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1

Porous Material Development for Boundary Layer Control.  

National Technical Information Service (NTIS)

A description is presented of the development of a new porous material that was undertaken specifically for the application of area suction boundary layer control to underwater vehicles. This material was subsequently used in the manufacture of several hy...

G. May W. B. Giles

1964-01-01

2

Turbulent boundary layers developing over compliant surfaces  

NASA Astrophysics Data System (ADS)

The problem of reducing drag due to skin friction remains of interest. This is the case because of the significant benefits that would result from an application of a drag reducing scheme on airplanes, ships or underwater vehicles. One of the techniques that have been proposed for such a scheme is wall compliance. Wall compliance could, in principle, work in two ways: either it could delay transition, or it could modify the inner part of a turbulent boundary layer so that reduced skin friction would result. The objective of this research program was to develop prediction techniques for high Reynolds number turbulent flows over compliant surfaces. This objective was pursued by evaluating the wall induced Reynolds stresses using solutions of the liner momentum equations.

Lekoudis, S. G.; Sengupta, T.

1983-05-01

3

Development of instrumentation for boundary layer transition detection  

Microsoft Academic Search

A steady state heat transfer technique is developed and evaluated for detecting boundary layer transition on a flat plate in incompressible flow. The method involves adhering encapsulated temperature sensitive liquid crystals to a constant heat flux surface. A heater composed of unidirectional carbon fibers is developed and tested with the aim of in-flight boundary layer transition detection on a natural

Steven B. Harrison

1991-01-01

4

Boundary-layer dynamics of a developing vortex  

NASA Astrophysics Data System (ADS)

The axisymmetric vortices in solid and nonsolid rotation are analyzed to investigate the dynamics of the boundary layer. The governing expressions are similarity transformed to nonlinear parabolic partial differential equations solved by a Galerkin method for simplified initial conditions; these conditions allow non-zero tangential and vertical velocities at the lower and upper boundaries. A time-dependent Taylor boundary condition at the lower extremity of the vortex induces gradual fluid spin-down, so that the non-slip steady-state solutions are progressively approached.

Raymond, W. H.; Rao, G. V.

1981-02-01

5

Further Development and Testing of a Second-Order Bulk Boundary Layer Model.  

National Technical Information Service (NTIS)

A one-layer bulk boundary layer model is developed. The model predicts the mixed layer values of the potential temperature, mixing ratio, and u- and v-momentum. The model also predicts the depth of the boundary layer and the vertically integrated turbulen...

R. D. Krasner

1993-01-01

6

Spatially developing secondary instabilities in compressible swept airfoil boundary layers  

Microsoft Academic Search

Two-dimensional eigenvalue analysis is used on a massive scale to study the spatial instabilities of compressible shear flows\\u000a with two inhomogeneous directions. The main focus of the study is crossflow dominated swept-wing boundary layers although\\u000a the methodology can also be applied to study other types of flows, such as the attachment-line flow. Certain unique aspects\\u000a of formulating a spatial, two-dimensional

Fei Li; Meelan M. Choudhari

2011-01-01

7

Further development and testing of a second-order bulk boundary layer model. Master's thesis  

SciTech Connect

A one-layer bulk boundary layer model is developed. The model predicts the mixed layer values of the potential temperature, mixing ratio, and u- and v-momentum. The model also predicts the depth of the boundary layer and the vertically integrated turbulence kinetic energy (TKE). The TKE is determined using a second-order closure that relates the rate of dissipation to the TKE. The fractional area covered by rising motion sigma and the entrainment rate (E) are diagnostically determined. The model is used to study the clear convective boundary layer (CBL) using data from the Wangara, Australia boundary layer experiment. The Wangara data is also used as an observation base to validate model results. A further study is accomplished by simulating the planetary boundary layer (PBL) over an ocean surface. This study is designed to find the steady-state solutions of the prognostic variable.

Krasner, R.D.

1993-05-03

8

Boundary Layer Simulator Improvement.  

National Technical Information Service (NTIS)

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 p...

S. C. Praharaj C. P. Schmitz J. A. Nouri

1989-01-01

9

Development of a turbulent boundary layer after a step from smooth to rough surface  

NASA Astrophysics Data System (ADS)

The flow developing downstream of a step change from smooth to rough surface condition is studied in the light of Townsend's wall similarity hypothesis. Previous studies seem to support the hypothesis for channel and pipe flows, but there are considerable controversies about its application to boundary layers and in particular to surface roughness formed by spanwise bars. It has been suggested that this controversy arises from insufficient separation of scales between the boundary layer thickness and the roughness length scale. An experimental investigation has therefore been undertaken where the flow evolves from a fully developed smooth wall boundary layer at high Reynolds numbers over a step in surface roughness ( Re ? = 13,400 at the step). The flow is mapped through the development of the internal layer until the flow is fully developed over the rough wall. The internal layer is found to grow as ? ˜ X 0.73, and after about 15 boundary layer thicknesses at the step, the internal layer has reached the outer edge of the incoming layer. At the last rough wall measurement station, the Reynolds number has grown to Re ? ? 32,600 and the ratio of boundary layer to roughness length scales is ?/ k ? 140. The outer layer differences between the smooth and the rough wall data were found to be sufficiently small to conclude that for this setup the Townsend's wall similarity hypothesis appears to hold.

Efros, Vladislav; Krogstad, Per-Ĺge

2011-12-01

10

DNS of a spatially developing turbulent boundary layer with passive scalar transport  

Microsoft Academic Search

A direct numerical simulation (DNS) of a spatially developing turbulent boundary layer over a flat plate under zero pressure gradient (ZPG) has been carried out. The evolution of several passive scalars with both isoscalar and isoflux wall boundary condition are computed during the simulation. The Navier–Stokes equations as well as the scalar transport equation are solved using a fully spectral

Qiang Li; Philipp Schlatter; Luca Brandt; Dan S. Henningson

2009-01-01

11

Boundary layer transition studies  

Microsoft Academic Search

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 &

Jonathan H. Watmuff

1995-01-01

12

Linear feedback control and estimation applied to instabilities in spatially developing boundary layers  

NASA Astrophysics Data System (ADS)

This paper presents the application of feedback control to spatially developing boundary layers. It is the natural follow-up of HSkan-Cooke boundary layers are estimated by use of wall measurements. The estimated state is in turn fed back for control in order to reduce the kinetic energy of the perturbations. The control actuation is achieved by means of unsteady blowing and suction at the wall. Flow perturbations are generated in the upstream region in the computational box and propagate in the boundary layer. Measurements are extracted downstream over a thin strip, followed by a second thin strip where the actuation is performed. It is shown that flow disturbances can be efficiently estimated and controlled in spatially evolving boundary layers for a wide range of base flows and disturbances.

Chevalier, Mattias; H?Pffner, J.?R.?Me; ?Kervik, Espen; Henningson, Dan S.

13

Effect of Surfactant Additives on Generation and Development of Laminar Boundary Layer on a Flat Plate  

NASA Astrophysics Data System (ADS)

The effect of surfactant solutions on laminar boundary layer over a flat plate has been investigated at Re < 15.3×103 by measuring the velocity profile using a PIV system. It was clarified that the boundary layer thickness of surfactant solutions increases significantly compared to that of tap water. In the upstream region of the leading edge, the boundary layer (or the stagnation area) has already been generated and the thickness of this area is already large. In the downstream region, the velocity profiles of all surfactant concentrations at the near-wall region, are similar, but not identical, to that of tap water. At the far-wall region of the boundary layer, the velocity profile is significantly different. For higher surfactant concentrations, the velocity profile describes like S-shape profile, which is greatly different from that of lower concentration. When the Reynolds number increases, the velocity profile of the surfactant solution gradually develops. The dependence of the boundary layer thickness of the surfactant solution on the distance downstream from the leading edge is similar to that of tap water. Consequently, the surfactant gives large effect for not only development of the boundary layer but also the generation of it.

Ogata, Satoshi; Fujita, Takeshi

14

Boundary layer development in axial compressors and turbines. Part 1 of 4: Composite picture  

SciTech Connect

Comprehensive experiments and computational analyses were conducted to understand boundary layer development on airfoil surfaces in multistage, axial-flow compressors and LP turbines. The tests were run over a broad range of Reynolds numbers and loading levels in large, low-speed research facilities which simulate the relevant aerodynamic features of modern engine components.Measurements of boundary layer characteristics were obtained by using arrays of densely packed, hot-film gauges mounted on airfoil surfaces and by making boundary layer surveys with hot wire probes. Computational predictions were made using both steady flow codes and an unsteady flow code. This is the first time that time-resolved boundary layer measurements and detailed comparisons of measured data with predictions of boundary layer codes have been reported for multistage compressor and turbine blading. Part 1 of this paper summarizes all of the experimental findings by using sketches to show how boundary layers develop on compressor and turbine blading. Parts 2 and 3 present the detailed experimental results for the compressor and turbine, respectively. Part 4 presents computational analyses and discusses comparisons with experimental data. Readers not interested in experimental detail can go directly from Part 1 to Part 4.

Halstead, D.E.; Wisler, D.C.; Shin, H.W. [GE Aircraft Engines, Cincinnati, OH (United States); Okiishi, T.H. [Iowa State Univ., Ames, IA (United States); Walker, G.J. [Univ. of Tasmania, Hobart (Australia); Hodson, H.P. [Univ. of Cambridge (United Kingdom)

1997-01-01

15

The atmospheric boundary layer  

Microsoft Academic Search

In this book, the author successfully reviews the current state of affairs in boundary-layer meteorology research. The book is organized into nine chapters. The first chapter is an introduction to the topic of the atmospheric boundary layer. The second chapter is a survey of turbulence theory. The third chapter reviews the similarity relationships that have been formulated for the various

J. R. Garratt

1992-01-01

16

The Atmospheric Boundary Layer  

ERIC Educational Resources Information Center

|Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)|

Tennekes, Hendrik

1974-01-01

17

Boundary layer transition  

Microsoft Academic Search

The boundary layer stability, its active control by sound and surface heating and the effect of curvature are studied numerically and experimentally for subsonic flow. In addition, the experimental and flight test data are correlated using the stability theory for supersonic Mach numbers. Active transition fixing and feedback control of boundary layer by sound interactions are experimentally investigated at low

L. Maestrello; A. Bayliss; S. M. Mangalam; M. R. Malik

1986-01-01

18

The Atmospheric Boundary Layer  

ERIC Educational Resources Information Center

Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)

Tennekes, Hendrik

1974-01-01

19

Atmospheric turbulent boundary layer development due to a change in surface roughness  

Microsoft Academic Search

The turbulent wind flow passing from a surface of one roughness to another is investigated analytically. The wind flow is modelled by a deep atmospheric turbulent boundary layer that assumes the possibility of self-preserving development in the course of flow modification. Closed form solutions are obtained describing the entire flow development and the characteristics of the wind velocity, surface stress

Andy T. Chan

2001-01-01

20

Boundary layer transition studies  

NASA Astrophysics Data System (ADS)

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 holes in the impervious test plate that used to establish the Blasius base flow. The suction is perturbed harmonically and data are averaged on the basis of the phase of the disturbance, for conditions corresponding to strong suction and without suction. develop spanwise irregularities which eventually form into clumps. -The spanwise clumping is evidence of a secondary instability that could be associated with suction vortices. Designers of porous surfaces use Goldsmith's Criterion to minimize cross-stream interactions. It is shown that partial TS wave cancellation is possible, depending on the hole spacing, disturbance frequency and free-stream velocity. %New high-performance Constant Temperature Hot-Wire Anemometers were designed and built, based on a linear system theory analysis that can be extended to arbitrary order. The motivation was to achieve the highest possible frequency reponse while ensuring overall system stability. The performance is equal to or superior to commercially available instruments at about 10% of the cost. Details, such as fabrication drawings and a parts list, have been published to enable the instrument to be construced by others.

Watmuff, Jonathan H.

1995-02-01

21

Boundary Layer Development over a Tropical Island during the Maritime Continent Thunderstorm Experiment  

Microsoft Academic Search

Data collected during the Maritime Continent Thunderstorm Experiment (MCTEX) (10 November-10 December 1995) have been used to analyze boundary layer development and circulations over two almost flat, tropical islands. The two adjacent islands have a combined length of about 170 km from east to west and 70 km from north to south. Intense thunderstorms formed over these islands every day

Robert Schafer; Peter T. May; Thomas D. Keenan; Kendal McGuffie; Warner L. Ecklund; Paul E. Johnston; Kenneth S. Gage

2001-01-01

22

Boundary layer receptivity - Theory  

NASA Astrophysics Data System (ADS)

The receptivity mechanisms by which free-stream disturbances generate instability waves in laminar boundary layers are discussed. Free-stream disturbances have wavelengths which are generally much longer than those of instability waves. Hence, the transfer of energy from the free-stream disturbance to the instability wave requires a wavelength conversion mechanism. Recent analyses using asymptotic methods have shown that the wavelength conversion takes place in regions of the boundary layer where the mean flow adjusts on a short streamwise length scale. This paper reviews recent progress in the theoretical understanding of these phenomena.

Kerschen, E. J.

23

Boundary Layer Transport of Small Particles.  

National Technical Information Service (NTIS)

The transport of small particles across the aerodynamic boundary layer that developed over a smooth, flat, acrylic plate and their subsequent deposition was investigated. The velocity boundary layer over the flat plate was characterized for a wind tunnel ...

D. McCready

1984-01-01

24

Nonequilibrium Chemistry Boundary Layer Integral Matrix Procedure.  

National Technical Information Service (NTIS)

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 ch...

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

1973-01-01

25

Plasma sheet boundary layer  

Microsoft Academic Search

The plasma sheet boundary layer is a temporally variable transition region located between the magnetotail lobes and the central plasma sheet. We have made a survey of these regions by using particle spectra and three-dimensional velocity-space distributions sampled by the ISEE 1 LEPEDEA. Ion composition measurements obtained by the Lockhead ion mass spectrometers indicate that ionospheric ions play a crucial

T. E. Eastman; L. A. Frank; W.K. Peterson; W. Lennartsson

1984-01-01

26

Development of a turbulent boundary layer after a step from smooth to rough surface  

Microsoft Academic Search

The flow developing downstream of a step change from smooth to rough surface condition is studied in the light of Townsend’s\\u000a wall similarity hypothesis. Previous studies seem to support the hypothesis for channel and pipe flows, but there are considerable\\u000a controversies about its application to boundary layers and in particular to surface roughness formed by spanwise bars. It\\u000a has been

Vladislav Efros; Per-Ĺge Krogstad

27

Experimental study on the effect of unsteadiness on boundary layer development on a linear turbine cascade  

Microsoft Academic Search

The results from an experimental investigation of unsteady boundary layer behavior on a linear turbine cascade are presented\\u000a in this paper. To perform a detailed study on unsteady cascade aerodynamics and heat transfer, a new large-scale, high-subsonic\\u000a research facility for simulating the periodic unsteady flow has been developed. It is capable of sequentially generating up\\u000a to four different unsteady inlet

M. T. Schobeiri; K. Pappu

1997-01-01

28

Turbulence management by active wall for fully developed two-dimensional boundary layer  

Microsoft Academic Search

Viscous drag reduction for flight vehicles and underwater vehicles is of current interest. Here, fully developed two-dimensional, incompressible turbulent boundary layers in the presence of a pressure gradient over moving wave surfaces are computed for the case of driven wall motion. The solution indicates strong interaction between the unsteady wave-induced flow and the time-averaged mean flow at a certain discrete

T. K. Sengupta; G. K. Suryanarayana; S. Selvarajan

1987-01-01

29

Streamwise development of turbulent boundary-layer drag reduction with polymer injection  

Microsoft Academic Search

Zero-pressure-gradient turbulent boundary-layer drag reduction by polymer injection has been studied with particle image velocimetry. Flow fields ranging from low to maximum drag reduction have been investigated. A previously developed technique y\\/ has been used to evaluate the skin friction, drag reduction and polymer stress. Current results agree well with the semi-log plot of drag reduction vs. normalized polymer flux

Y. X. Hou; V. S. R. Somandepalli; M. G. Mungal

2008-01-01

30

POD investigation of the unsteady turbulent boundary layer developing over porous moving flexible fishing net structure  

NASA Astrophysics Data System (ADS)

Particle image velocimetry (PIV) measurements are made to investigate the boundary layer developing over a modeled bottom trawl. The random motion of the fishing net structure as well as the flexibility and the porosity of this structure means that it is not enable to access the main characteristics of such a flow, using classical post-processing mathematical tools. An innovative post-treatment tool based on proper orthogonal decomposition (POD) is then developed to extract the mean velocity flow field from each available PIV instantaneous unsteady velocity field. In order to do so, the whole available velocity database is used to compute POD eigenfunctions and the first POD modes are identified as representing the mean flow field. It is then possible to deduce the mean boundary layer flow field for each position of the fishing net structure during PIV measurements. It is then observed that the mean flow field strongly depends on multiple parameters such as surface curvature, structure porosity, random motion of the structure. Streamwise evolution of classical thicknesses of boundary layer flow are also analyzed. The present work also provides benchmark PIV data of the unsteady flow developing on fishing net porous structures, which helps the progress in unsteady numerical codes for this investigation.

Druault, Philippe; Bouhoubeiny, Elkhadim; Germain, Grégory

2012-07-01

31

Synoptic Controls on Boundary-Layer Characteristics  

Microsoft Academic Search

We report the characteristics of the three-dimensional, time evolving, atmospheric boundary layer that develops beneath an idealised, dry, baroclinic weather system. The boundary-layer structure is forced by thermal advection associated with the weather system. Large positive heat fluxes behind the cold front drive a vigorous convective boundary layer, whereas moderate negative heat fluxes in the warm sector between the cold

Victoria A. Sinclair; Stephen E. Belcher; Suzanne L. Gray

2010-01-01

32

Development of sodar detection and its application for studies of atmospheric boundary layer in Beijing, China  

Microsoft Academic Search

In China the dovelopment of acoustic detection and the studies on the structure of atmospheric boundary layer over land and ocean and the assessment of atmospheric environment with the sodar data have been carried out for more than twenty years. The main achievements of these investigations have been comprehenced in this paper. Some phenomena in the atmospheric boundary layer, such

Mingyu Zhou

33

Laminar vortex boundary layers  

NASA Astrophysics Data System (ADS)

The interaction of a Burgers--Rott vortex with a rigid no-slip normal wall is investigated via direct numerical simulations of the unsteady axisymmetric Navier--Stokes equations. The flows in the boundary layer and away from the vortex core have a self-similar structure, i.e. the solutions at time t, radius r, height z, and Reynolds number Re can be reduced to single profiles for the angular momentum and the azimuthal vorticity dependent on a single similarity variable. The similarity variable is the direction normal to the wall scaled by Re^1/2 and a function of r and t. The boundary layer flow near the axis for low-Re consists of a matching between a Bödewadt-like flow near r=0, where the vortex flow is near solid-body rotation, and a potential vortex boundary layer flow. For medium Re, waves form within the core radius resulting from the inflection points in the Bödewadt-like profiles. At large Re, there are also waves that travel vertically along the interface between the rotational core and the irrotational flow outside the core at r? 1.

Arrese, Juan C.; Lopez, John M.

1996-11-01

34

Experiments on relative receptivity of three-dimensional supersonic boundary layer to controlled disturbances and its development  

NASA Astrophysics Data System (ADS)

Results of the controlled disturbance experiments in the supersonic boundary layer on a swept wing are considered. The high-frequency glow discharge technique is used for the disturbance generation. The linear development of wave trains is tested in smooth and rough surface conditions of the models. The relative receptivity of a three-dimensional (3D) boundary layer to stationary and nonstationary disturbances is estimated. Obtained that by using microroughness elements located in a swept wing boundary layer, it is possible to get a damping effect on the linear development of a spatial wave packet in the near field of the disturbances source.

Kosinov, A. D.; Kolosov, G. L.; Panina, A. V.; Semionov, N. V.; Yermolaev, Yu. G.

2013-06-01

35

Dynamical Model Simulation of the Morning Boundary Layer Development in Deep Mountain Valleys.  

NASA Astrophysics Data System (ADS)

A dry, two-dimensional version of the Colorado State University Multi-dimensional Cloud/Mesoscale Model was used to study the cross-valley evolution of the wind and temperature structures in an idealized east-west oriented mountain valley. Two simulations were performed, one in which the valley was heated symmetrically and a second in which a mid-latitude heating distribution was imposed. Both runs were initiated identically with a stable layer filling the valley to ridgetop and a neutral layer above the ridge. A specified sinusoidal surface potential temperature flux function approximating the diurnal cycle forced the model at the lower boundary.The results of the two simulations were remarkably similar. The model realistically reproduced the gross features found in actual valleys in both structure and timing. The simulated inversions were destroyed three and one-half hours after sunrise as a result of a neutral layer growing up from the surface meeting a descending inversion top. Slope winds with speeds of 3-5 m s1 developed over both sidewalls two and one-half hours after sunrise. Both cases revealed the development of strongly stable pockets of air over the sidewalls which form when cold air advected upslope loses its buoyancy at higher elevations. These stable pockets temporarily block the slope flow and force transient cross-valley circulations to form which act to destabilize the valley boundary layer. Cross-valley mixing and gravity waves rapidly redistribute heat across the valley to prevent large potential temperature gradients from forming. As a result, oven large differences in heating rates between opposing sidewalls do not result in significant cross-valley potential temperature differences. Organized cross-valley circulations and eddy motions enhance lateral mixing in the stable layer as well.

Bader, David C.; McKee, Thomas B.

1983-03-01

36

Numerical Simulation of Active Control of Boundary Layer Transition,  

National Technical Information Service (NTIS)

A numerical model has been developed for investigating boundary layer transition control for a three-dimensional flat plate boundary layer. Control of a periodically forced boundary layer in an incompressible fluid is studied using surface heating techniq...

H. F. Fasel L. D. Kral

1988-01-01

37

Large Eddy Simulation study of scalar transport in fully developed wind-turbine array boundary layers  

NASA Astrophysics Data System (ADS)

Large wind farms are attaining scales at which two-way interactions with the atmospheric boundary layer must be taken into account. A recent study by Baidya et al. (PNAS 2010) has shown that wind farms increase scalar fluxes at the surface. Numerical simulations from Calaf et al. (Pof 2010) together with laboratory experiments from Cal et al. (JSRE 2010) showed that the friction velocity underneath the wind turbines is decreased. Conversely, above the turbine, friction velocity is increased. To shed light onto the relevant phenomena, a suite of Large Eddy Simulations of an infinite (fully developed) wind turbine array boundary layer, including passive scalar transport, is performed. Results clearly show an overall increase of scalar fluxes in the presence of wind turbines, of about 10-15%. And this increase is not highly dependent on wind turbine loading or spacing. This resultant increase in the scalar fluxes can be explained through a balance between two competing effects. Further, following the approach of Calaf et al. (PoF 2010), a single-column model has been developed which confirms the observed trends.

Calaf, Marc; Parlange, Marc B.; Meneveau, Charles

2011-11-01

38

Magnetohydrodynamic boundary layer control system  

NASA Astrophysics Data System (ADS)

An active boundary layer control system for marine vehicles is disclosed. The boundary layer control system comprises a plurality of magnets and seawater electrodes placed in circumferential rows around the beam of the hull. The magnets and electrodes are positioned so that a Lorentz force generated by the interacting magnetic and electric fields will drive the boundary layer flow in an axial direction toward the aft end of the bull. The boundary control system reduces turbulence and may relaminarize boundary layer flow, thereby reducing radiated noise.

Meng, James C.

1993-12-01

39

Synoptic Controls on Boundary-Layer Characteristics  

Microsoft Academic Search

We report the characteristics of the three-dimensional, time evolving, atmospheric boundary layer that develops beneath an\\u000a idealised, dry, baroclinic weather system. The boundary-layer structure is forced by thermal advection associated with the\\u000a weather system. Large positive heat fluxes behind the cold front drive a vigorous convective boundary layer, whereas moderate\\u000a negative heat fluxes in the warm sector between the cold

Victoria A. Sinclair; Stephen E. Belcher; Suzanne L. Gray

2010-01-01

40

Microgravity Effects on Plant Boundary Layers  

NASA Astrophysics Data System (ADS)

The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental boundary layers in roots and leaves and to determine the effects of air flow on boundary layer development. It is hypothesized that microgravity induces larger boundary layers around plant organs because of the absence of buoyancy-driven convection. These larger boundary layers may affect normal metabolic function because they may reduce the fluxes of heat and metabolically active gases (e.g., oxygen, water vapor, and carbon dioxide. These experiments are to test whether there is a change in boundary layer associated with microgravity, quantify the change if it exists, and determine influence of air velocity on boundary layer thickness under different gravity conditions.

Stutte, Gary; Monje, Oscar

2005-08-01

41

Unsteady development of the boundary layer in the vicinity of a rear stagnation point  

NASA Astrophysics Data System (ADS)

Indications of a singularity associated with unsteady separation are reviewed within the framework of semi-similar solutions to the unsteady boundary layer equations. It is shown that when the boundary layer equations are formulated in semi-similar form there is an indication that a singularity exists in the solutions to these equations. In cases where the singularity occurs and separation is expected, it occurs at or near a point which has all the features of separation postulated in the Moore-Rott-Sears model.

Williams, J. C., III

42

Boundary layer sensitivity and receptivity  

NASA Astrophysics Data System (ADS)

The relation between the receptivity and the sensitivity of the incompressible flow in the boundary layer over a flat plate to harmonic perturbations is determined. Receptivity describes the birth of a disturbance, whereas sensitivity is a concept of larger breath, describing the modification incurred by the state of a system as a response to parametric variations. The governing equations ruling the system's state are the non-local stability equations. Receptivity and sensitivity functions can be obtained from the solution of the adjoint system of equations. An application to the case of Tollmien-Schlichting waves spatially developing in a flat plate boundary layer is studied. To cite this article: C. Airiau et al., C. R. Mecanique 330 (2002) 259-265.

Airiau, Christophe; Walther, Steeve; Bottaro, Alessandro

43

Streamwise development of the wind turbine boundary layer over a model wind turbine array  

NASA Astrophysics Data System (ADS)

The streamwise development of turbulence statistics and mean kinetic energy in a model wind farm consisting of 3 × 5 wind turbines is studied experimentally in a wind tunnel. The analysis uses planar Particle Image Velocimetry data obtained at the centerline plane of the wind farm, covering the inflow as well as four planes in between five downstream wind turbines. The data analysis is organized by dividing these measurement planes into three regions: the above-rotor, rotor-swept, and below-rotor regions. For each field, flow development is quantified using a properly defined relative difference norm based on an integration over each of the regions. Using this norm, it is found that the mean streamwise velocity approaches a fully developed state most rapidly, whereas the flow development is more gradual for the second-order statistics. The vertical entrainment flux of the mean kinetic energy by the Reynolds shear stress, , is observed to develop at a rate similar to that of the Reynolds shear stress rather than the mean streamwise velocity component. Its development is slowest in the layer nearest to the ground. Analysis of various terms in the mean kinetic energy equation shows that the wind turbine boundary layer has not yet reached fully developed conditions by the fifth turbine but that it is approaching such conditions. By comparing the vertical entrainment flux with the horizontal flux due to the mean flow, it is found that the former increases, whereas the latter decreases, as function of downstream distance, but that the former is already an important contributor in the developing region.

Newman, Jensen; Lebron, Jose; Meneveau, Charles; Castillo, Luciano

2013-08-01

44

Synoptic Controls on Boundary-Layer Characteristics  

NASA Astrophysics Data System (ADS)

We report the characteristics of the three-dimensional, time evolving, atmospheric boundary layer that develops beneath an idealised, dry, baroclinic weather system. The boundary-layer structure is forced by thermal advection associated with the weather system. Large positive heat fluxes behind the cold front drive a vigorous convective boundary layer, whereas moderate negative heat fluxes in the warm sector between the cold and warm fronts generate shallow, stably stratified or neutral boundary layers. The forcing of the boundary-layer structure is quantified by forming an Eulerian mass budget integrated over the depth of the boundary layer. The mass budget indicates that tropospheric air is entrained into the boundary layer both in the vicinity of the high-pressure centre, and behind the cold front. It is then transported horizontally within the boundary layer and converges towards the cyclone's warm sector, whence it is ventilated out into the troposphere. This cycling of air is likely to be important for the ventilation of pollution out of the boundary layer, and for the transformation of the properties of large-scale air masses.

Sinclair, Victoria A.; Belcher, Stephen E.; Gray, Suzanne L.

2010-03-01

45

Minimalist turbulent boundary layer model  

Microsoft Academic Search

We discuss an elementary model of a turbulent boundary layer over a flat surface given as a vertical random distribution of spanwise Lamb-Oseen vortex configurations placed over a nonslip boundary-condition line. We are able to reproduce several important features of realistic flows, such as the viscous and logarithmic boundary sublayers, and the general behavior of the first statistical moments (turbulent

L. Moriconi

2009-01-01

46

Nocturnal boundary layer characteristics and land breeze development in Houston, Texas during TexAQS II  

Microsoft Academic Search

The nocturnal boundary layer in Houston, Texas was studied using a high temporal and vertical resolution tethersonde system on four nights during the Texas Air Quality Study II (TexAQS II) in August and September 2006. The launch site was on the University of Houston campus located approximately 4 km from downtown Houston. Of particular interest was the evolution of the nocturnal

Bridget M. Day; Bernhard Rappenglück; Craig B. Clements; Sara C. Tucker; W. Alan Brewer

2010-01-01

47

NEW DEVELOPMENT IN DISPERSION EXPERIMENTS AND MODELS FOR THE CONVECTIVE BOUNDARY LAYER  

EPA Science Inventory

We present recent experiments and modeling studies of dispersion in the convective boundary layer (CBL) with focus on highly-buoyant plumes that "loft" near the CBL top and resist downward mixing. Such plumes have been a significant problem in earlier dispersion models; they a...

48

Development of an effusive inlet for mass spectrometric gas analysis of hypersonic boundary layer  

Microsoft Academic Search

The use of a microchannel plate (MCP) as a mass spectrometer inlet device to allow nonintrusive sampling of flight vehicle boundary layers is investigated. Two possible configurations for mounting the inlet are studied: (1) flow coaxial with the channels; and (2) flow perpendicular to the channel axis. The test gases are pure Kr; pure Ne; and a mixture of 10

Kenneth G. Brown; Charles E. Fishel; David R. Brown; Beverley W. Lewis; George M. Wood Jr.

1987-01-01

49

ENDOW (efficient development of offshore wind farms): modelling wake and boundary layer interactions  

Microsoft Academic Search

While experience gained through the offshore wind energy projects currently operating is valuable, a major uncertainty in estimating power production lies in the prediction of the dynamic links between the atmosphere and wind turbines in offshore regimes. The objective of the ENDOW project was to evaluate, enhance and interface wake and boundary layer models for utilization offshore. The project resulted

Rebecca Barthelmie; Gunner Larsen; Sara Pryor; Hans Jřrgensen; Hans Bergström; Wolfgang Schlez; Kostas Rados; Bernhard Lange; Per Vřlund; Sřren Neckelmann; Sřren Mogensen; Gerard Schepers; Terry Hegberg; Luuk Folkerts; Mikael Magnusson

2004-01-01

50

Boundary layers on a rotating disk  

Microsoft Academic Search

A numerical method is proposed for predicting the three-dimensional boundary layer that develops on a rotating disk in the presence of a steady incompressible axisymmetric flow. The method employs the eddy viscosity concept to model the Reynolds shear stress terms in the boundary layer equations. The governing nonlinear difference equations are solved by Newton's method using an efficient block-tridiagonal factorization

Tuncer Cebeci; D. E. Abbott

1975-01-01

51

Momentum transfer in boundary layers  

Microsoft Academic Search

The continuity and momentum equations of fluid flow are considered along with thin-shear-layer equations, the analysis of laminar shear layers, the analysis of turbulent shear layers, numerical methods for thin shear layers, numerical solutions of laminar and turbulent boundary layers, aspects of stability and transition, and complex shear layers and viscous\\/inviscid interactions. Three-dimensional and unsteady flows are discussed, taking into

T. Cebeci; P. Bradshaw

1977-01-01

52

Boundary layer receptivity and control  

NASA Astrophysics Data System (ADS)

Receptivity processes initiate natural instabilities in a boundary layer. The instabilities grow and eventually break down to turbulence. Consequently, receptivity questions are a critical element of the analysis of the transition process. Success in modeling the physics of receptivity processes thus has a direct bearing on technological issues of drag reduction. The means by which transitional flows can be controlled is also a major concern: questions of control are tied inevitably to those of receptivity. Adjoint systems provide a highly effective mathematical method for approaching many of the questions associated with both receptivity and control. The long term objective is to develop adjoint methods to handle increasingly complex receptivity questions, and to find systematic procedures for deducing effective control strategies. The most elementary receptivity problem is that in which a parallel boundary layer is forced by time-harmonic sources of various types. The characteristics of the response to such forcing form the building blocks for more complex receptivity mechanisms. The first objective of this year's research effort was to investigate how a parallel Blasius boundary layer responds to general direct forcing. Acoustic disturbances in the freestream can be scattered by flow non-uniformities to produce Tollmien-Schlichting waves. For example, scattering by surface roughness is known to provide an efficient receptivity path. The present effort is directed towards finding a solution by a simple adjoint analysis, because adjoint methods can be extended to more complex problems. In practice, flows are non-parallel and often three-dimensional. Compressibility may also be significant in some cases. Recent developments in the use of Parabolized Stability Equations (PSE) offer a promising possibility. By formulating and solving a set of adjoint parabolized equations, a method for mapping the efficiency with which external forcing excites the three-dimensional motions of a non-parallel boundary layer was developed. The method makes use of the same computationally efficient formulation that makes the PSE currently so appealing. boundary layers involves the application of localized mean wall suction.

Hill, D. C.

1993-12-01

53

About turbulence statistics in the outer part of a boundary layer developing over two-dimensional surface roughness  

NASA Astrophysics Data System (ADS)

The influence of surface roughness on a high Reynolds number turbulent boundary layer is investigated in the light of Townsend's wall similarity hypothesis. There is conflicting information in the literature about the effect of surface roughness on the flow structure in the outer layer. Flows over roughness consisting of spanwise rods appear to show unusually strong interaction between the wall and the wake region. It has been suggested that flows which show strong modifications in the outer layer suffer from lack of scale separation between the roughness scale and the largest scale given by the boundary layer thickness. One of the flows which have documented significant roughness effects across the entire layer is the boundary layer developing over roughness made up of spanwise aligned square bars. Here we compare one such flow taken at relatively low Reynolds number with measurements for a boundary layer which develops at much higher Reynolds number. The high Reynolds number (Re? = 32 600) assures that the range of scale is wide, while at the same time the size of the roughness elements is sufficiently large for the flow to be fully rough. Both sets of data are compared to a smooth wall reference boundary layer and from probability distributions, the quadrant contributions to the shear stress and triple correlation profiles, we show that the outer layer changes are significantly reduced when increasing the Reynolds number and thereby the range of scales. In this case the wall perturbation of the flow is shown to be much smaller than reported in other experiments using the same geometry. Here we find that the modifications in the turbulent structure are limited to about five times the roughness scale. This is in accordance with the wall similarity hypothesis.

Krogstad, Per-A.?ge; Efros, Vladislav

2012-07-01

54

Large Eddy Simulation study of fully developed thermal wind-turbine array boundary layers  

NASA Astrophysics Data System (ADS)

It is well known that when wind turbines are deployed in large arrays, their efficiency decreases due to complex interactions among themselves and with the atmospheric boundary layer (ABL). For wind farms whose length exceeds the height of the ABL by over an order of magnitude, a “fully developed” flow regime can be established. In this asymptotic regime, changes in the stream-wise direction can be neglected and the relevant exchanges occur in the vertical direction. Such a fully developed wind-turbine array boundary layer (WTABL) has recently been studied1 using Large Eddy Simulations (LES) under neutral stability conditions. The simulations showed the existence of two log-laws, one above and one below the wind turbine region. This enabled the development of more accurate parameterizations of the effective roughness scale for a wind farm. Now, a suite of Large Eddy Simulations, in which wind turbines are also modeled using the classical “drag disk” concept are performed but for non-neutral conditions. The aim is to study the effects of different thermal ABL stratifications, and thus to study the efficiency and characteristics of large wind farms and the associated land-atmosphere interactions for realistic atmospheric flow regimes. Such studies help to unravel the physics involved in extensive aggregations of wind turbines, allowing us to design better wind farm arrangements. By considering various turbine loading factors, surface roughness values and different atmospheric stratifications, it is possible to analyze the influence of these into the induced surface roughness, and the sensible heat roughness length. These last two can be used to model wind turbine arrays in simulations of atmospheric dynamics at larger (regional and global) scales2, where the coarse meshes used do not allow to account for the specifics of each wind turbine. Results from different sets of simulations under stable and unstable conditions will be presented, for which also the corresponding effective roughness length-scales will be determined. Simulations use imposed heat flux at the bottom or an imposed temperature. The simulation results will be analyzed to determine how stratification affects momentum and scalar transport processes in the wind turbine wakes.

Calaf, M.; Meneveau, C. V.; Parlange, M. B.

2010-12-01

55

Minimalist turbulent boundary layer model.  

PubMed

We discuss an elementary model of a turbulent boundary layer over a flat surface given as a vertical random distribution of spanwise Lamb-Oseen vortex configurations placed over a nonslip boundary-condition line. We are able to reproduce several important features of realistic flows, such as the viscous and logarithmic boundary sublayers, and the general behavior of the first statistical moments (turbulent intensity, skewness, and flatness) of the streamwise velocity fluctuations. As an application, we advance some heuristic considerations on the boundary layer underlying kinematics that could be associated with the phenomenon of drag reduction by polymers, finding a suggestive support from its experimental signatures. PMID:19518332

Moriconi, L

2009-04-06

56

Minimalist turbulent boundary layer model  

NASA Astrophysics Data System (ADS)

We discuss an elementary model of a turbulent boundary layer over a flat surface given as a vertical random distribution of spanwise Lamb-Oseen vortex configurations placed over a nonslip boundary-condition line. We are able to reproduce several important features of realistic flows, such as the viscous and logarithmic boundary sublayers, and the general behavior of the first statistical moments (turbulent intensity, skewness, and flatness) of the streamwise velocity fluctuations. As an application, we advance some heuristic considerations on the boundary layer underlying kinematics that could be associated with the phenomenon of drag reduction by polymers, finding a suggestive support from its experimental signatures.

Moriconi, L.

2009-04-01

57

Boundary layer visualization and mass transfer studies on a rotating electroplating mandrel: Exploratory experimentation and technique development  

SciTech Connect

An electrochemical technique for visualization of the laminar diffusion (concentration) boundary layer on a rotating mandrel is described. This technique utilizes the change in pH near the surface associated with formation of an alkaline solution formed by electrolysis of dilute sodium chloride solution at the rotating cathode. The alkaline boundary layer is made visible by phenolphthalein indicator. Development of a technique suitable for determining mass transfer rates on a rotating mandrel of arbitrary axisymmetric contour is also described. This technique utilizes dissolution of a thin coating of benzoic acid in water and has applicability to modeling of an electroplating process.

Keyes, J.L. Jr.; Capps, G.J.; Johnson, B.L. Sr.; White, C.P.

1987-04-01

58

Boundary Layers of Air Adjacent to Cylinders  

PubMed Central

Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the boundary layer of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated boundary-layer thickness agreed with that determined for water vapor diffusion from a moistened cylindrical surface 2 cm in diameter. It correctly predicted the resistance for water vapor movement across the boundary layers adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The boundary-layer thickness decreased as the turbulence intensity increased. For a turbulence intensity representative of field conditions (0.5) and for ?windd between 200 and 30,000 cm2/second (where ?wind is the mean wind velocity and d is the cylinder diameter), the effective boundary-layer thickness in centimeters was equal to [Formula: see text].

Nobel, Park S.

1974-01-01

59

Development of a nonlinear subgrid model for large-eddy simulation of the atmospheric boundary layer  

NASA Astrophysics Data System (ADS)

Subgrid-scale (SGS) modeling is a critical component in large-eddy simulation of the atmospheric boundary layer. A nonlinear SGS approach, as a simple alternative to the standard eddy-viscosity/diffusivity closure, has been introduced and implemented in simulations of a neutral atmospheric boundary layer and a stable atmospheric boundary layer. The new approach computes the structure of the SGS stress/flux (relative magnitude of components) based on the normalized gradient tensor/vector, which is derived from the Taylor expansion of the exact SGS stress/flux. The SGS magnitudes are estimated based on the local-equilibrium hypothesis. To resolve the instability issue of the original gradient model and ensure numerical stability, we adopt a clipping procedure to avoid local negative SGS dissipation rates. The approach using constant coefficients and coefficients determined using dynamic procedures is assessed through a systematic comparison with well-established theoretical predictions and reference results of various flow statistics. Simulation results show good agreement with the reference results and an evident improvement over results obtained using standard eddy-viscosity/diffusivity models.

Lu, Hao; Porté-Agel, Fernando

2013-04-01

60

Optimal control of Tollmien-Schlichting waves in a developing boundary layer  

NASA Astrophysics Data System (ADS)

Optimal control theory is used to determine the wall transpiration (unsteady blowing/suction) with zero net mass flux capable of attenuating Tollmien-Schlichting waves in a spatially developing boundary layer. The flow state is determined from the parabolized stability equations, in a linear setting. An appropriate cost functional is introduced and minimized iteratively by the numerical solution of the equations for the state and the dual state, coupled via transfer and optimality conditions. Central to the control is the determination of the wall Green's function expressing the receptivity of the flow to wall inhomogeneities. The optimal wall velocity is obtained in few iterations and a reduction of several orders of magnitude in output disturbance energy is demonstrated, as compared to the uncontrolled case, for control laws operating both over the whole wall length and over a finite strip. Finally, white noise disturbances are applied to the optimal wall velocities already determined, to assess the influence of an imperfectly operating controller on the final result, and to decide on the practical feasibility of the approach.

Walther, Steeve; Airiau, Christophe; Bottaro, Alessandro

2001-07-01

61

Near-field measurements and development of a new boundary layer over a flat plate with localized suction  

NASA Astrophysics Data System (ADS)

Suction on a turbulent boundary layer is applied through a narrow strip in order to understand the effects suction can have on the boundary layer development and turbulent structures in the flow. Detailed two-component laser Doppler velocimetry (LDV) and laser-induced fluorescence (LIF) based measurements have been undertaken in regions close to the suction strip and further downstream. The region close to the strip involves a flow reversal accompanied by a change in sign for the Reynolds shear stress and strong gradients in the flow variables. The mean streamwise velocity after suction remains larger than its corresponding no-suction value. Relative to the no-suction case, the velocity fluctuations first decrease with suction followed by a slow recovery which may involve a slight overshoot. LIF visualizations indicate that compared to the no-suction case, the low-speeds streaks stay closer to the wall and exhibit a smaller amount of spanwise and wall-normal oscillations with suction. The visualization results are consistent with two-point velocity correlation measurements. The streamwise and spanwise correlation measurements indicate that the structures are disrupted or removed from the boundary layer due to suction suggesting that the original boundary layer has been strongly influenced by suction. The results are explained by the development of a new inner layer that forms downstream of the suction strip.

Agrawal, Amit; Djenidi, Lyazid; Antonia, R. A.

2010-05-01

62

Boundary Layer Control on Airfoils.  

ERIC Educational Resources Information Center

|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)|

Gerhab, George; Eastlake, Charles

1991-01-01

63

Calculation and Measurement of Separated Turbulent Boundary Layers.  

National Technical Information Service (NTIS)

An inverse integral prediction method for the development of separated turbulent boundary layers developed from the lag-entrainment method is described. The inverse method uses the concept of equilibrium separated boundary layer flows and the predicted ch...

P. D. Smith R. C. Hastings B. R. Williams

1982-01-01

64

Boundary layer development on a semi-infinite suddenly heated vertical plate  

NASA Astrophysics Data System (ADS)

The flow resulting from suddenly heating a semi-infinite, vertical wall immersed in a stationary fluid has been described in the following way: at any fixed position on the plate, the flow is initially described as one-dimensional and unsteady, as though the plate is doubly infinite; at some later time, which depends on the position, a transition occurs in the flow, known as the leading-edge effect (LEE), and the flow becomes two-dimensional and steady. The transition is characterized by the presence of oscillatory behaviour in the flow parameters, and moves with a speed greater than the maximum fluid velocities present in the boundary layer. A stability analysis of the one-dimensional boundary layer flow performed by Armfield & Patterson (1992) showed that the arrival times of the LEE determined by numerical experiment were predicted well by the speed of the fastest travelling waves arising from a perturbation of the initial one-dimensional flow. In this paper, we describe an experimental investigation of the transient behaviour of the boundary layer on a suddenly heated semi-infinite plate for a range of Rayleigh and Prandtl numbers. The experimental results confirm that the arrival times of the LEE at specific locations along the plate, relatively close to the leading edge, are predicted well by the Armfield & Patterson theory. Further, the periods of the oscillations observed following the LEE are consistent with the period of the maximally amplified waves calculated from the stability result. The experiments also confirm the presence of an alternative mechanism for the transition from one-dimensional to two-dimensional flow, which occurs in advance of the arrival of the LEE at positions further from the leading edge.

Patterson, John C.; Graham, Tasman; Schöpf, Wolfgang; Armfield, S. W.

2002-02-01

65

Boundary-layer friction in midlatitude cyclones  

Microsoft Academic Search

SUMMARY Results from an idealized three-dimensional baroclinic life-cycle model are interpreted ina potential vorticity (PV) framework to identify the physical mechanisms by which frictional processes acting in the atmospheric boundary layer modify and reduce the baroclinic development of a midlatitude storm. Considering a life cycle where theonly non-conservative process acting is boundary-layer friction, therate of change of depth-averaged PV within

D. S. Adamson; S. E. Belcher; B. J. Hoskins; R. S. Plant

2006-01-01

66

Mean flow development of a longitudinal vortex embedded in an attached, three-dimensional, turbulent boundary layer  

SciTech Connect

The interaction of a longitudinal vortex with a pressure-driven, three dimensional turbulent boundary layer was investigated experimentally. The vortex was attenuated much more rapidly in the three dimensional layer than in a two-dimensional boundary layer. The persistence for the vortex-induced perturbation was strongly dependent on the sign of the vortex.

Shizawa, T. [Science Univ. of Tokyo (Japan); Eaton, J.K. [Stanford Univ., CA (United States). Dept. of Mechanical Engineering

1990-12-31

67

Formaldehyde instrument development and boundary layer sulfuric acid: Implications for photochemistry  

NASA Astrophysics Data System (ADS)

This work presents the development of a laser-induced fluorescence technique to measure atmospheric formaldehyde. In conjunction with the technique, the design of a compact, narrow linewidth, etalon-tuned titanium: sapphire laser cavity which is pumped by the second harmonic of a kilohertz Nd:YAG laser is also presented. The fundamental tunable range is from 690-1100 nm depending on mirror reflectivities and optics kit used. The conversion efficiency is at least 25% for the fundamental, and 2-3% for intracavity frequency doubling from 3.5-4W 532 nm pump power. The linewidth is <0.1 cm-1, and the pulsewidth is 18 nsec. Applications of this cavity include the measurement of trace gas species by laser-induced fluorescence, cavity ringdown spectroscopy, and micropulse lidar in the UV-visible region. Also presented are observations of gas-phase sulfuric acid from the NEAQS-ITCT 2K4 (New England Air Quality Study--- Intercontinental Transport and Chemical Transformation) field campaign in July and August 2004. Sulfuric acid values are reported for a polluted environment and possible nucleation events as well as particle growth within the boundary layer are explored. Sulfate production rates via gas phase oxidation of sulfur dioxide are also reported. This analysis allows an important test of our ability to predict sulfuric acid concentration and probe its use as a fast time response photochemical tracer for the hydroxyl radical, OH. In comparison, the NASA time-dependent photochemical box model is used to calculate OH concentration. Nighttime H2SO4 values are examined to test our understanding of nocturnal OH levels and oxidation processes. In comparison, sulfuric acid from a large ground based mission in Tecamac, Mexico (near the northern boundary of Mexico City) during MIRAGE-Mex field campaign (March 2006) is presented. This and other measurements are used to characterize atmospheric oxidation and predict sulfuric acid and OH concentrations at the site. The observations in conjunction with the NASA LARc Photochemical box model are used to explore ozone production, nitrate and sulfate formation, and radical levels and radical production rates during the day. The one minute observations of sulfuric acid, sulfur dioxide, and aerosol surface area were again used to calculate OH levels assuming steady state, and are in good agreement with observations of OH (R2 = 0.7). Photochemical activity is found to be a maximum during the morning hours, as seen in ozone and nitrate formation. Although the model predictions capture the observed diurnal profile, the model underpredicts RO2 concentrations in the morning hours and overpredicts in the afternoon (HO 2 + RO2 radical Model/observed (M/O) ˜ 1.15 and OH M/O ˜ 1.2).

Case Hanks, Anne Theresa

68

Linear optimal control applied to instabilities in spatially developing boundary layers  

NASA Astrophysics Data System (ADS)

The work presented extends previous research on linear controllers in temporal channel flow to spatially evolving boundary layer flow. The flows studied are those on an infinite swept wedge described by the Falkner Skan Cooke (FSC) velocity profiles, including the special case of the flow over a flat plate. These velocity profiles are used as the base flow in the Orr Sommerfeld Squire equations to compute the optimal feedback control through blowing and suction at the wall utilizing linear optimal control theory. The control is applied to a parallel FSC flow with unstable perturbations. Through an eigenvalue analysis and direct numerical simulations (DNS), it is shown that instabilities are stabilized by the controller in the parallel case. The localization of the convolution kernels for control is also shown for the FSC profiles.

Högberg, Markus; Henningson, Dan S.

2002-11-01

69

The initial transient period of gravitationally unstable diffusive boundary layers developing in porous media  

NASA Astrophysics Data System (ADS)

Gravitationally unstable, transient, diffusive boundary layers play an important role in carbon dioxide sequestration. Though the linear stability of these layers has been studied extensively, there is wide disagreement in the results, and it is not clear which methodology best reflects the physics of the instability. We demonstrate that this disagreement stems from an inherent sensitivity of the problem to how perturbation growth is measured. During an initial transient period, the concentration and velocity fields exhibit different growth rates and these rates depend on the norm used to measure perturbation amplitude. This sensitivity decreases at late times as perturbations converge to dominant quasi-steady eigenmodes. Therefore, we characterize the linear regime by measuring the duration of the initial transient period, and we interpret the convergence process by examining the growth rates and non-orthogonality of the quasi-steady eigenmodes. To judge the relevance of various methodologies and perturbation structures to physical systems, we demonstrate that every perturbation has a maximum allowable initial amplitude above which the sum of the base-state and perturbation produces unphysical negative concentrations. We then perform direct numerical simulations to demonstrate that optimal perturbations considered in previous studies cannot support finite initial amplitudes. Consequently, convection in physical systems is more likely triggered by ``sub-optimal'' perturbations that support finite initial amplitudes.

Tilton, Nils; Daniel, Don; Riaz, Amir

2013-09-01

70

Stability of Compressible Boundary Layers.  

National Technical Information Service (NTIS)

The stability of compressible 2-D and 3-D boundary layers is reviewed. The stability of 2-D compressible flows differs from that of incompressible flows in two important features: There is more than one mode of instability contributing to the growth of di...

A. H. Nayfeh

1989-01-01

71

Boundary Layer Over Uniform Roughness.  

National Technical Information Service (NTIS)

The boundary-layer survey is conducted of a rough plate consisting of uniform spherical particles arranged in a random and in highly compact fashion. Strong turbulent mixing is observed in a region within a quarter of the particle size from the top of the...

J. Wu

1970-01-01

72

Laminar boundary layer over riblets  

Microsoft Academic Search

Laser doppler anemometry (LDA) measurements and numerical calculations have been made for a laminar boundary layer on triangular riblets. Calculated mean velocity distributions along the riblet contour are in good agreement with the measured ones. The results show that no transversal motion exists above and within the riblet valleys (e.g., no secondary motion). It is found that despite the large

L. Djenidi; F. Anselmet; J. Liandrat; L. Fulachier

1994-01-01

73

Hypersonic Boundary Layer\\/Shockwave Interaction Problems  

Microsoft Academic Search

The hypersonic shockwave boundary layer-interaction problem was defined with the use of the full Navier- Stokes (NS) equations and a FORTRAN code was developed to provide numerical solutions to this problem. Further, this problem was studied under two specified sets of boundary conditions: adiabatic wall and constant wall conditions. The MacCormack Predictor-Corrector technique was used in developing this NS code.

Haile Lindsay; Frederick Ferguson

74

Hypersonic Boundary Layer\\/Oblique Shockwave Interaction  

Microsoft Academic Search

The hypersonic boundary layer\\/oblique shockwave interaction problem was defined with the use of the full Navier-Stokes (NS) equations and a FORTRAN code was developed to provide numerical solutions to this problem. Further, this problem was studied under two specified sets of boundary conditions: adiabatic wall and constant wall conditions. The MacCormack Technique was used in developing this NS code. To

Haile Lindsay

2005-01-01

75

Daytime Evolution of Relative Humidity at the Boundary Layer Top  

Microsoft Academic Search

Data from the HAPEX-MOBILHY field program and results from a one-dimensionalmodel of the soil and atmospheric boundary layer are analyzed to study the daytimeevolution of the relative humidity at the boundary-layer top. This evolution is thought tocontrol the development of boundary-layer clouds. This study examines thedependence of boundary-layer relative humidity on soil moisture, large-scale verticalmotion, and the moisture content and

M. Ek; L. Mahrt

1994-01-01

76

Boundary Layer Cloudiness Parameterizations Using ARM Observations  

SciTech Connect

This study used DOE ARM data and facilities to: (1) study macroscopic properties of continental stratus clouds at SGP and the factors controlling these properties, (2) develop a scientific basis for understanding the processes responsible for the formation of boundary layer clouds using ARM observations in conjunction with simple parametric models and LES, and (3) evaluate cumulus cloud characteristics retrieved from the MMCR operating at TWP-Nauru. In addition we have used high resolution 94 GHz observations of boundary layer clouds and precipitation to: (1) develop techniques for using high temporal resolution Doppler velocities to study large-eddy circulations and turbulence in boundary layer clouds and estimate the limitations of using current and past MMCR data for boundary layer cloud studies, (2) evaluate the capability and limitations of the current MMCR data for estimating reflectivity, vertical velocities, and spectral under low- signal-to-noise conditions associated with weak no n-precipitating clouds, (3) develop possible sampling modes for the new MMCR processors to allow for adequate sampling of boundary layer clouds, and (4) retrieve updraft and downdraft structures under precipitating conditions.

Bruce Albrecht

2004-09-15

77

Electric arc behavior in a boundary layer  

NASA Astrophysics Data System (ADS)

The objective of this work is to understand how the size of an arc on the electrode of a magneto-hydrodynamic (MHD) generator or accelerator depends on operating parameters such as boundary-layer shape and current density. Arc size has an important bearing on device lifetime and performance. A boundary layer in an MHD device is a region of exceedingly steep gradients including, in particular, the gradient of electrical conductivity. A theory relating arc size to the characteristics of these gradients is developed and compared with behavior observed in various MHD devices, most recently that in the Component Development and Integration Facility in Butte, Montana.

Rosa, Richard; Farrar, Larry; Trudnowski, Dan

1988-10-01

78

Boundary layer energy transport in plasma devices  

NASA Astrophysics Data System (ADS)

The purpose of this research was to develop a model of boundary-layer energy transport in electric launchers, and perform a numerical simulation to investigate the influence of turbulence, thermal radiation and ablation on energy flux to the surface. The model developed combines boundary-layer conservation equations with a k-o turbulence model and multi-group radiation transport, and uses plasma models for fluid properties such as viscosity, thermal conductivity and specific heat capacity. The resulting TURBFIRE computer code is the first code to model turbulence and radiation transport in a self-consistent manner for electric launchers. Although approximations have been made to simplify the physics enough to permit a numerical solution, this is the most comprehensive boundary-layer simulation of turbulence and radiation transport to date.

Orton, Nigel Paul

2000-11-01

79

Asymptotic similarity in turbulent boundary layers  

NASA Astrophysics Data System (ADS)

The turbulent boundary layer is one of the most fundamental and important applications of fluid mechanics. Despite great practical interest and its direct impact on frictional drag among its many important consequences, no theory absent of significant inference or assumption exists. Numerical simulations and empirical guidance are used to produce models and adequate predictions, but even minor improvements in modeling parameters or physical understanding could translate into significant improvements in the efficiency of aerodynamic and hydrodynamic vehicles. Classically, turbulent boundary layers and fully-developed turbulent channels and pipes are considered members of the same "family," with similar "inner" versus "outer" descriptions. However, recent advances in experiments, simulations, and data processing have questioned this, and, as a result, their fundamental physics. To address a full range of pressure gradient boundary layers, a new approach to the governing equations and physical description of wall-bounded flows is formulated, using a two variable similarity approach and many of the tools of the classical method with slight but significant variations. A new set of similarity requirements for the characteristic scales of the problem is found, and when these requirements are applied to the classical "inner" and "outer" scales, a "similarity map" is developed providing a clear prediction of what flow conditions should result in self-similar forms. An empirical model with a small number of parameters and a form reminiscent of Coles' "wall plus wake" is developed for the streamwise Reynolds stress, and shown to fit experimental and numerical data from a number of turbulent boundary layers as well as other wall-bounded flows. It appears from this model and its scaling using the free-stream velocity that the true asymptotic form of u'2 may not become self-evident until Retheta ? 275,000 or delta+ ? 105, if not higher. A perturbation expansion made possible by the novel inclusion of the scaled streamwise coordinate is used to make an excellent prediction of the shear Reynolds stress in zero pressure gradient boundary layers and channel flows, requiring only a streamwise mean velocity profile and the new similarity map. Extension to other flows is promising, though more information about the normal Reynolds stresses is needed. This expansion is further used to infer a three layer structure in the turbulent boundary layer, and modified two layer structure in fully-developed flows, by using the classical inner and logarithmic profiles to determine which portions of the boundary layer are dominated by viscosity, inertia, or turbulence. A new inner function for U+ is developed, based on the three layer description, providing a much more simplified representative form of the streamwise mean velocity nearest the wall.

Duncan, Richard D.

80

Field Observations of a Tidally Forced Developing Boundary Layer and the associated sediment resuspension and Nutrient Diffusion  

NASA Astrophysics Data System (ADS)

Field observations of sediment suspension within a developing tidal boundary layer were collected with a newly developed Nortek Vectrino II Profiling Velocimeter acoustic backscatter probe; while nutrient release and sediment chemistry were sampled with pore water samples from sediment core sections. The velocimeter is capable of measuring a three dimensional velocity profile at 1 mm increments over a range of 3 cm. The observations were obtained in the Great Bay tidal Estuary of New Hampshire. The monitored area was a long straight channel with maximum depth of 20 m MLLW, tidal range of 3 m and depth of 1.5 m MLLW at the sampling location. During the incoming half tidal cycle, the tidal forcing produces a fairly unidirectional flow over the flat sandy mud sediment bed. Three methods for estimating the bed stress were evaluated and compared against laboratory observations with a sediment core erosion chamber. When wind conditions are low to moderate and there are low hydrologic influences, the roughly 30 cm/s near the bed flows resulted in peak shields parameters near the threshold for motion of 0.07 to 0.16 for a dimensionless grain size of 1.96. During periods of larger wind and/or higher hydrologic conditions, the threshold is exceeded and there is evidence to suggest a local response in the sediment chemistry. During the developing phase of the tidal boundary layer, the observations provide evidence for a viscous sublayer in the lowest 0.5 cm of the water column before moving into turbulent boundary layer flow. Observations of the stress placed upon the bed in relation to the nutrient chemistry of the sediment column provide an image of the types of loads and stresses the Great Bay Estuary receives during various hydraulic and weather related forcing conditions.

Wengrove, M.; Foster, D.; Kalnejais, L. H.; Percuoco, V.

2011-12-01

81

Effect of Boundary Layer Thickness and Entropy Layer on Boundary Layer Combustion  

Microsoft Academic Search

This project investigates the possibilities of scramjet combustor performance enhancement by reducing the skin friction through boundary layer combustion. Experiments were conducted in the T4 Stalker tube to investigate the influence of boundary layer thickness and entropy layers on the ignition of a hydrogen air mixture near the wall of a constant area duct. The hydrogen was injected tangentially from

R. M. Kirchhartz; D. J. Mee; R. J. Stalker

82

Viscous drag reduction in boundary layers  

Microsoft Academic Search

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

Dennis M. Bushnell; Jerry N. Hefner

1990-01-01

83

Boundary condition effects on turbulent boundary layer wall pressure fluctuations  

Microsoft Academic Search

To better understand the flow and pressure field associated with automobile underbodies, laboratory experiments were conducted to map the velocity and pressure fluctuation statistics on two simulated underbodies operating next to a moving ground plane. The effect of boundary condition changes on the statistics for underbodies subject to equilibrium turbulent boundary layer flow and turbulent boundary layer flow perturbed by

Timothy Allen Brungart

1997-01-01

84

The development of a diode laser Doppler velocimeter for boundary layer measurements under ice: A feasibility investigation  

NASA Astrophysics Data System (ADS)

Measurements of the turbulent fluxes of momentum, heat, and salinity in the oceanic boundary layer are difficult to obtain, as both a stable platform and high-resolution instrumentation are required. The overall objective of the present investigation was to develop a boundary layer instrumentation system capable of measuring turbulent fluxes in the marginal ice zone environment. This investigation focuses on a feasibility study toward development of a diode laser Doppler velocimeter (DLDV) to be used as the velocity sensor for a high-resolution velocity/temperature/conductivity cluster, with a spatial resolution of 1 to 2 cm. Phase 1 findings show very promising results for the DLDV in laboratory environments. Measurements in a pipe flow facility demonstrated very distinctive Doppler burst signals, with more than adequate signal-to-noise ratio, even in clean tap water passed through a 10 micrometer filter. Excellent burst density was observed when a small quantity of Puget Sound water was added to the tap water. For all practical purposes, the performance of the DLDV is at least as good as that of a well-established LDV system using a helium-neon laser as the light source.

Schedvin, J. C.; Liu, H. T.

1984-05-01

85

Bursting frequency prediction in turbulent boundary layers  

SciTech Connect

The frequencies of the bursting events associated with the streamwise coherent structures of spatially developing incompressible turbulent boundary layers were predicted using global numerical solution of the Orr-Sommerfeld and the vertical vorticity equations of hydrodynamic stability problems. The structures were modeled as wavelike disturbances associated with the turbulent mean flow. The global method developed here involves the use of second and fourth order accurate finite difference formula for the differential equations as well as the boundary conditions. An automated prediction tool, BURFIT, was developed. The predicted resonance frequencies were found to agree very well with previous results using a local shooting technique and measured data.

LIOU,WILLIAM W.; FANG,YICHUNG

2000-02-01

86

Turbulent flow in converging nozzles, part one: boundary layer solution  

Microsoft Academic Search

The boundary layer integral method is used to investigate the development of the turbulent swirling flow at the entrance region\\u000a of a conical nozzle. The governing equations in the spherical coordinate system are simplified with the boundary layer assumptions\\u000a and integrated through the boundary layer. The resulting sets of differential equations are then solved by the fourth-order\\u000a Adams predictor-corrector method.

R. Maddahian; B. Farhanieh; B. Firoozabadi

2011-01-01

87

Technology Developments for Laminar Boundary Layer Control on Subsonic Transport Aircraft.  

National Technical Information Service (NTIS)

Since the beginning of the NASA Aircraft Energy Efficiency (ACEE) program in 1976, significant progress has been made in the development of laminar flow technology for commercial transports. Exploitation of new materials, fabrication methods, analysis tec...

R. D. Wagner D. V. Maddalon M. C. Fischer

1984-01-01

88

Compressible Ekman–Hartmann boundary layers  

Microsoft Academic Search

We consider the effect of compressibility on mixed Ekman–Hartmann boundary layers on an infinite plane (z = 0), in the presence of an external magnetic field oblique to the boundary. The aim is to investigate the influence of the magnetic pressure on the fluid density, and hence, via mass conservation, on the mass flow into or out of the boundary

Krzysztof A. Mizerski; David W. Hughes

2010-01-01

89

Formaldehyde instrument development and boundary layer sulfuric acid: Implications for photochemistry  

Microsoft Academic Search

This work presents the development of a laser-induced fluorescence technique to measure atmospheric formaldehyde. In conjunction with the technique, the design of a compact, narrow linewidth, etalon-tuned titanium: sapphire laser cavity which is pumped by the second harmonic of a kilohertz Nd:YAG laser is also presented. The fundamental tunable range is from 690-1100 nm depending on mirror reflectivities and optics

Anne Theresa Case Hanks

2008-01-01

90

Turbulent boundary layer on a moving surface  

Microsoft Academic Search

An integral and a numerical method are proposed for calculating the turbulent boundary layer on a moving surface (flap) in the presence of a longitudinal pressure gradient under conditions of monotonic velocity profiles. The integral method is a modification of Fediaevskii's et al. (1973) integral method (for calculating turbulent boundary layers in an incompressible fluid) to include an airfoil moving

A. S. Ginevskii; G. N. Emalianova; A. V. Kolesnikov

1976-01-01

91

Cyclone separator having boundary layer turbulence control  

DOEpatents

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.

Krishna, Coimbatore R. (Mt. Sinai, NY); Milau, Julius S. (Port Jefferson, NY)

1985-01-01

92

Drag reduction in liquid boundary layers by gas injection  

Microsoft Academic Search

The present evaluation of the development status of the introduction of gases into fluid boundary layers for viscous drag reduction emphasizes microbubble injection processes in which the bubbles form an emulsion in the background liquid's turbulent boundary layer. A considerable body of continuous-film surface lubrication research exists in the Soviet literature. The injection of a gas into a liquid turbulent

Charles L. Merkle; Steven Deutsch

1990-01-01

93

Receptivity of boundary layers to convected gusts  

NASA Astrophysics Data System (ADS)

The primary objective of this study is to determine experimentally the receptivity of a laminar boundary layer to convected gusts. Receptivity is the process by which external disturbances transfer energy to instabilities in the boundary layer. The term convected gust refers to a transient or periodic vortical disturbance convected by the freestream. The experimental approach consisted of hot-wire studies of the boundary layer response to vortical disturbances produced by an array of oscillating ribbons. The boundary layer is remarkably insensitive to large-scale vortical perturbations. No significant Tollmien-Schlichting waves were observed. The vortical disturbances are rapidly damped in the boundary layer and cause only weak oscillations that are primarily of the same frequency and wavelength as the external disturbance.

Parekh, D. E.

1993-03-01

94

Pressure gradient effects on the development of hairpin vortices in an initially laminar boundary layer  

NASA Astrophysics Data System (ADS)

An experimental study was conducted in Lehigh University's low-speed water channel to examine the effects of a zero, adverse, and favorable pressure gradients on the development of single hairpin vortices. Single hairpin vortices were generated in an initially laminar environment using controlled fluid injection through a streamwise slot at a Re(delta)* = 380, 440, and 570. Behavior of hairpin structures was determined by the use of dye and hydrogen bubble flow visualization techniques. Visualization results indicate that as a single hairpin vortex convects downstream a complicated growth process due to viscous-inviscid interactions and Biot-Savart deformation results in the generation of secondary and subsidiary vortices, eventually yielding a turbulent spot-like structure. The hairpin vortex structures are observed to be strongly affected by the presence of a pressure gradient, undergoing significant spatial growth changes, as well as experiencing significant flow structure modifications. As the hairpin initiation location is moved further into an adverse pressure gradient, the hairpin vortex lifts and rotates farther away from the surface relative to the behavior in a zero pressure gradient. Regions of low and high-velocity fluid near the surface are accentuated within an adverse pressure gradient, which amplifies the low-speed streak formation and breakdown process, accelerating the formation of vortical substructures and ejection of fluid from the surface.

Taylor, Blaine Keith

95

Problems of matter-antimatter boundary layers  

Microsoft Academic Search

This paper outlines the problems of the quasi-steady matter-antimatter boundary layers discussed in Klein-Alfvén's cosmological theory, and a crude model of the corresponding ambiplasma balance is presented:(i)At interstellar particle densities, no well-defined boundary layer can exist in presence of neutral gas, nor can such a layer be sustained in an unmagnetized fully ionized ambiplasma.(ii)Within the limits of applicability of the

B. Lehnert

1977-01-01

96

Effect of planetary boundary layer schemes on the development of intense tropical cyclones using a cloud-resolving model  

NASA Astrophysics Data System (ADS)

We studied the role of the planetary boundary layer (PBL) in intensity and inner core structure of extremely intense tropical cyclones (TC) using a 2 km mesh nonhydrostatic atmospheric model (NHM2) developed for operational use by the Japan Meteorological Agency. To investigate the effects of the PBL on simulated TCs, we used four PBL schemes: level 2.5 and level 3 Mellor-Yamada-Nakanishi-Niino closure schemes, a nonlocal scheme, and the Deardorff-Blackadar scheme. The numerical results indicated that the subgrid-scale mixing length determined by the PBL scheme plays a critical role in the determination of maximum TC intensity and inner core structure, even when the same expressions are provided for surface roughness lengths and the air-sea momentum and heat transfer coefficients. Different vertical eddy-diffusivity coefficient values derived from the PBL schemes cause differences in the TC intensity, inner core structure, and the relationship between maximum wind speed (MWS) and central pressure (CP). In particular, large vertical eddy diffusivities in lower layers (height <300 m) lead to large heat and water vapor transfers, resulting in extremely intense TCs accompanied by an upright, contracted eyewall structure. We also conducted numerical experiments using a 5 km mesh nonhydrostatic atmospheric model (NHM5) and the same PBL schemes to investigate the effect of horizontal resolution on simulated TCs. The NHM5 was insufficient to accurately represent the MWS or CP of an extremely intense TC, suggesting that NHM2 is required to simulate an extremely intense TC characterized by an upright, contracted eyewall structure.

Kanada, Sachie; Wada, Akiyoshi; Nakano, Masuo; Kato, Teruyuki

2012-02-01

97

Development of a micro-PIV/ LIF System for the Study of High Reynolds Number Turbulent Boundary Layers  

NASA Astrophysics Data System (ADS)

Skin friction constitutes a considerable proportion of the total drag on a ship. The flow mechanisms giving rise to friction drag occur mostly in a thin region near the solid surface. A HIgh Reynolds number, smooth, flat PLATE (HIPLATE) model is used to conduct equilibrium boundary layer experiments at scales approaching prototype applications. The plate measures 3 m wide by 12.9 m long, and Reynolds numbers (based on downstream distance) of 200 million have been achieved. This talk reports on a friction-drag-reduced flow study by means of injecting long-chain, water-soluble polymer into the boundary layer. We describe the details of a particle imaging velocimetry (PIV) system to measure the mean and fluctuating velocity profiles in the inner region of the boundary layer (y < 2 mm, or y+ < 400), with a vector spacing of approximately 40 microns. A laser induced fluorescence (LIF) system is also used to measure the mean and fluctuating concentration profiles of the injected polymer. Preliminary results are discussed. [Sponsored by DARAPA

Oweis, Ghanem; Winkel, Eric; Dowling, David; Ceccio, Steven

2004-11-01

98

Boundary layer processes in the Martian magnetosphere  

NASA Astrophysics Data System (ADS)

At Mars, in the absence of a global magnetic field, the flowing solar wind interacts directly with ionized atmospheric constituents, forming an induced magnetosphere. Turbulent boundary layer processes provide one means by which solar wind and atmospheric plasma can mix and exchange momentum, potentially leading to atmospheric escape. In this presentation, we describe MGS MAG/ER observations of Martian boundary layer oscillations, identified using a combination of magnetic field and electron data. We analyze electron distributions to identify interaction regions, and utilize magnetic field data to determine wave properties and boundary position and morphology. Our observations suggest several modes of interaction, including large-scale pulsations of a relatively smooth boundary, and corrugated boundary layer structures possibly indicative of the presence of boundary instabilities. We discuss each of these modes, and the implications for atmospheric escape process.

Halekas, J. S.; Brain, D. A.; Eastwood, J. P.

2010-12-01

99

The efficient calculation of turbulent boundary layers  

NASA Astrophysics Data System (ADS)

A simplified approach to the computation of turbulent boundary layers (TBL) by implicit-difference methods is developed and demonstrated. It is shown that the viscous sublayer can be neglected when integrating the TBL equations if the boundary conditions near the wall are appropriately modified. Logarithmic coordinates are introduced to improve the accuracy of the difference formulas. A number of numerical examples are calculated, and the results and computation times are compared in graphs and tables with those of the transformation of Cebeci and Smith (1968), which integrates the sublayer. In the case of the TBL on a plane surface, time savings of 56 and 65 percent are achieved for Reynolds numbers of 22,000 and 240,000, respectively.

Rotta, J. C.

1983-12-01

100

A comparison of boundary layer receptivity mechanisms  

NASA Astrophysics Data System (ADS)

Boundary layer receptivity mechanisms are investigated, and the implications of receptivity for the prediction of boundary layer transition are discussed. The receptivity of the Blasius boundary layer to a variety of freestream disturbances is first studied. Due to diffraction by the leading edge, oblique acoustic waves at low Mach numbers are found to produce the strongest receptivity. The case of the receptivity produced by acoustic waves interacting with porous suction surfaces in subsonic flow is then considered, and receptivity is shown to occur due to the rapid adjustment in the mean flow and to local scattering of the acoustic wave by the nonzero admittance of the porous surface.

Heinrich, R. A.; Choudhari, M.; Kerschen, E. J.

101

Boundary layers on longitudinally grooved walls (riblets)  

NASA Astrophysics Data System (ADS)

The boundary layer of riblets has been investigated in a hydrodynamic wind tunnel. For the case of triangularly grooved riblets, laser velocimetry visualizations show flow stabilization to occur for a turbulent boundary layer, and a decreased longitudinal velocity profile slope and a rapid relaxation downstream to occur for a laminar boundary layer. U-shaped grooves are found to have no effect. Visualizations of triangularly gooved riblets of several dimensions indicate that no counterrotating vortices exist in the grooves. This result is confirmed by profiles of the longitudinal velocity component, which show an increase in the velocity gradient near the crest and a significant decrease in the groove.

Fulachier, L.; Djenidi, L.; Anselmet, F.

1987-10-01

102

Bottom boundary layer flow profiling system  

SciTech Connect

An autonomous profiling system is being developed to measure physical and optical properties in ocean-bottom boundary layers. System sensors will include electromagnetic current meters, temperature sensors, transmissometers, and water sample bottles affixed in a vertical array to bottom-supported instrument frame at heights ranging from 0.25-5.00 m (1-16 ft) above its base. The instrumentation will measure high-frequency property fluctuations (5 Hz) as well as mean values. High-capacity tape recorders will permit unattended deployments for up to 3 months. Field tests will be conducted in the Gulf of Mexico.

Adams, C.E. Jr.; Fredericks, R.D.

1984-04-01

103

Modelling the low-latitude boundary layer with reconnection entry  

SciTech Connect

The authors develop a one-dimensional Low-Latitude Boundary Layer (LLBL) model for northward IMF. The boundary layer in this model is uniform in the direction normal to the magnetopause, a `plateau-type` boundary layer. The boundary layer motion is decoupled from the magnetosheath motion and driven by the plasma pressure associated with the incoming solar wind plasma near local noon, which has become entrained on closed field lines as a result of reconnection in the cusp region. Dissipation in the ionosphere at the feet of the boundary layer field lines opposes this motion. There are two physical solutions for the model. In one, the boundary layer reaches a terminal velocity in the tail as the boundary layer plasma effectively joins the solar wind flow. In the other solution, the flow is nearly stopped in the far tail. In combination with other mechanisms, this latter solution may correspond to the case in which the boundary layer plasma participates in magnetospheric convection and returns sunward. The density, velocity, and thickness as functions of distance from local noon are studied, assuming that the magnetopause has elliptical shape and the magnetospheric field is dipolar.

Song, P.; Holzer, T.E. [National Center for Atmospheric Research, Boulder, CO (United States); Russell, C.T.; Wang, Z. [Univ. of California, Los Angeles, CA (United States)

1994-04-01

104

Modelling the low-latitude boundary layer with reconnection entry  

NASA Astrophysics Data System (ADS)

We develop a one-dimensional Low Latitude Boundary Layer (LLBL) model for northward interplanetary magnetic field (IMF). The boundary layer in this model is uniform in the direction normal to the magnetopause, a 'plateau-type' boundary layer. The boundary layer motion is decoupled from the magnetosheath motion and driven by the plasma pressure associated with the incoming solar wind plasma near local noon, which has become entrained on closed field lines as a result of reconnection in the cusp region. Dissipation in the ionosphere at the feet of the boundary layer field lines opposes this motion. There are two physical solutions for the model. In one, the boundary layer reaches a terminal velocity in the tail as the boundary layer plasma effectively joins the solar wind flow. In the other solution, the flow is nearly stopped in the far tail. In combination with other mechanisms, this latter solution may correspond to the case in which the boundary layer plasma participates in magnetospheric convection and returns sunward. The density, velocity, and thickness as functions of distance from local noon are studied, assuming that the magnetopause hasa elliptical shape and the magnetospheric field is dipolar.

Song, P.; Holzer, T. E.; Russell, C. T.; Wang, Z.

1994-04-01

105

Turbulent boundary layer manipulation by outer-layer devices  

Microsoft Academic Search

A turbulent boundary layer manipulated by outer-layer devices has been studied. Experiments have been conducted in the 0.70 by 0.50 m2 low speed wind tunnel of the ‘Modesto Panetti’ Aeronautical Laboratory of the Politecnico di Torino. Mean values and turbulent quantities measured in the natural and manipulated boundary layers are shown for comparison. The mechanisms to explain the observed skin

G. Iuso; M. Onorato

1995-01-01

106

Analysis of Nosetip Boundary Layer Transition Data.  

National Technical Information Service (NTIS)

A critical analysis is presented of the available wind tunnel data simulating nosetip boundary layer transition on reentry vehicles. It is agreed that transition should depend on surface roughness, surface temperature, and surface curvature. The Reynolds ...

M. L. Finson

1976-01-01

107

Radiation from Air-Teflon Boundary Layers.  

National Technical Information Service (NTIS)

Radiation profiles in an ablating flat plate air-teflon laminar boundary layer were studied both experimentally and theoretically. The experiments were conducted in a one atmosphere, 3000 - 6000K, subsonic free stream produced by an arc jet. Spatially res...

R. A. Greenberg K. L. Wray L. A. Young N. H. Kemp

1970-01-01

108

Sound from Turbulent Boundary Layer Excited Panels.  

National Technical Information Service (NTIS)

The acoustic power radiated by thin flexible panels excited by turbulent boundary layer pressure fluctuations is estimated using a modal analysis, light fluid loading effects being included. Previous estimates of the modal radiation coefficients are impro...

H. G. Davies

1969-01-01

109

Reflection of sound by a boundary layer  

Microsoft Academic Search

A method is given for the calculation of the reflection coefficient for plane waves incident upon a plane boundary when the acoustic medium flows parallel to the plane and the resulting boundary layer is of finite thickness. Results are given for limited ranges of the important parameters, which are the Mach number of the flow, the angle of incidence, the

R. S. Brand; R. T. Nagel

1982-01-01

110

Turbulent Boundary Layers with Assigned Wall Shear.  

National Technical Information Service (NTIS)

This paper considers the problem of computing the external velocity distribution on a two-dimensional body in an incompressible boundary-layer flow for a specified wall shear. This leads to an 'overdetermined' boundary-value problem for a partial differen...

T. Cebeci N. Berkant I. Silivri H. B. Keller

1974-01-01

111

BUBBLE – an Urban Boundary Layer Meteorology Project  

Microsoft Academic Search

Summary The Basel UrBan Boundary Layer Experiment (BUBBLE) was a year-long experimental effort to investigate in detail the boundary layer structure in the City of Basel, Switzerland. At several sites over different surface types (urban, sub-urban and rural reference) towers up to at least twice the main obstacle height provided turbulence observations at many levels. In addition, a Wind Profiler

M. W. Rotach; R. Vogt; C. Bernhofer; E. Batchvarova; A. Christen; A. Clappier; B. Feddersen; S.-E. Gryning; G. Martucci; H. Mayer; V. Mitev; T. R. Oke; E. Parlow; H. Richner; M. Roth; Y.-A. Roulet; D. Ruffieux; J. A. Salmond; M. Schatzmann; J. A. Voogt

2005-01-01

112

Klebanoff modes in 3D boundary layers  

NASA Astrophysics Data System (ADS)

We present an investigation based on simplified direct numerical simulations of the generation of Klebanoff modes by free-stream vorticity in Falkner-Skan-Cooke boundary layers. The free-stream vorticity is generated by a source taking the form d(x)d(z-zf)exp(iby) derived from a body force, where (x,y,z) are the streamwise, spanwise and wall-normal co-ordinates, zf is located above the boundary layer and near its edge, and b is the spanwise wave-number. This vorticity source creates a diffused and corrugated sheet of streamwise vorticity that drives the boundary layer with a wall-normal velocity, thereby generating streak-like structures within the boundary layer. Simulations of streak evolution have been carried out for a range of 2D and 3D boundary layers with favourable and adverse streamwise pressure gradients. In general, increasing the degree of adverse pressure gradient and sweep makes the boundary layer more receptive to streak formation. The streaks also change form as the sweep angle is increased and there is also evidence of secondary instability.

Carpenter, Peter W.; Kudar, Karen; Davies, Chris

2004-11-01

113

3D (3 Dimensional) Boundary Layer Computations on Swept Wings.  

National Technical Information Service (NTIS)

A three-dimensional turbulent boundary layer code based on an integral method developed by Cousteix and Aupoix has been made operational on the NAL computer. The turbulent modeling is based on an improved mixing length hypothesis and similarity solutions....

N. R. Subramanian M. I. James

1987-01-01

114

Study on ground clutter prevention fences for boundary layer radars  

NASA Astrophysics Data System (ADS)

A low elevation sidelobe suppression algorithm based on the uniform physical theory of diffraction (PTD) is developed to simulate ground clutter prevention fences for boundary layer radars (BLRs). As applications to the algorithm, the most suitable fence is achieved for the lower troposphere radar (LTR) and the L-28 boundary layer radar, respectively. The developed algorithm can also be applied to other radar systems where reducing low elevation sidelobes is desired.

Rao, Qinjiang; Hashiguchi, Hiroyuki; Fukao, Shoichiro

2003-04-01

115

Theoretical and modeling studies of the marine planetary boundary layer  

NASA Astrophysics Data System (ADS)

The research goals were: (1) to gain an improved theoretical understanding of and a predictive capability for partly cloudy boundary layers, and to test these ideas against data acquired in the field and (2) to investigate the role of air-sea interactions in regulating cloud amount in the marine boundary layer. The objectives were to produce an extensive set of theoretical and numerical results, leading to better physical understanding of the cloudy marine boundary layer and provide a theoretical basis for the planning and execution of the Atlantic Stratocumulus Transition Experiment (ASTEX). A new type of boundary-layer model was developed that combines second order closure with a bulk representation of the vertical structure. The boundary-layer depth and turbulence kinetic energy (TKE) are prognostically determined. The large turbulent eddies that are primarily responsible for the fluxes are modeled as convective circulations, with ascending and descending branches. The interior of the boundary layer is bounded above by a thin entrainment layer and below by a thin ventilation layer. Conservative variables such as the the equivalent potential temperature have quadratic profiles in the interior. Convective circulations occur, with rising branches occupying fractional area sigma, which is predicted by the model. The upper ocean is represented by a mixed layer whose depth can be either fixed or variable, depending on the objectives of the numerical experiment being conducted.

Randall, David A.

1990-12-01

116

Historical review (pre-1980) of magnetospheric boundary layers and the low-latitude boundary layer  

NASA Astrophysics Data System (ADS)

This historical survey covers research on the magnetospheric boundary layers through 1979 with a focus on observations and on the low-latitude boundary layer (LLBL) of Earth's magnetosphere. An effort was made to identify and read every paper published prior to 1980 that made a significant contribution towards identifying and characterizing boundary regions of the outer magnetosphere. The total list of over 80 papers is available at http://www.plasmas.org/BL. A sketch of Earth's magnetosphere is shown in Figure 1, which illustrates the major regimes and boundary layers. The magnetospheric boundary layer denotes all exterior boundary layers adjoining the magnetopause, including the dayside and tail flank portions of the LLBL, the exterior cusp region and entry layer, and the plasma mantle. There is a plasma sheet boundary layer separating the lobe and plasma sheet regions, but that boundary layer is not reviewed here [see Eastman et al., 1984]. The magnetotail boundary layer refers to both the plasma mantle and the tail flank portion of the LLBL.

Eastman, Timothy E.

117

Near Critical Phenomena in Laminar Boundary Layers  

NASA Astrophysics Data System (ADS)

Recent developments in the construction of airfoils and rotorblades are characterized by an increasing interest in the application of so-called smart structures for active flow control. These are characterized by an interplay of sensors, actuators, real-time controlling data processing systems and the use of new materials e.g. shape alloys with the aim to increase manoeuvrability, reduce drag and radiated sound. The optimal use of such devices obviously requires a detailed insight into the flow phenomena to be controlled and in particular their sensitivity to external disturbances. In this connection locally separated boundary layer flows are of special interest. Asymptotic analysis of boundary layer separation in the limit of large Reynolds number Re? ? has shown that in a number of cases which are of importance from a practical point of view solutions of the resulting interaction equations describing two-dimensional steady flows exist up to a limiting value ? c of the relevant controlling parameter ? only while two branches of solutions exist in a regime ? < ? c . The present study aims at a better understanding of near critical flows ? ? — ? c ? ? 0 and in particular the changes of the flow behaviour associated with the passage of ? through ? c .

Kluwick, A.; Braun, S.; Cox, E. A.

118

Unified Prandtl number scaling for start-up and fully developed natural-convection boundary layers for both Pr ?1 and Pr ?1 fluids with isothermal heating.  

PubMed

Recent studies have used scaling analysis to obtain simple power-law relations that accurately predict the Prandtl (Pr) number dependency of natural-convection boundary layers subjected to both isothermal and ramped heating conditions, when Pr>1. The analysis used in those studies cannot be extended to Pr<1 fluids, and it is not clear at present whether such simple scaling relations can be developed for Pr<1 fluids. In the present study, the Pr>1 scalings are shown to perform well for the start-up stage of the Pr<1 flow, but not for the fully developed flow. The Pr>1 scalings are modified to provide unified Prandtl number scalings for fully developed natural-convection boundary layers for both Pr?1 and Pr?1, with the unknown powers obtained empirically via direct numerical simulation. The modified scalings are shown to perform well for the fully developed flow, with the exception being the prediction of the inner viscous boundary-layer thickness. PMID:23368043

Lin, Wenxian; Armfield, S W

2012-12-14

119

Dynamical Simulation of Cloudy Boundary Layer Flow during Cold Air Outbreaks  

Microsoft Academic Search

A two-dimensional primitive equation planetary boundary layer model has been constructed and applied to simulate downwind evolution of coupled dynamical, thermodynamical and cloud properties in the planetary boundary layer (PBL) developed during cold air outbreaks over warm ocean. A layered parametric approach is adopted to model the inversion -capped convective boundary layer filled with shallow cumuli, or topped by stratocumulus

Chiu-Wai Yuen

1983-01-01

120

An investigation of boundary-layer behavior on wavy walls  

Microsoft Academic Search

A numerical approach has been developed to study the viscous flow over wavy walls. It is based on two-dimensional compressible turbulent boundary-layer equations and involves functions for pressure gradient and pressure phase lag as well as for the effects of surface curvature on boundary-layer behavior. Results are presented for three kinds of wavy wall and provide further evidence of reduction

Suxun Li; Guang Li Chen

1989-01-01

121

High Reynolds number thick axisymmetric turbulent boundary layer measurements  

Microsoft Academic Search

Experimental measurements of the wall shear stress and momentum thickness for thick axisymmetric turbulent boundary layers are presented. The use of a full-scale towing tank allowed zero pressure gradient turbulent boundary layers to be developed on cylinders with diameters of 0.61, 0.89, and 2.5 mm and lengths ranging from 30 m to 150 m. Moderate to high Reynolds numbers (10 4Re ?5, 10

K. M. Cipolla; W. L. Keith

2003-01-01

122

Application of a Perturbation Recycling Method in the Large-Eddy Simulation of a Mesoscale Convective Internal Boundary Layer  

Microsoft Academic Search

An arrangement of boundary conditions is described and demonstrated that facilitates the large-eddy simulation (LES) of inhomogeneous boundary layers such as internal boundary layers. In addition to the domain where the internal boundary layer develops, the method requires a section of domain over the upwind surface that is of the order of 10 boundary layer thicknesses and thus similar in

Shane D. Mayor; Philippe R. Spalart; Gregory J. Tripoli

2002-01-01

123

Etude du Developpement d'Une Couche Limite Turbulente Compressible sur Une Paroi Rugueuse et Poreuse (Study of the Development of a Compressible Turbulent Boundary Layer on a Porous and Rough Wall).  

National Technical Information Service (NTIS)

A method to estimate the development of a boundary layer on a flat wall in the presence of mass transfer is studied. It follows the analysis of the interaction of a shock wave with a boundary layer subjected to either aspiration or blowing. The experiment...

A. Stassinopoulos R. Leblanc

1986-01-01

124

High Energy Benthic Boundary Layer Experiment: HEBBLE  

NASA Astrophysics Data System (ADS)

HEBBLE's precise aim is to develop and to test explicit predictions about the response of adhesive/cohesive marine sediments to imposed and controlled stresses [Hollister et al., 1980; Kerr, 1980]. Pursuit of this goal has necessitated a co-ordinated, interdisciplinary effort, to date including physical oceanographers, sedimentologists, radiochemists and biochemists, and biological oceanographers.Current produced bed features reflect significant momentum exchange between the fluid boundary layer and the sediment surface. From photographs, and the few current meter records available, it appears that vast areas of the deep sea are presently being modified by energetic flows. The bed forms range in scale from kilometers to millimeters and are found where near bottom currents have been delineated by maxima in near bottom potential temperature. Moreover, on the Scotian Rise for example, many of these bedforms are being produced by present day currents because rapid destruction of the features by benthic organisms is evidenced in stereo-photographs.

Nowell, Arthur R. M.; Hollister, Charles D.; Jumars, Peter A.

125

Boundary layer receptivity to freestream turbulence  

NASA Astrophysics Data System (ADS)

Freestream turbulence of weak but adjustable intensity incident upon a flat plate test model induced Tollmien-Schichting (TS) waves and wave packets. These were studied using a newly-developed sensor by which the packets could be followed from a station nearly as far forward as the minimum critical Reynolds number to the onset of transition. Conclusions reached from these studies were: (1) weak freestream turbulence induced TS wave packets in a Blasius boundary-layer, (2) packets gained strength during propagation through expansion of lateral and longitudinal scales, and through an increase in peak amplitude, (3) the average wave strength at stations of observation was not related to the freestream velocity fluctuation in a linear manner, and (4) packets typically evolved into turbulent spots.

Kendall, James M.

1990-06-01

126

Aerosol buffering of marine boundary layer cloudiness  

NASA Astrophysics Data System (ADS)

The role of aerosol particles in maintaining a cloudy boundary layer in the remote marine environment is explored. It has previously been shown that precipitation can result in the transition from a closed- to open-cellular state but that the boundary layer cannot maintain this open-cell state without a resupply of particles. Potential sources include wind-driven production of sea salt particles from the ocean, nucleation from the gas phase, and entrainment from the free troposphere. Here we investigate with model simulations how the interplay of cloud properties, aerosol production, and boundary layer dynamics results in aerosol sources acting as a buffer against processes that destabilize cloudiness and the dynamic state of the marine boundary layer. For example, at nighttime, cloud liquid water increases in the absence of solar heating, resulting in increased precipitation, stronger cloud top cooling, accelerated boundary layer turbulence, and faster surface wind speeds. Faster surface wind speeds drive an enhanced flux of sea salt aerosol, at a time when aerosol particles are scavenged more readily by enhanced precipitation. In contrast, absorption of solar radiation during daytime reduces cloud water, decelerates boundary layer turbulence, reduces surface wind speeds, and therefore slows surface emissions. This is compensated by nucleation of small aerosol particles from the gas phase in response to the nigh complete removal of cloud condensation nuclei in precipitating open cell walls. These newly formed particles need to grow to larger sizes before they can serve as cloud condensation nuclei (CCN), but will likely contribute to the CCN population during the nighttime and, together with ocean emissions, buffer the system against precipitation removal.

Kazil, J.; Feingold, G.; Wang, H.

2010-12-01

127

Waves which travel upstream in boundary layers  

NASA Astrophysics Data System (ADS)

Upstream propagation and diffusion of vorticity in a boundary layer is described by a numerical solution of the Orr-Sommerfeld equation. This traveling wave grows very rapidly in the downstream direction. The growth rate is approximately exp(+ R (sub delta)x) where R sub delta is the Reynolds number based on the characteristic boundary layer thickness, and x is the streamwise coordinate nondimensionalized against delta. Far from the boundary layer, the solution oscillates neutrally in the Y-direction. Analyses reveal high frequency wave which oscillates and decays in the y-direction approximately as exp(-i R(sub delta) y - omega Y) where omega is the frequency. This high frequency wave can survive into the freestream. Numerical solutions of the Orr-Sommerfeld equation with a Blasius layer are obtained by a series expansion of Chebyshev polynomials. Since the y-wavenumber of the oscillations increases with increasing Reynolds number, the calculations have been restricted to low Reynolds numbers. In the boundary-value problem, this solution appears as a branch line in Laplace space. It is one of the possible solutions in a mathematically complete description of the spatial evolution of fluctuations. This traveling wave represents one of the upstream influences of a boundary in a calculational domain. Another mechanism of upstream influence is the growing standing wave.

Rogler, H. L.

1985-07-01

128

Boundary layer halogens in coastal Antarctica.  

PubMed

Halogens influence the oxidizing capacity of Earth's troposphere, and iodine oxides form ultrafine aerosols, which may have an impact on climate. We report year-round measurements of boundary layer iodine oxide and bromine oxide at the near-coastal site of Halley Station, Antarctica. Surprisingly, both species are present throughout the sunlit period and exhibit similar seasonal cycles and concentrations. The springtime peak of iodine oxide (20 parts per trillion) is the highest concentration recorded anywhere in the atmosphere. These levels of halogens cause substantial ozone depletion, as well as the rapid oxidation of dimethyl sulfide and mercury in the Antarctic boundary layer. PMID:17641195

Saiz-Lopez, Alfonso; Mahajan, Anoop S; Salmon, Rhian A; Bauguitte, Stephane J-B; Jones, Anna E; Roscoe, Howard K; Plane, John M C

2007-07-20

129

Runup and boundary layers on sloping beaches  

NASA Astrophysics Data System (ADS)

The present study is devoted to discrepancies between experimental and theoretical runup heights on an inclined plane, which have occasionally been reported in the literature. In a new study on solitary wave-runup on moderately steep slopes, in a wave tank with 20 cm water depth, detailed observations are made for the shoreline motion and velocity profiles during runup. The waves are not breaking during runup, but they do break during the subsequent draw-down. Both capillary effects and viscous boundary layers are detected. In the investigated cases the onshore flow is close to the transitional regime between laminar and turbulent boundary layers. The flow behaviour depends on the amplitude of the incident wave and the location on the beach. Stable laminar flow, fluctuations (Tollmien-Schlichting waves), and formation of vortices are all observed. Comparison with numerical simulations showed that the experimental runup heights were markedly smaller than predictions from inviscid theory. The observed and computed runup heights are discussed in the context of preexisting theory and experiments. Similar deviations are apparent there, but have often been overlooked or given improper physical explanations. Guided by the absence of turbulence and irregular flow features in parts of the experiments we apply laminar boundary layer theory to the inundation flow. Outer flows from potential flow models are inserted in a nonlinear, numerical boundary layer model. Even though the boundary layer model is invalid near the moving the shoreline, the computed velocity profiles are found to compare well with experiments elsewhere, until instabilities are observed in the measurements. Analytical, linear boundary layer solutions are also derived both for an idealized swash zone motion and a polynomial representation of the time dependence of the outer flow. Due to lacking experimental or theoretical descriptions of the contact point dynamics no two-way coupling of the boundary layer model and the inviscid runup models is attempted. Instead, the effect of the boundary layer on the maximum runup is estimated through integrated losses of onshore volume transport and found to be consistent with the differences between inviscid theory and experiments.

Pedersen, G. K.; Lindstrřm, E.; Bertelsen, A. F.; Jensen, A.; Laskovski, D.; Sćlevik, G.

2013-01-01

130

Boundary-layer flows in rotating cavities  

NASA Astrophysics Data System (ADS)

Differential boundary layer equations modelling the flow between two corotating air-cooled gas-turbine disks are solved to study the velocity distribution inside the entraining and nonentraining boundary layers and in the inviscid core. The equations are discretized using the box scheme of Keller and Cebeci (1972), and the Cebeci-Smith (1974) eddy-viscosity model is used to treat the turbulent-flow case. Good agreement between the present computations and previous experimental results is obtained for a wide range of flow rates and rotational speeds.

Ong, C. L.; Owen, J. M.

1988-06-01

131

Improved boundary layer depth retrievals from MPLNET  

NASA Astrophysics Data System (ADS)

Continuous lidar observations of the planetary boundary layer (PBL) depth have been made at the Micropulse Lidar Network (MPLNET) site in Greenbelt, Maryland, since April 2001. However, because of issues with the operational PBL depth algorithm, the data are not reliable for determining seasonal and diurnal trends. Therefore, an improved PBL depth algorithm has been developed which uses a combination of the wavelet technique and image processing. The new algorithm is less susceptible to contamination by clouds and residual layers and, in general, produces lower PBL depths. A 2010 comparison shows the operational algorithm overestimates the daily mean PBL depth when compared to the improved algorithm (1.85 and 1.07 km, respectively). The improved MPLNET PBL depths are validated using radiosonde comparisons, which suggests the algorithm performs well to determine the depth of a fully developed PBL. A comparison with the Goddard Earth Observing System version 5 (GEOS-5) model suggests that the model may underestimate the maximum daytime PBL depth by ˜410 m during the spring and summer. The best agreement between MPLNET and GEOS-5 occurred during the fall and they differed the most in the winter.

Lewis, Jasper R.; Welton, Ellsworth J.; Molod, Andrea M.; Joseph, Everette

2013-09-01

132

Boundary layer control device for duct silencers  

NASA Astrophysics Data System (ADS)

A boundary layer control device includes a porous cover plate, an acoustic absorber disposed under the porous cover plate, and a porous flow resistive membrane interposed between the porous cover plate and the acoustic absorber. The porous flow resistive membrane has a flow resistance low enough to permit sound to enter the acoustic absorber and high enough to damp unsteady flow oscillations.

Schmitz, Fredric H.; Soderman, Paul T.

1993-11-01

133

Wall functions for unsteady turbulent boundary layers  

Microsoft Academic Search

A method for obtaining wall functions for a turbulent boundary layer flow, in which the free-stream velocity oscillates periodically about a nonzero mean, is presented. Particular expressions of these wall functions are proposed for a k-epsilon turbulence model.

A. N. Menendez; B. R. Ramaprian

1985-01-01

134

Simulating observed boundary layer clouds on Mars  

Microsoft Academic Search

A microphysical model for Mars dust and ice clouds has been applied in combination with a model of the planetary boundary layer (PBL) for the interpretation of measurements by the LIDAR instrument on the Phoenix Mars mission. The model simulates nighttime clouds and fall streaks within the PBL that are similar in structure to the LIDAR observations. The observed regular

F. Daerden; J. A. Whiteway; R. Davy; C. Verhoeven; L. Komguem; C. Dickinson; P. A. Taylor; N. Larsen

2010-01-01

135

Interaction between Trapped Waves and Boundary Layers  

Microsoft Academic Search

The absorption of trapped lee waves by the atmospheric boundary layer (BL) is investigated based on numerical simulations and theoretical formulations. It is demonstrated that the amplitude of trapped waves decays exponentially with downstream distance due to BL absorption. The decay coefficient, , defined as the inverse of the e-folding decay distance, is found to be sensitive to both surface

Qingfang Jiang; James D. Doyle; Ronald B. Smith

2006-01-01

136

Diagnosis of boundary-layer circulations.  

PubMed

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. PMID:23588045

Beare, Robert J; Cullen, Michael J P

2013-04-15

137

Reduction of turbulent drag: Boundary layer manipulators  

Microsoft Academic Search

The drag reduction on airbus profiles is investigated. External and internal boundary layer manipulators are applied. The wind tunnel wall geometry and the model surface geometry are modified, carving riblets in the sense of the main flow. The change induced in the flow are studied using hotwire anemometry and spectral analysis. Direct drag measurements on Airbus profiles indicate a drag

E. Coustols

1989-01-01

138

Turbulent boundary layer structure, drag reduction  

Microsoft Academic Search

The research work has progressed along the following lines: (1) continuation of theoretical work on the effects of large-eddy breakup devices on turbulent eddies; (2) theoretical study of the role of pressures in the wall turbulence generation process; (3) application of a theoretical model for designing smart wall boundary layer control; (4) use of a new bursting model for predicting

Marten T. Landahl; Joseph H. Haritonidis

1986-01-01

139

Particle-laden boundary layers and singularities  

NASA Astrophysics Data System (ADS)

The dusty-gas model for flow in dilute particle suspensions generates a singularity in particle volume fraction in a variety of viscous boundary layer problems. Such a singularity, at say x=xs along the wall, makes it impossible to continue the solution to the equations. Previously, we have found that computation of the Blasius boundary layer, with a modified equation set that permits fluid volume fraction significantly different from 1, still leads to a velocity singularity at a slightly modified location.ootnotetextFoster, Duck & Hewitt, Bull. Amer. Phys. Soc., November, 2006 Contrary to some published work, the Saffman force has not been found to mitigate the singularity for the conventional equation set, and again here, though the Saffman force does become comparable to the Stokes drag near the singularity, it alters the structure only slightly, and does not remove it. If ?o is the particle volume fraction of the fluid in which the boundary layer is embedded, then in certain re-scaled coordinates, the singularity occurs in a region ?ox?o/|?o| about xs, where a reduced set of equations applies. Within this region, there is a downstream-running ray from the origin on which ??1. However, the vertical fluid and particle velocity components are unbounded on that line. On replacing the line with a solid surface of particle material, a narrow boundary layer may be inserted, in which velocity singularities are removed.

Foster, M. R.

2007-11-01

140

Linear Optimal Controllers for Turbulent Boundary Layers  

Microsoft Academic Search

Several investigators have shown recently that controller design based on a system control-theoretic approach has led to significant viscous-drag reduction in turbulent boundary layers. Although these new approaches rely less on the investigator's physical insight into the flow (in contrast to most existing approaches), there still remain many design issues that need to be addressed. These are, but not limited

Junwoo Lim; John Kim; Sung Moon Kang; Jason Speyer

2001-01-01

141

Boundary layer relaxation from convex curvature  

Microsoft Academic Search

Convex curvature has promise as a means of viscous drag reduction because it has been shown to result in a decrease in skin friction. In order to improve the understanding of curvature effects and their potential for drag reduction, an examination was made of the flat plate relaxation behavior of a turbulent boundary layer recovering from 90 deg of strong

Amy Elsa Alving

1988-01-01

142

Turbulent boundary layer characteristics over streamwise grooves  

Microsoft Academic Search

Turbulent boundary layer characteristics over streamwise grooves (on the order of 15 wall units in height and spacing) have been quantified in a water channel using hot film anemometry. The turbulent structure over both smooth and riblet surfaces has been investigated using traditional cross correlations and triple correlations. The VITA technique has been used to detect and count turbulent bursts

J. A. Gallagher; A. S. W. Thomas

1984-01-01

143

A Wake Boundary Layer Mixing Experiment.  

National Technical Information Service (NTIS)

The mixing of a boundary layer was investigated under zero pressure gradient with a two dimensional wake shed from a plate. Measurements of mean and fluctuating quantities were carried out for this flow in particular, as well as for one of the component f...

P. J. Pot

1979-01-01

144

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...

145

Compressible Ekman layers on curved boundaries  

NASA Astrophysics Data System (ADS)

The effects of the compressible Ekman layer on a rotating nonsymmetric surface are described. Equivalent boundary conditions on the 'interior' flow are obtained in terms of the primitive variables of velocity and temperature. Expressions are derived for the local flux vector of mass in the Ekman layer and for the mass transport induced into the Ekman layer from the interior. The interior temperature at the boundary is given as an explicit function of the interior velocity there and the imposed wall conditions. The interior velocity is itself determined from the suction formula by a direct and fairly routine procedure. Examples are used to show that these formulas markedly simplify the problem of motion in a centrifuge of rather arbitrary shape.

Greenspan, H. P.

1984-04-01

146

Nonuniqueness in wakes and boundary layers  

NASA Astrophysics Data System (ADS)

Instreamlined flow past a flat plate aligned with a uniform stream, it is shown that the Goldstein near wake and the Blasius boundary layer are nonunique solutions locally for the classical boundary layer equations, whereas the Rott-Hakkien very near wake appears to be unique. Concerning non-streamlined flow, new similarity forms are described for the pressure free vicous symmetric closure of a predominantly slender long wake beyond a large-scale separation. Features arising include nonuniqueness, singularities and algebraic behavior, consistent with non-entraining shear layers with algebraic decay. Nonuniqueness also seems possible in reattachment onto a solid surface and for nonsymmetric or pressure controlled flows including the wake of a symmetric cascade.

Smith, F. T.

1983-05-01

147

A simple model of the atmospheric boundary layer; sensitivity to surface evaporation  

Microsoft Academic Search

A simple formulation of the boundary layer is developed for use in large-scale models and other situations where simplicity is required. The formulation is suited for use in models where some resolution is possible within the boundary layer, but where the resolution is insufficient for resolving the detailed boundary-layer structure and overlying capping inversion. Surface fluxes are represented in terms

I B Troen; L. Mahrt

1986-01-01

148

Computation of transonic cascade flows with shock and boundary layer interaction  

Microsoft Academic Search

Viscous phenomena in transonic turbomachine blade flow calculations are represented superimposing the effects of a boundary layer and wake on a inviscid flow. The inviscid flow is determined using a time marching calculation method. The boundary layer calculation is developed to treat the interaction effects of shock and expansion waves. The boundary layer is also modified to account for the

U. K. Singh

1980-01-01

149

Boundary layer effects on sound in a circular duct  

Microsoft Academic Search

Boundary layer effects on an acoustic field in a unidirectional flow with transverse shear are studied. The acoustic pressure variation in the direction normal to that of the flow is governed in the boundary layer by a second order differential equation. The problem in the boundary layer is reduced from a two point boundary value problem to a one point

R. T. Nagel; R. S. Brand

1982-01-01

150

The Near-Calm Stable Boundary Layer  

NASA Astrophysics Data System (ADS)

For the near-calm stable boundary layer, nominally 2-m mean wind speed <0.5 ms-1, the time-average turbulent flux is dominated by infrequent mixing events. These events are related to accelerations associated with wave-like motions and other more complex small-scale motions. In this regime, the relationship between the fluxes and the weak mean flow breaks down. Such near-calm conditions are common at some sites. For very weak winds and strong stratification, the characteristics of the fluctuating quantities change slowly with increasing scale and the separation between the turbulence and non-turbulent motions can become ambiguous. Therefore, a new analysis strategy is developed based on the scale dependence of selected flow characteristics, such as the ratio of the fluctuating potential energy to the kinetic energy. In contrast to more developed turbulence, correlations between fluctuating quantities are small, and a significant heat flux is sometimes carried by very weak vertical motions with large temperature fluctuations. The relation of the flux events to small-scale increases of wind speed is examined. Large remaining uncertainties are noted.

Mahrt, Larry

2011-09-01

151

Aeroelastically deflecting flaps for shock/boundary-layer interaction control  

NASA Astrophysics Data System (ADS)

An aeroelastic mesoflap system has been developed to improve the downstream flow properties of an oblique shock/boundary-layer interaction. The mesoflap system employs a set of small flaps over a cavity, whereby the flaps downstream of the interaction bend downward aeroelastically to bleed the flow and the upstream flaps bend upward to re-inject this same mass flow upstream. This recirculating system requires no net mass bleed and therefore has advantages for boundary layer control in external or mixed-compression supersonic aircraft inlets. In addition, the system may be applicable in other aerospace applications where boundary-layer control can help remedy the adverse effects of shock interactions. Several mesoflap systems have been fabricated and examined experimentally to investigate their aerodynamic and structural performance. Each mesoflap is rigidly attached to a spar on its upstream end while the remainder of the flap is free to deflect aeroelastically. The flap length is nominally a few boundary-layer thicknesses in dimension, while the flap thickness is small enough to allow tip deflections that are of the order of the boundary-layer momentum thickness. Experiments were conducted for a Mach 2.41 impinging oblique shock wave interaction with a turbulent boundary layer. Spanwise-centered laser Doppler velocimeter measurements indicate that certain mesoflap designs can show significant flow improvement as compared to the solid-wall case, including increased stagnation pressure recovery and a 7% reduction in boundary layer thickness and sonic thickness. However, one drawback of the mesoflap system is the potential for fatigue, which in some cases led to microcracking followed by flap failure. Structural design improvements to alleviate and avoid this problem included a lower profile spar design, substitution of Nitinol for aluminum as the flap material, and use of stress-relieving holes at the ends of the flap cut-outs.

Gefroh, D.; Loth, E.; Dutton, C.; Hafenrichter, E.

2003-06-01

152

Boundary layer control of rotating convection systems.  

PubMed

Turbulent rotating convection controls many observed features of stars and planets, such as magnetic fields, atmospheric jets and emitted heat flux patterns. It has long been argued that the influence of rotation on turbulent convection dynamics is governed by the ratio of the relevant global-scale forces: the Coriolis force and the buoyancy force. Here, however, we present results from laboratory and numerical experiments which exhibit transitions between rotationally dominated and non-rotating behaviour that are not determined by this global force balance. Instead, the transition is controlled by the relative thicknesses of the thermal (non-rotating) and Ekman (rotating) boundary layers. We formulate a predictive description of the transition between the two regimes on the basis of the competition between these two boundary layers. This transition scaling theory unifies the disparate results of an extensive array of previous experiments, and is broadly applicable to natural convection systems. PMID:19148097

King, Eric M; Stellmach, Stephan; Noir, Jerome; Hansen, Ulrich; Aurnou, Jonathan M

2009-01-15

153

Turbulent Boundary Layers on Rough Surfaces  

Microsoft Academic Search

The incompressible zero-pressure-gradient turbulent boundary layers on rough surface are investigated in light of the effects of the Reynolds number and roughness. The experimental data from various researchers were collected and analyzed. The true asymptotic profile (self-preserving solution) for the outer flow is found when the profiles are normalized by the Zagarola\\/Smits (1998) scaling, U_? delta\\/delta. This scaling successfully remove

Junghwa Seo; Luciano Castillo

2003-01-01

154

Active Control of Laminar Boundary Layer Disturbances  

Microsoft Academic Search

\\u000a Active suppression of the naturally occurring travelling wave disturbances that amplify in laminar boundary layers and cause\\u000a the transition from laminar to turbulent flow is considered. Both open-loop and closed-loop schemes are discussed. Numerical\\u000a predictions, based on linear stability theory, have been used to model the behaviour of the flow disturbances and the controlled\\u000a waves. Predictions based on these models

M. Gaster

155

Turbulent boundary layer drag reduction using riblets  

Microsoft Academic Search

An experimental study of low-speed turbulent boundary layer flow over longitudinally grooved surfaces (i.e., riblets) is discussed. Results obtained with a highly accurate drag balance indicate that v-groove riblet surfaces can produce consistent net drag reductions as large as 8 percent provided the height and spacing of the grooves in terms of law of the wall variables are less than

M. J. Walsh

1982-01-01

156

Reduction of turbulent drag: Boundary layer manipulators  

NASA Astrophysics Data System (ADS)

The drag reduction on airbus profiles is investigated. External and internal boundary layer manipulators are applied. The wind tunnel wall geometry and the model surface geometry are modified, carving riblets in the sense of the main flow. The change induced in the flow are studied using hotwire anemometry and spectral analysis. Direct drag measurements on Airbus profiles indicate a drag reduction of 3.5 percent. Experiments using cylindrical bodies in transonic flow show a drag reduction of 8 percent.

Coustols, E.

1989-03-01

157

Linearization of turbulent boundary-layer equations  

NASA Astrophysics Data System (ADS)

In previous solutions of the turbulent boundary layer equations that use the eddy viscosity concept in algebraic form, Newton's method has been applied to all terms except the viscous term, where the values of the eddy viscosity were assumed from a previous iteration. The method presently set out and evaluated was devised to allow the application of Newton's method to all terms of the momentum equation, using the eddy viscosity formulation of Cebeci and Smith (1974).

Cebeci, T.; Chang, K. C.; Mack, D. P.

1984-12-01

158

Effect of variability on boundary layer separation  

NASA Astrophysics Data System (ADS)

The behavior of a boundary layer during the accelerated motion of a cylinder in flow of a liquid was investigated experimentally using a hydrodynamic testing apparatus. Test results are presented for cylinders of 0.5-1 cm in diameter over the Reynolds number range 0.1-50,000 along the cylinder diameter for both laminar and turbulent external flow. The results can be used in the design of different kinds of process equipment involving nonstationary flow past various bodies.

Gudkov, V. A.

1991-10-01

159

Kahuku kite wind study. I. Kahuka beach boundary layer  

SciTech Connect

In the coastal plain of Kahuku, Oahu, during August 1980 and February to April 1981, the boundary layer and the mechanism that creates it were investigated. Four sets of two automatically-recording tethered aerodynamically lifting anemometer (TALA) kites flying continuously at 100 and 300 ft, and conventional 30 ft instruments were used concurrently at four sites along a transect parallel to the prevailing trade winds. Hand-held short-term kite measurements were used to verify the data from the prototype automatic kites during the first survey. Because of surface heating and vertical mixing, a rapidly expanding boundary develops soon after sunrise. Other forces that modify the daytime air flow in the lower layers are: surface friction, local scale thermal wind, a sea breeze and mechanical forcing. The nighttime boundary is established through heat conduction from the surface air to the ground. This layer grows slowly and reaches only a few hundred feet in depth. Other mechanisms that modify the winds in and around the nighttime boundary layer include: confluence into the boundary layer, local scale thermal wind, land breeze-drainage winds, and friction. In the second survey, the boundary layer was neither as high nor as well-developed as in the first because the ground was saturated after the winter rains. The consequent latent heat exchange prevented extreme surface temperature fluctuation. The commonly-used wind profile law exponent was found to depend on speed in the lower 100 ft of the atmosphere above which the exponent is constant. Estimates of long-term speeds at some sites differed by up to four mph between the two surveys. This underlines the importance of surveying not only all major wind regimes but also under different surface conditions. Long term speed estimates for the sties are high enough to make the area probably profitable for wind power development.

Daniels, P.A.; Oshiro, N.E.

1982-09-01

160

Linear Stability Theory and Three-Dimensional Boundary Layer Transition.  

National Technical Information Service (NTIS)

The viewgraphs and discussion of linear stability theory and three dimensional boundary layer transition are provided. The ability to predict, using analytical tools, the location of boundary layer transition over aircraft-type configurations is of great ...

R. E. Spall M. R. Malik

1992-01-01

161

Lag model for turbulent boundary layers over rough bleed surfaces  

NASA Astrophysics Data System (ADS)

Boundary-layer mass removal (bleed) through spanwise bands of holes on a surface is used to prevent or control separation and to stabilize the normal shock in supersonic inlets. The addition of a transport equation lag relationship for eddy viscosity to the rough wall algebraic turbulence model of Cebeci and Chang was found to improve agreement between predicted and measured mean velocity distributions downstream of a bleed band. The model was demonstrated for a range of bleed configurations, bleed rates, and local freestream Mach numbers. In addition, the model was applied to the boundary-layer development over acoustic lining materials for the inlets and nozzles of commercial aircraft. The model was found to yield accurate results for integral boundary-layer properties unless there was a strong adverse pressure gradient.

Lee, J.; Sloan, M. L.; Paynter, G. C.

1994-07-01

162

Extended self-similarity in boundary layer turbulence  

NASA Astrophysics Data System (ADS)

It is shown that a lack of isotropy narrows the range of spatial scales where turbulent flows exhibit extended self-similarity (ESS), namely, self-scaling of velocity structure functions. This effect holds irrespectively of the order of the structure functions and explains why early experiments on turbulent boundary layers failed to observe ESS. The shrinking of the ESS range of scales is well captured by the approximate analytical scaling functions developed by Sreenivasan and co-workers [Phys. Rev. E 48, R33 (1993); 48, 5 (1993); 48, R3217 (1993)] to fit atmospheric boundary layer data.

Amati, G.; Benzi, R.; Succi, S.

1997-06-01

163

Remote Sensing of Boundary layer Trace Gases in the Presence of dynamic boundary layer events  

NASA Astrophysics Data System (ADS)

With the suite of instruments located at UMBC we are able to analyze how low level jets and convective rolls affect boundary layer carbon monoxide and ozone. Low level jets are an excellent transport mechanism for boundary layer air. These jets alter the nominal nocturnal ozone cycle and inhibit the total depletion of ozone during night time. Using BBAERI (Baltimore Bomem Atmospheric Emitted Radiance Interferometer) we retrieve boundary layer CO and total column ozone during both day and night. Comparing inactive to active nights we can better understand the effect jets have on the ozone cycle. The WRF regional model is used to simulate nocturnal jet events to elucidate source regions for the BBAERI retrievals of trace gas abundances. Previous studies using the AERI at the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program Southern Great Plains (SGP) site near Lamont, Oklahoma have demonstrated the impact of horizontal convective rolls on boundary layer water vapor profiles. We will present results of CO retrievals from BBAERI and AERI in the presence of convective rolls to better understand how they mix CO. These observations demonstrate the utility of BBAERI and other AERIs for remotely monitoring boundary layer composition and dynamics.

Wilson, R. C.; McMillan, W. W.; Delgado, R.; Hoff, R.; Weldegabar, M.

2008-12-01

164

A simple model of the hurricane boundary layer  

Microsoft Academic Search

A simple, steady, moist, axisymmetric, constant depth, slab model for the hurricane boundary layer is investigated. High-resolution solutions of the boundary layer equations are obtained by integrating inwards from some large radius, at which it is assumed that geostrophic balance and convective-radiative balance exists. In all the solutions obtained, the tangential wind speed in the boundary layer approaches that above

Roger K. Smith

2002-01-01

165

Mixing length in low Reynolds number compressible turbulent boundary layers  

Microsoft Academic Search

The paper studies the effect of low Reynolds number in high-speed turbulent boundary layers on variations of mixing length. Boundary layers downstream of natural transition on plates, cones and cylinders, and boundary layers on nozzle walls without laminarization-retransition are considered. The problem of whether low Reynolds number amplification of shear stress is a result of transitional flow structure is considered.

D. M. Bushnell; A. M. Cary Jr.; B. B. Holley

1975-01-01

166

Stability and drag reduction in a boundary layer with microbubbles  

Microsoft Academic Search

When microbubbles are injected in a turbulent boundary layer, they promote a reduction of the local skin friction and a sharp mean velocity gradient between the two microbubble free regions in the boundary layer, i.e., the outer edge and the near wall region. In connection with the apparent stability of the bubbles in the boundary layer, the stability of a

Joao M. Neves

1988-01-01

167

THE EFFECTS OF PERIODIC WAKE STRUCTURES ON TURBULENT BOUNDARY LAYERS  

Microsoft Academic Search

Compressor and turbine blade boundary layers in axial-flow turbomachines are subject to periodically disturbed flow. This study modelled these conditions in a wind tunnel with circular cylinders traversing in front of a flat plate. Turbulent boundary layer velocity profiles on the flat plate were measured with a hot-wire anemometer. The turbulence intensity in the boundary layer was found to be

R. M. Holland; R. L. Evans

1996-01-01

168

Aircraft measurements within the planetary boundary layer over water  

Microsoft Academic Search

The basic overall objective of the program has been to develop a relatively inexpensive airborne sensing system for study of the marine boundary layer in support of the NAVAIR Marine Fog Investigation. This extends into the third dimension measurement of most of the significant parameters which have been studied from ships and land stations. The operational flexibility of the aircraft

R. Markson

1977-01-01

169

A Boundary-Layer Parametrisation for Martian General Circulation Model  

Microsoft Academic Search

The representation of the Planetary Boundary-Layer (PBL) is essential for use of General Circulation Models (GCM) results for planetary exploration missions design (prediction of near surface profiles of wind and temperature means, as well as turbulent fluctuations). However, the representation of the PBL was considered of secondary importances in early developments of General Circulation Models (GCM). Now, long duration simulations

R. Fournier; E. Deleersnijder; F. Hourdin; A. Lahellec; F. Forget; O. Talagrand

1996-01-01

170

ANALYTICAL PARAMETERIZATIONS OF DIFFUSION: THE CONVECTIVE BOUNDARY LAYER  

EPA Science Inventory

A brief review is made of data bases which have been used for developing diffusion parameterizations for the convective boundary layer (CBL). A variety of parameterizations for lateral and vertical dispersion, (sigma sub) and (sigma sub z), are surveyed; some of these include mec...

171

Unsteady boundary layers with an intelligent numerical scheme  

Microsoft Academic Search

A numerical method has been developed to represent unsteady boundary layers with large flow reversal. It makes use of the characteristic box scheme which examines the finite-difference grid in relation to the magnitude and direction of local velocity and reaches and implements a decision to ensure that the Courant, Friedricks and Lewey stability criterion is not violated. The method has

Tuncer Cebeci

1986-01-01

172

A boundary-layer collision in a curved duct  

Microsoft Academic Search

It is shown that the boundary layer, generated at the entrance to a curved duct by an incoming flow at large values of the Dean number, develops a collision structure in the neighborhood of the inner wall, after evolving for a finite distance down the duct. This result is not to be anticipated from the results of previous studies of

KEITH STEWARTSON; TUNCER CEBECI; K. C. Chang

1980-01-01

173

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

National Technical Information Service (NTIS)

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 vel...

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

2006-01-01

174

Stationary Flow in the Planetary Boundary Layer with an Inversion Layer and a Sea Breeze  

Microsoft Academic Search

An analysis is made of the effects of an inversion layer and a sea breeze on the stationary flow in a planetary boundary layer. It is shown that an intense temperature inver- sion virtually acts as a boundary surface which separates a planetry boundary layer into two layers. In the lower layer the flow is primarily thermally driven whereas in

S.-K. Kao

1960-01-01

175

The minisodar and planetary boundary layer studies  

SciTech Connect

The minisodar, in addition to being smaller than conventional sodar, operates at higher frequencies, obtains usable signal returns closer to the surface, and can use smaller range gates. Because the max range is generally limited to the lower 200 m above the surface, the minisodar is not able to interrogate the entire daytime atmospheric Planetary Boundary Layer (PBL); however it can be a very useful tool for understanding the PBL. In concert with other instruments, the minisodar can add significant new insights to our understanding of the PBL. This paper gives examples of past and potential uses of minisodars in such situations.

Coulter, R.L.

1996-06-01

176

Consideration on boundary-layer receptivity  

NASA Astrophysics Data System (ADS)

On the boundary layer receptivity, the present paper describes the results of numerical simulations and laboratory experiments to clarify the condition under which external disturbances such as sound and free stream turbulence can excite Tollmien Schlichting (T-S) waves. The most important finding is that the unsteady pressure gradient on the wall imposed by the external disturbance need to have such proper spatial scales as to match lambda(sub TS), the wavelength of T-S wave to be excited. In this case, the unsteady pressure gradient induces the vortical wave of the proper scale and then T-S wave.

Nishioka, Michio

1991-09-01

177

Chaotic motion in an oscillatory boundary layer.  

PubMed

The chaotic time oscillations in an incompressible fluid driven into motion by a harmonic time-varying pressure gradient is examined. Special attention is given to centrifugal destabilization of the viscous boundary layer. The basic flow is shown to be linearly unstable. For increasing modulation amplitude, the flow exhibits chaotic oscillations. The energy exchange between subharmonics and superharmonics of the least-stable spanwise wave number is considered. The presence of subharmonic Fourier modes are shown to accelerate the transition to temporally chaotic motion. (c) 1996 American Institute of Physics. PMID:12780290

Mehta, V.; Thompson, C.; Mulpur, A.; Chandra, K.

1996-12-01

178

Influence of an Axial Magnetic Field on the Steady Linear Ekman Boundary Layer  

Microsoft Academic Search

A hydromagnetic version of the Ekman boundary layer is developed in a simple form in order to study how the geophysically important Ekman suction velocity is affected by magnetic fields. The problem treated consists of a viscous, incompressible, conducting fluid in the presence of an infinite, flat, insulating boundary which rotates at speed ?0. Outside the boundary layer, the fluid

Peter A. Gilman; Edward R. Benton

1968-01-01

179

Coherent Structure of a Turbulent Boundary Layer in a Convected Reference Frame.  

National Technical Information Service (NTIS)

This is an interim annual report for an ongoing research program studying coherent structure in turbulent boundary layers. The design and development of a water channel facility for use in flow visualization studies of coherent turbulent boundary structur...

C. R. Smith S. L. Huston J. J. Brown

1977-01-01

180

A study of unsteady turbulent boundary layer separation under conditions relevant to helicopter rotor dynamics  

NASA Astrophysics Data System (ADS)

An experimental investigation focused on the study of the physics of unsteady turbulent boundary layer separation under conditions relevant to the dynamic stall process that occurs in helicopter rotors is presented. A flat boundary layer development plate allows for the growth of a turbulent boundary layer of thickness sufficient for high spatial resolution measurements. Downstream of the flat plate, a convex ramp section imposes a streamwise adverse pressure gradient that gives rise to boundary layer separation. In order to impose an unsteady pressure gradient, an airfoil equipped with leading edge plasma flow control is located above the ramp section. Plasma flow control is used to alternately attach and separate the airfoil flow which gives rise to unsteady turbulent boundary layer separation on the convex ramp. Measurements of the resulting unsteady turbulent boundary layer separation via phase-locked two-component PIV, unsteady surface pressure measurements, and high speed digital imaging capture and quantify the dynamics the separation process at the wall and throughout the unsteady boundary layer. Two-component LDA measurements are used to characterize the motions of ejection and sweep events within the unsteady boundary layer using a quadrant splitting technique. Large amplitude quadrant 4 sweep events are the most dynamically significant in the near wall region during the unsteady separation process. The adverse pressure gradient boundary layer profiles throughout the unsteady cycle collapse remarkably well when scaled with embedded shear layer parameters. The implications of the experimental results for the development of flow control strategies for unsteady boundary layer separation are discussed.

Schatzman, David M.

181

Navier-Stokes simulation of boundary-layer transition  

NASA Astrophysics Data System (ADS)

This report describes the successful efforts to computationally model the receptivity of the laminar boundary layer on a semi-infinite flat plat with an elliptic leading edge by a spatial simulation. The compressible flow is simulated by solving the governing full Navier-Stokes equations in general curvilinear coordinates by a finite difference method. First, the steady basic-state solution is obtained in a transient approach using spatially varying time steps. Then, a small-amplitude acoustic disturbances of the freestream velocity are applied as unsteady boundary conditions, and the governing equations are solved time-accurately to evaluate the spatial and temporal developments of the perturbation leading to instability waves (Tollmien-Schlichting waves) in the boundary layer. The effect of leading type radius on receptivity is determined.

Reed, Helen L.

1990-05-01

182

The influence of bulges on boundary-layer instability  

NASA Astrophysics Data System (ADS)

Local disturbances caused by a spanwise surface corrugation affect the position of the boundary-layer transition, and so the drag, of an object. This premature transition from laminar to turbulent flow is often associated with a separation of the laminar boundary-layer from its surface. Also the roughness-induced separation bubble provides an important link between the pressure and velocity fluctuations in the environment and the development of the disturbance in the laminar boundary-layer, i.e., the receptivity problem. To investigate the influence of a laminar separation bubble on boundary-layer instability, a separated flow generated by a velocity gradient over a flat plate was analyzed by direct numerical simulation using finite-difference solutions of the Navier-Stokes equations. The bubble acts as a strong amplifier of the instability waves and a highly nonlinear flow field is shown to develop downstream of the bubble. Consequently, the results of the direct numerical simulation differ noticeably from those of the classical linear stability theory proving the fact that the nonparallel effects together with the nonlinear interactions are crucial to this flow development. In the present paper, the effect of physical perturbations such as humps and hollows on boundary-layer instability is analyzed. This problem has been considered theoretically by several researchers (e.g., Nayfeh et al., 1987 and 1990; Cebeci et al., 1988). They used linear stability theory in their approach which does not include the nonparallel nor the nonlinear effects. Therefore, to account for these important effects in studying flow over humps and hollows the direct simulation technique is being implemented in generalized coordinates.

Elli, S.; Vandam, C. P.

183

Hair receptor sensitivity to changes in laminar boundary layer shape.  

PubMed

Biologists have shown that bat wings contain distributed arrays of flow-sensitive hair receptors. The hair receptors are hypothesized to feedback information on airflows over the bat wing for enhanced stability or maneuverability during flight. Here, we study the geometric specialization of hair-like structures for the detection of changes in boundary layer velocity profiles (shapes). A quasi-steady model that relates the flow velocity profile incident on the longitudinal axis of a hair to the resultant moment and shear force at the hair base is developed. The hair length relative to the boundary layer momentum thickness that maximizes the resultant moment and shear-force sensitivity to changes in boundary layer shape is determined. The sensitivity of the resultant moment and shear force is shown to be highly dependent on hair length. Hairs that linearly taper to a point are shown to provide greater output sensitivity than hairs of uniform cross-section. On an order of magnitude basis, the computed optimal hair lengths are in agreement with the range of hair receptor lengths measured on individual bat species. These results support the hypothesis that bats use hair receptors for detecting changes in boundary layer shape and provide geometric guidelines for artificial hair sensor design and application. PMID:20157224

Dickinson, B T

2010-02-16

184

Sources of iodine in the tropical marine boundary layer  

NASA Astrophysics Data System (ADS)

The importance of halogens in the chemical processes of the marine boundary layer has long been recognized, although many uncertainties remain. The role of iodine is particularly uncertain, especially with regard to its atmospheric sources. In this work, iodine chemistry in the tropical marine boundary layer was studied using a one dimensional model constrained to measured fluxes of iodinated hydrocarbons. The concentrations of iodocarbons were simultaneously measured in marine air and water during the RHaMBLe cruise, which took place in May-June 2007 around the Cape Verde archipelago. The sea-air fluxes of selected iodocarbons calculated from these measurements were used in a 1-D model to calculate the atmospheric concentrations of inorganic iodine species in the marine boundary layer at the latitude of Cape Verde (17 degrees N). The model was a revised version of MISTRA, with an updated module of gas-phase inorganic and DMS chemistry, and included the new iodine aqueous-phase chemical mechanism developed by Pechtl et al. (2007). The model results were qualitatively compared with the observations of IO taken at the Cape Verde Atmospheric Observatory during a previous campaign. The model was then used to determine the role of the measured iodocarbons as sources of iodine in the marine boundary layer and to study their impact on the concentration of tropospheric ozone.

Sommariva, R.; von Glasow, R.; Jones, C. E.; Hornsby, K. E.; Carpenter, L. J.; McFiggans, G.

2009-04-01

185

Propagation of propeller tone noise through a fuselage boundary layer  

NASA Astrophysics Data System (ADS)

In earlier experimental and analytical studies, it was found that the boundary layer on an aircraft could provide significant shielding from propeller noise at typical transport airplane cruise Mach numbers. In this paper a new three-dimensional theory is described that treats the combined effects of refraction and scattering by the fuselage and boundary layer. The complete wave field is solved by matching analytical expressions for the incident and scattered waves in the outer flow to a numerical solution in the boundary layer flow. The model for the incident waves is a near-field frequency-domain propeller source theory developed previously for free field studies. Calculations for an advanced turboprop (Prop-Fan) model flight test at 0.8 Mach number show a much smaller than expected pressure amplification at the noise directivity peak, strong boundary layer shielding in the forward quadrant, and shadowing around the fuselage. Results are presented showing the difference between fuselage surface and free-space noise predictions as a function of frequency and Mach number. Comparison of calculated and measured effects obtained in a Prop-Fan model flight test show good agreement, particularly near and aft of the plane of rotation at high cruise Mach number.

Hanson, D. B.; Magliozzi, B.

1984-01-01

186

Irregularity excitation associated with charged dust cloud boundary layers  

NASA Astrophysics Data System (ADS)

Irregularity generation associated with dust cloud expansion through a background plasma along a magnetic field is investigated. Because of the dust charging process, a boundary layer is produced, separating the dusty plasma generated and the background plasma. It is observed that under appropriate conditions, localized plasma irregularities may be generated in this boundary layer. Theoretical and computational models are used to study the evolution of relevant plasma instabilities thought to play a dominant role in irregularity production. An electron flow develops along the boundary layer of the dust cloud, and plasma irregularities are generated in response to this flow. Several aspects of the cloud's structure (thickness of the boundary layer, average particle size and density, collisional processes, and cloud expansion speed) and the ambient plasma are varied to determine the effect of these quantities on the resulting irregularities. The relevance of these results to past experimental observations in space and the laboratory for applications to the expansion of naturally or artificially created dust clouds is discussed.

Mahmoudian, A.; Scales, W. A.

2012-02-01

187

The role of acoustic feedback in boundary-layer instability  

NASA Astrophysics Data System (ADS)

In this paper, the classical triple-deck formalism is employed to investigate two instability problems in which acoustic feedback loop plays an essential role. The first concerns a boundary layer over a flat plate, on which two well separated roughness elements are present. A spatially amplifying Tollmien-Schlichting (T-S) wave between the roughness elements is scattered by the downstream roughness to emit a sound wave, which propagates upstream and impinges on the upstream roughness to regenerate the T-S wave thereby forming a closed feedback loop in the streamwise direction. Numerical calculations suggest that at high Reynolds numbers and for moderate roughness heights the long-range acoustic coupling may lead to global instability, which is characterized by self-sustained oscillations at discrete frequencies. The dominant peak frequency may jump from one value to another as the Reynolds number, or the distance between the roughness elements, is varied gradually. The second problem concerns supersonic 'twin boundary layers', which develop along the two well-separated parallel flat plates. The two boundary layers are in mutual interaction through the impinging and reflected acoustic waves. It is found that the interaction leads to a new instability that is absent in the usual unconfined boundary layer.

Wu, Xuesong

2013-10-01

188

Mean flow in turbulent boundary layers disturbed to alter skin friction  

Microsoft Academic Search

A comparative evaluation is made of recent developments in methods for the reduction of boundary layer drag, encompassing longitudinal surface riblets, 'outer layer' devices, (OLDs) and longitudinal convex surface curvature. The boundary layer of a surface with a longitudinal concave curvature is also studied, to complement the convex case results. The net drag reductions achievable by both riblets and OLDs

P. R. Bandyopadhyay

1986-01-01

189

On a numerical solution of incompressible turbulent boundary layer flow  

NASA Astrophysics Data System (ADS)

The application of the finite element-differential method for turbulent flow problems is considered for a steady two-dimensional incompressible boundary layer flow past a semiinfinite flat plate, in which the boundary layer region is composed of laminar, transitional, and turbulent regimes. The two-layer Cebeci-Smith (1974) closure model was chosen for the eddy viscosity. For the first numerical experiment, a fixed 16-element discretization model is selected with H chosen as 7.0 to cover a large range of local Reynolds numbers. The computed effective eddy profile exhibits oscillatory behavior in the inner region. The next experiment uses an adjustable 15-element model. Finally, a simple adaptive element generation technique for the turbulent flow problem is developed and successfully tested.

Hsu, C.-C.; Chang, T.-H.

190

Lidar probing the urban nocturnal boundary layer  

NASA Astrophysics Data System (ADS)

Lidar observations to study the nocturnal boundary layer in the atmosphere were made on selected evenings during December 1997 - March 1998 at the City University of Hong Kong (lat. 20 degree(s)20'6', long. 114 degree(s)10'18', at 57 m AMSL), Hong Kong. The ground-based Nd:YAG lidar has been operated to detect the vertical distribution of aerosols in the NBL at a subtropical urban site. It is shown that the vertical relative signal profiles can be employed to determine the heights of the single or multiple nocturnal inversions. In a clear sky and light wind evening transition period, the strong radiative cooling caused the air near the ground becomes stably stratified. The nocturnal inversion starts to emerge soon before sunset and grows vertically as the night progresses. The study also showed that the temporal evolution of the nocturnal inversion depth was rapidly increased soon after sunset and a slower rate in the midnight hours. The results of the study indicate that the vertical aerosol distribution in the multiple-layer is more complicated than that in the single-layer, of NBL. The early morning transition of the NBL is also discussed. A comparison of the lidar aerosol signals and radiosonde measurements was performed to evaluate the consistency of observations between the different systems.

Mok, T. M.; Leung, Kang M.; Ho, A. H.; Chan, J. C.; Ng, C. N.

1998-08-01

191

Planetary boundary layer feedbacks in climate system  

NASA Astrophysics Data System (ADS)

A remarkable feature of the ongoing global warming is the asymmetry in trends of the daily minima, ?min, and maxima, ?max, of the surface air temperature (SAT): ?min increases faster than ?max, so that the daily temperature range (DTR), ?max-?min, basically decreases. The state of the art general circulation and climate models (GCMs) do not reproduce it and predict approximately the same change rates for ?min and ?max. We propose that the difference in trends of ?min and ?max is caused by the strong stability dependence of the height, h, of the planetary boundary layer (PBL). Indeed, the daytime warming is associated with deep convective (C) PBLs (with the heights hC ~ 103m), in contrast to the nocturnal and/or wintertime cooling associated with shallower mid-latitudinal nocturnal stable (NS) PBLs (with hNS ~ 200m) and even shallower high-latitudinal long-lived stable (LS) PBLs (with hLS ~ 30-50m) developing during longer than night periods of the persistent surface cooling. As a result, one and the same increment, ?Q0, in the surface heat flux leads to only minor increment in ?max in deep C PBLs, but essential increments in ?min in shallow NS and especially NS PBLs. The latter type of the PBL has been discovered only recently and is not yet accounted for in modern GCMs. In the present paper, we derive theoretical estimates of the variations, ??min and ??max, in the SAT minima and maxima associated with the stable and convective PBLs, respectively, and by this means explain the observed asymmetry in the growth rates of ?min and ?max. To characterise the role of PBLs in the climate system, we introduce the concepts of local and general PBL feedbacks. Besides the strengths of feedbacks, we propose to take into account the reaction times of different mechanisms. The proposed concepts could be applied to different climate-change problems from global (as in this paper) to local, in particular, to those caused by the land-use modification.

Zilitinkevich, S.; Esau, I.

2009-09-01

192

Transitional and turbulent boundary layer with heat transfer  

NASA Astrophysics Data System (ADS)

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, ?w,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 Re?=1900 are found to display well-resolved signatures of hairpin vortices, which indicates the persistence of the hairpin forests.

Wu, Xiaohua; Moin, Parviz

2010-08-01

193

Hydrodynamical calculations towards steady state structures in boundary layers in accretion disks. 1: 1-D polytropic boundary layers  

NASA Astrophysics Data System (ADS)

We apply the one dimensional version of the multi-dimensional robust solver developed by Hujeirat & Rannacher (1994) to follow the viscous evolution of various models of polytropic boundary layers in accretion disks around a non-magnetic white dwarf. In this paper, we present the results of 13 different time-dependent hydrodynamical calculations. The results indicate that (1) no steady structure of the flow in the boundary layer is encountered. The solutions show that a quasi-standing shock is always present for very small alpha and high stellar rotation, (2) the rate of accreted angular momentum into the central object is much less than the corresponding Keplerian one, (3) the radial extent of the boundary layer (delta RBL) is much smaller than the vertical one as well as the radial extent of classical viscous boundary layers, (4) delta RBL increases with the rotational speed of the star, (5) an instability of the shock position is detected as well as quasi-periodic oscillations which are viscosity-dependent, (6) the polytropic equation of state with gamma = 2 yields unstable and chaotic behavior of the flow in the disk region.

Hujeirat, A.

1995-03-01

194

Linear Optimal Controllers for Turbulent Boundary Layers  

NASA Astrophysics Data System (ADS)

Several investigators have shown recently that controller design based on a system control-theoretic approach has led to significant viscous-drag reduction in turbulent boundary layers. Although these new approaches rely less on the investigator's physical insight into the flow (in contrast to most existing approaches), there still remain many design issues that need to be addressed. These are, but not limited to, the choice of cost functions for control and estimation, system model reduction, system dynamics estimation, robustness of the controlled system, and centralized vs. de-centralized control. We have performed a comparative study with different reduced-order models and cost functions in our numerical experiments of a low-Reynolds number turbulent channel flow in order to address some of the issues mentioned above. Results from these controllers and those from existing controllers and their implications will be presented.

Lim, Junwoo; Kim, John; Kang, Sung Moon; Speyer, Jason

2001-11-01

195

Boundary-layer instability noise on aerofoils  

NASA Astrophysics Data System (ADS)

An experimental and theoretical investigation has been carried out to understand the tonal noise generation mechanism on aerofoils at moderate Reynolds number. Experiments were conducted on a NACA0012 aerofoil section in a low-turbulence closed working section wind tunnel. Narrow band acoustic tones were observed up to 40 dB above background noise. The ladder structure of these tones was eliminated by modifying the tunnel to approximate to anechoic conditions. High-resolution flow velocity measurements have been made with a three-component laser-Doppler anemometer (LDA) which have revealed the presence of strongly amplified boundary-layer instabilities in a region of separated shear flow just upstream of the pressure surface trailing edge, which match the frequency of the acoustic tones. Flow visualization experiments have shown these instabilities to roll up to form a regular Kármán-type vortex street.

Nash, Emma C.; Lowson, Martin V.; McAlpine, Alan

1999-03-01

196

Turbulent boundary layer drag reduction using riblets  

NASA Astrophysics Data System (ADS)

An experimental study of low-speed turbulent boundary layer flow over longitudinally grooved surfaces (i.e., riblets) is discussed. Results obtained with a highly accurate drag balance indicate that v-groove riblet surfaces can produce consistent net drag reductions as large as 8 percent provided the height and spacing of the grooves in terms of law of the wall variables are less than 25 wall units. Momentum balances confirmed these direct drag measurements. Conditionally sampled data indicate that the burst frequency for riblets is approximately the same as that for a flat plate but turbulence intensity is reduced. Attempts to optimize the net drag reduction by varying riblet cross-sectional geometry and alignment are also discussed.

Walsh, M. J.

1982-01-01

197

Halogen chemistry in the marine boundary layer  

NASA Astrophysics Data System (ADS)

Important atmospheric sources of iodine include the air-sea exchange of biogenic iodocarbons, and the emission of I2 from macro-algae. The major source of bromine is the release of bromide ions from sea-salt aerosol. The subsequent atmospheric chemistry of these halogens (1), changes the oxidizing capacity of the marine boundary layer by destroying ozone and changing the hydroxyl radical concentration; (2), reacts efficiently with dimethyl sulphide and mercury (in the polar regions); and (3), leads to the formation of ultra-fine particles which may contribute to cloud condensation nuclei (CCN) and hence affect climate. This paper will report observations of IO, BrO, OIO and I2 made by the technique of differential optical absorption spectroscopy, in several contrasting marine environments: the equatorial mid-Atlantic (Cape Verde); mid-latitude clean coastal (Mace Head, Ireland); polluted coastal (Roscoff, France); and the polar marine boundary layer (Hudson Bay, Canada). Both IO and BrO are observed in all these locations at significant concentrations (> 1 pptv), and so have a major impact on (1) and (2) above. To complement the field campaigns we have also carried out wide-ranging laboratory investigation. A new study of OIO photochemistry shows that absorption in the visible bands between 490 and 630 nm leads to I atom production with a quantum yield of unity, which now means that iodine is a particularly powerful ozone-depleting agent. We have also studied the formation and growth kinetics of iodine oxide nano-particles, and their uptake of water, sulphuric acid and di-carboxylic organic acids, in order to model their growth to a size where they can act as CCN. Their ice-nucleating properties will also be reported.

Plane, J. M. C.; Gomez Martin, J. C.; Kumar, R.; Mahajan, A. S.; Oetjen, H.; Saunders, R. W.

2009-04-01

198

Boundary layer (shear-band) in frustrated viscoplastic flows  

NASA Astrophysics Data System (ADS)

We show that frustrated creep flows of yield stress fluids give rise to a boundary layer, which takes the form of a liquid region of uniform significant thickness separating two solid regions. In this boundary layer the shear rate is approximately constant for a given flow rate and the layer thickness varies extremely slowly with the flow rate.

Chevalier, T.; Rodts, S.; Chateau, X.; Boujlel, J.; Maillard, M.; Coussot, P.

2013-05-01

199

Saturn's low-latitude boundary layer: 2. Electron structure  

Microsoft Academic Search

The boundary of a planetary magnetosphere is the site of mass, momentum, and energy transport. This transport produces a layer of mixed solar wind and magnetospheric plasma inside and adjacent to the boundary. In the case of Earth, the electron structure of this layer is distinctive, and has been explained by models of the layer on open magnetic field lines.

A. Masters; A. P. Walsh; A. N. Fazakerley; A. J. Coates; M. K. Dougherty

2011-01-01

200

Behaviour of Atmospheric Boundary Layer Height at Dome C, Antarctica  

NASA Astrophysics Data System (ADS)

The Antarctic Atmospheric Boundary Layer presents characteristics which are substantially different from the mid-latitudes ABLs. On the Antarctic plateau two different extreme situations are observed. During the summer a mixing height develops during the warmer hours of the day although the sensible heat flux is reduced compared to that at mid-latitudes. During the winter a long lived stable boundary layer is continuously present, the residual layer is never observed, consequently the inversion layer is connected at the free atmosphere. To understand the stable ABL process the STABLEDC (Study of the STAble Boundary Layer Environmental at Dome C) experimental field was held at Concordia, the French Italian plateau station at Dome C, during 2005. In the same period the RMO (Routine Measurements Observations) started. The data included turbulence data at the surface, temperature profiles by a microwave profiler (MTP-5P), a mini-sodar and radio-soundings. In this work we will show the results of a comparison of the ABL height at Concordia (3233 m a.s.l) during the summer and the winter using direct measurements and parameterization. The winter ABL height was estimated directly using experimental data (radio-soundings and radiometer temperature and wind velocity profiles) and different methods proposed in literature. The stable ABL height was also estimated using the formulation proposed by Zilitinkevich et al. (2007) for the long-lived stable boundary layer. The correlation of ABL height with the temperature and wind speed is also shown. The summer mixing height was instead estimated by mini-sodar data and compared with the height given by the model suggested by Batchvarova and Gryning (1991) which use as input the turbulence data.

Pietroni, I.; Argentini, S.

2009-09-01

201

Mesoscale boundary layer evolution over complex terrain. Part I: Numerical simulation of the diurnal cycle  

Microsoft Academic Search

The continuous development of a meso-..beta..-scale boundary layer over sloping terrain upwind of a high mountain barrier was simulated through a complete diurnal cycle using a nonhydrostatic boundary-layer model. The simulation detailed the evolution of a 500--800-m deep nocturnal boundary layer containing 1--3 m s⁝š thermal circulations in the region upwind of a high ridge. Shear between the 5 m

David C. Bader; Thomas B. McKee; Gregory J. Tripoli

1987-01-01

202

Shock\\/boundary-layer interaction model for three-dimensional transonic flow calculations  

Microsoft Academic Search

A new computational model for three-dimensional shock-boundary layer interaction has been developed for use in viscous transonic flow calculations. In general, the new model has been found to be an improvement over the old method in which the boundary-layer equations are simply integrated through the shock. The basic empirical content of the method was tested against detailed boundary-layer measurements in

J. D. McLean; T. K. Matoi

1984-01-01

203

Advancing assessments on aerosol radiative effect by measurement-based direct effect estimation and through developing an explicit climatological convective boundary layer model  

NASA Astrophysics Data System (ADS)

The first part of the thesis assesses the aerosol direct radiative effect (ADRE) with a focus on ground-based AERONET and satellite MODIS measurements. The AERONET aerosol climatology is used, in conjunction with surface albedo and cloud products from MODIS, to calculate the ADRE and its normalized form (NADRE) for distinct aerosol regimes. The NADRE is defined as the ADRE normalized by optical depth at 550 nm and is mainly determined by internal aerosol optical properties and geographical parameters. These terms are evaluated for cloud-free and cloudy conditions and for all-mode and fine-mode aerosols. Because of stronger absorption (smaller single-scattering albedo) by the smoke over South Africa, the average NADRE over South America is ˜35% larger at the TOA but ˜38% smaller at the surface than that over South Africa. As the surface albedo varies from ˜0.1 to ˜0.35, it is observed that the dust NADRE ranges from -44 to -17 Wm-2tau-1 at the TOA and from -80 to -48 Wm-2tau -1 at the surface over the Saharan deserts, Arabian Peninsula, and their surrounding oceans. We find that the NADRE of fine-mode aerosol is larger at the TOA but smaller at the surface in comparison to that of all-mode aerosol because of its larger single-scattering albedo and smaller asymmetry factor. Cloudy-sky ADRE is usually not negligible for the observed cloud optical thickness but the TOA ADRE with clouds is sensitive to the relative location of aerosols and cloud layer. The high-resolution MODIS land surface albedo is applied, together with aerosol optical properties from an integrated MODIS retrieval and a chemical transport model simulation, to study the clear-sky ADRE over North Africa and the Arabian Peninsula for summer 2001, where surface is highly reflective with considerable spatial variability but poorly described by modeling. TOA ADRE shows the high spatial variability with close similarity to that of surface albedo. The albedos derived from the Common Land Model changes the regionally averaged positive TOA ADRE (3 ˜ 4 Wm-2) based on MODIS albedo to negative (˜ -2 Wm-2). The second part of the thesis is to develop a 2-D conceptual model for a climatological convective boundary layer over land as a persistent and distinct component in climate models, where the convective-scale motion is explicitly described by fluid dynamics and thermodynamics while the smaller scale effect is parameterized for a neutral stratification. Our conceptual model reasonably reproduces essential statistics of a convective boundary layer in comparison to large eddy simulations. The major difference is that our model produces a better organized and more constrained spatial distribution with coherent convective cells. The simulations for a climatological convective boundary layer are conducted for a prescribed constant and homogenous surface heat flux and a specified cooling term representing the background large scale thermal balance. The results show: the 2-D coherent structures of convective cells with horizontal and vertical characteristic scales comparable with PBL height; downward maximum velocities being 70-80% of the accompanying upward maxima; vertical profiles of a constant potential temperature and linear decreasing heat fluxes; a nearly proportional increase in the mixed-layer temperature and square-root increase in the velocity magnitude with increasing surface heat flux.

Zhou, Mi

204

Quadrature formulas for functions with a boundary-layer component  

NASA Astrophysics Data System (ADS)

Quadrature formulas for one-variable functions with a boundary-layer component are constructed and studied. It is assumed that the integrand can be represented as the sum of a regular and a boundary-layer component, the latter having high gradients that reduce the accuracy of classical quadrature formulas, such as the trapezoidal and Simpson rules. The formulas are modified so that their error is independent of the gradients of the boundary-layer component. Results of numerical experiments are presented.

Zadorin, A. I.; Zadorin, N. A.

2011-11-01

205

Self-preservation of rough-wall turbulent boundary layers  

Microsoft Academic Search

It is proposed that all fully rough-wall boundary layers should satisfy self-preservation more closely than a smooth-wall boundary layer. Previous work has shown that the self-preserving forms of the momentum and turbulent kinetic energy equations for a zero pressure gradient turbulent boundary layer, at sufficiently high Reynolds number, require that the wall shear stress is constant with x, and the

R. J. Smalley; R. A. Antonia; L. Djenidi

2001-01-01

206

Seasonal Simulations of the Planetary Boundary Layer and Boundary-Layer Stratocumulus Clouds with a General Circulation Model  

Microsoft Academic Search

The UCLA general circulation model (GCM) has been used to simulate the seasonally varying planetary boundary layer (PBL), as well as boundary-layer stratus and stratocumulus clouds. The PBL depth is a prognostic variable of the GCM, incorporated through the use of a vertical coordinate system in which the PBL is identified with the lowest model layer.Stratocumulus clouds are assumed to

David A. Randall; James A. Abeles; Thomas G. Corsetti

1985-01-01

207

Mixing of Ozone at Boundary Layer Top - A Lidar Study  

NASA Astrophysics Data System (ADS)

Studies of boundary layer dynamics and entrainment were carried out using field campaign data from the mobile aerosol and ozone profiler operated by the Facility for Ground based Atmospheric Measurements (FGAM) in the United Kingdom (UK). The UK-based field campaigns investigated include the Tropospheric ORganic CHemistry experiment (TORCH) in 2003, the Convective Storm Initiation Project (CSIP) in 2005 and the Leicester Air quality Measurement Project (LAMP) in 2007. The profiler is a DIfferential Absorption Lidar (DIAL) system that operates at five wavelengths simultaneously in the near ultraviolet (266nm, 289nm, 299nm, 316nm and 355nm) and has a range between 100m and 5km, depending on the meteorological conditions. Vertical aerosol backscatter profiles were calculated and ozone profiles of the boundary layer were deduced. The error in ozone mixing ratio was +/- 3ppbv. Unlike other ozone lidars, the UFAM profiler can be run at high temporal resolutions of down to 1 minute. From these profiles it was possible to follow entrainment events and the mixing of aerosol and ozone at the top of the convective boundary layer. Case studies are presented including re-entrainment of previously detrained polluted air and development of residual layers from preceding days. The chemical and physical properties of the air parcels were looked at in greater detail using accompanying instruments at each measurement site.

Ricketts, H. M. A.; Vaughan, G.; Norton, E. G.; Wareing, D. P.

2009-09-01

208

Studies of the Marine Boundary Layer at Tarapur  

NASA Astrophysics Data System (ADS)

Simultaneous observations were made of the Marine Boundary Layer at Tarapur, a site near Bombay on the sea coast, by acoustic sounder and instrumented tower. The meteorological tower was used to sense wind and temperature at various levels up to a height of 120 m while the acoustic sounder was used to examine the thermal structure of the boundary layer up to a height of 700 m. Data recorded for the year 1982 have been analysed. Analysis of the data shows that while the normal structures of thermal echoes and shear echoes represent the mixing depth of the atmospheric boundary layer, the often observed elevated layers are due to sea breeze reversals with their base giving a measure of the depth of the sea-breeze circulation during the day. A sea breeze has been detected during both spring (March to May) and autumn (October to December) months. The onset times are around 1000 hr during spring months and around noon during the autumn period, the height of development being respectively up to 500 and 350 m. The capability of the sodar to detect the base and thickness of the sea breeze, is clearly revealed.

Singal, S. P.; Aggarwal, S. K.; Pahwa, D. R.; Adiga, B. B.

1986-12-01

209

Observations of mesoscale and boundary-layer circulations affecting dust uplift and transport in the Saharan boundary layer  

NASA Astrophysics Data System (ADS)

Observations of the Saharan boundary layer, made during the GERBILS field campaign, show that mesoscale land surface temperature variations (which were related to albedo variations) induced mesoscale circulations, and that mesoscale and boundary-layer circulations affected dust uplift and transport. These processes are unrepresented in many climate models, but may have significant impacts on the vertical transport and uplift of desert dust. Mesoscale effects in particular tend to be difficult to parameterise. With weak winds along the aircraft track, land surface temperature anomalies with scales of greater than 10 km are shown to significantly affect boundary-layer temperatures and winds. Such anomalies are expected to affect the vertical mixing of the dusty and weakly stratified Saharan Air Layer (SAL). Mesoscale variations in winds are also shown to affect dust loadings in the boundary-layer. In a region of local uplift, with strong along-track winds, boundary-layer rolls are shown to lead to warm moist dusty updraughts in the boundary layer. Large eddy model (LEM) simulations suggest that these rolls increased uplift by approximately 30%. The modelled effects of boundary-layer convection on uplift is shown to be larger when the boundary-layer wind is decreased, and most significant when the mean wind is below the threshold for dust uplift and the boundary-layer convection leads to uplift which would not otherwise occur.

Marsham, J. H.; Parker, D. J.; Grams, C. M.; Grey, W. M. F.; Johnson, B. T.

2008-05-01

210

Computation of unsteady laminar boundary layers subject to traveling-wave freestream fluctuations  

NASA Astrophysics Data System (ADS)

Simple modifications to the boundary conditions for an unsteady boundary-layer calculation method developed by Cebeci and Carr (1978) are developed to accomodate both standing-wave and traveling-wave free stream fluctuations. Calculations using the modified procedure are presented for both types of fluctuations. The calculations are conducted for a laminar boundary layer developing on a flat plate in air. Comparisons are made with available experimental and analytical results. It is found that, depending on whether the free stream perturbations consist of a standing wave or traveling waves, unsteady laminar boundary layers exhibit quite different behavior.

Evans, R. L.

1989-11-01

211

Clues and modelling for missing boundary layer in cataclysmic variables  

SciTech Connect

Recently, it has become observationally evident that during a dwarf nova (DN) outburst, a significant portion of the gravitational energy accreted onto the white dwarf (WD) may not be radiated away instantly from a narrow boundary layer as predicted by the standard disk theory. Instead, it may be stored in the WD through various mechanisms and the radiative area may be much larger; thus the long-puzzling {ital missing boundary layer} may be accounted for when the response of the WD to the accretion is considered. The results from our group and collaborators on this aspect are outlined in the first part. A progress report on the development, of a new numerical model forms the second.

Huang, M.; Sion, E.M. [Villanova Univ., PA (United States); Sparks, W.M. [Los Alamos National Lab., NM (United States)

1996-12-31

212

Leading-edge effects on boundary-layer receptivity  

NASA Astrophysics Data System (ADS)

Numerical calculations are presented for the incompressible flow over a parabolic cylinder. The computational domain extends from a region upstream of the body downstream to the region where the Blasius boundary-layer solution holds. A steady mean flow solution is computed and the results for the scaled surface vorticity, surface pressure and displacement thickness are compared to previous studies. The unsteady problem is then formulated as a perturbation solution starting with and evolving from the mean flow. The response to irrotational time harmonic pulsation of the free-stream is examined. Results for the initial development of the velocity profile and displacement thickness are presented. These calculations will be extended to later times to investigate the initiation of instability waves within the boundary-layer.

Gatski, Thomas B.; Kerschen, Edward J.

1990-07-01

213

Calculation of hypersonic laminar boundary layers with chemical kinetics  

NASA Astrophysics Data System (ADS)

CLIM, a computer program developed to calculate the laminar boundary layer in axisymmetric steady hypersonic flows such as those on reentry vehicles, is described and demonstrated. CLIM takes into account the effects of transverse or longitudinal curvature, wall injection, and chemical reactions of equilibrium or nonequilibrium gases, permitting the treatment of ablation phenomena. The basic hypotheses are outlined; the program equations are derived; the finite-difference discretization is explained; and results are presented graphically for test problems involving a 10-deg-half-angle cone, a Shuttle-like hyperboloid, and the ablation of a carbon wall. When programmed on an IBM 3081, CLIM comprises about 3000 lines and can compute the wall stresses and the boundary-layer thickness, velocity, temperature, density, and concentration profiles for a 50-section body and 10 gas species in less than 1 min for nondissociated air, about 1 min for equilibrium air, and less than 10 min for nonequilibrium air.

Noel, F.; Boukhobza, P.

1986-11-01

214

Acoustic explorations of the upper ocean boundary layer  

NASA Astrophysics Data System (ADS)

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.

Vagle, Svein

2005-04-01

215

On Internal Gravity Waves Associated with the Stable Boundary Layer  

NASA Astrophysics Data System (ADS)

The stable planetary boundary layer at the baseof the residual layer supports internalwaves that are unambiguously boundary layer incharacter. Some of these wavesare instabilities and some are neutrally stable modes, but they all have critical levelsin the residual layer. These waves exist for a broad range of conditions and should bea major component of any ducted disturbance that propagates within ninety degreesof the wind direction. The wave properties can be computed without the numericaldifficulties usually associated with critical-level systems.

Chimonas, George

216

Helical circulations in the typhoon boundary layer  

NASA Astrophysics Data System (ADS)

Low-level wind data from the WSR-88D in Guam obtained in Typhoon Dale (1996) and Typhoon Keith (1997) are analyzed for coherent structures. Consistent with the results of previous studies of Atlantic hurricanes, velocity anomalies associated with coherent structures were found in the boundary layer of both storms. A total of 99 cases of coherent structures, also known as roll vortices, were documented during a 6 h evaluation period for each storm. Storm-relative roll location, roll vorticity, asymmetries in the upward and downward momentum fluxes, and signatures of circulations transverse to the mean flow associated with roll circulations were explored. The effects of terrain and convective precipitation systems, such as rainbands, on the occurrence of rolls were investigated. The results support and extend prior findings of roll observations, and can be used to help validate theoretical and numerical models of coherent structures within tropical cyclones. Moreover, the wind variations documented in this study may have application for wave runup and wind damage potential in tropical cyclones.

Ellis, Ryan; Businger, Steven

2010-03-01

217

Pattern Formation in Cathode Boundary Layer Microdischarges  

NASA Astrophysics Data System (ADS)

Direct current glow discharges in xenon between a planar, 100 ?m thick cathode and a ring shaped anode, separated by 250 ?m, were found to be stable up to atmospheric pressure. Photographs in the visible and VUV (172 nm) range of the spectrum show the transition from a homogeneous to a structured plasma. The plasma patterns, regularly arranged filaments that are most pronounced at lower pressures (100 Torr), show discrete changes when the current is decreased by fractions of mA. This selforganization of the plasma requires the presence of a second stable branch in addition to the abnormal cathode fall in the voltage-current density characteristic of the "cathode boundary layer" (CBL) discharges. A model of the cathode fall by von Engel and Steenbeck [1], which was modified to take thermal conduction as a loss process into account, in addition to radiation, indicates the presence of stable plasma filaments at current densities in the range from 10 to 100 A/cm^2, before transition into an arc. [1] A. von Engel and M. Steenbeck, "Elektrische Gasentladungen, ihre Physik und Technik," Vol. 2, p. 121. Work supported by NSF (CTS-0078618 and INT-0001438).

Schoenbach, K. H.; Moselhy, M. M.

2003-10-01

218

DNS of Hypersonic Turbulent Boundary Layers  

NASA Astrophysics Data System (ADS)

We present a direct numerical simulation database of supersonic and hypersonic turbulent boundary layers. The systematic procedure for initializing the turbulent flow fields at controlled Mach number and Reynolds number conditions is described. It is shown that simulation transients are less than 10% of the time required for gathering statistical data of the turbulent flows. The experimental conditions of Debičve ( Debieve, Gouin, and Gaviglio, Proceedings ICHMT/IUTAM Symposium on the Structure of Turbulence and Heat and Mass Transfer, Dubrovnik, 1981. ) ( Debieve, Thčse Université d'Aix Marseille II, 1983, Marseille, France. ) and Elena ( Eléna, Lacharme, and Gaviglio, In: Dybb, A. & Pfund, P.A. (eds), International Symposium on Laser Anemometry. ASME, 1985.) ( Eléna and Lacharme, ) are simulated and the simulation and experimental data are in excellent agreement. Using the direct numerical simulation database we perform parametric studies varying freestream Mach number in the range of 3 to 8 and wall-temperature condition for wall-to-freestream-temperature ratio of 2 to 5.5.

Pino Martin, M.

2004-11-01

219

Excitation of secondary instabilities in boundary layers  

NASA Astrophysics Data System (ADS)

The receptivity to fundamental and subharmonic secondary instabilities is analysed for two-dimensional boundary layers. Fundamental modes are excited by the direct scattering of Tollmien Schlichting (TS) waves over surface variations. The excitation of subharmonic modes stems from the combined scattering of acoustic free-stream disturbances and TS waves over surface variations. The surface variations are localized in their streamwise extent and are the result of roughness or suction. The velocity field is expanded in terms of small parameters characterizing the acoustic disturbance and the surface variation. The TS wave is included as part of the base flow leading to a non-homogeneous system with periodic coefficients governing the receptivity. The receptivity amplitudes show a strong dependence on the TS-wave amplitude, and for subharmonic modes a strong dependence on the TS-wave phase at the location of the surface variation. The receptivity analysis shows a significant bias toward fundamental modes of secondary instability for larger TS-wave amplitudes except for conditions of extremely high free-stream sound level. A combination of receptivity results and stability results suggests a bias toward subharmonic modes for TS-wave amplitudes below 0.5% and toward fundamental modes for TS-wave amplitudes above 0.5% (normalized by the local edge velocity).

Crouch, J. D.

1997-04-01

220

Computation and simulation of wake-generated unsteady pressure and boundary layers in cascades. Part 2: Simulation of unsteady boundary layer flow physics  

SciTech Connect

The unsteady pressure and boundary layers on a turbomachinery blade row arising from periodic wakes due to upstream blade rows are investigated in this paper. Numerical simulations are carried out to understand the effects of the wake velocity defect and the wake turbulence intensity on the development of unsteady blade boundary layers. The boundary layer transition on the blade is found to be strongly influenced by the unsteady wake passing. Periodic transitional patches are generated by the high turbulence intensity in the passing wakes and transported downstream. The time-dependent transition results in large unsteadiness in the instantaneous local skin friction coefficient and a smoother time-averaged transition curve than the one observed in the steady boundary layer. A parametric study is then carried out to determine the influence of wake parameters on the development of the unsteady blade boundary layers. It is shown that the unsteadiness in the blade boundary layer increases with a decrease in the axial gap, an increase in wake/blade count ratio, or an increase in the wake traverse speed. The time-averaged boundary layer momentum thickness at the trailing edge of the blade is found to increase significantly for higher wake/blade count ratio and larger wake traverse speed. Increase of the wake/blade count ratio also results in higher frictional drag of the blade.

Fan, S.; Lakshminarayana, B. [Pennsylvania State Univ., University Park, PA (United States). Center for Gas Turbines and Power

1996-01-01

221

Discrete dislocation dynamics simulation and continuum modeling of plastic boundary layers in tricrystal micropillars  

NASA Astrophysics Data System (ADS)

Since the mid 80s various gradient plasticity models have been developed for obtaining the plastic response of materials at the micron- and submicron- scales. In particular, gradient terms have been proven to be crucial for understanding size effects in constrained plastic flow, which are related to the emergence of plasticity boundary layers near passive (plastically not deformable) boundaries. In spite of the success of gradient theories in modeling boundary layer formation, there remain unresolved issues concerning the physical interpretation of the internal length scale involved in the theoretical formulation. Physically, boundary layer formation is related to the piling up of dislocations against the boundaries. This phenomenon is investigated by performing discrete dislocation dynamics (DDD) simulations on a tri-crystal with plastically non-deforming grain boundaries. Strain distributions are derived from the DDD simulations and matched with the results of gradient plasticity calculations, in order to identify the internal length scale governing the boundary layer width.

Aifantis, K. E.; Senger, J.; Weygand, D.; Zaiser, M.

2009-07-01

222

The Coriolis effect on coherent structures in planetary boundary layers  

Microsoft Academic Search

Coherent structures are often visible in atmospheric boundary layers as convective clouds and irregular fog. Large eddy simulations (LES) provide data to study the coherent structures by means of multivariate methods of statistical analysis. One of such methods is a proper orthogonal decomposition (POD). A POD can isolate most energetic three-dimensional structures in turbulent boundary layers. Coherent structures in planetary

Igor N Esau

2003-01-01

223

The Boundary Layer on a Flat Plate in Anisotropic Magnetohydrodynamics.  

National Technical Information Service (NTIS)

It is demonstrated that when calculating the boundary layer, despite the presence of thermal flow due to Larmor precession of electrons, it is possible to consider the temperature at the limit of the boundary layer as fixed. For this purpose the problem o...

V. B. Varanov A. G. Kukilovskii G. A. Lyubimov

1965-01-01

224

The mesoscale responses of a locally heated planetary boundary layer  

Microsoft Academic Search

The steady boundary layer responses that occur over the Great Lakes region during wintertime cold air outbreaks are examined using a 2-D, linear, analytic model. The boundary layer is modeled as an idealized, constantly stratified, viscous, rotating Boussinesq fluid that move uniformly between two horizontally infinite, rigid, stress free plates. The heat from the lakes is parameterized in terms of

Peter John Sousounis

1990-01-01

225

Impact of Injection Schemes on Transition in Hypersonic Boundary Layers.  

National Technical Information Service (NTIS)

Three geometries are explored for injecting CO2 into the boundary layer of a sharp five degree half-angle cone. The impact of the injection geometry, namely discrete injection holes or a porous conical section, on tripping the boundary layer is examined, ...

H. G. Hornung I. A. Leyva J. Shepherd J. S. Jewell S. Laurence

2009-01-01

226

Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer.  

National Technical Information Service (NTIS)

An experimental investigation of the response of a hypersonic turbulent boundary layer to a step change in surface roughness has been performed. The boundary layer on a flat nozzle wall of a Mach 6 wind tunnel was subjected to abrupt changes in surface ro...

T. Kubota D. E. Berg

1977-01-01

227

Vertical Transport of Water in the Martian Boundary Layer.  

National Technical Information Service (NTIS)

We are continuing our examination of the transport of H2O through the martian boundary layer, and we have written a one-dimensional numerical model of the exchange of H2O between the atmosphere and subsurface of Mars through the planetary boundary layer (...

A. P. Zent R. M. Haberle H. C. Houben

1993-01-01

228

Entrainment process of carbon dioxide in the atmospheric boundary layer  

Microsoft Academic Search

Aircraft and surface measurements of turbulent thermodynamic variables and carbon dioxide (CO2) were taken above a grassland in a convective atmospheric boundary layer. The observations were analyzed to assess the importance of the entrainment process for the distribution and evolution of carbon dioxide in the boundary layer. From the observations we were able to estimate the vertical profiles of the

Jordi Vilŕ-Guerau de Arellano; Beniamino Gioli; Franco Miglietta; Harm J. J. Jonker; Henk Klein Baltink; Ronald W. A. Hutjes; Albert A. M. Holtslag

2004-01-01

229

Bristled shark skin: a microgeometry for boundary layer control?  

Microsoft Academic Search

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

230

Boundary layer phenomena in combustion-driven MHD power generators  

Microsoft Academic Search

An analytic and experimental study of boundary layer phenomena in combustion-driven MHD power generators has been conducted. Measurements of heat transfer rates and velocity, temperature, and electron number density profiles were compared with numerical calculations. The analysis is based on the two-dimensional boundary layer equations. The velocity, temperature, and electron number density profiles were measured at the downstream end of

J. W. Daily

1975-01-01

231

Beta limitation of matter-antimatter boundary layers  

Microsoft Academic Search

A model for a boundary layer which separates a cloud of matter from one of antimatter in a magnetized ambiplasma, in which steady pressure equilibrium ceases to exist when a certain beta limit is exceeded is discussed. The latter is defined as the ratio between the ambiplasma and magnetic field pressures which balance each other in the boundary layer. Thus,

B. Lehnert

1987-01-01

232

On fluid dynamic drag reduction in some boundary layer flows  

Microsoft Academic Search

Summary The problem of boundary layer flow on a flat plate with injection and a constant velocity opposite in direction to that of the uniform mainstream is analyzed. It is shown that the solution of this boundary layer problem not only depends on the ratio of the velocity of the plate to the velocity of the free stream (?), but

K. Vajravelu; R. N. Mohapatra

1990-01-01

233

Effects of coastal forcing on turbulence and boundary- layer structure  

Microsoft Academic Search

Coastal mountains of significant elevation impose constraints for the surrounding flow. The aim of this study is to describe the modifications of the marine atmospheric boundary layer that occur offshore of the west coast of the United States. Aircraft measurements, up to 1000 km off the coast from two experiments, are used. This boundary layer is capped by a subsidence

Linda Maria Viktoria Strom

1999-01-01

234

Hydrodynamic resistance of concentration polarization boundary layers in ultrafiltration  

Microsoft Academic Search

The influence of concentration polarization on the permeate flux in the ultrafiltration of aqueous Dextran T70 solutions can be described by (i) the osmotic pressure model and (ii) the boundary layer resistance model. In the latter model the hydrodynamic resistance of the non-gelled boundary layer is computed using permeability data of the Dextran molecules obtained by sedimentation experiments. It is

J. G. Wijmans; S. Nakao; Berg van den J. W. A; F. R. Troelstra; C. A. Smolders

1985-01-01

235

Microbubble Drag Reduction in Liquid Turbulent Boundary Layers  

Microsoft Academic Search

The interactions between a dense cloud of small bubbles and a liquid turbulent boundary layer are reviewed on the basis of available experimental observations to understand and quantify their capability for reducing skin friction. Gas bubbles are generally introduced into the boundary layer by injection through a porous surface or by electrolysis. After injection, the bubbles stay near the wall

Charles L. Merkle; Steven Deutsch

1992-01-01

236

A planetary boundary layer observational capability in Kansas  

SciTech Connect

An initiative is underway to establish the Argonne Boundary Layer Experiments (ABLE) facility to provide continuous, long-term observations of the planetary boundary layer (PBL) with state-of-the-art instruments. Planning for ABLE began during 1995, and implementation is expected to be mostly complete by 1998. ABLE will be located within the area now occupied by the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site of DOE`s Atmospheric Radiation Measurement (ARM) program. The Argonne facility will concentrate on measuring at spatial scales considerably smaller than addressed with CART. When it is fully functional, ABLE will offer atmospheric scientists the opportunity to remotely {open_quote}collect{close_quote} data in real time without necessarily leaving their home offices. Specialized computer analysis and visualization software will be developed and provided by ABLE to facilitate analysis by remote users. ABLE will host specialized field campaigns for which it can provide supplementary measurements and the required facilities for shorter-term instrument deployments. In addition, ABLE will function as the proving ground for new technologies for atmospheric boundary layer research. 1 ref., 1 fig.

Wesely, M.L.; Coulter, R.L.; Klazura, G.E. [and others

1997-03-01

237

Boundary layer structure during sea breeze conditions at Ahtopol, Bulgaria  

NASA Astrophysics Data System (ADS)

Continuous sodar (Scintec MFAS) and ultrasonic anemometer (Typhoon - Obninsk make) measurements were initiated in summer 2008 at the meteorological observatory of Ahtopol at the Black Sea coast (south-east Bulgaria) under a Bulgarian-Russian collaborative programme. These observations of high resolution form the basis for studies of the atmospheric boundary layer turbulence and vertical structure at a coastal site. This sodar is unique in Bulgaria and provides the first continuous high resolution data on the wind profile up to 400 - 500 m above the ground. In addition, the continuous turbulence parameters monitoring allows atmospheric boundary studies needed for different applications. The meteorological observatory at Ahtopol is under development as a background atmospheric composition station in coastal area and the wind data are essential for the studies of gases exchange under breeze conditions. The measurements revealed quite different sea breeze seasons during the years 2008 to 2011 and within the individual seasons, a number of different sea breeze types were identified depending on the interaction of local and larger-scale forcing. In this study we investigate the turbulence parameters and the vertical structure of the boundary layer related to only to sea breeze conditions. We also study the wind profile within the first 400 - 500 m above the ground. For the surface layer, we test the free convection theory against the sodar observations.

Barantiev, D.; Batchvarova, E.; Novitzky, M. A.

2012-04-01

238

Measurements of Instability and Transition in Hypersonic Boundary Layers  

NASA Astrophysics Data System (ADS)

Several studies on boundary-layer instability and transition have been conducted in the Boeing/AFOSR-Mach 6 Quiet Tunnel (BAM6QT) and the Sandia Hypersonic Wind Tunnels (HWT) at Mach 5 and 8. The first study looked at the effect of freestream noise on roughness- induced transition on a blunt cone. Temperature-sensitive paints were used to visualize the wake of an isolated roughness element at zero deg angle of attack in the BAM6QT. Transition was always delayed under quiet flow compared to noisy flow, even for an effective trip height. The second study measured transitional surface pressure fluctuations on a seven degree half-angle sharp cone in the HWT under noisy flow and in the BAM6QT under noisy and quiet flow. Fluctuations under laminar boundary layers reflected tunnel noise levels. Transition on the model only occurred under noisy flow, and fluctuations peaked during transition. Measurements of second- mode waves showed the waves started to grow under a laminar boundary layer, saturated, and then broke down near the peak in transitional pressure fluctuations. The third study looked at the development of wave packets and turbulent spots on the BAM6QT nozzle wall. A spark perturber was used to generate controlled disturbances. Measurements of the internal structure of the pressure field of the disturbances were made.

Casper, K. M.; Schneider, S. P.; Beresh, S. J.

2011-08-01

239

Automated large-eddy simulations of realistic atmospheric boundary layers  

NASA Astrophysics Data System (ADS)

Large-eddy simulations (LES) are the most realistic numerical model available for studies of flow in the Atmospheric Boundary Layer (ABL). However, since large scale processes cannot be solved within the LES domain of typically 10x10x5km, LES is nearly always limited to idealized circumstances. In this study, we use the mean state of a regional model to drive and relaxing LES with the analysis of a regional model, in analogy to the way single column models (SCMs) are driven. That way, many different days can be studied, each with their own meteorological characterization. Specifically, diurnal cycles of clear and cloud-topped boundary layers are investigated, including effects of precipitation and soil feed backs. The focus of this study lies on the meteorology around the Cabauw tower in the Netherlands during May 2008. During this month, Cabauw was the focus of the Intensive Observation Period of the EUCAARI-IMPACT campaign, which gives a very rich set of observations to compare with. Given a sufficiently large relaxation time, boundary layer processes are given the room in LES to fully develop, and characteristics such as cloud height and boundary layer thermodynamics compare well with the environment. In order to robustly run LES for the various days without strong assumptions, it turns out to be important to have a reliable radiation and surface model. The LES results are embedded in an intercomparison test bed, where LES, several SCMs, and observations can be compared with each other on a daily basis. In this way, a wide range of studies can be done. For instance, the role of individual processes, like radiation, cloud microphysics, or soil and vegetation, can be directly assessed in the controlled environment of LES. Furthermore, the availability in LES of all relevant variables in three dimensions and with a high time resolution in LES allows us to diagnose relations that form the basic assumptions of large-scale model parametrizations.

Heus, T.; Siebesma, A. P.; Neggers, R. A. J.

2009-09-01

240

On the unsteady hydromagnetic boundary layer flow induced by torsional oscillations of a disk  

Microsoft Academic Search

A study is made of the unsteady hydromagnetic boundary layer flow induced by the torsional oscillations of an infinite disk in an electrically conducting rotating fluid in the presence of a uniform magnetic field. Information is obtained about: (i) the structure of the steady and the unsteady flow field; (ii) the development of the Stokes-Ekman-Hartmann boundary layers with their physical

L. Debnath

1974-01-01

241

Turbulent boundary layer at the initial portion of a pipe with rough walls  

Microsoft Academic Search

The development of a turbulent boundary layer at the initial portion of a pipe with rough walls is considered in the framework of the boundary-layer theory. It is shown that the consideration of roughness can be carried out by introducing into the “standard” law of friction a function which takes into account this factor. An experimental investigation is carried out

V. V. Kuz'min; A. A. Tupichenkov; A. V. Fafurin

1971-01-01

242

Prediction of the effects of surface curvature and rotation in a turbulent boundary layer  

NASA Astrophysics Data System (ADS)

A method has been developed to predict the effects of the surface curvature and rotation in the turbulent boundary layer. The Cebeci-eddy-viscosity model and Richardson number correction were checked for fourteen tests. The boundary layer equations are solved by the 'Box' numerical procedure. The results are presented and compared with experimental data.

Kortikov, N.; Hirsch, Ch.

243

Turbulent boundary layer flow subject to streamwise oscillation of spanwise wall-velocity  

Microsoft Academic Search

Direct numerical simulations have been performed to study the effect of a stationary distribution of spanwise wall-velocity that oscillates in the streamwise direction on a turbulent boundary layer. For the first time, a spatially developing flow with this type of forcing is studied. The part of the boundary layer which flows over the alternating wall-velocity section is greatly affected with

M. Skote

2011-01-01

244

Drag reduction in a flat-plate boundary layer flow by polymer additives  

Microsoft Academic Search

This paper presents a theoretical study on the velocity distribution and the friction factor of boundary layer flows with polymer additives starting from the concept of ``stress deficit.'' A novel method of order of magnitude analysis is developed, which converts the governing equations of boundary layer flow into a solvable ordinary differential equation, thus the total shear stress distribution is

Shu-Qing Yang; G. Dou

2005-01-01

245

Determination of the Atmospheric Boundary-Layer within the Urban Environment  

Microsoft Academic Search

In this paper, novel mathematical methods are implemented. In particular a mesh refinement technique is developed that allows the larger scale topographical effects on the atmospheric boundary-layer to be taken into account, yet still enabling the fine resolution of the boundary-layer within the smaller scale of the urban environment, as well as a parameterisation for urban effects. In the latter,

Lionel Elliott; Derek Binns Ingham; Stephen David Wright

2006-01-01

246

Analytical study of the neutral stability of a model hypersonic boundary layer  

Microsoft Academic Search

The neutral modes of a hypersonic boundary layer flow over an adiabatic flat plate are considered. A formulation of the governing second-order linear equation for the pressure disturbance is developed that lends itself to the application of the WKB method over the entire boundary layer. This formulation provides analytic eigenvalues and eigenfunction relations for the pressure distrubances and is applicable

Daniel R. Bower; Ching Shi Liu

1994-01-01

247

Dusty boundary layer in a surface-burst explosion  

SciTech Connect

Dusty boundary layers are an inherent feature of explosions over ground surfaces. Detailed knowledge of dusty boundary layer characteristics is needed in explosion safety analysis (e.g., to calculate the drag loads on structures). Also, to predicct the amount of dust in the rising fireball of an explsion, one must know the dusty boundary layer swept up during the positive and negative phases of the blast wave and how much of this boundary layer dust is entrained into the stem of the dust cloud. This paper describes the results of numerical simulations of the dusty boundary layer created by a surface burst explosion. The evolution of the flow was calculated by a high-order Godunov code that solves the nonsteady conservation laws.

Kuhl, A.L. [Lawrence Livermore National Lab., El Segundo, CA (United States); Ferguson, R.E.; Chien, K.Y.; Collins, J.P. [Naval Surface Warfare Center, Silver Spring, MD (United States)

1993-08-01

248

Effects of Normal Swirling Jet on a Boundary Layer Flow  

NASA Astrophysics Data System (ADS)

To investigate the effects of hurricane flow on its surrounding boundary layer, a normal counter clockwise swirling jet at 14.4 m/s average velocity is created in a flat-plate boundary layer flow at 8.1 m/s. The boundary layer parameters and, mean and root mean-squared velocity data are measured at the four quadrants (port, windward, starboard and leeward) of the swirling jet using a Pitot tube and a hot wire anemometer. The boundary layer flow is decelerated due to the opposing flow created by the swirl on the port side. The starboard side flow is accelerated due to the swirl direction being parallel to the freestream. On the windward side, the boundary layer flow is slightly decelerated. At this location the swirl direction is normal to the free stream and acts as wall with slippage. For the leeward location boundary layer flow is decelerated due to the wake and blockage effects created by the normal swirling jet. The boundary layer turbulence intensity on the port side increases to its peak at about half boundary layer thickness and drops as it approaches the free stream. Whereas the boundary layer intensity on the starboard side is small near the wall but increases linearly up until it reaches two times the boundary layer thickness. From that point on it decreases linearly. There is a greatest loss of momentum or momentum flux on the leeward location, primarily due to the wake and flow blockage. The Log-law appears to be completely washed-out in the port side velocity profile

Caballero, Irving I.; Subramanian, Chelakara S.

2002-11-01

249

Entrainment and detrainment from a model boundary layer  

NASA Astrophysics Data System (ADS)

A two-dimensional inviscid flow with piecewise-uniform regions of vorticity is studied as a model of the high-Reynolds-number mixing between a boundary layer and an outer layer. It is found that an initial disturbance to the boundary-layer thickness breaks down into a wave field plus, if the initial disturbance is steep enough, a volume of entrained fluid. The entrained fluid is drawn from the outer layer and then folded into a crevice. The crevice stretches, and eventually pinches off, becoming completely enveloped within the boundary layer. Though the entrained fluid is slender in shape, its volume is significant. Very steep disturbances result in detrainment, in which a small parcel of fluid detaches from the boundary layer and curls into the outer layer. The v-velocity field agrees with many features of Kovasznay et al.'s (1970) measurements in the turbulent boundary layer. This correspondence with fully turbulent flow, plus the characteristics of folding and stretching large volumes of fluid, make the process presented here a candidate for a mechanism by which high-Reynolds-number boundary layers mix with outer-layer fluid.

Sun, Meihong; Lichter, Seth

2003-06-01

250

Drag reduction in a flat-plate boundary layer flow by polymer additives  

NASA Astrophysics Data System (ADS)

This paper presents a theoretical study on the velocity distribution and the friction factor of boundary layer flows with polymer additives starting from the concept of ``stress deficit.'' A novel method of order of magnitude analysis is developed, which converts the governing equations of boundary layer flow into a solvable ordinary differential equation, thus the total shear stress distribution is obtained, then the formulas for the mean velocity profiles and the friction factor for a boundary layer flow are derived after introducing appropriate expressions for the ``effective viscosity'' and the thickness of viscous sublayer. The derived velocity equation is able to depict the velocity from a solid wall to the outer edge of boundary layer with or without polymer additives using only one fitted parameter D* that is a function of polymer species, its concentration, and Reynolds number. By integrating the velocity profiles, the friction factor and the thickness of boundary layer development are obtained. Experimental data agree well with the theoretical results.

Yang, Shu-Qing; Dou, G.

2005-06-01

251

Coupling the dynamics of boundary layers and evolutionary dunes.  

PubMed

A theoretical formulation and corresponding numerical solutions are presented for fluid flow and sediment transport past evolutionary sand dunes. Time-dependent curvilinear coordinates are employed to fully couple flow aloft with the developing landform. The differential conservation law that defines shape of the lower boundary depends on details of local surface stress, thereby favoring the large eddy simulation of the boundary layer. To shrink the gap between the time scales characteristic of planetary boundary layer flows O(10(3)) s and sand dune evolution O(10(6)) s, a hypothetical "severe-wind scenario" is adopted with the saltation flux amplified up to 3 orders of magnitude. While the results are largely insensitive to the rescaling, the efficacy of computations is greatly improved. The flux-form partial differential equation for the interface profile--via saltation and sand avalanches--is formulated as an advection-diffusion equation, to facilitate discrete integrations. Numerical experiments verify the adopted theoretical framework by reproducing scaling results reported in the literature. The versatility of the approach is illustrated with evolution of a sandhole--an example of application likely never addressed in the literature, yet realizable in nature. PMID:19518224

Ortiz, Pablo; Smolarkiewicz, Piotr K

2009-04-20

252

Matter-antimatter boundary layers with a magnetic neutral sheet  

Microsoft Academic Search

An earlier model of matter-antimatter boundary layers has been extended to include a sheet with a reversed magnetic field. The derived layer thickness is largely unaffected by a magnetic field-reversal, provided that the width of the corresponding magnetic neutral sheet becomes substantially smaller than the layer thickness. This condition is likely to be satisfied within parameter ranges of cosmical interest.

B. Lehnert

1978-01-01

253

Saltating Particles in a Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

Experiments on aeolian sand transport were carried out in a wind tunnel at the University of Aarhus in Denmark for a wide range of wind speeds. The saltating particles were analyzed using imaging techniques (PIV and PTV). Vertical profiles of particle concentration and velocity were extracted. The particle concentration was found to decrease exponentially with the height above the bed and the characteristic decay height was independent of the wind speed [1]. In contrast with the logarithmic profile of the wind speed, the particle velocity was found to vary linearly with the height. In addition, the particle slip velocity is finite and invariant with the wind speed. These results are shown to be closely related to the features of the splash function that characterizes the impact of the saltating particles onto a sand bed. A numerical simulation was developed that explicitly incorporates low velocity moments of the splash function in a calculation of the boundary conditions that apply at the bed [1]. The overall features of the experimental measurements are well reproduced by the simulation.

Valance, A.; El Moctar, A. Ould; Dupont, P.; Cantat, I.; Jenkins, J. T.

2010-05-01

254

Marine Boundary-layer Height Estimated From The Hirlam Model  

NASA Astrophysics Data System (ADS)

Two weeks of radiosonde measurements of the boundary-layer height over a small island (Christiansoe) in the Baltic Sea is discussed. During the experiment the water was generally warmer than the air which is a typical feature of the Baltic Sea during the late summer, autumn and early winter. This results in a positive heat flux over the sea and the generation of convectively driven marine boundary layer. The boundary-layer heights that could be inferred from the measurements were compared to estimates derived from the operational numerical weather prediction High Resolution Limited Area Model HIRLAM (a version of the Swedish Meteorological and Hydrological Institute with grid resolution of 22.5 km times 22.5 km). The hight of the boundary layer does not form a part from the HIRLAM model, but has to be estimated from them. In this study we applied and compared two methods to extract the boundary- layer height from the Hirlam output data; both are based on a bulk Richardson-number approach. For both methods the boundary-layer height is defined as the height where the bulk Richardson number reaches a critical value, typically 0.25. For southwesterly winds it was found that a relatively large island (Bornholm) lying 20 km upwind of the measuring site influences the boundary-layer height. In this situation Richardson- number based methods with the HIRLAM data fail most likely because the island of Bornholm and the water fatch to the measuring site are about the size of the grid resolution of HIRLAM model and therefore poorly resolved. The grid resolution is too coarse to reflect the mesoscale features that control the boundary-layer height over Christiansoe. For northerly wind the water fatch to the measuring site is about 100 km and the Richardson-number methods reproduce the measured height of the boundary layer. This suggests that the HIRLAM model adequately resolves a water fatch of 100 km with respect predictions of the height of the marine boundary layer. Originally the critical Richarson numbers for both methods are determined from measurements of the height of the boundary layer over land. In this study the boundary-layer height predicted by one of the Richardson-number methods is systematically higher than for the other. This suggests, considering the low roughness of the sea surface, that there is dependence between the surface roughness and the critical Richardon numbers and that the dependence is not the same for the numbers used.

Batchvarova, E.; Gryning, S.-E.; Jensen, N.-O.

255

Boundary layer receptivity to convected gusts and sound  

NASA Astrophysics Data System (ADS)

The receptivity of a laminar boundary layer to sound and convected gusts is examined experimentally, considering the coupling between these external disturbances and the boundary layer in the vicinity of a 24:1 elliptic leading edge, a porous strip, and a forward-facing step. A conventional loudspeaker generates the acoustic disturbance, and an array of oscillating ribbons produces a vortical disturbance in the form of a periodic convected gust. Techniques for decoupling the excitation from the boundary layer response and comparisons of receptivity mechanisms are discussed.

Parekh, D. E.; Pulvin, P.; Wlezien, R. W.

256

Boundary Layer Control by Means of Plasma Actuators  

SciTech Connect

The development of controlled transition in a flat-plate boundary layer is investigated using Large Eddy Simulations (LES) with the dynamic Smagorinsky model. The analysis of flow control with the objective to optimize the effects of Tollmien-Schlichting waves on a flat plate by means of plasma actuators was studied. The plasma effect is modeled as a body force in the momentum equations. These equations are solved in a uniform grid using a 2nd-order finite difference scheme in time and space. The response of plasma actuators operating in different time-dependent conditions, produced by transient or periodic inputs at different frequencies, is also analyzed.

Quadros, R. [UFRGS/PPGMAp-TUD-Stroemungslehre und Aerodynamik, Technische Universitaet Darmstadt, Petersenstr. 30, 64287 Darmstadt (Germany); Bortoli, A. L. de [UFRGS/DMPA-Departamento de Matematica Pura e Aplicada, Bento Goncalves 9500, Agronomia-P.O. Box 15080, Porto Alegre-RS (Brazil); Tropea, C. [TUD/SLA-Stroemungslehre und Aerodynamik, Technische Universitaet Darmstadt, Petersenstr. 30, 64287 Darmstadt (Germany)

2007-09-06

257

Evaluation of Local Similarity Functions in the Convective Boundary Layer.  

NASA Astrophysics Data System (ADS)

A parameterization method developed by Sorbjan is used to derive expressions for various statistical moments of vertical velocity, potential temperature, and humidity (or passive scalar concentration) in the convective boundary layer. The method is based on decomposing statistical moments into nonpenetrative and residual components, and their local (height-dependent) scaling. The resulting expressions are compared with atmospheric and laboratory data, and also with the results of large-eddy simulation models. An agreement between the similarity functions and the experimental data is obtained.

Sorbjan, Zbigniew

1991-12-01

258

Drag on intruders in granular beds: A boundary layer approach  

NASA Astrophysics Data System (ADS)

We performed a parametric study of the drag on vertical intruders with uniform cross sections of different sizes and shapes, from which we developed a semiempirical model. Baffling techniques were used to isolate the contributions of the intruder's different subsurfaces, and we observed size effects and force focusing on edges. We propose a boundary layer approach, whereby the drag is the surface integral of an effective stress over a monolayer of particles contacting the intruder. The stress has a simple lithostatic dependence and is a function of the orientation relative to the intruder's direction of motion. This approach is experimentally verified and is consistent with the semiempirical model.

Goldsmith, Jonathan; Guo, Hong; Hunt, Shelby N.; Tao, Mingjiang; Koehler, Stephan

2013-09-01

259

Experimental study of unsteady turbulent boundary layer separation under conditions relevant to dynamic stall  

NASA Astrophysics Data System (ADS)

An experimental investigation focused on the study of the physics of unsteady turbulent boundary layer separation under conditions relevant to the dynamic stall process is presented. A flat boundary layer development plate allows for the growth of a turbulent boundary layer of thickness sufficient for high spatial resolution measurements. Downstream of the flat plate, a convex ramp section imposes a streamwise adverse pressure gradient that gives rise to boundary layer separation. In order to impose an unsteady pressure gradient, an airfoil section is located above the convex ramp. Leading edge plasma flow control is used to alternately attach and separate the airfoil flow which gives rise to unsteady turbulent boundary layer separation on the convex ramp. Measurements of the resulting unsteady turbulent boundary layer separation via phase-locked two-component PIV, unsteady surface pressure measurements, and wall-mounted hot-films quantify the dynamics of the separation process at the wall and throughout the unsteady boundary layer. Two-component LDA measurements are used to characterize the motions of ejection and sweep events within the unsteady boundary layer using a quadrant splitting technique.

Schatzman, David; Thomas, Flint

2010-11-01

260

Vertical ozone characteristics in urban boundary layer in Beijing.  

PubMed

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. PMID:23129408

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

2012-11-06

261

Non-uniqueness in wakes and boundary layers  

NASA Astrophysics Data System (ADS)

In streamlined flow past a flat plate aligned with a uniform stream, it is shown that (a) the Goldstein near-wake and (b) the Blasius boundary layer are nonunique solutions locally for the classical boundary layer equations, whereas (c) the Rott-Hakkinen (1965) very-near-wake appears to be unique. In each of (a) and (b) an alternative solution exists, which has reversed flow and which apparently cannot be discounted on immediate grounds. So, depending mainly on how the alternatives for (a), (b) develop downstream, the symmetric flow at high Reynolds numbers could have two, four or more steady forms. Concerning nonstreamlined flow, for example past a bluff obstacle, new similarity forms are described for the pressure-free viscous symmetric closure of a predominantly slender long wake beyond a large-scale separation. Features arising include nonuniqueness, singularities and algebraic behavior, consistent with nonentraining shear layers with algebraic decay. Nonuniqueness also seems possible in reattachment onto a solid surface and for nonsymmetric or pressure-controlled flows including the wake of a symmetric cascade.

Smith, F. T.

1984-01-01

262

Boundary-Layer Stress Instabilities in Neutral, Rotating Turbulent Flows  

NASA Astrophysics Data System (ADS)

Boundary-layer instabilities are studied by analyzing the results of laboratory simulations of wall turbulence in a shear-driven rotating flow. The experiments were carried out in the Turin University Laboratory rotating water tank, where a circular flow was generated by either increasing (spin-up) or decreasing (spin-down) the rotation speed of the platform. The flow was measured using a Particle Image Velocimetry technique and the developed turbulence analyzed. Two cases were accounted for, in the former the measurements were performed over a smooth surface (bottom of the tank), while in the latter a rough-to-smooth transition was considered. The turbulent boundary layer developed inside the tank is analyzed by means of vertical profiles of mean and turbulent quantities and on the basis of drag coefficients. Then turbulent structures developed in the different cases are shown and discussed in terms of the vorticity fields. Finally, an analysis based on the concept of swirling strength was carried out to select among the vortex extremes those associated with a coherent structure.

Ferrero, Enrico; Mortarini, Luca; Manfrin, Massimigliano; Longhetto, Arnaldo; Genovese, Rita; Forza, Renato

2009-03-01

263

A thermal plume model for the Martian convective boundary layer  

NASA Astrophysics Data System (ADS)

The Martian planetary boundary layer (PBL) is a crucial component of the Martian climate system. Global climate models (GCMs) and mesoscale models (MMs) lack the resolution to predict PBL mixing which is therefore parameterized. Here we propose to adapt the "thermal plume" model, recently developed for Earth climate modeling, to Martian GCMs, MMs, and single-column models. The aim of this physically based parameterization is to represent the effect of organized turbulent structures (updrafts and downdrafts) on the daytime PBL transport, as it is resolved in large-eddy simulations (LESs). We find that the terrestrial thermal plume model needs to be modified to satisfyingly account for deep turbulent plumes found in the Martian convective PBL. Our Martian thermal plume model qualitatively and quantitatively reproduces the thermal structure of the daytime PBL on Mars: superadiabatic near-surface layer, mixing layer, and overshoot region at PBL top. This model is coupled to surface layer parameterizations taking into account stability and turbulent gustiness to calculate surface-atmosphere fluxes. Those new parameterizations for the surface and mixed layers are validated against near-surface lander measurements. Using a thermal plume model moreover enables a first-order estimation of key turbulent quantities (e.g., PBL height and convective plume velocity) in Martian GCMs and MMs without having to run costly LESs.

Colaďtis, A.; Spiga, A.; Hourdin, F.; Rio, C.; Forget, F.; Millour, E.

2013-07-01

264

Energy dissipating structures in turbulent boundary layers  

NASA Astrophysics Data System (ADS)

We present numerical experiments of a dipole crashing into a wall, a generic event in two-dimensional incompressible flows with solid boundaries. The Reynolds number Re is varied from 985 to 7880, and no-slip boundary conditions are approximated by Navier boundary conditions with a slip length proportional to Re-1. Energy dissipation is shown to first set up within a vorticity sheet of thickness proportional to Re-1 in the neighborhood of the wall, and to continue as this sheet rolls up into a spiral and detaches from the wall. The energy dissipation rate integrated over these regions appears to converge towards Rey-independent values, indicating the existence of energy dissipating structures that persist in the vanishing viscosity limit. Details can be found in Nguyen van yen, Farge and Schneider, PRL, 106, 184502 (2011).

Farge, Marie; Nguyen van Yen, Romain; Schneider, Kai

2011-11-01

265

Boundary layer aerosols at Trivandrum tropical coast  

NASA Astrophysics Data System (ADS)

Most of the atmospheric particulate matter produced from the earth's surface and injected into the Atmospheric Boundary Layer (ABL) through various natural and anthropogenic processes subsequently intrude into the free troposphere and above depending on prevailing turbulent and meteorological features. Properties of ABL aerosols at Trivandrum (8.5°N, 77 °E), a typical coastal station situated near the Arabian Sea uncontaminated by any major industrial sources, are studied using a High Volume Sampler (HVS), a Low Pressure Impactor (LPI), a CW lidar at 0.5?m wavelength (CWL) and a multi-wavelength (0.4-1.02 ?m) solar radiometer (MWR). While HVS provides hourly variation of surface TSP (Total Suspended Particles) concentration, LPI measures the size resolved aerosol mass concentration (in the aerodynamic radius range 0.05 to 14 ?m) in 12 size-bins averaged for a few days in a month, CWL gives altitude profile of aerosol extinction and number density (Na) up to ~2km and MWR gives the columnar aerosol optical depth (AOD). While the diurnal variation of TSP concentration strongly depends on features of mesoscale circulation, the seasonal TSP pattern depends on local meteorology and synoptic circulation. In winter, TSP concentration is low during sea breeze (SB) and high during land breeze (LB). This TSP contrast decreases in summer and reverses during the monsoon period. On an average, TSP concentration varies in the range 30 to 160 ?g/m 3 with two maxima, during winter and monsoon periods (attributed respectively to increased production of continental aerosols and that of sea-spray aerosols by surface winds). Relative concentration of small particles (radius r < 0.15?m) is high in winter and low during the monsoon period, while that for particles in the intermediate size range (0.151.5?m) remains almost steady through out the year. Though on an average the number -size distribution approximates to a power law type decrease with increase in size (size index 4.05 +/-0.15), three modes are discernable around 0.05, 0.5 and 5 ?m. Altitude profile of Na is characterised by well-mixed region, entrainment region and upper mixing region. Aerosol -mixing height generally lies in the range 150 to 400m depending on the strength of vertical eddy mixing in ABL. Above this, Na decreases almost exponentially with a scale height of 0.5-1.5km. Sea-spray contribution to Na shows a significant non-linear dependence on surface wind speed. About 10-30% of the columnar AOD is contributed (high in winter and monsoon periods) by the mixing region. An increasing trend in mixing region AOD also is observed at this site from 1989.

Parameswaran, K.; Kumar, S. Sunil; Rajeev, K.; Nair, P.; Krishna Murthy, K.

266

Turbulent Transfer in the Marine Planetary Boundary Layer.  

National Technical Information Service (NTIS)

Work under this contract focused on turbulent processes in the marine atmospheric boundary layer (MABL) and how they effect mixing between ocean and the free atmosphere. In particular, we investigated specific mechanisms of this turbulence within the MABL...

S. Jodha S. Khalsa H. P. Hanson

1994-01-01

267

Structure of the Laminar Ablating Air-Teflon Boundary Layer.  

National Technical Information Service (NTIS)

Radiation profiles in an ablating flat plate air-teflon laminar boundary layer were studied both experimentally and theoretically. The experiments were conducted in a one atmosphere, 3000 - 6000K, subsonic free stream produced by an arc jet. Spatially res...

R. A. Greenberg N. H. Kemp K. L. Wray

1968-01-01

268

Computational Evaluation of Quiet Tunnel Hypersonic Boundary Layer Stability Experiments.  

National Technical Information Service (NTIS)

A computational evaluation of two stability experiments conducted in the NASA Langley Mach 6 axisymmetric quiet nozzle test chamber facility is conducted. Navier- Stokes analysis of the mean flow and linear stability theory analysis of boundary layer dist...

M. L. Manning

2000-01-01

269

Stability of Boundary Layers at High Supersonic and Hypersonic Speeds.  

National Technical Information Service (NTIS)

The thrust of this research program has been the improvement of our capabilities for analyzing stability and transition of boundary layers at supersonic speeds. During the first phase, our efforts were primarily directed toward analytical studies, establi...

T. Herbert

1992-01-01

270

Cross Stream Differencing for Integral Boundary Layer Equations.  

National Technical Information Service (NTIS)

An efficient, stable, explicit, first-order cross-stream differencing scheme having low truncation error is derived and applied to three dimensional integral boundary layer equations. The analysis is considered in detail for the particular case of the mom...

D. Hally

1987-01-01

271

ATMOSPHERIC DISPERSION MODELING BASED UPON BOUNDARY LAYER PARAMETERIZATION  

EPA Science Inventory

Characteristic scaling parameters in the planetary boundary layer have been applied to estimate the dispersion of nonbuoyant gaseous pollutants. Vertical and lateral spread are treated separately, and the choice of parameters for the dispersion models depends upon the actual stat...

272

Hybrid spectral element/asymptotic method for boundary layers problems  

SciTech Connect

This report presents an efficient higher-order numerical approach to many-dimensional problems the boundary layers. This method uses a coarse mesh penalty-spectral element method with a one-dimensional asymptotic approximation.

Zrahia, U.; Orszag, S.A. [Princeton Univ., NJ (United States); Israeli, M. [Israel Institute of Technology, Haifa (Israel)

1997-12-01

273

Differences in the structure of a planetary magnetopause boundary layer  

NASA Astrophysics Data System (ADS)

The boundary of a planetary magnetosphere is known as a magnetopause, and is the site of energy, mass, and momentum transfer. The structure of internal boundary layers adjacent to these boundaries is intimately related to the processes responsible for this transport. We use thermal electron observations made by the Cassini spacecraft to examine the structure of Saturn’s low-latitude internal boundary layer. By analyzing the relationship between the electron density and temperature during the crossings we demonstrate that the structure of the layer is variable. At some of the crossings the major changes in electron density and temperature occur in distinct regions of the layer (as for previously reported examples at Earth), whereas at others the two quantities change over a similar region. We discuss the possible explanations for this phenomenon, and what this could tell us about how the solar wind interacts with a planetary magnetosphere.

Coates, A. J.; Masters, A.; Walsh, A. P.; Fazakerley, A. N.; Dougherty, M. K.

2010-12-01

274

Investigation of the Stable Atmospheric Boundary Layer at Halley Antarctica  

NASA Astrophysics Data System (ADS)

Boundary-layer measurements from the Brunt Ice Shelf, Antarctica are analyzed to determine flux-profile relationships. Dimensionless quantities are derived in the standard approach from estimates of wind shear, potential temperature gradient, Richardson number, eddy diffusivities for momentum and heat, Prandtl number, mixing length and turbulent kinetic energy. Nieuwstadt local scaling theory for the stable atmospheric boundary-layer appears to work well departing only slightly from expressions found in mid-latitudes. An - single-column model of the stable boundary layer is implemented based on local scaling arguments. Simulations based on the first GEWEX Atmospheric Boundary-Layer Study case study are validated against ensemble-averaged profiles for various stability classes. A stability-dependent function of the dimensionless turbulent kinetic energy allows a better fit to the ensemble profiles.

Rodrigo, Javier Sanz; Anderson, Philip S.

2013-09-01

275

Boundary-Layer-Tripping Studies of Compressible Dynamic Stall Flow.  

National Technical Information Service (NTIS)

The challenging task of 'properly' tripping the boundary layer near the leading edge of an airfoil experiencing compressible dynamic stall has been addressed. Real-time interferometry studies have been conducted on an oscillating airfoil undergoing compre...

M. S. Chandrasekhara M. C. Wilder L. W. Carr

1996-01-01

276

Some Topics Relating to Modelling of Dispersion in Boundary Layer.  

National Technical Information Service (NTIS)

This special report discusses six topics all of the major current interest in modelling of dispersion in the atmospheric boundary layer. These are the second-order closure modelling of turbulence, crosswind dispersion and the properties of turbulence, win...

F. Pasquill

1975-01-01

277

The Behaviour of Similar Solutions in a Compressible Boundary Layer.  

National Technical Information Service (NTIS)

The paper discusses the mathematical properties of similar solutions of the boundary-layer equations in a compressible model fluid. Assuming a favourable pressure gradient and that backflow is not present, the results include (among other things) a rigoro...

J. B. McLeod J. Serrin

1968-01-01

278

Research applications of a boundary-layer wind profiler  

SciTech Connect

A small UHF radar wind profiler was operated over a 40-day period during the summer of 1990 at a site on the windward coast of the island of Hawaii. It provided continuous measurements of winds up to the height of the trade-wind inversion, which varied in altitude from about 2 to 4 km during the course of the experiments. The inversion was readily discernible in the data as an elevated layer of high reflectivity, caused by the sharp gradient of refractive index at that level. With a wavelength of 33 cm, the profiler has about the same sensitivity to light rain as to moderately reflective clear air. The data have provided unexpected information on rain development, wave motions on the inversion, sustained vertical air motions at low levels, and interactions between convection and the inversion echo. This paper gives examples of some of the observations, indicating the wide range of applications of boundary-layer profilers.

Rogers, R.R.; Ethier, S.A. (McGill Univ., Montreal, Quebec (Canada)); Ecklund, W.L.; Carter, D.A.; Gage, K.S. (NOAA, Boulder, CO (United States))

1993-04-01

279

Calculation of three-dimensional boundary layers on rotor blades using integral methods  

SciTech Connect

The important effects of rotation and compressibility on rotor blade boundary layers are theoretically investigated. The calculations are based on the momentum integral method and results from calculations of a transonic compressor rotor are presented. Influence of rotation is shown by comparing the incompressible rotating flow with the stationary one. Influence of compressibility is shown by comparing the compressible rotating flow with the incompressible rotating one. Two computer codes for three-dimensional laminar and turbulent boundary layers, originally developed by SSPA Maritime Consulting AB, have been further developed by introducing rotation and compressibility terms into the boundary layer equations. The effect of rotation and compressibility on the transition have been studied. The Coriolis and centrifugal forces that contribute to the development of the boundary layers and influence its behavior generate crosswise flow inside the blade boundary layers, the magnitude of which depends upon the angular velocity of the rotor and the rotor geometry. The calculations show the influence of rotation and compressibility on the boundary layer parameters. Momentum thickness and shape factor increase with increasing rotation and decrease when compressible flow is taken into account. For skin friction such effects have inverse influences. The different boundary layer parameters behave similarly on the suction and pressure sides with the exception of the crossflow angle, the crosswise momentum thickness, and the skin friction factor. The codes use a nearly orthogonal streamline coordinate system, which is fixed to the blade surface and rotates with the blade.

Karimipanah, M.T.; Olsson, E. (Chalmers Univ. of Technology, Goeteborg (Sweden))

1993-04-01

280

A multidisciplinary optimization method for designing boundary layer ingesting inlets  

Microsoft Academic Search

The Blended-Wing-Body is a conceptual aircraft design with rear-mounted, over-wing engines. Two types of engine installations have been considered for this aircraft. One installation is quite conventional with podded engines mounted on pylons. The other installation has partially buried engines with boundary layer ingesting inlets. Although ingesting the low-momentum flow in a boundary layer can improve propulsive efficiency, poor inlet

David Leonard Rodriguez

2001-01-01

281

Benthic boundary layer processes in coastal environments: An introduction  

Microsoft Academic Search

This special issue ofGeo-Marine Letters “Benthic Boundary Layer Processes in Coastal Environments” includes 20 papers devoted to results of recent near-shore experiments supported by the Coastal Benthic Boundary Layer (CBBL) program. Experiments were conducted in gas-rich muddy sediments of Eckernförde Bay of the Baltic Sea and on relict sandy sediments of the West Florida Sand Sheet. In this introductory paper

M. D. Richardson; W. R. Bryant

1996-01-01

282

The behavior of vertically integrated boundary-layer winds  

Microsoft Academic Search

This research provides a study of the behavior of vertically integrated boundary-layer winds (IBLWs). This information should be helpful for both theoretical and practical applications, e.g., boundary-layer parameterization in general circulation models, air pollution models, and low-level parachuting operations. The study concerned itself with winds integrated up to a height of 300 m in the United States. The only data

René V. Cormier

1975-01-01

283

Boundary Layer Structure and Processes in Mid - Ocean Storms  

Microsoft Academic Search

Measurements taken during the Storm Transfer and Response Experiment (STREX) are used to analyze boundary layer structures and processes in the vicinity of North Pacific storms. Case studies are carried out for the pre -frontal, post-frontal, and frontal sectors of storms. The effects of sub-grid scale processes on the boundary layer and the overlying atmosphere receive special emphasis. The pre-frontal

Nicholas A. Bond

1986-01-01

284

Drag and heat transfer relations for the planetary boundary layer  

Microsoft Academic Search

A theory is offered for the drag and heat transfer relations in the statistically steady, horizontally homogeneous, diabatic, barotropic planetary boundary layer. The boundary layer is divided into three regionsR1,R2, andR3, in which the heights are of the order of magnitude ofz0,L, andh, respectively, wherez0 is the roughness length for either momentum or temperature,L is the Obukhov length, andh is

Robert R. Long; Larry J. Guffey

1977-01-01

285

Boundary-Layer Turbulence Over The Nebraska Sandhills  

Microsoft Academic Search

Data from National Centre for Atmospheric Research (NCAR) Queen Air boundary-layer flights over the Nebraska Sandhills are analyzed to investigate the effects of these low hills on boundary-layer turbulence. The Sandhills are an area of anisotropic rolling terrain with characteristic wavelengths of order 2km and rms height variations of order 25m. The biggest impact is found in early morning flight

Yoseph G. Mengesha; Peter A. Taylor; Donald H. Lenschow

2001-01-01

286

Boundary layer polarization and voltage in the 14 MLT region  

NASA Astrophysics Data System (ADS)

Viking midlatitude observations of ions and electrons in the postnoon auroral region show that field-aligned acceleration of electrons and ions with energies up to a few kiloelectron volts takes place. The characteristics of the upgoing ion beams and the local transverse electric field observed by Viking indicate that parallel ion acceleration is primarily due to a quasi-electrostatic field-aligned acceleration process below Viking altitudes, i.e., below 10,000-13,500 km. A good correlation is found between the maximum upgoing ion beam energy and the depth of the local potential well determined by the Viking electric field experiment within dayside 'ion inverted Vs.' The total transverse potential throughout the entire region near the ion inverted Vs. is generally much higher than the field-aligned potential and may reach well above 10 kV. However, the detailed mapping of the transverse potential out to the boundary layer, a fundamental issue which remains controversial, was not attempted here. An important finding in this study is the strong correlation between the maximum up going ion beam energy of dayside ion inverted Vs and the solar wind velocity. This suggests a direct coupling of the solar wind plasma dynamo/voltage generator to the region of field-aligned particle acceleration. The fact that the center of dayside ion inverted Vs coincide with convection reversals/flow stagnation and upward Birkeland currents on what appears to be closed field lines (Woch et al., 1993), suggests that field-aligned potential structures connect to the inner part of an MHD dyanmo in the low-latitude boundary layer. Thus the Viking observations substantiate the idea of a solar wind induced boundary layer polarization where negatively charged perturbations in the postnoon sector persistently develops along the magnetic field lines, establishing accelerating potential drops along the geomagnetic field lines in the 0.5-10 kV range.

Lundin, R.; Yamauchi, M.; Woch, J.; Marklund, G.

1995-05-01

287

A multidisciplinary optimization method for designing boundary layer ingesting inlets  

NASA Astrophysics Data System (ADS)

The Blended-Wing-Body is a conceptual aircraft design with rear-mounted, over-wing engines. Two types of engine installations have been considered for this aircraft. One installation is quite conventional with podded engines mounted on pylons. The other installation has partially buried engines with boundary layer ingesting inlets. Although ingesting the low-momentum flow in a boundary layer can improve propulsive efficiency, poor inlet performance can offset and even overwhelm this potential advantage. For both designs, the tight coupling between the aircraft aerodynamics and the propulsion system poses a difficult design integration problem. This dissertation presents a design method that solves the problem using multidisciplinary optimization. A Navier-Stokes flow solver, an engine analysis method, and a nonlinear optimizer are combined into a design tool that correctly addresses the tight coupling of the problem. The method is first applied to a model 2D problem to expedite development and thoroughly test the scheme. The low computational cost of the 2D method allows for several inlet installations to be optimized and analyzed. The method is then upgraded by using a validated 3D Navier-Stokes solver. The two candidate engine installations are analyzed and optimized using this inlet design method. The method is shown to be quite effective at integrating the propulsion and aerodynamic systems of the Blend-Wing-Body for both engine installations by improving overall performance and satisfying any specified design constraints. By comparing the two optimized designs, the potential advantages of ingesting boundary layer flow for this aircraft are demonstrated.

Rodriguez, David Leonard

2001-07-01

288

Turbulent oceanic western-boundary layers at low latitude  

NASA Astrophysics Data System (ADS)

Low latitude oceanic western-boundary layers range within the most turbulent regions in the worlds ocean. The Somali current system with the Great Whirl and the Brazilian current system with its eddy shedding are the most prominent examples. Results from analytical calculations and integration of a one layer reduced-gravity fine resolution shallow water model is used to entangle this turbulent dynamics. Two types of wind-forcing are applied: a remote Trade wind forcing with maximum shear along the equator and a local Monsoon wind forcing with maximum shear in the vicinity of the boundary. For high values of the viscosity (> 1000m2s-1) the stationary solutions compare well to analytical predictions using Munk and inertial layer theory. When lowering the friction parameter time dependence results. The onset of instability is strongly influenced by inertial effects. The unstable boundary current proceeds as a succession of anti-cyclonic coherent eddies performing a chaotic dynamics in a turbulent flow. The dynamics is governed by the turbulent fluxes of mass and momentum. We determine these fluxes by analyzing the (potential) vorticity dynamics. We demonstrate that the boundary-layer can be separated in four sub-layers, which are (starting from the boundary): (1) the viscous sub-layer (2) the turbulent buffer-layer (3) the layer containing the coherent structures and (4) the extended boundary layer. The characteristics of each sub-layer and the corresponding turbulent fluxes are determined, as are the dependence on latitude and the type of forcing. A new pragmatic method of determining the eddy viscosity, based on Munk-layer theory, is proposed. Results are compared to observations and solutions of the multi-level primitive equation model (DRAKKAR).

Quam Cyrille Akuetevi, Cataria; Wirth, Achim

2013-04-01

289

Drag Reduction for External and Internal Boundary Layers Using Riblets and Polymers.  

National Technical Information Service (NTIS)

Two hydrodynamic experiments were conducted to measure drag reduction using riblets in turbulent boundary layers. The first was an external boundary layer experiment using a flat plate in a water tunnel, and the second was an internal boundary layer exper...

L. W. Reidy G. W. Anderson

1988-01-01

290

Influences on the Height of the Stable Boundary Layer as Seen in LES.  

National Technical Information Service (NTIS)

Climate models, numerical weather prediction (NWP) models, and atmospheric dispersion models often rely on parameterizations of planetary boundary layer height. In the case of a stable boundary layer, errors in boundary layer height estimation can result ...

B. Kosovic J. K. Lundquist

2004-01-01

291

Similarity of a Problem in Concentration-Dependent Diffusion and Flow in a Free Boundary Layer.  

National Technical Information Service (NTIS)

The mathematical similarity of a problem in one-dimensional diffusion in a semi-infinite medium when the diffusion coefficient varies linearly with concentration to the problem of the fully developed boundary layer between two fluid streams was demonstrat...

C. E. Willbanks

1967-01-01

292

The Role of S-Shaped Crossflow Profiles in Three-Dimensional Boundary Layer Theory.  

National Technical Information Service (NTIS)

A method is developed which allows the calculation of characteristic parameters (scale factor delta, main flow parameter m, crossflow parameter B) of three-dimensional turbulent boundary layers under the assumption of a third-degree polynomial for the tem...

E. A. Eichlbrenner J. L. Peube

1966-01-01

293

Numerical Simulation of Unsteady Three-Dimensional Turbulent Structures in Boundary Layer Flows.  

National Technical Information Service (NTIS)

The capabilities for numerical simulations of the dynamical effects of the underlying structures occurring in turbulent boundary layers have been developed. A mathematically operational model of hairpin vortex, which closely resembles the experimentally o...

N. S. Lui S. J. Shamroth H. McDonald

1985-01-01

294

Numerical investigation of influence of rotor/stator interaction on blade boundary layer flow in a low speed compressor  

NASA Astrophysics Data System (ADS)

Numerical method was applied to the unsteady flow simulation at the mid span of a two-stage low speed compressor, and the blade boundary layer flow under rotor/stator interaction was investigated. By the model of wake/boundary layer interaction provided in this paper, the simulated blade frictional force and the boundary layer turbulent kinetic energy, the influence of wake/potential flow interaction on the blade boundary layer flow was analyzed in detail. The results show that under the condition of rotor/stator interaction, the wake is able to induce the stator laminar boundary layer flow to develop into turbulent flow within a certain range of wake interaction. In the stator suction boundary layer, an undisturbed region occurs behind the rotor wake, which extends the laminar flow range, and the wake with high turbulent intensity has the capability to control the boundary layer separation under adverse pressure gradient.

Yao, Hongwei; Yan, Peigang; Han, Wanjin

2011-02-01

295

Incompressible Boundary Layer Transition Flight Experiments Over a Nonaxisymmetric Fuselage Forebody and Comparisons with Laminar Boundary Layer Stability Theory  

Microsoft Academic Search

Analyses of previous boundary-layer transition experiments over axisymmetric bodies indicates a potential for achieving substantial amounts of laminar flow over such shapes. Achievement of natural laminar flow over portions of nonlifting aircraft geometries, such as fuselage forebodies, tip tanks or engine nacelles, could significantly contribute to the reduction of total aircraft viscous drag. A modern surface-panel method, a streamwise boundary-layer

Paul M. H. W. Vijgen

1990-01-01

296

Self-sustained localized structures in a boundary-layer flow.  

PubMed

When a boundary layer starts to develop spatially over a flat plate, only disturbances of sufficiently large amplitude survive and trigger turbulence subcritically. Direct numerical simulation of the Blasius boundary-layer flow is carried out to track the dynamics in the region of phase space separating transitional from relaminarizing trajectories. In this intermediate regime, the corresponding disturbance is fully localized and spreads slowly in space. This structure is dominated by a robust pair of low-speed streaks, whose convective instabilities spawn hairpin vortices evolving downstream into transient disturbances. A quasicyclic mechanism for the generation of offspring is unfolded using dynamical rescaling with the local boundary-layer thickness. PMID:22400847

Duguet, Yohann; Schlatter, Philipp; Henningson, Dan S; Eckhardt, Bruno

2012-01-25

297

The receptivity of laminar boundary layer flow to leading edge vibrations  

NASA Astrophysics Data System (ADS)

The receptivity of laminar boundary layer flow to leading edge vibrations has been studied experimentally. The experiments reported on in this paper include (1) a stable case and (2) an unstable case. These experiments identify the forcing field imposed by the vibrating leading edge and track the subsequent development of the unstable Tollmien-Schlichting waves. Detailed velocity measurements around the leading edge help in the identification of the source of such unstable boundary layer waves. The near-singular nature of the response of the fluid around the vibrating leading edge is found to be responsible for the generation of unstable boundary layer waves.

Chiu, W. K.; Norton, M. P.

1990-08-01

298

Stereoscopic PIV Measurements in an Urban-type Boundary Layer  

NASA Astrophysics Data System (ADS)

An experimental investigation of the flow through urban-type boundary layers (4 rows of 3 cuboid Plexiglas blocks) in a modeled atmospheric boundary layer, will be presented. This study utilizes SPIV, hot-wire and oil-film interferometry measurements. Hot-wire measurements provide input on the incoming flow while direct measurements of the wall shear stress are realized using oil-film interferometry. Flow dispersion in urban areas is highly 3-D; therefore, a 2D traverse system carrying the entire SPIV system was designed which allows us to precisely position the measurement plane. All three velocity components are measured in 2-D planes throughout the model. More than 300 data planes in a 102mm by 50mm by 500mm domain corresponding to the middle street of the urban model are presented. The spacing between adjacent planes is chosen in order to resolve details close to the edges of the blocks. 3D streamlines, vorticity contours, isosurfaces of the second invariant of velocity gradient and Reynolds stresses will be presented and serve as a unique database for the numerical model being developed in parallel at IIT (see talk by Kandala, Rempfer, Wark and Fischer).

Monnier, Bruno; Neiswander, Brian; Wark, Candace; Rempfer, Dietmar

2007-11-01

299

Vortex Roll Breakup in Three-Dimensional Turbulent Boundary Layers  

NASA Astrophysics Data System (ADS)

Large helical vortex rolls with axes in the general direction of the mean wind commonly appear in the unstably stratified atmospheric boundary layer. When a rapid shift in the mean wind direction occurs, the vertical transport of momentum and heat flux is sharply reduced compared to the equilibrium value. At long times, this non-equilibrium turbulent flow may develop back into a stable pattern of organized vortex rolls, now aligned with the new wind direction. This transition process is studied via direct numerical simulation of plane channel flow heated from below with impulsively started transverse pressure gradient (Ri = -Ra/PrRe^2 = -0.25, Ra = 10^7, and Pr = 0.71). The timescale for heat flux recovery is approximately the same for turning angles larger than 30 degrees. For higher turning angles, however, the Nusselt number will temporarily drop below one due to a significant reduction in vertical transport. Horizontal velocity and temperature spectra suggest that scale separation between large-scale, organized convective motions and turbulent eddies can prevent heat transfer reduction in transversely accelerated three-dimensional turbulent boundary layers.

Hamman, Curtis; Moin, Parviz

2011-11-01

300

Boundary Layer Height and Structure during the NATO LASIE Campaign  

NASA Astrophysics Data System (ADS)

The NATO Ligurian Air-Sea Interaction Experiment (LASIE) took place in 2007, from 16 to 22 June, in the Mediterranean Sea. This filed campaign was organized under the auspices of the NATO Undersea Research Centre (NURC), located in La Spezia, Italy. The main scientific goal was to contribute to the evaluation and development of parameterizations of the oceanic and atmospheric boundary layers and their interactions. Extensive meteorological and oceanographic measurements were collected, on board the research vessels Leonardo, Planet, and Urania, and from the spar buoy ODAS Italia 1. In this study ceilometer (Vaisala CL31) and atmospheric radiosondes (Vaisala DigiCORA) measurements are used to assess the evolution of the marine atmospheric boundary layer (MABL) structure and height during the LASIE cruise. The ceilometer measured continuously the cloud height base, while the radiosondes, launched every 3 hours, recorded vertical profiles of wind speed, wind direction, potential temperature and relative humidity. Several methods available in the literature are used to determine the height of the MABL from observations. The results from these methods are compared with the MABL heights from the limited-area numeric weather prediction models WRF (Weather Research and Forecasting) and MM5 (Fifth-Generation Mesoscale Model).

Tomé, R.; Sempreviva, A. M.; Schiano, E.; Bozzano, R.; Miranda, P. M.; Pensieri, S.; Semedo, A.; Teixeira, J.

2009-09-01

301

Low Cost Geothermal Separators BLISS Boundary Layer Inline Separator Scrubber  

SciTech Connect

A new compact, low cost, and high performance separator is being developed to help reduce the installed and O and M cost of geothermal power generation. This device has been given the acronym ''BLISS'' that stands for ''Boundary Layer Inline Separator Scrubber''. The device is the first of a series of separators, and in the case of injectates, scrubbers to address the cost-reduction needs of the industry. The BLISS is a multi-positional centrifugal separator primarily designed to be simply installed between pipe supports, in a horizontal position. This lower profile reduces the height safety concern for workers, and significantly reduces the total installation cost. The vessel can demand as little as one-quarter (25%) the amount of steel traditionally required to fabricate many large vertical separators. The compact nature and high separating efficiency of this device are directly attributable to a high centrifugal force coupled with boundary layer control. The pseudo isokinetic flow design imparts a self-cleaning and scale resistant feature. This polishing separator is designed to remove moderate amounts of liquid and entrained solids.

Jung, Douglas; Wai, King

2000-05-26

302

ON AERODYNAMIC AND BOUNDARY LAYER RESISTANCES WITHIN DRY DEPOSITION MODELS  

EPA Science Inventory

There have been many empirical parameterizations for the aerodynamic and boundary layer resistances proposed in the literature, e.g. those of the Meyers Multi-Layer Deposition Model (MLM) used with the nation-wide dry deposition network. Many include arbitrary constants or par...

303

Mean flow study of two-dimensional subsonic turbulent boundary layers  

NASA Astrophysics Data System (ADS)

This paper presents some mean flow data for subsonic compressible boundary layers obtained during the calibration of a newly built boundary layer wind tunnel. The measurements were carried out at zero pressure gradient and at subsonic speeds. The freestream Reynolds number ranged from 11 x 10(exp 6) to 44 x 10(exp 6)/m. Different boundary-layer profiles and parameters were examined and compared with the universally accepted data for two-dimensional compressible equilibrium turbulent boundary layers. The van Driest transformation was used to compare the data with the well-known incompressible correlations. The results together with the estimates of the wake component suggest that the tested turbulent boundary layer is fully developed, two dimensional, and in equilibrium condition. The data indicate that Reynolds number based on the integral length scale of Delta * is well correlated with the momentum thickness Reynolds number. This is similar to the proposed correlation of Fernholz and Finley for supersonic flows but with an average vertical shift of about 0.18 and in contrast to the suggestion of Fernholz is Mach number dependent. The results also indicate that although the constancy of the strength of the wake component can be used in defining the state of a turbulent boundary layer the existence of a universal value for the classification of turbulent boundary layers must still be investigated.

Motallebi, Fariborz

1994-11-01

304

Finite difference form of the compressible boundary layer equations in generalized curvilinear coordinates  

Microsoft Academic Search

The development of a finite difference form of the unsteady boundary layer equations for two dimensional flow is presented. The equations are written in body-conformal coordinates, non-dimensionalized, transformed to a generalized curvilinear coordinate system, and expanded to yield equations suitable for use in a tridiagonal solver. The boundary conditions are also presented.

Denis Bergeron

1990-01-01

305

The modified differential transform method for investigating nano boundary-layers over stretching surfaces  

Microsoft Academic Search

Purpose – The purpose of this paper is to investigate the nano boundary-layer flows over stretching surfaces with Navier boundary condition. This problem is mapped into the ordinary differential equation by presented similarity transformation. The resulting nonlinear ordinary differential equation is solved analytically by applying a newly developed method. The authors consider two types of flows: viscous flows over a

Mohammad Mehdi Rashidi; Eemaeel Erfani

2011-01-01

306

Stability of boundary layers within high-speed viscous flows  

NASA Astrophysics Data System (ADS)

A numerical study was undertaken to predict the stability of a variety of high-speed boundary-layer flows. Using a finite-volume code, the Navier-Stokes equations were solved for a series of flows around spherically blunted cones. These solutions were used to perform linear-stability analyses for second-mode disturbances. Two investigations were undertaken using an ideal-gas model: the Stetson experiment and a recent experiment conducted at the Institute of Theoretical and Applied Mechanics in Russia. Comparisons were made with both basic-state and disturbance state quantities. For both cases, linear-growth regions have been identified. For the Stetson case, using an experimentally determined wall-temperature distribution for the basic-state appeared to give better agreement with the experimentally measured growth than does the classical adiabatic-wall boundary condition. For the Russian experiment, initial comparisons were made in order to continue a careful collaboration. A third investigation was made which used a chemical non-equilibrium model, considering a Mach 13.5 flow in upper-atmospheric conditions. The goal of this investigation was to evaluate the sensitivity of second-mode growth predictions to changes (within accepted uncertainties) in thermodynamic, reaction-rate; and transport models. The magnitude of change in the stability results correlated strongly with changes in the basic-state thermal boundary-layer profile, consistent with second-mode theory. The largest change in the stability behavior was observed for the case where the transport model was changed. For high-speed flows, the development of computational techniques is in some ways ahead of the experimental community's ability to verify the results. As these techniques are applied to flows in thermochemical non-equilibrium, the fidelity of the constitutive relationships should be considered.

Lyttle, Ian John

2003-10-01

307

Numerical studies of boundary-layer receptivity  

NASA Astrophysics Data System (ADS)

Direct numerical simulations (DNS) of the acoustic receptivity process on a semi-infinite flat plate with a modified-super-elliptic (MSE) leading edge are performed. The incompressible Navier-Stokes equations are solved in stream-function/vorticity form in a general curvilinear coordinate system. The steady basic-state solution is found by solving the governing equations using an alternating direction implicit (ADI) procedure which takes advantage of the parallelism present in line-splitting techniques. Time-harmonic oscillations of the farfield velocity are applied as unsteady boundary conditions to the unsteady disturbance equations. An efficient time-harmonic scheme is used to produce the disturbance solutions. Buffer-zone techniques have been applied to eliminate wave reflection from the outflow boundary. The spatial evolution of Tollmien-Schlichting (T-S) waves is analyzed and compared with experiment and theory. The effects of nose-radius, frequency, Reynolds number, angle of attack, and amplitude of the acoustic wave are investigated. This work is being performed in conjunction with the experiments at the Arizona State University Unsteady Wind Tunnel under the direction of Professor William Saric. The simulations are of the same configuration and parameters used in the wind-tunnel experiments.

Reed, Helen L.

1995-09-01

308

A top specified boundary layer (TSBL) approximation approach for the simulation of groundwater contamination processes  

USGS Publications Warehouse

This paper presents improvements in the 'classical boundary layer' (CBL) approximation method to obtain simple but robust initial characterization of aquifer contamination processes. Contaminants are considered to penetrate into the groundwater through the free surface of the aquifer. The improved method developed in this study is termed the 'top specified boundary layer' (TSBL) approach. It involves the specification of the contaminant concentration at the top of the contaminated 'region of interest' (ROI), which is simulated as a boundary layer. the TSBL modification significantly improves the ability of the boundary layer method to predict the development of concentration profiles over both space and time. The TSBL method can be useful for the simulation of cases in which the contaminant concentration is prescribed at the aquifer's free surface as well as for cases in which the contaminant mass flux is prescribed at the surface.

Rubin, H.; Buddemeier, R. W.

1996-01-01

309

Continuum emission and broadband electrostatic noise at the low latitude boundary layer: A diagnostic of boundary layer dynamics  

NASA Astrophysics Data System (ADS)

We examine the plasma and radio waves near the inner edge of the low latitude boundary layer (LLBL) during a period of time when the layer is in a ``pulsed'' oscillating configuration. Previous work suggests there are numerous possible explanations for such oscillations including a Kelvin-Helmholtz instability, flux transfer events, and a boundary response to solar wind pressure oscillations. We demonstrate that the inner edge of the LLBL is indeed in motion, based upon the influence this motion has on the incident freely-propagating continuum emission. We also demonstrate that the inner boundary contains impulsive broadband events that appear, in high resolution, as a series of bipolar solitary pulses. These are the result of a kinetic electron beam instability occurring in association with the boundary fluid motion. We suggest that the large-scale fluid motion drives the kinetic instability via particle evacuation near the oscillating boundary.

Farrell, W. M.; Fitzenreiter, R. J.; Kaiser, M. L.; Goetz, K.; Maksimovic, M.; Reiner, M. J.

2002-06-01

310

The Asymmetric Boundary layer Flow Under a Translating Hurricane.  

NASA Astrophysics Data System (ADS)

An investigation is made of the role of the translation of a hurricane in determining the distribution of boundary layer winds and in the organization of convection. A slab boundary layer model of constant depth is used to analyze the steady flow under a specified translating symmetric vortex in gradient balance. A truncated spectral formulation is used, including asymmetries through wavenumber 2. The role of linear and nonlinear asymmetric effects in the determination of the boundary layer response is diagnosed. These effects am relevant to relatively slowly and rapidly translating hurricanes, respectively.The analysis is compared to observations of Hurricanes Frederic of 1979 and Allen of 1980, as well as to other observational and theoretical cures. Allen's translation speed was approximately twice that of Frederic. It is found that the simple boundary layer formulation simulates the qualitative features of the wind field observed in Frederic. The distribution of convection in Frederic and Allen compares favorably with boundary layer convergence diagnosed from the model.

Shapiro, Lloyd J.

1983-08-01

311

A numerical study of compressible turbulent boundary layers  

NASA Astrophysics Data System (ADS)

Compressible turbulent boundary layers with free-stream Mach number ranging from 2.5 up to 20 are analyzed by means of direct numerical simulation of the Navier-Stokes equations. The fluid is assumed to be an ideal gas with constant specific heats. The simulation generates its inflow condition using the rescaling-recycling method. The main objective is to study the effect of Mach number on turbulence statistics and near-wall turbulence structures. The present study shows that supersonic/hypersonic boundary layers at zero pressure gradient exhibit close similarities to incompressible boundary layers and that the main turbulence statistics can be correctly described as variable-density extensions of incompressible results. The study also shows that the spanwise streak's spacing of 100 wall units in the inner region (y+~15) still holds for the considered high Mach numbers. The probability density function of the velocity dilatation shows significant variations as the Mach number is increased, but it can also be normalized by accounting for the variable-density effect. The compressible boundary layer also shows an additional similarity to the incompressible boundary layer in the sense that without the linear coupling term, near-wall turbulence cannot be sustained.

Lagha, M.; Kim, J.; Eldredge, J. D.; Zhong, X.

2011-01-01

312

Transonic Aeroelastic Analysis of Aircraft Wings Considering the Boundary-Layer Effects  

Microsoft Academic Search

Aerodynamic solver using the transonic small-disturbance (TSD) equation has frequently been used to perform practical aeroelastic analysis for many aircraft models. In the present study, the more accurate aeroelastic analysis solver using the TSD equation was developed by considering the viscous effects of the boundary-layer. The viscous effects were considered using Green's lag-entrainment equations and an inverse boundary-layer method. Through

Jong-Yun Kim; Kyung-Seok Kim; Seung-Jun Lee; In Lee

2009-01-01

313

Shipboard measurements of the cloud-capped marine boundary layer during FIRE/ASTEX  

SciTech Connect

Results are reported on measurements of the cloud-capped marine boundary layer during FIRE/ASTEX. A method was developed from the ASTEX dataset for measuring profiles of liquid water content, droplet size and concentration from cloud radar/microwave radiometer data in marine boundary layer clouds. Profiles were also determined from the first three moments of the Doppler spectrum measured in drizzle with the ETL cloud radar during ASTEX.

NONE

1997-09-01

314

Observations and Large-Eddy Simulations of Entrainment in the Sheared Sahelian Boundary Layer  

NASA Astrophysics Data System (ADS)

At the top of the planetary boundary layer, the entrainment of air, which incorporates dry and warm air from the free troposphere into the boundary layer, is a key process for exchanges with the free troposphere since it controls the growth of the boundary layer. Here, we focus on the semi-arid boundary layer where the entrainment process is analyzed using aircraft observations collected during the African Monsoon Multidisciplinary Analysis experiment and large-eddy simulations. The role of the entrainment is specifically enhanced in this region where very large gradients at the planetary boundary-layer top can be found due to the presence of the moist, cold monsoon flow on which the dry, warm Harmattan flow is superimposed. A first large-eddy simulation is designed based on aircraft observations of 5 June 2006 during the transition period between dry conditions and the active monsoon phase. The simulation reproduces the boundary-layer development and dynamics observed on this day. From this specific case, sensitivity tests are carried out to cover a range of conditions observed during seven other flights made in the same transition period in order to describe the entrainment processes in detail. The combination of large-eddy simulations and observations allows us to test the parametrization of entrainment in a mixed-layer model with zero-order and first-order approximations for the entrainment zone. The latter representation of the entrainment zone gives a better fit with the conditions encountered in the Sahelian boundary layer during the transition period because large entrainment thicknesses are observed. The sensitivity study also provides an opportunity to highlight the contribution of shear stress and scalar jumps at the top of the boundary layer in the entrainment process, and to test a relevant parametrization published in the recent literature for a mixed-layer model.

Canut, Guylaine; Couvreux, Fleur; Lothon, Marie; Pino, David; Saďd, Frédérique

2012-01-01

315

Boundary layer flow and heat transfer over a stretching sheet with convective boundary conditions  

NASA Astrophysics Data System (ADS)

In this paper, the steady boundary layer flow and heat transfer over a stretching sheet with convective boundary conditions are studied, where the heat is supplied to the convecting fluid through a bounding surface with a finite heat capacity. The nonlinear boundary layer equations are transformed into ordinary differential equations which are then solved numerically via the Keller-box method. Numerical solutions are obtained for the wall temperature, the local heat transfer coefficient for various values of the Prandtl number and the conjugate parameter. The effect of these parameters is discussed and it was found that the boundary layer thickness increases as conjugate parameter increases but opposite trend is observed for the increasing value of Pr.

Sarif, N. M.; Salleh, M. Z.; Nazar, R.

2013-04-01

316

Hypersonic turbulent wall boundary layer computations  

NASA Astrophysics Data System (ADS)

The Baldwin-Lomax algebraic turbulence model was modified for hypersonic flow conditions. Two coefficients in the outer layer eddy viscosity model were determined as functions of Mach number and temperature ratio. By matching the solutions from the Baldwin-Lomax model to those from the Cebeci-Smith model for a flat plate at hypersonic speed, the new values of the coefficient were obtained. The results show that the values of C sub cp and C sub kleb are functions of both Mach number and wall temperature ratio. The C sub cp and C sub kleb variations with Mach number and wall temperature were used for the calculations of both a 4 deg wedge flow at Mach 18 and an axisymmetric Mach 20 nozzle flow. The Navier-Stokes equations with thin layer approximation were solved for the above hypersonic flow conditions and the results were compared with existing experimental data. The agreement between the numerical solutions and the existing experimental data were good. The modified Baldwin-Lomax model thus is useful in the computations of hypersonic flows.

Kim, S. C.; Harloff, G. J.

1988-05-01

317

Correlations study in shock wave\\/turbulent boundary layer interaction  

Microsoft Academic Search

The shock waves\\/turbulent boundary layer interaction is a problem of critical importance that is frequently encountered in\\u000a designing flying vehicles. Presently, the most topical issue is the investigation of nonstationary phenomena (in particular,\\u000a low-frequency effects) involved in this interaction. We have experimentally studied separated flows in the zone of interaction\\u000a between an obliquely incident shock wave and a turbulent boundary

P. A. Polivanov; A. A. Sidorenko; A. A. Maslov

2010-01-01

318

Spatial Optimal Disturbances in Three-Dimensional Boundary Layers  

NASA Astrophysics Data System (ADS)

A parabolised set of equations is used to compute spatial optimal disturbances in Falkner-Skan-Cooke boundary layers. These disturbances associated with maximum energy growth initially take the form of vortices which are tilted against the direction of the mean crossflow shear. They evolve into bended streaks while traveling downstream and finally into crossflow disturbances when entering the supercritical domain of the boundary layer. Two physical mechanisms, namely the lift-up and the Orr-mechanism, can be identified as being responsible for nonmodal growth in three-dimensional boundary layers. A parametric study is presented where, amongst others, the influences of pressure gradient and sweep angle on optimal growth are investigated. It turns out that substantial disturbance growth is already found in regions of the flow where modal disturbances are damped.

Tempelmann, David; Hanifi, Ardeshir; Henningson, Dan S.

319

Nonlocalized receptivity of boundary layers to three-dimensional disturbances  

NASA Astrophysics Data System (ADS)

The nonlocalized receptivity of the Blasius boundary layer over a wavy surface is analyzed using two different approaches. First, a mode-interaction theory is employed to unveil basic mechanisms and to explore the interplay between different components of the disturbance field. The second approach is derived from the parabolized stability equations. These nonlinear equations incorporate the effects of the stream-wise divergence of the boundary layer. The analysis provides results for three-dimensional disturbances and also considers nonparallel effects. Results for two-dimensional disturbances demonstrate that nonparallel effects are negligible and substantiates the mechanism described by the mode-interaction theory. Nonparallel effects become significant with increasing three-dimensionality. Receptivity amplitudes are shown to be large over a broad range of surface wave numbers. When operative, this mechanism is likely to dominate the boundary-layer receptivity.

Crouch, J. D.; Bertolotti, F. P.

1992-01-01

320

Measurement of boundary-layer receptivity at suction surfaces  

NASA Astrophysics Data System (ADS)

The receptivity of a boundary layer to external acoustic disturbances in the vicinity of a narrow suction slot is experimentally investigated. The relative importance of the leading-edge and suction-slot receptivity mechanisms is explored. A flat-plate, zero-pressure-gradient boundary layer with and without passive suction surfaces is irradiated by acoustic plane waves, and the coupling between the incident sound field and Tollmien-Schlichting waves is characterized. Suction slot locations and forcing frequencies are chosen so that the slot is positioned near the streamwise location corresponding to the lower branch of the neutral stability curve. Both amplified and damped modes are considered. The slot receptivity mechanism is validated and shown to produce a boundary-layer response at the slot of the same order as waves convected from the leading edge.

Wlezien, R. W.

1989-03-01

321

The effects of forcing on a single stream shear layer and its parent boundary layer  

NASA Astrophysics Data System (ADS)

Forcing and its effect on fluid flows has become an accepted tool in the study and control of flow systems. It has been used both as a diagnostic tool, to explore the development and interaction of coherent structures, and as a method of controlling the behavior of the flow. A number of forcing methods have been used in order to provide a perturbation to the flow; among these are the use of an oscillating trailing edge, acoustically driven slots, external acoustic forcing, and mechanical piston methods. The effect of a planar mechanical piston forcing on a single stream shear layer is presented; it can be noted that this is one of the lesser studied free shear layers. The single stream shear layer can be characterized by its primary flow velocity scale and the thickness of the separating boundary layer. The velocity scale is constant over the length of the flow field; theta (x) can be used as a width scale to characterize the unforced shear layer. In the case of the forced shear layer the velocity field is a function of phase time and definition of a width measure becomes somewhat problematic.

Haw, Richard C.; Foss, John F.

1990-02-01

322

A solution method for the three-dimensional compressible turbulent boundary-layer equations  

NASA Astrophysics Data System (ADS)

The development of a new calculation method for compressible 3D boundary layers is described. The method involves a finite-difference discretisation of the governing mean-flow equations. In particular, the differencing scheme used to discretise spanwise derivatives adapts automatically to the sign of the local crossflow within the boundary layer. A plane-by-plane solution procedure in the spanwise direction enables second-order accuracy to be maintained throughout the whole flowfield. A normal coordinate scaling with the local total momentum thickness removes most of the boundary layer growth in computational space. The Cebeci-Smith algebraic turbulence model is used for the initial validation of the calculation method. A simple modification to this model is tested, involving an explicit dependence of the outer eddy viscosity on the crossflow within the boundary layer. There results a significantly improved prediction of the NLR infinite swept wing flow experiment.

Johnston, L. J.

1989-04-01

323

Three-dimensional turbulent boundary layers; Proceedings of the Symposium, Berlin, West Germany, March 29-April 1, 1982  

NASA Astrophysics Data System (ADS)

Papers are presented on recent research concerning three-dimensional turbulent boundary layers. Topics examined include experimental techniques in three-dimensional turbulent boundary layers, turbulence measurements in ship-model flow, measurements of Reynolds-stress profiles in the stern region of a ship model, the effects of crossflow on the vortex-layer-type three-dimensional flow separation, and wind tunnel investigations of some three-dimensional separated turbulent boundary layers. Also examined are three-dimensional boundary layers in turbomachines, the boundary layers on bodies of revolution spinning in axial flows, the effect on a developed turbulent boundary layer of a sudden local wall motion, three-dimensional turbulent boundary layer along a concave wall, the numerical computation of three-dimensional boundary layers, a numerical study of corner flows, three-dimensional boundary calculations in design aerodynamics, and turbulent boundary-layer calculations in design aerodynamics. For individual items see A83-47012 to A83-47036

Fernholz, H. H.; Krause, E.

324

Experimental Study of Boundary Layer Transition on an Airfoil Induced by Periodically Passing Wake  

NASA Astrophysics Data System (ADS)

Hot-wire measurements are performed in boundary layers developing on NACA0012 airfoil over which wakes pass periodically. The Reynolds number based on chord length of the airfoil is 200,000 and the wakes are generated by circular cylinders rotating clockwise and counterclockwise around the airfoil. The phase as well as the time averaged streamwise mean velocity, turbulent fluctuations and integral parameters are provided to investigate the phenomena of wake-induced transition. Especially, the phase averaged wall shear stresses are reasonably evaluated using the principle of computational Preston tube method. Due to the passing wake, the turbulent stripe is generated in the laminar boundary layer on the airfoil and the boundary layer become temporalily transitional. The stripes convect downstream with constant propagation rate and merge each other at futher downstream station and finally boundary layer become turbulent. In this transition process, the present experimental data show very similar features to the DNS result of X. Wu et al. (1999) and previous experimental studies. The two phase averaged mean velocitiy dips appear in the outer region of transitional boundary layer for each passing cycle and the calm regions exist in the boundary layer after turbulent stripes pass. Relatively high values of turbulent fluctuations in the outer region indicate the possibility that breakdown occurs in the outer layer not near the wall. * Supported by the grant of Korea Ministry of Education(96ME-B-03)

Kang, Shin-Hyoung; Jeon, Woo-Pyung; Park, Tae-Choon

1999-11-01

325

Field observations of the wave bottom boundary layer  

NASA Astrophysics Data System (ADS)

This paper presents a comprehensive set of velocity and suspended sediment observations in the nearshore wave bottom boundary layer, collected during the Duck94 field experiment on the Outer Banks of the North Carolina coast. Cross-shore velocity measurements in the wave bottom boundary layer were made using five hot film anemometers, nominally spaced from 1 to 5 cm above the bed in 2 m of water depth. The time-varying location of the seabed was estimated to roughly 1 cm with a stacked set of bed-penetrating fiber-optic backscatter sensors. The instrument array was intermittently located in the surf zone on the crest of a bar. The location of the bottom varied several centimeters over a 34 min data run. Even over 4 min segments of quasi-steady statistics, occasional large waves caused short erosion and redeposition events, complicating the definition of bottom location and causing the root-mean-square velocity statistics to be nonzero below the mean bed location. This leads to obvious difficulties in comparisons with two, one-dimensional time-dependent, eddy viscosity wave bottom boundary layer models. For example, bed shears based on rms amplitude decay were lower than predicted. The observations show some evidence for a velocity overshoot region within the wave bottom boundary layer. The observations were compared with two linear eddy viscosity models. Larger estimates of a constant eddy viscosity and smaller than predicted phase leads are indicative of more rapid mixing of momentum than predicted by the models. The phase and amplitude frequency response estimated with frequency domain empirical orthogonal functions shows a nonlinear response of the wave bottom boundary layer over the incident band. These observations are among the first coherent looks at the wave bottom boundary layer under conditions of significant sediment response. They highlight the added complexity of the dynamics in natural environments.

Foster, D. L.; Beach, R. A.; Holman, R. A.

2000-08-01

326

Advective heat transport and boundary layer decoupling controlling the melt dynamics of a patchy snow cover  

NASA Astrophysics Data System (ADS)

Once the mountain snow-cover gets patchy in the course of the ablation season two processes are expected to increase in magnitude: the advective heat ransport and the near-surface boundary layer decoupling. These two processes, which have an opposite effect on sensible heat transport onto the snow surface, are, however, not well understood. The aim of this study is to investigate the effects of locally developing atmospheric stratification over snow patches. Especially stable internal boundary layers over cold surfaces can result in a decoupling of the near-surface air from the warmer atmosphere. In this investigation we are particularly interested in the effect of boundary layer decoupling on the net sensible heat flux towards the snow surface. At two experimental sites we applied local eddy flux measurements over snow patches at three different heights above the snow surface. The measurement results suggested wind velocity, turbulence intensity, wind fetch distance and topographical curvature to be driving factors for boundary layer growth above patchy snow covers. These factors also control the efficiency of advective heat transport to contribute to snow ablation. The turbulence data clearly show that boundary layer decoupling inhibits the transfer of additional energy to the snow cover potentially gained from advective heat transport, leading to an upward flux of sensible heat above the stable internal layer. The atmospheric decoupling primarily occurs for shallow stable internal boundary layers, calm winds and low friction velocities. Contrary, the transfer of sensible heat towards the snow cover is promoted by high mechanical turbulence initiated by strong winds. Advective heat transport is shown to be especially effective under these conditions. Thus, strong winds additionally increase the role of advective heat transport by decreasing boundary layer decoupling. Furthermore, concave topographies reduce snow ablation by enhancing the potential of boundary layer decoupling. The atmospheric decoupling is thus shown to be a key mechanism in snow patch survival.

Mott, R.; Gromke, C.; Grünewald, T.; Lehning, M.

2012-04-01

327

Velocity measurements in a turbulent natural convection boundary layer  

NASA Astrophysics Data System (ADS)

The initial results from an investigation of the velocity and temperature profiles for a turbulent natural convective boundary layer using laser Doppler anemometry (LDA) are reported. A DISA type seeding generator spewed corn oil droplets over a flat plate immersed in a flow in order to obtain velocity fluctuations, and thermocouples provided data for the temperature profiles. The plate was maintained at a surface temperature of 80 C. Sufficient measurements were made to characterize the laminar, transition, and the turbulent regions. The measurements taken in the boundary layer satisfied an integral energy balance, with residence time weighting of the values yielding corrections that amounted to only 2-3 percent.

Cheesewright, R.; Ierokiopitis, E.

328

Skin friction in zero-pressure-gradient boundary layers.  

PubMed

A global approach leading to a self-consistent solution to the Navier-Stokes-Prandtl equations for zero-pressure-gradient boundary layers is presented. It is shown that as Re(?)? ?, the dynamically defined boundary layer thickness ?(x) ? x/ln2 ?Rex and the skin friction ? = 2?(w)/?U(0)(2) ? 1/ln2 ??(x). Here ?(w) and U0 are the wall shear stress and free stream velocity, respectively. The theory is formulated as an expansion in powers of a small dimensionless parameter d?(x)/dx ? 0 in the limit x ? ?. PMID:21230338

Yakhot, Victor

2010-10-04

329

Grain-boundary layering transitions in a model bicrystal  

NASA Astrophysics Data System (ADS)

We investigate numerically a series of layering transitions associated with grain-boundary segregation in a lattice-gas model of a binary alloy. By examining the dependence of the excess composition on temperature and relative chemical potential, we find a series of first-order layering transitions that depend on the nature of the grain boundary. Diagrams are constructed to illustrate the richness of the phase-like behavior (complexion transitions) and its dependence on grain misorientation and stress. Finally, the connection between the thermodynamics of this prototypical model and recent observations of complexion transitions associated with interfaces in metals and ceramics is explored.

Rickman, J. M.; Chan, H. M.; Harmer, M. P.; Luo, J.

2013-12-01

330

Skin friction in zero-pressure-gradient boundary layers  

NASA Astrophysics Data System (ADS)

A global approach leading to a self-consistent solution to the Navier-Stokes-Prandtl equations for zero-pressure-gradient boundary layers is presented. It is shown that as Re??? , the dynamically defined boundary layer thickness ?(x)?x/ln2Rex and the skin friction ?=(2?w)/(?U02)?1/ln2?(x) . Here ?w and U0 are the wall shear stress and free stream velocity, respectively. The theory is formulated as an expansion in powers of a small dimensionless parameter (d?(x))/(dx)?0 in the limit x?? .

Yakhot, Victor

2010-10-01

331

Control of 3D turbulent boundary layer separation caused by a wing–body junction  

Microsoft Academic Search

In three-dimensional flows, boundary layer separation leads to the formation of vortical structures formed by the rolling up of the viscous flow sheet previously confined in a thin layer attached to the wall. Several characteristics of the vortex flow development have negative effects; for example, it may be responsible for unsteadiness or generating unwanted vibration or noise. There are several

D Barberis; P Molton; T Malaterre

1998-01-01

332

DNS of high speed boundary layers over ablating surfaces  

NASA Astrophysics Data System (ADS)

Ablation of thermal protection shields is an important design problem in developing reentry vehicles. Development of predictive computational models for this problem will enable optimization of the size and hence weight of the protective layer. In this work, direct numerical simulation (DNS) of a compressible ablating boundary layer is used to understand the modeling issues in the context of Reynolds-averaged Navier Stokes (RANS) equations. The DNS is performed at conditions obtained from a detailed RANS study of a reentry vehicle. The free stream conditions of the two simulations are Mach 0.6, temperature 5940 K, and Re? 1000; and Mach 1.2, temperature 5580 K, and Re? 2000. The surface ablation of a graphite ablator is modeled using a locally 1-D, quasi-steady state formulation with control volume mass and energy balances over the interior of the ablator. A 10-species gas phase chemistry mechanism is used. A priori studies are used to evaluate scalar flux models and the reaction source term closure in RANS.

Braman, Kalen; Raman, Venkat; Upadhyay, Rochan; Ezekoye, Ofodike

2010-11-01

333

An experimental study of polymer drag reduction and boundary layer diffusion characteristics for incompressible flow over a flat plate  

Microsoft Academic Search

The effect of injecting polymer into a developing boundary layer was determined through the measurement of polymer boundary layer concentration distributions and velocity profiles. To reach this objective, methods to predict local skin friction coefficients were developed as a function of local polymer concentrations and experimentally verified. Tests were also performed using the injection of water and solutions of a

J. Miguel

1978-01-01

334

A Theory of Gravity Wave Absorption by a Boundary Layer  

Microsoft Academic Search

A one-layer model of the atmospheric boundary layer (BL) is proposed to explain the nature of lee-wave attenuation and gravity wave absorption seen in numerical simulations. Two complex coefficients are defined: the compliance coefficient and the wave reflection coefficient. A real-valued ratio of reflected to incident wave energy is also useful. The key result is that, due to horizontal friction,

Ronald B. Smith; Qingfang Jiang; James D. Doyle

2006-01-01

335

Surface heating due to turbulent boundary-layer flows  

SciTech Connect

Numerical analysis is made of surface-heating history when a surface is exposed to transient thermal fluxes from a turbulent compressible boundary layer. The conservation equations are solved by means of a factored ADI method. Results display high heat fluxes at the surface, causing sufficient rise in surface temperatures to quickly reach melting in some substances. The melting liquid-layer case is also briefly discussed.

Kang, S.W.; Levatin, J.L.

1981-01-20

336

Turbulent Boundary Layer Structure and Drag Reduction.  

National Technical Information Service (NTIS)

During the grant period the research work has progressed along the following lines: 1) Development of a localized three-dimensional disturbance in a shear flow; 2) Exploration of new instability modes for inviscid and viscous shear flows; 3) Analysis of p...

M. T. Landahl S. E. Widnall

1980-01-01

337

Two boundary layers in Titan's lower troposphere inferred from a climate model  

NASA Astrophysics Data System (ADS)

Saturn's moon Titan has a dense atmosphere, but its thermal structure is poorly known. Conflicting information has been gathered on the nature, extent and evolution of Titan's planetary boundary layer--the layer of the atmosphere that is influenced by the surface--from radio-occultation observations by the Voyager 1 spacecraft and the Cassini orbiter, measurements by the Huygens probe and by dune-spacing analyses. Specifically, initial analyses of the Huygens data suggested a boundary layer of 300m depth with no diurnal evolution, incompatible with alternative estimates of 2-3km (refs , , ). Here we use a three-dimensional general circulation model, albeit not explicitly simulating the methane cycle, to analyse the dynamics leading to the thermal profile of Titan's lowermost atmosphere. In our simulations, a convective boundary layer develops in the course of the day, rising to an altitude of 800m. In addition, a seasonal boundary of 2km depth is produced by the reversal of the Hadley cell at the equinox, with a dramatic impact on atmospheric circulation. We interpret fog that had been discovered at Titan's south pole earlier as boundary layer clouds. We conclude that Titan's troposphere is well structured, featuring two boundary layers that control wind patterns, dune spacing and cloud formation at low altitudes.

Charnay, Benjamin; Lebonnois, Sébastien

2012-02-01

338

High Energy Benthic Boundary Layer Experiment: HEBBLE  

Microsoft Academic Search

HEBBLE's precise aim is to develop and to test explicit predictions about the response of adhesive\\/cohesive marine sediments to imposed and controlled stresses [Hollister et al., 1980; Kerr, 1980]. Pursuit of this goal has necessitated a co-ordinated, interdisciplinary effort, to date including physical oceanographers, sedimentologists, radiochemists and biochemists, and biological oceanographers.Current produced bed features reflect significant momentum exchange between the

Arthur R. M. Nowell; Charles D. Hollister; Peter A. Jumars

1982-01-01

339

The collapse of turbulence in the atmospheric boundary layer  

NASA Astrophysics Data System (ADS)

A well-known phenomenon in the atmospheric boundary layer is the fact that winds may become very weak in the evening after a clear sunny day. In these quiet conditions usually hardly any turbulence is present. Consequently this type of boundary layer is referred to as the quasi-laminar boundary layer. In spite of its relevance, the appearance of laminar boundary layers is poorly understood and forms a long standing problem in meteorological research. Here we investigate an analogue problem in the form of a stably stratified channel flow. The flow is studied with a simplified atmospheric model as well as with Direct Numerical Simulations. Both models show remarkably similar behaviour with respect to the mean variables such as temperature and wind speed. The similarity between both models opens new way for understanding and predicting the laminarization process. Mathematical analysis on the simplified model shows that relaminarization can be understood from the existence of a definite limit in the maximum sustainable heat flux under stably stratified conditions. This fascinating aspect will be elaborated in future work.

van de Wiel, B. J. H.; Moene, A. F.; Jonker, H. J. J.; Clercx, H. J. H.

2011-12-01

340

On the origin of the high-latitude boundary layer  

Microsoft Academic Search

This paper presents a statistical study of the high-latitude boundary layer (HLBL) performed on 53 Interball-1 magnetopause crossings. In the study we verify if antiparallel merging is the main source of HLBL formation when the IMF is nearly horizontal. To provide such a study we designed a new coordinate system which allowed us to analyze HLBL under varied interplanetary conditions.

A. Fedorov; E. Budnik; J.-A. Sauvaud

2002-01-01

341

CFD simulation of the atmospheric boundary layer: wall function problems  

Microsoft Academic Search

Accurate Computational Fluid Dynamics (CFD) simulations of atmospheric boundary layer (ABL) flow are essential for a wide variety of atmospheric studies including pollutant dispersion and deposition. The accuracy of such simulations can be seriously compromised when wall-function roughness modifications based on experimental data for sand-grain roughened pipes and channels are applied at the bottom of the computational domain. This type

Bert Blocken; Ted Stathopoulos; Jan Carmeliet

342

A Qualitative Description of Boundary Layer Wind Speed Records  

Microsoft Academic Search

The complexity of the atmosphere endows it with the property of turbulence by virtue of which, wind speed variations in the atmospheric boundary layer (ABL) exhibit highly irregular fluctuations that persist over a wide range of temporal and spatial scales. Despite the large and significant body of work on microscale turbulence, understanding the statistics of atmospheric wind speed variations has

Radhakrishnan Nagarajan

2006-01-01

343

Iodine monoxide in the Western Pacific marine boundary layer  

NASA Astrophysics Data System (ADS)

A latitudinal cross-section and vertical profiles of iodine monoxide (IO) are reported from the marine boundary layer of the Western Pacific. The measurements were taken using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) during the TransBrom cruise of the German research vessel Sonne, which led from Tomakomai, Japan (42° N, 141° E) through the Western Pacific to Townsville, Australia (19° S, 146° E) in October 2009. In the marine boundary layer within the tropics (between 20° N and 5° S), IO mixing ratios ranged between 1 and 2.2 ppt, whereas in the subtropics and at mid-latitudes typical IO mixing ratios were around 1 ppt in the daytime. The profile retrieval reveals that the bulk of the IO was located in the lower part of the marine boundary layer. Photochemical simulations indicate that the organic iodine precursors observed during the cruise (CH3I, CH2I2, CH2ClI, CH2BrI) are not sufficient to explain the measured IO mixing ratios. Reasonable agreement between measured and modelled IO can only be achieved, if an additional sea-air flux of inorganic iodine (e.g. I2) is assumed in the model. Our observations add further evidence to previous studies that reactive iodine is an important oxidant in the marine boundary layer.

Großmann, K.; Frieß, U.; Peters, E.; Wittrock, F.; Lampel, J.; Yilmaz, S.; Tschritter, J.; Sommariva, R.; von Glasow, R.; Quack, B.; Krüger, K.; Pfeilsticker, K.; Platt, U.

2012-10-01

344

Iodine monoxide in the Western Pacific marine boundary layer  

NASA Astrophysics Data System (ADS)

A latitudinal cross-section and vertical profiles of iodine monoxide (IO) are reported from the marine boundary layer of the Western Pacific. The measurements were taken using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) during the TransBrom cruise of the German research vessel Sonne, which led from Tomakomai, Japan (42° N, 141° E) through the Western Pacific to Townsville, Australia (19° S, 146° E) in October 2009. In the marine boundary layer within the tropics (between 20° N and 5° S), IO mixing ratios ranged between 1 and 2.2 ppt, whereas in the subtropics and at mid-latitudes typical IO mixing ratios were around 1 ppt in the daytime. The profile retrieval reveals that the bulk of the IO was located in the lower part of the marine boundary layer. Photochemical simulations indicate that the organic iodine precursors observed during the cruise (CH3I, CH2I2, CH2ClI, CH2BrI) are not sufficient to explain the measured IO mixing ratios. Reasonable agreement between measured and modelled IO can only be achieved if an additional sea-air flux of inorganic iodine (e.g., I2) is assumed in the model. Our observations add further evidence to previous studies that reactive iodine is an important oxidant in the marine boundary layer.

Großmann, K.; Frieß, U.; Peters, E.; Wittrock, F.; Lampel, J.; Yilmaz, S.; Tschritter, J.; Sommariva, R.; von Glasow, R.; Quack, B.; Krüger, K.; Pfeilsticker, K.; Platt, U.

2013-03-01

345

ATMOSPHERIC DISPERSION IN THE ARCTIC: WINTERTIME BOUNDARY-LAYER MEASUREMENTS  

EPA Science Inventory

The wintertime arctic atmospheric boundary layer was investigated with micro-meteorological and SF6 tracer measurements collected in Prudhoe Bay, AK. he flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. he relatively warm maritime ...

346

The core-mantle boundary layer and deep Earth dynamics  

Microsoft Academic Search

Recent seismological work has revealed new structures in the boundary layer between the Earth's core and mantle that are altering and expanding perspectives of the role this region plays in both core and mantle dynamics. Clear challenges for future research in seismological, experimental, theoretical and computational geophysics have emerged, holding the key to understanding both this dynamic system and geological

Thorne Lay; Quentin Williams; Edward J. Garnero

1998-01-01

347

Acoustic explorations of the upper ocean boundary layer  

Microsoft Academic Search

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

Svein Vagle

2005-01-01

348

On the Stability of 3D Boundary Layers  

Microsoft Academic Search

We have extended the parabolized stability equations (PSE) to fully 3D boundary layers that vary with all spatial variables. The extended PSE permit the calculation of streamwise and spanwise growth rates of disturbances based on first principles. The method provides improved N factors for the design of turbine vanes and blades, realistic wings with taper, twist, root, tip, and engines,

Th. Herbert

1996-01-01

349

Thickness and concentration profile of the boundary layer in electrodialysis  

Microsoft Academic Search

Back electrical motive force (emf) measurements with spiral electrodialysis (SpED) modules showed that obtaining the profile of the back emf transient curves during depolarization is difficult from the Nernst model, and the assumption of a linear concentration profile in a stirred polarized boundary layer is oversimplified. A non-linear concentration distribution model derived from the error function is introduced.

M. Law; T. Wen; G. S. Solt

1997-01-01

350

Torpedo Drag Reduction Using Magnetohydrodynamic Boundary-Layer Control.  

National Technical Information Service (NTIS)

Study for the drag reduction effect by use of MHD boundary-layer control had been carried out by the present investigators, with the assumption of non-zero electric field. The momentum integral method was used to obtain an optimum magnetic field distribut...

Y. K. Wu G. F. Anderson

1972-01-01

351

Stable Boundary-Layer Scaling Regimes: The Sheba Data  

Microsoft Academic Search

Turbulent and mean meteorological data collected at five levels on a 20-m tower over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are analyzed to examine different regimes of the stable boundary layer (SBL). Eleven months of measurements during SHEBA cover a wide range of stability conditions, from the weakly unstable regime to

Andrey A. Grachev; Christopher W. Fairall; P. Ola G. Persson; Edgar L. Andreas; Peter S. Guest

2005-01-01

352

Basic study on blockage effects in turbulent boundary layer flows  

Microsoft Academic Search

The blockage effects on aerostatic forces such as the drag coefficient, CD, and the base pressure coefficient, Cpb, were experimentally examined by using two-dimensional rectangular cylinders, Blh = 1.0, placed on the floor normal to the flow direction in turbulent boundary layer flows (TBLF). At the same time, the effects of the wind characteristics of the TBLF on the aerostatic

M. Noda; H. Utsunomiya; F. Nagao

1995-01-01

353

On boundary-layer transition in transonic flow  

Microsoft Academic Search

Boundary-layer transition in transonic external flow is addressed theoretically. The transonic area is rich in different flow structures, and transition paths, and the work has wide potential application in transonic aerodynamics, including special reference to the example of flow transition over an engine nacelle. The investigation is intended partly to aid, compare with, and detect any limitations of, a quasi-parallel

R. I. Bowles; F. T. Smith

1993-01-01

354

Beta Limitation of Matter-Antimatter Boundary Layers.  

National Technical Information Service (NTIS)

A model for a boundary layer which separates a cloud of matter from one of antimatter in a magnetized ambiplasma, in which steady pressure equilibrium ceases to exist when a certain beta limit is exceeded, is discussed. The latter is defined as the ratio ...

B. Lehnert

1987-01-01

355

Beta limitation of matter-antimatter boundary layers  

Microsoft Academic Search

A model has earlier been proposed for a boundary layer which separates a cloud of matter from one of antimatter in a magnetized ambiplasma. In this model steady pressure equilibrium ceases to exist when a certain beta limit is exceeded. The latter is defined as the ratio between the ambiplasma and magnetic field pressures which balance each other in the

B. Lehnert

1988-01-01

356

Vertical velocity structure of nonprecipitating continental boundary layer stratocumulus clouds  

Microsoft Academic Search

Continental boundary layer (BL) stratocumulus clouds affect the local weather by modulating the surface energy and moisture budgets and are also intimately tied to the diurnal cycle of the turbulence in the BL. Vertical velocity structure of these clouds is studied using data from the Atmospheric Radiation Measurement Program's Southern Great Plains observing facility located near Lamont, Oklahoma. Data from

Virendra P. Ghate; Bruce A. Albrecht; Pavlos Kollias

2010-01-01

357

Nighttime Chemistry in the Polluted Boundary Layer (Invited)  

Microsoft Academic Search

Chemistry in the urban nocturnal boundary layer (NBL) has received surprisingly little attention in the past. Surface observations often see low ozone and high NO levels, which lead to low nocturnal radical levels and consequently slow chemistry near the ground. Above the surface, however, ozone and radical levels, for example of NO3, are considerably higher, and more efficient chemical pathways

J. Stutz; K. Wong; C. Tsai; O. Pikelnaya

2009-01-01

358

Shock Wave / Boundary Layer Interaction Experiment on Control Surface.  

National Technical Information Service (NTIS)

The shock wave / boundary layer interaction (SWBLI) experiment is part of the EXPERT mission. SWBLI is studied on two identical fixed compression ramps made of C/SiC, which are models for control surfaces. The flow separates on the flat surfaces upstream ...

L. Prochazka S. Schlamp T. Rosgen

2007-01-01

359

COMPRESSIBLE TURBULENT BOUNDARY-LAYER FLOW CONTROL OVER A WEDGE  

Microsoft Academic Search

The effects of blowing and suction on the steady compressible boundary-layer flow with adverse pressure gradient and heat transfer over a wedge are numerically examined. The fluid is considered to be a compressible, viscous and Newtonian ideal gas (air) and it is subjected to a constant velocity of suction\\/injection applied globally to the wedge or locally to specific slots on

M. Xenos; E. Tzirtzilakis; N. Kafoussias

360

The effects of cylindrical surface modifications on turbulent boundary layers  

Microsoft Academic Search

A study employing a combination of hydrogen bubble-wire flow visualization and hot-film anemometry measurements has been conducted to determine the effects sublayer scale streamwise surface modifications on the structure and flow characteristics of turbulent boundary layers. The surface modifications were created using very fine monofilament fishing line of an approximate non-dimensional height of h + = 4. Spanwise line spacings

J. B. Johansen; C. R. Smith

1983-01-01

361

Power laws for rough wall turbulent boundary layers  

Microsoft Academic Search

An assessment of the ability of power laws to describe the mean velocity profile in the overlap region of a zero pressure gradient turbulent boundary layer is reported. The experiments were performed in a wind tunnel on smooth and four different types of rough surfaces at moderate Reynolds numbers. A novel modification to the power law velocity profile is proposed

N. A. Kotey; D. J. Bergstrom; M. F. Tachie

2003-01-01

362

Theoretical investigation of turbulent boundary layer over a wavy surface  

Microsoft Academic Search

The important features of the two-dimensional incompressible turbulent flow over a wavy surface of wavelength comparable with the boundary layer thickness are analyzed. A turbulent field method using a model equation for turbulent shear stress was employed with suitable modification to cover the viscous sublayer. The governing differential equations are linearized based on the small but finite amplitude to wavelength

L. C. Chang

1975-01-01

363

Atmospheric boundary layer modification in the marginal ice zone  

Microsoft Academic Search

A case study of the Andreas et al. (1984) data on atmospheric boundary layer modification in the marginal ice zone is made. Our 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., we find

Theodore J. Bennett; Kenneth Hunkins

1986-01-01

364

Why Rolls are Prevalent in the Hurricane Boundary Layer  

Microsoft Academic Search

Recent remote sensing observations show that the hurricane boundary layer flow, although energetic, is not a region of homogeneous turbulence. In fact, the observations convincingly demonstrate that a large fraction of the turbulent flow in the regions away from the deep convective rainbands is highly organized into intense horizontal roll vortices that are approximately aligned with the mean wind and

Ralph C. Foster

2005-01-01

365

Numerical Solution of the Turbulent-Boundary-Layer Equations.  

National Technical Information Service (NTIS)

The report presents a numerical solution of turbulent boundary-layer equations for both compressible and incompressible flows. An eddy viscosity concept is used to eliminate the Reynolds shear-stress term, and an eddy-conductivity concept is used to elimi...

A. M. O. Smith T. Cebeci

1967-01-01

366

Calculation of incompressible rough-wall boundary-layer flows  

Microsoft Academic Search

The algebraic eddy viscosity model of Cebeci and Smith has been modified to account for wall roughness by incorporating a suggestion of Rotta. The boundary-layer equations are solved, with this model, by the accurate and efficient Keller Box scheme for a wide variety of experimental configurations. These include adverse, zero, and favorable pressure gradients, and roughness elements that approach the

T. Cebeci; K. C. Chang

1978-01-01

367

Drag reduction by microbubbles in a turbulent boundary layer  

Microsoft Academic Search

An experimental characterization of the turbulent boundary layer over a flat plate in the presence of small amounts of microbubbles is performed. The average diameter of the injected bubbles is comparable with the local Kolmogorov lengthscale, and the bulk void fraction C is approximately 0.1%. The velocity field of the liquid phase, as well as the bubble characteristics, is acquired

Boris Jacob; Angelo Olivieri; Massimo Miozzi; Emilio F. Campana; Renzo Piva

2010-01-01

368

Polymer drag reduction of a zero pressure gradient boundary layer  

Microsoft Academic Search

The objective was to determine the response of a zero pressure gradient boundary layer to slot injection of drag reducing polymer solution. Attention was focused on the region far downstream of the injector. Two-component velocity data were acquired with a laser Doppler velocimeter. Mean concentration data were measured using a laser induced fluorescence technique. A 1000 ppm solution of Separan

John E. Koskie; William G. Tiederman

1991-01-01

369

Boundary layer effects above a Himalayan valley near Mount Everest  

Microsoft Academic Search

Periodical Wind Profiler and Radio Acoustic Sounding System observations have been commenced at the Himalayas' northern slope nearby Mount Everest in September 2005. Primarily data sets obtained 25 km remote from the glacier edge are utilized for a preliminary discussion of planetary boundary layer circulation resembling high alpine mountainous regions. Substantial findings include the detection of two wind shears and

Fanglin Sun; Yaoming Ma; Maoshan Li; Weiqiang Ma; Hui Tian; Stefan Metzger

2007-01-01

370

Turbulent dispersion in the Atmospheric Convective Boundary Layer  

Microsoft Academic Search

The dispersion of a plume in the Atmospheric Boundary Layer is a very complex phenomenon that includes the transport, the mixing and the chemical transformations of the plume material. When a plume is dispersed in the ABL, its shape, evolution, and internal structure are determined by the interaction between the plume and the turbulent eddies that characterize the atmospheric motion.

A. Dosio

2005-01-01

371

The bottom boundary layer of the deep ocean  

Microsoft Academic Search

Some aspects of the bottom boundary layer of the deep ocean are exhibited in profiles of salinity and temperature made with a Woods Hole Oceanographic Institution\\/Brown CTD microprofiler. Profiles from the center of the Hatteras Abyssal Plain have a signature that is characteristic of mixing up a uniformly stratified region. Over rough or sloping topography, to the east and west

Laurence Armi; Robert C. Millard

1976-01-01

372

Retinal layer segmentation of macular OCT images using boundary classification  

PubMed Central

Optical coherence tomography (OCT) has proven to be an essential imaging modality for ophthalmology and is proving to be very important in neurology. OCT enables high resolution imaging of the retina, both at the optic nerve head and the macula. Macular retinal layer thicknesses provide useful diagnostic information and have been shown to correlate well with measures of disease severity in several diseases. Since manual segmentation of these layers is time consuming and prone to bias, automatic segmentation methods are critical for full utilization of this technology. In this work, we build a random forest classifier to segment eight retinal layers in macular cube images acquired by OCT. The random forest classifier learns the boundary pixels between layers, producing an accurate probability map for each boundary, which is then processed to finalize the boundaries. Using this algorithm, we can accurately segment the entire retina contained in the macular cube to an accuracy of at least 4.3 microns for any of the nine boundaries. Experiments were carried out on both healthy and multiple sclerosis subjects, with no difference in the accuracy of our algorithm found between the groups.

Lang, Andrew; Carass, Aaron; Hauser, Matthew; Sotirchos, Elias S.; Calabresi, Peter A.; Ying, Howard S.; Prince, Jerry L.

2013-01-01

373

Simultaneous profiling of the Arctic Atmospheric Boundary Layer  

Microsoft Academic Search

The structure of the Arctic atmospheric boundary layer (AABL) and the heat and moisture fluxes between relatively warm water and cold air above non-sea-ice-covered water (such as fjords, leads and polynyas) are of great importance for the sensitive Arctic climate system. So far, such processes are not sufficiently resolved in numerical weather prediction (NWP) and climate models. Especially for regions

S. Mayer; M. Jonassen; J. Reuder

2009-01-01

374

Impulse response of laminar boundary layer and receptivity  

NASA Astrophysics Data System (ADS)

Impulse response of a laminar boundary layer of a flat plate to periodic surface suction and blowing is analyzed through a numerical computation based on parallel flow approximation. Bilateral Laplace transform is used to eliminate the problem of individually identifying the various eigen modes and contributions of other singularities.

Sengupta, Tapan K.

375

On the growth of turbulent regions in laminar boundary layers  

NASA Astrophysics Data System (ADS)

Turbulent spots evolving in a laminar boundary layer on a nominally zero pressure gradient flat plate are investigated. The plate is towed through an 18 m water channel, using a carriage that rides on a continuously replenished oil film giving a vibrationless tow. Turbulent spots are initiated using a solenoid valve that ejects a small amount of fluid through a minute hole on the working surface. A novel visualization technique that utilizes fluorescent dye excited by a sheet of laser light is employed. Some new aspects of the growth and entrainment of turbulent spots, especially with regard to lateral growth, are inferred from the present experiments. To supplement the information on lateral spreading, a turbulent wedge created by placing a roughness element in the laminar boundary layer is also studied both visually and with probe measurements. The present results show that, in addition to entrainment, another mechanism is needed to explain the lateral growth characteristics of a turbulent region in a laminar boundary layer. This mechanism, termed growth by destabilization, appears to be a result of the turbulence destabilizing the unstable laminar boundary layer in its vicinity. To further understand the growth mechanisms, the turbulence in the spot is modulated using drag-reducing additives and salinity stratification.

Gad-El-Hak, M.; Riley, J. J.; Blackwelder, R. F.

1981-09-01

376

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,...

377

Flat plate turbulent boundary-layer control using vertical LEBUs  

NASA Astrophysics Data System (ADS)

Necessity of aerodynamic drag reduction of aircrafts and other moving objects stimulates researchers for finding out new means of the near-wall turbulence control. In [1] it has been found that the vertical positioning of the LEBUs in boundary layer can be much more efficient compared to the conventional horizontal one, although, according to the same authors, the devices were far from being optimized. Present work is focused upon the study of possibility of turbulent skin-friction reduction using flow-aligned vertical LEBUs, the LEBUs being mounted perpendicular to the flat plate surface in nominally gradient-free incompressible turbulent boundary layer. The Reynolds number based on the momentum thickness of the boundary layer at the LEBUs' position was 1099. All measurements were performed using a computer-controlled automated system of space/time hot wire visualization of mean and fluctuating components of the velocity field. The system provided accuracy not worse than approximately ą2 ľm along x, y, and z coordinates. Local skin friction C f in the regular (unmodified) shear flow was determined from the condition of the best correspondence between measured and and classic velocity coefficient profiles in the region of the law of the wall functionality U^+ = A log y+ + B with known coefficients A and B. In the modified boundary layer C f was determined by the mean velocity gradient at the wall (partial U/partial y)_{y=0}. The measurement technique is given in more detail in [2].

Kornilov, V. I.; Boiko, A. V.

378

Numerical investigation of the stable nocturnal boundary layer  

NASA Astrophysics Data System (ADS)

The governing equations for the wind field and temperature field within the flat nocturnal atmospheric boundary layer (FNABL, (30)) are a highly nonlinear system of parabolic PDEs. This system is discretized into a crude two-layer numerical model via the finite difference approximation and the Monin-Obukhov similarity theory ( (22)), and analyzed as a set of ODEs. The steady state problem is also transformed into an equivalent system of first order ODEs and then discretized into a very accurate 'multi-layer' model using the orthogonal collocation method ( (12)). Some numerical techniques for nonlinear problems such as numerical continuation and bifurcation analysis are used to study the steady state solutions as some physical parameters vary. The resulting bifurcation diagrams from the two layer and multilayer models have qualitatively similar behavior. This implies that the two-layer model, though mathematically crude, does capture some essential features of the original system. Time dependent solutions of the two layer model are computed via the fourth-order Runge-Kutta technique, for various combinations of parameters, and they match and support related bifurcation diagrams. Physically realistic wind and temperature profiles over the boundary layer are computed from the 'multi-layer' model. Our results imply that operational application of this type of model of frost or pollution dispersion may not be made with confidence for certain parameter regimes, and they have important implications for the predictability of the nocturnal boundary layer for frost prediction or pollution dispersion. Space discretization for simple parabolic PDEs from an AUTO demo via pseudospectral method with Chebyshev basis functions is very accurate, and seems promising for future application to our problem.

Shi, Xingzhong

1997-10-01

379

Characteristics of nonlinear evolution of wavepackets in boundary layers  

NASA Astrophysics Data System (ADS)

The nonlinear evolution of a finite-amplitude disturbance in a 3-D supersonic boundary layer over a cone was investigated recently by Liu et al. using direct numerical simulation (DNS). It was found that certain small-scale 3-D disturbances amplified rapidly. These disturbances exhibit the characteristics of second modes, and the most amplified components have a well-defined spanwise wavelength, indicating a clear selectivity of the amplification. In the case of a cone, the three-dimensionality of the base flow and the disturbances themselves may be responsible for the rapid amplification. In order to ascertain which of these two effects are essential, in this study we carried out DNS of the nonlinear evolution of a spanwise localized disturbance (wavepacket) in a flat-plate boundary layer. A similar amplification of small-scale disturbances was observed, suggesting that the direct reason for the rapid amplification is the three-dimensionality of the disturbances rather than the three-dimensional nature of the base flow, even though the latter does alter the spanwise distribution of the disturbance. The rapid growth of 3-D waves may be attributed to the secondary instability mechanism. Further simulations were performed for a wavepacket of first modes in a supersonic boundary layer and of Tollmien-Schlichting (T-S) waves in an incompressible boundary layer. The results show that the amplifying components are in the band centered at zero spanwise wavenumber rather than at a finite spanwise wavenumber. It is therefore concluded that the rapid growth of 3-D disturbances in a band centered at a preferred large spanwise wavenumber is the main characteristic of nonlinear evolution of second mode disturbances in supersonic boundary layers.

Yu, Min; Luo, JiSheng; Li, Jia

2013-02-01

380

Development of free shear layer  

Microsoft Academic Search

The relation between the evolution of coherent structures and self-preservation in a mixing layer is investigated. It is shown that in a mixing layer with an initially laminar boundary layer, the three-dimensional transition is triggered by the large straining produced by the merging of spanwise coherent structures. At a short distance from the transition, the mean flow reaches self-preservation.

L. S. Huang; C. M. Ho

1984-01-01

381

Mean Structure of the Nocturnal Boundary Layer under Strong and Weak Wind Conditions: EPRI Case Study.  

NASA Astrophysics Data System (ADS)

The major objective of this study was to analyze the mean structure and evolution of the nocturnal boundary layer (NBL) under strong and weak wind conditions. Meteorological data collected during the plume-validation experiment conducted by the Electric Power Research Institute (EPRI) over a flat homogeneous terrain at Kincaid, Illinois (39°35N, 89°25W), were utilized. A one-dimensional meteorological boundary layer model originally developed by R. A. Pielke, modified with turbulent kinetic energy mixing-length closure, a layer-by-layer emissivity-based radiation scheme, and nonlinear nondimensional temperature and wind profiles in the surface layer, was used. In the four cases that were considered, ranging from strong to weak geostrophic forcing, the model reproduced the observed mean profiles, their evolutions in the NBL, and the inertial oscillations reasonably well. The NBL developed into three layers wherein 1) very close to the surface, radiative cooling dominated over turbulence cooling; 2) a layer above, turbulent cooling was the dominant mechanism; and 3) near the top of the turbulent layer and above, clear-air radiative cooling was the dominating mechanism. However, depending on the geostrophic wind, the structure of these layers varied from one situation to another. The wind maximum, which was at least above 200 m of altitude under windy conditions, was located at an altitude of less than 100 m for the weak-wind case, probably because of weaker diffusion in the boundary layer during transition.

Krishna, T. B. P. S. Rama V.; Sharan, Maithili; Gopalakrishnan, S. G.; Aditi

2003-07-01

382

Saturn's low-latitude boundary layer: 2. Electron structure  

NASA Astrophysics Data System (ADS)

The boundary of a planetary magnetosphere is the site of mass, momentum, and energy transport. This transport produces a layer of mixed solar wind and magnetospheric plasma inside and adjacent to the boundary. In the case of Earth, the electron structure of this layer is distinctive, and has been explained by models of the layer on open magnetic field lines. In this paper we examine the electron structure of Saturn's low-latitude boundary layer (LLBL) using observations made by the Cassini spacecraft; the typical properties and variability of Saturn's LLBL are examined in a companion paper. By analyzing the relationship between the electron density and temperature measured during Cassini magnetopause crossings we demonstrate that the electron structure of Saturn's LLBL is highly variable. At some of the crossings the structure of Saturn's LLBL is similar to previously reported examples of the structure of Earth's LLBL, where the major changes in electron density and temperature clearly occur in different regions of the layer, producing a distinctive shape to the temperature-density distribution. However, at many crossings the structure of Saturn's LLBL is unlike the previously reported examples of the structure of Earth's LLBL, since they lack the same distinctive shape to the distribution. We discuss the possible explanations for these differences in the electron structure of Saturn's LLBL, and what these differences could tell us about how the solar wind interacts with a planetary magnetosphere.

Masters, A.; Walsh, A. P.; Fazakerley, A. N.; Coates, A. J.; Dougherty, M. K.

2011-06-01

383

Atmospheric controls on soil moisture-boundary layer interactions  

NASA Astrophysics Data System (ADS)

This thesis addresses the question of how the early morning atmospheric thermodynamic structure affects the interaction between the soil moisture state and the growth and development of the boundary layer (BL), leading to the triggering of convection. It is concluded that in mid-latitudes, for matters of convective triggering and response to land surface conditions, the critical portion of the atmosphere-approximately 1 to 3 km above the ground surface-is independent of geographic location and local synoptic setting. As long as the low levels of the troposphere are relatively humid but not extremely close to saturation, a negative feedback between soil moisture and rainfall is likely when the early morning temperature lapse rate in this region is dry adiabatic; a positive feedback is likely when it is moist adiabatic; and when there is a temperature inversion in this region, deep convection cannot occur, independent of the soil moisture. Additionally, when the low levels of the troposphere are extremely dry or very close to saturation, the occurrence of convection is determined solely by the atmospheric conditions. Essential characteristics of the temperature structure of the early-morning atmosphere are captured by a new thermodynamic measure, the Convective Triggering Potential (CTP), developed to distinguish between soundings favoring rainfall over dry soils from those favoring rainfall over wet soils. A one-dimensional model of the planetary boundary layer (BL) and surface energy budget has been modified to allow the growing BL to entrain air from an observed atmospheric sounding. The model is used to analyze the impact of soil saturation on BL development and the triggering of convection in different atmospheric settings. Analyses of CTP-HIlow scatter plots from radiosonde stations across the contiguous 48 United States reveal that positive feedbacks are likely in much of the eastern half of the country. Use of the 1D BL model at four additional stations confirms that the CTP-HI low framework used in this nationwide analysis is valid for regions far removed from Illinois, where it was originally developed. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253- 1690.) (Abstract shortened by UMI.)

Findell, Kirsten Lynn

2001-11-01

384

The Role of Lateral Boundary Conditions and Boundary Layer in air Quality Modelling System  

NASA Astrophysics Data System (ADS)

Often in Europe, high concentrations of O3 and NOx exceed the allowed maximum levels defined by the European Commission. The model system WRF-CMAQ is a regional air quality modelling system, which we applied to the European continent with a horizontal resolution of 12km × 12km and 8 vertical layers for CMAQ. The EMEP emission inventory was compiled and applied to the model domain. Due to uncertain external influence, the definition of adequate lateral boundary conditions for gas phase chemistry in a regional model is a complex issue and an important source of errors. Sensitivity studies were performed for a tested month (May 2004) to assess the impact of boundary conditions and boundary layer on the quality of the simulations. In order to evaluate the performances of the model, model simulations were compared to 70 and 21 stations from the EMEP network for O3 and NO2, respectively, throughout Europe. Basically, synthetic boundary conditions over 6 vertical layers were used in preliminary simulations. Then, climatological data provided by the global climate-chemistry model LMDz-INCA2 were used to define consistent lateral conditions and simulations were also performed using the May-2004 data from this model (both over 6 or 15 layers). Climatological data provided reliable conditions for the model boundaries but did not improve the quality of simulated O3 in the model domain (mean normalized gross error (MNGE) of 23% compared to 20% for synthetic profiles). Besides, the use of higher vertical resolution notably improved the trend and daily variations of O3 and hindered unrealistic subsidence of O3-enriched air from aloft, reducing the MNGE from 23% to 18%. The chemistry of NO2 was found to be mostly governed by local emissions, with little influence of the boundary conditions. A best-fitting configuration of boundary conditions will be discussed. Also, this work analyzes the influence of two different planetary boundary layer (PBL) parameterization schemes: the YSU PBL scheme based on Hong. et al (1996) and a new stable boundary layer scheme allowing the computation of vertical diffusion coefficients at all timesteps. The two schemes do not differ sufficiently from one another to lead to a significant improvement in the simulation of the chemistry. In the view of excessive NO2 simulated at night, other PBL parameterizations will be discussed.

Piot, M.; Jorba, O.; Jimenez, P.; Baldasano, J.

2008-12-01

385

Incompressible boundary layer transition flight experiments over a nonaxisymmetric fuselage forebody and comparisons with laminar boundary layer stability theory  

Microsoft Academic Search

Analyses of previous boundary-layer transition experiments over axisymmetric bodies indicates a potential for achieving substantial amounts of laminar flow over such shapes. Achievement of natural laminar flow over portions of nonlifting aircraft geometries, such as fuselage to forebodies, tip tanks or engine nacelles, could significantly contribute to the reduction of total aircraft viscous drag. A modern surface-panel method, a streamwise

Paul M. H. W. Vijgen

1990-01-01

386

Asymptotic analysis of the k-epsilon turbulent boundary layer  

NASA Astrophysics Data System (ADS)

Matched expansions in the limit of infinite Reynolds number are presently used to analyze the representation of attached turbulent boundary-layer flows yielded by the standard form of the k-epsilon model, whose structure is made up of a thin viscous wall-layer, a thick outer 'defect layer' region, and a thin region at the outer edge of the defect layer. Similarity equations governing the outer-layer flow are obtained for equilibrium flow situations, yielding profiles that are not analytic at the outer edge; the asymptotic behavior at the outer edge has a strong influence on the shape of the profiles throughout a significant portion of the entire outer region. The asymptotic results may be the basis of zonal modeling for complex turbulent flow fields.

Bogucz, E. A.

387

The possibility of drag reduction by outer layer manipulators in turbulent boundary layers  

Microsoft Academic Search

Experiments were carried out with the aim of investigating the possibility of obtaining a net drag reduction on a finite body by manipulating the outer layer structure of the turbulent boundary layer. The experiments were carried out in a 260 m long towing tank, where large eddy breakup devices (LEBU’s) were used in single and tandem configurations on a large

Alexander Sahlin; Arne V. Johansson; P. Henrik Alfredsson

1988-01-01

388

Pressure field due to drag reducing outer layer devices in turbulent boundary layers  

Microsoft Academic Search

The wall static pressure in the vicinity of drag reducing outer layer devices in flat wall turbulent boundary layers has been measured and compared with an inviscid theory. Symmetric and cambered airfoil devices have been examined at small angles of attack and very low chord Reynolds numbers. Airfoil devices impose a sequence of strong favorable and adverse pressure gradients on

P. R. Bandyopadhyay; R. D. Watson

1987-01-01

389

Formation of elevated refractive layers in the oceanic boundary layer by modification of land air flowing offshore  

Microsoft Academic Search

The usual picture of the development of temperature and humidity boundary layers in a land air mass that moves offshore is shown to be very wrong under one type of Foehn condition in southern California, and it is probable that similar conditions can prevail in widespread areas around the globe, notably the Mediterranean Sea and the monsoonal regions of the

Earl E. Gossard

1982-01-01

390

Environmental boundaries to energy development  

SciTech Connect

Public concern about the environment, health and safety consequences of energy technology has been growing steadily for more than two decades in the United States. This concern forms an important boundary condition as the United States seeks to develop a new National Energy Strategy. Furthermore, the international aspects of the energy/environment interface such as acid rain global climate change and stratospheric ozone depletion are very prominent in US thinking. In fact, the energy systems of the world are becoming more closely coupled environmentally and otherwise. Now where is this coupling more important than that between the industrialized and developing world; the choices made by each will have profound effects on the other. The development of energy technologies compatible with both economic growth and improving and sustaining environmental quality represents a major R D challenge to the US and USSR. Decision about adoption of new technology and R D priorities can be improved by better measurements of how energy sources and uses are changing throughout the world and better methods to project the potential consequences of these decisions. Such projection require understanding relative risks of alternating existing and evolving technologies. All of these R D areas, technology improvement energy system monitoring and projection and comparative risk assessment are the topics of this seminar. Progress in each may be enhanced by collaboration and cooperation between our two countries. 7 refs., 27 figs., 5 tabs.

Trivelpiece, A.W.

1989-01-01

391

Boundary Layer Depth, Entrainment, and Decoupling in the Cloud-Capped Subtropical and Tropical Marine Boundary Layer.  

NASA Astrophysics Data System (ADS)

Estimates of marine boundary layer (MBL) depth and degree of decoupling for two regions of the subtropical and tropical east Pacific are presented using satellite observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). These data are combined in a novel way with NCEP reanalysis data and a mixing line parameterization to estimate the mean entrainment rate we over the two regions. Mean entrainment rates vary geographically and have maxima just downwind of the Californian coast (e 4 5 mm s-1), and also in the core of the equatorial east Pacific cold tongue where mean we exceeds 6 mm s-1. Entrainment exceeds subsidence by 30% or less in the subtropical stratocumulus regions. North of the equatorial cold tongue entrainment greatly exceeds subsidence, producing a rapid deepening of the MBL as air flows over a marked SST gradient.Shallow MBLs (zi < 500 700 m) are found to be well mixed in general. The decoupling increases markedly for deeper boundary layers and is well parameterized as a function of the thickness of the layer extending from the top of the surface mixed layer to the MBL inversion. This study demonstrates new ways in which large-scale observational and reanalysis datasets may be used to aid understanding of MBL boundary layer and cloud systems.


Wood, Robert; Bretherton, Christopher S.

2004-09-01

392

Boundary Layer Structure and Dynamics in Outer Hurricane Rainbands.  

NASA Astrophysics Data System (ADS)

Results of hurricane boundary layer experiments conducted in outer rainbands of Hurricanes Josephine (1984) and Earl (1986) are presented. Comparisons of precipitation, kinematic, and thermodynamic structures in these storms and in Hurricane Floyd (1981) indicate that principal rainbands have common characteristic mesoscale and convective scale features in the boundary layer. The two-dimensional mesoscale structure suggests that rainbands are made up of a linear aggregate of cellular reflectivity elements (on the inner, upshear side of the band) and stratiform rain (on the outer downshear side). The band is oriented perpendicular to the shear above the boundary layer and cells move downband at about 80% of the maximum wind. Alongband and crossband wind maxima, and maximum equivalent potential temperatures are located on the outer side of the band axis, with minima 4-8 km to the inner side. Updrafts and downdrafts are preferentially located on the inner side of the band axis, along with maximum crossband convergence, cyclonic shear vorticity, and minimum equivalent potential temperatures. Downdraft transport of cool and dry air from middle levels on the inner side of the rainband was responsible for modifying mixed layer structure adjacent to the band on alongband scales of 100 km. An undisturbed mixed layer of 500 m was present on the outer side of the band while a variety of structures were observed on the inner side indicative of both disturbed and recovering mixed layers. Application of a mixed layer model to low level flow trajectories from the outer rainband to the eyewall indicates that under some conditions, the mixed layer may not recover sufficiently and low surface equivalent potential temperature air may reach the eyewall. These conditions are associated with suppressed flow in a region of positive divergence with moderate rainfall from a middle level anvil cloud. Incomplete recovery was most evident when a recovering mixed layer exhibited a negative jump in water vapor mixing ratio. Differential evaporation cooling over the transition layer drives entrainment of dry air from above which overcomes any evaporation moistening, resulting in a drier mixed layer (with lower surface equivalent potential temperature). Depending on the humidity profile and spatial scale of the initial disturbed mixed layer, the model results suggest that incomplete recovery may be responsible for transitional changes in hurricane intensity.

Powell, Mark Dillon

393

A numerical study of compressible turbulent boundary layers  

NASA Astrophysics Data System (ADS)

Compressible turbulent boundary layers with free-stream Mach number ranging from 2.5 up to 20 are analyzed by means of direct numerical simulation of the Navier--Stokes equations. The simulation generates its inflow condition using the rescaling-recycling method. The main objective is to study the effect of Mach number on turbulence statistics and near-wall turbulence structures. The present study shows that the main turbulence statistics can be correctly described as variable-density extensions of incompressible results. We show that the apparent increase in the magnitude of the fluctuating Mach number with increasing free-stream Mach number is a variable-property effect. Using the mean density to scale the fluctuating Mach number collapses results for different freestream Mach number. The increase in the pdf tails of the dilatation is also shown to be a variable-property effect. Compressible boundary layers are shown to be similar to incompressible boundary layers in that, without the linear coupling term, the turbulence cannot be sustained. The linear coupling term is necessary to generate the wall-layer streaks. For an adiabatic wall, the near-wall structure exhibits the same characteristics as in incompressible turbulent flow in terms of the spanwise spacing of the streaks ( 100^+). For isothermal walls, near-wall turbulence structures show their dependence on the surface heat flux.

Lagha, Maher; Kim, John; Eldredge, Jeff; Zhong, Xiaolin

2010-11-01

394

Transitionally rough zero pressure gradient turbulent boundary layers  

NASA Astrophysics Data System (ADS)

Near-wall measurements are performed to study the effects of surface roughness and viscous shear stresses on the transitionally rough regime (5 < k + < 70) of a zero pressure gradient turbulent boundary layer. The x-dependence is known from the eleven consecutive measurements in the streamwise direction, which allows for the computation of the streamwise gradients in the boundary layer equations. Thus, the skin friction is computed from the integrated boundary layer equation with errors of 3 and 5% for smooth and rough, respectively. It is found that roughness destroys the viscous layer near the wall, thus, reducing the contribution of the viscous stress in the wall region. As a result, the contribution in the wall shear stress due to form drag increases, while the viscous stress decreases. This yields Reynolds number invariance in the skin friction as k + increases into the fully rough regime. Furthermore, the roughness at the wall reduces the high peak of the streamwise component of the Reynolds stress in the near-wall region. However, for the Reynolds wall-normal and shear stress components, its contribution is not significantly altered for sand grain roughness.

Brzek, Brian G.; Cal, Raúl Bayoán; Johansson, Gunnar; Castillo, Luciano

2008-01-01

395

Inner-Layer Structure of a Shear-Driven 3-D Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

An investigation of a planar, shear-driven 3-D turbulent boundary layer (3DTBL) was performed to examine the effects of variable skewing on the turbulence structure and flow physics of the non-equilibrium flow field. Particle image velocimetry (PIV) measurements were acquired in both the xy-plane (perpendicular to the wall) and the xz-plane (parallel to the wall) to examine modifications to the near-wall turbulence when subject to varying strengths of crossflow. These measurements reveal significant changes to the inner region of the boundary layer, particularly at higher shear rates. Increased spanwise shear leads to the breakup of larger organized flow structures into smaller structures that are displaced out from the near-wall region of the boundary layer, leading to increased transport and a thickening of the inner region of the boundary layer. The crossflow is also associated with increases in the (normal and shear) Reynolds stresses, particularly over the translating wall section. The discontinuity at the trailing edge of the translating wall results in an initial decrease of the streamwise normal stress, which subsequently recovers and increases above 2-D levels. Another effect of the crossflow is the disruption of the initial 2-D boundary layer spanwise vorticity layer, contributing to the increased momentum transfer in this region.

Kiesow, Robert; Plesniak, Michael

1999-11-01

396

Lidar analysis techniques for use in the atmospheric boundary layer  

NASA Astrophysics Data System (ADS)

There is a growing body of observational and theoretical evidence which suggests that local climate characteristics are associated with variations in the earth's surface. The link between surface variability and local-scale processes must be made if we are to improve our understanding of the feedback mechanisms involved in surface-atmosphere dynamics. However, to understand these interactions, the surface-atmosphere interface must be studied as a large-scale spatial system. Lidars are ideal tools to study the spatial properties of the atmosphere. The described techniques were developed for use with the Los Alamos Water Raman-Lidar, but are applicable to many other types of lidar. The methodology of the analysis of lidar data is summarized in order to determine meteorological parameters in the atmospheric boundary layer. The techniques are not exhaustive but are intended to show the depth and breadth of the information which can be obtained from lidars. Two methods for the computation of water-vapor fluxes were developed. The first uses the fact that the water vapor concentration in the vertical direction follows a logarithmic profile when corrected for atmospheric stability. The second method involves using inertial dissipation techniques in which lidar-derived spatial and temporal power spectra are used to determine the flux.

Eichinger, William E.; Cooper, Daniel I.; Hof, Doug; Holtkamp, David; Quick, Robert, Jr.; Tiee, Joe; Karl, Robert

1992-07-01

397

Observations of Surface Energy Fluxes and Boundary-Layer Structure Over Heron Reef, Great Barrier Reef, Australia  

NASA Astrophysics Data System (ADS)

Over warm, shallow coral reefs the surface radiation and energy fluxes differ from those of the open ocean and result in modification to the marine atmospheric boundary layer via the development of convective internal boundary layers. The complex interrelationships between the surface energy balance and boundary-layer characteristics influence local weather (wind, temperature, humidity) and hydrodynamics (water temperature and currents), as well as larger scale processes, including cloud field properties and precipitation. The nature of these inter-relationships has not been accurately described for coral reef environments. This study presents the first measurements of the surface energy balance, radiation budget and boundary layer thermodynamics made over a coral reef using an eddy-covariance system and radiosonde aerological profiling of the lower atmosphere. Results show that changes in surface properties and the associated energetics across the ocean-reef boundary resulted in modification to the marine atmospheric boundary layer during the Austral winter and summer. Internal convective boundary layers developed within the marine atmospheric boundary layer over the reef and were found to be deeper in the summer, yet more unstable during the winter when cold and drier flow from the mainland enhances heat and moisture fluxes to the atmosphere. A mixed layer was identified in the marine atmospheric boundary layer varying from 375 to 1,200 m above the surface, and was deeper during the summer, particularly under stable anticyclonic conditions. Significant cloud cover and at times rain resulted in the development of a stable stratified atmosphere over the reef. Our findings show that, for Heron Reef, a lagoonal platform reef, there was a horizontal discontinuity in surface energy fluxes across the ocean-reef boundary, which modified the marine atmospheric boundary layer.

MacKellar, Mellissa C.; McGowan, Hamish A.; Phinn, Stuart R.; Soderholm, Joshua S.

2013-02-01

398

A Study of stable Atmospheric Boundary Layer over highveld South Africa  

NASA Astrophysics Data System (ADS)

The study is part of the South African - Norwegian Programme for Research and Co-operation Phase II "Analysis and Possibility for Control of Atmospheric Boundary Layer Processes to Facilitate Adaptation to Environmental Changes". The research strategy of the project is based on 4 legged approach. 1) Application and further development of contemporary atmospheric boundary layer theory. 2) Use of modeling based on large eddy simulation techniques. 3) Experimental investigation of turbulent fluxes. 4) Training and developing academics capable of dealing with the present and new challenges. The paper presents some preliminary results on the micrometeorological variability of the basic meteorological parameters and turbulent fluxes.

Luhunga, P.; Esau, I.; Djolov, G.

2010-08-01

399

Boundary layer ozone - An airborne survey above the Amazon Basin  

NASA Astrophysics Data System (ADS)

Ozone data obtained over the forest canopy of the Amazon Basin during July and August 1985 in the course of NASA's Amazon Boundary Layer Experiment 2A are discussed, and ozone profiles obtained during flights from Belem to Tabatinga, Brazil, are analyzed to determine any cross-basin effects. The analyses of ozone data indicate that the mixed layer of the Amazon Basin, for the conditions of undisturbed meteorology and in the absence of biomass burning, is a significant sink for tropospheric ozone. As the coast is approached, marine influences are noted at about 300 km inland, and a transition from a forest-controlled mixed layer to a marine-controlled mixed layer is noted.

Gregory, Gerald L.; Browell, Edward V.; Warren, Linda S.

1988-02-01

400

Numerical study of light scattering by a boundary-layer flow.  

PubMed

Temperature inhomogeneities in free, isotropic turbulence have the effect of scattering light in near-forward angles. We investigate numerically modifications of free turbulence by a rigid wall and its effect on the propagation of light through turbulence. The wall is a 5 cm optical window placed at the leading edge of an instrument towed with speeds of 0.1 and 1 m/s in free turbulence. The turbulent flow field presents inhomogeneities of an embedded passive scalar (Pr = 7, temperature in water), which are modified by the boundary layer developing on the window. We find that the developing laminar boundary layer has a negligible effect on light scattering for the investigated geometry when considered in terms of the volume-scattering function (differential cross section). This indicates that the boundary layer is not an obstacle for optical measurements of turbulence. PMID:16149351

Bogucki, Darek J; Domaradzki, Julian A

2005-09-01

401

Receptivity and stability of the boundary layer at a high turbulence level  

NASA Astrophysics Data System (ADS)

The results of experimental studies on the boundary layer stability in gradient flow at high turbulence level are presented. The question is considered on the possibility of artificial generation, further development, and influence on laminar-turbulent transition of instability waves (Tollmien-Schlichting waves) in the boundary layer of the airfoil when the level of turbulence in the onflow constitutes 1.75 percent of the onflow velocity; the flow receptivity to disturbances and their control using the suction of the boundary layer are studied. Results of the investigations on the modeling of a turbulent spot generated from the solitary nonlinear wave packet are shown, and the characteristics of the development turbulent spot are presented at onflow turbulence degrees higher than that in earlier papers.

Grek, G. R.; Kozlov, V. V.; Ramazanov, M. P.

402

The Boundary Layer Flows of a Rivlin-Ericksen Fluid  

NASA Astrophysics Data System (ADS)

The present work deals with the two-dimensional incompressible, laminar, steady-state boundary layer equations. First, we determine a family of velocity distributions outside the boundary layer such that these problems may have similarity solutions. We study the Falkner-Skan flow of a viscoelastic fluid governed by second order model, as the Reynolds number Re? ?. We obtain an ordinary forth order differential equation to obtain the stream function, velocity profile and the stress. The stream function is then governed by a generalized Falkner-Skan equation. In comparison with Newtonian Falkner-Skan equation that has two coefficients this new one has four coefficients that two of them represent elastic properties of the fluid. The effects of the elastic parameter on the velocity filed have been discussed. As it is shown in the figure there is a good agreement between numerical results and previous special cases confirm the validity of the presented algorithm.

Sadeghy, K.; Khabazi, N.; Taghavi, S. M.

403

Aerosol Observations by Lidar in the Nocturnal Boundary Layer  

NASA Astrophysics Data System (ADS)

Aerosol observations by lidar in the nocturnal boundary layer (NBL) were performed in Potenza, Southern Italy, from 20 January to 20 February 1997. Measurements during nine winter nights were considered, covering a variety of boundary-layer conditions. The vertical profiles of the aerosol backscattering coefficient at 355 and 723.37 nm were determined through a Klett-modified iterative procedure, assuming the extinction-to-backscattering ratio within the NBL has a constant value. Aerosol average size characteristics were retrieved from almost simultaneous profiles of the aerosol backscattering coefficient at 355 and 723.37 nm, the measurements being consistent with an accumulation mode radius not exceeding 0.4 m. Similar results in terms of aerosol sizes were obtained from measurements of the extinction-to-backscattering ratio profile at 355 nm performed on six nights during the measurement campaign. Backscattering profiles at 723.37 nm were also converted into profiles of aerosol liquid water content.

di Girolamo, Paolo; Ambrico, Paolo Francesco; Amodeo, Aldo; Boselli, Antonella; Pappalardo, Gelsomina; Spinelli, Nicola

1999-07-01

404

On multiscale homogenization problems in boundary layer theory  

NASA Astrophysics Data System (ADS)

This paper is concerned with the homogenization of the equations describing a magnetohydrodynamic boundary layer flow past a flat plate, the flow being subjected to velocities caused by injection and suction. The fluid is assumed incompressible, viscous and electrically conducting with a magnetic field applied transversally to the direction of the flow. The velocities of injection and suction and the applied magnetic field are represented by rapidly oscillating functions according to several scales. We derive the homogenized equations, prove convergence results and establish error estimates in a weighted Sobolev norm and in C 0-norm. We also examine the asymptotic behavior of the solutions of the equations governing a boundary layer flow past a rough plate with a locally periodic oscillating structure.

Amirat, Youcef; Chechkin, Gregory A.; Romanov, Maxim

2012-06-01

405

Boundary layer study. Phase 4: Experimental validation test plan  

NASA Astrophysics Data System (ADS)

The trend towards very large area ratio nozzles, which result in performance gains for space propulsion applications, has increased the need for detailed knowledge of the momentum losses due to nozzle viscous effects (i.e., boundary layer). These losses degrade overall system performance, such as increasing system weight, decreasing useful payload weight, and/or decreasing effective system range. Another important factor in designing propulsive nozzles is the detailed knowledge of heat transfer at the wall for regeneratively cooled walls and/or material performance. Phase 4 (described in this report) consists of preparing an experimental test plan, which, if executed, would validate computational techniques used in evaluating propulsion performance losses due to boundary layers in rocket nozzles. The importance of the loss and the basis for the experimental work are established. Experimental techniques are also reviewed. Visits to numerous experimental facilities are described along with recommendations from these facilities. Finally, recommendations as to the diagnostic techniques of choice are made.

Kehtarnavaz, H.; Coats, D. E.

1990-11-01

406

Receptivity of boundary layers - Asymptotic theory and experiment  

NASA Astrophysics Data System (ADS)

The sources of disturbance (vibrators, small jets, vortices, sound waves) in a boundary layer are considered, emphasizing their ability to provoke the onset of eigenoscillations with exponentially growing amplitude. Harmonic sources give rise to the Tollmien-Schlichting waves, whereas impulsive sources excite wave packets. General requirements are stated for the temporal and spatial characteristics of the signals emitted by the devices causing disturbance, as well as for obstacles met by signals when propagating. To scale the frequencies and wavenumbers in terms of the Reynolds number taking on indefinitely large values, the asymptotic theory of an interacting boundary layer with the triple-deck structure is used. The conclusions from the asymptotic analysis are in line with the results of measurements in wind tunnels when the Reynolds numbers were moderate.

Kozlov, V. V.; Ryzhov, O. S.

1990-06-01

407

Entropy generation in the viscous parts of turbulent boundary layers  

SciTech Connect

The local (pointwise) entropy generation rate per unit volume S is a key to improving many energy processes and applications. Consequently, in the present study, the objectives are to examine the effects of Reynolds number and favorable streamwise pressure gradients on entropy generation rates across turbulent boundary layers on flat plates and—secondarily—to assess a popular approximate technique for their evaluation. About two-thirds or more of the entropy generation occurs in the viscous part, known as the viscous layer. Fundamental new results for entropy generation in turbulent boundary layers are provided by extending available direct numerical simulations. It was found that, with negligible pressure gradients, results presented in wall coordinates are predicted to be near “universal” in the viscous layer. This apparent universality disappears when a significant pressure gradient is applied; increasing the pressure gradient decreases the entropy generation rate. Within the viscous layer, the approximate evaluation of S differs significantly from the “proper” value but its integral, the entropy generation rate per unit surface area S, agrees within 5% at its edge.

Donald M. McEligot; Edmund J. Walsh; Eckart Laurien; Philippe R. Spalart

2008-06-01

408

Boundary-layer equations in generalized curvilinear coordinates  

Microsoft Academic Search

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

Argyris G. Panaras

1987-01-01

409

A zonal grid algorithm for DNS of turbulent boundary layers  

Microsoft Academic Search

A zonal grid algorithm for direct numerical simulation (DNS) of incompressible turbulent flows within a Finite-Volume framework is presented. The algorithm uses fully coupled embedded grids and a conservative treatment of the grid-interface variables. A family of conservative prolongation operators is tested in a 2D vortex dipole and a 3D turbulent boundary layer flow. These tests show that both, first-

Michael Manhart

2004-01-01

410

Weak Boundary Layers in Styrene-Butadiene Rubber  

Microsoft Academic Search

In this paper two kinds of weak boundary layers (WBL) in synthetic vulcanized styrene-butadiene rubber are described.i) WBL produced by the presence of antiadhesion compounds of the rubber formulation (zinc stearate, microcrystalline paraffin wax). These WBL cannot be effectively removed by solvent wiping, whether followed by washing with an ethanol\\/water mix or not. Although this treatment allowed a significant removal

M. M. Pastor-Blas; M. S. Sánchez-Adsuar; J. M. Martín-Martínez

1995-01-01

411

The Amazon Boundary Layer Experiment: Wet season 1987  

Microsoft Academic Search

The Amazon Boundary Layer Experiment (ABLE 2B) used data from aircraft, ground-based, and satellite platforms to characterize the chemistry and dynamics of the lower atmosphere over the Amazon Basin during wet season (April-May 1987) conditions. This paper reports the experimental design for ABLE 2B and a brief summary of the results for the combined ABLE 2A and ABLE 2B. The

R. C. Harriss; M. Garstang; S. C. Wofsy; S. M. Beck; R. J. Bendura; J. R. B. Coelho; J. W. Drewry; J. M. Hoell; P. A. Matson; R. J. McNeal; L. C. B. Molion; R. L. Navarro; V. Rabine; R. L. Snell

1990-01-01

412

The Turbulent Structure of Drag Reducing Boundary Layer Flows  

Microsoft Academic Search

The turbulent structure of wall-bounded drag reduced flow has been studied with particle image velocimetry (PIV) in a zero-pressure-gradient boundary layer. Drag reduction was achieved by injection of a concentrated polymer solution through a spanwise slot along the test wall at a distance approximately 2 m upstream of the PIV measurement station. For comparison, water was injected at the same

C. M. White; V. Somandepalli; M. G. Mungal

413

Nanodiamonds in the Younger Dryas Boundary Sediment Layer  

Microsoft Academic Search

We report abundant nanodiamonds in sediments dating to 12.9 ą 0.1 thousand calendar years before the present at multiple locations across North America. Selected area electron diffraction patterns reveal two diamond allotropes in this boundary layer but not above or below that interval. Cubic diamonds form under high temperature-pressure regimes, and n-diamonds also require extraordinary conditions, well outside the range

D. J. Kennett; J. P. Kennett; C. Mercer; S. S. Que Hee; L. Bement; T. E. Bunch; M. Sellers; W. S. Wolbach

2009-01-01

414

Correlation study in shock wave–turbulent boundary layer interaction  

Microsoft Academic Search

Shock wave–turbulent boundary layer interaction is a critical problem in aircraft design. Therefore, a thorough understanding\\u000a of the processes occurring in such flows is necessary. The most important task is to study the unsteady phenomena, in particular,\\u000a the low-frequency ones, for this interaction. An experimental study of separated flow has been performed in the zone of interaction\\u000a of the incident

P. A. Polivanov; A. A. Sidorenko; A. A. Maslov

2011-01-01

415

Transient boundary-layer flows in combustion environments  

SciTech Connect

Unsteady boundary-layer flow equations characterizing hot, burning environments are solved numerically by means of a factored ADI method under transient and/or streamwise varying core-flow conditions. Calculated results for compressible, turbulent flow cases show that high heat fluxes at the wall due to turbulence and changing edge conditions may bring about severe temperature increase at the wall, causing melting and hence erosion of the surface itself.

Kang, S.W.; Levatin, J.L.

1980-11-01

416

The effects of cylindrical surface modifications on turbulent boundary layers  

Microsoft Academic Search

A study employing hydrogen bubble-wire flow visualization and hot-film anemometry measurements has been conducted to determine the effects of sublayer-scale streamwise surface modifications of approximate nondimensional height of h(+) = 4 on the structure and flow characteristics of turbulent boundary layers. The visualization results indicate that the surface modifications did affect the streak spacing characteristics, with the greatest effect occurring

J. B. Johansen; C. R. Smith

1985-01-01

417

Some physical aspects of shock wave/boundary layer interactions  

NASA Astrophysics Data System (ADS)

When the flow past a vehicle flying at high velocity becomes supersonic, shock waves form, caused either by a change in the slope of a surface, a downstream obstacle or a back pressure constraining the flow to become subsonic. In modern aerodynamics, one can cite a large number of circumstances where shock waves are present. The encounter of a shock wave with a boundary layer results in complex phenomena because of the rapid retardation of the boundary layer flow and the propagation of the shock in a multilayered structure. The consequence of shock wave/boundary layer interaction (SWBLI) are multiple and often critical for the vehicle or machine performance. The shock submits the boundary layer to an adverse pressure gradient which may strongly distort its velocity profile. At the same time, in turbulent flows, turbulence production is enhanced which amplifies the viscous dissipation leading to aggravated performance losses. In addition, shock-induced separation most often results in large unsteadiness which can damage the vehicle structure or, at least, severely limit its performance. The article first presents basic and well-established results on the physics of SWBLI corresponding to a description in terms of an average two-dimensional steady flow. Such a description allows apprehending the essential properties of SWBLIs and drawing the main features of the overall flow structure associated with SWBLI. Then, some emphasis is placed on unsteadiness in SWBLI which constitutes a salient feature of this phenomenon. In spite of their importance, fluctuations in SWBLI have been considered since a relatively recent date although they represent a domain which deserves a special attention because of its importance for a clear physical understanding of interactions and of its practical consequences as in aeroelasticity.

Délery, Jean; Dussauge, Jean-Paul

2009-12-01

418

Perturbed boundary layer diffusion flames. Ph. D. thesis  

SciTech Connect

Thermal cracking is shown to have a significant effect on the temperature profiles in a boundary layer diffusion flame. Measurements of temperature profiles in a sooting free flow flame are compared with classic flame sheet model results. This comparison reveals a large overprediction of temperatures in the region between the fuel surface and the flame. The principle cause of this overprediction is the neglect of thermal cracking in the flame sheet model. The endothermicity of the cracking phenomena is analytically treated in a forced flow flame through the introduction of new Shvab-Zeldovich variables and a simple cracking sheet model, analogous to the flame sheet model. Two new parameters D sub cr and Q' are found which control the temperature at which cracking occurs and the amount of energy absorbed in the process. A second possible cause for the temperature overprediction is the sink effect of radiative heat transfer from soot in the boundary layer. This effect and the effects of wall emission and normal buoyancy on a horizontal boundary layer diffusion flame are studied by perturbing the cracking sheet solution. The principle effect of soot radiation is an increased blowing rate at the wall. This blowing is offset by the radiative wall emission. The postulated sink effect of soot emission is negligible. The major buoyancy effect is primarily the inducement of a velocity overshoot.

Ang, J.A.

1987-03-01

419

Linear stability of three-dimensional boundary layers  

NASA Astrophysics Data System (ADS)

Stability of compressible three-dimensional boundary layers on a swept wing model is studied within the framework of the linear theory. The analysis based on the approximation of local self-similarity of the mean flow was performed within the Falkner-Skan-Cooke solution extended to compressible flows. The calculated characteristics of stability for a subsonic boundary layer are found to agree well with the measured results. In the case of a supersonic boundary layer, the results calculated for a Mach number M = 2 are also in good agreement with the measured spanwise scales of nonstationary vortices of the secondary flow. The calculated growth rates of disturbances, however, are substantially different from the measured values. This difference can be attributed to a high initial amplitude of disturbances generated in the experiment, which does not allow the linear stability theory to be applied. The evolution of natural disturbances with moderate amplitudes is fairly well predicted by the theory. The effect of compressibility on crossflow instability modes is demonstrated to be insignificant.

Gaponov, S. A.; Smorodskii, B. V.

2008-03-01

420

Concentration boundary layers in osmotic membrane transport processes  

NASA Astrophysics Data System (ADS)

It has long been recognized, that the osmotic transport characteristics of membranes may be strongly influenced by the presence of unstirred concentration boundary layers adjacent to the membrane [1,2]. Previous experimental as well as theoretical works have focused on the case where the solution on both sides of the membrane remain well-mixed due to an external stirring mechanism. We present a theoretical investigation the effects of concentration boundary layers on the efficiency of osmotic pumping processes in the absence of external stirring i.e. when the stirring is provided by the osmotically generated flow itself. For such systems, we show that no well defined boundary layer thickness exist and that the reduction in concentration can be estimated by a surprisingly simple mathematical relation valid across a wide range of geometries and P'eclet numbers. [4pt] [1] T.J.Pedley, Q. Rev. Biophys., 1983, 16, 115[0pt] [2] K.H.Jensen et al., Lab Chip, 2009, 9, 2093

Jensen, Kaare; Bohr, Tomas; Bruus, Henrik

2009-11-01

421

An analytical model of capped turbulent oscillatory bottom boundary layers  

NASA Astrophysics Data System (ADS)

An analytical model of capped turbulent oscillatory bottom boundary layers (BBLs) is proposed using eddy viscosity of a quadratic form. The common definition of friction velocity based on maximum bottom shear stress is found unsatisfactory for BBLs under rotating flows, and a possible extension based on turbulent kinetic energy balance is proposed. The model solutions show that the flow may slip at the top of the boundary layer due to capping by the water surface or stratification, reducing the bottom shear stress, and that the Earth's rotation induces current and bottom shear stress components perpendicular to the interior flow with a phase lag (or lead). Comparisons with field and numerical experiments indicate that the model predicts the essential characteristics of the velocity profiles, although the agreement is rather qualitative due to assumptions of quadratic eddy viscosity with time-independent friction velocity and a well-mixed boundary layer. On the other hand, the predicted linear friction coefficients, phase lead, and veering angle at the bottom agreed with available data with an error of 3%-10%, 5°-10°, and 5°-10°, respectively. As an application of the model, the friction coefficients are used to calculate e-folding decay distances of progressive internal waves with a semidiurnal frequency.

Shimizu, Kenji

2010-03-01

422

Transient deployment of flat winglets inside a turbulent boundary layer  

NASA Astrophysics Data System (ADS)

An experiment has been designed to investigate the flow mechanisms responsible for the augmented force generation during the transient flapping of winglets. Square and triangular flaps hinged at the wall beneath the flow have been used which were rotated with angular velocities between 10 and 100 rad/s. Strouhal numbers between 0.05 and 0.4 and Stokes numbers between 3800 and 38,000 were achieved. Experiments with two different boundary layers were also carried out. In the first one, the boundary layer thickness to the winglet's height ratio was 1.3 and in the second 0.6. Particle Image Velocimetry was used to provide qualitative and quantitative information of the flow field. The dynamic lift and drag force coefficients during the transient deployment are different than the corresponding coefficients under stationary conditions at the same deployment angle after adjusting for inertial effects. These effects are enhanced with increasing Strouhal number and decrease with increasing boundary layer thickness.

Pierides, Alexis; Andreopoulos, Yiannis

2008-11-01

423

Effect of thermally induced perturbation in supersonic boundary layers  

NASA Astrophysics Data System (ADS)

This paper investigates the mechanism of steady and unsteady thermal perturbation (also denoted as thermal bump) in a Mach 1.5 flat plate boundary layer. A high-fidelity upwind-biased third-order Roe scheme is used with the compressive van Leer harmonic limiter on a suitably refined mesh. The study consists of two parts. In the first part, the effects of the steady and pulsed thermal bumps are explored. It is shown that the finite-span thermal bumps generate streamwise vortices. With steady heating, the disturbance decays downstream. However, when the thermal bump is pulsed, vortex shedding is observed and the streamwise vortical disturbance grows with downstream distance, consistent with linear stability analysis. The integrated disturbance energy indicates that streamwise kinetic disturbance energy growth dominates over those associated with other two velocity and thermodynamic components. The second part of this paper explores the physical consequences of the nonlinear dynamics between the vortices produced by the pulsed bump and the compressible boundary layer. The resulting three-dimensional flow distortion generates hairpin structures which are aligned in the streamwise direction, suggesting that the transition process bears some similarity to K-type breakdown. The arrangement of these vortices is connected to the low-speed streaks observed in the evolving boundary layer. The shape factor, velocity, and Reynolds stress profiles suggest that the perturbed flow shows initiation of transition to turbulence, but remains transitional at the end of the plate.

Yan, Hong; Gaitonde, Datta

2010-06-01

424

Aerosol measurements by lidar in the nocturnal boundary layer  

NASA Astrophysics Data System (ADS)

A lidar system capable to perform simultaneous measurements of atmospheric water vapor and aerosols have been developed in Tito Scalo, in the context of a cooperation between Universita della Baslicata and Istituo di Metodolgoie Avanzate di Analisis Ambientale. Aerosol observations by lidar in the nocturnal boundary laser (NBL) have been performed in the period 20 January- 20 February 1997, Radiosondes were launched during the measurement campaign simultaneously to lidar operation. Lidar observations have been sued to retrieve aerosol properties and dimensional characteristics. Aerosol sizes are determined by comparison measured and theoretical values of (beta) A,723(z)/(beta) A,355(z), with (beta) A,723(z) and (beta) A,355(z) being the aerosol backscattering coefficient at 723.37 and 355 nm, respectively. Furthermore, lidar and radiosonde data have been compared in order to study the NBL vertical structure and evolution. Lidar measurements of (beta) A,723(z) are compared with simultaneous radiosonde data expressed in terms of potential temperature and relative humidity, with particular emphasis on the estimate of the residual layer height from both lidar and radiosonde data. Results from the present measurements campaign will be reported and discussed in this presentation.

Di Girolamo, Paolo; Ambrico, Paolo F.; Amodeo, Aldo; Boselli, Antonella; Pappalardo, Gelsomina

2000-02-01

425

Nocturnal boundary layer turbulence over a tree canopy  

NASA Astrophysics Data System (ADS)

This dissertation is a compilation of studies that probe into many facets of nocturnal boundary layer (NBL) turbulence over tree canopies. Primarily, these studies focused on investigations into scales of NBL motions, stability classification, vertical dispersion and kinematic flux calculations. The chapters present: (1)a NBL wind component signal analysis where fast response data were used to determine the resolution of NBL turbulence, (2)a NBL vertical dispersion study where a lidar system was used to measure plume growth over a deciduous forest in the NBL, and (3)a new method for rotating NBL three-dimensional wind data measurements. The main work was prompted by questions raised by earlier studies that are included in the appendices. The main conclusions of this research were: (1)a sampling rate of 50 Hz is required to capture an unbiased NBL turbulence signal, (2)a gradient based stability parameter offers a more precise description of stability in the NBL due to the low levels of turbulence present, (3)the ergodic condition, which assumes that time and space averages are equal, was found to be met in the NBL above a tree canopy as demonstrated by a consistent prediction of vertical dispersion to actual dispersion as measured with a lidar system, and (4)a frequency-weighted technique was developed to reduce flow intermittency effects that skew NBL calculations using the traditional rotation techniques.

Stoughton, Thomas Ellsworth

426

Stability of flat plate boundary layer over monolithic viscoelastic coatings  

NASA Astrophysics Data System (ADS)

It is well known that compliant coatings of a wetted surface can affect the stability of hydrodynamic flows. The mechanism of this influence is related to viscoelastic properties of the coatings particularly to their reaction on the disturbing impact. However, the majority of corresponding studies are devoted to investigation of the effect of soft compliant coatings which are unpractical. Moreover, up to now only model computations of flow stability over the compliant coatings have been performed, as experimental data on viscoelastic properties (the modulus of elasticity E characterizing the elastic features, and the loss tangent ? characterizing the viscous or damping features) as functions of frequency for the coatings promising from the point of view of their practical application have been absent. Such data were obtained only last years for some materials (silicon rubbers) in a series of studies [1-3]. The coatings are prospective first of all because of their adequate stiffness (about 1 MPa). In the present paper, results of computations of boundary layer stability performed for the first time for the flow developed over compliant coatings with real properties.

Boiko, A. V.; Kulik, V. M.

2012-07-01

427

Simultaneous profiling of the Arctic Atmospheric Boundary Layer  

NASA Astrophysics Data System (ADS)

The structure of the Arctic atmospheric boundary layer (AABL) and the heat and moisture fluxes between relatively warm water and cold air above non-sea-ice-covered water (such as fjords, leads and polynyas) are of great importance for the sensitive Arctic climate system. So far, such processes are not sufficiently resolved in numerical weather prediction (NWP) and climate models. Especially for regions with complex topography as the Svalbard mountains and fjords the state and diurnal evolution of the AABL is not well known yet. Knowledge can be gained by novel and flexible measurement techniques such as the use of an unmanned aerial vehicle (UAV). An UAV can perform vertical profiles as well as horizontal surveys of the mean meteorological parameters: temperature, relative humidity, pressure and wind. A corresponding UAV called Small Unmanned Meteorological Observer (SUMO) has been developed at the Geophysical Institute at the University of Bergen in cooperation with Müller Engineering (www.pfump.org) and the Paparazzi Project (http://paparazzi.enac.fr). SUMO will be used under Arctic conditions in March/April 2009. This time the special purpose will be to send two SUMOs simultaneously on mission; one over the ice and snow-covered land surface and the other one above the open water of Isfjorden. This will be the first step of future multiple UAV operations in so called "swarms" or "flocks". With this, corresponding measurements of the diurnal evolution of the AABL can be achieved with minimum technical efforts and costs.

Mayer, S.; Jonassen, M.; Reuder, J.

2009-04-01

428

Boundary layer separation method for recycling of sodium ions from industrial wastewater.  

PubMed

The most effective technological solution for waste treatment is recycling. We have developed a new method for the treatment of industrial wastewaters and have called it the boundary layer separation method (BLSM). We have used the phenomenon that, on the surface of an electrically charged electrode, ions can be enriched in the boundary layer, as compared with the inside of the phase. The essence of the method is that, with an appropriately chosen velocity, the boundary layer can be removed from the wastewater, and the boundary layer, which is rich in ions, can be recycled. The BLSM can be executed as a cyclic procedure. The capacitance of the boundary layer was examined. The best mass transport can be achieved with the use of 1000 and 1200 mV polarization potentials in the examined system, with its value being 1200 mg/m2 per cycle. The necessary operation times were determined by the examination of the velocity of the electrochemical processes. When using 1000 mV polarization potential, the necessary adsorption time is at least 25 seconds, and the desorption time at least 300 seconds. The advantage of the procedure is that it does not use dangerous chemicals, only inert electrodes. The drawback is that it is not selective to ions, the achievable separation in one step is low, and the hydrogen that emerges during the electrolysis might be dangerous. PMID:21214032

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

2010-12-01

429

A solution to Prandtl's boundary layer equations using direct, formal integration  

NASA Astrophysics Data System (ADS)

Direct, Formal Integration (DFI) is a new solution technique for differential equations. It is a simple method. The differential equation at hand is integrated formally with respect to any of the independent variables as many times as required. This results in an integral or an integro-differential equation. The resulting Volterra equation is then solved numerically using a simple quadrature formula such as the trapezoidal rule. To date DFI has been applied to numerous problems, mostly in the area of boundary layer flow, with very good results. Some details of its application to the linear heat equation are given. It was applied to the incompressible boundary layer with great success. The code generated was used to study the development of similarity profiles starting from non-similar initial conditions. It is also used to study the inverse boundary layer problem. Some results of these successful studies are included. The new method is implemented for the 2-D compressible boundary layer equations expressed in primitive variables. Numerical results are compared to those obtained from the Keller-Cebeci box method. DFI compares extremely well both in accuracy and in CPU time. Also, since the last major implementation of DFI, that is, to the incompressible boundary layer flow, numerous algorithmic enhancements were made. These are given in some detail.

Mokkapati, Ramakrishna

1988-06-01

430

Probing high-Reynolds-number effects in numerical boundary layers  

NASA Astrophysics Data System (ADS)

We study the high-Reynolds-number behavior of a turbulent boundary layer in the low supersonic regime through very-large-scale direct numerical simulation (DNS). For the first time a Reynolds number is attained in DNS (Re?=?/?v~4000, where ? is the boundary layer thickness and ?v is the viscous length scale) at which theoretical predictions and experiments suggest the occurrence of phenomena pertaining to the asymptotic Reynolds number regime. From comparison with previous DNS data at lower Reynolds number we find evidence of a continuing trend toward a stronger imprint of the outer-layer structures onto the near-wall region. This effect is clearly manifested both in flow visualizations, and in energy spectra. More than a decade of nearly-logarithmic variation is observed in the mean velocity profiles, with log-law constants k ~ 0.394, C ~ 4.84, and a trend similar to experiments. We find some supporting evidence for the debated existence of a k-1 region in the power spectrum of streamwise velocity fluctuations, which extends up to y+ ~ 150, and of a k-5/3 spectral range in the outer layer.

Pirozzoli, Sergio; Bernardini, Matteo

2013-02-01

431

The Benthic Boundary Layer: Transport Processes and Biogeochemistry  

NASA Astrophysics Data System (ADS)

Interdisciplinary research is certainly one of the current buzzwords that needs to be incorporated in virtually every grant proposal. The idea that integration of different scientific fields is a prerequisite for progress in Earth sciences is now well recognized. The benthic boundary layer (BBL) is one area of research in which physicists, chemists, biologists, geologists, and engineers have worked in close and fruitful cooperation for several decades. The BBL comprises the near-bottom layer of water, the sediment-water interface, and the top layer of sediment that is directly influenced by the overlying water. In 1974, a BBL conference in France resulted in a book titled The Benthic Boundary Layer edited by I.N. McCave. This publication contained contributions from scientists from a wide range of disciplines and gave an overview of the state-of-the-art of BBL research. However, science has moved on in the past 25 years. Significant conceptual and technological progress has been made, and it is definitely time for an update.

van Duren, Luca A.; Middelburg, Jack J.

432

Transpiration and Film Cooling Boundary Layer Computer Program. Volume 2 Computer Program and Users Manual.  

National Technical Information Service (NTIS)

A finite difference turbulent boundary layer computer program which allows for mass transfer wall cooling and equilibrium chemistry effects is presented. The program is capable of calculating laminar or turbulent boundary layer solutions for an arbitrary ...

R. J. Gloss

1971-01-01

433

Calculation of Hypersonic Non-Equilibrium Viscous Flow Using Second Order Boundary Layer Theory.  

National Technical Information Service (NTIS)

A method is presented for the calculation of hypersonic boundary layers in chemical nonequilibrium. The second order boundary layer equations are solved using a finite difference space marching method. The flow and the chemistry are solved simultaneously ...

C. Mundt F. Monnoyer

1990-01-01

434

An Experimental and Analytical Study of Boundary Layers in Highly Turbulent Freestreams.  

National Technical Information Service (NTIS)

Experimental research has been conducted to determine the influence of free-stream turbulence on zero pressure gradient, incompressible, fully turbulent boundary layer flow. During this period convective heat transfer coefficients, boundary layer mean vel...

M. F. Blair

1979-01-01

435

The Influence of Free-Stream Turbulence on the Zero Pressure Gradient Fully Turbulent Boundary Layer.  

National Technical Information Service (NTIS)

Experimental research has been conducted to determine the influence of free-stream turbulence on zero pressure gradient fully turbulent boundary layer flow. During this period convective heat transfer coefficients, boundary layer mean velocity and tempera...

M. F. Blair M. J. Werle

1980-01-01

436

Direct Numerical Simulation of Turbulent Boundary Layers on a Large Domains  

NASA Astrophysics Data System (ADS)

Direct numerical simulation data of spatially-developing subsonic, supersonic and hypersonic turbulent boundary layers with matching similarity parameters are presented. The simulations are performed on large computational domains, using the rescaling technique with large rescaling lengths to minimize numerical correlation of the inflow and recycling planes. The simulations are run for long times without forcing the artificial acoustic modes in the free stream. We investigate the evolution of the boundary layer parameters and basic statistics with streamwise distance through the computational box and examine the turbulence structure through spectral analysis and filtered instantaneous flow fields. We pay special attention to the largest structures, with turbulence modeling, especially aspects unique to compressible boundary layers, in mind.

Kan, Yin-Chiu; Helm, Clara; Beekman, Izaak; Martin, Pino

2011-11-01

437

Calculation of three-dimensional boundary layers on rotating turbine blades  

NASA Astrophysics Data System (ADS)

An assessment has been made of the applicability of a three dimensional boundary layer analysis to the calculation of heat transfer and streamline flow patterns on the surfaces of both stationary and rotating turbine passages. In support of this effort, an analysis has been developed to calculate a general nonorthogonal surface coordinate system for arbitrary three dimensional surfaces and also to calculate the boundary layer edge conditions for compressible flow using the surface Euler equations and experimental pressure distributions. Using available experimental data to calibrate the method, calculations are presented for the endwall, and suction surfaces of a stationary cascade and for the pressure surface of a rotating turbine blade. The results strongly indicate that the three dimensional boundary layer analysis can give good predictions of the flow field and heat transfer on the pressure, suction, and endwall surfaces in a gas turbine passage.

Anderson, O. L.

438

User's manual for three dimensional boundary layer (BL3-D) code  

NASA Astrophysics Data System (ADS)

An assessment has been made of the applicability of a 3-D boundary layer analysis to the calculation of heat transfer, total pressure losses, and streamline flow patterns on the surface of both stationary and rotating turbine passages. In support of this effort, an analysis has been developed to calculate a general nonorthogonal surface coordinate system for arbitrary 3-D surfaces and also to calculate the boundary layer edge conditions for compressible flow using the surface Euler equations and experimental data to calibrate the method, calculations are presented for the pressure endwall, and suction surfaces of a stationary cascade and for the pressure surface of a rotating turbine blade. The results strongly indicate that the 3-D boundary layer analysis can give good predictions of the flow field, loss, and heat transfer on the pressure, suction, and endwall surface of a gas turbine passage.

Anderson, O. L.; Caplin, B.

1985-08-01

439

Numerical study of boundary layer separation control using magnetogasdynamic plasma actuators  

SciTech Connect

In this study, an efficient, time dependent, two-dimensional Navier-Stokes numerical code for shockwave boundary layer interaction in air is developed. Nonthermal surface plasma actuation is evaluated for effective shockwave induced boundary layer separation control within supersonic inlets. Specifically, high speed magnetogasdynamic plasma actuators are of interest. In these, localized ionization is produced close to the wall surface and then the flow is accelerated using strong magnetic fields. To replicate the experiments done at large boundary layer thickness, the code is divided into time independent and time dependent regimes to significantly reduce computation time. Computational results are in good agreement with experiments in terms of the flow structure as shown by Schlieren imaging, acetone planar laser scattering, and the static pressure profile on the test section wall.

Kalra, Chiranjeev S.; Shneider, Mikhail N.; Miles, Richard B. [Department of Mechanical and Aerospace Engineering, Applied Physics Group, Princeton University, Princeton, New Jersey 08544 (United States)

2009-10-15

440

A boundary layer computational model for predicting the flow and heat transfer in sudden expansions  

NASA Astrophysics Data System (ADS)

Fully developed turbulent and laminar flows through symmetric planar and axisymmetric expansions with heat transfer were modeled using a finite-difference discretization of the boundary-layer equations. By using the boundary-layer equations to model separated flow in place of the Navier-Stokes equations, computational effort was reduced permitting turbulence modeling studies to economically carried out. The continuity and momentum equations were solved in a coupled matter. For laminar constant property flow, the equations were nodimensionalized so that the solution was independent of Reynolds number. Two different dependent hydrodynamic variable sets were tried: the primitive variable set (u-v), and the streamwise velocity steam function variable set (u-psi). The predictions of the boundary-layer equations for parameters associated with the trapped eddy compared well with the predictions of the Navier-Stokes equations and experimental measurements for laminar isothermal flow.

Lewis, J. P.

1985-12-01

441

Temporal variability of the trade wind inversion: Measured with a boundary layer vertical profiler. Master's thesis  

SciTech Connect

This study uses Hawaiian Rainband Project (HaRP) data, from the summer of 1991, to show a boundary layer wind profiler can be used to measure the trade wind inversion. An algorithm has been developed for the profiler that objectively measures the depth of the moist oceanic boundary layer. The Hilo inversion, measured by radiosonde, is highly correlated with the moist oceanic boundary layer measured by the profiler at Paradise Park. The inversion height on windward Hawaii is typically 2253 + or - 514 m. The inversion height varies not only on a daily basis, but on less than an hourly basis. It has a diurnal, as well as a three to four day cycle. There appears to be no consistent relationship between inversion height and precipitation. Currently, this profiler is capable of making high frequency (12 minute) measurements of the inversion base variation, as well as other features.

Grindinger, C.M.

1992-05-01

442

A numerical study of hydrogen-air combustion within a supersonic boundary layer  

SciTech Connect

A numerical study of the ignition and spread of combustion within a supersonic boundary layer is presented for case where ignition is triggered by viscous dissipation and/or wall temperature effects. Three important regions are found in the boundary layer in the streamwise direction. They are: (1) an induction region where the process is mainly controlled by streamwise convection and chemical kinetics in the presence of transverse molecular transports, (2) a thermal runaway region corresponding to a large chemical heat release, (3) a flame region which develops at the end of the thermal runaway region where a flame is stabilized at the outer edge of the boundary layer. The whole chemical process becomes endothermic for large values of free-stream Mach numbers due to intense dissociation effects. 11 refs.

Figueira da silva, L.F.; Deshaies, B.; Champion, M. (Ecole Nationale Superieure de Mecanique et d'Aerotechnique, Poitiers, (France))

1992-01-01

443

Linear compensator control of a pointsource induced perturbation in a Falkner-Skan-Cooke boundary layer  

NASA Astrophysics Data System (ADS)

We focus on the problem of controlling pointsource induced perturbations on an infinite swept wing using linear control theory. Based on wall measurements in a spatial simulation of localized disturbances in Falkner-Skan-Cooke boundary layers, an extended Kalman filter is used to estimate the full three-dimensional wave packet. The estimated field is in turn used to calculate a feedback control which changes the growth of the disturbance into decay. This is the first time that optimal control and estimation concepts are successfully applied to construct a dynamic output feedback compensator which is used to control disturbances in spatially developing boundary layers.

Högberg, Markus; Chevalier, Mattias; Henningson, Dan S.

2003-08-01

444

Transonic Aeroelastic Analysis of Aircraft Wings Considering the Boundary-Layer Effects  

NASA Astrophysics Data System (ADS)

Aerodynamic solver using the transonic small-disturbance (TSD) equation has frequently been used to perform practical aeroelastic analysis for many aircraft models. In the present study, the more accurate aeroelastic analysis solver using the TSD equation was developed by considering the viscous effects of the boundary-layer. The viscous effects were considered using Green's lag-entrainment equations and an inverse boundary-layer method. Through aerodynamic analyses for several aircraft wings, the viscous-inviscid interaction approach could improve the accuracy of the aerodynamic computation using the TSD equation. Finally, the aeroelastic characteristics were investigated using comparisons of the time responses between the inviscid and viscous flows.

Kim, Jong-Yun; Kim, Kyung-Seok; Lee, Seung-Jun; Lee, In

445

Analytical study of the neutral stability of a model hypersonic boundary layer  

NASA Astrophysics Data System (ADS)

The neutral modes of a hypersonic boundary layer flow over an adiabatic flat plate are considered. A formulation of the governing second-order linear equation for the pressure disturbance is developed that lends itself to the application of the WKB method over the entire boundary layer. This formulation provides analytic eigenvalues and eigenfunction relations for the pressure distrubances and is applicable to flows at moderate Mach numbers as well. Solutions are determined for the cases of the wave speed c = 0 and c = 1, and show good qualitative agreement with numerical computations as well as results in the limit M(sub infinity) approaches infinity.

Bower, Daniel R.; Liu, Ching Shi

1994-12-01

446

Dynamics of a bubbly turbulent boundary layer along a surface piercing flat plate  

NASA Astrophysics Data System (ADS)

The behaviour of a bubble-laden turbulent boundary layer has been studied experimentally in an open channel water flow with Reynolds number up to 10^6. A poly-dispersed bubble cloud with mean diameter around 200 ? m is injected at the leading edge of a vertical, surface piercing flat plate. The high void fraction bubble layer rises along the plate, developing a Kelvin Helmholtz type instability due to the vertical shear. As a result of this instability, streamwise vorticity is generated that combines with the vertical vorticity associated with the boundary layer, tilting the vortex lines. Bubbles are, for the most part, confined to the boundary layer and accumulate as they interact with the turbulent structures present in this type of flows. The flow at the junction between the flat plate and the free surface is also studied in the presence of bubbles. An streamwise submerged vortex is observed, in agreement with previous studies of single phase junction flows. Vorticity originated by the bouyancy-driven instability of the bubbly layer is convected away from the plate when it reaches the surface, and reconects with the streamwise vortex. Thus, the vortex gains strength and starts to accumulate bubbles stripped from the boundary layer, becoming a dominant feature of the flow.

Aliseda, Alberto; Lasheras, Juan C.

2003-11-01

447

Bifurcation of the cusp: Implications for understanding boundary layers  

NASA Astrophysics Data System (ADS)

Event analyses and magnetohydrodynamic (MHD) modeling provide complementary insights into solar-wind/magnetosphere-ionosphere coupling when the interplanetary magnetic field (IMF) has a stronger Y than Z component. The sources for convection and particle precipitation within the cusp become spatially bifurcated. Incoming surfaces of constant phase in the interplanetary electric field (IEF) can be tilted with respect to the Sun-Earth line. This forces the two hemispheres to respond to the same elements of the solar wind stream at significantly different times. We consider a case in which ground and rocket measurements indicate that IEF phase planes interacted first with the magnetopause in the Southern Hemisphere at lag times significantly less than the simple adjection time between an L1 monitor and Earth. Magnetic merging on the Northern Hemisphere magnetopause occurred later. The timing differences are related to the phase-plane tilts and the strong IMF BX. Auroral emissions created by electrons injected from the Southern Hemisphere merging line can appear in close proximity to those from Northern Hemisphere sites, within an all-sky imager's field-of-view. Bifurcation is driven by IMF BY, while BX controls differences in the timing of interactions with the two hemispheres. Detailed harmonization of auroral features with interplanetary drivers strongly supports the utility of the antiparallel merging criterion for estimating when and where the IMF-magnetosphere interactions occur. We compare empirical results with MHD simulations to help constrain interpretations of magnetospheric boundary layers. Merging at high latitudes creates layers of open field lines that drape over the dayside magnetosphere to form an open boundary layer. MHD modeling suggests that open boundary layers may become quite thick along the magnetospheric flank equatorward of the sash. Simulations and the empirical results indicate that merging in the conjugate hemisphere drives the smaller ionospheric convection cell.

Maynard, N. C.; Burke, W. J.; Moen, J.; Sandholt, P. E.; Lester, M.; Ober, D. M.; Weimer, D. R.; White, W. E.

448

Turbulent boundary layer pressure fluctuations at large scales  

NASA Astrophysics Data System (ADS)

The pressure fluctuations underneath a turbulent boundary are an important excitation source for noise and vibration for both aircraft and ships. This presentation describes experimental results from a new study of flat-plate turbulent boundary layer pressure fluctuations in water at large scales and high Reynolds number. The experiments were performed at the U.S. Navy's William B. Morgan Large Cavitation Channel in Memphis, TN on a polished flat plate 3.05 m wide, 12.8 m long, and 0.18 m thick. Flow velocity, skin friction, surface pressure, and plate acceleration measurements were made at multiple downstream locations at flow speeds ranging from 0.5 m/s to 19 m/s for a Reynolds number (based on downstream distance) range of several million to 200 million. Dynamic surface pressures were recorded with 16 flush mounted pressure transducers forming an L-array with streamwise dimension of 0.264 m and cross-stream dimension of 0.391 m. Measured 99% boundary-layer thicknesses were typically of order 0.10 m. Results for spatial and temporal correlation functions, as well as auto- and cross-spectra are presented and compared with prior lower-Reynolds-number results using either inner or outer variable scaling. [Work sponsored by the Defense Advanced Research Projects Agency and ONR Code 333.

Sanders, Wendy; Judge, Carolyn; Winkel, Eric; Ceccio, Steven; Dowling, David; Perlin, Marc

2002-05-01

449

A numerical calculation of three dimensional incompressible laminar, transition and turbulent boundary layers  

Microsoft Academic Search

A method is presented for calculating the 3D boundary layers in incompressible viscous flow, including a differential method for laminar boundary layers, an integral method for turbulent boundary layers, and a numerical solution method for the Orr-Sommerfeld equation in which transition occurs only if the amplification of the disturbance reaches a certain level. These methods are used to calculate a

Jiaxiang Yan; Bin Yu

1991-01-01

450

The Adaptation of the Atmospheric Boundary Layer to a Change in Surface Roughness  

Microsoft Academic Search

The adaptation of the atmospheric boundary layer to a change in the underlying surface roughness is an interesting problem and hence much research, theoretical, experimental, and numerical, has been undertaken. Within the atmospheric boundary layer an accurate numerical model for the turbulent properties of the atmospheric boundary layer needs to be implemented if physically realistic results are to be obtai