerts, Dries; Meyers, Johan

2014-05-01

Atmospheric boundary layers (ABL) are frequently capped by an inversion layer limiting the entrainment rate and boundary layer growth. Commonly used analytical models state that the entrainment rate is inversely proportional to the inversion strength. The height of the inversion turns out to be a second important parameter. Conventionally neutral atmospheric boundary layers (CNBL) are ABLs with zero surface heat flux developing against a stratified free atmosphere. In this regime the inversion-filling process is merely driven by the downward heat flux at the inversion base. As a result, CNBLs are strongly dependent on the heating history of the boundary layer and strong inversions will fail to erode during the course of the day. In case of large wind farms, the power output of the farm inside a CNBL will depend on the height and strength of the inversion above the boundary layer. On the other hand, increased turbulence levels induced by wind farms may partially undermine the rigid lid effect of the capping inversion, enhance vertical entrainment of air into the farm, and increase boundary layer growth. A suite of large eddy simulations (LES) is performed to investigate the effect of the capping inversion on the conventionally neutral atmospheric boundary layer and on the wind farm performance under varying initial conditions. For these simulations our in-house pseudo-spectral LES code SP-Wind is used. The wind turbines are modelled using a non-rotating actuator disk method. In the absence of wind farms, we find that a decrease in inversion strength corresponds to a decrease in the geostrophic angle and an increase in entrainment rate and geostrophic drag. Placing the initial inversion base at higher altitudes further reduces the effect of the capping inversion on the boundary layer. The inversion can be fully neglected once it is situated above the equilibrium height that a truly neutral boundary layer would attain under the same external conditions such as

An Examination of the Effect of Boundary Layer Ingestion on Turboelectric Distributed Propulsion Systems

NASA Technical Reports Server (NTRS)

Felder, James L.; Kim, Huyn Dae; Brown, Gerald V.; Chu, Julio

2011-01-01

A Turboelectric Distributed Propulsion (TeDP) system differs from other propulsion systems by the use of electrical power to transmit power from the turbine to the fan. Electrical power can be efficiently transmitted over longer distances and with complex topologies. Also the use of power inverters allows the generator and motors speeds to be independent of one another. This decoupling allows the aircraft designer to place the core engines and the fans in locations most advantageous for each. The result can be very different installation environments for the different devices. Thus the installation effects on this system can be quite different than conventional turbofans where the fan and core both see the same installed environments. This paper examines a propulsion system consisting of two superconducting generators, each driven by a turboshaft engine located so that their inlets ingest freestream air, superconducting electrical transmission lines, and an array of superconducting motor driven fan positioned across the upper/rear fuselage area of a hybrid wing body aircraft in a continuous nacelle that ingests all of the upper fuselage boundary layer. The effect of ingesting the boundary layer on the design of the system with a range of design pressure ratios is examined. Also the impact of ingesting the boundary layer on off-design performance is examined. The results show that when examining different design fan pressure ratios it is important to recalculate of the boundary layer mass-average Pt and MN up the height for each inlet height during convergence of the design point for each fan design pressure ratio examined. Correct estimation of off-design performance is dependent on the height of the column of air measured from the aircraft surface immediately prior to any external diffusion that will flow through the fan propulsors. The mass-averaged Pt and MN calculated for this column of air determine the Pt and MN seen by the propulsor inlet. Since the height

Superfluid Boundary Layer.

PubMed

Stagg, G W; Parker, N G; Barenghi, C F

2017-03-31

We model the superfluid flow of liquid helium over the rough surface of a wire (used to experimentally generate turbulence) profiled by atomic force microscopy. Numerical simulations of the Gross-Pitaevskii equation reveal that the sharpest features in the surface induce vortex nucleation both intrinsically (due to the raised local fluid velocity) and extrinsically (providing pinning sites to vortex lines aligned with the flow). Vortex interactions and reconnections contribute to form a dense turbulent layer of vortices with a nonclassical average velocity profile which continually sheds small vortex rings into the bulk. We characterize this layer for various imposed flows. As boundary layers conventionally arise from viscous forces, this result opens up new insight into the nature of superflows.

Boundary layer effects on liners for aircraft engines

NASA Astrophysics Data System (ADS)

Gabard, Gwénaël

2016-10-01

The performance of acoustic treatments installed on aircraft engines is strongly influenced by the boundary layer of the grazing flow on the surface of the liner. The parametric study presented in this paper illustrates the extent of this effect and identifies when it is significant. The acoustic modes of a circular duct with flow are calculated using a finite difference method. The parameters are representative of the flow conditions, liners and sound fields found in current turbofan engines. Both the intake and bypass ducts are considered. Results show that there is a complex interplay between the boundary layer thickness, the direction of propagation and the liner impedance and that the boundary layer can have a strong impact on liner performance for typical configurations (including changes of the order of 30 dB on the attenuation of modes associated with tonal fan noise). A modified impedance condition including the effect of a small but finite boundary layer thickness is considered and compared to the standard Myers condition based on an infinitely thin boundary layer. We show how this impedance condition can be implemented in a mode calculation method by introducing auxiliary variables. This condition is able to capture the trends associated with the boundary layer effects and in most cases provides improved predictions of liner performance.

Transitions of cloud-topped marine boundary layers characterized by AIRS, MODIS, and a large eddy simulation model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yue, Qing; Kahn, Brian; Xiao, Heng

2013-08-16

Cloud top entrainment instability (CTEI) is a hypothesized positive feedback between entrainment mixing and evaporative cooling near the cloud top. Previous theoretical and numerical modeling studies have shown that the persistence or breakup of marine boundary layer (MBL) clouds may be sensitive to the CTEI parameter. Collocated thermodynamic profile and cloud observations obtained from the Atmospheric Infrared Sounder (AIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments are used to quantify the relationship between the CTEI parameter and the cloud-topped MBL transition from stratocumulus to trade cumulus in the northeastern Pacific Ocean. Results derived from AIRS and MODIS are compared withmore » numerical results from the UCLA large eddy simulation (LES) model for both well-mixed and decoupled MBLs. The satellite and model results both demonstrate a clear correlation between the CTEI parameter and MBL cloud fraction. Despite fundamental differences between LES steady state results and the instantaneous snapshot type of observations from satellites, significant correlations for both the instantaneous pixel-scale observations and the long-term averaged spatial patterns between the CTEI parameter and MBL cloud fraction are found from the satellite observations and are consistent with LES results. This suggests the potential of using AIRS and MODIS to quantify global and temporal characteristics of the cloud-topped MBL transition.« less

Turbulent boundary layers over nonstationary plane boundaries

NASA Technical Reports Server (NTRS)

Roper, A. T.; Gentry, G. L., Jr.

1978-01-01

Methods of predicting integral parameters and skin friction coefficients of turbulent boundary layers developing over moving ground planes were evaluated. The three methods evaluated were: relative integral parameter method; relative power law method; and modified law of the wall method.

Heat and mass transfer in a dissociated laminar boundary layer of air with consideration of the finite rate of chemical reaction

NASA Technical Reports Server (NTRS)

Oyegbesan, A. O.; Algermissen, J.

1986-01-01

A numerical investigation of heat and mass transfer in a dissociated laminar boundary layer of air on an isothermal flat plate is carried out for different degrees of cooling of the wall. A finite-difference chemical model is used to study elementary reactions involving NO2 and N2O. The analysis is based on equations of continuity, momentum, energy, conservation and state for the two-dimensional viscous flow of a reacting multicomponent mixtures. Attention is given to the effects of both catalyticity and noncatalyticity of the wall.

Control of a shock wave-boundary layer interaction using localized arc filament plasma actuators

NASA Astrophysics Data System (ADS)

Webb, Nathan Joseph

Supersonic flight is currently possible, but expensive. Inexpensive supersonic travel will require increased efficiency of high-speed air entrainment, an integral part of air-breathing propulsion systems. Although mixed compression inlet geometry can significantly improve entrainment efficiency, numerous Shock Wave-Boundary Layer Interactions (SWBLIs) are generated in this configuration. The boundary layer must therefore develop through multiple regions of adverse pressure gradient, causing it to thicken, and, in severe cases, separate. The associated increase in unsteadiness can have adverse effects on downstream engine hardware. The most severe consequence of these interactions is the increased aerodynamic blockage generated by the thickened boundary layer. If the increase is sufficient, it can choke the flow, causing inlet unstart, and resulting in a loss of thrust and high transient forces on the engine, airframe, and aircraft occupants. The potentially severe consequences associated with SWBLIs require flow control to ensure proper operation. Traditionally, boundary layer bleed has been used to control the interaction. Although this method is effective, it has inherent efficiency penalties. Localized Arc Filament Plasma Actuators (LAFPAs) are designed to generate perturbations for flow control. Natural flow instabilities act to amplify certain perturbations, allowing the LAFPAs to control the flow with minimal power input. LAFPAs also have the flexibility to maintain control over a variety of operating conditions. This work seeks to examine the effectiveness of LAFPAs as a separation control method for an oblique, impinging SWBLI. The low frequency unsteadiness in the reflected shock was thought to be the natural manifestation of a Kelvin-Helmholtz instability in the shear layer above the separation region. The LAFPAs were therefore placed upstream of the interaction to allow their perturbations to convect to the receptivity region (near the shear layer origin

Modeling Electrothermal Plasma with Boundary Layer Effects

NASA Astrophysics Data System (ADS)

AlMousa, Nouf Mousa A.

Electrothermal plasma sources produce high-density (1023-10 28 /m3) and high temperature (1-5 eV) plasmas that are of interest for a variety of applications such as hypervelocity launch devices, fusion reactor pellet injectors, and pulsed thrusters for small satellites. Also, the high heat flux (up to 100 GW/m2) and high pressure (100s MPa) of electrothermal (ET) plasmas allow for the use of such facilities as a source of high heat flux to simulate off-normal events in Tokamak fusion reactors. Off-normal events like disruptions, thermal and current quenches, are the perfect recipes for damage of plasma facing components (PFC). Successful operation of a fusion reactor requires comprehensive understanding of material erosion behavior. The extremely high heat fluxes deposited in PFCs melt and evaporate or directly sublime the exposed surfaces, which results in a thick vapor/melt boundary layer adjacent to the solid wall structure. The accumulating boundary layers provide a self-protecting nature by attenuating the radiant energy transport to the PFCs. The ultimate goal of this study is to develop a reliable tool to adequately simulate the effect of the boundary layers on the formation and flow of the energetic ET plasma and its impact on exposed surfaces erosion under disruption like conditions. This dissertation is a series of published journals/conferences papers. The first paper verified the existence of the vapor shield that evolved at the boundary layer under the typical operational conditions of the NC State University ET plasma facilities PIPE and SIRENS. Upon the verification of the vapor shield, the second paper proposed novel model to simulate the evolution of the boundary layer and its effectiveness in providing a self-protecting nature for the exposed plasma facing surfaces. The developed models simulate the radiant heat flux attenuation through an optically thick boundary layer. The models were validated by comparing the simulation results to experimental

Determination of monomethylmercury and dimethylmercury in the Arctic marine boundary layer.

PubMed

Baya, Pascale A; Gosselin, Michel; Lehnherr, Igor; St Louis, Vincent L; Hintelmann, Holger

2015-01-06

Our understanding of the biogeochemical cycling of monomethylmercury (MMHg) in the Arctic is incomplete because atmospheric sources and sinks of MMHg are still unclear. We sampled air in the Canadian Arctic marine boundary layer to quantify, for the first time, atmospheric concentrations of methylated Hg species (both MMHg and dimethylmercury (DMHg)), and, estimate the importance of atmospheric deposition as a source of MMHg to Arctic land- and sea-scapes. Overall atmospheric MMHg and DMHg concentrations (mean ± SD) were 2.9 ± 3.6 and 3.8 ± 3.1 (n = 37) pg m(-3), respectively. Concentrations of methylated Hg species in the marine boundary layer varied significantly among our sites, with a predominance of MMHg over Hudson Bay (HB), and DMHg over Canadian Arctic Archipelago (CAA) waters. We concluded that DMHg is of marine origin and that primary production rate and sea-ice cover are major drivers of its concentration in the Canadian Arctic marine boundary layer. Summer wet deposition rates of atmospheric MMHg, likely to be the product of DMHg degradation in the atmosphere, were estimated at 188 ± 117.5 ng m(-2) and 37 ± 21.7 ng m(-2) for HB and CAA, respectively, sustaining MMHg concentrations available for biomagnification in the pelagic food web.

Modelling of surface fluxes and Urban Boundary Layer over an old mediterannean city core

NASA Astrophysics Data System (ADS)

Lemonsu, A.; Masson, V.; Grimmond, Cs. B.

2003-04-01

In the frameworks of the UBL(Urban Boundary Layer)-ESCOMPTE campaign, the Town Energy Balance (TEB) model was run in off-line mode for Marseille. TEB's performance is evaluated with observations of surface temperatures and surface energy balance fluxes collected during the campaign. Parameterization improvements allow to better represent the energy exchanges between the air inside the canyon and the atmosphere above the roof level. Then, high resolution Méso-NH simulations are done to study the 3-D structure and the evolution of the Urban Boundary Layer (UBL) over Marseille. Will will give a special attention to the impact of the seabord effects (sea-breeze circulation) on the UBL.

Simultaneous measurement of aero-optical distortion and turbulent structure in a heated boundary layer

NASA Astrophysics Data System (ADS)

Saxton-Fox, Theresa; McKeon, Beverley; Smith, Adam; Gordeyev, Stanislav

2014-11-01

This study examines the relationship between turbulent structures and the aero-optical distortion of a laser beam passing through a turbulent boundary layer. Previous studies by Smith et al. (AIAA, 2014--2491) have found a bulk convection velocity of 0 . 8U∞ for aero-optical distortion in turbulent boundary layers, motivating a comparison of the distortion with the outer boundary layer. In this study, a turbulent boundary layer is developed over a flat plate with a moderately-heated section of length 25 δ . Density variation in the thermal boundary layer leads to aero-optical distortion, which is measured with a Malley probe (Smith et al., AIAA, 2013--3133). Simultaneously, 2D PIV measurements are recorded in a wall-normal, streamwise plane centered on the Malley probe location. Experiments are run at Reθ = 2100 and at a Mach number of 0.03, with the heated wall 10 to 20°C above the free stream temperature. Correlations and conditional averages are carried out between Malley probe distortion angles and flow features in the PIV vector fields. Aero-optical distortion in this study will be compared to distortion in higher Mach number flows studied by Gordeyev et al. (J. Fluid Mech., 2014), with the aim of extending conclusions into compressible flows. This research is made possible by the Department of Defense through the National Defense & Engineering Graduate Fellowship (NDSEG) Program and by the Air Force Office of Scientific Research Grant # FA9550-12-1-0060.

Observations of the magnetopause current layer: Cases with no boundary layer and tests of recent models

NASA Technical Reports Server (NTRS)

Eastman, Timothy E.

1995-01-01

Evidence for the probable existence of magnetospheric boundary layers was first presented by Hones, et al. (1972), based on VELA satellite plasma observations (no magnetic field measurements were obtained). This magnetotail boundary layer is now known to be the tailward extension of the high-latitude boundary layer or plasma mantle (first uniquely identified using HEOS 2 plasma and field observations by Rosenbauer et al., 1975) and the low-latitude boundary layer (first uniquely identified using IMP 6 plasma and field observations by Eastman et al., 1976). The magnetospheric boundary layer is the region of magnetosheath-like plasma located Earthward of, but generally contiguous with the magnetopause. This boundary layer is typically identified by comparing low-energy (less than 10 keV) ion spectra across the magnetopause. Low-energy electron measurements are also useful for identifying the boundary layer because the shocked solar wind or magnetosheath has a characteristic spectral signature for electrons as well. However, there are magnetopause crossings where low-energy electrons might suggest a depletion layer outside the magnetopause even though the traditional field-rotation signature indicates that this same region is a boundary layer Earthward of the current layer. Our analyses avoided crossings which exhibit such ambiguities. Pristine magnetopause crossings are magnetopause crossings for which the current layer is well defined and for which there is no adjoining magnetospheric boundary layer as defined above. Although most magnetopause models to date apply to such crossings, few comparisons between such theory and observations of pristine magnetopause crossings have been made because most crossings have an associated magnetospheric boundary layer which significantly affects the applicable boundary conditions for the magnetopause current layer. Furthermore, almost no observational studies of magnetopause microstructure have been done even though key

The Kinematics of Turbulent Boundary Layer Structure

NASA Technical Reports Server (NTRS)

Robinson, Stephen Kern

1991-01-01

The long history of research into the internal structure of turbulent boundary layers has not provided a unified picture of the physics responsible for turbulence production and dissipation. The goals of the present research are to: (1) define the current state of boundary layer structure knowledge; and (2) utilize direct numerical simulation results to help close the unresolved issues identified in part A and to unify the fragmented knowledge of various coherent motions into a consistent kinematic model of boundary layer structure. The results of the current study show that all classes of coherent motion in the low Reynolds number turbulent boundary layer may be related to vortical structures, but that no single form of vortex is representative of the wide variety of vortical structures observed. In particular, ejection and sweep motions, as well as entrainment from the free-streem are shown to have strong spatial and temporal relationships with vortical structures. Disturbances of vortex size, location, and intensity show that quasi-streamwise vortices dominate the buffer region, while transverse vortices and vortical arches dominate the wake region. Both types of vortical structure are common in the log region. The interrelationships between the various structures and the population distributions of vortices are combined into a conceptual kinematic model for the boundary layer. Aspects of vortical structure dynamics are also postulated, based on time-sequence animations of the numerically simulated flow.

Free-stream disturbance, continuous Eigenfunctions, boundary-layer instability and transition

NASA Technical Reports Server (NTRS)

Grosch, C. E.

1980-01-01

A rational foundation is presented for the application of the linear shear flows to transition prediction, and an explicit method is given for carrying out the necessary calculations. The expansions used are shown to be complete. Sample calculations show that a typical boundary layer is very sensitive to vorticity disturbances in the inner boundary layer, near the critical layer. Vorticity disturbances three or four boundary layer thicknesses above the boundary are nearly uncoupled from the boundary layer in that the amplitudes of the discrete Tollmien-Schlicting waves are an extremely small fraction of the amplitude of the disturbance.

Towards Natural Transition in Compressible Boundary Layers

DTIC Science & Technology

2016-06-29

Behaviour of a natural laminar flow aerofoil in flight through atmospheric turbulence. Journal of Fluid Mechanics, 767:394–429, 003 2015. [70] O...DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited See report Wave packet, compressible boundary layer, subsonic flow ...Base flow generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.1.1 Boundary layer profiles

Entrainment of stratospheric air and Asian pollution by the convective boundary layer in the southwestern U.S.

NASA Astrophysics Data System (ADS)

Langford, A. O.; Alvarez, R. J.; Brioude, J.; Fine, R.; Gustin, M. S.; Lin, M. Y.; Marchbanks, R. D.; Pierce, R. B.; Sandberg, S. P.; Senff, C. J.; Weickmann, A. M.; Williams, E. J.

2017-01-01

A series of deep stratospheric intrusions in late May 2013 increased the daily maximum 8 h surface ozone (O3) concentrations to more than 70 parts per billion by volume (ppbv) at rural and urban surface monitors in California and Nevada. This influx of ozone-rich lower stratospheric air and entrained Asian pollution persisted for more than 5 days and contributed to exceedances of the 2008 8 h national ambient air quality standard of 75 ppbv on 21 and 25 May in Clark County, NV. Exceedances would also have occurred on 22 and 23 May had the new standard of 70 ppbv been in effect. In this paper, we examine this episode using lidar measurements from a high-elevation site on Angel Peak, NV, and surface measurements from NOAA, the Clark County, Nevada Department of Air Quality, the Environmental Protection Agency Air Quality System, and the Nevada Rural Ozone Initiative. These measurements, together with analyses from the National Centers for Environmental Prediction/North American Regional Reanalysis; NOAA Geophysical Fluid Dynamics Laboratory AM3 model; NOAA National Environmental Satellite, Data, and Information Service Real-time Air Quality Modeling System; and FLEXPART models, show that the exceedances followed entrainment of 20 to 40 ppbv of lower stratospheric ozone mingled with another 0 to 10 ppbv of ozone transported from Asia by the unusually deep convective boundary layers above the Mojave desert. Our analysis suggests that this vigorous mixing can affect both high and low elevations and help explain the springtime ozone maximum in the southwestern U.S.

Response of the Atmospheric Boundary Layer and Soil Layer to a High Altitude, Dense Aerosol Cover.

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Pittock, A. B.; Walsh, K.

1990-01-01

The response of the atmospheric boundary layer to the appearance of a high-altitude smoke layer has been investigated in a mesoscale numerical model of the atmosphere. Emphasis is placed on the changes in mean boundary-layer structure and near-surface temperatures when smoke of absorption optical depth (AOD) in the, range 0 to 1 is introduced. Calculations have been made at 30°S, for different soil thermal properties and degrees of surface wetness, over a time period of several days during which major smoke-induced cooling occurs. The presence of smoke reduces the daytime mixed-layer depth and, for large enough values of AOD, results in a daytime surface inversion with large cooling confined to heights of less than a few hundred meters. Smoke-induced reductions in daytime soil and air temperatures of several degrees are typical, dependent critically upon soil wetness and smoke AOD. Locations near the coast experience reduced cooling whenever there is a significant onshore flow related to a sea breeze (this would also be the case with a large-scale onshore flow). The sea breeze itself disappears for large enough smoke AOD and, over sloping coastal terrain, a smoke-induced, offshore drainage flow may exist throughout the diurnal cycle.

Modeling marine boundary-layer clouds with a two-layer model: A one-dimensional simulation

NASA Technical Reports Server (NTRS)

Wang, Shouping

1993-01-01

A two-layer model of the marine boundary layer is described. The model is used to simulate both stratocumulus and shallow cumulus clouds in downstream simulations. Over cold sea surfaces, the model predicts a relatively uniform structure in the boundary layer with 90%-100% cloud fraction. Over warm sea surfaces, the model predicts a relatively strong decoupled and conditionally unstable structure with a cloud fraction between 30% and 60%. A strong large-scale divergence considerably limits the height of the boundary layer and decreases relative humidity in the upper part of the cloud layer; thus, a low cloud fraction results. The efffects of drizzle on the boundary-layer structure and cloud fraction are also studied with downstream simulations. It is found that drizzle dries and stabilizes the cloud layer and tends to decouple the cloud from the subcloud layer. Consequently, solid stratocumulus clouds may break up and the cloud fraction may decrease because of drizzle.

Pitot-probe displacement in a supersonic turbulent boundary layer

NASA Technical Reports Server (NTRS)

Allen, J. M.

1972-01-01

Eight circular pitot probes ranging in size from 2 to 70 percent of the boundary-layer thickness were tested to provide experimental probe displacement results in a two-dimensional turbulent boundary layer at a nominal free-stream Mach number of 2 and unit Reynolds number of 8 million per meter. The displacement obtained in the study was larger than that reported by previous investigators in either an incompressible turbulent boundary layer or a supersonic laminar boundary layer. The large probes indicated distorted Mach number profiles, probably due to separation. When the probes were small enough to cause no appreciable distortion, the displacement was constant over most of the boundary layer. The displacement in the near-wall region decreased to negative displacement in some cases. This near-wall region was found to extend to about one probe diameter from the test surface.

Boundary-Layer Receptivity and Integrated Transition Prediction

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan; Choudhari, Meelan

2005-01-01

The adjoint parabold stability equations (PSE) formulation is used to calculate the boundary layer receptivity to localized surface roughness and suction for compressible boundary layers. Receptivity efficiency functions predicted by the adjoint PSE approach agree well with results based on other nonparallel methods including linearized Navier-Stokes equations for both Tollmien-Schlichting waves and crossflow instability in swept wing boundary layers. The receptivity efficiency function can be regarded as the Green's function to the disturbance amplitude evolution in a nonparallel (growing) boundary layer. Given the Fourier transformed geometry factor distribution along the chordwise direction, the linear disturbance amplitude evolution for a finite size, distributed nonuniformity can be computed by evaluating the integral effects of both disturbance generation and linear amplification. The synergistic approach via the linear adjoint PSE for receptivity and nonlinear PSE for disturbance evolution downstream of the leading edge forms the basis for an integrated transition prediction tool. Eventually, such physics-based, high fidelity prediction methods could simulate the transition process from the disturbance generation through the nonlinear breakdown in a holistic manner.

Boundary-Layer Transition on a Slender Cone in Hypervelocity Flow with Real Gas Effects

NASA Astrophysics Data System (ADS)

Jewell, Joseph Stephen

The laminar to turbulent transition process in boundary layer flows in thermochemical nonequilibrium at high enthalpy is measured and characterized. Experiments are performed in the T5 Hypervelocity Reflected Shock Tunnel at Caltech, using a 1 m length 5-degree half angle axisymmetric cone instrumented with 80 fast-response annular thermocouples, complemented by boundary layer stability computations using the STABL software suite. A new mixing tank is added to the shock tube fill apparatus for premixed freestream gas experiments, and a new cleaning procedure results in more consistent transition measurements. Transition location is nondimensionalized using a scaling with the boundary layer thickness, which is correlated with the acoustic properties of the boundary layer, and compared with parabolized stability equation (PSE) analysis. In these nondimensionalized terms, transition delay with increasing CO2 concentration is observed: tests in 100% and 50% CO2, by mass, transition up to 25% and 15% later, respectively, than air experiments. These results are consistent with previous work indicating that CO2 molecules at elevated temperatures absorb acoustic instabilities in the MHz range, which is the expected frequency of the Mack second-mode instability at these conditions, and also consistent with predictions from PSE analysis. A strong unit Reynolds number effect is observed, which is believed to arise from tunnel noise. NTr for air from 5.4 to 13.2 is computed, substantially higher than previously reported for noisy facilities. Time- and spatially-resolved heat transfer traces are used to track the propagation of turbulent spots, and convection rates at 90%, 76%, and 63% of the boundary layer edge velocity, respectively, are observed for the leading edge, centroid, and trailing edge of the spots. A model constructed with these spot propagation parameters is used to infer spot generation rates from measured transition onset to completion distance. Finally, a novel

INDIVIDUAL TURBULENT CELL INTERACTION: BASIS FOR BOUNDARY LAYER ESTABLISHMENT

EPA Science Inventory

Boundary layers are important in determining the forces on objects in flowing fluids, mixing characteristics, and other phenomena. For example, benthic boundary layers are frequently active resuspension layers that determine bottom turbidity and transniissivity. Traditionally, bo...

Analysis of turbulent free-convection boundary layer on flat plate

NASA Technical Reports Server (NTRS)

Eckert, E R G; Jackson, Thomas W

1950-01-01

A calculation was made for the flow and heat transfer in the turbulent free-convection boundary layer on a vertical flat plate. Formulas for the heat-transfer coefficient, boundary layer thickness, and the maximum velocity in the boundary layer were obtained.

Internal and external 2-d boundary layer flows

NASA Technical Reports Server (NTRS)

Crawford, M. E.; Kays, W. M.

1978-01-01

Computer program computes general two dimensional turbulent boundary-layer flow using finite-difference techniques. Structure allows for user modification to accommodate unique problems. Program should prove useful in many applications where accurate boundary-layer flow calculations are required.

Boundary-layer stability and airfoil design

NASA Technical Reports Server (NTRS)

Viken, Jeffrey K.

1986-01-01

Several different natural laminar flow (NLF) airfoils have been analyzed for stability of the laminar boundary layer using linear stability codes. The NLF airfoils analyzed come from three different design conditions: incompressible; compressible with no sweep; and compressible with sweep. Some of the design problems are discussed, concentrating on those problems associated with keeping the boundary layer laminar. Also, there is a discussion on how a linear stability analysis was effectively used to improve the design for some of the airfoils.

Determination of Boundary-Layer Transition on Three Symmetrical Airfoils in the NACA Full-Scale Wind Tunnel

NASA Technical Reports Server (NTRS)

Silverstein, Abe; Becker, John V

1938-01-01

For the purpose of studying the transition from laminar to turbulent flow, boundary-layer measurements were made in the NACA full-scale wind tunnel on three symmetrical airfoils of NACA 0009, 0012, and 0018 sections. The effects of variations in lift coefficient, Reynolds number, and airfoil thickness on transition were investigated. Air speed in the boundary layer was measured by total-head tubes and by hot wires; a comparison of transition as indicated by the two techniques was obtained. The results indicate no unique value of Reynolds number for the transition, whether the Reynolds number is based upon the distance along the chord or upon the thickness of the boundary layer at the transition point. In general, the transition is not abrupt and occurs in a region that varies in length as a function of the test conditions.

Structure of turbulence in three-dimensional boundary layers

NASA Technical Reports Server (NTRS)

Subramanian, Chelakara S.

1993-01-01

This report provides an overview of the three dimensional turbulent boundary layer concepts and of the currently available experimental information for their turbulence modeling. It is found that more reliable turbulence data, especially of the Reynolds stress transport terms, is needed to improve the existing modeling capabilities. An experiment is proposed to study the three dimensional boundary layer formed by a 'sink flow' in a fully developed two dimensional turbulent boundary layer. Also, the mean and turbulence field measurement procedure using a three component laser Doppler velocimeter is described.

GASEOUS ELEMENTAL MERCURY IN THE MARINE BOUNDARY LAYER: EVIDENCE FOR RAPID REMOVAL IN ANTHROPOGENIC POLLUTION

EPA Science Inventory

In this study, gas-phase elemental mercury (Hg0) and related species (including inorganic reactive gaseous mercury (RGM) and particulate mercury (PHg)) were measured at Cheeka Peak Observatory (CPO), Washington State, in the marine boundary layer (MBL) during 2001-2002. Air of...

Lidar observations of vertically organized convection in the planetary boundary layer over the ocean

NASA Technical Reports Server (NTRS)

Melfi, S. H.; Spinhirne, J. D.; Chou, S.-H.; Palm, S. P.

1985-01-01

Observations of a convective planetary boundary layer (PBL) were made with an airborne, downward-looking lidar system over the Atlantic Ocean during a cold air outbreak. The lidar data revealed well-organized, regularly spaced cellular convection with dominant spacial scales between two and four times the height of the boundary layer. It is demonstrated that the lidar can accurately measure the structure of the PBL with high vertical and horizontal resolution. Parameters important for PBL modeling such as entrainment zone thickness, entrainment rate, PBL height and relative heat flux can be inferred from the lidar data. It is suggested that wind shear at the PBL top may influence both entrainment and convective cell size.

Cyclone separator having boundary layer turbulence control

DOEpatents

Krishna, Coimbatore R.; Milau, Julius S.

1985-01-01

A cyclone separator including boundary layer turbulence control that is operable to prevent undue build-up of particulate material at selected critical areas on the separator walls, by selectively varying the fluid pressure at those areas to maintain the momentum of the vortex, thereby preventing particulate material from inducing turbulence in the boundary layer of the vortical fluid flow through the separator.

Hypersonic Boundary Layer Instability Over a Corner

NASA Technical Reports Server (NTRS)

Balakumar, Ponnampalam; Zhao, Hong-Wu; McClinton, Charles (Technical Monitor)

2001-01-01

A boundary-layer transition study over a compression corner was conducted under a hypersonic flow condition. Due to the discontinuities in boundary layer flow, the full Navier-Stokes equations were solved to simulate the development of disturbance in the boundary layer. A linear stability analysis and PSE method were used to get the initial disturbance for parallel and non-parallel flow respectively. A 2-D code was developed to solve the full Navier-stokes by using WENO(weighted essentially non-oscillating) scheme. The given numerical results show the evolution of the linear disturbance for the most amplified disturbance in supersonic and hypersonic flow over a compression ramp. The nonlinear computations also determined the minimal amplitudes necessary to cause transition at a designed location.

Three-Dimensional Boundary Layers.

DTIC Science & Technology

1985-02-01

layer edge, We, is seen to increase fast in downstream direction. Near measuring station 9 the wall flow angle exceeds w = 55’, which means that the...leading edge along wing upper and lower surface to the trailing edge. As an excercise , such a boundary layer flow was computed for a simple symmetric...D.I.A. Poll The Development of Intermittent Turbulence on a Swept - Attachment Line Including the Effects of Compressibility. Aero. Qu. (Feb. 1983) 10

Observations of high droplet number concentrations in Southern Ocean boundary layer clouds

NASA Astrophysics Data System (ADS)

Chubb, T.; Huang, Y.; Jensen, J.; Campos, T.; Siems, S.; Manton, M.

2015-09-01

Data from the standard cloud physics payload during the NSF/NCAR High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) Pole-to-Pole Observations (HIPPO) campaigns provide a snapshot of unusual wintertime microphysical conditions in the boundary layer over the Southern Ocean. On 29 June 2011, the HIAPER sampled the boundary layer in a region of pre-frontal warm air advection between 58 and 48° S to the south of Tasmania. Cloud droplet number concentrations were consistent with climatological values in the northernmost profiles but were exceptionally high for wintertime in the Southern Ocean at 100-200 cm-3 in the southernmost profiles. Sub-micron (0.06boundary layer. Instead, the gale force surface winds in this case (wind speed at 167 m above sea level was >25 m s-1) were most likely responsible for production of sea spray aerosol which influenced the microphysical properties of the boundary layer clouds. The smaller size and higher number concentration of cloud droplets is inferred to increase the albedo of these clouds, and these conditions occur regularly, and are expected to increase in frequency, over windy parts of the Southern Ocean.

A Comparison of Active and Passive Methods for Control of Hypersonic Boundary Layers on Airbreathing Configurations

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Nowak, Robert J.

2003-01-01

Active and passive methods for control of hypersonic boundary layers have been experimentally examined in NASA Langley Research Center wind tunnels on a Hyper-X model. Several configurations for forcing transition using passive discrete roughness elements and active mass addition, or blowing, methods were compared in two hypersonic facilities, the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air tunnels. Heat transfer distributions, obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the nominal Mach 7 flight trajectory of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For the passive roughness examination, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The prior passive roughness study resulted in a swept ramp configuration being selected for the Mach 7 flight vehicle that was scaled to be roughly 0.6 of the calculated boundary layer thickness. For the active jet blowing study, the blowing manifold pressure was systematically varied for each configuration, while monitoring the mass flow, to determine the jet penetration height with schlieren and transition movement with the phosphor system for comparison to the passive results. All the blowing concepts tested were adequate for providing transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model static pressure or higher.

Practical calculation of laminar and turbulent bled-off boundary layers

NASA Technical Reports Server (NTRS)

Eppler, R.

1978-01-01

Bleed-off of boundary layer material is shown to be an effective means for reducing drag by conserving the laminar boundary layer and preventing separation of the turbulent boundary layer. The case in which the two effects of bleed-off overlap is examined. Empirical methods are extended to the case of bleed-off. Laminar and turbulent boundary layers are treated simultaneously and the approximation differential equations are solved without an uncertain error. The case without bleed-off is also treated.

Estimation of evaporation from equilibrium diurnal boundary layer humidity

NASA Astrophysics Data System (ADS)

Salvucci, G.; Rigden, A. J.; Li, D.; Gentine, P.

2017-12-01

Simplified conceptual models of the convective boundary layer as a well mixed profile of potential temperature (theta) and specific humidity (q) impinging on an initially stably stratified linear potential temperature profile have a long history in atmospheric sciences. These one dimensional representations of complex mixing are useful for gaining insights into land-atmosphere interactions and for prediction when state of the art LES approaches are infeasible. As previously shown (e.g. Betts), if one neglects the role of q in bouyancy, the framework yields a unique relation between mixed layer Theta, mixed layer height (h), and cumulative sensible heat flux (SH) throughout the day. Similarly assuming an initially q profile yields a simple relation between q, h, and cumulative latent heat flux (LH). The diurnal dynamics of theta and q are strongly dependent on SH and the initial lapse rates of theta (gamma_thet) and q (gamma q). In the estimation method proposed here, we further constrain these relations with two more assumptions: 1) The specific humidity is the same at the start of the period of boundary layer growth and at the collapse; and 2) Once the mixed layer reaches the LCL, further drying occurs proportionally to the deardorff convective velocity scale (omega) multiplied by q. Assumption (1) is based on the idea that below the cloud layer, there are no sinks of moisture within the mixed layer (neglecting lateral humidity divergence). Thus the net mixing of dry air aloft with evaporation from the surface must balance. Inclusion of the simple model of moisture loss above the LCL into the bulk-CBL model allows definition of an equilibrium humidity (q) condition at which the diurnal cycle of q repeats (i.e. additions of q from surface balance entrainment of dry air from above). Surprisingly, this framework allows estimation of LH from q, theta, and estimated net radiation by solving for the value of Evaporative Fraction (EF) for which the diurnal cycle of q

Viscous drag reduction in boundary layers

NASA Technical Reports Server (NTRS)

Bushnell, Dennis M. (Editor); Hefner, Jerry N. (Editor)

1990-01-01

The present volume discusses the development status of stability theory for laminar flow control design, applied aspects of laminar-flow technology, transition delays using compliant walls, the application of CFD to skin friction drag-reduction, active-wave control of boundary-layer transitions, and such passive turbulent-drag reduction methods as outer-layer manipulators and complex-curvature concepts. Also treated are such active turbulent drag-reduction technique applications as those pertinent to MHD flow drag reduction, as well as drag reduction in liquid boundary layers by gas injection, drag reduction by means of polymers and surfactants, drag reduction by particle addition, viscous drag reduction via surface mass injection, and interactive wall-turbulence control.

Acoustic sounding in the planetary boundary layer

NASA Technical Reports Server (NTRS)

Kelly, E. H.

1974-01-01

Three case studies are presented involving data from an acoustic radar. The first two cases examine data collected during the passage of a mesoscale cold-air intrusion, probably thunderstorm outflow, and a synoptic-scale cold front. In these studies the radar data are compared to conventional meteorological data obtained from the WKY tower facility for the purpose of radar data interpretation. It is shown that the acoustic radar echoes reveal the boundary between warm and cold air and other areas of turbulent mixing, regions of strong vertical temperature gradients, and areas of weak or no wind shear. The third case study examines the relationship between the nocturnal radiation inversion and the low-level wind maximum or jet in the light of conclusions presented by Blackadar (1957). The low-level jet is seen forming well above the top of the inversion. Sudden rapid growth of the inversion occurs which brings the top of the inversion to a height equal that of the jet. Coincident with the rapid growth of the inversion is a sudden decrease in the intensity of the acoustic radar echoes in the inversion layer. It is suggested that the decrease in echo intensity reveals a decrease in turbulent mixing in the inversion layer as predicted by Blackadar. It is concluded that the acoustic radar can be a valuable tool for study in the lower atmosphere.

Radiative transfer in a polluted urban planetary boundary layer

NASA Technical Reports Server (NTRS)

Viskanta, R.; Johnson, R. O.; Bergstrom, R. W.

1977-01-01

Radiative transfer in a polluted urban atmosphere is studied using a dynamic model. The diurnal nature of radiative transfer for summer conditions is simulated for an urban area 40 km in extent and the effects of various parameters arising in the problem are investigated. The results of numerical computations show that air pollution has the potential of playing a major role in the radiative regime of the urban area. Absorption of solar energy by aerosols in realistic models of urban atmosphere are of the same order of magnitude as that due to water vapor. The predicted effect of the air pollution aerosol in the city is to warm the earth-atmosphere system, and the net effect of gaseous pollutant is to warm the surface and cool the planetary boundary layer, particularly near the top.

First simultaneous space measurements of atmospheric pollutants in the boundary layer from IASI: a case study in the North China Plain

NASA Astrophysics Data System (ADS)

Boynard, Anne; Clerbaux, Cathy; Clarisse, Lieven; Safieddine, Sarah; Pommier, Matthieu; Van Damme, Martin; Bauduin, Sophie; Oudot, Charlotte; Hadji-Lazaro, Juliette; Hurtmans, Daniel; Coheur, Pierre-François

2014-05-01

An extremely severe and persistent smog episode occurred in January 2013 over China. The levels of air pollution have been dangerously high, reaching 40 times recommended safety levels and have affected health of millions of people. China faced one of the worst periods of air quality in recent history and drew worldwide attention. This pollution episode was caused by the combination of anthropogenic emissions and stable meteorological conditions (absence of wind and temperature inversion) that trapped pollutants in the boundary layer. To characterize this episode, we used the IASI (Infrared Atmospheric Sounding Interferometer) instrument onboard the MetOp-A platform. IASI observations show high concentrations of key trace gases such as carbon monoxide (CO), sulfur dioxide (SO2) and ammonia (NH3) along with ammonium sulfate aerosol. We show that IASI is able to detect boundary layer pollution in case of large negative thermal contrast combined with high levels of pollution. Our findings demonstrate the ability of thermal infrared instrument such as IASI to monitor boundary layer pollutants, which can support air quality evaluation and management.

Hypersonic Laminar Boundary Layer Velocimetry with Discrete Roughness on a Flat Plate

NASA Technical Reports Server (NTRS)

Bathel, Brett; Danehy, Paul M.; Inman, Jennifer A.; Watkins, A. Neal; Jones, Stephen B.; Lipford, William E.; Goodman, Kyle Z.; Ivey, Christopher B.; Goyne, Christopher P.

2010-01-01

insight into the behavior of the boundary layers. The experiments were performed at the NASA Langley Research Center 31-Inch Mach 10 Air tunnel.

Stability of boundary layer flow based on energy gradient theory

NASA Astrophysics Data System (ADS)

Dou, Hua-Shu; Xu, Wenqian; Khoo, Boo Cheong

2018-05-01

The flow of the laminar boundary layer on a flat plate is studied with the simulation of Navier-Stokes equations. The mechanisms of flow instability at external edge of the boundary layer and near the wall are analyzed using the energy gradient theory. The simulation results show that there is an overshoot on the velocity profile at the external edge of the boundary layer. At this overshoot, the energy gradient function is very large which results in instability according to the energy gradient theory. It is found that the transverse gradient of the total mechanical energy is responsible for the instability at the external edge of the boundary layer, which induces the entrainment of external flow into the boundary layer. Within the boundary layer, there is a maximum of the energy gradient function near the wall, which leads to intensive flow instability near the wall and contributes to the generation of turbulence.

A general integral form of the boundary-layer equation for incompressible flow with an application to the calculation of the separation point of turbulent boundary layers

NASA Technical Reports Server (NTRS)

Tetervin, Neal; Lin, Chia Chiao

1951-01-01

A general integral form of the boundary-layer equation, valid for either laminar or turbulent incompressible boundary-layer flow, is derived. By using the experimental finding that all velocity profiles of the turbulent boundary layer form essentially a single-parameter family, the general equation is changed to an equation for the space rate of change of the velocity-profile shape parameter. The lack of precise knowledge concerning the surface shear and the distribution of the shearing stress across turbulent boundary layers prevented the attainment of a reliable method for calculating the behavior of turbulent boundary layers.

Nonlinear Transient Growth and Boundary Layer Transition

NASA Technical Reports Server (NTRS)

Paredes, Pedro; Choudhari, Meelan M.; Li, Fei

2016-01-01

Parabolized stability equations (PSE) are used in a variational approach to study the optimal, non-modal disturbance growth in a Mach 3 at plate boundary layer and a Mach 6 circular cone boundary layer. As noted in previous works, the optimal initial disturbances correspond to steady counter-rotating streamwise vortices, which subsequently lead to the formation of streamwise-elongated structures, i.e., streaks, via a lift-up effect. The nonlinear evolution of the linearly optimal stationary perturbations is computed using the nonlinear plane-marching PSE for stationary perturbations. A fully implicit marching technique is used to facilitate the computation of nonlinear streaks with large amplitudes. To assess the effect of the finite-amplitude streaks on transition, the linear form of plane- marching PSE is used to investigate the instability of the boundary layer flow modified by spanwise periodic streaks. The onset of bypass transition is estimated by using an N- factor criterion based on the amplification of the streak instabilities. Results show that, for both flow configurations of interest, streaks of sufficiently large amplitude can lead to significantly earlier onset of transition than that in an unperturbed boundary layer without any streaks.

Influence of Evaporating Droplets in the Turbulent Marine Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Peng, Tianze; Richter, David

2017-12-01

Sea-spray droplets ejected into the marine atmospheric boundary layer take part in a series of complex transport processes. By capturing the air-droplet coupling and feedback, we focus on how droplets modify the total heat transfer across a turbulent boundary layer. We implement a high-resolution Eulerian-Lagrangian algorithm with varied droplet size and mass loading in a turbulent open-channel flow, revealing that the influence from evaporating droplets varies for different dynamic and thermodynamic characteristics of droplets. Droplets that both respond rapidly to the ambient environment and have long suspension times are able to modify the latent and sensible heat fluxes individually, however the competing signs of this modification lead to an overall weak effect on the total heat flux. On the other hand, droplets with a slower thermodynamic response to the environment are less subjected to this compensating effect. This indicates a potential to enhance the total heat flux, but the enhancement is highly dependent on the concentration and suspension time.

Investigation of wintertime cold-air pools and aerosol layers in the Salt Lake Valley using a lidar ceilometer

NASA Astrophysics Data System (ADS)

Young, Joseph Swyler

This thesis investigates the utility of lidar ceilometers, a type of aerosol lidar, in improving the understanding of meteorology and air quality in persistent wintertime stable boundary layers, or cold-air pools, that form in urbanized valley and basin topography. This thesis reviews the scientific literature to survey the present knowledge of persistent cold-air pools, the operating principles of lidar ceilometers, and their demonstrated utility in meteorological investigations. Lidar ceilometer data from the Persistent Cold-Air Pool Study (PCAPS) are then used with meteorological and air quality data from other in situ and remote sensing equipment to investigate cold-air pools that formed in Utah's Salt Lake Valley during the winter of 2010-2011. The lidar ceilometer is shown to accurately measure aerosol layer depth and aerosol loading, when compared to visual observations. A linear relationship is found between low-level lidar backscatter and surface particulate measurements. Convective boundary layer lidar analysis techniques applied to cold-air pool ceilometer profiles can detect useful layer characteristics. Fine-scale waves are observed and analyzed within the aerosol layer, with emphasis on Kelvin-Helmholz waves. Ceilometer aerosol backscatter profiles are analyzed to quantify and describe mixing processes in persistent cold-air pools. Overlays of other remote and in-situ observations are combined with ceilometer particle backscatter to describe specific events during PCAPS. This analysis describes the relationship between the aerosol layer and the valley inversion as well as interactions with large-scale meteorology. The ceilometer observations of hydrometers are used to quantify cloudiness and precipitation during the project, observing that 50% of hours when a PCAP was present had clouds or precipitation below 5 km above ground level (AGL). Then, combining an objective technique for determining hourly aerosol layer depths and correcting this

Effects of non-adiabatic walls on shock/boundary-layer interaction using direct numerical simulations

NASA Astrophysics Data System (ADS)

Volpiani, Pedro S.; Bernardini, Matteo; Larsson, Johan

2017-11-01

The influence of wall thermal conditions on the properties of an impinging shock wave interacting with a turbulent supersonic boundary layer is a research topic that still remains underexplored. In the present study, direct numerical simulations (DNS) are employed to investigate the flow properties of a shock wave interacting with a turbulent boundary layer at free-stream Mach number M∞ = 2.28 with distinct wall thermal conditions and shock strengths. Instantaneous and mean flow fields, wall quantities and the low-frequency unsteadiness are analyzed. While heating contributes to increase the extent of the interaction zone, wall cooling turns out to be a good candidate for flow control. The distribution of the Stanton number shows a good agreement with prior experimental studies and confirms the strong heat transfer and complex pattern within the interaction region. Numerical results indicate that the changes in the interaction length are mainly linked to the incoming boundary layer as suggested in previous studies (Souverein et al., 2013 and Jaunet et al., 2014). This work was supported by the Air Force Office of Scientific Research, Grant FA95501610385.

Aircraft measurements to characterize polluted winter boundary layers: Overview of twin otter flights during the Utah Winter Fine Particulate Matter Study

NASA Astrophysics Data System (ADS)

Brown, S. S.; Baasandorj, M.; Franchin, A.; Middlebrook, A. M.; Goldberger, L.; Thornton, J. A.; Dube, W. P.; McDuffie, E. E.; Womack, C.; Fibiger, D. L.; Moravek, A.; Clark, J. C.; Murphy, J. G.; Mitchell, R.

2017-12-01

Winter air pollution is a significant public health concern. In many regions of the U.S., Europe and Asia, wintertime particulate matter concentrations exceed national and / or international air quality standards. Winter air pollution also represents a scientific challenge because these events occur during stagnation events in shallow, vertically stratified boundary layers whose composition is difficult to probe from surface level measurements. Chemical processes responsible for the conversion of primary emissions to secondary pollutants such as ammonium nitrate aerosol vary with height above ground level. Sources of oxidants are poorly understood and may result from both local chemical production and mixing between shallow inversion layers and background air. During the Utah Winter Fine Particulate Study (UWFPS) in January - February 2017, the NOAA twin otter executed 23 research flights with a payload designed to characterize the formation of ammonium nitrate aerosol in three mountain valleys of northern Utah (Salt Lake, Cache, and Utah). These valleys are subject to periodic episodes of winter aerosol pollution well in excess of U.S. national ambient air quality standards. This presentation will describe the measurement strategy of the twin otter flights to address the specific features of aerosol pollution within winter boundary layer of this region. This strategy is relevant to understanding the broader issue of winter air pollution in other regions and potentially to the design of future studies. The presentation will summarize findings from UWFPS related to boundary layer structure, emissions and chemical processes responsible for ammonium nitrate aerosol in this region.

Stability of an oscillating boundary layer

NASA Technical Reports Server (NTRS)

Levchenko, V. Y.; Solovyev, A. S.

1985-01-01

Levchenko and Solov'ev (1972, 1974) have developed a stability theory for space periodic flows, assuming that the Floquet theory is applicable to partial differential equations. In the present paper, this approach is extended to unsteady periodic flows. A complete unsteady formulation of the stability problem is obtained, and the stability characteristics over an oscillating period are determined from the solution of the problem. Calculations carried out for an oscillating incompressible boundary layer on a plate showed that the boundary layer flow may be regarded as a locally parallel flow.

Nocturnal Boundary Layer Measurements during the Amazonian Aerosol Characterization Experiment (amaze)

NASA Astrophysics Data System (ADS)

Tota, J.; Santos, R.; Fisch, G.; Querino, C.; Silva Dias, M.; Artaxo, P.; Guenther, A.; Martin, S.; Manzi, A.

2008-12-01

To characterize the Nocturnal Boundary Layer (NBL) hourly profiles of wind, pressure, temperature, humidity and 5 sizes particles concentration, were made by using tethered balloon at INPA tropical Amazon rainforest Reserve (Cuieiras) 100 km northwest from Manaus city. The measurements were made during the wet season March/2008. The NBL height was 100 to 150m, with a very well mixed layer close to surface associate with temperature inversion. The wind profiles shows a very clear low level in two nights, about 500 to 900 m, and, in general, all nights show an stable and cooler air layer close the surface uncoupled with outer residual boundary layer above. At the site a very clear drainage flow from north quadrant down slope eastward quadrant during very the stable cases. This findings is correlates with particles profiles where was commonly trapped by stable layer presenting high concentrations, for all 5 sizes measured, close to the surface at vegetation level and just above it. All nights presents high humidity with fog formation in three cases, associates with temperature below the 23°C. The wind speed were very low about 0.5 to calm, in generally associate with drainage flow down hill. The NBL dynamics is a discussion issue associate to the aerosol nocturnal mixing in complex terrain with tall vegetation, the currently AMAZE site case.

Nocturnal Boundary Layer Measurements during the Amazonian Aerosol Characterization Experiment (AMAZE)

NASA Astrophysics Data System (ADS)

Tota, J.; Fisch, G.; Santos, R.; Silva Dias, M.

2009-05-01

To characterize the Nocturnal Boundary Layer (NBL) hourly profiles of wind, pressure, temperature, humidity and 5 sizes particles concentration, were made by using tethered balloon at INPA tropical Amazon rainforest Reserve (Cuieiras) 100 km northwest from Manaus city. The measurements were made during the wet season March/2008. The NBL height was 100 to 150m, with a very well mixed layer close to surface associate with temperature inversion. The wind profiles shows a very clear low level in two nights, about 500 to 900 m, and, in general, all nights show an stable and cooler air layer close the surface uncoupled with outer residual boundary layer above. At the site a very clear drainage flow from north quadrant down slope eastward quadrant during very the stable cases. This findings is correlates with particles profiles where was commonly trapped by stable layer presenting high concentrations, for all 5 sizes measured, close to the surface at vegetation level and just above it. All nights presents high humidity with fog formation in three cases, associates with temperature below the 23C. The wind speed were very low about 0.5 to calm, in generally associate with drainage flow down hill. The NBL dynamics is a discussion issue associate to the aerosol nocturnal mixing in complex terrain with tall vegetation, the currently AMAZE site case.

Wake Dynamics in the Atmospheric Boundary Layer Over Complex Terrain

NASA Astrophysics Data System (ADS)

Markfort, Corey D.

The goal of this research is to advance our understanding of atmospheric boundary layer processes over heterogeneous landscapes and complex terrain. The atmospheric boundary layer (ABL) is a relatively thin (˜ 1 km) turbulent layer of air near the earth's surface, in which most human activities and engineered systems are concentrated. Its dynamics are crucially important for biosphere-atmosphere couplings and for global atmospheric dynamics, with significant implications on our ability to predict and mitigate adverse impacts of land use and climate change. In models of the ABL, land surface heterogeneity is typically represented, in the context of Monin-Obukhov similarity theory, as changes in aerodynamic roughness length and surface heat and moisture fluxes. However, many real landscapes are more complex, often leading to massive boundary layer separation and wake turbulence, for which standard models fail. Trees, building clusters, and steep topography produce extensive wake regions currently not accounted for in models of the ABL. Wind turbines and wind farms also generate wakes that combine in complex ways to modify the ABL. Wind farms are covering an increasingly significant area of the globe and the effects of large wind farms must be included in regional and global scale models. Research presented in this thesis demonstrates that wakes caused by landscape heterogeneity must be included in flux parameterizations for momentum, heat, and mass (water vapor and trace gases, e.g. CO2 and CH4) in ABL simulation and prediction models in order to accurately represent land-atmosphere interactions. Accurate representation of these processes is crucial for the predictions of weather, air quality, lake processes, and ecosystems response to climate change. Objectives of the research reported in this thesis are: 1) to investigate turbulent boundary layer adjustment, turbulent transport and scalar flux in wind farms of varying configurations and develop an improved

Bristled shark skin: a microgeometry for boundary layer control?

PubMed

Lang, A W; Motta, P; Hidalgo, P; Westcott, M

2008-12-01

There exists evidence that some fast-swimming shark species may have the ability to bristle their scales during fast swimming. Experimental work using a water tunnel facility has been performed to investigate the flow field over and within a bristled shark skin model submerged within a boundary layer to deduce the possible boundary layer control mechanisms being used by these fast-swimming sharks. Fluorescent dye flow visualization provides evidence of the formation of embedded cavity vortices within the scales. Digital particle image velocimetry (DPIV) data, used to evaluate the cavity vortex formation and boundary layer characteristics close to the surface, indicate increased momentum in the slip layer forming above the scales. This increase in flow velocity close to the shark's skin is indicative of boundary layer control mechanisms leading to separation control and possibly transition delay for the bristled shark skin microgeometry.

Structure of the low-latitude boundary layer. [in magnetopause

NASA Technical Reports Server (NTRS)

Sckopke, N.; Paschmann, G.; Haerendel, G.; Sonnerup, B. U. OE.; Bame, S. J.; Forbes, T. G.; Hones, E. W., Jr.; Russell, C. T.

1981-01-01

High temporal resolution observations of the frontside magnetopause and plasma boundary layer made with the fast plasma analyzer aboard the ISEE 1 and 2 spacecraft are reported. The data are found to be compatible with a boundary layer that is always attached to the magnetopause but where the layer thickness has a large-scale spatial modulation pattern which travels tailward past the spacecraft. Periods are included when the thickness is essentially zero and others when it is of the order of 1 earth radius. The duration of these periods is highly variable but is typically in the range of 2-5 min corresponding to a distance along the magnetopuase of approximately 3-8 earth radii. The observed boundary layer features include a steep density gradient at the magnetopause with an approximately constant boundary layer plasma density amounting to about 25% of the magnetosheath density, and a second abrupt density decrease at the inner edge of the layer.

Comparison of turbulence in a transitional boundary layer to turbulence in a developed boundary layer*

NASA Astrophysics Data System (ADS)

Park, G. I.; Wallace, J.; Wu, X.; Moin, P.

2010-11-01

Using a recent DNS of a flat-plate boundary layer, statistics of turbulence in transition at Reθ= 500 where spots merge (distributions of the mean velocity, rms velocity and vorticity fluctuations, Reynolds shear stress, kinetic energy production and dissipation rates and enstrophy) have been compared to these statistics for the developed boundary layer turbulence at Reθ= 1850. When the distributions in the transitional region, determined in narrow planes 0.03 Reθ wide, exclude regions and times when the flow is not turbulent, they closely resemble those in the developed turbulent state at the higher Reynolds number, especially in the buffer and sublayers. The skin friction coefficient, determined in this conditional manner in the transitional flow is, of course, much larger than that obtained by including both turbulent and non-turbulent information there, and is consistent with a value obtained by extrapolating from the developed turbulent region. We are attempting to perform this data analysis even further upstream in the transitioning flow at Reθ= 300 where the turbulent spots are individuated. These results add further evidence to support the view that the structure of a developed turbulent boundary layer is little different from its structure in its embryonic form in turbulent spots. *CTR 2010 Summer Program research.

Energy efficient engine, low-pressure turbine boundary layer program

NASA Technical Reports Server (NTRS)

Gardner, W. B.

1981-01-01

A study was conducted to investigate development of boundary layers under the influence of velocity distributions simulating the suction side of two state-of-the-art turbine airfoils: a forward loaded airfoil (squared-off design) and an aft loaded airfoil (aft-loaded design). These velocity distributions were simulated in a boundary layer wind tunnel. Detailed measurements of boundary layer mean velocity and turbulence intensity profiles were obtained for an inlet turbulence level of 2.4 percent and an exit Reynolds number of 800,000. Flush-mounted hot film probes identified the boundary layer transition regimes in the adverse pressure gradient regions for both velocity distributions. Wall intermittency data showed good agreement with the correlations of Dhawan and Narasimha for the intermittency factor distribution in transitional flow regimes.

Analysis and Modeling of Boundary Layer Separation Method (BLSM).

PubMed

Pethő, Dóra; Horváth, Géza; Liszi, János; Tóth, Imre; Paor, Dávid

2010-09-01

Nowadays rules of environmental protection strictly regulate pollution material emission into environment. To keep the environmental protection laws recycling is one of the useful methods of waste material treatment. We have developed a new method for the treatment of industrial waste water and named it boundary layer separation method (BLSM). We apply the phenomena that ions can be enriched in the boundary layer of the electrically charged electrode surface compared to the bulk liquid phase. The main point of the method is that the boundary layer at correctly chosen movement velocity can be taken out of the waste water without being damaged, and the ion-enriched boundary layer can be recycled. Electrosorption is a surface phenomenon. It can be used with high efficiency in case of large electrochemically active surface of electrodes. During our research work two high surface area nickel electrodes have been prepared. The value of electrochemically active surface area of electrodes has been estimated. The existence of diffusion part of the double layer has been experimentally approved. The electrical double layer capacity has been determined. Ion transport by boundary layer separation has been introduced. Finally we have tried to estimate the relative significance of physical adsorption and electrosorption.

Large-Eddy Simulation in Planetary Boundary-Layer Research

NASA Technical Reports Server (NTRS)

Wyngaard, J. C.

1985-01-01

The structure and dynamics of the convective boundary layer are discussed. The vertical transport of a conservative, passive scalar was simulated. Also studied were the statistics by top-down and bottom-up scalar fields. Substantial differences were found between them due, presumably, to the asymmetry in the convective boundary layer. A generalization of mixed-layer scaling was developed which allows one to include the effects of top-down diffusion.

Sound transmission through double cylindrical shells lined with porous material under turbulent boundary layer excitation

NASA Astrophysics Data System (ADS)

Zhou, Jie; Bhaskar, Atul; Zhang, Xin

2015-11-01

This paper investigates sound transmission through double-walled cylindrical shell lined with poroelastic material in the core, excited by pressure fluctuations due to the exterior turbulent boundary layer (TBL). Biot's model is used to describe the sound wave propagating in the porous material. Three types of constructions, bonded-bonded, bonded-unbonded and unbonded-unbonded, are considered in this study. The power spectral density (PSD) of the inner shell kinetic energy is predicted for two turbulent boundary layer models, different air gap depths and three types of polyimide foams, respectively. The peaks of the inner shell kinetic energy due to shell resonance, hydrodynamic coincidence and acoustic coincidence are discussed. The results show that if the frequency band over the ring frequency is of interest, an air gap, even if very thin, should exist between the two elastic shells for better sound insulation. And if small density foam has a high flow resistance, a superior sound insulation can still be maintained.

Boundary layer transition studies

NASA Technical Reports Server (NTRS)

Watmuff, Jonathan H.

1995-01-01

A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated

Unsteady turbulent boundary layers in swimming rainbow trout.

PubMed

Yanase, Kazutaka; Saarenrinne, Pentti

2015-05-01

The boundary layers of rainbow trout, Oncorhynchus mykiss, swimming at 1.02±0.09 L s(-1) (mean±s.d., N=4), were measured by the particle image velocimetry (PIV) technique at a Reynolds number of 4×10(5). The boundary layer profile showed unsteadiness, oscillating above and beneath the classical logarithmic law of the wall with body motion. Across the entire surface regions that were measured, local Reynolds numbers based on momentum thickness, which is the distance that is perpendicular to the fish surface through which the boundary layer momentum flows at free-stream velocity, were greater than the critical value of 320 for the laminar-to-turbulent transition. The skin friction was dampened on the convex surface while the surface was moving towards a free-stream flow and increased on the concave surface while retreating. These observations contradict the result of a previous study using different species swimming by different methods. Boundary layer compression accompanied by an increase in local skin friction was not observed. Thus, the overall results may not support absolutely the Bone-Lighthill boundary layer thinning hypothesis that the undulatory motions of swimming fish cause a large increase in their friction drag because of the compression of the boundary layer. In some cases, marginal flow separation occurred on the convex surface in the relatively anterior surface region, but the separated flow reattached to the fish surface immediately downstream. Therefore, we believe that a severe impact due to induced drag components (i.e. pressure drag) on the swimming performance, an inevitable consequence of flow separation, was avoided. © 2015. Published by The Company of Biologists Ltd.

Comments on Hypersonic Boundary-Layer Transition

DTIC Science & Technology

1990-09-01

mechanism by which boundary-layer disturbance growth is generally initiated and establishes the initial distur- banca amplitude at the onset of disturbance...Patankar, S. V., and Spalding, P. B., Heat and Mass Transfer in Boundary Lavers, CRC Press , Cleveland, Ohio, 1968. 87. Neumann, R. D., and Patterson, .J. 1

Low Ozone in the Marine Boundary Layer of the Tropical Pacific Ocean

NASA Technical Reports Server (NTRS)

Singh, Hanwant B.; Gregory, G. L.; Andesrson, B.; Browell, E.; Sachse, G. W.; Davis, D. D.; Crawford, J.; Bradshaw, J. D.; Talbot, R.; Blake, D. R.;

Orbiter Entry Aeroheating Working Group Viscous CFD Boundary Layer Transition Trailblazer Solutions

NASA Technical Reports Server (NTRS)

Wood, William A.; Erickson, David W.; Greene, Francis A.

2007-01-01

Boundary layer transition correlations for the Shuttle Orbiter have been previously developed utilizing a two-layer boundary layer prediction technique. The particular two-layer technique that was used is limited to Mach numbers less than 20. To allow assessments at Mach numbers greater than 20, it is proposed to use viscous CFD to the predict boundary layer properties. This report addresses if the existing Orbiter entry aeroheating viscous CFD solutions, which were originally intended to be used for heat transfer rate predictions, adequately resolve boundary layer edge properties and if the existing two-layer results could be leveraged to reduce the number of needed CFD solutions. The boundary layer edge parameters from viscous CFD solutions are extracted along the wind side centerline of the Space Shuttle Orbiter at reentry conditions, and are compared with results from the two-layer boundary layer prediction technique. The differences between the viscous CFD and two-layer prediction techniques vary between Mach 6 and 18 flight conditions and Mach 6 wind tunnel conditions, and there is not a straightforward scaling between the viscous CFD and two-layer values. Therefore: it is not possible to leverage the existing two-layer Orbiter flight boundary layer data set as a substitute for a viscous CFD data set; but viscous CFD solutions at the current grid resolution are sufficient to produce a boundary layer data set suitable for applying edge-based boundary layer transition correlations.

A cloudiness transition in a marine boundary layer

NASA Technical Reports Server (NTRS)

Betts, Alan K.; Boers, Reinout

1990-01-01

Boundary layer cloudiness plays several important roles in the energy budget of the earth. Low level stratocumulus are highly reflective clouds which reduce the net incoming shortwave radiation at the earth's surface. Climatically, the transition to a small area fraction of scattered cumulus clouds occurs as the air flows over warmer water. Although these clouds reflect less sunlight, they still play an important role in the boundary layer equilibrium by transporting water vapor upwards, and enhancing the surface evaporation. The First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE) included a marine stratocumulus experiment off the southern California coast from June 29 to July 19, 1987. The objectives of this experiment were to study the controls on fractional cloudiness, and to assess the role of cloud-top entrainment instability (CTEI) and mesoscale structure in determining cloud type. The focus is one research day, July 7, 1987, when coordinated aircraft missions were flown by four research aircraft, centered on a LANDSAT scene at 1830 UTC. The remarkable feature of this LANDSAT scene is the transition from a clear sky in the west through broken cumulus to solid stratocumulus in the east. The dynamic and thermodynamic structure of this transition in cloudiness is analyzed using data from the NCAR Electra. By averaging the aircraft data, the internal structure of the different cloud regimes is documented, and it is shown that the transition between broken cumulus and stratocumulus is associated with a change in structure with respect to the CTEI condition. However, this results not from sea surface temperature changes, but mostly from a transition in the air above the inversion, and the breakup appears to be at a structure on the unstable side of the wet virtual adiabat.

Shock-like structures in the tropical cyclone boundary layer

NASA Astrophysics Data System (ADS)

Williams, Gabriel J.; Taft, Richard K.; McNoldy, Brian D.; Schubert, Wayne H.

2013-06-01

This paper presents high horizontal resolution solutions of an axisymmetric, constant depth, slab boundary layer model designed to simulate the radial inflow and boundary layer pumping of a hurricane. Shock-like structures of increasing intensity appear for category 1-5 hurricanes. For example, in the category 3 case, the u>(∂u/∂r>) term in the radial equation of motion produces a shock-like structure in the radial wind, i.e., near the radius of maximum tangential wind the boundary layer radial inflow decreases from approximately 22 m s-1 to zero over a radial distance of a few kilometers. Associated with this large convergence is a spike in the radial distribution of boundary layer pumping, with updrafts larger than 22 m s-1 at a height of 1000 m. Based on these model results, it is argued that observed hurricane updrafts of this magnitude so close to the ocean surface are attributable to the dry dynamics of the frictional boundary layer rather than moist convective dynamics. The shock-like structure in the boundary layer radial wind also has important consequences for the evolution of the tangential wind and the vertical component of vorticity. On the inner side of the shock the tangential wind tendency is essentially zero, while on the outer side of the shock the tangential wind tendency is large due to the large radial inflow there. The result is the development of a U-shaped tangential wind profile and the development of a thin region of large vorticity. In many respects, the model solutions resemble the remarkable structures observed in the boundary layer of Hurricane Hugo (1989).

On an Asymptotically Consistent Unsteady Interacting Boundary Layer

NASA Technical Reports Server (NTRS)

Bartels, Robert E.

2007-01-01

This paper develops the asymptotic matching of an unsteady compressible boundary layer to an inviscid flow. Of particular importance is the velocity injection or transpiration boundary condition derived by this theory. It is found that in general the transpiration will contain a slope of the displacement thickness and a time derivative of a density integral. The conditions under which the second term may be neglected, and its consistency with the established results of interacting boundary layer are discussed.

Structure measurements in a synthetic turbulent boundary layer

NASA Astrophysics Data System (ADS)

Arakeri, Jaywant H.

Extensive hot-wire measurements were made to determine the structure of the large eddy in a synthetic turbulent boundary layer on a flat-plate model. The experiments were carried out in a wind tunnel at a nominal free-stream velocity of 12 m/s. The synthetic turbulent boundary layer had a hexagonal pattern of eddies and a ratio of streamwise scale to spanwise scale of 3.2:1. The measured celerity of the large eddy was 84.2 percent of the free-stream velocity. There was some loss of coherence, but very little distortion, as the eddies moved downstream. Several mean properties of the synthetic boundary layer were found to agree quite well with the mean properties of a natural turbulent boundary layer at the same Reynolds number. The large eddy is composed of a pair of primary counter-rotating vortices about five delta long in the steamwise direction and about one delta apart in the spanwise direction, where delta is the mean boundary-layer thickness. Definite signatures are obtained in terms of the mean skin-friction coefficient and the mean wake parameter averaged at constant phase. Velocities induced by the vortices are partly responsible for entrainment of irrotational fluid, for transport of momentum, for generation of Reynolds stresses, and for maintenance of streamwise and normal velocity in the outer flow.

Understanding Micro-Ramp Control for Shock Boundary Layer Interactions

DTIC Science & Technology

2008-02-07

micro-ramps on a supersonic boundary layer at M=3.0 was investigated using monotone integrated Large Eddy Simulations (MILES) and Reynolds Averaged Navier... Supersonic boundary layer flow with micro-ramp and no shock wave 3.2 SBLI with no micro-ramp 3.3 SBLI with micro-ramp 3.4 Micro-ramp size and location IV . C...ramps on a supersonic boundary layer at M=3.0 was investigated using monotone integrated Large Eddy Simulations (MILES) and Reynolds Averaged Navier

Compressible Boundary Layer Investigation for Ramjet/scramjet Inlets and Nozzles

NASA Astrophysics Data System (ADS)

Goldfeld, M. A.; Starov, A. V.; Semenova, Yu. V.

2005-02-01

The results of experimental investigation of a turbulent boundary layer on compression and expansion surfaces are presented. They include the study of the shock wave and/or expansion fan action upon the boundary layer, boundary layer separation and its relaxation. Complex events of paired interactions and the flow on compression convex-concave surfaces were studied [M. Goldfeld, 1993]. The possibility and conditions of the boundary layer relaminarization behind the expansion fan and its effect on the relaxation length are presented. Different model configurations for wide range conditions were investigated. Comparison of results for different interactions was carried out.

Numerical simulations of the stratified oceanic bottom boundary layer

NASA Astrophysics Data System (ADS)

Taylor, John R.

Numerical simulations are used to consider several problems relevant to the turbulent oceanic bottom boundary layer. In the first study, stratified open channel flow is considered with thermal boundary conditions chosen to approximate a shallow sea. Specifically, a constant heat flux is applied at the free surface and the lower wall is assumed to be adiabatic. When the surface heat flux is strong, turbulent upwellings of low speed fluid from near the lower wall are inhibited by the stable stratification. Subsequent studies consider a stratified bottom Ekman layer over a non-sloping lower wall. The influence of the free surface is removed by using an open boundary condition at the top of the computational domain. Particular attention is paid to the influence of the outer layer stratification on the boundary layer structure. When the density field is initialized with a linear profile, a turbulent mixed layer forms near the wall, which is separated from the outer layer by a strongly stable pycnocline. It is found that the bottom stress is not strongly affected by the outer layer stratification. However, stratification reduces turbulent transport to the outer layer and strongly limits the boundary layer height. The mean shear at the top of the boundary layer is enhanced when the outer layer is stratified, and this shear is strong enough to cause intermittent instabilities above the pycnocline. Turbulence-generated internal gravity waves are observed in the outer layer with a relatively narrow frequency range. An explanation for frequency content of these waves is proposed, starting with an observed broad-banded turbulent spectrum and invoking linear viscous decay to explain the preferential damping of low and high frequency waves. During the course of this work, an open-source computational fluid dynamics code has been developed with a number of advanced features including scalar advection, subgrid-scale models for large-eddy simulation, and distributed memory

Solute boundary layer on a rotating crystal

NASA Astrophysics Data System (ADS)

Povinelli, Michelle L.; Korpela, Seppo A.; Chait, Arnon

1994-11-01

A perturbation analysis has been carried out for the solutal boundary layer next to a rotating crystal. Our aim is to extend the classical results of Burton, Prim and Slicher [1] in order to obtain higher order terms in asymptotic expansions for the concentration field and boundary-layer thickness. Expressions for the effective segregation coefficient are directly obtained from the concentration solution in the two limits that correspond to weak and strong rotation.

Calculations of unsteady turbulent boundary layers with flow reversal

NASA Technical Reports Server (NTRS)

Nash, J. F.; Patel, V. C.

1975-01-01

The results are presented of a series of computational experiments aimed at studying the characteristics of time-dependent turbulent boundary layers with embedded reversed-flow regions. A calculation method developed earlier was extended to boundary layers with reversed flows for this purpose. The calculations were performed for an idealized family of external velocity distributions, and covered a range of degrees of unsteadiness. The results confirmed those of previous studies in demonstrating that the point of flow reversal is nonsingular in a time-dependent boundary layer. A singularity was observed to develop downstream of reversal, under certain conditions, accompanied by the breakdown of the boundary-layer approximations. A tentative hypothesis was advanced in an attempt to predict the appearance of the singularity, and is shown to be consistent with the calculated results.

Experimental measurements of unsteady turbulent boundary layers near separation

NASA Technical Reports Server (NTRS)

Simpson, R. L.

1982-01-01

Investigations conducted to document the behavior of turbulent boundary layers on flat surfaces that separate due to adverse pressure gradients are reported. Laser and hot wire anemometers measured turbulence and flow structure of a steady free stream separating turbulent boundary layer produced on the flow of a wind tunnel section. The effects of sinusoidal and unsteadiness of the free stream velocity on this separating turbulent boundary layer at a reduced frequency were determined. A friction gage and a thermal tuft were developed and used to measure the surface skin friction and the near wall fraction of time the flow moves downstream for several cases. Abstracts are provided of several articles which discuss the effects of the periodic free stream unsteadiness on the structure or separating turbulent boundary layers.

Differences in the concentrations of atmospheric trace gases in and above the tropical boundary layer

NASA Technical Reports Server (NTRS)

Rasmussen, R. A.; Khalil, M. A. K.

1981-01-01

Weekly air samples were collected at Cape Kumakahi (0 km) and at nearby Mauna Loa Observatory (3.4 km) which is above the boundary layer. EC/GC and GC/FID techniques were used to measure CH3I, CHCl3, CO and CH4 which are largely natural in origin, and C2Cl4, CCl4, CH3CCl3, (F-11), CCl2F2, (F-12), CHClF, (F-22) and C2F3Cl3 (F-113), which are due to anthropogenic (CCl3F) etc. activities. It was found that all these gases are significantly (alpha is equal to or less than 0.05) more abundant in the boundary layer than above it.

Experiments with a wing from which the boundary layer is removed by pressure or suction

NASA Technical Reports Server (NTRS)

Wieland, K

1928-01-01

With an unsymmetrical wing and a rotating Magnus cylinder, the lift is produced by the superposition of parallel and circulatory flows. An explanation of the circulatory flow is furnished by the boundary-layer theory of Prandtl and the consequent vortex formation. According to this explanation, it must evidently be possible to increase the circulation either by increasing the size of the stronger (lower) vortex or by decreasing the size of the weaker (upper) vortex. In this sense, according to Professor H. Zickendraht, we have a new type of wing from which the boundary layer is removed by forcing air out or sucking it in through openings in the upper surface of the wing near its trailing edge.

Characteristics of Boundary Layer Structure during a Persistent Haze Event in the Central Liaoning City Cluster, Northeast China

NASA Astrophysics Data System (ADS)

Li, Xiaolan; Wang, Yangfeng; Shen, Lidu; Zhang, Hongsheng; Zhao, Hujia; Zhang, Yunhai; Ma, Yanjun

2018-04-01

The characteristics of boundary layer structure during a persistent regional haze event over the central Liaoning city cluster of Northeast China from 16 to 21 December 2016 were investigated based on the measurements of particulate matter (PM) concentration and the meteorological data within the atmospheric boundary layer (ABL). During the observational period, the maximum hourly mean PM2.5 and PM10 concentrations in Shenyang, Anshan, Fushun, and Benxi ranged from 276 to 355 μg m-3 and from 378 to 442 μg m-3, respectively, and the lowest hourly mean atmospheric visibility (VIS) in different cities ranged from 0.14 to 0.64 km. The central Liaoning city cluster was located in the front of a slowly moving high pressure and was mainly controlled by southerly winds. Wind speed (WS) within the ABL (< 2 km) decreased significantly and WS at 10-m height mostly remained below 2 m s-1 during the hazy episodes, which was favorable for the accumulation of air pollutants. A potential temperature inversion layer existed throughout the entire ABL during the earlier hazy episode [from 0500 Local Time (LT) 18 December to 1100 LT 19 December], and then a potential temperature inversion layer developed with the bottom gradually decreased from 900 m to 300 m. Such a stable atmospheric stratification further weakened pollutant dispersion. The atmospheric boundary layer height (ABLH) estimated based on potential temperature profiles was mostly lower than 400 m and varied oppositely with PM2.5 in Shenyang. In summary, weak winds due to calm synoptic conditions, strong thermal inversion layer, and shallow atmospheric boundary layer contributed to the formation and development of this haze event. The backward trajectory analysis revealed the sources of air masses and explained the different characteristics of the haze episodes in the four cities.

Differences of atmospheric boundary layer characteristics between pre-monsoon and monsoon period over the Erhai Lake

NASA Astrophysics Data System (ADS)

Xu, Lujun; Liu, Huizhi; Du, Qun; Wang, Lei; Yang, Liu; Sun, Jihua

2018-01-01

The differences in planetary boundary layer characteristics, in particular atmospheric boundary layer height (ABLH), humidity, and local circulations in pre-monsoon and monsoon period over the Erhai Lake, were simulated by the lake-atmosphere coupled model WRF v3.7.1. No lake simulations were also conducted to investigate lake effects over complex topography. During pre-monsoon period, local circulation was fully developed under weak synoptic system. The ABLH ran up to 2300 m or so. During monsoon period, temperature difference between land and lake became smaller, resulting in weaker local circulations. The height of circulation reduced by 500 m, and ABLH ran up to 1100 m during the day. Enhanced soil moisture and low surface temperature due to monsoon rainfalls in July could be the main reason for the slightly lower ABLH over the Erhai Lake area. Specific humidity of the boundary layer increased 8.8 g kg-1 or so during monsoon period. The Erhai Lake enlarged thermal contrast between valley and mountain slope in the Dali Basin. The lake reduced air temperature by 2 3 °C during daytime and increased air temperature by nearly 2 °C in the evening. Due to its small roughness length and large thermal capacity, the Erhai Lake enlarged lake-land temperature difference and local wind speed. A cyclonic circulation was maintained by the combination of mountain breeze and land breeze in the south of the lake. The lake decreased air temperature, increased specific humidity, and reduced ABLH during daytime, whereas the opposite effect is presented at night.

Planetary boundary layer height retrieval at UMBC in the frame of NOAA/ARL campaign

NASA Astrophysics Data System (ADS)

Lolli, S.; Delgado, R.; Compton, J.; Hoff, R.

2011-11-01

The determination of the depth of daytime and nighttime Planetary Boundary Layer Height (PBLH) must be known very accurately to relate boundary layer concentrations of gases or particles to upstream fluxes. Moreover, the air quality forecasts rely upon semi-empirical parameterizations within numerical models for the description of dispersion, formation and fate of pollutants influenced by the spatial and temporal distribution of emissions in cities, topography, and weather. The particulate matter (PM) mass measured at the ground level is a common way to quantify the amount of aerosol particles in the atmosphere and is the standard used to evaluate air quality. Remote sensing of atmospheric aerosols in the lower troposphere that affect air quality is done at the University of Maryland, Baltimore County (UMBC) by the Atmospheric Lidar Group, that supported the joint NOAA/ARL and NCEP ad hoc field study. These campaigns launched radiosondes from Howard University (HU) (26.6km south of UMBC) and RFK Stadium (29.15 km south of UMBC) during September 14-22, 2009 to develop a database to investigate the evolution and spatial variability of the PBLH. In this paper, we examined the potential for continual observation of PBLH by performing a statistical comparison of the spatial and temporal resolution of PBLH from lidars, wind profiler, and radiosonde measurements

Insights into Evaporative Droplet Dynamics in the High-Wind Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Peng, T.; Richter, D. H.

2017-12-01

Sea-spray droplets ejected into the air-sea boundary layer take part in a series of complex transport processes. To model the air-sea exchange of heat and moisture under high-wind conditions, it is important yet challenging to understand influences of evaporative droplets in the atmospheric boundary layer. We implement a high-resolution Eulerian-Lagrangian algorithm with droplets laden in a turbulent open-channel flow to reveal the dynamic and thermodynamic characteristics of evaporating sea spray. Our past numerical simulations demonstrated an overall weak modification to the total heat flux by evaporative droplets. This is due to redistributed sensible and latent heat fluxes from relatively small droplets that respond rapidly to the ambient environment or the limited residence time of larger droplets. However, droplets with a slower thermodynamic response to the environment indicate a potential to enhance the total heat flux, but this is dependent on concentration and suspension time. In the current study, we focus on correlations between the residence time and thermodynamic statistics of droplets in order to better understand how best to parameterize in large-scale models. In addition, we focus in detail on the different scales of turbulence to further characterize the range of influence that evaporating droplets have on the surrounding fluid.

Process analysis of characteristics of the boundary layer during a heavy haze pollution episode in an inland megacity, China.

PubMed

Wang, Shan; Liao, Tingting; Wang, Lili; Sun, Yang

2016-02-01

Ground observation data from 8 meteorological stations in Xi'an, air mass concentration data from 13 environmental quality monitoring sites in Xi'an, as well as radiosonde observation and wind profile radar data, were used in this study. Thereby, the process, causes and boundary layer meteorological characteristics of a heavy haze episode occurring from 16 to 25 December 2013 in Xi'an were analyzed. Principal component analysis showed that this haze pollution was mainly caused by the high-intensity emission and formation of gaseous pollutants (NO2, CO and SO2) and atmospheric particles (PM2.5 (fine particles) and PM10 (respirable suspended particle). The second cause was the relative humidity and continuous low temperature. The third cause was the allocation of the surface pressure field. The presence of a near-surface temperature inversion at the boundary layer formed favorable stratification conditions for the formation and maintenance of heavy haze pollution. The persistent thick haze layer weakened the solar radiation. Meanwhile, a warming effect in the urban canopy layer and in the transition zone from the urban friction sublayer to the urban canopy was indicated. All these conditions facilitated the maintenance and reinforcement of temperature inversion. The stable atmospheric stratification finally acted on the wind field in the boundary layer, and further weakened the exchange capacity of vertical turbulence. The superposition of a wind field with the horizontal gentle wind induced the typical air stagnation and finally caused the deterioration of air quality during this haze event. Copyright © 2015. Published by Elsevier B.V.

Boundary layer temperature measurements of a noctual urban boundary layer

NASA Astrophysics Data System (ADS)

Holloway, Simon; Ricketts, Hugo; Vaughan, Geraint

2018-04-01

A low-power lidar system based in Manchester, United Kingdom has been developed to measure temperature profiles in the nocturnal urban boundary layer. The lidar transmitter uses a 355nm diode-pumped solid state Nd:YAG laser and two narrow-band interference filters in the receiver filter out rotational Raman lines that are dependent on temperature. The spectral response of the lidar is calibrated using a monochromator. Temperature profiles measured by the system are calibrated by comparison to co-located radiosondes.

A novel concept for subsonic inlet boundary-layer control

NASA Technical Reports Server (NTRS)

Miller, B. A.

1977-01-01

A self-bleeding method for boundary layer control is described and tested for a subsonic inlet designed to operate in the flowfield generated by high angles of attack. Naturally occurring surface static pressure gradients are used to remove the boundary layer from a separation-prone region of the inlet and to reinject it at a less critical location with a net performance gain. The results suggest that this self-bleeding method for boundary-layer control might be successfully applied to other inlets operating at extreme aerodynamic conditions.

Interferometric data for a shock-wave/boundary-layer interaction

NASA Technical Reports Server (NTRS)

Dunagan, Stephen E.; Brown, James L.; Miles, John B.

1986-01-01

An experimental study of the axisymmetric shock-wave / boundary-layer strong interaction flow generated in the vicinity of a cylinder-cone intersection was conducted. The study data are useful in the documentation and understanding of compressible turbulent strong interaction flows, and are part of a more general effort to improve turbulence modeling for compressible two- and three-dimensional strong viscous/inviscid interactions. The nominal free stream Mach number was 2.85. Tunnel total pressures of 1.7 and 3.4 atm provided Reynolds number values of 18 x 10(6) and 36 x 10(6) based on model length. Three cone angles were studied giving negligible, incipient, and large scale flow separation. The initial cylinder boundary layer upstream of the interaction had a thickness of 1.0 cm. The subsonic layer of the cylinder boundary layer was quite thin, and in all cases, the shock wave penetrated a significant portion of the boundary layer. Owing to the thickness of the cylinder boundary layer, considerable structural detail was resolved for the three shock-wave / boundary-layer interaction cases considered. The primary emphasis was on the application of the holographic interferometry technique. The density field was deduced from an interferometric analysis based on the Able transform. Supporting data were obtained using a 2-D laser velocimeter, as well as mean wall pressure and oil flow measurements. The attached flow case was observed to be steady, while the separated cases exhibited shock unsteadiness. Comparisons with Navier-Stokes computations using a two-equation turbulence model are presented.

The analysis of a nonsimilar laminar boundary layer

NASA Technical Reports Server (NTRS)

Stalmach, D. D.; Bertin, J. J.

1978-01-01

A computer code is described which yields accurate solutions for a broad range of laminar, nonsimilar boundary layers, providing the inviscid flow field is known. The boundary layer may be subject to mass injection for perfect-gas, nonreacting flows. If no mass injection is present, the code can be used with either perfect-gas or real-gas thermodynamic models. Solutions, ranging from two-dimensional similarity solutions to solutions for the boundary layer on the Space Shuttle Orbiter during reentry conditions, have been obtained with the code. Comparisons of these solutions, and others, with solutions presented in the literature; and with solutions obtained from other codes, demonstrate the accuracy of the present code.

Inverse boundary-layer theory and comparison with experiment

NASA Technical Reports Server (NTRS)

Carter, J. E.

1978-01-01

Inverse boundary layer computational procedures, which permit nonsingular solutions at separation and reattachment, are presented. In the first technique, which is for incompressible flow, the displacement thickness is prescribed; in the second technique, for compressible flow, a perturbation mass flow is the prescribed condition. The pressure is deduced implicitly along with the solution in each of these techniques. Laminar and turbulent computations, which are typical of separated flow, are presented and comparisons are made with experimental data. In both inverse procedures, finite difference techniques are used along with Newton iteration. The resulting procedure is no more complicated than conventional boundary layer computations. These separated boundary layer techniques appear to be well suited for complete viscous-inviscid interaction computations.

Delimitation of air space and outer space - Is such a boundary needed now?

NASA Technical Reports Server (NTRS)

Hosenball, S. N.

1983-01-01

A discussion is presented of the question of establishing a boundary between air space and outer space. Four theories and approaches for establishing a delimitation between air space and outer space are examined. Spatial approaches include demarcation based on the division of the atmosphere into layers, demarcation based on aerodynamic characteristics of flight instrumentalities (von Karman Line), demarcation according to the lowest perigee of an orbiting satellite, and demarcation based upon the earth's gravitational effects. The functionalist approach is based on the delimitation or definition of the air space/outer space regime by the purpose and activities for which an object is designed in air space or outer space. The arbitrarist approach is supported by those who wish to draw an arbitrary line between air space and outer space. It is proposed that a pragmatist approach will be more useful than the other three approaches. The pragmatist approach advocates not establishing a boundary between air space and outer space at the present time or in the immediate future. It is argued that there are at present no serious problems that can be resolved by the definition/delimitation of air space and outer space.

Destiny of earthward streaming plasma in the plasmasheet boundary layer

NASA Technical Reports Server (NTRS)

Green, J. L.; Horwitz, J. L.

1986-01-01

The dynamics of the earth's magnetotail have been investigated, and it has become clear that the plasmasheet boundary layer field lines map into the Region I Field-Aligned Currents (FAC) of the auroral zone. It is pointed out that the role of earthward streaming ions in the plasmasheet boundary layer may be of fundamental importance in the understanding of magnetotail dynamics, auroral zone physics, and especially for ionospheric-magnetospheric interactions. The present paper has the objective to evaluate propagation characteristics for the earthward streaming ions observed in the plasmasheet boundary layer. An investigation is conducted of the propagation characteristics of protons in the plasmasheet boundary layer using independent single particle dynamics, and conclusions are discussed. The density of earthward streaming ions found in the plasmasheet boundary layer should include the ring current as well as the auroral zone precipitaiton and inner plasmasheet regions of the magnetosphere.

Computer graphic visualization of orbiter lower surface boundary-layer transition

NASA Technical Reports Server (NTRS)

Throckmorton, D. A.; Hartung, L. C.

1984-01-01

Computer graphic techniques are applied to the processing of Shuttle Orbiter flight data in order to create a visual presentation of the extent and movement of the boundary-layer transition front over the orbiter lower surface during entry. Flight-measured surface temperature-time histories define the onset and completion of the boundary-layer transition process at any measurement location. The locus of points which define the spatial position of the boundary-layer transition front on the orbiter planform is plotted at each discrete time for which flight data are available. Displaying these images sequentially in real-time results in an animated simulation of the in-flight boundary-layer transition process.

Characterization of the Shear Layer in a Mach 3 Shock/Turbulent Boundary Layer Interaction

NASA Astrophysics Data System (ADS)

Helm, Clara; Priebe, Stephan; Li, Justine; Dupont, Pierre; Martin, Pino

2013-11-01

The unsteady motion of fully separated shock and turbulent boundary layers interactions (STBLIs) is characterized by an energized low-frequency motion that is two orders of magnitude lower than that of the incoming turbulence. In addition, the spectra shows significant energy content at frequency that is between the characteristic low frequency and the higher frequency motions of the incoming turbulence. The intermediate frequency content is hypothesized to be associated with the existence of Kelvin-Helmholtz type structures, which form in the shear layer downstream of the separation shock and are shed near the reattachment point downstream of the interaction. The current research is concerned with investigating the origins of the intermediate frequencies, and how they may be related to or possibly influence the low-frequency unsteadiness. Specifically, LES data of a Mach 3 STBLI over a 24o ramp are used to estimate convection velocities within the shear layer downstream of the shock. In addition, Brown and Thomas type correlations are used to estimate time and length scales of the eddies in the shear layer. This work is supported by the Air Force Office of Scientific Research under grant AF/9550-10-1-0164.

Boundary layer friction of solvate ionic liquids as a function of potential.

PubMed

Li, Hua; Rutland, Mark W; Watanabe, Masayoshi; Atkin, Rob

2017-07-01

Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl)amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li + cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI - anion rich boundary layer at positive potentials is more lubricating than the Li + cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li + cations for both surfaces at negative potentials. However, at Au(111), the TFSI - rich boundary layer is less lubricating than the Li + rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO 3 at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO 3 - rich boundary layer.

Transitional and turbulent boundary layer with heat transfer

NASA Astrophysics Data System (ADS)

Wu, Xiaohua; Moin, Parviz

2010-08-01

We report on our direct numerical simulation of an incompressible, nominally zero-pressure-gradient flat-plate boundary layer from momentum thickness Reynolds number 80-1950. Heat transfer between the constant-temperature solid surface and the free-stream is also simulated with molecular Prandtl number Pr=1. Skin-friction coefficient and other boundary layer parameters follow the Blasius solutions prior to the onset of turbulent spots. Throughout the entire flat-plate, the ratio of Stanton number and skin-friction St/Cf deviates from the exact Reynolds analogy value of 0.5 by less than 1.5%. Mean velocity and Reynolds stresses agree with experimental data over an extended turbulent region downstream of transition. Normalized rms wall-pressure fluctuation increases gradually with the streamwise growth of the turbulent boundary layer. Wall shear stress fluctuation, τw,rms'+, on the other hand, remains constant at approximately 0.44 over the range, 800boundary layer edge with no near-wall secondary peak, in good agreement with previous boundary layer heat transfer experiments. In the transitional region, turbulent spots are tightly packed with numerous hairpin vortices. With the advection and merging of turbulent spots, these young isolated hairpin forests develop into the downstream turbulent region. Isosurfaces of temperature up to Reθ=1900 are found to display well-resolved signatures of hairpin vortices, which indicates the persistence of the hairpin forests.

Similarity theory of the buoyantly interactive planetary boundary layer with entrainment

NASA Technical Reports Server (NTRS)

Hoffert, M. I.; Sud, Y. C.

1976-01-01

A similarity model is developed for the vertical profiles of turbulent flow variables in an entraining turbulent boundary layer of arbitrary buoyant stability. In the general formulation the vertical profiles, internal rotation of the velocity vector, discontinuities or jumps at a capping inversion and bulk aerodynamic coefficients of the boundary layer are given by solutions to a system of ordinary differential equations in the similarity variable. To close the system, a formulation for buoyantly interactive eddy diffusivity in the boundary layer is introduced which recovers Monin-Obukhov similarity near the surface and incorporates a hypothesis accounting for the observed variation of mixing length throughout the boundary layer. The model is tested in simplified versions which depend only on roughness, surface buoyancy, and Coriolis effects by comparison with planetary-boundary-layer wind- and temperature-profile observations, measurements of flat-plate boundary layers in a thermally stratified wind tunnel and observations of profiles of terms in the turbulent kinetic-energy budget of convective planetary boundary layers. On balance, the simplified model reproduced the trend of these various observations and experiments reasonably well, suggesting that the full similarity formulation be pursued further.

Saharan Air Layer Interaction with Hurricane Claudette (2003)

NASA Astrophysics Data System (ADS)

Rothman, G. S.; Gill, T. E.; Chang, C.

2004-12-01

It has long been observed that the Saharan Air Layer (SAL), a large and seasonally-persistent layer of West African aeolian dust suspended over the Atlantic Ocean, may influence the variability and intensity of easterly waves and tropical cyclones in the Atlantic basin. The radiative and conductive properties of the Saharan aerosols may contribute to warming within the dust layer, creating an anomalous baroclinic zone in the tropical North Atlantic. Environmental baroclinic instability is a mechanism for conversion of potential energy to eddy kinetic energy, facilitating wave growth. However, this same baroclinic mechanism, along with the dry properties of the SAL, could also promote asymmetry in a tropical cyclone, limiting its intensity. Detailed investigations of specific cases are necessary to better understand the radiative heating or cooling impact that the Saharan aerosols cause as well as potential influences on cyclone track and intensity stemming from the aeolian dust cloud. Here, we consider the case of Claudette in 2003. On June 29, 2003, an easterly wave embedded near the southern boundary of a broad Saharan dust layer emerged from the West African Coastal Bend region into the Atlantic Ocean. The wave propagated westward, reaching tropical storm intensity as Claudette in the Caribbean and developing into a hurricane just before making landfall on the southern Texas Gulf of Mexico coast on July 15. The SAL propagated in phase with this system throughout almost its entire evolution. Rapid intensification of Claudette into a hurricane in the last 15 hours prior to landfall was concurrent with a decoupling from the Saharan dust intrusion, with the two following separate tracks into North America at the end of the period. We performed an investigation to understand and diagnose the interaction between the Saharan Air Layer and Claudette. HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory Model) along-trajectory potential temperature plots as

Orbiter Boundary Layer Transition Prediction Tool Enhancements

NASA Technical Reports Server (NTRS)

Berry, Scott A.; King, Rudolph A.; Kegerise, Michael A.; Wood, William A.; McGinley, Catherine B.; Berger, Karen T.; Anderson, Brian P.

2010-01-01

Updates to an analytic tool developed for Shuttle support to predict the onset of boundary layer transition resulting from thermal protection system damage or repair are presented. The boundary layer transition tool is part of a suite of tools that analyze the local aerothermodynamic environment to enable informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each d agmea site or repair, the expected time (and thus Mach number) of transition onset is predicted to help define proper environments for use in subsequent thermal and stress analysis of the thermal protection system and structure. The boundary layer transition criteria utilized within the tool were updated based on new local boundary layer properties obtained from high fidelity computational solutions. Also, new ground-based measurements were obtained to allow for a wider parametric variation with both protuberances and cavities and then the resulting correlations were calibrated against updated flight data. The end result is to provide correlations that allow increased confidence with the resulting transition predictions. Recently, a new approach was adopted to remove conservatism in terms of sustained turbulence along the wing leading edge. Finally, some of the newer flight data are also discussed in terms of how these results reflect back on the updated correlations.

Lidar Measurements of Wind, Moisture and Boundary Layer Evolution in a Dryline During IHOP2002

NASA Technical Reports Server (NTRS)

Demoz, Belay; Evans, Keith; DiGirolamo, Paolo; Wang, Zhien; Whiteman, David; Schwemmer, Geary; Gentry, Bruce; Miller, David

2003-01-01

Variability in the convective boundary layer moisture, wind and temperature fields and their importance in the forecasting and understanding of storms have been discussed in the literature. These variations have been reported in relation to frontal zones, stationary boundaries and during horizontal convective rolls. While all three vary substantially in the convective boundary layer, moisture poses a particular challenge. Moisture or water vapor concentration (expressed as a mass mixing ratio, g/kg), is conserved in all meteorological processes except condensation and evaporation. The water vapor mixing ratio often remains distinct across an air -mass boundary even when the temperature difference is indistinct. These properties make it an ideal choice in visualizing and understanding many of the atmosphere's dynamic features. However, it also presents a unique measurement challenge because water vapor content can vary by more than three orders of magnitude in the troposphere. Characterization of the 3D-distribution of water vapor is also difficult as water vapor observations can suffer from large sampling errors and substantial variability both in the vertical and horizontal. This study presents groundbased measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars. This presentation will focus on the evolution and variability of moisture and wind in the boundary layer during a dry line event that occurred on 22 May 2002. These data sets and analyses are unique in that they combine simultaneous measurements of wind, moisture and CBL structure to study the detailed thermal variability in and around clear air updrafts during a dryline event. It will quantify the variation caused by, in and around buoyant plumes and across a dryline. The data presented here were collected in the panhandle of Oklahoma as part of the International BO Project (IHOP-2002), a field experiment that took place over the

Linking Dynamics of the Near-surface Flow to Deeper Boundary Layer Forcing in the Nocturnal Boundary Layer

DTIC Science & Technology

2012-06-01

Kaimal and Finnigan (1994), modified) Figure 2.2 illustrates the evolution from unstable CBL to a nocturnal Stable Bound- ary Layer ( SBL ) in the absence...mixed layer acts as a cap for the SBL . The SBL persists through the night until sunrise when surface heating resumes and a new unstable layer begins...to form at the surface, gradually returning to a CBL. 7 2.2.1 Dynamics of the stable boundary layer Because the SBL is stably stratified, buoyancy

Study of boundary-layer transition using transonic-cone preston tube data

NASA Technical Reports Server (NTRS)

Reed, T. D.; Moretti, P. M.

1980-01-01

The laminar boundary layer on a 10 degree cone in a transonic wind tunnel was studied. The inviscid flow and boundary layer development were simulated by computer programs. The effects of pitch and yaw angles on the boundary layer were examined. Preston-tube data, taken on the boundary-layer-transition cone in the NASA Ames 11 ft transonic wind tunnel, were used to develope a correlation which relates the measurements to theoretical values of laminar skin friction. The recommended correlation is based on a compressible form of the classical law-of-the-wall. The computer codes successfully simulates the laminar boundary layer for near-zero pitch and yaw angles. However, in cases of significant pitch and/or yaw angles, the flow is three dimensional and the boundary layer computer code used here cannot provide a satisfactory model. The skin-friction correlation is thought to be valid for body geometries other than cones.

The actuation of microflaps inspired by shark scales deeply embedded in a boundary layer

NASA Astrophysics Data System (ADS)

Morris, Jackson; Lang, Amy; Hubner, Paul

2016-11-01

Thanks to millions of years of natural selection, sharks have evolved to become quick apex predators. Shark skin is made up of microscopic scales on the order of 0.2 mm in size. This array of scales is hypothesized to be a flow control mechanism where individual scales are capable of being passively actuated by reversed flow in water due to their preferential orientation to attached flow. Previous research has proven shark skin to reduce flow separation in water, which would result in lower pressure drag. We believe shark scales are strategically sized to interact with the lower 5 percent of the boundary layer, where reversed flow occurs close to the wall. To test the capability of micro-flaps to be actuated in air various sets of flaps, inspired by shark scale geometry, were rapidly prototyped. These microflaps were tested in a low-speed wind tunnel at various flow speeds and boundary layer thicknesses. Boundary layer flow conditions were measured using a hot-wire probe and microflap actuation was observed. Microflap actuation in airflow would mean that this bio-inspired separation control mechanism found on shark skin has potential application for aircraft. Boeing.

Unsteady transonic viscous-inviscid interaction using Euler and boundary-layer equations

NASA Technical Reports Server (NTRS)

Pirzadeh, Shahyar; Whitfield, Dave

1989-01-01

The Euler code is used extensively for computation of transonic unsteady aerodynamics. The boundary layer code solves the 3-D, compressible, unsteady, mean flow kinetic energy integral boundary layer equations in the direct mode. Inviscid-viscous coupling is handled using porosity boundary conditions. Some of the advantages and disadvantages of using the Euler and boundary layer equations for investigating unsteady viscous-inviscid interaction is examined.

Discussion of boundary-layer characteristics near the casing of an axial-flow compressor

NASA Technical Reports Server (NTRS)

Mager, Artur; Mahoney, John J; Budinger, Ray E

1951-01-01

Boundary-layer velocity profiles on the casing of an axial-flow compressor behind the guide vanes and rotor were measured and resolved into two components: along the streamline of the flow and perpendicular to it. Boundary-layer thickness and the deflection of the boundary layer at the wall were the generalizing parameters. By use of these results and the momentum-integral equations, the characteristics of boundary on the walls of axial-flow compressor are qualitatively discussed. Important parameters concerning secondary flow in the boundary layer appear to be turning of the flow and the product of boundary-layer thickness and streamline curvature outside the boundary layer. Two types of separation are shown to be possible in three dimensional boundary layer.

Heat transfer to the transpired turbulent boundary layer.

NASA Technical Reports Server (NTRS)

Kays, W. M.

1972-01-01

This paper contains a summarization of five years work on an investigation on heat transfer to the transpired turbulent boundary layer. Experimental results are presented for friction coefficient and Stanton number over a wide range of blowing and suction for the case of constant free-stream velocity, holding certain blowing parameters constant. The problem of the accelerated turbulent boundary layer with transpiration is considered, experimental data are presented and discussed, and theoretical models for solution of the momentum equation under these conditions are presented. Data on turbulent Prandtl number are presented so that solutions to the energy equation may be obtained. Some examples of boundary layer heat transfer and friction coefficient predictions are presented using one of the models discussed, employing a finite difference solution method.

Optical measurements of degradation in aircraft boundary layers

NASA Technical Reports Server (NTRS)

Kelsall, D.

1980-01-01

Visible wavelength measurements of the degradation of optical beams when transmitted through the thin aerodynamic boundary layers around an aircraft are reviewed. The measured results indicated degradation levels for the KC-135 airplanes between 0.10 to 0.13 lambda increasing to 0.18 lambda (rms wavefront distortion). For the Lear Jet, degradation with a 25 mm diameter optics was roughly 0.07 lambda. The corresponding infinite aperture degradation levels are also calculated. The corresponding measured correlation lengths of roughly 12 mm for the KC-135 aircraft and 6 mm for the Lear Jet scale to roughly 20 and 25 mm, respectively, for infinite apertures. These boundary layer correlation lengths do not appear to reflect the different boundary layer thicknesses on the two different aircraft.

Boundary layer and fundamental problems of hydrodynamics (compatibility of a logarithmic velocity profile in a turbulent boundary layer with the experience values)

NASA Astrophysics Data System (ADS)

Zaryankin, A. E.

2017-11-01

The compatibility of the semiempirical turbulence theory of L. Prandtl with the actual flow pattern in a turbulent boundary layer is considered in this article, and the final calculation results of the boundary layer is analyzed based on the mentioned theory. It shows that accepted additional conditions and relationships, which integrate the differential equation of L. Prandtl, associating the turbulent stresses in the boundary layer with the transverse velocity gradient, are fulfilled only in the near-wall region where the mentioned equation loses meaning and are inconsistent with the physical meaning on the main part of integration. It is noted that an introduced concept about the presence of a laminar sublayer between the wall and the turbulent boundary layer is the way of making of a physical meaning to the logarithmic velocity profile, and can be defined as adjustment of the actual flow to the formula that is inconsistent with the actual boundary conditions. It shows that coincidence of the experimental data with the actual logarithmic profile is obtained as a result of the use of not particular physical value, as an argument, but function of this value.

Boundary-layer equations in generalized curvilinear coordinates

NASA Technical Reports Server (NTRS)

Panaras, Argyris G.

1987-01-01

A set of higher-order boundary-layer equations is derived valid for three-dimensional compressible flows. The equations are written in a generalized curvilinear coordinate system, in which the surface coordinates are nonorthogonal; the third axis is restricted to be normal to the surface. Also, higher-order viscous terms which are retained depend on the surface curvature of the body. Thus, the equations are suitable for the calculation of the boundary layer about arbitrary vehicles. As a starting point, the Navier-Stokes equations are derived in a tensorian notation. Then by means of an order-of-magnitude analysis, the boundary-layer equations are developed. To provide an interface between the analytical partial differentiation notation and the compact tensor notation, a brief review of the most essential theorems of the tensor analysis related to the equations of the fluid dynamics is given. Many useful quantities, such as the contravariant and the covariant metrics and the physical velocity components, are written in both notations.

Sheared boundary layers in turbulent Rayleigh-Benard convection

NASA Astrophysics Data System (ADS)

Solomon, T. H.; Gollub, J. P.

1990-05-01

Thermal boundary layers in turbulent Rayleigh-Benard convection are studied experimentally using a novel system in which the convecting fluid is sheared from below with a flowing layer of mercury. Oscillatory shear substantially alters the spatial structure and frequency of the eruptions, with minimal effect on the heat flux (less than 5 percent). The temperature probability distribution function (PDF) just above the lower boundary layer changes from Gaussian to exponential without significant changes in the interior PDF. Implications for theories of 'hard' turbulence are discussed.

Numerical Modeling Studies of Wake Vortex Transport and Evolution Within the Planetary Boundary Layer

NASA Technical Reports Server (NTRS)

Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael L.; Shen, Shaohua

1998-01-01

In support of the wake vortex effect of the Terminal Area Productivity program, we have put forward four tasks to be accomplished in our proposal. The first task is validation of two-dimensional wake vortex-turbulence interaction. The second task is investigation of three-dimensional interaction between wake vortices and atmospheric boundary layer (ABL) turbulence. The third task is ABL studies. The, fourth task is addition of a Klemp-Durran condition at the top boundary for TASS model. The accomplishment of these tasks will increase our understanding of the dynamics of wake vortex and improve forecasting systems responsible for air safety and efficiency. The first two tasks include following three parts: (a) Determine significant length scale for vortex decay and transport, especially the length scales associated with the onset of Crow instability (Crow, 1970); (b) Study the effects of atmospheric turbulence on the decay of the wake vortices; and (c) Determine the relationships between decay rate, transport properties and atmospheric parameters based on large eddy simulation (LES) results and the observational data. These parameters may include turbulence kinetic energy, dissipation rate, wind shear and atmospheric stratification. The ABL studies cover LES modeling of turbulence structure within planetary boundary layer under transition and stable stratification conditions. Evidences have shown that the turbulence in the stable boundary layer can be highly intermittent and the length scales of eddies are very small compared to those in convective case. We proposed to develop a nesting grid mesh scheme and a modified Klemp-Durran conditions (Klemp and Wilhelmson, 1978) at the top boundary for TASS model to simulate planetary boundary layer under stable stratification conditions. During the past year, our group has made great efforts to carry out the above mentioned four tasks simultaneously. The work accomplished in the last year will be described in the next

Flat Plate Boundary Layer Stimulation Using Trip Wires and Hama Strips

NASA Astrophysics Data System (ADS)

Peguero, Charles; Henoch, Charles; Hrubes, James; Fredette, Albert; Roberts, Raymond; Huyer, Stephen

2017-11-01

Water tunnel experiments on a flat plate at zero angle of attack were performed to investigate the effect of single roughness elements, i.e., trip wires and Hama strips, on the transition to turbulence. Boundary layer trips are traditionally used in scale model testing to force a boundary layer to transition from laminar to turbulent flow at a single location to aid in scaling of flow characteristics. Several investigations of trip wire effects exist in the literature, but there is a dearth of information regarding the influence of Hama strips on the flat plate boundary layer. The intent of this investigation is to better understand the effects of boundary layer trips, particularly Hama strips, and to investigate the pressure-induced drag of both styles of boundary layer trips. Untripped and tripped boundary layers along a flat plate at a range of flow speeds were characterized with multiple diagnostic measurements in the NUWC/Newport 12-inch water tunnel. A wide range of Hama strip and wire trip thicknesses were used. Measurements included dye flow visualization, direct skin friction and parasitic drag force, boundary layer profiles using LDV, wall shear stress fluctuations using hot film anemometry, and streamwise pressure gradients. Test results will be compared to the CFD and boundary layer model results as well as the existing body of work. Conclusions, resulting in guidance for application of Hama strips in model scale experiments and non-dimensional predictions of pressure drag will be presented.

AERMOD: A DISPERSION MODEL FOR INDUSTRIAL SOURCE APPLICATIONS PART I: GENERAL MODEL FORMULATION AND BOUNDARY LAYER CHARACTERIZATION

EPA Science Inventory

The formulations of the AMS/EPA Regulatory Model Improvement Committee's applied air dispersion model (AERMOD) as related to the characterization of the planetary boundary layer are described. This is the first in a series of three articles. Part II describes the formulation of...

BLSTA: A boundary layer code for stability analysis

NASA Technical Reports Server (NTRS)

Wie, Yong-Sun

1992-01-01

A computer program is developed to solve the compressible, laminar boundary-layer equations for two-dimensional flow, axisymmetric flow, and quasi-three-dimensional flows including the flow along the plane of symmetry, flow along the leading-edge attachment line, and swept-wing flows with a conical flow approximation. The finite-difference numerical procedure used to solve the governing equations is second-order accurate. The flow over a wide range of speed, from subsonic to hypersonic speed with perfect gas assumption, can be calculated. Various wall boundary conditions, such as wall suction or blowing and hot or cold walls, can be applied. The results indicate that this boundary-layer code gives velocity and temperature profiles which are accurate, smooth, and continuous through the first and second normal derivatives. The code presented herein can be coupled with a stability analysis code and used to predict the onset of the boundary-layer transition which enables the assessment of the laminar flow control techniques. A user's manual is also included.

Three dimensional flow field inside compressor rotor, including blade boundary layers

NASA Technical Reports Server (NTRS)

Galmes, J. M.; Pouagere, M.; Lakshminarayana, B.

1982-01-01

The Reynolds stress equation, pressure strain correlation, and dissipative terms and diffusion are discussed in relation to turbulence modelling using the Reynolds stress model. Algebraic modeling of Reynolds stresses and calculation of the boundary layer over an axial cylinder are examined with regards to the kinetic energy model for turbulence modelling. The numerical analysis of blade and hub wall boundary layers, and an experimental study of rotor blade boundary layer in an axial flow compressor rotor are discussed. The Patankar-Spalding numerical method for two dimensional boundary layers is included.

The structure of the stably stratified internal boundary layer in offshore flow over the sea

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Ryan, B. F.

1989-04-01

Observations obtained mainly from a research aircraft are presented of the mean and turbulent structure of the stably stratified internal boundary layer (IBL) over the sea formed by warm air advection from land to sea. The potential temperature and humidity fields reveal the vertical extent of the IBL, for fetches out to several hundred of kilometres, geostrophic winds of 20 25 m s-1, and potential temperature differences between undisturbed continental air and the sea surface of 7 to 17 K. The dependence of IBL depth on these external parameters is discussed in the context of the numerical results of Garratt (1987), and some discrepancies are noted. Wind observations show the development of a low-level wind maximum (wind component normal to the coast) and rotation of the wind to smaller cross-isobar flow angles. Potential temperature (θ) profiles within the IBL reveal quite a different structure to that found in the nocturnal boundary layer (NBL) over land. Over the sea, θ profiles have large positive curvature with vertical gradients increasing monotonically with height; this reflects the dominance of turbulent cooling within the layer. The behaviour is consistent with known behaviour in the NBL over land where curvature becomes negative (vertical gradients of θ decreasing with height) as radiative cooling becomes dominant. Turbulent properties are discussed in terms of non-dimensional quantities, normalised by the surface friction velocity, as functions of normalised height using the IBL depth. Vertical profiles of these and the normalised wavelength of the spectral maximum agree well with known results for the stable boundary layer over land (Caughey et al., 1979).

Highly buoyant bent-over plumes in a boundary layer

NASA Astrophysics Data System (ADS)

Tohidi, Ali; Kaye, Nigel B.

2016-04-01

Highly buoyant plumes, such as wildfire plumes, in low to moderate wind speeds have initial trajectories that are steeper than many industrial waste plumes. They will rise further into the atmosphere before bending significantly. In such cases the plume's trajectory will be influenced by the vertical variation in horizontal velocity of the atmospheric boundary layer. This paper examined the behavior of a plume in an unstratified environment with a power-law ambient velocity profile. Examination of previously published experimental measurements of plume trajectory show that inclusion of the boundary layer velocity profile in the plume model often provides better predictions of the plume trajectory compared to algebraic expressions developed for uniform flow plumes. However, there are many cases in which uniform velocity profile algebraic expressions are as good as boundary layer models. It is shown that it is only important to model the role of the atmospheric boundary layer velocity profile in cases where either the momentum length (square root of source momentum flux divided by the reference wind speed) or buoyancy length (buoyancy flux divided by the reference wind speed cubed) is significantly greater than the plume release height within the boundary layer. This criteria is rarely met with industrial waste plumes, but it is important in modeling wildfire plumes.

A low-density boundary-layer wind tunnel facility

NASA Technical Reports Server (NTRS)

White, B. R.

1987-01-01

This abstract describes a low-density wind-tunnel facility that was established at NASA Ames in order to aid interpretation and understanding of data received from the Mariner and Viking spacecraft through earth-based simulation. The wind tunnel is a boundary-layer type which is capable of operating over a range of air densities ranging from 0.01 to 1.24 kg/cu m, with the lower values being equivalent to the near-surface density of the planet Mars. Although the facility was developed for space and extraterrestrial simulation, it also can serve as a relatively large-scale, low-density aerodynamic test facility. A description of this unique test facility and some Pitot-tube and hot-wire anemometry data acquired in the facility are presented.

Nature, theory and modelling of geophysical convective planetary boundary layers

NASA Astrophysics Data System (ADS)

Zilitinkevich, Sergej

2015-04-01

Geophysical convective planetary boundary layers (CPBLs) are still poorly reproduced in oceanographic, hydrological and meteorological models. Besides the mean flow and usual shear-generated turbulence, CPBLs involve two types of motion disregarded in conventional theories: 'anarchy turbulence' comprised of the buoyancy-driven plumes, merging to form larger plumes instead of breaking down, as postulated in conventional theory (Zilitinkevich, 1973), large-scale organised structures fed by the potential energy of unstable stratification through inverse energy transfer in convective turbulence (and performing non-local transports irrespective of mean gradients of transporting properties). C-PBLs are strongly mixed and go on growing as long as the boundary layer remains unstable. Penetration of the mixed layer into the weakly turbulent, stably stratified free flow causes turbulent transports through the CPBL outer boundary. The proposed theory, taking into account the above listed features of CPBL, is based on the following recent developments: prognostic CPBL-depth equation in combination with diagnostic algorithm for turbulence fluxes at the CPBL inner and outer boundaries (Zilitinkevich, 1991, 2012, 2013; Zilitinkevich et al., 2006, 2012), deterministic model of self-organised convective structures combined with statistical turbulence-closure model of turbulence in the CPBL core (Zilitinkevich, 2013). It is demonstrated that the overall vertical transports are performed mostly by turbulence in the surface layer and entrainment layer (at the CPBL inner and outer boundaries) and mostly by organised structures in the CPBL core (Hellsten and Zilitinkevich, 2013). Principal difference between structural and turbulent mixing plays an important role in a number of practical problems: transport and dispersion of admixtures, microphysics of fogs and clouds, etc. The surface-layer turbulence in atmospheric and marine CPBLs is strongly enhanced by the velocity shears in

Experimental Results from a Flat Plate, Turbulent Boundary Layer Modified for the Purpose of Drag Reduction

NASA Astrophysics Data System (ADS)

Elbing, Brian R.

2006-11-01

Recent experiments on a flat plate, turbulent boundary layer at high Reynolds numbers (>10^7) were performed to investigate various methods of reducing skin friction drag. The methods used involved injecting either air or a polymer solution into the boundary layer through a slot injector. Two slot injectors were mounted on the model with one located 1.4 meters downstream of the nose and the second located 3.75 meters downstream. This allowed for some synergetic experiments to be performed by varying the injections from each slot and comparing the skin friction along the plate. Skin friction measurements were made with 6 shear stress sensors flush mounted along the stream-wise direction of the model.

Temperature and Relative Humidity Vertical Profiles within Planetary Boundary Layer in Winter Urban Airshed

NASA Astrophysics Data System (ADS)

Bendl, Jan; Hovorka, Jan

2017-12-01

The planetary boundary layer is a dynamic system with turbulent flow where horizontal and vertical air mixing depends mainly on the weather conditions and geomorphology. Normally, air temperature from the Earth surface decreases with height but inversion situation may occur, mainly during winter. Pollutant dispersion is poor during inversions so air pollutant concentration can quickly rise, especially in urban closed valleys. Air pollution was evaluated by WHO as a human carcinogen (mostly by polycyclic aromatic hydrocarbons) and health effects are obvious. Knowledge about inversion layer height is important for estimation of the pollution impact and it can give us also information about the air pollution sources. Temperature and relative humidity vertical profiles complement ground measurements. Ground measurements were conducted to characterize comprehensively urban airshed in Svermov, residential district of the city of Kladno, about 30 km NW of Prague, from the 2nd Feb. to the 3rd of March 2016. The Svermov is an air pollution hot-spot for long time benzo[a]pyrene (B[a]P) limit exceedances, reaching the highest B[a]P annual concentration in Bohemia - west part of the Czech Republic. Since the Svermov sits in a shallow valley, frequent vertical temperature inversion in winter and low emission heights of pollution sources prevent pollutant dispersal off the valley. Such orography is common to numerous small settlements in the Czech Republic. Ground measurements at the sports field in the Svermov were complemented by temperature and humidity vertical profiles acquired by a Vaisala radiosonde positioned at tethered He-filled balloon. Total number of 53 series of vertical profiles up to the height of 300 m was conducted. Meteorology parameters were acquired with 4 Hz frequency. The measurements confirmed frequent early-morning and night formation of temperature inversion within boundary layer up to the height of 50 m. This rather shallow inversion had significant

The Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Garratt, J. R.

1994-05-01

A comprehensive and lucid account of the physics and dynamics of the lowest one to two kilometers of the Earth's atmosphere in direct contact with the Earth's surface, known as the atmospheric boundary layer (ABL). Dr. Garratt emphasizes the application of the ABL problems to numerical modeling of the climate, which makes this book unique among recent texts on the subject. He begins with a brief introduction to the ABL before leading to the development of mean and turbulence equations and the many scaling laws and theories that are the cornerstone of any serious ABL treatment. Modeling of the ABL is crucially dependent for its realism on the surface boundary conditions, so chapters four and five deal with aerodynamic and energy considerations, with attention given to both dry and wet land surfaces and the sea. The author next treats the structure of the clear-sky, thermally stratified ABL, including the convective and stable cases over homogeneous land, the marine ABL, and the internal boundary layer at the coastline. Chapter seven then extends this discussion to the cloudy ABL. This is particularly relevant to current research because the extensive stratocumulus regions over the subtropical oceans and stratus regions over the Arctic have been identified as key players in the climate system. In the final chapters, Dr. Garratt summarizes the book's material by discussing appropriate ABL and surface parameterization schemes in general circulation models of the atmosphere that are being used for climate stimulation.

RACORO Extended-Term Aircraft Observations of Boundary-Layer Clouds

NASA Technical Reports Server (NTRS)

Vogelmann, Andrew M.; McFarquhar, Greg M.; Ogren, John A.; Turner, David D.; Comstock, Jennifer M.; Feingold, Graham; Long, Charles N.; Jonsson, Haflidi H.; Bucholtz, Anthony; Collins, Don R.;

A magnetic boundary layer at the magnetopause

NASA Astrophysics Data System (ADS)

Kartalev, M. D.; Simeonov, G.

A new approach in the boundary layer description of the magnetopause is proposed. The magnetopause is considered as a mixing region of two streams of plasma with different parameters. The assumption is made that wave-particle interactions cause the plasma to be resistive. Thus only the magnetic viscosity is supposed to be essential. Other dissipation effects are neglected. The plasma and magnetic field conditions at the outer boundary of the layer can be obtained from the solution of the nondissipative problem for the magnetosheath. The magnetic field is assumed to be known at the inner boundary. No further conditions are needed in our formulation of the problem. The variation of the flow parameters and the magnetic field can be obtained numerically.

An experimental investigation of turbulent boundary layers along curved surfaces

NASA Technical Reports Server (NTRS)

So, R. M. C.; Mellor, G. L.

1972-01-01

A curved wall tunnel was designed, and an equilibrium turbulent boundary layer was set up on the straight section preceding the curved test section. Turbulent boundary layer flows with uniform and adverse pressure distributions along convex and concave walls were investigated. Hot-wire measurements along the convex surface indicated that turbulent mixing between fluid layers was very much reduced. However, the law of the wall held and the skin friction, thus determined, correlated well with other measurements. Hot-wire measurements along the concave test wall revealed a system of longitudinal vortices inside the boundary layer and confirmed that concave curvature enhances mixing. A self-consistent set of turbulent boundary layer equations for flows along curved surfaces was derived together with a modified eddy viscosity. Solution of these equations together with the modified eddy viscosity gave results that correlated well with the present data on flows along the convex surface with arbitrary pressure distribution. However, it could only be used to predict the mean characteristics of the flow along concave walls because of the existence of the system of longitudinal vortices inside the boundary layer.

Boundary layer separation on isolated boattail nozzles. M.S. Thesis; [conducted in the Langley 16-foot transonic wind tunnel

NASA Technical Reports Server (NTRS)

Abeyounis, W. K.

1977-01-01

The phenomenon of separated flow on a series of circular-arc afterbodies was investigated using the Langley 16-foot transonic tunnel at free-stream Mach numbers from 0.40 to 0.95 at 0 deg angle of attack. Both high-pressure air and solid circular cylinders with a diameter equal to the nozzle exit diameter were used to simulate jet exhausts. A detailed data base of boundary layer separation locations was obtained using oil-flow techniques. The results indicate that boundary layer separation is most extensive on steep boattails at high Mach numbers.

Boundary Layer Transition on X-43A

NASA Technical Reports Server (NTRS)

Berry, Scott; Daryabeigi, Kamran; Wurster, Kathryn; Bittner, Robert

2008-01-01

The successful Mach 7 and 10 flights of the first fully integrated scramjet propulsion systems by the Hyper-X (X-43A) program have provided the means with which to verify the original design methodologies and assumptions. As part of Hyper-X s propulsion-airframe integration, the forebody was designed to include a spanwise array of vortex generators to promote boundary layer transition ahead of the engine. Turbulence at the inlet is thought to provide the most reliable engine design and allows direct scaling of flight results to groundbased data. Pre-flight estimations of boundary layer transition, for both Mach 7 and 10 flight conditions, suggested that forebody boundary layer trips were required to ensure fully turbulent conditions upstream of the inlet. This paper presents the results of an analysis of the thermocouple measurements used to infer the dynamics of the transition process during the trajectories for both flights, on both the lower surface (to assess trip performance) and the upper surface (to assess natural transition). The approach used in the analysis of the thermocouple data is outlined, along with a discussion of the calculated local flow properties that correspond to the transition events as identified in the flight data. The present analysis has confirmed that the boundary layer trips performed as expected for both flights, providing turbulent flow ahead of the inlet during critical portions of the trajectory, while the upper surface was laminar as predicted by the pre-flight analysis.

Observations From the Coupled Boundary Layer Air-Sea Transfer Experiment in Hurricanes

NASA Astrophysics Data System (ADS)

Black, P. G.

2006-12-01

The CBLAST field program conducted from 2002-2004 has shown that the wind speed range for which turbulent momentum and moisture exchange coefficients have been derived based upon direct flux measurements has been extended by 30 and 60 percent, respectively, from airborne observations in Hurricanes Fabian and Isabel in 2003. The drag coefficient (CD) values derived from CBLAST momentum flux measurements show CD becoming invariant with wind speed near a 23 ms-1 threshold rather than a hurricane-force threshold near 33 ms-1. Values above 23 ms-1 are lower than previous open ocean measurements. The Dalton number estimates (CE) derived from CBLAST moisture flux measurements are shown to be invariant with wind speed to 30 ms-1, in approximate agreement with previous measurements at lower winds. These observations imply a CE/CD ratio of approximately 0.7, suggesting that additional energy sources are necessary for hurricanes to achieve their maximum potential intensity. Two such additional mechanisms for augmented moisture flux in the boundary layer might be 1) augmented wave breaking by short-crested, fetch limited waves suggested by whitecap aerial coverage measurements, and 2) sea spray at high winds suggested by laboratory spray source function measurements. Linear coherent features in the hurricane boundary layer are a third mechanism, observed during CBLAST 2002 aircraft measurements, to have wavelengths of 0.9 to 1.2 km. Linear features of the same wavelength range were observed in nearly-concurrent RADARSAT Synthetic Aperture Radar (SAR) imagery. Arrays of drifting buoys and subsurface floats were successfully deployed ahead of Hurricanes Fabian (2003) and Frances (2004): 16 (6) and 38 (14) drifters (floats). Two types of surface drifters and three types of floats provided observations of surface and subsurface oceanic currents, temperature, salinity, gas exchange, bubble concentrations and surface wave spectra to a depth of 200 m on a continuous basis before

Methods and results of boundary layer measurements on a glider

NASA Technical Reports Server (NTRS)

Nes, W. V.

1978-01-01

Boundary layer measurements were carried out on a glider under natural conditions. Two effects are investigated: the effect of inconstancy of the development of static pressure within the boundary layer and the effect of the negative pressure difference in a sublaminar boundary layer. The results obtained by means of an ion probe in parallel connection confirm those results obtained by means of a pressure probe. Additional effects which have occurred during these measurements are briefly dealt with.

Rotor blade boundary layer measurement hardware feasibility demonstration

NASA Technical Reports Server (NTRS)

Clark, D. R.; Lawton, T. D.

1972-01-01

A traverse mechanism which allows the measurement of the three dimensional boundary layers on a helicopter rotor blade has been built and tested on a full scale rotor to full scale conditions producing centrifugal accelerations in excess of 400 g and Mach numbers of 0.6 and above. Boundary layer velocity profiles have been measured over a range of rotor speeds and blade collective pitch angles. A pressure scanning switch and transducer were also tested on the full scale rotor and found to be insensitive to centrifugal effects within the normal main rotor operating range. The demonstration of the capability to measure boundary layer behavior on helicopter rotor blades represents the first step toward obtaining, in the rotating system, data of a quality comparable to that already existing for flows in the fixed system.

Bypass transition and spot nucleation in boundary layers

NASA Astrophysics Data System (ADS)

Kreilos, Tobias; Khapko, Taras; Schlatter, Philipp; Duguet, Yohann; Henningson, Dan S.; Eckhardt, Bruno

2016-08-01

The spatiotemporal aspects of the transition to turbulence are considered in the case of a boundary-layer flow developing above a flat plate exposed to free-stream turbulence. Combining results on the receptivity to free-stream turbulence with the nonlinear concept of a transition threshold, a physically motivated model suggests a spatial distribution of spot nucleation events. To describe the evolution of turbulent spots a probabilistic cellular automaton is introduced, with all parameters directly obtained from numerical simulations of the boundary layer. The nucleation rates are then combined with the cellular automaton model, yielding excellent quantitative agreement with the statistical characteristics for different free-stream turbulence levels. We thus show how the recent theoretical progress on transitional wall-bounded flows can be extended to the much wider class of spatially developing boundary-layer flows.

Trip-Induced Transition Measurements in a Hypersonic Boundary Layer Using Molecular Tagging Velocimetry

NASA Technical Reports Server (NTRS)

Bathel, Brett F.; Danehy, Paul M.; Jones, Stephen B.; Johansen, Craig T.; Goyne, Christopher P.

2013-01-01

Measurements of mean streamwise velocity, fluctuating streamwise velocity, and instantaneous streamwise velocity profiles in a hypersonic boundary layer were obtained over a 10-degree half-angle wedge model. A laser-induced fluorescence-based molecular tagging velocimetry technique was used to make the measurements. The nominal edge Mach number was 4.2. Velocity profiles were measured both in an untripped boundary layer and in the wake of a 4-mm diameter cylindrical tripping element centered 75.4 mm downstream of the sharp leading edge. Three different trip heights were investigated: k = 0.53 mm, k = 1.0 mm and k = 2.0 mm. The laminar boundary layer thickness at the position of the measurements was approximately 1 mm, though the exact thickness was dependent on Reynolds number and wall temperature. All of the measurements were made starting from a streamwise location approximately 18 mm downstream of the tripping element. This measurement region continued approximately 30 mm in the streamwise direction. Additionally, measurements were made at several spanwise locations. An analysis of flow features show how the magnitude, spatial location, and spatial growth of streamwise velocity instabilities are affected by parameters such as the ratio of trip height to boundary layer thickness and roughness Reynolds number. The fluctuating component of streamwise velocity measured along the centerline of the model increased from approximately 75 m/s with no trip to +/-225 m/s with a 0.53-mm trip, and to +/-240 m/s with a 1-mm trip, while holding the freestream Reynolds number constant. These measurements were performed in the 31-inch Mach 10 Air Tunnel at the NASA Langley Research Center.

An experimental study of the compressor rotor blade boundary layer

NASA Technical Reports Server (NTRS)

Pouagare, M.; Lakshminarayana, B.; Galmes, J. M.

1984-01-01

The three-dimensional turbulent boundary layer developing on a rotor blade of an axial flow compressor was measured using a miniature 'x' configuration hot-wire probe. The measurements were carried out at nine radial locations on both surfaces of the blade at various chordwise locations. The data derived includes streamwise and radial mean velocities and turbulence intensities. The validity of conventional velocity profiles such as the 'power law profile' for the streamwise profile, and Mager and Eichelbrenner's for the radial profile, is examined. A modification to Mager's crossflow profile is proposed. Away from the blade tip, the streamwise component of the blade boundary layer seems to be mainly influenced by the streamwise pressure gradient. Near the tip of the blade, the behavior of the blade boundary layer is affected by the tip leakage flow and the annulus wall boundary layer. The 'tangential blockage' due to the blade boundary layer is derived from the data. The profile losses are found to be less than that of an equivalent cascade, except in the tip region of the blade.

An interacting boundary layer model for cascades

NASA Technical Reports Server (NTRS)

Davis, R. T.; Rothmayer, A. P.

1983-01-01

A laminar, incompressible interacting boundary layer model is developed for two-dimensional cascades. In the limit of large cascade spacing these equations reduce to the interacting boundary layer equations for a single body immersed in an infinite stream. A fully implicit numerical method is used to solve the governing equations, and is found to be at least as efficient as the same technique applied to the single body problem. Solutions are then presented for a cascade of finite flat plates and a cascade of finite sine-waves, with cusped leading and trailing edges.

Numerical Study of Boundary-Layer in Aerodynamics

NASA Technical Reports Server (NTRS)

Shih, Tom I-P.

1997-01-01

The accomplishments made in the following three tasks are described: (1) The first task was to study shock-wave boundary-layer interactions with bleed - this study is relevant to boundary-layer control in external and mixed-compression inlets of supersonic aircraft; (2) The second task was to test RAAKE, a code developed for computing turbulence quantities; and (3) The third task was to compute flow around the Ames ER-2 aircraft that has been retrofitted with containers over its wings and fuselage. The appendices include two reports submitted to AIAA for publication.

Sea-air boundary meteorological sensor

NASA Astrophysics Data System (ADS)

Barbosa, Jose G.

2015-05-01

The atmospheric environment can significantly affect radio frequency and optical propagation. In the RF spectrum refraction and ducting can degrade or enhance communications and radar coverage. Platforms in or beneath refractive boundaries can exploit the benefits or suffer the effects of the atmospheric boundary layers. Evaporative ducts and surface-base ducts are of most concern for ocean surface platforms and evaporative ducts are almost always present along the sea-air interface. The atmospheric environment also degrades electro-optical systems resolution and visibility. The atmospheric environment has been proven not to be uniform and under heterogeneous conditions substantial propagation errors may be present for large distances from homogeneous models. An accurate and portable atmospheric sensor to profile the vertical index of refraction is needed for mission planning, post analysis, and in-situ performance assessment. The meteorological instrument used in conjunction with a radio frequency and electro-optical propagation prediction tactical decision aid tool would give military platforms, in real time, the ability to make assessments on communication systems propagation ranges, radar detection and vulnerability ranges, satellite communications vulnerability, laser range finder performance, and imaging system performance predictions. Raman lidar has been shown to be capable of measuring the required atmospheric parameters needed to profile the atmospheric environment. The atmospheric profile could then be used as input to a tactical decision aid tool to make propagation predictions.

Coupling of magnetopause-boundary layer to the polar ionosphere

NASA Technical Reports Server (NTRS)

Wei, C. Q.; Lee, L. C.

1993-01-01

The plasma dynamics in the low-latitude boundary layer and its coupling to the polar ionosphere under boundary conditions at the magnetopause are investigated. In the presence of a driven plasma flow along the magnetopause, the Kelvin-Helmholtz instability can develop, leading to the formation and growth of plasma vortices in the boundary layer. The finite ionospheric conductivity leads to the decay of these vortices. The competing effect of the formation and decay of vortices leads to the formation of strong vortices only in a limited region. Several enhanced field-aligned power density regions associated with the boundary layer vortices and the upward field-aligned current (FAC) filaments can be found along the postnoon auroral oval. These enhanced field-aligned power density regions may account for the observed auroral bright spots.

Steady Boundary Layer Disturbances Created By Two-Dimensional Surface Ripples

NASA Astrophysics Data System (ADS)

Kuester, Matthew

2017-11-01

Multiple experiments have shown that surface roughness can enhance the growth of Tollmien-Schlichting (T-S) waves in a laminar boundary layer. One of the common observations from these studies is a ``wall displacement'' effect, where the boundary layer profile shape remains relatively unchanged, but the origin of the profile pushes away from the wall. The objective of this work is to calculate the steady velocity field (including this wall displacement) of a laminar boundary layer over a surface with small, 2D surface ripples. The velocity field is a combination of a Blasius boundary layer and multiple disturbance modes, calculated using the linearized Navier-Stokes equations. The method of multiple scales is used to include non-parallel boundary layer effects of O (Rδ- 1) ; the non-parallel terms are necessary, because a wall displacement is mathematically inconsistent with a parallel boundary layer assumption. This technique is used to calculate the steady velocity field over ripples of varying height and wavelength, including cases where a separation bubble forms on the leeward side of the ripple. In future work, the steady velocity field will be the input for stability calculations, which will quantify the growth of T-S waves over rough surfaces. The author would like to acknowledge the support of the Kevin T. Crofton Aerospace & Ocean Engineering Department at Virginia Tech.

Stably Stratified Atmospheric Boundary Layers

NASA Astrophysics Data System (ADS)

Mahrt, L.

2014-01-01

Atmospheric boundary layers with weak stratification are relatively well described by similarity theory and numerical models for stationary horizontally homogeneous conditions. With common strong stratification, similarity theory becomes unreliable. The turbulence structure and interactions with the mean flow and small-scale nonturbulent motions assume a variety of scenarios. The turbulence is intermittent and may no longer fully satisfy the usual conditions for the definition of turbulence. Nonturbulent motions include wave-like motions and solitary modes, two-dimensional vortical modes, microfronts, intermittent drainage flows, and a host of more complex structures. The main source of turbulence may not be at the surface, but rather may result from shear above the surface inversion. The turbulence is typically not in equilibrium with the nonturbulent motions, sometimes preventing the formation of an inertial subrange. New observational and analysis techniques are expected to advance our understanding of the very stable boundary layer.

A molecular Rayleigh scattering setup to measure density fluctuations in thermal boundary layers

NASA Astrophysics Data System (ADS)

Panda, J.

2016-12-01

A Rayleigh scattering-based density fluctuation measurement system was set up inside a low-speed wind tunnel of NASA Ames Research Center. The immediate goal was to study the thermal boundary layer on a heated flat plate. A large number of obstacles had to be overcome to set up the system, such as the removal of dust particles using air filters, the use of photoelectron counting electronics to measure low intensity light, an optical layout to minimize stray light contamination, the reduction in tunnel vibration, and an expanded calibration process to relate photoelectron arrival rate to air density close to the plate surface. To measure spectra of turbulent density fluctuations, a two-PMT cross-correlation system was used to minimize the shot noise floor. To validate the Rayleigh measurements, temperature fluctuations spectra were calculated from density spectra and then compared with temperature spectra measured with a cold-wire probe operated in constant current mode. The spectra from the downstream half of the plate were found to be in good agreement with cold-wire probe, whereas spectra from the leading edge differed. Various lessons learnt are discussed. It is believed that the present effort is the first measurement of density fluctuations spectra in a boundary layer flow.

Computation of Three-Dimensional Boundary Layers Including Separation

DTIC Science & Technology

1987-02-01

As demonstrated by the 1968 and 1980 -1981 STANFORD Conferences, integral methods remain a valuable engineering tool to calculate the effects of...has been given by WHITFIELD, 1980 , which is valid over the whole thickness of the boundary layer. Another method to generate a velocity profiles...boundary layer equations and inviscid equations. A very clear presentation of the problem is given for example by VELOMAN, 1980 . 6.3. Three-dimensional

Observations of ozone-poor air in the tropical tropopause layer

NASA Astrophysics Data System (ADS)

Newton, Richard; Vaughan, Geraint; Hintsa, Eric; Filus, Michal T.; Pan, Laura L.; Honomichl, Shawn; Atlas, Elliot; Andrews, Stephen J.; Carpenter, Lucy J.

2018-04-01

Ozonesondes reaching the tropical tropopause layer (TTL) over the west Pacific have occasionally measured layers of very low ozone concentrations - less than 15 ppbv - raising the question of how prevalent such layers are and how they are formed. In this paper, we examine aircraft measurements from the Airborne Tropical Tropopause Experiment (ATTREX), the Coordinated Airborne Studies in the Tropics (CAST) and the Convective Transport of Active Species in the Tropics (CONTRAST) experiment campaigns based in Guam in January-March 2014 for evidence of very low ozone concentrations and their relation to deep convection. The study builds on results from the ozonesonde campaign conducted from Manus Island, Papua New Guinea, as part of CAST, where ozone concentrations as low as 12 ppbv were observed between 100 and 150 hPa downwind of a deep convective complex. TTL measurements from the Global Hawk unmanned aircraft show a marked contrast between the hemispheres, with mean ozone concentrations in profiles in the Southern Hemisphere between 100 and 150 hPa of between 10.7 and 15.2 ppbv. By contrast, the mean ozone concentrations in profiles in the Northern Hemisphere were always above 15.4 ppbv and normally above 20 ppbv at these altitudes. The CAST and CONTRAST aircraft sampled the atmosphere between the surface and 120 hPa, finding very low ozone concentrations only between the surface and 700 hPa; mixing ratios as low as 7 ppbv were regularly measured in the boundary layer, whereas in the free troposphere above 200 hPa concentrations were generally well in excess of 15 ppbv. These results are consistent with uplift of almost-unmixed boundary-layer air to the TTL in deep convection. An interhemispheric difference was found in the TTL ozone concentrations, with values < 15 ppbv measured extensively in the Southern Hemisphere but seldom in the Northern Hemisphere. This is consistent with a similar contrast in the low-level ozone between the two hemispheres found by

Select strengths and biases of models in representing the Arctic winter boundary layer over sea ice: the Larcform 1 single column model intercomparison

DOE PAGES

Pithan, Felix; Ackerman, Andrew; Angevine, Wayne M.; ...

2016-08-27

We struggle to represent lower tropospheric temperature and moisture profiles and surface fluxes in Artic winter using weather and climate models, partly because they lack or misrepresent physical processes that are specific to high latitudes. Observations have revealed two preferred states of the Arctic winter boundary layer. In the cloudy state, cloud liquid water limits surface radiative cooling, and temperature inversions are weak and elevated. In the radiatively clear state, strong surface radiative cooling leads to the build-up of surface-based temperature inversions. Many large-scale models lack the cloudy state, and some substantially underestimate inversion strength in the clear state. Themore » transformation from a moist to a cold dry air mass is modeled using an idealized Lagrangian perspective. The trajectory includes both boundary layer states, and the single-column experiment is the first Lagrangian Arctic air formation experiment (Larcform 1) organized within GEWEX GASS (Global atmospheric system studies). The intercomparison reproduces the typical biases of large-scale models: some models lack the cloudy state of the boundary layer due to the representation of mixed-phase microphysics or to the interaction between micro- and macrophysics. In some models, high emissivities of ice clouds or the lack of an insulating snow layer prevent the build-up of surface-based inversions in the radiatively clear state. Models substantially disagree on the amount of cloud liquid water in the cloudy state and on turbulent heat fluxes under clear skies. Finally, observations of air mass transformations including both boundary layer states would allow for a tighter constraint of model behavior.« less

Select strengths and biases of models in representing the Arctic winter boundary layer over sea ice: the Larcform 1 single column model intercomparison

PubMed Central

Pithan, Felix; Ackerman, Andrew; Angevine, Wayne M.; Hartung, Kerstin; Ickes, Luisa; Kelley, Maxwell; Medeiros, Brian; Sandu, Irina; Steeneveld, Gert-Jan; Sterk, HAM; Svensson, Gunilla; Vaillancourt, Paul A.; Zadra, Ayrton

2017-01-01

Weather and climate models struggle to represent lower tropospheric temperature and moisture profiles and surface fluxes in Arctic winter, partly because they lack or misrepresent physical processes that are specific to high latitudes. Observations have revealed two preferred states of the Arctic winter boundary layer. In the cloudy state, cloud liquid water limits surface radiative cooling, and temperature inversions are weak and elevated. In the radiatively clear state, strong surface radiative cooling leads to the build-up of surface-based temperature inversions. Many large-scale models lack the cloudy state, and some substantially underestimate inversion strength in the clear state. Here, the transformation from a moist to a cold dry air mass is modelled using an idealized Lagrangian perspective. The trajectory includes both boundary layer states, and the single-column experiment is the first Lagrangian Arctic air formation experiment (Larcform 1) organized within GEWEX GASS (Global atmospheric system studies). The intercomparison reproduces the typical biases of large-scale models: Some models lack the cloudy state of the boundary layer due to the representation of mixed-phase micro-physics or to the interaction between micro-and macrophysics. In some models, high emissivities of ice clouds or the lack of an insulating snow layer prevent the build-up of surface-based inversions in the radiatively clear state. Models substantially disagree on the amount of cloud liquid water in the cloudy state and on turbulent heat fluxes under clear skies. Observations of air mass transformations including both boundary layer states would allow for a tighter constraint of model behaviour. PMID:28966718

Select strengths and biases of models in representing the Arctic winter boundary layer over sea ice: the Larcform 1 single column model intercomparison

NASA Astrophysics Data System (ADS)

Pithan, Felix; Ackerman, Andrew; Angevine, Wayne M.; Hartung, Kerstin; Ickes, Luisa; Kelley, Maxwell; Medeiros, Brian; Sandu, Irina; Steeneveld, Gert-Jan; Sterk, H. A. M.; Svensson, Gunilla; Vaillancourt, Paul A.; Zadra, Ayrton

2016-09-01

Weather and climate models struggle to represent lower tropospheric temperature and moisture profiles and surface fluxes in Arctic winter, partly because they lack or misrepresent physical processes that are specific to high latitudes. Observations have revealed two preferred states of the Arctic winter boundary layer. In the cloudy state, cloud liquid water limits surface radiative cooling, and temperature inversions are weak and elevated. In the radiatively clear state, strong surface radiative cooling leads to the build-up of surface-based temperature inversions. Many large-scale models lack the cloudy state, and some substantially underestimate inversion strength in the clear state. Here, the transformation from a moist to a cold dry air mass is modeled using an idealized Lagrangian perspective. The trajectory includes both boundary layer states, and the single-column experiment is the first Lagrangian Arctic air formation experiment (Larcform 1) organized within GEWEX GASS (Global atmospheric system studies). The intercomparison reproduces the typical biases of large-scale models: some models lack the cloudy state of the boundary layer due to the representation of mixed-phase microphysics or to the interaction between micro- and macrophysics. In some models, high emissivities of ice clouds or the lack of an insulating snow layer prevent the build-up of surface-based inversions in the radiatively clear state. Models substantially disagree on the amount of cloud liquid water in the cloudy state and on turbulent heat fluxes under clear skies. Observations of air mass transformations including both boundary layer states would allow for a tighter constraint of model behavior.

Select strengths and biases of models in representing the Arctic winter boundary layer over sea ice: the Larcform 1 single column model intercomparison.

PubMed

Pithan, Felix; Ackerman, Andrew; Angevine, Wayne M; Hartung, Kerstin; Ickes, Luisa; Kelley, Maxwell; Medeiros, Brian; Sandu, Irina; Steeneveld, Gert-Jan; Sterk, Ham; Svensson, Gunilla; Vaillancourt, Paul A; Zadra, Ayrton

2016-09-01

Weather and climate models struggle to represent lower tropospheric temperature and moisture profiles and surface fluxes in Arctic winter, partly because they lack or misrepresent physical processes that are specific to high latitudes. Observations have revealed two preferred states of the Arctic winter boundary layer. In the cloudy state, cloud liquid water limits surface radiative cooling, and temperature inversions are weak and elevated. In the radiatively clear state, strong surface radiative cooling leads to the build-up of surface-based temperature inversions. Many large-scale models lack the cloudy state, and some substantially underestimate inversion strength in the clear state. Here, the transformation from a moist to a cold dry air mass is modelled using an idealized Lagrangian perspective. The trajectory includes both boundary layer states, and the single-column experiment is the first L agrangian Arc tic air form ation experiment (Larcform 1) organized within GEWEX GASS (Global atmospheric system studies). The intercomparison reproduces the typical biases of large-scale models: Some models lack the cloudy state of the boundary layer due to the representation of mixed-phase micro-physics or to the interaction between micro-and macrophysics. In some models, high emissivities of ice clouds or the lack of an insulating snow layer prevent the build-up of surface-based inversions in the radiatively clear state. Models substantially disagree on the amount of cloud liquid water in the cloudy state and on turbulent heat fluxes under clear skies. Observations of air mass transformations including both boundary layer states would allow for a tighter constraint of model behaviour.

Effect of Sub-Boundary Layer Vortex Generations on Incident Turbulence

NASA Technical Reports Server (NTRS)

Casper, J.; Lin, J. C.; Yao, C. S.

2003-01-01

Sub-boundary layer vortex generators were tested in a wind tunnel to assess their effect on the velocity field within the wake region of a turbulent boundary layer. Both mean flow quantities and turbulence statistics were measured. Although very small relative to the boundary layer thickness, these so-called micro vortex generators were found to have a measurable effect on the power spectra and integral length scales of the turbulence at a distance many times the height of the devices themselves. In addition, the potential acoustic impact of these devices is also discussed. Measured turbulence spectra are used as input to an acoustic formulation in a manner that compares predicted sound pressure levels that result from the incident boundary-layer turbulence, with and without the vortex generators in the flow.

Thermal boundary layer profiles in turbulent Rayleigh-Benard convection

NASA Astrophysics Data System (ADS)

Tong, Penger; Wang, Yin; He, Xiaozhou

2015-11-01

We have studied the mean temperature boundary layer profile T(z) and root-mean-square (rms) temperature profile S(z) in turbulent Rayleigh-Benard convection along the central axis z of a convection cell, which has a thin vertical disk shape with an inner diameter D = 18 cm. The temperature measurements were made at fixed Prandtl numbers Pr = 4.3 and Pr = 7.6 and with the Rayleigh number Ra varied in the range between 1 ×109 and 1 ×1010 . The measured T(z) for different values of Pr and Ra can all be well described by the newly proposed boundary layer model with a parameter c varying from 1 to 2.1. The measured rms temperature profile S(z) is found to be a single-peaked function with the peak position located at z ~= 0 . 8 δ , where δ is the boundary layer thickness. The measured S(z) has two separate scaling lengths. Within the boundary layer, it scales with δ and can be fitted to a power law, S (z) ~(z / δ) α with α ~= 0 . 6 . Outside the boundary layer, it scales with the cell size D and follows a different power law, S (z) ~(z / D) β , with β = - 0 . 42 . This work was supported by the Research Grants Council of Hong Kong SAR.

Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.; Smeltzer, Stanley S., III

2000-01-01

A study of the attenuation of bending boundary layers in balanced and unbalanced, symmetrically and unsymmetrically laminated cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize the effects of laminate orthotropy and anisotropy on the bending boundary-layer decay length in a very general manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all laminates considered, the results show that the differences between results obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that, in some cases, neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and, in other cases, results in an overestimation.

Interaction of Atmospheric Turbulence with Blade Boundary Layer Dynamics on a 5MW Wind Turbine using Blade-Boundary-Layer-Resolved CFD with hybrid URANS-LES.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vijayakumar, Ganesh; Brasseur, James; Lavely, Adam

We describe the response of the NREL 5 MW wind turbine blade boundary layer to the passage of atmospheric turbulence using blade-boundary-layer-resolved computational fluid dynamics with hybrid URANS-LES modeling.

Nonmethane hydrocarbon chemistry in the remote marine boundary layer

NASA Technical Reports Server (NTRS)

Donahue, Neil M.; Prinn, Ronald G.

1990-01-01

A photochemical model of the remote marine boundary layer (MBL) is presented, with focus placed on the role of reactive nonmethane hydrocarbons (NMHC). A wide range of NMHC air-sea fluxes with various relative distributions of NMHC regions are considered. In particular, the flux magnitude at which NMHC emissions become significant, and then dominant, players in MBL chemistry is identified. Emphasis is placed on diurnal variability, diurnal ozone variations and sensitivity to NMHC emission fluxes, to CO, O3, H2O, and UV light, and to kinetics and isometric composition. Model runs indicate that, in the range consistent with current observations, the NMHCs may either dominate MBL chemistry, or simply be contributors at the 10-percent level. These model runs also show that existing observations of NMHCs in ocean water find them to scarce for fluxes from bulk-flux air-sea gas exchange models to be consistent with the fluxes needed in the proposed model to maintain the lowest observed MBL NMHC.

Boundary layer integral matrix procedure: Verification of models

NASA Technical Reports Server (NTRS)

Bonnett, W. S.; Evans, R. M.

1977-01-01

The three turbulent models currently available in the JANNAF version of the Aerotherm Boundary Layer Integral Matrix Procedure (BLIMP-J) code were studied. The BLIMP-J program is the standard prediction method for boundary layer effects in liquid rocket engine thrust chambers. Experimental data from flow fields with large edge-to-wall temperature ratios are compared to the predictions of the three turbulence models contained in BLIMP-J. In addition, test conditions necessary to generate additional data on a flat plate or in a nozzle are given. It is concluded that the Cebeci-Smith turbulence model be the recommended model for the prediction of boundary layer effects in liquid rocket engines. In addition, the effects of homogeneous chemical reaction kinetics were examined for a hydrogen/oxygen system. Results show that for most flows, kinetics are probably only significant for stoichiometric mixture ratios.

The Effects of Rotation on Boundary Layers in Turbomachine Rotors

NASA Technical Reports Server (NTRS)

Johnston, J. P.

1974-01-01

The boundary layers in turbomachine rotors are subject to Coriolis forces which can (1) contribute directly to the development of secondary flows and (2) indirectly influence the behavior of boundary layers by augmentation and/or suppression of turbulence production in the boundary layers on blades. Both these rotation-induced phenomena are particularly important in the development of understanding of flow and loss mechanisms in centrifugal and mixed flow machines. The primary objective of this paper is to review the information available on these effects.

Boundary-layer cumulus over land: Some observations and conceptual models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stull, R.B.

1993-09-01

Starting in 1980, the Boundary Layer Research Team at the University of Wisconsin has been systematically studying the formation and evolution of nonprecipitating boundary-layer cumulus clouds (BLCu) in regions of fair weather (anticyclones) over land (Stull, 1980). Our approach is to quantify the average statistical characteristics of the surface, thermals, boundary layer, and clouds over horizontal regions of roughly 20 km in diameter. Within such a region over land, there is typically quite a variation in land use, and associated variations in surface albedo and moisture.

Seasonality of mercury in the Atlantic marine boundary layer

NASA Astrophysics Data System (ADS)

Soerensen, Anne L.; Sunderland, Elsie; Skov, Henrik; Holmes, Christopher; Jacob, Daniel J.

2010-05-01

Around one third of the mercury emissions today are from primary anthropogenic sources, with the remaining two-thirds from secondary reemissions of earlier deposition and natural sources (AMAP/UNEP 2008). Mercury exchange at the air-sea interface is important for the global distribution of atmospheric mercury as parts of deposited mercury will reenter the atmosphere through evasion. The exchange at the air-sea interface also affects the amount of inorganic mercury in the ocean and thereby the conversion to the neuro-toxic methylmercury. Here we combine new cruise measurements in the atmospheric marine boundary layer (MBL) of the Atlantic Ocean (Northern Hemisphere) from the fall of 2006 and the spring of 2007 with existing data from cruises in the Atlantic Ocean since 1978. We observe from these data a seasonal cycle in Hg(0) concentrations in the Atlantic marine boundary later (MBL) that exhibits minimum concentrations during summer and high concentrations during fall to spring. These observations suggest a local, seasonally dependent Hg(0) source in the MBL that causes variability in concentrations above the open ocean. To further investigate controls on Hg(0) concentrations in the MBL, we developed an improved representation of oceanic air-sea exchange processes within the GEOS-Chem global 3-D biogeochemical mercury model. Specifically, we used new data on mercury redox reactions in the surface ocean as a function of biological and photochemical processes, and implemented new algorithms for mercury dynamics associated with suspended particles. Our coupled atmospheric-oceanic modeling results support the premise that oceanic evasion is a main driver controlling Hg(0) concentrations in the MBL. We also use the model to investigate what drivers the evasion across the air-sea interface on shorter timescales. This is done by tracking evasion rates and other model components on an hourly basis for chosen locations in the Atlantic Ocean.

Investigation of Gas Seeding for Planar Laser-Induced Fluorescence in Hypersonic Boundary Layers

NASA Technical Reports Server (NTRS)

Arisman, C. J.; Johansen, C. T.; Bathel, B. F.; Danehy, P. M.

2015-01-01

Numerical simulations of the gas-seeding strategies required for planar laser-induced fluorescence in a Mach 10 (approximately Mach 8.2 postshock) airflow were performed. The work was performed to understand and quantify the adverse effects associated with gas seeding and to assess various types of seed gas that could potentially be used in future experiments. In prior experiments, NO and NO2 were injected through a slot near the leading edge of a flatplate wedge model used in NASA Langley Research Center's 31 in. Mach 10 air tunnel facility. In this paper, nitric oxide, krypton, and iodine gases were simulated at various injection rates. Simulations showing the deflection of the velocity boundary layer for each of the cases are presented. Streamwise distributions of velocity and concentration boundary-layer thicknesses, as well as vertical distributions of velocity, temperature, and mass distributions, are presented for each of the cases. A comparison between simulated streamwise velocity profiles and experimentally obtained molecular tagging velocimetry profiles using a nitric oxide seeding strategy is performed to verify the influence of such a strategy on the boundary layer. The relative merits of the different seeding strategies are discussed. The results from a custom solver based on OpenFOAM version 2.2.1 are compared against results obtained from ANSYS® Fluent version 6.3.

Sensitivity of boundary layer variables to PBL schemes over the central Tibetan Plateau

NASA Astrophysics Data System (ADS)

Xu, L.; Liu, H.; Wang, L.; Du, Q.; Liu, Y.

2017-12-01

Planetary Boundary Layer (PBL) parameterization schemes play critical role in numerical weather prediction and research. They describe physical processes associated with the momentum, heat and humidity exchange between land surface and atmosphere. In this study, two non-local (YSU and ACM2) and two local (MYJ and BouLac) planetary boundary layer parameterization schemes in the Weather Research and Forecasting (WRF) model have been tested over the central Tibetan Plateau regarding of their capability to model boundary layer parameters relevant for surface energy exchange. The model performance has been evaluated against measurements from the Third Tibetan Plateau atmospheric scientific experiment (TIPEX-III). Simulated meteorological parameters and turbulence fluxes have been compared with observations through standard statistical measures. Model results show acceptable behavior, but no particular scheme produces best performance for all locations and parameters. All PBL schemes underestimate near surface air temperatures over the Tibetan Plateau. By investigating the surface energy budget components, the results suggest that downward longwave radiation and sensible heat flux are the main factors causing the lower near surface temperature. Because the downward longwave radiation and sensible heat flux are respectively affected by atmosphere moisture and land-atmosphere coupling, improvements in water vapor distribution and land-atmosphere energy exchange is meaningful for better presentation of PBL physical processes over the central Tibetan Plateau.

Turbulent Helicity in the Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Chkhetiani, Otto G.; Kurgansky, Michael V.; Vazaeva, Natalia V.

2018-05-01

We consider the assumption postulated by Deusebio and Lindborg (J Fluid Mech 755:654-671, 2014) that the helicity injected into the Ekman boundary layer undergoes a cascade, with preservation of its sign (right- or alternatively left-handedness), which is a signature of the system rotation, from large to small scales, down to the Kolmogorov microscale of turbulence. At the same time, recent direct field measurements of turbulent helicity in the steppe region of southern Russia near Tsimlyansk Reservoir show the opposite sign of helicity from that expected. A possible explanation for this phenomenon may be the joint action of different scales of atmospheric flows within the boundary layer, including the sea-breeze circulation over the test site. In this regard, we consider a superposition of the classic Ekman spiral solution and Prandtl's jet-like slope-wind profile to describe the planetary boundary-layer wind structure. The latter solution mimics a hydrostatic shallow breeze circulation over a non-uniformly heated surface. A 180°-wide sector on the hodograph plane exists, within which the relative orientation of the Ekman and Prandtl velocity profiles favours the left rotation with height of the resulting wind velocity vector in the lowermost part of the boundary layer. This explains the negative (left-handed) helicity cascade toward small-scale turbulent motions, which agrees with the direct field measurements of turbulent helicity in Tsimlyansk. A simple turbulent relaxation model is proposed that explains the measured positive values of the relatively minor contribution to turbulent helicity from the vertical components of velocity and vorticity.

Boundary Layer Transition Results From STS-114

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Horvath, Thomas J.; Cassady, Amy M.; Kirk, Benjamin S.; Wang, K. C.; Hyatt, Andrew J.

2006-01-01

The tool for predicting the onset of boundary layer transition from damage to and/or repair of the thermal protection system developed in support of Shuttle Return to Flight is compared to the STS-114 flight results. The Boundary Layer Transition (BLT) Tool is part of a suite of tools that analyze the aerothermodynamic environment of the local thermal protection system to allow informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each damage site or repair, the expected time of transition onset is predicted to help determine the proper aerothermodynamic environment to use in the subsequent thermal and stress analysis of the local structure. The boundary layer transition criteria utilized for the tool was developed from ground-based measurements to account for the effect of both protuberances and cavities and has been calibrated against flight data. Computed local boundary layer edge conditions provided the means to correlate the experimental results and then to extrapolate to flight. During STS-114, the BLT Tool was utilized and was part of the decision making process to perform an extravehicular activity to remove the large gap fillers. The role of the BLT Tool during this mission, along with the supporting information that was acquired for the on-orbit analysis, is reviewed. Once the large gap fillers were removed, all remaining damage sites were cleared for reentry as is. Post-flight analysis of the transition onset time revealed excellent agreement with BLT Tool predictions.

Aircraft observations of East-Asian cyclone induced uplift and long-range transport of polluted boundary layer air to the lowermost stratosphere

NASA Astrophysics Data System (ADS)

Schlager, Hans; Arnold, Frank; Aufmhoff, Heinrich; Baumann, Robert; Priola, Lisa; Roiger, Anke; Sailer, Tomas; Wirth, Martin; Schumann, Ulrich

2013-04-01

We report on the airborne detection of a large-scale stratified pollution layer in the lowermost stratosphere which contained increased concentrations of sulfur dioxide, reactive nitrogen, water vapour and sulfate aerosols. The measurements were performed over Central Europe with a chemical ionization mass spectrometer and a high spectral resolution Lidar on board the new German research aircraft HALO. Transport model simulations indicate the East-Asian planetary boundary layer (PBL) as the source region of this layer. The PBL air was uplifted by an East Asian warm conveyor belt (WCB) and thereafter experienced mostly horizontal transport and dispersion covering significant part of the northern hemisphere. The pollution layer extent up to 2 km above the thermal tropopause and appears to be trapped in the upper part of the tropopause inversion layer (TIL). Accompanying chemistry and aerosol model simulations indicate efficient SO2 conversion to sulfuric acid during the horizontal transport in the TIL, accelerated by increased OH resulting from the increased water vapour. Low temperature and increased water vapour led to efficient binary H2SO4/H2O nucleation. The uplifted anthropogenic nitrogen oxides experienced OH and particle mediated conversion to HNO3. The layer of sulfate particles formed in the upper part of the TIL was observed in the Lidar backscatter signal. Since mid-latitude East Asia is a region with very large SO2 emissions and a very high frequency of WCBs, SO2 uplift into the lowermost stratosphere from this region may occur frequently, eventually leading very often to corresponding pollution layers in the northern-hemisphere TIL.

Linear segmentation algorithm for detecting layer boundary with lidar.

PubMed

Mao, Feiyue; Gong, Wei; Logan, Timothy

2013-11-04

The automatic detection of aerosol- and cloud-layer boundary (base and top) is important in atmospheric lidar data processing, because the boundary information is not only useful for environment and climate studies, but can also be used as input for further data processing. Previous methods have demonstrated limitations in defining the base and top, window-size setting, and have neglected the in-layer attenuation. To overcome these limitations, we present a new layer detection scheme for up-looking lidars based on linear segmentation with a reasonable threshold setting, boundary selecting, and false positive removing strategies. Preliminary results from both real and simulated data show that this algorithm cannot only detect the layer-base as accurate as the simple multi-scale method, but can also detect the layer-top more accurately than that of the simple multi-scale method. Our algorithm can be directly applied to uncalibrated data without requiring any additional measurements or window size selections.

The structure of a three-dimensional turbulent boundary layer

NASA Technical Reports Server (NTRS)

Degani, A. T.; Smith, F. T.; Walker, J. D. A.

1993-01-01

The three-dimensional turbulent boundary layer is shown to have a self-consistent two-layer asymptotic structure in the limit of large Reynolds number. In a streamline coordinate system, the streamwise velocity distribution is similar to that in two-dimensional flows, having a defect-function form in the outer layer which is adjusted to zero at the wall through an inner wall layer. An asymptotic expansion accurate to two orders is required for the cross-stream velocity which is shown to exhibit a logarithmic form in the overlap region. The inner wall-layer flow is collateral to leading order but the influence of the pressure gradient, at large but finite Reynolds numbers, is not negligible and can cause substantial skewing of the velocity profile near the wall. Conditions under which the boundary layer achieves self-similarity and the governing set of ordinary differential equations for the outer layer are derived. The calculated solution of these equations is matched asymptotically to an inner wall-layer solution and the composite profiles so formed describe the flow throughout the entire boundary layer. The effects of Reynolds number and cross-stream pressure gradient on the crossstream velocity profile are discussed and it is shown that the location of the maximum cross-stream velocity is within the overlap region.

Particle motion in atmospheric boundary layers of Mars and Earth

NASA Technical Reports Server (NTRS)

White, B. R.; Iversen, J. D.; Greeley, R.; Pollack, J. B.

1975-01-01

To study the eolian mechanics of saltating particles, both an experimental investigation of the flow field around a model crater in an atmospheric boundary layer wind tunnel and numerical solutions of the two- and three-dimensional equations of motion of a single particle under the influence of a turbulent boundary layer were conducted. Two-dimensional particle motion was calculated for flow near the surfaces of both Earth and Mars. For the case of Earth both a turbulent boundary layer with a viscous sublayer and one without were calculated. For the case of Mars it was only necessary to calculate turbulent boundary layer flow with a laminar sublayer because of the low values of friction Reynolds number; however, it was necessary to include the effects of slip flow on a particle caused by the rarefied Martian atmosphere. In the equations of motion the lift force functions were developed to act on a single particle only in the laminar sublayer or a corresponding small region of high shear near the surface for a fully turbulent boundary layer. The lift force functions were developed from the analytical work by Saffman concerning the lift force acting on a particle in simple shear flow.

3D LDV Measurements in Oscillatory Boundary Layers

NASA Astrophysics Data System (ADS)

Mier, J. M.; Garcia, M. H.

2012-12-01

The oscillatory boundary layer represents a particular case of unsteady wall-bounded flows in which fluid particles follow a periodic sinusoidal motion. Unlike steady boundary layer flows, the oscillatory flow regime and bed roughness character change in time along the period for every cycle, a characteristic that introduces a high degree of complexity in the analysis of these flows. Governing equations can be derived from the general Navier-Stokes equations for the motion of fluids, from which the exact solution for the laminar oscillatory boundary layer is obtained (also known as the 2nd Stokes problem). No exact solution exists for the turbulent case, thus, understanding of the main flow characteristics comes from experimental work. Several researchers have reported experimental work in oscillatory boundary layers since the 1960's; however, larger scale facilities and the development of newer measurement techniques with improved temporal and spatial resolution in recent years provides a unique opportunity to achieve a better understanding about this type of flows. Several experiments were performed in the Large Oscillatory Water and Sediment Tunnel (LOWST) facility at the Ven Te Chow Hydrosystems Laboratory, for a range of Reynolds wave numbers between 6x10^4 < Rew < 6x10^6 over a flat and smooth bottom. A 3D Laser Doppler Velocimetry (LDV) system was used to measure instantaneous flow velocities with a temporal resolution up to ~ 1,000 Hz. It was mounted on a 3-axis traverse with a spatial resolution of 0.01 mm in all three directions. The closest point to the bottom was measured at z = 0.2 mm (z+ ≈ 4), which allowed to capture boundary layer features with great detail. In order to achieve true 3D measurements, 2 probes were used on a perpendicular configuration, such that u and w components were measured from a probe on the side of the flume and v component was measured from a probe pointing down through and access window on top of the flume. The top probe

Finite volume solution of the compressible boundary-layer equations

NASA Technical Reports Server (NTRS)

Loyd, B.; Murman, E. M.

1986-01-01

A box-type finite volume discretization is applied to the integral form of the compressible boundary layer equations. Boundary layer scaling is introduced through the grid construction: streamwise grid lines follow eta = y/h = const., where y is the normal coordinate and h(x) is a scale factor proportional to the boundary layer thickness. With this grid, similarity can be applied explicity to calculate initial conditions. The finite volume method preserves the physical transparency of the integral equations in the discrete approximation. The resulting scheme is accurate, efficient, and conceptually simple. Computations for similar and non-similar flows show excellent agreement with tabulated results, solutions computed with Keller's Box scheme, and experimental data.

Impacts of synoptic condition and planetary boundary layer structure on the trans-boundary aerosol transport from Beijing-Tianjin-Hebei region to northeast China

NASA Astrophysics Data System (ADS)

Miao, Yucong; Guo, Jianping; Liu, Shuhua; Zhao, Chun; Li, Xiaolan; Zhang, Gen; Wei, Wei; Ma, Yanjun

2018-05-01

The northeastern China frequently experiences severe aerosol pollution in winter under unfavorable meteorological conditions. How and to what extent the meteorological factors affect the air quality there are not yet clearly understood. Thus, this study investigated the impacts of synoptic patterns on the aerosol transport and planetary boundary layer (PBL) structure in Shenyang from 1 to 3 December 2016, using surface observations, sounding measurements, satellite data, and three-dimensional simulations. Results showed that the aerosol pollution occurred in Shenyang was not only related to the local emissions, but also contributed by trans-boundary transport of aerosols from the Beiijng-Tianjin-Hebei (BTH) region. In the presence of the westerly and southwesterly synoptic winds, the aerosols emitted from BTH could be brought to Shenyang. From December 2 to 3, the aerosols emitted from BTH accounted for ∼20% of near-surface PM2.5 in Shenyang. In addition, the large-scale synoptic forcings could affect the vertical mixing of pollutants through modulating the PBL structure in Shenyang. The westerly and southwesterly synoptic winds not only brought the aerosols but also the warmer air masses from the southwest regions to Shenyang. The strong warm advections above PBL could enhance the already existing thermal inversion layers capping over PBL in Shenyang, leading to the suppressions of PBL. Both the trans-boundary transport of aerosols and the suppressions of PBL caused by the large-scale synoptic forcings should be partly responsible for the poor air quality in Shenyang, in addition to the high pollutant emissions. The present study revealed the physical mechanisms underlying the aerosol pollution in Shenyang, which has important implications for better forecasting and controlling the aerosols pollution.

Modeling evaporation using models that are not boundary-layer regulated.

PubMed

Fingas, Merv F

2004-02-27

Experimentation shows that oil is not strictly air boundary-layer regulated. The fact that oil evaporation is not strictly boundary-layer regulated implies that a simplistic evaporation equation suffices to describe the process. The following processes do not require consideration: wind velocity, turbulence level, area, thickness, and scale size. The factors important to evaporation are time and temperature. The equation parameters found experimentally for the evaporation of oils can be related to commonly available distillation data for the oil. Specifically, it has been found that the distillation percentage at 180 degrees C correlates well with the equation parameters. Relationships have been developed enabling calculation of evaporation equations directly from distillation data: percentage evaporated = 0.165 (%D)ln(t) where %D is the percentage (by weight) distilled at 180 degrees C and t is the time in minutes. These equations were combined with the equations generated to account for the temperature variations: percentage evaporated = [0.165(%D)+0.045(T-15))ln(t) The results have application in oil spill prediction and modeling. The simple equations can be applied using readily available data such as sea temperature and time. Old equations required oil vapour pressure, specialized distillation data, spill area, wind speed, and mass transfer coefficients, all of which are difficult to obtain.

Notes on the Prediction of Shock-induced Boundary-layer Separation

NASA Technical Reports Server (NTRS)

Lange, Roy H.

1953-01-01

The present status of available information relative to the prediction of shock-induced boundary-layer separation is discussed. Experimental results showing the effects of Reynolds number and Mach number on the separation of both laminar and turbulent boundary layer are given and compared with available methods for predicting separation. The flow phenomena associated with separation caused by forward-facing steps, wedges, and incident shock waves are discussed. Applications of the flat-plate data to problems of separation on spoilers, diffusers, and scoop inlets are indicated for turbulent boundary layers.

The atmospheric boundary layer — advances in knowledge and application

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Hess, G. D.; Physick, W. L.; Bougeault, P.

1996-02-01

We summarise major activities and advances in boundary-layer knowledge in the 25 years since 1970, with emphasis on the application of this knowledge to surface and boundary-layer parametrisation schemes in numerical models of the atmosphere. Progress in three areas is discussed: (i) the mesoscale modelling of selected phenomena; (ii) numerical weather prediction; and (iii) climate simulations. Future trends are identified, including the incorporation into models of advanced cloud schemes and interactive canopy schemes, and the nesting of high resolution boundary-layer schemes in global climate models.

Forward-facing steps induced transition in a subsonic boundary layer

NASA Astrophysics Data System (ADS)

Zh, Hui; Fu, Song

2017-10-01

A forward-facing step (FFS) immersed in a subsonic boundary layer is studied through a high-order flux reconstruction (FR) method to highlight the flow transition induced by the step. The step height is a third of the local boundary-layer thickness. The Reynolds number based on the step height is 720. Inlet disturbances are introduced giving rise to streamwise vortices upstream of the step. It is observed that these small-scale streamwise structures interact with the step and hairpin vortices are quickly developed after the step leading to flow transition in the boundary layer.

Vertical structure of boundary layer convection during cold-air outbreaks at Barrow, Alaska

NASA Astrophysics Data System (ADS)

Wang, Yonggang; Geerts, Bart; Chen, Yaosheng

2016-01-01

Boundary layer convection (BLC) is common over high-latitude oceans and adjacent coastal regions when a cold airmass becomes exposed to a sufficient fetch of open water. The vertical structure of mixed-phase BLC clouds and precipitation is examined using the Atmospheric Radiation Measurement Program data set collected at the North Slope of Alaska (NSA) site at Barrow, Alaska. BLC may occur at this location in autumn, when cold air masses originating at higher latitudes advect southward over the still ice-free coastal waters north of Alaska. This study identifies such BLC and documents its occurrence and characteristics. Instruments used for this study include profiling Ka band radars, a depolarization backscatter profiling lidar, a scanning X band radar, a microwave radiometer, a ceilometer, surface meteorological probes, and radiosondes. Six criteria are applied to objectively identify the BLC events, using data collected between 2004 and 2013. BLC episodes are relatively common at the NSA site, but almost exclusively in the month of October, and most episodes are relatively short, less than 10 h in duration. Liquid water is commonly found in these mixed-phase BLC clouds, with a typical liquid water path of 150 g/m2, and snowfall rates average ~3 mm h-1 (water equivalent), in some cases over 10 mm h-1, notwithstanding the low cloud echo tops (~1.0-1.5 km). In one rather weak but persistent episode fall speed estimates derived from the profiling Ka band radar indicates the presence of rimed particles, confirming the convective nature of this precipitation.

Structure measurements in a synthetic turbulent boundary layer

NASA Astrophysics Data System (ADS)

Arakeri, Jaywant H.

1987-09-01

Extensive hot-wire measurements have been made to determine the structure of the large eddy in a synthejc turbulent boundary layer on a flat-plate model. The experiments were carried out in a wind tunnel at a nominal free-stream velocity of 12 m/s. The synthetic turbulent boundary layer had a hexagonal pattern of eddies and a ratio of streamwise scale to spanwise scale of 3.2:1. The measured celerity of the large eddy was 84.2 percent of the free-stream velocity. There was some loss of coherence, but very little distortion, as the eddies moved downstream. Several mean properties of the synthetic boundary layer were found to agree quite well with the mean properties of a natural turbulent boundary layer at the same Reynolds number. The large eddy is composed of a pair of primary counter-rotating vortices about five [...] long in the streamwise direction and about one [...] apart in the spanwise direction, where [...] is the mean boundary-layer thickness. The sense of the primary pair is such as to pump fluid away from the wall in the region between the vortices. A secondary pair of counter-rotating streamwise vortices, having a sense opposite to that of the primary pair, is observed outside of and slightly downstream from the primary vortices. Both pairs of vortices extend across the full thickness of the boundary layer and are inclined at a shallow angle to the surface of the flat plate. The data show that the mean vorticity vectors are not tangential to the large-eddy vortices. In fact, the streamwise and normal vorticity components that signal the presence of the eddy are of the same order of magnitude. Definite signatures are obtained in terms of the mean skin-friction coefficient and the mean wake parameter averaged at constant phase. Velocities induced by the vortices are partly responsible for entrainment of irrotational fluid, for transport of momentum, for generation of Reynolds stresses, and for maintenance of streamwise and normal vorticity in the outer

A method for the direct numerical simulation of hypersonic boundary-layer instability with finite-rate chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marxen, Olaf, E-mail: olaf.marxen@vki.ac.be; Aeronautics and Aerospace Department, von Karman Institute for Fluid Dynamics, Chaussée de Waterloo, 72, 1640 Rhode-St-Genèse; Magin, Thierry E.

2013-12-15

A new numerical method is presented here that allows to consider chemically reacting gases during the direct numerical simulation of a hypersonic fluid flow. The method comprises the direct coupling of a solver for the fluid mechanical model and a library providing the physio-chemical model. The numerical method for the fluid mechanical model integrates the compressible Navier–Stokes equations using an explicit time advancement scheme and high-order finite differences. This Navier–Stokes code can be applied to the investigation of laminar-turbulent transition and boundary-layer instability. The numerical method for the physio-chemical model provides thermodynamic and transport properties for different gases as wellmore » as chemical production rates, while here we exclusively consider a five species air mixture. The new method is verified for a number of test cases at Mach 10, including the one-dimensional high-temperature flow downstream of a normal shock, a hypersonic chemical reacting boundary layer in local thermodynamic equilibrium and a hypersonic reacting boundary layer with finite-rate chemistry. We are able to confirm that the diffusion flux plays an important role for a high-temperature boundary layer in local thermodynamic equilibrium. Moreover, we demonstrate that the flow for a case previously considered as a benchmark for the investigation of non-equilibrium chemistry can be regarded as frozen. Finally, the new method is applied to investigate the effect of finite-rate chemistry on boundary layer instability by considering the downstream evolution of a small-amplitude wave and comparing results with those obtained for a frozen gas as well as a gas in local thermodynamic equilibrium.« less

Assessing sea wave and spray effects on Marine Boundary Layer structure

NASA Astrophysics Data System (ADS)

Stathopoulos, Christos; Galanis, George; Patlakas, Platon; Kallos, George

2017-04-01

Air sea interface is characterized by several mechanical and thermodynamical processes. Heat, moisture and momentum exchanges increase the complexity in modeling the atmospheric-ocean system. Near surface atmospheric levels are subject to sea surface roughness and sea spray. Sea spray fluxes can affect atmospheric stability and induce microphysical processes such as sea salt particle formation and condensation/evaporation of water in the boundary layer. Moreover, presence of sea spray can alter stratification over the ocean surface with further insertion of water vapor. This can lead to modified stability conditions and to wind profiles that deviate significantly from the logarithmic approximation. To model these effects, we introduce a fully coupled system consisting of the mesoscale atmospheric model RAMS/ICLAMS and the wave model WAM. The system encompasses schemes for ocean surface roughness, sea salt aerosols and droplet thermodynamic processes and handles sea salt as predictive quantity. Numerical experiments using the developed atmospheric-ocean system are performed over the Atlantic and Mediterranean shoreline. Emphasis is given to the quantification of the improvement obtained in the description of the marine boundary layer, particularly in its lower part as well as in wave characteristics.

Boundary layers in cataclysmic variables: The HEAO-1 X-ray constraints

NASA Technical Reports Server (NTRS)

Jensen, K. A.

1983-01-01

The predictions of the boundary layer model for the X-ray emission from novae are summarized. A discrepancy between observations and theory in the X-ray observations is found. Constraints on the nature of the boundary layers in novae, based on the lack of detections of novae in the HEAO-1 soft X-ray survey are provided. Temperature and column densities for optically thick boundary layers in novae are estimated.

Parallelization of the Flow Field Dependent Variation Scheme for Solving the Triple Shock/Boundary Layer Interaction Problem

NASA Technical Reports Server (NTRS)

Schunk, Richard Gregory; Chung, T. J.

2001-01-01

A parallelized version of the Flowfield Dependent Variation (FDV) Method is developed to analyze a problem of current research interest, the flowfield resulting from a triple shock/boundary layer interaction. Such flowfields are often encountered in the inlets of high speed air-breathing vehicles including the NASA Hyper-X research vehicle. In order to resolve the complex shock structure and to provide adequate resolution for boundary layer computations of the convective heat transfer from surfaces inside the inlet, models containing over 500,000 nodes are needed. Efficient parallelization of the computation is essential to achieving results in a timely manner. Results from a parallelization scheme, based upon multi-threading, as implemented on multiple processor supercomputers and workstations is presented.

Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.; Smeltzer, Stanley S., III

2000-01-01

An analytical, parametric study of the attenuation of bending boundary layers or edge effects in balanced and unbalanced, symmetrically and unsymmetrically laminated thin cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize and quantify the effects of laminate orthotropy and laminate anisotropy on the bending boundary-layer decay length in a very general and encompassing manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all the laminate constructions considered, the results show that the differences between results that were obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that in some cases neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and in other cases it results in an overestimation.

Some Basic Aspects of Magnetohydrodynamic Boundary-Layer Flows

NASA Technical Reports Server (NTRS)

Hess, Robert V.

1959-01-01

An appraisal is made of existing solutions of magnetohydrodynamic boundary-layer equations for stagnation flow and flat-plate flow, and some new solutions are given. Since an exact solution of the equations of magnetohydrodynamics requires complicated simultaneous treatment of the equations of fluid flow and of electromagnetism, certain simplifying assumptions are generally introduced. The full implications of these assumptions have not been brought out properly in several recent papers. It is shown in the present report that for the particular law of deformation which the magnetic lines are assumed to follow in these papers a magnet situated inside the missile nose would not be able to take up any drag forces; to do so it would have to be placed in the flow away from the nose. It is also shown that for the assumption that potential flow is maintained outside the boundary layer, the deformation of the magnetic lines is restricted to small values. The literature contains serious disagreements with regard to reductions in heat-transfer rates due to magnetic action at the nose of a missile, and these disagreements are shown to be mainly due to different interpretations of reentry conditions rather than more complicated effects. In the present paper the magnetohydrodynamic boundary-layer equation is also expressed in a simple form that is especially convenient for physical interpretation. This is done by adapting methods to magnetic forces which in the past have been used for forces due to gravitational or centrifugal action. The simplified approach is used to develop some new solutions of boundary-layer flow and to reinterpret certain solutions existing in the literature. An asymptotic boundary-layer solution representing a fixed velocity profile and shear is found. Special emphasis is put on estimating skin friction and heat-transfer rates.

A diagnostic approach to obtaining planetary boundary layer winds using satellite-derived thermal data

NASA Technical Reports Server (NTRS)

Belt, Carol L.; Fuelberg, Henry E.

1984-01-01

The feasibility of using satellite derived thermal data to generate realistic synoptic scale winds within the planetary boundary layer (PBL) is examined. Diagnostic modified Ekman wind equations from the Air Force Global Weather Central (AFGWC) Boundary Layer Model are used to compute winds at seven levels within the PBL transition layer (50 m to 1600 m AGL). Satellite derived winds based on 62 predawn TIROS-N soundings are compared to similarly derived wind fields based on 39 AVE-SESAME II rawinsonde (RAOB) soundings taken 2 h later. Actual wind fields are also used as a basis for comparison. Qualitative and statistical comparisons show that the Ekman winds from both sources are in very close agreement, with an average vector correlation coefficient of 0.815. Best results are obtained at 300 m AGL. Satellite winds tend to be slightly weaker than their RAOB counterparts and exhibit a greater degree of cross-isobaric flow. The modified Ekman winds show a significant improvement over geostrophic values at levels nearest the surface.

On the Time Scale of Nocturnal Boundary Layer Cooling in Valleys and Basins and over Plains

NASA Astrophysics Data System (ADS)

de Wekker, Stephan F. J.; Whiteman, C. David

2006-06-01

Sequences of vertical temperature soundings over flat plains and in a variety of valleys and basins of different sizes and shapes were used to determine cooling-time-scale characteristics in the nocturnal stable boundary layer under clear, undisturbed weather conditions. An exponential function predicts the cumulative boundary layer cooling well. The fitting parameter or time constant in the exponential function characterizes the cooling of the valley atmosphere and is equal to the time required for the cumulative cooling to attain 63.2% of its total nighttime value. The exponential fit finds time constants varying between 3 and 8 h. Calculated time constants are smallest in basins, are largest over plains, and are intermediate in valleys. Time constants were also calculated from air temperature measurements made at various heights on the sidewalls of a small basin. The variation with height of the time constant exhibited a characteristic parabolic shape in which the smallest time constants occurred near the basin floor and on the upper sidewalls of the basin where cooling was governed by cold-air drainage and radiative heat loss, respectively.

Stability characteristics of compressible boundary layers over thermo-mechanically compliant walls

NASA Astrophysics Data System (ADS)

Dettenrieder, Fabian; Bodony, Daniel

2017-11-01

Transition prediction at hypersonic flight conditions continues to be a challenge and results in conservative safety factors that increase vehicle weight. The weight and thus cost reduction of the outer skin panels promises significant impact; however, fluid-structure interaction due to unsteady perturbations in the laminar boundary layer regime has not been systematically studied at conditions relevant for reusable, hypersonic flight. In this talk, we develop and apply convective and global stability analyses for compressible boundary layers over thermo-mechanically compliant panels. This compliance is shown to change the convective stability of the boundary layer modes, with both stabilization and destabilization observed. Finite panel lengths are shown to affect the global stability properties of the boundary layer.

Boundary-layer cumulus over heterogeneous landscapes: A subgrid GCM parameterization. Final report, December 1991--November 1995

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stull, R.B.; Tripoli, G.

1996-01-08

The authors developed single-column parameterizations for subgrid boundary-layer cumulus clouds. These give cloud onset time, cloud coverage, and ensemble distributions of cloud-base altitudes, cloud-top altitudes, cloud thickness, and the characteristics of cloudy and clear updrafts. They tested and refined the parameterizations against archived data from Spring and Summer 1994 and 1995 intensive operation periods (IOPs) at the Southern Great Plains (SGP) ARM CART site near Lamont, Oklahoma. The authors also found that: cloud-base altitudes are not uniform over a heterogeneous surface; tops of some cumulus clouds can be below the base-altitudes of other cumulus clouds; there is an overlap regionmore » near cloud base where clear and cloudy updrafts exist simultaneously; and the lognormal distribution of cloud sizes scales to the JFD of surface layer air and to the shape of the temperature profile above the boundary layer.« less

Recent Advances in Modeling of the Atmospheric Boundary Layer and Land Surface in the Coupled WRF-CMAQ Model

EPA Science Inventory

Advances in the land surface model (LSM) and planetary boundary layer (PBL) components of the WRF-CMAQ coupled meteorology and air quality modeling system are described. The aim of these modifications was primarily to improve the modeling of ground level concentrations of trace c...

Hypersonic three-dimensional nonequilibrium boundary-layer equations in generalized curvilinear coordinates

NASA Technical Reports Server (NTRS)

Lee, Jong-Hun

1993-01-01

The basic governing equations for the second-order three-dimensional hypersonic thermal and chemical nonequilibrium boundary layer are derived by means of an order-of-magnitude analysis. A two-temperature concept is implemented into the system of boundary-layer equations by simplifying the rather complicated general three-temperature thermal gas model. The equations are written in a surface-oriented non-orthogonal curvilinear coordinate system, where two curvilinear coordinates are non-orthogonial and a third coordinate is normal to the surface. The equations are described with minimum use of tensor expressions arising from the coordinate transformation, to avoid unnecessary confusion for readers. The set of equations obtained will be suitable for the development of a three-dimensional nonequilibrium boundary-layer code. Such a code could be used to determine economically the aerodynamic/aerothermodynamic loads to the surfaces of hypersonic vehicles with general configurations. In addition, the basic equations for three-dimensional stagnation flow, of which solution is required as an initial value for space-marching integration of the boundary-layer equations, are given along with the boundary conditions, the boundary-layer parameters, and the inner-outer layer matching procedure. Expressions for the chemical reaction rates and the thermodynamic and transport properties in the thermal nonequilibrium environment are explicitly given.

Response of a hypersonic boundary layer to freestream pulse acoustic disturbance.

PubMed

Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing

2014-01-01

The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter.

Response of a Hypersonic Boundary Layer to Freestream Pulse Acoustic Disturbance

PubMed Central

Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing

2014-01-01

The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter. PMID:24737993

Boundary layer concentrations and landscape scale emissions of volatile organic compounds in early spring

NASA Astrophysics Data System (ADS)

Haapanala, S.; Rinne, J.; Hakola, H.; Hellén, H.; Laakso, L.; Lihavainen, H.; Janson, R.; Kulmala, M.

2006-10-01

Boundary layer concenrations of several volatile organic compounds (VOC) were measured during two campaigns in springs of 2003 and 2006. Measurements were conducted over boreal forests near SMEAR II measurement station in Hyytiälä, Southern Finland. In 2003 the measuremens were performed using light aircraft and in 2006 using hot air ballon. Isoprene concentrarions were low, usually below detection limit. This is explained by low biogenic production due to cold weather. Monoterpenes were observed frequently. Average total monoterpene concentration in the boundary layer was 33 pptv. Many anthropogenic compounds e.g. benzene, xylene and toluene, were observed in high amounts. Ecosystem scale surface emissions were estimated using simple mixed box budget methodology. Total monoterpene fluxes varied up to 80 μg m-2 h-1, α-pinene contributing typically more than two thirds of that. Highest fluxes of anthropogenic compounds were those of p/m xylene.

A theoretical study of mixing downstream of transverse injection into a supersonic boundary layer

NASA Technical Reports Server (NTRS)

Baker, A. J.; Zelazny, S. W.

1972-01-01

A theoretical and analytical study was made of mixing downstream of transverse hydrogen injection, from single and multiple orifices, into a Mach 4 air boundary layer over a flat plate. Numerical solutions to the governing three-dimensional, elliptic boundary layer equations were obtained using a general purpose computer program. Founded upon a finite element solution algorithm. A prototype three-dimensional turbulent transport model was developed using mixing length theory in the wall region and the mass defect concept in the outer region. Excellent agreement between the computed flow field and experimental data for a jet/freestream dynamic pressure ratio of unity was obtained in the centerplane region of the single-jet configuration. Poorer agreement off centerplane suggests an inadequacy of the extrapolated two-dimensional turbulence model. Considerable improvement in off-centerplane computational agreement occured for a multi-jet configuration, using the same turbulent transport model.

Stereoscopic Imaging in Hypersonics Boundary Layers using Planar Laser-Induced Fluorescence

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; Bathel, Brett; Inman, Jennifer A.; Alderfer, David W.; Jones, Stephen B.

2008-01-01

Stereoscopic time-resolved visualization of three-dimensional structures in a hypersonic flow has been performed for the first time. Nitric Oxide (NO) was seeded into hypersonic boundary layer flows that were designed to transition from laminar to turbulent. A thick laser sheet illuminated and excited the NO, causing spatially-varying fluorescence. Two cameras in a stereoscopic configuration were used to image the fluorescence. The images were processed in a computer visualization environment to provide stereoscopic image pairs. Two methods were used to display these image pairs: a cross-eyed viewing method which can be viewed by naked eyes, and red/blue anaglyphs, which require viewing through red/blue glasses. The images visualized three-dimensional information that would be lost if conventional planar laser-induced fluorescence imaging had been used. Two model configurations were studied in NASA Langley Research Center's 31-Inch Mach 10 Air Wind tunnel. One model was a 10 degree half-angle wedge containing a small protuberance to force the flow to transition. The other model was a 1/3-scale, truncated Hyper-X forebody model with blowing through a series of holes to force the boundary layer flow to transition to turbulence. In the former case, low flowrates of pure NO seeded and marked the boundary layer fluid. In the latter, a trace concentration of NO was seeded into the injected N2 gas. The three-dimensional visualizations have an effective time resolution of about 500 ns, which is fast enough to freeze this hypersonic flow. The 512x512 resolution of the resulting images is much higher than high-speed laser-sheet scanning systems with similar time response, which typically measure 10-20 planes.

Measurements of thermal updraft intensity over complex terrain using American white pelicans and a simple boundary-layer forecast model

USGS Publications Warehouse

Shannon, H.D.; Young, G.S.; Yates, M.; Fuller, Mark R.; Seegar, W.

2003-01-01

An examination of boundary-layer meteorological and avian aerodynamic theories suggests that soaring birds can be used to measure the magnitude of vertical air motions within the boundary layer. These theories are applied to obtain mixed-layer normalized thermal updraft intensity over both flat and complex terrain from the climb rates of soaring American white pelicans and from diagnostic boundary-layer model-produced estimates of the boundary-layer depth zi and the convective velocity scale w*. Comparison of the flatland data with the profiles of normalized updraft velocity obtained from previous studies reveals that the pelican-derived measurements of thermal updraft intensity are in close agreement with those obtained using traditional research aircraft and large eddy simulation (LES) in the height range of 0.2 to 0.8 zi. Given the success of this method, the profiles of thermal vertical velocity over the flatland and the nearby mountains are compared. This comparison shows that these profiles are statistically indistinguishable over this height range, indicating that the profile for thermal updraft intensity varies little over this sample of complex terrain. These observations support the findings of a recent LES study that explored the turbulent structure of the boundary layer using a range of terrain specifications. For terrain similar in scale to that encountered in this study, results of the LES suggest that the terrain caused less than an 11% variation in the standard deviation of vertical velocity.

Stability of the Boundary Layer and the Spot

NASA Technical Reports Server (NTRS)

Wygnanski, I.

2007-01-01

The similarity among turbulent spots observed in various transition experiments, and the rate in which they contaminate the surrounding laminar boundary layer is only cursory. The shape of the spot depends on the Reynolds number of the surrounding boundary layer and on the pressure gradient to which it and the surrounding laminar flow are exposed. The propagation speeds of the spot boundaries depend, in addition, on the location from which the spot originated and do not simply scale with the local free stream velocity. The understanding of the manner in which the turbulent manner in which the turbulent spot destabilizes the surrounding, vortical fluid is a key to the understanding of the transition process. We therefore turned to detailed observations near the spot boundaries in general and near the spanwise tip of the spot in particular.

Boundary layer control by a fish: Unsteady laminar boundary layers of rainbow trout swimming in turbulent flows

PubMed Central

Saarenrinne, Pentti

2016-01-01

ABSTRACT The boundary layers of rainbow trout, Oncorhynchus mykiss [0.231±0.016 m total body length (L) (mean±s.d.); N=6], swimming at 1.6±0.09 L s−1 (N=6) in an experimental flow channel (Reynolds number, Re=4×105) with medium turbulence (5.6% intensity) were examined using the particle image velocimetry technique. The tangential flow velocity distributions in the pectoral and pelvic surface regions (arc length from the rostrum, lx=71±8 mm, N=3, and lx=110±13 mm, N=4, respectively) were approximated by a laminar boundary layer model, the Falkner−Skan equation. The flow regime over the pectoral and pelvic surfaces was regarded as a laminar flow, which could create less skin-friction drag than would be the case with turbulent flow. Flow separation was postponed until vortex shedding occurred over the posterior surface (lx=163±22 mm, N=3). The ratio of the body-wave velocity to the swimming speed was in the order of 1.2. This was consistent with the condition of the boundary layer laminarization that had been confirmed earlier using a mechanical model. These findings suggest an energy-efficient swimming strategy for rainbow trout in a turbulent environment. PMID:27815242

Boundary layer control by a fish: Unsteady laminar boundary layers of rainbow trout swimming in turbulent flows.

PubMed

Yanase, Kazutaka; Saarenrinne, Pentti

2016-12-15

The boundary layers of rainbow trout, Oncorhynchus mykiss [0.231±0.016 m total body length (L) (mean±s.d.); N=6], swimming at 1.6±0.09 L s -1 (N=6) in an experimental flow channel (Reynolds number, Re=4×10 5 ) with medium turbulence (5.6% intensity) were examined using the particle image velocimetry technique. The tangential flow velocity distributions in the pectoral and pelvic surface regions (arc length from the rostrum, l x =71±8 mm, N=3, and l x =110±13 mm, N=4, respectively) were approximated by a laminar boundary layer model, the Falkner-Skan equation. The flow regime over the pectoral and pelvic surfaces was regarded as a laminar flow, which could create less skin-friction drag than would be the case with turbulent flow. Flow separation was postponed until vortex shedding occurred over the posterior surface (l x =163±22 mm, N=3). The ratio of the body-wave velocity to the swimming speed was in the order of 1.2. This was consistent with the condition of the boundary layer laminarization that had been confirmed earlier using a mechanical model. These findings suggest an energy-efficient swimming strategy for rainbow trout in a turbulent environment. © 2016. Published by The Company of Biologists Ltd.

Ventilation of multi-entranced rodent burrows by boundary layer eddies.

PubMed

Brickner-Braun, Inbal; Zucker-Milwerger, Daniel; Braun, Avi; Turner, J Scott; Pinshow, Berry; Berliner, Pedro

2014-12-01

Rodent burrows are often assumed to be environments wherein the air has a high concentration of CO₂. Although high burrow [CO₂] has been recorded, many studies report burrow [CO₂] that differs only slightly from atmospheric concentrations. Here, we advocate that one of the reasons for these differences is the penetration into burrows of air gusts (eddies), which originate in the turbulent boundary layer and prevent build-up of CO₂. We have characterized the means by which burrows of Sundevall's jird, which are representative of the burrows of many rodent species with more than one entrance, are ventilated. Our results demonstrate that, even at low wind speeds, the random penetration of eddies into a burrow through its openings is sufficient to keep the burrow [CO₂] low enough to be physiologically inconsequential, even in its deep and remote parts. © 2014. Published by The Company of Biologists Ltd.

A compilation of unsteady turbulent boundary-layer experimental data

NASA Technical Reports Server (NTRS)

Carr, L. W.

1981-01-01

An extensive literature search was conducted and those experiments related to unsteady boundary layer behavior were cataloged. In addition, an international survey of industrial, university, and governmental research laboratories was made in which new and ongoing experimental programs associated with unsteady turbulent boundary layer research were identified. Pertinent references were reviewed and classified based on the technical emphasis of the various experiments. Experiments that include instantaneous or ensemble averaged profiles of boundary layer variables are stressed. The experimental apparatus and flow conditions are described and summaries of acquired data and significant conclusions are summarized. Measurements obtained from the experiments which exist in digital form were stored on magnetic tape. Instructions are given for accessing these data sets for further analysis.

Rotor boundary layer development with inlet guide vane (IGV) wake impingement

NASA Astrophysics Data System (ADS)

Jia, Lichao; Zou, Tengda; Zhu, Yiding; Lee, Cunbiao

2018-04-01

This paper examines the transition process in a boundary layer on a rotor blade under the impingement of an inlet guide vane wake. The effects of wake strengths and the reduced frequency on the unsteady boundary layer development on a low-speed axial compressor were investigated using particle image velocimetry. The measurements were carried out at two reduced frequencies (fr = fIGVS0/U2i, fr = 1.35, and fr = 0.675) with the Reynolds number, based on the blade chord and the isentropic inlet velocity, being 97 500. At fr = 1.35, the flow separated at the trailing edge when the wake strength was weak. However, the separation was almost totally suppressed as the wake strength increased. For the stronger wake, both the wake's high turbulence and the negative jet behavior of the wake dominated the interaction between the unsteady wake and the separated boundary layer on the suction surface of the airfoil. The boundary layer displacement thickened first due to the negative jet effect. Then, as the disturbances developed underneath the wake, the boundary layer thickness reduced gradually. The high disturbance region convected downstream at a fraction of the free-stream velocity and spread in the streamwise direction. The separation on the suction surface was suppressed until the next wake's arrival. Because of the long recovery time at fr = 0.675, the boundary layer thickened gradually as the wake convected further downstream and finally separated due to the adverse pressure gradient. The different boundary layer states in turn affected the development of disturbances.

Turbulent boundary layers subjected to multiple curvatures and pressure gradients

NASA Technical Reports Server (NTRS)

Bandyopadhyay, Promode R.; Ahmed, Anwar

1993-01-01

The effects of abruptly applied cycles of curvatures and pressure gradients on turbulent boundary layers are examined experimentally. Two two-dimensional curved test surfaces are considered: one has a sequence of concave and convex longitudinal surface curvatures and the other has a sequence of convex and concave curvatures. The choice of the curvature sequences were motivated by a desire to study the asymmetric response of turbulent boundary layers to convex and concave curvatures. The relaxation of a boundary layer from the effects of these two opposite sequences has been compared. The effect of the accompaying sequences of pressure gradient has also been examined but the effect of curvature dominates. The growth of internal layers at the curvature junctions have been studied. Measurements of the Gortler and corner vortex systems have been made. The boundary layer recovering from the sequence of concave to convex curvature has a sustained lower skin friction level than in that recovering from the sequence of convex to concave curvature. The amplification and suppression of turbulence due to the curvature sequences have also been studied.

Boundary Layer Effect on Behavior of Discrete Models

PubMed Central

Eliáš, Jan

2017-01-01

The paper studies systems of rigid bodies with randomly generated geometry interconnected by normal and tangential bonds. The stiffness of these bonds determines the macroscopic elastic modulus while the macroscopic Poisson’s ratio of the system is determined solely by the normal/tangential stiffness ratio. Discrete models with no directional bias have the same probability of element orientation for any direction and therefore the same mechanical properties in a statistical sense at any point and direction. However, the layers of elements in the vicinity of the boundary exhibit biased orientation, preferring elements parallel with the boundary. As a consequence, when strain occurs in this direction, the boundary layer becomes stiffer than the interior for the normal/tangential stiffness ratio larger than one, and vice versa. Nonlinear constitutive laws are typically such that the straining of an element in shear results in higher strength and ductility than straining in tension. Since the boundary layer tends, due to the bias in the elemental orientation, to involve more tension than shear at the contacts, it also becomes weaker and less ductile. The paper documents these observations and compares them to the results of theoretical analysis. PMID:28772517

Boundary Layer Effect on Behavior of Discrete Models.

PubMed

Eliáš, Jan

2017-02-10

The paper studies systems of rigid bodies with randomly generated geometry interconnected by normal and tangential bonds. The stiffness of these bonds determines the macroscopic elastic modulus while the macroscopic Poisson's ratio of the system is determined solely by the normal/tangential stiffness ratio. Discrete models with no directional bias have the same probability of element orientation for any direction and therefore the same mechanical properties in a statistical sense at any point and direction. However, the layers of elements in the vicinity of the boundary exhibit biased orientation, preferring elements parallel with the boundary. As a consequence, when strain occurs in this direction, the boundary layer becomes stiffer than the interior for the normal/tangential stiffness ratio larger than one, and vice versa. Nonlinear constitutive laws are typically such that the straining of an element in shear results in higher strength and ductility than straining in tension. Since the boundary layer tends, due to the bias in the elemental orientation, to involve more tension than shear at the contacts, it also becomes weaker and less ductile. The paper documents these observations and compares them to the results of theoretical analysis.