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1

Boundary layer response to wind gusts  

E-print Network

Souadary- Layer Oscillstioas and Transition on a Plat Plate. " NACA Report 909. 2. pailer, c. E. ) sErperlaental Heat 'Transfer snd soundary Layer Sehavior uith 100 c. P. s. Plow Oscll, lstions. RASA TH S-2521. 3. Noore, p, K. and Ostrach, S...

Morland, Bruce Thomas

1968-01-01

2

Response of the Tropical Boundary Layer to Weak Surface Forcing  

NASA Technical Reports Server (NTRS)

During the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE), a series of airborne thermal infrared observations and in situ atmospheric measurements were made near the sea surface through heights exceeding 4 km. Air movements associated with the sea surface temperature and the marine atmospheric boundary layer were studied.

Hagan, D.; Rogers, D.

1995-01-01

3

Modeling the Atmospheric Boundary Layer Wind Response to Mesoscale Sea Surface Temperature  

E-print Network

Modeling the Atmospheric Boundary Layer Wind Response to Mesoscale Sea Surface Temperature, a number of recent modeling studies have addressed the response of the atmospheric boundary layer-Bretherton-McCaa (GBM) boundary layer mixing scheme (sU =0.40 m s-1 °C-1 ), and a COAMPS simulation with a form

4

Total Solar Eclipses and Atmospheric Boundary Layer Response  

NASA Astrophysics Data System (ADS)

The effect of three total solar eclipses on meteorological parameters is discussed in the paper. Measurements were conducted at the village of Ravnets,General Toshevo municipality, Bulgaria, 1999,in Manavgat, near Antalya, Turkey, 2006 and in Tian Huang Ping, China, 2009. The observed decrease of the sky illumination (incoming solar radiation) during the eclipses was proportional to the percentage of solar coverage. The after eclipse sky illumination level is due to the effect of the natural change of the solar elevation angle. For the 1999 TSE it did not regain its pre eclipse value, it has exactly the same value for the 2006 TSE, and, It is three times larger than the pre eclipse value for the 2009 TSE. This fact can be easily explained by the Local Time of the maximum of the eclipses: LT 13:12, LT 12:58, and LT 09:34, respectively. Measurements showed significant changes in the surface air temperature. The minimum of the air temperature during the 2009 TSE (Tmin=4.5°C) was measured 6 min after the end of the total phase. This minimal temperature drop and larger time lag can be explained with the huge artificial lake near the place of observation, which minimizes the temperature response due to its larger heat capacity. During the 1999 TSE, minimal temperature (Tmin=6.4°C) is measured 7 min 30 s after the total phase, and for the 2006 TSE (Tmin=5°C) - 5 min. It is in accordance with the fact that the temperature minima at residential/commercial stations occurred in general, before the minima at stations in agricultural terrains. In 2006 we were at the yard of the hotel, and in 1999 in the countryside. The wind velocity drops during the total phase as a result of the cooling and stabilization of the atmospheric boundary layer. The wind direction during the total phase changes and the wind begins to blow in the same direction as the direction of motion of the lunar shadow on the earth. Cirrus and cirrostratus clouds were observed during the 2006 total solar eclipse. Cloud structures in the form of narrow concentric arcs, equally detached from one another were observed for 20 minutes, after the beginning of the maximum phase of the 1999 TSE.

Stoev, A.; Stoeva, P.; Kuzin, S.

2012-11-01

5

Response of a Hypersonic Boundary Layer to Freestream Pulse Acoustic Disturbance  

PubMed Central

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

Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing

2014-01-01

6

Forced Response Analysis of a Fan with Boundary Layer Inlet Distortion  

NASA Technical Reports Server (NTRS)

Boundary layer ingesting propulsion systems have the potential to significantly reduce fuel burn for future generations of commercial aircraft, but these systems must be designed to overcome the challenge of high dynamic stresses in fan blades due to forced response. High dynamic stresses can lead to high cycle fatigue failures. High-fidelity computational analysis of the fan aeromechanics is integral to an ongoing effort to design a boundary layer ingesting inlet and fan for a wind-tunnel test. An unsteady flow solution from a Reynoldsaveraged Navier Stokes analysis of a coupled inlet-fan system is used to calculate blade unsteady loading and assess forced response of the fan to distorted inflow. Conducted prior to the mechanical design of a fan, the initial forced response analyses performed in this study provide an early look at the levels of dynamic stresses that are likely to be encountered. For the boundary layer ingesting inlet, the distortion contains strong engine order excitations that act simultaneously. The combined effect of these harmonics was considered in the calculation of the forced response stresses. Together, static and dynamic stresses can provide the information necessary to evaluate whether the blades are likely to fail due to high cycle fatigue. Based on the analyses done, the overspeed condition is likely to result in the smallest stress margin in terms of the mean and alternating stresses. Additional work is ongoing to expand the analyses to off-design conditions, on-resonance conditions, and to include more detailed modeling of the blade structure.

Bakhle, Milind A.; Reddy, T. S. R.; Coroneos, Rula M.

2014-01-01

7

Stratified Atmospheric Boundary Layers  

Microsoft Academic Search

Various features of different stability regimes of the stable boundary layer are discussed. Traditional layering is examined in terms of the roughness sublayer, surface layer, local similarity, z-less stratification and the region near the boundary-layer top. In the very stable case, the strongest turbulence may be detached from the surface and generated by shear associated with a low level jet,

L. Mahrt

1999-01-01

8

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

9

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

10

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

11

Parabolic - hyperbolic boundary layer  

E-print Network

A boundary value problem related to a parabolic higher order operator with a small parameter is analized. When the small parameter tends to zero, the reduced operator is hyperbolic. When t tends to infinity a parabolic hyperbolic boundary layer appears. In this paper a rigorous asymptotic approximation uniformly valid for all t is established.

Monica De Angelis

2012-07-09

12

The response of a laminar boundary layer in supersonic flow to small amplitude progressive waves  

NASA Technical Reports Server (NTRS)

The effect of a small amplitude progressive wave on the laminar boundary layer on a semi-infinite flat plate, due to a uniform supersonic freestream flow, is considered. The perturbation to the flow divides into two streamwise zones. In the first, relatively close to the leading edge of the plate, on a transverse scale comparable to the boundary layer thickness, the perturbation flow is described by a form of the unsteady linearized compressible boundary layer equations. In the freestream, this component of flow is governed by the wave equation, the solution of which provides the outer velocity conditions for the boundary layer. This system is solved numerically, and also the asymptotic structure in the far downstream limit is studied. This reveals a breakdown and a subsequent second streamwise zone, where the flow disturbance is predominantly inviscid. The two zones are shown to match in a proper asymptotic sense.

Duck, Peter W.

1989-01-01

13

The response of a compressible turbulent boundary layer to short regions of concave surface curvature  

NASA Technical Reports Server (NTRS)

An experimental investigation of the supersonic flow of a boundary layer over short regions of concave surface curvature, using radii of curvature equivalent to 10 and 50 (models I and II, respectively) initial boundary layer thicknesses and 8-deg turning angle, notes that the boundary layer experienced a strong adverse pressure gradient as the boundary layer passed through the curved region. Attention is given to the mean and turbulent field for each flow, with comparisons of results to those for an 8-deg ramp. In the ramp and model I, turbulence levels increased significantly, together with structural parameters; in model II, despite an increase in turbulence levels, structural parameters remained essentially unchanged. The former results suggest that the perturbation is rapid, and describable in terms of total rather than local strains.

Jayaram, Mohan; Taylor, Margaret W.; Smits, Alexander J.

1987-01-01

14

Time-dependent boundary-layer response in a propeller slipstream  

NASA Technical Reports Server (NTRS)

The time-dependent behavior of a wing boundary layer immersed in a propeller slipstream has been studied experimentally in wind-tunnel tests and in flight. Hot-wire anemometer measurements were made through the boundary layer for time-dependent, ensemble-average velocity and turbulence-intensity profiles at various chord locations. The boundary layer has a coherent, time-dependent cycle of transitional behavior, varying from a laminar to a turbulent-transitional state. Local drag coefficients determined from the velocity profiles for the freewheeling propeller case in flight show that the time-dependent drag in the propeller slipstream varies from the undisturbed laminar value to a value less than that predicted for fully turbulent flow. Local drag coefficients determined from the thrusting propeller case in the wind tunnel indicate that the effects of the slipstream are to enhance the stability of the boundary layer and to reduce the drag coefficient in the laminar portion of the cycle below its undisturbed laminar value.

Howard, Richard M.; Miley, Stan J.

1989-01-01

15

Wall-Functions and Boundary Layer Response to Pul sating and Oscillating Turbulent Channel Flows  

Microsoft Academic Search

Some limitations of the classical Wall-Function approach for the near-wall boundary layer treatment in LES and URANS are presented for isothermal oscillating and pulsating channel flows. Despite their simple geometry, pulsating and oscillating fl ows are interesting unsteady flow test cases representative of many industrial components. A special attention will be focused on the unsteady wall- shear stress prediction since

D. Panara; M. Porta; R. Dannecker; B. Noll

16

Atmospheric boundary layer response to sea surface temperatures during the SEMAPHORE experiment  

Microsoft Academic Search

The sensitivity of the marine atmospheric boundary layer (MABL) subjected to sea surface temperatures (SST) during the Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) experiment in 1993 has been studied. Atmospheric analyses produced by the Action de Recherche, Petite Echelle, Grande Echelle (ARPEGE) operational model at the French meteorological weather service assimilated data sets collected between

Hervé Giordani; Serge Planton; Bruno Benech; Byung-Hyuk Kwon

1998-01-01

17

Response of a spatially developing turbulent boundary layer to a spanwise oscillating electromagnetic force  

Microsoft Academic Search

Direct numerical simulations were performed to investigate the physics of a spatially developing turbulent boundary layer flow subjected to a spanwise oscillating electromagnetic force. The electromagnetic force was applied beneath a finite length of the flat plate. A fully implicit fractional step method was employed to simulate the flow. The mean and turbulent flow properties were obtained to analyze the

Joung-Ho Lee; Hyung Jin Sung

2005-01-01

18

The Indirect Boundary Element Method (IBEM) for Seismic Response of Topographical Irregularities in Layered Media  

NASA Astrophysics Data System (ADS)

The seismic hazard assessment of extended developments, such as a dam, a bridge or a pipeline, needs the strong ground motion simulation taking into account the effects of surface geology. In many cases the incoming wave field can be obtained from attenuation relations or simulations for layered media using Discrete Wave Number (DWN). Sometimes there is a need to include in simulations the seismic source as well. A number of methods to solve these problems have been developed. Among them the Finite Element and Finite Difference Methods (FEM and FDM) are generally preferred because of the facility of use. Nevertheless, the analysis of realistic dynamic loading induced by earthquakes requires a thinner mesh of the entire domain to consider high frequencies. Consequently this may imply a high computational cost. The Indirect Boundary Element Method (IBEM) can also be employed. Here it is used to study the response of a site to historical seismic activity. This method is particularly suited to model wave propagation through wide areas as it requires only the meshing of boundaries. Moreover, it is well suited to represent finely the diffraction that can occur on a fault. However, the IBEM has been applied mainly to simple geometrical configurations. In this communication significant refinements of the formulation are presented. Using IBEM we can simulate wave propagation in complex geometrical configurations such as a stratified medium crossed by thin faults or having a complex topography. Two main developments are here described; one integrates the DWN method inside the IBEM in order to represent the Green's functions of stratified media with relatively low computational cost but assuming unbounded parallel flat layers, and the other is the extension of IBEM to deal with multi-regions in contact which allows more versatility with a higher computational cost compared to the first one but still minor to an equivalent FEM formulation. The two approaches are fully described here and their results compared within the hazard studies of CFE-Las Cruces, Nayarit, Mexico, hydroelectrical project. ACKNOWLEDGEMENTS. This study is partially supported by DGAPA-UNAM under Project IN104712.

Contreras Zazueta, M. A.; Perton, M.; Sanchez-Sesma, F. J.; Sánchez-Alvaro, E.

2013-12-01

19

The atmospheric boundary layer  

SciTech Connect

This book is aimed at researchers in the atmospheric and associated sciences who require a moderately advanced text on the Atmospheric Boundary Layer (ABL) in which the many links between turbulence, air-surface transfer, boundary-layer structure and dynamics, and numerical modeling are discussed and elaborated upon. Chapter 1 serves as an introduction, with Chapters 2 and 3 dealing with the development of mean and turbulence equations, and the many scaling laws and theories that are the cornerstone of any serious ABL treatment. Modelling of the ABL is crucially dependent for its realism on the surface boundary conditions, and Chapters 4 and 5 deal with aerodynamic and energy considerations, with attention to both dry and wet land surfaces and the sea. The structure of the clear-sky, thermally stratified ABL is treated in Chapter 6, including the convective and stable cases over homogeneous land, the marine ABL and the internal boundary layer at the coastline. Chapter 7 then extends the discussion to the cloudy ABL. This is seen as particularly relevant since the extensive stratocumulus regions over the sub-tropical oceans and stratus regions over the Arctic are now identified as key players in the climate system. Finally, Chapters 8 and 9 bring much of the book's material together in a discussion of appropriate ABL and surface parameterization schemes for the general circulation models of the atmosphere that are being used for climate simulation.

Garratt, J.R.

1992-01-01

20

Boundary Layer Meteorology (METR 5103)  

E-print Network

of the atmospheric boundary layer dynamics and thermodynamics will be taught. Basic concepts of turbulence theory will be discussed and analyzed. Applications of this theory in the atmospheric boundary layer and mesoscale modeling and simulation of turbulent flows in atmospheric boundary layers under different meteorological conditions

Droegemeier, Kelvin K.

21

METEOROLOGY 130 Boundary Layer Meteorology  

E-print Network

is designed to introduce the student to the atmospheric boundary layer and its properties. The course 1. To be able to describe the atmospheric boundary layer conceptually using figures and plots. 2. To understand how measurements of the atmospheric boundary layer are made. Reading and Textbook Roland Stull

Clements, Craig

22

5, 31913223, 2005 Boundary layer  

E-print Network

atmospheric research station (53.32 N, 9.90 W) on the west coast of Ireland.25 Boundary layer depthACPD 5, 3191­3223, 2005 Boundary layer structure during NAMBLEX E. G. Norton et al. Title Page Discussions Boundary layer structure and decoupling from synoptic scale flow during NAMBLEX E. G. Norton 1 , G

Boyer, Edmond

23

Boundary Layer Meteorology (METR 5103)  

E-print Network

of the atmospheric boundary layer dynamics and thermodynamics, including the basic concepts of turbulence theory conditions will be discussed and critically analyzed. Role of the boundary layer in atmospheric processes be considered. Atmospheric boundary layer types ranging from strongly stable to neutral and to strongly unstable

Droegemeier, Kelvin K.

24

10, 1990119938, 2010 Boundary layer  

E-print Network

ACPD 10, 19901­19938, 2010 Boundary layer dynamics over London J. F. Barlow et al. Title Page (ACP). Please refer to the corresponding final paper in ACP if available. Boundary layer dynamics over Boundary layer dynamics over London J. F. Barlow et al. Title Page Abstract Introduction Conclusions

Weber, Rodney

25

THE MARTIAN ATMOSPHERIC BOUNDARY LAYER  

E-print Network

THE MARTIAN ATMOSPHERIC BOUNDARY LAYER A. Petrosyan,1 B. Galperin,2 S. E. Larsen,3 S. R. Lewis,4 A September 2011. [1] The planetary boundary layer (PBL) represents the part of the atmosphere), The Martian atmospheric boundary layer, Rev. Geophys., 49, RG3005, doi:10.1029/2010RG000351. 1. INTRODUCTION

Spiga, Aymeric

26

Response Timescales and Multiple Equilibria in Boundary-Layer Cloud-Aerosol Interaction  

NASA Astrophysics Data System (ADS)

Large-eddy simulations (LES) of subtropical stratocumulus-topped boundary layers coupled to an interactive aerosol model are run for multiday periods to examine their coupled equilibria and adjustment timescales. The LES includes two-moment Morrison microphysics, interactive radiation, and Razzak-Ghan cloud droplet activation from a single log-normal size distribution of hygroscopic aerosol with prognosed total aerosol mass and number. The aerosol evolves due to surface and entrainment sources, dry coalescence, precipitation sinks coupled to the Morrison microphysics due to autoconversion and accretion of cloud droplets (and a source due to raindrop evaporation), and cloud and rain scavenging of interstitial aerosol. Simulations are initialized with an idealized southeast Pacific stratocumulus sounding based on observations during VOCALS REx and forced with specified SST, mean subsidence, geostrophic wind, and free-tropospheric aerosol concentration. The surface aerosol source is based on the Clarke parameterization for the dependence of sea-salt number concentration on wind speed. Both surface and free-tropospheric aerosol are assumed to quickly grow to a specified size due to a surface DMS source. The goal is to explore the adjustment timescales and long-term equilibria produced by this model, to compare with studies such as Wood et al. (2012) that postulate that remote marine boundary layer aerosol concentrations are controlled as much by the precipitation sink as the surface and entrainment sources. We show that the coupled cloud-aerosol model supports rapid transitions from a solid, high aerosol, stratocumulus-capped state to a cumulus-like state reminisniscent of pockets of open cells as the liquid water path rises above a threshold supporting sufficient precipitation. The system can support multiple long-term equilibria for the same boundary forcing, or slow oscillations between a collapsed POC-like state and a deepening, thickening stratocumulus-capped boundary layer for other plausible choices of forcing. The behavior of the system is analyzed in terms of a two-dimensional 'slow manifold' characterized by the boundary-layer mean depth and aerosol number concentration.

Bretherton, C. S.; Berner, A.; Wood, R.

2012-12-01

27

Boundary layer transition studies  

NASA Technical Reports Server (NTRS)

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. The technique was enhanced by using up to nine multiple probes to reduce the experimental run-time. In both cases, 3D contour surfaces in the vicinity of the hole show highly 3D TS waves which fan out in the spanwise direction forming bow-shaped waves downstream. The case without suction has proved useful for evaluating calculation methods. With suction, the perturbations on the centerline are much stronger and decay less rapidly, while the TS waves in the far field are similar to the case without suction. Downstream, the contour surfaces of the TS waves 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.

1995-01-01

28

Boundary layer transition  

NASA Astrophysics Data System (ADS)

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 speed over an airfoil. Numerical simulation of active control by surface heating and cooling in air shows that by appropriate phase adjustment a reduction in the level of perturbation can be obtained. This simulation is based on the solution of two-dimensional compressible Navier-Stokes equations for a flat plate. Goertler vortices are studied experimentally on an airfoil in the Low Turbulence Pressure Tunnel (LTPT). The flow pattern was visualized using the sublimating chemical technique and data were obtained using a three component laser velocimeter. The effect of curvature on swept leading-edge stability on a cylinder was numerically studied. The results suggest that transition is dominated by traveling disturbance waves and that the waves with the greatest total amplification has an amplitude ratio of e sup 11. Experimental data from the quiet supersonic tunnel and flight tests are analyzed using linear compressible stability theory.

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

1986-12-01

29

Boundary layer transition  

NASA Technical Reports Server (NTRS)

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 speed over an airfoil. Numerical simulation of active control by surface heating and cooling in air shows that by appropriate phase adjustment a reduction in the level of perturbation can be obtained. This simulation is based on the solution of two-dimensional compressible Navier-Stokes equations for a flat plate. Goertler vortices are studied experimentally on an airfoil in the Low Turbulence Pressure Tunnel (LTPT). The flow pattern was visualized using the sublimating chemical technique and data were obtained using a three component laser velocimeter. The effect of curvature on swept leading-edge stability on a cylinder was numerically studied. The results suggest that transition is dominated by traveling disturbance waves and that the waves with the greatest total amplification has an amplitude ratio of e sup 11. Experimental data from the quiet supersonic tunnel and flight tests are analyzed using linear compressible stability theory.

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

1986-01-01

30

Boundary layer receptivity and control  

NASA Technical Reports Server (NTRS)

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. In the area of flow control, adjoint systems offer a powerful insight into the effect of control forces. One of the simplest control strategies for boundary layers involves the application of localized mean wall suction.

Hill, D. C.

1993-01-01

31

Scaling the atmospheric boundary layer  

Microsoft Academic Search

We review scaling regimes of the idealized Atmospheric Boundary Layer. The main emphasis is given on recent findings for stable conditions. We present diagrams in which the scaling regimes are illustrated as a function of the major boundary-layer parameters. A discussion is given on the different properties of the scaling regimes in unstable and stable conditions.

A. A. M. Holtslag; F. T. M. Nieuwstadt

1986-01-01

32

Modeling the urban boundary layer  

NASA Technical Reports Server (NTRS)

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

Bergstrom, R. W., Jr.

1976-01-01

33

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

2009-04-01

34

Final Boundary Layer Research and Findings Report Draft Boundary Layer Research and Findings Report  

E-print Network

IV Final Boundary Layer Research and Findings Report #12;Draft Boundary Layer Research and Findings Cases Associated with Boundary Layer Model Problems ............. 6 1.1 Problems Related to Atmospheric ......................................................... 9 2.1.3 Boundary Layer Formulation Factors

35

Removing Boundary Layer by Suction  

NASA Technical Reports Server (NTRS)

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

Ackeret, J

1927-01-01

36

Atmospheric Boundary Layer (ABL) Spring 2013  

E-print Network

ATS 623 Atmospheric Boundary Layer (ABL) Spring 2013 Tues and Thurs 9 a.m. (2 contact hours per@atmos.colostate.edu) Course notes: Atmospheric Boundary Layer Notes (2013) by Richard H. Johnson (available online at http · Schlichting (1960) Boundary­Layer Theory · Sorbjan (1989) Structure of the Atmospheric Boundary Layer

37

Novel parameterisations in the boundary layer  

E-print Network

Novel parameterisations in the boundary layer Bob Plant Department of Meteorology, University of Reading NCAS Boundary-Layer Workshop 1st July 2011 With thanks to: Emilie Carter, Chris Holloway, Sonja with the boundary layer: perspectives from ensemble forecasting Novel parameterisations in the boundary layer ­ p.1

Plant, Robert

38

The kinematics of turbulent boundary layer structure  

NASA Technical Reports Server (NTRS)

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

Robinson, Stephen Kern

1991-01-01

39

Stability of compressible boundary layers  

NASA Technical Reports Server (NTRS)

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 disturbances in supersonic laminar boundary layers and the most unstable first mode wave is 3-D. Whereas viscosity has a destabilizing effect on incompressible flows, it is stabilizing for high supersonic Mach numbers. Whereas cooling stabilizes first mode waves, it destabilizes second mode waves. However, second order waves can be stabilized by suction and favorable pressure gradients. The influence of the nonparallelism on the spatial growth rate of disturbances is evaluated. The growth rate depends on the flow variable as well as the distance from the body. Floquet theory is used to investigate the subharmonic secondary instability.

Nayfeh, Ali H.

1989-01-01

40

Response of a spatially developing turbulent boundary layer to active control strategies in the framework of opposition control  

NASA Astrophysics Data System (ADS)

Opposition control is a simple feedback control method which can be used to attenuate near-wall turbulence and reduce drag in wall-bounded turbulent flows [H. Choi, P. Moin, and J. Kim, J. Fluid Mech. 262, 75 (1994)]. The idea is to impose blowing and suction at the wall to counteract near-wall quasistreamwise vortical structures. Unfortunately, the effectiveness of this method decreases as the Reynolds number increases [Y. Chang, S. Scott Collis, and S. Ramakrishnan, Phys. Fluids 14, 4069 (2002)]. The present study proposes using a simple modification of opposition control (OC) to increase its performance at high Reynolds numbers. We demonstrate a significant improvement on drag reduction when performing a blowing-only opposition control, where the suction part of OC has been removed, on a spatially developing turbulent boundary layer at Re? ,?=960, based on the boundary layer thickness and the friction velocity.

Pamiès, Mathieu; Garnier, Eric; Merlen, Alain; Sagaut, Pierre

2007-10-01

41

Tropical cyclone boundary layer shocks  

E-print Network

This paper presents numerical solutions and idealized analytical solutions of axisymmetric, $f$-plane models of the tropical cyclone boundary layer. In the numerical model, the boundary layer radial and tangential flow is forced by a specified pressure field, which can also be interpreted as a specified gradient balanced tangential wind field $v_{\\rm gr}(r)$ or vorticity field $\\zeta_{\\rm gr}(r)$. When the specified $\\zeta_{\\rm gr}(r)$ field is changed from one that is radially concentrated in the inner core to one that is radially spread, the quasi-steady-state boundary layer flow transitions from a single eyewall shock-like structure to a double eyewall shock-like structure. To better understand these structures, analytical solutions are presented for two simplified versions of the model. In the simplified analytical models, which do not include horizontal diffusion, the $u(\\partial u/\\partial r)$ term in the radial equation of motion and the $u[f+(\\partial v/\\partial r)+(v/r)]$ term in the tangential equat...

Slocum, Christopher J; Taft, Richard K; Schubert, Wayne H

2014-01-01

42

The Martian Surface Boundary Layer  

NASA Technical Reports Server (NTRS)

The acquisition of meteorological data from the surface of Mars by the two Viking Landers and Mars Pathfinder make it possible to estimate atmospheric boundary layer parameters and surface properties at three different locations on the planet. Because the Martian atmosphere is so thin the majority of the solar radiance is converted to heat at the surface. The difference between surface and atmospheric temperature can also constraint surface albedo, thermal inertia, and infrared emissivity. The Mars Pathfinder Atmospheric Structure Instrument/Meteorological package (ASI/MET) was the most capable weather monitoring system ever sent to the surface of another planet to date. One of the prime objectives of the ASI/MET package is to characterize the surface boundary layer parameters, particularly the heat and momentum fluxes, scaling temperature and friction velocity, and estimate surface roughness. Other important boundary layer parameters, such as Richardson Number, Monin-Obukhov length, analysis of turbulence characteristics of wind and temperature, and atmospheric stability class can also be determined from these measurements.

Wilson, G. R.; Joshi, M.

1999-01-01

43

Boundary Layer Transition Flight Experiment Implementation on OV-103  

NASA Technical Reports Server (NTRS)

This slide presentation reviews the boundary layer transition experiment flown on Discovery. The purpose of the boundary layer transition flight experiment was to obtain hypersonic aero-thermodynamic data for the purpose of better understanding the flow transition from a laminar to turbulent boundary layer using a known height protuberance. The preparation of the shuttle is described, with the various groups responsibilities outlined. Views of the shuttle in flight with the experimental results are shown.

Spanos, Theodoros A.

2009-01-01

44

Observational and numerical analysis of atmospheric boundary-layer response to summertime thermal and dynamic forcings in Miers Valley, Antarctica  

NASA Astrophysics Data System (ADS)

In response to solar insolation the McMurdo Dry Valleys (MDVs) summertime airflow patterns show bimodal oscillations, either up-valley or down-valley. Miers Valley (78°6'S, 164°0'E) is one of the four, east-west oriented ice-free valleys in the Denton Hill area of southern Victoria Land and one of the biodiversity 'hotspots'. This glacially excavated valley is considerably smaller than the larger valley systems such as Wright or Victoria. While most atmospheric research has been carried out in the larger valley systems, little work has been done on this part of the MDVs; this research presents the first investigation of Miers valley's microclimate. We aim to provide insight into diurnal evolution of boundary layer and physical mechanism(s) responsible for local circulations, and determine their spatial extent during summer 2012 (13-25 January). This was achieved through high-resolution numerical modeling using a polar optimized weather prediction model (PWRF) alongside data obtained from an eddy-covariance system and a wind profiler (SODAR) to elucidate the role of local thermal forcing during synoptic quiescence. Measurements showed that persistent up-valley winds were present within and above a mixed layer (120 ± 30 mAGL), peaking around 75 mAGL upto 6 m/s between 1800 to 2000 LST. Several mechanisms that can produce up-valley flows in MDVs have been proposed. A regional intrusion of sea breeze currents originating from McMurdo Sound and the Ross Sea area is one of the possible forcings for such valley winds. Another suggested forcing is flow deflection due to the blocking effect of Ross Island (RI). Numerical simulations confirm that up-valley easterlies have both local and regional thermal and dynamic forcings. The thermal forcing is controlled by the variation in solar elevation, topographic shadowing, and clouds, which cause a heterogeneous thermal pattern and produce a cross-valley thermal gradient, and spatially larger gradient between the valley atmosphere and the Ross Ice Shelf (RIS) forcing the local wind system. PWRF simulates different spatial wind pattern for each half of the valley, mainly because of the shape of topography and the distance from RIS. The eastern half of the valley constantly showed up-valley wind whereas the valley interior, (which includes the measurement site) experienced a weak and shallow down-valley flow when the surface is topographically shadowed. The dynamic forcing results from the build-up of a meso-high pressure zone south of RI due to katabatic interaction with topography and the channeling effect of RI and the adjacent coastal topography, which cause intrusion of an easterly flow against the pressure gradient pattern lying over the nearby Koettlitz Glacier.

Soltanzadeh, Iman; Katurji, Marwan; Zawar-Reza, Peyman; Storey, Bryan

2013-04-01

45

Nonequilibrium chemistry boundary layer integral matrix procedure  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

46

Streak breakup in turbulent boundary layers  

NASA Astrophysics Data System (ADS)

Direct numerical simulations are used to compute the evolution of a single streak in a laminar boundary layer (Re* = 450) and a turbulent boundary on a flat plate at zero pressure gradient (Re* = 900). The single streak is formed through fluid injection at the wall as in Acarlar and Smith (1987). It is found that the single streak undergoes an instability resulting in the formation of hairpin vortices. The resulting flow field is in very good agreement with the experimental results of Acarlar and Smith (1987). The instability can be explained through an Orr-Sommerfeld analysis of the velocity profile on the plane of symmetry of the streak. The predicted wavelength and eigenfunctions are in very good agreement with those obtained from the simulations. Application of the same analysis to streaks in a fully turbulent boundary layer reveal as good an agreement. It is argued that this instability is the basic mechanism responsible for streak breakup. Acarlar, M.S. and Smith, C.R., 1987. A study of hairpin vortices in a laminar boundary layer. Part 2. Hairpin vortices generated by fluid injection. J. Fluid Mech., 175, pp. 43-83.

Haritonidis, Joseph H.; Skote, Martin

1999-11-01

47

Radiation-viscous boundary layer  

NASA Technical Reports Server (NTRS)

A viscous boundary layer (BL) is studied which is most likely to occur in astrophysical systems dominated by radiation pressure, in particular compact objects surrounded by a very optically thick envelope and radiating at close to the Eddington limit. Calculations are reported which show that a BL due to radiation viscosity behaves very differently from a 'classical' incompressible BL for flows with Mach number M much greater than unity far from the BL. In these flows the width of the BL is much larger than its incompressible value and scales as M-squared times the width of the imcompressible BL. The density inside the BL is much lower than that in the undisturbed fluid and scales as 1/M-squared with respect to the value far away from the BL. It is concluded that under certain circumstances a cocoon of low-density material will develop between a jet and its surrounding medium.

Arav, Nahum; Begelman, Mitchell C.

1992-01-01

48

Atmospheric boundary layer research at Cabauw  

Microsoft Academic Search

At Cabauw, The Netherlands, a 213 m high mast specifically built for meteorological research has been operational since 1973. Its site, construction, instrumentation and observation programs are reviewed. Regarding analysis of the boundary layer at Cabauw, the following subjects are discussed:- terrain roughness;- Monin-Obukhov theory in practice;- the structure of stable boundary layers;- observed evolution of fog layers;- inversion rise

A. P. VAN ULDEN; J. Wieringa

1996-01-01

49

Numerical study of the response of a compressible, turbulent boundary layer to a short region of surface curvature  

NASA Technical Reports Server (NTRS)

Calculations were performed to investigate the supersonic flow of a turbulent boundary layer over short regions of concave surface curvature. Upstream of each curved surface the freestream Mach number was 2.9. Three different constant radii of curvature models were investigated to cover a range of curvatures and turning angles. The numerical technique solved the full, Reynolds-averaged Navier-Stokes equations using two different turbulence models: the algebraic eddy viscosity model due to Baldwin and Lomax (1978), and the one-equation model to Rubesin (1976). The calculations were compared with the experimental data of Taylor and Smits (1984), and the agreement was very satisfactory, especially for the computations using the one-equation model.

Degani, D.; Smits, A. J.

1985-01-01

50

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

51

Microgravity Effects on Plant Boundary Layers  

NASA Technical Reports Server (NTRS)

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

2005-01-01

52

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.

53

A Nonperturbing Boundary-Layer Transition Detector  

NASA Astrophysics Data System (ADS)

A laser interferometer technique is being applied to the characterization of boundary-layer conditions on models in supersonic and hypersonic wind tunnels in the von Kaman Facility at Arnold Engineering Development Center (AEDC). The Boundary-Layer Transition Detector (BLTD), based on lateral interferometry, is applicable for determining the turbulence frequency spectrum of boundary layers in compressible flow. The turbulence, in terms of air density fluctuations, is detected by monitoring interferometric fringe phase shifts (in real time) formed by one beam which passes through the boundary layer and a reference beam which is outside the boundary layer. This technique is nonintrusive to the flow field unlike other commonly used methods such as pitot tube probing and hot-wire anemometry. Model boundary-layer data are presented at Mach 8 and compared with data recorded using other methods during boundary-layer transition from laminar to turbulent flow. Spectra from the BLTD reveal the presence of a high-frequency peak during transition, which is characteristic of spectra obtained with hot wires. The BLTD is described along with operational requirements and limitations.

O'Hare, J. E.

1986-01-01

54

Planetary Boundary Layer Simulation Using TASS  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

55

Boundary layer influence on cavity noise generation.  

E-print Network

]. Experiments were conducted in a open jet wind tunnel facility. The cavity took place in a flat plate such as the cavity geometry, the free stream velocity and the incoming boundary layer properties, [1]. In this paper

Lindken, Ralph

56

Propulsion via buoyancy driven boundary layer  

E-print Network

Heating a sloped surface generates a well-studied boundary layer flow, but the resulting surface forces have never been studied in propulsion applications. We built a triangular wedge to test this effect by mounting a ...

Doyle, Brian Patrick

2011-01-01

57

Boundary-layer stability and airfoil design  

NASA Technical Reports Server (NTRS)

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

Viken, Jeffrey K.

1986-01-01

58

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

59

Large Eddy Simulation of Atmospheric Convective Boundary Layer with Realistic  

E-print Network

Large Eddy Simulation of Atmospheric Convective Boundary Layer with Realistic Environmental atmospheric environmental forcings. Analysis of several simulated convec- tive boundary layer (CBL) cases toward dynamic adjustment of environmental parameters in LES of atmospheric boundary layer flows

Fedorovich, Evgeni

60

Modeling the summertime Arctic cloudy boundary layer  

SciTech Connect

Global climate models have particular difficulty in simulating the low-level clouds during the Arctic summer. Model problems are exacerbated in the polar regions by the complicated vertical structure of the Arctic boundary layer. The presence of multiple cloud layers, a humidity inversion above cloud top, and vertical fluxes in the cloud that are decoupled from the surface fluxes, identified in Curry et al. (1988), suggest that models containing sophisticated physical parameterizations would be required to accurately model this region. Accurate modeling of the vertical structure of multiple cloud layers in climate models is important for determination of the surface radiative fluxes. This study focuses on the problem of modeling the layered structure of the Arctic summertime boundary-layer clouds and in particular, the representation of the more complex boundary layer type consisting of a stable foggy surface layer surmounted by a cloud-topped mixed layer. A hierarchical modeling/diagnosis approach is used. A case study from the summertime Arctic Stratus Experiment is examined. A high-resolution, one-dimensional model of turbulence and radiation is tested against the observations and is then used in sensitivity studies to infer the optimal conditions for maintaining two separate layers in the Arctic summertime boundary layer. A three-dimensional mesoscale atmospheric model is then used to simulate the interaction of this cloud deck with the large-scale atmospheric dynamics. An assessment of the improvements needed to the parameterizations of the boundary layer, cloud microphysics, and radiation in the 3-D model is made.

Curry, J.A.; Pinto, J.O. [Univ. of Colorado, Boulder, CO (United States); McInnes, K.L. [CSIRO Division of Atmospheric Research, Mordialloc (Australia)

1996-04-01

61

On similarity in the atmospheric boundary layer  

Microsoft Academic Search

A similarity theory for the atmospheric boundary layer is presented. The Monin-Obukhov similarity theory for the surface layer is a particular case of this new theory, for the case of z ? 0. Universal functions which are in agreement with empirical data are obtained for the stable and convective regimes.

Zbigniew Sorbjan

1986-01-01

62

A case study of boundary layer ventilation by convection and coastal processes  

E-print Network

; published 12 September 2007. [1] It is often assumed that ventilation of the atmospheric boundary layer responsible for ventilation of the atmospheric boundary layer during a nonfrontal day that occurred on 9 May of the pollution in the atmosphere originates from emissions in the atmospheric boundary layer, the region

Dacre, Helen

63

DNS of Rough Surface Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

A dynamic method for prescribing realistic inflow boundary conditions is presented for simulations of spatially developing turbulent boundary layers subject to surface roughness. Direct Numerical Simulation (DNS) of a moderate Reynolds number, zero pressure gradient (ZPG) turbulent boundary layer was performed. The boundary layer was subjected to transitional, 24-grit sand grain surface roughness, modeled with a roughness parameter of k^+ ˜12 and a Reynolds number of R?= 2400. The computational method involves a synergy of the multi-scale dynamic approach and a new methodology for mapping high-resolution topographical surface data into a computational fluid dynamics environment. It is shown here that the multi-scale dynamic approach can be successfully extended to simulations, which incorporate surface roughness. In terms of the mean velocity and Reynolds stresses, the DNS results are encouraging as they demonstrate good agreement with the LDA measurements performed under similar conditions.

Cardillo, James; Araya, Guillermo; Chen, Yi; Jansen, Kenneth; Sahni, Onkar; Castillo, Luciano

2011-11-01

64

Dependence of Boundary Layer Mixing On Lateral Boundary Conditions  

NASA Astrophysics Data System (ADS)

Ocean circulation models often show strong mixing in association with lateral bound- ary layers. Such mixing is generally considered to be artifactual rather than real. Fur- thermore, the severity of the problem is boundary condition dependent. For example, an inconsistency between geostrophy and insulating boundary conditions on tempera- ture and salinity cause many modelers to opt for the no slip, rather than slip boundary condtion on the tangential component of momentum. As modellers increasingly move into the eddy revealing regime, biharmonic, rather than harmonic dissipative operators are likely to become more common. Biharmonic operators, however, require specifi- cation of additional boundary conditions. For example, there are several `natural ex- tensions' to each of the slip and no slip conditions. Here, these various possiblities are considered in the context of a simple model. Particular attention is payed to how mixing (and the associated overturning cell) is affected by the choice of boundary condition.

Straub, D.

65

Lear jet boundary layer/shear layer laser propagation experiments  

NASA Technical Reports Server (NTRS)

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

Gilbert, K.

1980-01-01

66

Boundary layer emission in luminous LMXBs  

E-print Network

We show that aperiodic and quasiperiodic variability of bright LMXBs - atoll and Z- sources, on ~sec - msec time scales is caused primarily by variations of the boundary layer luminosity. The accretion disk emission is less variable on these time scales and its power density follows 1/f law, contributing to observed flux variation at low frequencies and low energies only. The kHz QPOs have the same origin as variability at lower frequencies - independent of the nature of the "clock", the actual luminosity modulation takes place on the NS surface. The boundary layer spectrum remains nearly constant during luminosity variations and can be represented by the Fourier frequency resolved spectrum. In the range of Mdot~(0.1-1)*Mdot_Edd it depends weakly on the global mass accretion rate and in the limit Mdot~Mdot_Edd is close to Wien spectrum with kT~2.4 keV. Its independence on the Mdot lends support to the suggestion by Inogamov & Sunyaev (1999) that the boundary layer is radiation pressure supported. Based on the knowledge of the boundary layer spectrum we attempt to relate the motion along the Z-track to changes of physically meaningful parameters. Our results suggest that the contribution of the boundary layer to the observed emission decreases along the Z-track from conventional ~50% on the horizontal branch to a rather small number on the normal branch. This decrease can be caused, for example, by obscuration of the boundary layer by the geometrically thickened accretion disk at Mdot~Mdot_Edd. Alternatively, this can indicate significant change of the structure of the accretion flow at Mdot~Mdot_Edd and disappearance of the boundary layer as a distinct region of the significant energy release associated with the NS surface.

M. Gilfanov; M. Revnivtsev

2005-12-14

67

FIFE atmospheric boundary layer budget methods  

NASA Technical Reports Server (NTRS)

The budget methods and the mixed layer model employed to analyze the aircraft data from the First ISLSCP Field Experiment (FIFE) are described. Vector budgets for the mixed layer are discussed on conserved variable diagrams. Theoretical solutions are presented for the critical surface Bowen ratio that produces no boundary layer moistening or equivalent potential temperature rise as a function of the Bowen ratio at the inversion.

Betts, A. K.

1992-01-01

68

Boundary-Layer-Ingesting Inlet Flow Control  

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

69

High enthalpy hypersonic boundary layer flow  

NASA Technical Reports Server (NTRS)

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

Yanow, G.

1972-01-01

70

Boundary-layer depth and entrainment zone characterization with a boundary-layer profiler  

Microsoft Academic Search

A technique for determining the height of the convective atmospheric boundary layer (CBL) with a 915 MHz boundary-layer profiler is discussed. The results are compared with CBL heights determined from radiosonde measurements. The profiler provides continuous CBL height measurements with very good time resolution (30 minutes or less), allowing for detailed understanding of the growth and fluctuations of the CBL.

Wayne M. Angevine; Allen B. White; S. K. Avery

1994-01-01

71

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

NASA Technical Reports Server (NTRS)

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

Mack, L. M.

1967-01-01

72

Stability of separating subsonic boundary layers  

NASA Technical Reports Server (NTRS)

The primary and subharmonic instabilities of separating compressible subsonic two-dimensional boundary layers in the presence of a two-dimensional roughness element on a flat plate are investigated. The roughness elements considered are humps and forward- and backward-facing steps. The use of cooling and suction to control these instabilities is studied. The similarities and differences between the instability characteristics of separating boundary layers and those of the boundary layer over a flat plate with a zero pressure gradient are pointed out and discussed. The theoretical results agree qualitatively and quantitatively with the experimental data of Dovgal and Kozlov. Cooling and suction decrease the growth rates of primary and subharmonic waves in the attached-flow regions but increase them in the separated-flow regions.

Masad, Jamal A.; Nayfeh, Ali H.

1994-01-01

73

Numerical simulation of supersonic boundary layer transition  

NASA Technical Reports Server (NTRS)

The present contribution reviews some of the recent progress obtained at our group in the direct numerical simulation (DNS) of compressible boundary layer transition. Elements of the different simulation approaches and numerical techniques employed are surveyed. Temporal and spatial simulations, as well as comparisons with results obtained from Parabolized Stability Equations, are discussed. DNS results are given for flat plate boundary layers in the Mach number range 1.6 to 4.5. A temporal DNS at Mach 4.5 has been continued through breakdown all the way to the turbulent stage. In addition results obtained with a recently developed extended temporal DNS approach are presented, which takes into account some nonparallel effects of a growing boundary layer. Results from this approach are quite close to those of spatial DNS, while preserving the efficiency of the temporal DNS.

Guo, Y.; Adams, N. A.; Sandham, N. D.; Kleiser, L.

1994-01-01

74

A novel technique for response function determination of shear sensitive cholesteric liquid crystals for boundary layer investigations  

NASA Technical Reports Server (NTRS)

A description of the design and setup of an experimental technique for measurement of the response function in shear sensitive liquid crystals has been reported. Utilizing the selective reflection characteristics of cholesteric liquid crystals, the method is capable of measuring the delay, rise, and relaxation times in response to a given dynamic shear stress as a function of the wavelength of the incident light. Application of a step input shear stress results in a liquid crystal time response that can be described as consisting of an initial delay, a shear induced helix deformation, and a relaxation to the initial state through diffusion processes. The method has been used for quantitative calibration of a shear sensitive liquid crystal by observing the peak in reflected light intensity, at a given wavelength, as a function of the shear stress.

Parmar, D. S.

1991-01-01

75

Calculation methods for compressible turbulent boundary layers, 1976  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

76

ESE 134: BOUNDARY LAYER AND CLOUD DYNAMICS -SPRING 2013 SYLLABUS  

E-print Network

of clouds and atmospheric boundary layers, from a phenomenological overview of cloud and boundary layer) · The Atmospheric Boundary Layer, J. R. Garratt (Cambridge UP, 1992) · Turbulence in the Atmosphere, J. C. WyngaardESE 134: BOUNDARY LAYER AND CLOUD DYNAMICS - SPRING 2013 SYLLABUS Introduction to the dynamics

Bordoni, Simona

77

Boundary-Layer Meteorology An International Journal of Physical,  

E-print Network

Processes in the Atmospheric Boundary Layer ISSN 0006-8314 Volume 147 Number 1 Boundary-Layer Meteorol (20131 23 Boundary-Layer Meteorology An International Journal of Physical, Chemical and Biological after publication. #12;Boundary-Layer Meteorol (2013) 147:41­50 DOI 10.1007/s10546-012-9777-7 ARTICLE

Marusic, Ivan

78

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.; Lindstrøm, E.; Bertelsen, A. F.; Jensen, A.; Laskovski, D.; Sælevik, G.

2013-01-01

79

Evaluation of boundary-layer type forecasts 1 Evaluation of boundary-layer type in a weather forecast model  

E-print Network

Evaluation of boundary-layer type forecasts 1 Evaluation of boundary-layer type in a weather Many studies evaluating model boundary-layer schemes focus either on near-surface parameters, combined in a way to match model representation of the boundary layer as closely as possible, can be used

Hogan, Robin

80

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...

81

Orbiter Boundary Layer Transition Prediction Tool Enhancements  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

82

Secondary Görtler Instability in Hypersonic Boundary Layers  

NASA Astrophysics Data System (ADS)

In general, boundary layer flows become turbulent in three steps: 1) receptivity, 2) linear growth of disturbance, and 3) nonlinear effects in which the flow breaks down to turbulence. Görtler instability is one of the many B-L instability mechanisms. Görtler vortices appear in boundary layer flow along concave surfaces due to the imbalance between the pressure and centrifugal force. Many practical engineering designs, such as engine inlet, involve concave surfaces. Therefore, Görtler instability is an important subject in fluid mechanics. In this paper, Görtler instability is investigated using two approaches: Linear Stability Theory(LST) and Direct Numerical Simulation(DNS). Initial forcing disturbances are obtained from the LST, and subsequent linear and nonlinear development is simulated using Navier-Stokes equations. We investigate linear and nonlinear growth of Görtler vortices in hypersonic boundary layers. DNS is used to simulate Görtler vortices in hypersonic boundary layers. Two dimensional steady mean flow is computed using a fifth order explicit upwind scheme. Linear growth of disturbances is compared with the LST code to verify the DNS. Nonlinear effects of Görtler vortices are also investigated using DNS. Inflectional profiles develop due to the distortion of the mean flow caused by nonlinear growth of Görtler vortices which induces secondary instability. Secondary instability will be investigated using secondary instability theory and DNS.

Whang, C. W.; Zhong, X.

2000-11-01

83

Advection in Accretion Disk Boundary Layers  

NASA Technical Reports Server (NTRS)

Recent numerical simulations of accretion disk boundary layers have shown qualitatively the importance tance of advected energy in the inner region of the disk. In this short paper we present quantitative results of advective boundary layers in the optically thick regime. Numerical results are obtained for various systems, by means of a one-dimensional time-dependent numerical code. At high accretion mass rates, dot-M approx. = 10(exp -4) solar mass/yr, or low values of the viscosity parameter, alpha approx. = 0.001-0.01 (characteristic of FU Orionis systems and some symbiotic stars), the optical thickness in the inner part of the disk becomes very large (tau much greater than 1). The disk, unable to cool efficiently, becomes geometrically thick (H/r approx. = 0.5). The energy dissipated in the dynamical boundary layer is radiated outward to larger radii and advected into the star. The boundary-layer luminosity is only a fraction of its expected value; the rest of the energy is advected into the star. The fraction of the advected energy is zeta = L(sub adv)/L(sub acc) approx. = 0.1 in symbiotic stars (accretion onto a low-mass main-sequence star) and zeta approx. = 0.2 in FU Ori systems (accretion onto a pre-main sequence star).

Godon, Patrick

1997-01-01

84

Numerical methods in boundary-layer theory  

Microsoft Academic Search

Two particular methods, the Crank-Nicolson scheme and the Box scheme, appear to have a dominating position among the large variety of numerical methods which are used to solve the many flow problems to which boundary-layer theory is applied. Of the two methods, the Box scheme has the advantage that it can very easily be adapted to new classes of problems.

H. B. Keller

1978-01-01

85

Sound radiation from a turbulent boundary layer  

Microsoft Academic Search

Sound radiation due to fluctuating viscous wall shear stresses in a plane turbulent boundary layer is investigated by a two-stage procedure using direct numerical simulation (DNS) databases for incompressible turbulent Poiseuille flow in a plane channel, at Reynolds numbers up to Re?=1440. The power spectral density of radiated pressure and spectra of sound power per unit wall area are calculated

Zhiwei Hu; Christopher L. Morfey; Neil D. Sandham

2006-01-01

86

Sound radiation from a turbulent boundary layer  

Microsoft Academic Search

Sound radiation due to fluctuating viscous wall shear stresses in a plane turbulent boundary layer is investigated by a two-stage procedure using direct numerical simulation (DNS) databases for incompressible turbulent Poiseuille flow in a plane channel, at Reynolds numbers up to Retau=1440. The power spectral density of radiated pressure and spectra of sound power per unit wall area are calculated

Zhiwei Hu; Christopher L. Morfey; Neil D. Sandham

2006-01-01

87

Boundary Layer Transition on X-43A  

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

88

Regional Carbon Fluxes and Boundary Layer Heights  

E-print Network

Regional Carbon Fluxes and Boundary Layer Heights from the Airborne Carbon in the Mountains - Madison Department of Atmospheric and Oceanic Sciences Advisor Signature Date #12;i ABSTRACT The Central Rocky Mountains, with its abundant forests ecosystem, is likely an im- portant carbon sink

Wisconsin at Madison, University of

89

Heat Transport in the Atmospheric Boundary Layer  

Microsoft Academic Search

The structure of turbulence and transport of heat is examined from data obtained from 11 aircraft soundings executed in heated boundary layers during the Air Mass Transformation Experiment. Various influences on the turbulent transport are revealed by analyzing properties of the joint frequency distribution in polar coordinate. Such an analysis allows determination of a correlation coefficient and fluctuation amplitude as

L. Mahrt; J. Paumier

1984-01-01

90

Boundary layer control device for duct silencers  

NASA Technical Reports Server (NTRS)

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. (inventor); Soderman, Paul T. (inventor)

1993-01-01

91

Sea-salt injections into the low-latitude marine boundary layer: The transient response in three Earth system models  

NASA Astrophysics Data System (ADS)

proposed mechanisms for counteracting global warming through solar radiation management is the deliberate injection of sea salt acting via marine cloud brightening and the direct effect of sea-salt aerosols. In this study, we show results from multidecadal simulations of such sea-salt climate engineering (SSCE) on top of the RCP4.5 emission scenario using three Earth system models. As in the proposed "G3" experiment of the Geoengineering Model Intercomparison Project, SSCE is designed to keep the top-of-atmosphere radiative forcing at the 2020 level for 50 years. SSCE is then turned off and the models run for another 20 years, enabling an investigation of the abrupt warming associated with a termination of climate engineering ("termination effect"). As in former idealized studies, the climate engineering in all three models leads to a significant suppression of evaporation from low-latitude oceans and reduced precipitation over low-latitude oceans as well as in the storm-track regions. Unlike those studies, however, we find in all models enhanced evaporation, cloud formation, and precipitation over low-latitude land regions. This is a response to the localized cooling over the low-latitude oceans imposed by the SSCE design. As a result, the models obtain reduced aridity in many low-latitude land regions as well as in southern Europe. Terminating the SSCE leads to a rapid near-surface temperature increase, which, in the Arctic, exceeds 2 K in all three models within 20 years after SSCE has ceased. In the same period September Arctic sea ice cover shrinks by over 25%.

Alterskjær, Kari; Kristjánsson, Jón Egill; Boucher, Olivier; Muri, Helene; Niemeier, Ulrike; Schmidt, Hauke; Schulz, Michael; Timmreck, Claudia

2013-11-01

92

Method for laminar boundary layer transition visualization in flight  

NASA Technical Reports Server (NTRS)

Disclosed is a method of visualizing laminar to turbulent boundary layer transition, shock location, and laminar separation bubbles around a test surface. A liquid crystal coating is formulated using an unencapsulated liquid crystal operable in a temperature bandwidth compatible with the temperature environment around the test surface. The liquid crystal coating is applied to the test surface, which is preferably pretreated by painting with a flat, black paint to achieve a deep matte coating, after which the surface is subjected to a liquid or gas flow. Color change in the liquid crystal coating is produced in response to differences in relative shear stress within the boundary layer around the test surface. The novelty of this invention resides in the use of liquid crystals which are sensitive to shear stress to show aerodynamic phenomena such as a boundary layer transition, shock location, and laminar separation bubbles around a test surface.

Holmes, Bruce J. (inventor); Gall, Peter D. (inventor)

1988-01-01

93

Hairpin vortices in turbulent boundary layers  

NASA Astrophysics Data System (ADS)

The present work addresses the question whether hairpin vortices are a dominant feature of near-wall turbulence and which role they play during transition. First, the parent-offspring mechanism is investigated in temporal simulations of a single hairpin vortex introduced in a mean shear flow corresponding to turbulent channels and boundary layers up to Re? = 590. Using an eddy viscosity computed from resolved simulations, the effect of a turbulent background is also considered. Tracking the vortical structure downstream, it is found that secondary hairpins are created shortly after initialization. Thereafter, all rotational structures decay, whereas this effect is enforced in the presence of an eddy viscosity. In a second approach, a laminar boundary layer is tripped to transition by insertion of a regular pattern of hairpins by means of defined volumetric forces representing an ejection event. The idea is to create a synthetic turbulent boundary layer dominated by hairpin-like vortices. The flow for Re? < 250 is analysed with respect to the lifetime of individual hairpin-like vortices. Both the temporal and spatial simulations demonstrate that the regeneration process is rather short-lived and may not sustain once a turbulent background has formed. From the transitional flow simulations, it is conjectured that the forest of hairpins reported in former DNS studies is an outer layer phenomenon not being connected to the onset of near-wall turbulence.

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

2014-04-01

94

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

95

Enthalpy effects on hypervelocity boundary layers  

NASA Astrophysics Data System (ADS)

More than 50 shots with air and 35 shots with carbon dioxide were carried out in the T5 shock tunnel at GALCIT to study enthalpy effects on hypervelocity boundary layers. The model tested was a 5° half-angle cone measuring approximately 1 meter in length. It was instrumented with 51 chromel-constantan coaxial thermocouples and the surface heat transfer rate was computed to deduce the state of the boundary layer and, when applicable, the transition location. Transitional boundary layers obtained confirm the stabilizing effect of enthalpy. As the reservoir enthalpy is increased, the transition Reynolds number evaluated at the reference conditions increases as well. The stabilizing effect is more rapid in gases with lower dissociation energy and it seems to level off when no further dissociation can be achieved. These effects do not appear when the transition location is normalized with the edge conditions. Further normalizing the reservoir enthalpy with the edge enthalpy appears to collapse the data for all gases onto a single curve. A similar collapse is obtained when normalizing both the transition location and the reservoir enthalpy with maximum temperature conditions obtained with BLIMPK, a nonequilibrium boundary layer code. The observation that the reference conditions seem more appropriate to normalize high enthalpy transition data was taken a step further by comparing the tunnel data with results from a reentry experiment. When the edge conditions are used, the tunnel data are around an order of magnitude below the flight data. This is commonly attributed to the fact that disturbance levels in tunnels are high, causing the boundary layer to transition prematurely. However, when the conditions at the reference temperature are used instead, the data come within striking distance of one another although the trend with enthalpy seems to be a destabilizing one for the flight data. This difference could be due to the cone bending and blunting observed during the reentry. Experimental laminar heat transfer levels were compared to numerical results obtained with BLIMPK. Results for air indicate that the reactions are probably in nonequilibrium and that the wall is catalytic. The catalycity is seen to yield higher surface heat transfer rates than the noncatalytic and frozen chemistry models. The results for carbon dioxide, however, are inconclusive. This is, perhaps, because of inadequate modeling of the actual reactions. Experimentally, an anomalous yet repeatable, rise in the laminar heat transfer level can be seen at medium enthalpies in carbon dioxide boundary layers.

Adam, Philippe H.

96

Enthalpy effects on hypervelocity boundary layers  

NASA Astrophysics Data System (ADS)

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

Adam, Philippe H.

97

Interaction between soil hydrology and boundary-layer development  

Microsoft Academic Search

A two-layer model of soil hydrology and thermodynamics is combined with a one-dimensional model of the planetary boundary layer to study various interactions between evolution of the boundary layer and soil moisture transport. Boundary-layer moistening through surface evaporation reduces the potential and actual surface evaporation as well as the boundary-layer growth. With more advanced stages of soil drying, the restricted

H.-L. Pan; L. Mahrt

1987-01-01

98

Two-fluid boundary layer stability  

NASA Astrophysics Data System (ADS)

The stability of a two-fluid boundary layer is investigated. A boundary layer shears a second fluid that is bounded by the wall and the shearing fluid. The eigenvalue problem governing the linear stability of the configuration is solved using an efficient shooting-search method. Besides the Tollmien-Schlichting mode (hard mode) found in the classical hydrodynamical stability theory an additional Yih-mode (interfacial mode) exists due to the two-fluid interface. Effects of viscosity and density stratifications, thickness of the bounded fluid, gravity, surface tension as well as the non-Newtonian character of the lower fluid on the stability characteristics are determined. The interfacial mode is found to be very sensitive against viscosity stratification. However, with a highly viscous liquid layer, the system approaches a single-layer behavior. The shear-thinning non-Newtonian liquid layer is observed to have a stabilizing effect for both of the modes. Surface tension is stabilizing for short waves for the interfacial mode but a more complex effect was observed for the hard mode. Gravity is stabilizing with a favorable density stratification. Density stratification alone is destabilizing for low and moderate values of this parameter but becomes stabilizing for higher values. When the external boundary layer profile is turbulent, the interfacial mode is more likely to be observed in an experiment. Agreement of the obtained results with experimental, theoretical and numerical results reported in the literature is good. This is encouraging as the study is intended for solving the stability characteristics of de/anti-icing fluid-air systems and comparing the results with the experimental data when they become available.

Özgen, S.; Degrez, G.; Sarma, G. S. R.

1998-11-01

99

Study of the marine atmospheric boundary layer  

NASA Astrophysics Data System (ADS)

The temporal and spatial (vertical) evolution of the atmospheric marine boundary layer in subtropical regions is investigated through observational and numerical approaches. The observational part was done with field experiments using simultaneous soundings from both atmosphere and ocean in the Cabo Frio region (23 deg S, 42 deg 08 min W). The numerical study used a second order closure model, as suggested by Mellor and Yamada (1982), coupled to an oceanic mixing layer model (OML) in order to determine the temperature of OML in terms of the energy balance. Although the field experiment had been done under a frontal system passage, that could create drawbacks in using those data, comparing the simulations against observations it was found that the simulated atmosphere boundary layer is consistent with the observed one during the experiment; it is also similar to that observed by Fitzjarrald and Garstang (1981) during the GATE. The simulated vertical profiles of the zonal, meridional and vertical components of the speed variance are typical from situations where the mechanic forcing is the main cause of mixing layer formation (forced convection). The increasing of temperature in the oceanic mixing layer, simultaneously with the deepening of OML is associated with the warm water advection, from the current of Brazil. The simulations of the OML during the experiment was intensified due the subsidence of South Atlantic Central Water (SACW).

Dourado, Marcelo Sandin

1994-02-01

100

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

101

BOREAS AFM-6 Boundary Layer Height Data  

NASA Technical Reports Server (NTRS)

The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) site. This data set provides boundary layer height information over the site. The data were collected from 21 May 1994 to 20 Sep 1994 and are stored in tabular ASCII files. The boundary layer height data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

2000-01-01

102

Nano boundary layers over stretching surfaces  

NASA Astrophysics Data System (ADS)

In this paper, we present similarity solutions for the nano boundary layer flows with Navier boundary condition. We consider viscous flows over a two-dimensional stretching surface and an axisymmetric stretching surface. The resulting nonlinear ordinary differential equations are solved analytically by the Homotopy Analysis Method. Numerical solutions are obtained by using a boundary value problem solver, and are shown to agree well with the analytical solutions. The effects of the slip parameter K and the suction parameter s on the fluid velocity and on the tangential stress are investigated and discussed. As expected, we find that for such fluid flows at nano scales, the shear stress at the wall decreases (in an absolute sense) with an increase in the slip parameter K.

Van Gorder, Robert A.; Sweet, Erik; Vajravelu, K.

2010-06-01

103

Progress in modeling hypersonic turbulent boundary layers  

NASA Technical Reports Server (NTRS)

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

Zeman, Otto

1993-01-01

104

The boundary layer on compressor cascade blades  

NASA Technical Reports Server (NTRS)

Some redesign of the cascade facility was necessary in order to incoporate the requirements of the LDA system into the design. Of particular importance was the intended use of a combination of suction upstream of the blade pack with diverging pack walls, as opposed to blade pack suction alone, for spanwise dimensionality control. An ARL blade was used to redo some tests using this arrangement. Preliminary testing and boundary layer measurements began on the double circular arc blades.

Deutsch, S.

1981-01-01

105

Boundary Layer Transition Results From STS-114  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

106

Boundary Layer Control for Hypersonic Airbreathing Vehicles  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

107

JANNAF boundary layer integral matrix procedure. [turbulent boundary layer/rocket nozzles - prediction analysis techniques  

NASA Technical Reports Server (NTRS)

Accurate predictions of the thrust loss due to boundary layer effects and of the wall heat flux are very important to the design and performance evaluation of rocket nozzles. A method used in analytical procedures for liquid fuel rocket engine performance prediction and evaluation is presented. A computer program is examined that is a fast and accurate procedure for solving the set of boundary layer equation (momentum, energy, and species) for laminar or turbulent, chemically reacting flows with a wide variety of boundary conditions. Results of comparison of the various turbulent models are presented. A summary of the modifications and additions to the program is examined.

Evans, R. M.

1975-01-01

108

Response to ``Comment on `Primary instability mechanisms on the magnetohydrodynamic boundary layer flow over a rotating disk subject to a uniform radial flow''' [Phys. Fluids 22, 029102 (2010)  

NASA Astrophysics Data System (ADS)

It was pointed out by Thess [``Comment on `Oblique axisymmetric stagnation flows in magnetohydrodynamics [Phys. Fluids 19, 114106 (2007)]','' Phys. Fluids 20, 069102 (2008)] by Amaouche that the model used in the paper "Primary instability mechanisms on the magnetohydrodynamic boundary layer flow over a rotating disk subject to a uniform radial flow" by Turkyilmazoglu [Phys. Fluids 21, 074103 (2009)] is incomplete since the electric potential was neglected. This point is clarified here, and the ambiguity present in the magnetohydrodynamic flow research of this kind among the fluid dynamic community is remedied. As a consequence, the qualitative validity of the results in the work of Turkyilmazoglu ["Primary instability mechanisms on the magnetohydrodynamic boundary layer flow over a rotating disk subject to a uniform radial flow," Phys. Fluids 21, 074103 (2009)] from both the physical and mathematical viewpoints is justified.

Turkyilmazoglu, M.

2010-02-01

109

Turbulent boundary layers subjected to multiple curvatures and pressure gradients  

NASA Technical Reports Server (NTRS)

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

Bandyopadhyay, Promode R.; Ahmed, Anwar

1993-01-01

110

Entropy production in relativistic jet boundary layers  

NASA Astrophysics Data System (ADS)

Hot relativistic jets, passing through a background medium with a pressure gradient p ? r-? where 2 < ? ? 8/3, develop a shocked boundary layer containing a significant fraction of the jet power. In previous work, we developed a self-similar description of the boundary layer assuming isentropic flow, but we found that such models respect global energy conservation only for the special case ? = 8/3. Here, we demonstrate that models with ? < 8/3 can be made self-consistent if we relax the assumption of constant specific entropy. Instead, the entropy must increase with increasing r along the boundary layer, presumably due to multiple shocks driven into the flow as it gradually collimates. The increase in specific entropy slows the acceleration rate of the flow and provides a source of internal energy that could be channelled into radiation. We suggest that this process may be important for determining the radiative characteristics of tidal disruption events and gamma-ray bursts from collapsars.

Kohler, Susanna; Begelman, Mitchell C.

2015-01-01

111

The role of nonlinear critical layers in boundary layer transition  

NASA Technical Reports Server (NTRS)

Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear spatially growing instability waves evolve downstream in nominally two-dimensional laminar boundary layers. The first nonlinear reaction takes place locally within a so-called 'critical layer', with the flow outside this layer consisting of a locally parallel mean flow plus a pair of oblique instability waves - which may or may not be accompanied by an associated plane wave. The amplitudes of these waves, which are completely determined by nonlinear effects within the critical layer, satisfy either a single integro-differential equation or a pair of integro-differential equations with quadratic to quartic-type nonlinearities. The physical implications of these equations are discussed.

Goldstein, M.E.

1995-01-01

112

The Role of Boundary Layer Processes in Limiting PV Homogenization  

E-print Network

A ?-plane multilevel quasigeostrophic channel model with interactive static stability and a simplified parameterization of atmospheric boundary layer physics is used to study the role of different boundary layer processes ...

Zhang, Yang

113

Scaling the heterogeneously heated convective boundary layer  

NASA Astrophysics Data System (ADS)

We have studied the heterogeneously heated convective boundary layer (CBL) by means of large-eddy simulations (LES) and direct numerical simulations (DNS). What makes our study different from previous studies on this subject are our very long simulations in which the system travels through multiple states and that from there we have derived scaling laws. In our setup, a stratified atmosphere is heated from below by square patches with a high surface buoyancy flux, surrounded by regions with no or little flux. By letting a boundary layer grow in time we let the system evolve from the so-called meso-scale to the micro-scale regime. In the former the heterogeneity is large and strong circulations can develop, while in the latter the heterogeneity is small and does no longer influence the boundary layer structure. Within each simulation we can now observe the formation of a peak in kinetic energy, which represents the 'optimal' heterogeneity size in the meso-scale, and the subsequent decay of the peak and the development towards the transition to the micro-scale. We have created a non-dimensional parameter space that describes all properties of this system. By studying the previously described evolution for different combinations of parameters, we have derived three important conclusions. First, there exists a horizontal length scale of the heterogeneity (L) that is a function of the boundary layer height (h) and the Richardson (Ri) number of the inversion at the top of the boundary layer. This relationship has the form L = h Ri^(3/8). Second, this horizontal length scale L allows for expressing the time evolution, and thus the state of the system, as a ratio of this length scale and the distance between two patches Xp. This ratio thus describes to which extent the circulation fills up the space that exists between two patch centers. The timings of the transition from the meso- to the micro-scale collapse under this scaling for all simulations sharing the same flux difference between patch and surroundings. Third, we found that the presence of a flux in the surroundings of patches is essential to create a circulation. The timing of the 'optimal' heterogeneity size follows the same scaling as that of the transition. We thus conclude that the optimum heterogeneity size, which results in the strongest circulations, should be expressed in a ratio of L and Xp. This is different than most previous studies, which express this as a ratio of the boundary layer height h and patch distance Xp. We believe that with our derived scalings, we are able to provide a general picture of the properties of the 'optimum' heterogeneity size and the transition between the meso- and micro-scale regime. Structure of the heterogeneously heated boundary layer at the onset of the merge from the meso-scale to the micro-scale regime.

Van Heerwaarden, C.; Mellado, J.; De Lozar, A.

2013-12-01

114

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

115

OFFSHORE BOUNDARY-LAYER MODELLING H. Bergstrm1  

E-print Network

for this are excluded. Field experiments in the Baltic Sea area, [1], have shown that the atmospheric boundary layer farOFFSHORE BOUNDARY-LAYER MODELLING H. Bergström1 and R. Barthelmie2 1) Uppsala Univ., Dept. of Earth and low-level jets. The paper describes results from the boundary-layer modelling work package (WP4

116

CIRES Research Associate Arctic Cloud and Boundary Layer Processes  

E-print Network

for a research associate, postdoctoral scientist to study Arctic atmospheric boundary- layer processes, the atmospheric boundary layer and the surface in the Arctic environment using existing observational data setsCIRES Research Associate Arctic Cloud and Boundary Layer Processes The Cooperative Institute

Colorado at Boulder, University of

117

Near surface turbulence in a smooth wall atmospheric boundary layer  

E-print Network

1 Near surface turbulence in a smooth wall atmospheric boundary layer Scott C. Morris (s is to acquire measurements in the atmospheric boundary layer. For example, Van Atta and Chen (1970) used hot-wires in the atmospheric boundary layer over an ocean sur- face to learn more about structure functions in wall bounded

Morris, Scott C.

118

Thermal Effects in the Atmospheric Boundary Layer above the North  

E-print Network

Thermal Effects in the Atmospheric Boundary Layer above the North Sea by Saskia Tautz A thesis Background 6 2.1 Atmospheric Boundary Layer . . . . . . . . . . . . . . . . . . . . 6 2.1.1 Basics.1.5 Fluxes in the Boundary layer . . . . . . . . . . . . . . . . 8 2.2 Measurement of Fluxes

Heinemann, Detlev

119

On the transition from stratocumulus to cumulus toped boundary layers  

NASA Astrophysics Data System (ADS)

Large areas of the subtropical and tropical oceans are dominated by moist convective boundary layers. These boundary layers are often associated with different types of low-level cloud regimes, including stratocumulus (Sc), shallow cumulus (Cu) and deep convective clouds. Since these boundary layers (in particular Sc) play a key role in modulating the Earth's global climate through radiative forcing, understanding the Sc to Cu transition is of paramount importance for simulating present day and future climate change. Although numerous studies examined the possible physical mechanisms that lead to the transition from Sc to Cu dominated boundary layers, there is still no agreement on which are the key processes responsible for the transition. In this study we combine single column modeling results, reanalysis and observational data to derive a simple model that describes the transition from Sc to Cu. This model is based on vertically integrated bulk equations. We show that the simplification of these equations leads to some of the well-known criteria for the transition, including ones involving lower-tropospheric-stability and top-entrainment-instability parameters. We further propose to use the results of this study to investigate the realism of the Sc to Cu transition in the global climate models.

Suselj, K.; Teixeira, J.

2012-04-01

120

Boundary Layer Turbulence Index: Progress and Recent Developments  

E-print Network

A boundary layer turbulence index (TIBL) product has been developed to assess the potential for turbulence in the lower troposphere, generated using RUC-2 numerical model data. The index algorithm approximates boundary layer turbulent kinetic energy by parameterizing vertical wind shear, responsible for mechanical production of TKE, and kinematic heat flux, parameterized by the vertical temperature lapse rate and responsible for buoyant production of TKE. Validation for the TIBL product has been conducted for selected nonconvective wind events during the 2008 winter season over the Idaho National Laboratory mesonet domain. This paper presents studies of four significant wind events between December 2007 and February 2008 over southeastern Idaho. Based on the favorable results highlighted from validation statistics and in the case studies, the RUC TIBL product has demonstrated operational utility in assessing turbulence hazards to low-flying aircraft and ground transportation, and in the assessment of wildfire...

Pryor, Kenneth L

2008-01-01

121

Hydrodynamic, Bottom Boundary Layer and Sedimentary Responses to Two Contrasting Winter Storms on the Low-Energy Inner Shelf of the Northern Gulf of Mexico  

NASA Astrophysics Data System (ADS)

Results are presented from the deployment of three bottom-mounted instrumentation systems in water depths of 6-9 m on the sandy inner shelf of Louisiana. The 62-day deployment, occurring between November 24, 1998 and January 25, 1999, included numerous intervals of fair weather as well as nine cold front passages. Two energetic frontal passages were characterized by distinct meteorological, hydrodynamic, bottom boundary layer, and sedimentary responses, and may be treated as end-member types on a continuum of regional winter storms. The first frontal passage, deemed a Northwest storm, was dominated by a nearby low-pressure cell, and had strong southerly pre-frontal winds (11.5 m s-1), followed by northwesterly post-frontal winds of up to 14.5 m s-1. Peaks in significant wave height of 1.83 and 1.7 m, respectively, occurred during the pre- and post-frontal phases of the storm. The wave field consisted of energetic northerly swell that gradually gave way to a southerly sea-band as the post-frontal phase progressed. Mean currents during the storm were moderate and northerly during the pre-frontal phase, but became much stronger (up to 53 cm s-1) and southeasterly during the post-frontal phase. Sediment transport was highest following the frontal passage and was directed southeasterly at a rate of 2.66 mg cm-1 s-1. The second storm, labeled a Northeast storm, had a weak pre-frontal phase, followed by an energetic post-frontal phase during which northeasterly winds of up to 15 m s-1 dominated. The storm generated moderately-high (1.34 m), short-period (4.1 s), southerly-propagating waves subsequent to the frontal passage. Mean currents were weak and northerly during the pre-frontal phase, but became strong (22 cm s-1) and southwesterly following the passage. Shear velocity was greater than 2 cm s-1 during the post-frontal phase, and sediment transport was southwesterly at 0.24 g cm-1 s-1. Clearly, cold front passages cause significant hydrodynamic and sedimentary responses on the Louisiana inner shelf, although their impact may vary considerably from storm to storm. This has a great deal of importance to continental shelves throughout the mid-latitudes, where cold fronts are a dominant atmospheric forcing mechanism during the winter.

Pepper, D. A.; Stone, G. W.

2001-05-01

122

Boundary layer elasto-optic switching in ferroelectric liquid crystals  

NASA Technical Reports Server (NTRS)

The first experimental observation of a change in the director azimuthal angle due to applied shear stress is reported in a sample configuration involving a liquid-crystal-coated top surface exposed directly to gas flow. The electrooptic response caused by the shear stress is large, fast, and reversible. These findings are relevant to the use of liquid crystals in boundary layer investigations on wind tunnel models.

Parmar, D. S.

1992-01-01

123

Boundary-Layer-Ingesting Inlet Flow Control  

NASA Technical Reports Server (NTRS)

This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCPavg) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.

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

2006-01-01

124

Boundary-Layer-Ingesting Inlet Flow Control  

NASA Technical Reports Server (NTRS)

This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCP(sub avg)) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.

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

2006-01-01

125

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

126

Supersonic and Hypersonic Boundary-Layer Flows  

Microsoft Academic Search

Supersonic and hypersonic numerical research activities of the “Lehrstuhl für Aerodynamik” at the Technische Universität München\\u000a are presented in this paper.\\u000a \\u000a Based on the ADM (Approximate Deconvolution Method), LES simulations of a turbulent ramp flow with a subsequent decompression\\u000a corner at M=2.95 are conducted (the Reynolds number based on the boundary-layer thickness at the inflow is Red<\\/font\\u000a>0=63 560Re_{\\\\delta_0}=63 560

Christian Stemmer; Nikolaus A. Adams

127

Boundary Layer Depth In Coastal Regions  

NASA Astrophysics Data System (ADS)

The results of earlier studies performed about sea breezes simulations have shown that this is a relevant feature of the Planetary Boundary Layer that still requires effort to be diagnosed properly by atmospheric models. Based on the observations made during the ESCOMPTE campaign, over the Mediterranean Sea, different CBL and SBL height estimation processes have been tested with a meso-scale model, TVM. The aim was to compare the critical points of the BL height determination computed using turbulent kinetic energy profile with some other standard evaluations. Moreover, these results have been analysed with different mixing length formulation. The sensitivity of formulation is also analysed with a simple coastal configuration.

Porson, A.; Schayes, G.

128

The boundary layer on compressor cascade blades  

NASA Technical Reports Server (NTRS)

The characteristics of the flow field about highly loaded turbocompressor blades in a cascade wind tunnel were investigated. Experimental tests were conducted at chord Reynolds number (R sub c) near 500,000. A laser Doppler anemometer was employed in flow velocity measurement. Suction surface mean velocity and turbulence intensity profiles at a single incidence angle are presented. These data contribute to further understanding of two-dimensional boundary layer profiles, points of separation, and transition zones for turbomachine blades, and concomitantly, to compressor cascade predictive models.

Deutsch, S.; Zierke, W. C.

1984-01-01

129

Boundary-layer Transition at Supersonic Speeds  

NASA Technical Reports Server (NTRS)

Recent results of the effects of Mach number, stream turbulence, leading-edge geometry, leading-edge sweep, surface temperature, surface finish, pressure gradient, and angle of attack on boundary-layer transition are summarized. Factors that delay transition are nose blunting, surface cooling, and favorable pressure gradient. Leading-edge sweep and excessive surface roughness tend to promote early transition. The effects of leading-edge blunting on two-dimensional surfaces and surface cooling can be predicted adequately by existing theories, at least in the moderate Mach number range.

Low, George M

1956-01-01

130

Performance and boundary-layer evaluation of a sonic inlet  

NASA Technical Reports Server (NTRS)

Tests were conducted to determine the boundary layer characteristics and aerodynamic performance of a radial vane sonic inlet with a length/diameter ratio of 1 for several vane configurations. The sonic inlet was designed with a slight wavy wall type of diffuser geometry, which permits operation at high inlet Mach numbers (sufficiently high for good noise suppression) without boundary layer flow separation and with good total pressure recovery. A new method for evaluating the turbulent boundary layer was developed to separate the boundary layer from the inviscid core flow, which is characterized by a total pressure variation from hub to tip, and to determine the experimental boundary layer parameters.

Schmidt, J. F.; Ruggeri, R. S.

1976-01-01

131

Sound radiation due to boundary layer transition  

NASA Technical Reports Server (NTRS)

This report describes progress made to date towards calculations of noise produced by the laminar-turbulence transition process in a low Mach number boundary layer formed on a rigid wall. The primary objectives of the study are to elucidate the physical mechanisms by which acoustic waves are generated, to clarify the roles of the fluctuating Reynolds stress and the viscous stress in the presence of a solid surface, and to determine the relative efficiency as a noise source of the various transition stages. In particular, we will examine the acoustic characteristics and directivity associated with three-dimensional instability waves, the detached high-shear layer, and turbulent spots following a laminar breakdown. Additionally, attention will be paid to the unsteady surface pressures during the transition, which provide a source of flow noise as well as a forcing function for wall vibration in both aeronautical and marine applications.

Wang, Meng

1993-01-01

132

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

133

Sound Radiation from a Turbulent Boundary Layer  

NASA Technical Reports Server (NTRS)

If the restriction of incompressibility in the turbulence problem is relaxed, the phenomenon of energy radiation in the form of sound from the turbulent zone arises. In order to calculate this radiated energy, it is shown that new statistical quantities, such as time-space correlation tensors, have to be known within the turbulent zone in addition to the conventional quantities. For the particular case of the turbulent boundary layer, indications are that the intensity of radiation becomes significant only in supersonic flows. Under these conditions, the recent work of Phillips is examined together with some experimental findings of the author. It is shown that the qualitative features of the radiation field (intensity, directionality) as predicted by the theory are consistent with the measurements; however, even for the highest Mach number flow, some of the assumptions of the asymptotic theory are not yet satisfied in the experiments. Finally, the question of turbulence damping due to radiation is discussed, with the result that in the Mach number range covered by the experiments, the energy lost from the boundary layer due to radiation is a small percentage of the work done by the wall shearing stresses.

Laufer, J.

1961-01-01

134

Transonic laminar boundary layers with surface curvature.  

NASA Technical Reports Server (NTRS)

The effect of surface curvature (both longitudinal and transverse) and the associated pressure gradient across the flow is investigated analytically for a laminar boundary layer subjected to pressure gradients along the flow. Property variation which results from heat transfer and compressibility is taken into account. Numerical solutions of the boundary layer equations are obtained for locally similar sonic flow through the throat of a nozzle for a range of flow conditions and for various shaped nozzle surfaces with different amounts of wall cooling. A few solutions were also obtained for the analogous flow around the shoulder of a flat-faced body in a supersonic flow. The effect of various parameters that arise in the equations upon application of the Levy-Mangler transformation are investigated and discussed with respect to their influence on the velocity and total enthalpy profiles and the corresponding profile slopes at the surface to which the shear stress and heat transfer are related. An important finding is that at throat Reynolds numbers less than 100,000 the heat transfer parameter at a nozzle throat decreases as the throat radius of curvature decreases.

Back, L. H.

1973-01-01

135

Boundary Layer Transition Flight Experiment Overview  

NASA Technical Reports Server (NTRS)

In support of the Boundary Layer Transition Flight Experiment (BLT FE) Project, a manufactured protuberance tile was installed on the port wing of Space Shuttle Orbiter Discovery for STS-119, STS-128, STS-131 and STS-133 as well as Space Shuttle Endeavour for STS-134. Additional instrumentation was installed in order to obtain more spatially resolved measurements downstream of the protuberance. This paper provides an overview of the BLT FE Project with emphasis on the STS-131 and STS-133 results. A high-level overview of the in-situ flight data is presented, along with a summary of the comparisons between pre- and post-flight analysis predictions and flight data. Comparisons show that empirically correlated predictions for boundary layer transition onset time closely match the flight data, while predicted surface temperatures were significantly higher than observed flight temperatures. A thermocouple anomaly observed on a number of the missions is discussed as are a number of the mitigation actions that will be taken on the final flight, STS-134, including potential alterations of the flight trajectory and changes to the flight instrumentation.

Berger, Karen T.; Anderson, Brian P.; Campbell, Charles H.; Garske, Michael T.; Saucedo, Luis A.; Kinder, Gerald R.; Micklos, Ann M.

2011-01-01

136

Bypass transition in compressible boundary layers  

NASA Technical Reports Server (NTRS)

Transition to turbulence in aerospace applications usually occurs in a strongly disturbed environment. For instance, the effects of free-stream turbulence, roughness and obstacles in the boundary layer strongly influence transition. Proper understanding of the mechanisms leading to transition is crucial in the design of aircraft wings and gas turbine blades, because lift, drag and heat transfer strongly depend on the state of the boundary layer, laminar or turbulent. Unfortunately, most of the transition research, both theoretical and experimental, has focused on natural transition. Many practical flows, however, defy any theoretical analysis and are extremely difficult to measure. Morkovin introduced in his review paper the concept of bypass transition as those forms of transition which bypass the known mechanisms of linear and non-linear transition theories and are currently not understood by experiments. In an effort to better understand the mechanisms leading to transition in a disturbed environment, experiments are conducted studying simpler cases, viz. the effects of free stream turbulence on transition on a flat plate. It turns out that these experiments are very difficult to conduct, because generation of free stream turbulence with sufficiently high fluctuation levels and reasonable homogeneity is non trivial. For a discussion see Morkovin. Serious problems also appear due to the fact that at high Reynolds numbers the boundary layers are very thin, especially in the nose region of the plate where the transition occurs, which makes the use of very small probes necessary. The effects of free-stream turbulence on transition are the subject of this research and are especially important in a gas turbine environment, where turbulence intensities are measured between 5 and 20 percent, Wang et al. Due to the fact that the Reynolds number for turbine blades is considerably lower than for aircraft wings, generally a larger portion of the blade will be in a laminar transitional state. The effects of large free stream turbulence in compressible boundary layers at Mach numbers are examined both in the subsonic and transonic regime using direct numerical simulations. The flow is computed over a flat plate and curved surface. while many applications operate in the transonic regime. Due the nature of their numerical scheme, a non-conservation formulation of the Navier-Stokes equations, it is a non-trivial extension to compute flow fields in the transonic regime. This project aims at better understanding the effects of large free-stream turbulence in compressible boundary layers at mach number both in the subsonic and transonic regime using direct numerical simulations. The present project aims at computing the flow over a flat plate and curved surface. This research will provide data which can be used to clarify mechanisms leading to transition in an environment with high free stream turbulence. This information is useful for the development of turbulence models, which are of great importance for CFD applications, and are currently unreliable for more complex flows, such as transitional flows.

Vandervegt, J. J.

1992-01-01

137

Bypass transition in compressible boundary layers  

NASA Astrophysics Data System (ADS)

Transition to turbulence in aerospace applications usually occurs in a strongly disturbed environment. For instance, the effects of free-stream turbulence, roughness and obstacles in the boundary layer strongly influence transition. Proper understanding of the mechanisms leading to transition is crucial in the design of aircraft wings and gas turbine blades, because lift, drag and heat transfer strongly depend on the state of the boundary layer, laminar or turbulent. Unfortunately, most of the transition research, both theoretical and experimental, has focused on natural transition. Many practical flows, however, defy any theoretical analysis and are extremely difficult to measure. Morkovin introduced in his review paper the concept of bypass transition as those forms of transition which bypass the known mechanisms of linear and non-linear transition theories and are currently not understood by experiments. In an effort to better understand the mechanisms leading to transition in a disturbed environment, experiments are conducted studying simpler cases, viz. the effects of free stream turbulence on transition on a flat plate. It turns out that these experiments are very difficult to conduct, because generation of free stream turbulence with sufficiently high fluctuation levels and reasonable homogeneity is non trivial. For a discussion see Morkovin. Serious problems also appear due to the fact that at high Reynolds numbers the boundary layers are very thin, especially in the nose region of the plate where the transition occurs, which makes the use of very small probes necessary. The effects of free-stream turbulence on transition are the subject of this research and are especially important in a gas turbine environment, where turbulence intensities are measured between 5 and 20 percent, Wang et al. Due to the fact that the Reynolds number for turbine blades is considerably lower than for aircraft wings, generally a larger portion of the blade will be in a laminar transitional state. The effects of large free stream turbulence in compressible boundary layers at Mach numbers are examined both in the subsonic and transonic regime using direct numerical simulations. The flow is computed over a flat plate and curved surface. while many applications operate in the transonic regime. Due the nature of their numerical scheme, a non-conservation formulation of the Navier-Stokes equations, it is a non-trivial extension to compute flow fields in the transonic regime. This project aims at better understanding the effects of large free-stream turbulence in compressible boundary layers at mach number both in the subsonic and transonic regime using direct numerical simulations. The present project aims at computing the flow over a flat plate and curved surface.

Vandervegt, J. J.

1992-09-01

138

Diagnosing Monthly Mean Boundary Layer Properties from Reanalysis Data Using a Bulk Boundary Layer Model  

E-print Network

s 1 ) mark the ITCZ and South Pacific convergence zone. Unreasonably large surface latent heat fluxes forecasting and climate simulation. Errors in the parameterized surface fluxes are particularly dangerous of a simple bulk boundary layer model (BBLM) to diagnose entrainment velocity, cumulus mass flux, and surface

Randall, David A.

139

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

NASA Technical Reports Server (NTRS)

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

Spina, Eric F.

1995-01-01

140

Persistent Structures in the Turbulent Boundary Layer  

NASA Technical Reports Server (NTRS)

Persistent structures in the turbulent boundary layer are located and analyzed. The data are taken from flight experiments on large commercial aircraft. An interval correlation technique is introduced which is able to locate the structures. The Morlet continuous wavelet is shown to not only locates persistent structures but has the added benefit that the pressure data are decomposed in time and frequency. To better understand how power is apportioned among these structures, a discrete Coiflet wavelet is used to decompose the pressure data into orthogonal frequency bands. Results indicate that some structures persist a great deal longer in the TBL than would be expected. These structure contain significant power and may be a primary source of vibration energy in the airframe.

Palumbo, Dan; Chabalko, Chris

2005-01-01

141

The boundary layer on compressor cascade blades  

NASA Technical Reports Server (NTRS)

The flow field about an airfoil in a cascade at chord Reynolds number (R sub C) near 50,000. The program is experimental and combines laser Doppler anemometry (LDA) with flow visualization techniques in order to obtain detailed flow data (e.g., boundary layer profiles, points of separation and the transition zone) on a cascade of highly-loaded compressor blades. The information provided is to serve as benchmark data for the evaluation of current and future compressor cascade predictive models, in this way aiding in the compressor design process. The completed pressure surface mean velocity profiles, as well as two detailed near wake velocity profiles, all at a single incidence angle are provided.

Deutsch, S.; Zierke, W. C.

1984-01-01

142

Atmospheric boundary layer over steep surface waves  

NASA Astrophysics Data System (ADS)

Turbulent air-sea interactions coupled with the surface wave dynamics remain a challenging problem. The needs to include this kind of interaction into the coupled environmental, weather and climate models motivate the development of a simplified approximation of the complex and strongly nonlinear interaction processes. This study proposes a quasi-linear model of wind-wave coupling. It formulates the approach and derives the model equations. The model is verified through a set of laboratory (direct measurements of an airflow by the particle image velocimetry (PIV) technique) and numerical (a direct numerical simulation (DNS) technique) experiments. The experiments support the central model assumption that the flow velocity field averaged over an ensemble of turbulent fluctuations is smooth and does not demonstrate flow separation from the crests of the waves. The proposed quasi-linear model correctly recovers the measured characteristics of the turbulent boundary layer over the waved water surface.

Troitskaya, Yuliya; Sergeev, Daniil A.; Druzhinin, Oleg; Kandaurov, Alexander A.; Ermakova, Olga S.; Ezhova, Ekaterina V.; Esau, Igor; Zilitinkevich, Sergej

2014-08-01

143

Nonstationary atmospheric boundary layer turbulence simulation  

NASA Technical Reports Server (NTRS)

Report on a new and general technique for simulating atmospheric turbulence-like random processes which are statistically homogeneous along the horizontal and nonhomogeneous along the vertical. This technique is general in the sense that it can be used for a broad class of similar problems. Like the other presently available schemes, the techniques presented are based on the Dryden hypothesis and Taylor's frozen eddy hypothesis; however, they go a step further by utilizing certain self-similarity properties of the Dryden spectral density function which permits the development of height invariant filters. These filters are in turn used to generate vertically homogeneous (statistically) random processes from which turbulence at any specified level in the boundary layer can be simulated, thus facilitating the simulation of a nonstationary turbulence process along the flight path of an aircraft during take-off or landing.

Fichtl, G. H.; Perlmutter, M.

1974-01-01

144

Chemistry of a polluted cloudy boundary layer  

NASA Technical Reports Server (NTRS)

A one-dimensional photochemical model for cloud-topped boundary layers has been developed to include descriptions of gas- and aqueous-phase chemistry and the radiation field in and below the cloud. The model is applied to the accumulation of pollutants during a wintertime episode with low stratus over Bakersfield, CA. The mechanisms of sulfate production and the balance between the concentrations of acids and bases are examined. It is shown that most of the sulfate production may be explained by the Fe(III)-catalyzed autoxidation of S(IV). Another source of sulfate is the oxidation of SO2 by OH in both the gas and the aqueous phase. It is shown that the sulfate production in the model is controlled by the availability of NH3. It is suggested that this explains the balance observed between total concentration of acids and bases.

Jacob, Daniel J.; Gottlieb, Elaine W.; Prather, Michael J.

1989-01-01

145

Chemistry of a polluted cloudy boundary layer  

NASA Astrophysics Data System (ADS)

A one-dimensional photochemical model for cloud-topped boundary layers has been developed to include descriptions of gas- and aqueous-phase chemistry and the radiation field in and below the cloud. The model is applied to the accumulation of pollutants during a wintertime episode with low stratus over Bakersfield, CA. The mechanisms of sulfate production and the balance between the concentrations of acids and bases are examined. It is shown that most of the sulfate production may be explained by the Fe(III)-catalyzed autoxidation of S(IV). Another source of sulfate is the oxidation of SO2 by OH in both the gas and the aqueous phase. It is shown that the sulfate production in the model is controlled by the availability of NH3. It is suggested that this explains the balance observed between total concentration of acids and bases.

Jacob, Daniel J.; Gottlieb, Elaine W.; Prather, Michael J.

1989-09-01

146

Acoustics of laminar boundary layers breakdown  

NASA Astrophysics Data System (ADS)

Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable mathematical difficulties, theoretical predictions either are limited to early linear and weakly nonlinear stages of transition, or employ acoustic analogy theories based on approximate source field data, often in the form of empirical correlation. In the present work, an approach which combines direct numerical simulation of the source field with the Lighthill acoustic analogy is utilized. This approach takes advantage of the recent advancement in computational capabilities to obtain detailed information about the flow-induced acoustic sources. The transitional boundary layer flow is computed by solving the incompressible Navier-Stokes equations without model assumptions, thus allowing a direct evaluation of the pseudosound as well as source functions, including the Lighthill stress tensor and the wall shear stress. The latter are used for calculating the radiated pressure field based on the Curle-Powell solution of the Lighthill equation. This procedure allows a quantitative assessment of noise source mechanisms and the associated radiation characteristics during transition from primary instability up to the laminar breakdown stage. In particular, one is interested in comparing the roles played by the fluctuating volume Reynolds stress and the wall-shear-stresses, and in identifying specific flow processes and structures that are effective noise generators.

Wang, Meng

1994-12-01

147

Acoustics of laminar boundary layers breakdown  

NASA Technical Reports Server (NTRS)

Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable mathematical difficulties, theoretical predictions either are limited to early linear and weakly nonlinear stages of transition, or employ acoustic analogy theories based on approximate source field data, often in the form of empirical correlation. In the present work, an approach which combines direct numerical simulation of the source field with the Lighthill acoustic analogy is utilized. This approach takes advantage of the recent advancement in computational capabilities to obtain detailed information about the flow-induced acoustic sources. The transitional boundary layer flow is computed by solving the incompressible Navier-Stokes equations without model assumptions, thus allowing a direct evaluation of the pseudosound as well as source functions, including the Lighthill stress tensor and the wall shear stress. The latter are used for calculating the radiated pressure field based on the Curle-Powell solution of the Lighthill equation. This procedure allows a quantitative assessment of noise source mechanisms and the associated radiation characteristics during transition from primary instability up to the laminar breakdown stage. In particular, one is interested in comparing the roles played by the fluctuating volume Reynolds stress and the wall-shear-stresses, and in identifying specific flow processes and structures that are effective noise generators.

Wang, Meng

1994-01-01

148

Wind-tunnel simulation of thick turbulent boundary layer  

NASA Astrophysics Data System (ADS)

An experimental study aimed at revealing the possibility of simulation, in a subsonic wind tunnel, of enhanced Reynolds numbers Re** via modeling a thick flat-plate boundary layer possessing the properties of a Clauser-equilibrium shear flow is reported. We show that turbulators prepared in the form of variable-height cylinders of height h and diameter d = 3 mm and installed in two rows along the normal to the streamlined wall offer rather an efficient means for modification of turbulent boundary layer in solving the problem. In the majority of cases, mean and fluctuating characteristics of the boundary layer exhibit values typical of naturally developing turbulent boundary layers at a distance of 530 cylinder diameters. The profiles of mean velocity with artificially enhanced boundary-layer thickness can be well approximated, in the law-of-the-wall variables, with the well-known distribution of velocities for canonical boundary layer.

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

2012-06-01

149

Winds in the Marine Boundary Layer: A Forecaster's Guide  

NSDL National Science Digital Library

This module is intended for experienced forecasters moving from a land-based area to a coastal or Great Lakes region where both over-land and over-water forecast areas exist. This module highlights the differences between marine boundary layer and terrestrial boundary layer winds. The experienced forecaster is relatively familiar with the boundary layer over land and the associated implications for the wind field. Using this as a base, the module compares this known quantity with the lesser-known processes that occur in the marine boundary layer. Three major topics that influence marine boundary layer winds are discussed: stability within the boundary layer, isallobaric influence, and the effects of convection and tropical cyclones.

Comet

2006-12-01

150

Transition Zone as a Boundary Layer  

NASA Astrophysics Data System (ADS)

Three dimensional Earth models (Ritsema et al., 2004; Panning and Romanowicz, 2006; Kustowski et al., 2006) derived using data that have good control on the structure in the transition zone (body-wave waveforms or overtone measurements) all show a discontinuous or very rapid change in the spectrum of lateral heterogeneity at the boundary between the upper and lower mantle. This was first pointed out by Woodward et al. (1994) and discussed in detail by Gu et al. (2001). All models have a strong chemical/thermal/mechanical boundary layer beginning just under the Moho and extending to 200-250 km; this heterogeneity is dominated by degrees five and six caused by the distribution of cratons and mid-oceanic ridges. The power spectrum decreases rapidly below that depth, but then begins to increase at about 400 km. It is dominated by degree two down to the 660 km discontinuity. There, it changes from very red to white at the top of the lower mantle. This is a planetary scale phenomenon that which must affect the flow of material and mixing in the mantle. Similar spectra have been generated in mantle convection models that considered the effect of an endothermic phase change (Tackley et al., 1994). The existence of this boundary layer is supported by the pattern of large scale positive velocity anomalies in the transition zone in places where subduction occurs (thus indicating ponding of slabs), large-wavelength variations in the topography of the 660 km discontinuity, variations in thickness of the transition zone and deep earthquakes outside the main Wadati-Benioff zones as well as changes in their mechanisms. During the last decade, the debate on the scale of mantle convection was strongly affected by images of slabs appearing to penetrate into the lower mantle. Relatively detailed mapping of velocity anomalies in the vicinity of slabs is feasible, because of illumination of these regions by earthquakes; these models do not tell much aboutt velocity anomalies in other places. However, the power spectra estimates are global and tell us about the behavior of the mantle as the whole. The reported pattern of the power spectra does not exclude an exchange of material between the upper and lower mantle; there may be local penetration of subducted material or there may be episodic events such as "avalanches". However, successful models of mantle convection should be able to explain the change in the spectra of lateral heterogeneity such as revealed by global tomographic models, obtained with the requisite data sets.

Dziewonski, A. M.; Lekic, V.; Kustowski, B.; Romanowicz, B. A.

2006-12-01

151

Improved Boundary Layer Depth Retrievals from MPLNET  

NASA Technical Reports Server (NTRS)

Continuous lidar observations of the planetary boundary layer (PBL) depth have been made at the Micropulse Lidar Network (MPLNET) site in Greenbelt, MD since April 2001. However, because of issues with the operational PBL depth algorithm, the data is 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 diered the most in the winter.

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

2013-01-01

152

Spectral instability of characteristic boundary layer flows  

E-print Network

In this paper, we construct growing modes of the linearized Navier-Stokes equations about generic stationary shear flows of the boundary layer type in a regime of sufficiently large Reynolds number: $R \\to \\infty$. Notably, the shear profiles are allowed to be linearly stable at the infinite Reynolds number limit, and so the instability presented is purely due to the presence of viscosity. The formal construction of approximate modes is well-documented in physics literature, going back to the work of Heisenberg, C.C. Lin, Tollmien, Drazin and Reid, but a rigorous construction requires delicate mathematical details, involving for instance a treatment of primitive Airy functions and singular solutions. Our analysis gives exact unstable eigenvalues and eigenfunctions, showing that the solution could grow slowly at the rate of $e^{t/\\sqrt {R}}$. A new, operator-based approach is introduced, avoiding to deal with matching inner and outer asymptotic expansions, but instead involving a careful study of singularity in the critical layers by deriving pointwise bounds on the Green function of the corresponding Rayleigh and Airy operators.

Emmanuel Grenier; Yan Guo; Toan T. Nguyen

2014-06-15

153

The simulation of coherent structures in a laminar boundary layer  

NASA Technical Reports Server (NTRS)

Coherent structures in turbulent shear flows were studied extensively by several techniques, including the VITA technique which selects rapidly accelerating or decelerating regions in the flow. The evolution of a localized disturbance in a laminar boundary layer shows strong similarity to the evolution of coherent structures in a turbulent-wall bounded flow. Starting from a liftup-sweep motion, a strong shear layer develops which shares many of the features seen in conditionally-sampled turbulent velocity fields. The structure of the shear layer, Reynolds stress distribution, and wall pressure footprint are qualitatively the same, indicating that the dynamics responsible for the structure's evolution are simple mechanisms dependent only on the presence of a high mean shear and a wall and independent of the effects of local random fluctuations and outer flow effects. As the disturbance progressed, the development of streak-like-high- and low-speed regions associated with the three-dimensionality.

Breuer, Kenny; Landahl, Marten T.; Spalart, Philippe R.

1987-01-01

154

Passive hypervelocity boundary layer control using an ultrasonically absorptive surface  

Microsoft Academic Search

A series of exploratory boundary layer transition experiments was performed on a sharp 5.06 degree half-angle round cone at zero angle-of-attack in the T5 Hypervelocity Shock Tunnel in order to test a novel hypersonic boundary layer control scheme. Recently performed linear stability analyses suggested that transition could be delayed in hypersonic boundary layers by using an ultrasonically absorptive surface that

Adam Rasheed

2001-01-01

155

Stratified Atmospheric Boundary Layers and Breakdown of Models  

Microsoft Academic Search

:   The goal of this study is to assess complications in atmospheric stable boundary layers which are not included in numerical\\u000a models of the stably stratified boundary layer and to provide a formulation of surface fluxes for use in numerical models.\\u000a Based on an extensive interpretive literature survey and new eddy correlation data for the stable boundary layer, this study

L. Mahrt

1998-01-01

156

Wind flow over ridges in simulated atmospheric boundary layers  

Microsoft Academic Search

The flows over four two-dimensional triangular hills and three two-dimensional bell-shaped hills have been investigated in a simulated rural atmospheric boundary layer modelled to a scale of 1:300: Further measurements were made over two of the triangular hills in a simulated rural boundary layer of 1: 3000 scale and in a simulated urban boundary layer modelled to a scale of

J. R. Pearse; D. Lindley; D. C. Stevenson

1981-01-01

157

Mechanics of chemical species transport in the marine atmospheric boundary layer  

NASA Technical Reports Server (NTRS)

Marine atmospheric boundary layer (MABL) drafts are modeled as steady-state plumes using the approach proposed by Telford (1966), and the model response to varying forcing and boundary conditions is examined. Since most of the chemical species are passive tracers within the MABL, variations in the implied fluxes are determined as a combination of the boundary conditions for the chemical species and the thermodynamic forcing implied by the stability and thermal boundary conditions.

Hanson, Howard P.

1989-01-01

158

A Sensitivity Theory for the Equilibrium Boundary Layer Over Land  

NASA Astrophysics Data System (ADS)

Due to the intrinsic complexities associated with modeling land-atmosphere interactions, global models typically use elaborate land surface and boundary layer physics parameterizations. Unfortunately, it is difficult to use elaborate models, by themselves, to develop a deeper understanding of how land surface parameters affect the coupled land-atmosphere system. At the same time, it is also increasingly important to gain a deeper understanding of the role of changes in land cover, land use, and ecosystem function as forcings and feedbacks in past and future climate change. Here, we outline the new framework of boundary layer climate sensitivity, which is based on surface energy balance, just as global climate sensitivity is based on top-of-atmosphere energy balance. We develop an analytic theory for the boundary layer climate sensitivity of an idealized model of a diurnally-averaged well-mixed boundary layer over land (Betts, 2000). This analytic sensitivity theory identifies changes in the properties of the land surface - including moisture availability, albedo, and aerodynamic roughness - as forcings, and identifies strong negative feedbacks associated with the surface fluxes of latent and sensible heat. We show that our theory can explain nearly all of the sensitivity of the Betts (2000) full system of equations, and find that nonlinear forcing functions are key to understanding changes in temperature caused by large changes in surface properties; this is directly analogous to the case of climate sensitivity, where nonlinear radiative forcing functions are key to understanding the response of global temperature to large changes in greenhouse gas concentrations. Favorable comparison of the theory and the simulation results from a two-column radiative convective model suggests that the theory may be broadly useful for unifying our understanding of how changes in land use or ecosystem function may affect climate change.

Cronin, T.

2013-12-01

159

Nonparallel stability of boundary layers with pressure gradients and suction  

NASA Technical Reports Server (NTRS)

An analysis is presented for the linear nonparallel stability of boundary layer flows with pressure gradients and suction. The effect of the boundary layer growth is included by using the method of multiple scales. The present analysis is compared with those of Bouthier and Gaster and the roles of the different definitions of the amplification rates are discussed. The results of these theories are compared with experimental data for the Blasius boundary layer. Calculations are presented for stability characteristics of boundary layers with pressure gradients and nonsimilar suction distributions.

Saric, W. S.; Nayfeh, A. H.

1977-01-01

160

Measurements of Flow in Boundary Layer Ingesting Serpentine Inlets.  

E-print Network

??Highly integrated airframe-propulsion systems featuring ingestion of the airframe boundary layer oer reduced noise, emissions, and fuel consumption. Embedded engine systems are envisioned which require… (more)

Ferrar, Anthony Maurice

2012-01-01

161

Incorporation of the planetary boundary layer in atmospheric models  

NASA Technical Reports Server (NTRS)

The topics discussed include the following: perspectives on planetary boundary layer (PBL) measurements; current problems of PBL parameterization in mesoscale models; and convective cloud-PBL interactions.

Moeng, Chin-Hoh; Wyngaard, John; Pielke, Roger; Krueger, Steve

1993-01-01

162

Control of the Transitional Boundary Layer  

NASA Astrophysics Data System (ADS)

This work makes advances in the delay of boundary layer transition from laminar to turbulent flow via feedback control. The applications include the reduction of drag over streamline bodies (e.g., airplane wings) and the decrease of mixing and heat transfer (e.g., over turbine blades in jet engines). A difficulty in many fields is designing feedback controllers for high-dimensional systems, be they experiments or high-fidelity simulations, because the required time and resources are too large. A cheaper alternative is to approximate the high-dimensional system with a reduced-order model and design a controller for the model. We implement several model reduction algorithms in "modred", an open source and publicly available library that is applicable to a wide range of problems. We use this library to study the role of sensors and actuators in feedback control of transition in the 2D boundary layer. Previous work uses a feedforward configuration in which the sensor is upstream of the actuator, but we show that the actuator-sensor pair is unsuitable for feedback control due to an inability to sense the exponentially-growing Tollmien-Schlichting waves. A new actuator-sensor pair is chosen that more directly affects and measures the TS waves, and as a result it is effective in a feedback configuration. Lastly, the feedback controller is shown to outperform feedforward controllers in the presence of unmodeled disturbances. Next, we focus on a specific type of actuator, the single dielectric barrier discharge (SDBD) plasma actuator. An array of these plasma actuators is oriented to produce stream-wise vorticity and thus directly cancel the structures with the largest transient growth (so-called stream-wise streaks). We design a feedback controller using only experimental data by first developing an empirical input-output quasi-steady model. Then, we design feedback controllers for the model such that the controllers perform well when applied to the experiment. Lastly, we also simulate the plasma actuators and determine a suitable numerical model for the forces they create by comparing with experimental results. This physical force model is essential to future numerical studies on delaying bypass transition via feedback control and plasma actuation.

Belson, Brandt A.

163

Boundary layer features observed during NAME 2004  

NASA Astrophysics Data System (ADS)

S-Pol radar data from the North American Monsoon Experiment (NAME) are examined to investigate the characteristics of sea breezes that occurred during the North American Monsoon in the late summer of 2004, as well as their role in modulating monsoon convection. Zero degree plan position indicated (PPI) scans were examined to determine the presence of a sea breeze fine line in the S-Pol radar data. Sea breeze fine lines were typically observed over land very near the coast of the Gulf of California (GoC), and usually moved onshore around 1700--1800 UTC (11:00 AM--12:00 PM local time), and then continued to move slowly inland on the coastal plain. The sea breezes typically moved on land and dissipated before any significant interactions with Sierra Madre Occidental (SMO) convection could occur. Fine lines varied in reflectivity strength, but were typically around 10 to 20 dBZ. Surface winds from the Estacion Obispo (ETO) supersite were analyzed to confirm the presence of a shift in wind direction on days in which a fine line had been identified. Typically winds changed from light and variable to consistently out of the west or southwest. Vertical plots of S-Pol reflectivity were created to examine sea breeze structure in the vertical, but these were not found to be useful as the sea breeze signature was nearly impossible to distinguish from other boundary layer features. Horizontal structure was further investigated using wind profiler relative reflectivity, vertical velocity, and horizontal winds from the profiler located at ETO. Relative reflectivity and vertical velocity fields revealed a complex boundary layer structure on some days of repeating updrafts and downdrafts. Further examination of S-Pol PPI data revealed that these vertical motions are likely due to the presence of horizontal convective rolls. Profiler horizontal winds revealed that the depth and vertical structure of the sea breezes varied significantly from day to day, but that the height of the sea breeze is around 1 km above the ground. Sea breezes observed during NAME almost never initiated convection on their own. It is hypothesized that a weak thermal contrast between the GoC and the land leads to comparatively weak sea breezes, which don't have enough lift to trigger convection.

Stuckmeyer, Elizabeth A.

2011-12-01

164

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

165

Transition in Hypersonic Boundary Layers: Role of Dilatational Waves  

E-print Network

Transition and turbulence production in a hypersonic boundary layer is investigated in a Mach 6 quiet wind tunnel using Rayleigh-scattering visualization, fast-response pressure measurements, and particle image velocimetry. It is found that the second instability acoustic mode is the key modulator of the transition process. The second mode experiences a rapid growth and a very fast annihilation due to the effect of bulk viscosity. The second mode interacts strongly with the first vorticity mode to directly promote a fast growth of the latter and leads to immediate transition to turbulence.

Zhu, Yiding; Yuan, Huijing; Wu, Jiezhi; Chen, Shiyi; Lee, Cunbiao; Gad-el-Hak, Mohamed

2015-01-01

166

Aeromechanics Analysis of a Boundary Layer Ingesting Fan  

NASA Technical Reports Server (NTRS)

Boundary layer ingesting propulsion systems have the potential to significantly reduce fuel burn but these systems must overcome the challe nges related to aeromechanics-fan flutter stability and forced response dynamic stresses. High-fidelity computational analysis of the fan a eromechanics is integral to the ongoing effort to design a boundary layer ingesting inlet and fan for fabrication and wind-tunnel test. A t hree-dimensional, time-accurate, Reynolds-averaged Navier Stokes computational fluid dynamics code is used to study aerothermodynamic and a eromechanical behavior of the fan in response to both clean and distorted inflows. The computational aeromechanics analyses performed in th is study show an intermediate design iteration of the fan to be flutter-free at the design conditions analyzed with both clean and distorte d in-flows. Dynamic stresses from forced response have been calculated for the design rotational speed. Additional work is ongoing to expan d the analyses to off-design conditions, and for on-resonance conditions.

Bakhle, Milind A.; Reddy, T. S. R.; Herrick, Gregory P.; Shabbir, Aamir; Florea, Razvan V.

2013-01-01

167

Secondary instabilities in compressible boundary layers  

NASA Technical Reports Server (NTRS)

The secondary instability mechanisms in a two-dimensional (2-D) compressible boundary layer over a flat plate have been examined for a range of Mach numbers up to 4.5. For subsonic and low supersonic flows, fundamental resonance dominates when the amplitude of the (2-D) primary disturbance is high, while subharmonic resonance prevails in an environment with a low primary disturbance. At a high supersonic Mach number of 4.5, the secondary instability of the second-mode primary is stronger than that of the first-mode primary. Further, the subharmonic and the combination resonance modes, which are slightly detuned from the subharmonic, are the dominant instabilities. The influence of the propagation direction of the primary disturbance on secondary instabilities is investigated at Mach 1.6. Whereas the fundamental and the subharmonic disturbances propagate synchronously with a 2-D primary wave, this is not true for an oblique primary. A subset of the secondary instability results is verified against direct numerical simulations. Some comparisons between spatial and temporal secondary instabilities have been made at Mach 1.6.

Ng, Lian L.; Erlebacher, Gordon

1992-01-01

168

Secondary instabilities in compressible boundary layers  

NASA Technical Reports Server (NTRS)

Secondary instabilities are examined in compressible boundary layers at Mach numbers M(sub infinity) = 0, 0.8, 1.6, and 4.5. It is found that there is a broad-band of highly unstable 3-d secondary disturbances whose growth rates increase with increasing primary wave amplitude. At M(sub infinity) is less than or equal to 1.6, fundamental resonance dominates at relatively high (2-d) primary disturbance amplitude, while subharmonic resonance is characterized by a low (2-d) primary amplitude. At M(sub infinity) = 4.5, the subharmonic instability which arises from the second mode disturbance is the strongest type of secondary instability. The influence of the inclination, theta, of the primary wave with respect to the mean flow direction on secondary instability is investigated at M(sub infinity) = 1.6 for small to moderate values of theta. It is found that the strongest fundamental instability occurs when the primary wave is inclined at 10 deg to the mean flow direction, although a 2-d primary mode yields the most amplified subharmonic. The subharmonic instability at a high value of theta (namely, theta = 45 deg) is also discussed. Finally, a subset of the secondary instability results are compared against direct numerical simulations.

Ng, Lian; Erlebacher, Gordon

1990-01-01

169

Effect of sound on boundary layer stability  

NASA Technical Reports Server (NTRS)

Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-traveling sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2 lambda(sub TS)/pi of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations, and the Stokes wave subtracted) show the generation of 3-D T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modeling are observed.

Saric, William S.; Spencer, Shelly Anne

1993-01-01

170

The boundary layer on compressor cascade blades  

NASA Technical Reports Server (NTRS)

The purpose of NASA Research Grant NSG-3264 is to characterize the flowfield about an airfoil in a cascade at chord Reynolds number(R sub C)near 5 x 10 to the 5th power. The program is experimental and combines laser Doppler velocimeter (LDV) measurements with flow visualization techniques in order to obtain detailed flow data, e.g., boundary layer profiles, points of separation and the transition zone, on a cascade of highly-loaded compressor blades. The information provided by this study is to serve as benchmark data for the evaluation of current and future compressor cascade predictive models, in this way aiding in the compressor design process. Summarized is the research activity for the period 1 December 1985 through 1 June 1986. Progress made from 1 June 1979 through 1 December 1985 is presented. Detailed measurements have been completed at the initial cascade angle of 53 deg. (incidence angle 5 degrees). A three part study, based on that data, has been accepted as part of the 1986 Gas Turbine Conference and will be submitted for subsequent journal publication. Also presented are data for a second cascade angle of 45 deg (an incidence angle of 3 degrees).

Deutsch, S.; Zierke, W. C.

1986-01-01

171

A boundary-layer treatment for turbulent detonation waves  

NASA Technical Reports Server (NTRS)

The profile of turbulent intensity versus Reynolds number from bursts found in an ignition front agrees with the Orr-Sommerfeld solutions for unstable boundary-layer flow. This result provides the first evidence of a formal connection between bursting transition to turbulence in flows which share the boundary-layer approximation but which are otherwise unrelated.

Johnson, J. A., III

1980-01-01

172

Helical circulations in the typhoon boundary layer Ryan Ellis1  

E-print Network

., 2008]. Numerical studies include two-scale boundary layer models [Ginis et al., 2004] and 3-D idealized observations of Zhang et al. [2008] and the two-scale boundary layer model of Ginis et al. [2004]. Ginis et al. [2008]. This may help explain damage patterns observed by Fujita [1992] in hurricanes Andrew and Iniki

Businger, Steven

173

Planetary boundary layer dynamics over the Amazon rain forest  

Microsoft Academic Search

Observations of the diurnal evolution of the planetary boundary layer (PBL) over the Amazon rain forest, in the area of the Amazon boundary layer experiment (ABLE) 2A and 2B experiments showed the existence of a low level circulation with low level nocturnal maxima winds. These circulations are shown to be induced by the thermal contrast between the river and the

Amauri Pereiradeoliveira

1990-01-01

174

Numerical prediction of boundary layers and transitional flows  

Microsoft Academic Search

Mathematical models and numerical prediction methods for two dimensional boundary layer flows in turbomachines are reviewed. Special emphasis is given to the prediction of laminar turbulent transition, transitional flow and relaminarization. The various physical phenomena affecting the development of blade boundary layers are discussed. The various forms of laminar turbulent transition are physically described. A general classification of mathematical models

Georg Scheuerer

1991-01-01

175

The Application of Optimal Control to Boundary Layer Flow  

Microsoft Academic Search

Modern optimal control theory can be used to calculate the optimal steady suction needed to e.g. relaminarize the flow or to delay transition. This has been used to devise the best possible suction distributions for keeping the flow laminar, and applied for flat plate boundary layers as well as boundary layers on swept wings of airplanes. Optimal control theory can

D. Henningson; A. Hanifi

176

Experiments on the wind tunnel simulation of atmospheric boundary layers  

Microsoft Academic Search

The simulation of atmospheric boundary layers using spires, a barrier wall, and a fetch of roughness elements is discussed in the light of experiments carried out to reproduce the characteristics of a boundary layer for urban terrain conditions. Comparisons of wind tunnel and atmospheric data are presented, including mean-velocity profiles, turbulence intensities, turbulence spectra, and turbulence length scales, in particular

Cesar Farell; Arun K. S. Iyengar

1999-01-01

177

Turbulent boundary layer at moving surface of cylindrical body  

Microsoft Academic Search

An analysis is made of the two dimensional turbulent boundary on the moving surface of a cylindrical body (a Rankine oval with an aspect ratio of 4) moving at constant velocity in an incompressible fluid. A numerical simulation is used in which the boundary layer is divided in accordance with a two layer model into inner and outer regions, for

V. M. Zubarev

1986-01-01

178

Boundary layer calculations for the MHD insulator wall  

Microsoft Academic Search

A computer model has been used to obtain predictions concerning the current distribution, the friction, and the heat transfer on an insulating wall in the case of an inclusion of MHD effects. The model is based on a boundary-layer program developed by Crawford and Kays (1975). Modifications for the sidewall boundary layer take into account the electric fields and the

R. R. Rankin; R. H. Eustis

1976-01-01

179

Pitot-probe displacement in a supersonic turbulent boundary layer  

NASA Technical Reports Server (NTRS)

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

Allen, J. M.

1972-01-01

180

DNS of shock-turbulent boundary layer interaction  

NASA Astrophysics Data System (ADS)

A novel DNS/LES capability for high speed viscous flows on unstructured grids is being developed. Shock-turbulent boundary layer interaction results in flow separation, shock unsteadiness, and increased aerodynamic and thermal loads. This paper focuses on the DNS of a Mach 3 turbulent boundary layer flow past a 24 degree compression corner. In our simulations, the upstream turbulent boundary layer is obtained by roughness--induced transition of a laminar boundary layer, and not by rescaling methods. The simulations are performed at the conditions of experiments by Bookey et al (AIAA Paper 2005). The results will be compared to experimental data. We will present the evolution of the boundary layer flow across the shock, low frequency unsteadiness, and the upstream influence of the corner. Both numerical issues and their physical implications will be discussed.

Muppidi, Suman; Mahesh, Krishnan

2010-11-01

181

Experiment on turbulent boundary layers on a concave wall  

NASA Technical Reports Server (NTRS)

The present experiment describes the behavior of a turbulent boundary layer on a concave wall. At the onset of curvature there appears a fairly coherent wavelike transverse profile of mean velocity. This disturbance might be interpreted as a kind of large scale Taylor-Goertler type instability superimposed on a conventional turbulent boundary layer; further downstream the coherence degenerates as the turbulence level increases. Boundary-layer profile measurements were made at positions of maxima and minima of transverse profiles of (U-component) mean velocity. The boundary layer at the minima positions is found to be twice as thick as that at the maxima positions. Also, turbulent intensities inside the boundary layer are substantially increased as a result of the concave curvature of the surface.

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

1975-01-01

182

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

183

An Equation for the Mean Velocity Distribution of Boundary Layers  

NASA Technical Reports Server (NTRS)

A general relation, empirical in origin, for the mean velocity distribution of both laminar and turbulent boundary layers is proposed. The equation, in general, accurately describes the profiles in both laminar and turbulent flows. The calculation of profiles is based on a prior knowledge of momentum, displacement, and boundary-layer thickness together with free-stream conditions. The form for turbulent layers agrees with the present concepts of similarity of the outer layer. For the inner region or turbulent boundary layers the present relation agrees very closely with experimental measurements even in cases where the logarithmic law of the wall is inadequate. A unique relation between profile form factors and the ratio of displacement thickness to boundary-layer thickness is obtained for turbulent separation. A similar criterion is also obtained for laminar separation. These relations are demonstrated to serve as an accurate criterion for identifying separation in known profiles.

Sandborn, V. A.

1959-01-01

184

Symmetries in Turbulent Boundary Layer Flows  

NASA Technical Reports Server (NTRS)

The objective is the development of a new theory which enables the algorithmic computation of all self-similar mean velocity profiles. The theory is based on Liegroup analysis and unifies a large set of self-similar solutions for the mean velocity of stationary parallel turbulent shear flows. The results include the logarithmic law of the wall, an algebraic law, the viscous sublayer, the linear region in the middle of a Couette flow and in the middle of a rotating channel flow, and a new exponential mean velocity profile not previously reported. Experimental results taken in the outer parts of a high Reynolds number flat-plate boundary layer, strongly support the exponential profile. From experimental as well as from DNS data of a turbulent channel flow the algebraic scaling law could be confirmed in both the center region and in the near wall region. In the case of the logarithmic law of the wall, the scaling with the wall distance arises as a result of the analysis and has not been assumed in the derivation. The crucial part of the derivation of all the different mean velocity profiles is to consider the invariance of the equation for the velocity fluctuations at the same time as the invariance of the equation for the velocity product equations. The latter is the dyad product of the velocity fluctuations with the equation for the velocity fluctuations. It has been proven that all the invariant solutions are also consistent with similarity of all velocity moment equations up to any arbitrary order.

Oberlack, M.

1996-01-01

185

Boundary-layer receptivity and laminar-flow airfoil design  

NASA Technical Reports Server (NTRS)

Boundary-layer receptivity examines the way in which external disturbances generate instability waves in boundary layers. Receptivity theory is complementary to stability theory, which studies the evolution of disturbances that are already present in the boundary layer. A transition prediction method which combines receptivity with linear stability theory would directly account for the influence of free-stream disturbances and also consider the characteristics of the boundary layer upstream of the neutral stability point. The current e sup N transition prediction methods require empirical correlations for the influence of environmental disturbances, and totally ignore the boundary layer characteristics upstream of the neutral stability point. The regions where boundary-layer receptivity occurs can be separated into two classes, one near the leading edges and the other at the downstream points where the boundary layer undergoes rapid streamwise adjustments. Analyses were developed for both types of regions, and parametric studies which examine the relative importance of different mechanisms were carried out. The work presented here has focused on the low Mach number case. Extensions to high subsonic and supersonic conditions are presently underway.

Kerschen, Edward J.

1987-01-01

186

Titan's planetary boundary layer structure at the Huygens landing site  

Microsoft Academic Search

Huygens Atmospheric Structure Instrument (HASI) for the first time performed an in situ measurement of the thermal structure in Titan's atmosphere with a vertical resolution sufficient to analyze the planetary boundary layer (PBL). The vertical potential temperature profile reveals the presence of a weakly convective PBL, with a surface layer thickness of 10 m and an outer layer with a

Tetsuya Tokano; Francesca Ferri; Giacomo Colombatti; Teemu Mäkinen; Marcello Fulchignoni

2006-01-01

187

Chemistry of a polluted cloudy boundary layer  

SciTech Connect

A one-dimensional photochemical model for cloud-topped boundary layers is developed which includes detailed descriptions of gas-phase and aqueous-phase chemistry, and of the radiation field in and below cloud. The model is used to interpret the accumulation of pollutants observed over Bakersfield, California, during a wintertime stagnation episode with low stratus. The main features of the observations are well simulated; in particular, sulfate accumulates progressively over the course of the episode due to sustained aqueous-phase oxidation of SO{sub 2} in the stratus cloud. The major source of sulfate is the reaction S(IV)+Fe(III), provided that this reaction proceeds by a non radical mechanism in which Fe(III) is not reduced. A radical mechanism with SO{sup {minus}}{sub 3} and Fe(II) as immediate products would quench sulfate production because of depletion of Fe(III). The model results suggest that the non radical mechanism is more consistent with observations, although this result follows from the absence of a rapid Fe(II) oxidation pathway in the model. Even with the non-radical mechanis most of the soluble iron is present as FE(II) because Fe(III) is rapidly reduced by O{sup {minus}}{sub 2}. The S(IV)+Fe(III) reacton provides the principal source of H{sub 2}O{sub 2} in the model; photochemical production of H{sub 2}O{sub 2} from HO{sub 2} or O{sub 2}({minus}I) is slow because HO{sub 2} is depleted by high levels of NO{sub {ital x}}. The aqueous-phase reaction S(IV)+OH initiates a radical-assisted S(IV) oxidation chain but we find that the chain is not propagated due to efficient termination by SO{sup {minus}}{sub 4}+Cl{sup {minus}} followed by Cl+H{sub 2}O. A major uncertainty attached to that result is that the reactivities of S(IV)-carbonyl adducts with radical oxidants are unknown.

Jacob, D.J.; Gottlieb, E.W. (Department of Earth and Planetary Sciences and Division of Applied Sciences, Harvard University, Cambridge, Massachusetts (US)); Prather, M.J. (NASA Goddard Institute of Space Studies, New York, New York)

1989-09-20

188

Influences on the Height of the Stable Boundary Layer as seen in LES  

SciTech Connect

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 in gross errors in boundary-layer evolution and in prediction of turbulent mixing within the boundary layer.

Kosovic, B; Lundquist, J

2004-06-15

189

Structure of the zero-pressure-gradient turbulent boundary layer.  

PubMed

A processing of recent experimental data by Nagib and Hites [Nagib, H. & Hites, M. (1995) AIAA paper 95-0786, Reno, NV) shows that the flow in a zero-pressure-gradient turbulent boundary layer, outside the viscous sublayer, consists of two self-similar regions, each described by a scaling law. The results concerning the Reynolds-number dependence of the coefficients of the wall-region scaling law are consistent with our previous results concerning pipe flow, if the proper definition of the boundary layer Reynolds number (or boundary layer thickness) is used. PMID:11038559

Barenblatt, G I; Chorin, A J; Hald, O H; Prostokishin, V M

1997-07-22

190

Structure of turbulence in three-dimensional boundary layers  

NASA Technical Reports Server (NTRS)

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

Subramanian, Chelakara S.

1993-01-01

191

Shock wave-boundary layer interactions in rarefied gas flows  

NASA Technical Reports Server (NTRS)

A numerical study is presented, using the direct simulation Monte Carlo (DSMC) method, of shock wave-boundary layer interactions in low density supersonic flows. Test cases include two-dimensional, axially-symmetric and three-dimensional flows. The effective displacement angle of the boundary layer is calculated for representative flat plate, wedge, and cone flows. The maximum pressure, shear stress, and heat transfer in the shock formation region is determined in each case. The two-dimensional reflection of an oblique shock wave from a flat plate is studied, as is the three-dimensional interaction of such a wave with a sidewall boundary layer.

Bird, G. A.

1991-01-01

192

A novel concept for subsonic inlet boundary-layer control  

NASA Technical Reports Server (NTRS)

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

Miller, B. A.

1977-01-01

193

Further Improvements to Nozzle Boundary Layer Calculations in BLIMPJ  

NASA Technical Reports Server (NTRS)

Further improvements made to advance the current Boundary Layer Integral Matrix Procedure - Version J (BLIMPJ) containing previously modeled simplified calculation methods by accounting for condensed phase, thick boundary layer and free stream turbulence effects are discussed. The condensed phase effects were included through species composition effect considered via input to the code and through particle damping effect considered via a turbulence model. The thrust loss calculation procedure for thick boundary layer effects was improved and the optimization of net thrust with respect to nozzle length was performed. The effects of free stream turbulence were approximately modeled in the turbulence model.

Praharaj, S. C.; Gross, Klaus W.

1989-01-01

194

Pressure power spectra beneath a supersonic turbulent boundary layer.  

SciTech Connect

Wind tunnel experiments up to Mach 3 have provided fluctuating wall-pressure spectra beneath a supersonic turbulent boundary layer to frequencies reaching 400 kHz by combining signals from piezoresistive silicon pressure transducers effective at low- and mid-range frequencies and piezoelectric quartz sensors to detect high frequency events. Data were corrected for spatial attenuation at high frequencies and for wind-tunnel noise and vibration at low frequencies. The resulting power spectra revealed the {omega}{sup -1} dependence for fluctuations within the logarithmic region of the boundary layer, but are essentially flat at low frequency and do not exhibit the theorized {omega}{sup 2} dependence. Variations in the Reynolds number or streamwise measurement location collapse to a single curve for each Mach number when normalized by outer flow variables. Normalization by inner flow variables is successful for the {omega}{sup -1} region but less so for lower frequencies. A comparison of the pressure fluctuation intensities with fifty years of historical data shows their reported magnitude chiefly is a function of the frequency response of the sensors. The present corrected data yield results in excess of the bulk of the historical data, but uncorrected data are consistent with lower magnitudes. These trends suggest that much of the historical compressible database may be biased low, leading to the failure of several semi-empirical predictive models to accurately represent the power spectra acquired during the present experiments.

Beresh, Steven Jay; Spillers, Russell Wayne; Henfling, John Francis; Pruett, Brian O. M.

2010-06-01

195

Pulsed boundary layers observed during a Geotail magnetopause skimming orbit  

NASA Astrophysics Data System (ADS)

On January 8, 1996, the Geotail satellite skimmed along the dayside magnetopause from the dawnside to the duskside and observed a series of quasiperiodically recurring pulsed boundary layers in the prenoon (~0900-1000 LT) and the postnoon (~1400-1500 LT) sectors. For both intervals the interplanetary magnetic field observed by the Wind satellite upstream of the bow shock was inferred to be southward from an estimated convection time between Wind and Geotail. During the pulsed events, Geotail observed bipolar signatures in the magnetic field component normal to the nominal magnetopause. In the prenoon sector the bipolar variation had the inward-then-outward polarity, while in the postnoon sector the polarity was opposite (i.e., outward-then-inward). The plasma flows normal to the nominal magnetopause showed bipolar signatures with the inward-then-outward polarity in the prenoon and postnoon sectors. They were accompanied by sunward flows for the lower-density pulsed events and by tailward flows for the higher-density pulsed events. We have interpreted the sunward flow as the local plasma response to a tailward moving flux tube. This may imply that the sunward plasma flow near the magnetopause does not always reflect the direction of the motion of the flux tube. On the basis of these observations, we suggest that the observed pulsed boundary layers are attributed to the passage of a train of flux transfer events propagating tailward.

Kim, K.-H.; Lin, N.; Cattell, C. A.; Song, Y.; Wygant, J. R.; Lee, D.-H.; Kawano, H.; Kokubun, S.; Mukai, T.; Tsuruda, K.

2001-02-01

196

Performance of a boundary layer ingesting propulsion system  

E-print Network

This thesis presents an assessment of the aerodynamic performance of an aircraft propulsion system, with embedded engines, in the presence of aircraft fuselage boundary layer ingestion (BLI). The emphasis is on defining ...

Plas, Angélique (Angélique Pascale)

2006-01-01

197

Mathematical models of momentum transfer in the boundary layer  

NASA Astrophysics Data System (ADS)

Consideration has been given to the processes of momentum transfer in the laminar and turbulent boundary layers on a plate and in a tube. Original models for calculation of the tangential stress, friction factors, boundary-layer thickness, and coefficients of momentum transfer in the boundary layers on a plate and in a tube have been obtained under different conditions of motion of the gas medium. Examples of calculation of the indicated characteristics have been given; the results obtained have been compared to the existing experimental data. The obtained equations and methods of determination of the characteristics of the boundary layer can be used in designing industrial heat- and mass-exchange apparatuses of various structures and other equipment.

Laptev, A. G.; Farakhov, T. M.

2013-05-01

198

Distributed Roughness Receptivity in a Flat Plate Boundary Layer  

E-print Network

(Re_(k) = 220), the discrete element created a turbulent wedge 15 boundary layer thicknesses downstream. When the distributed roughness was added around the discrete roughness, the wake amplitude decreased at the sub-critical Reynolds number...

Kuester, Matthew Scott

2014-04-18

199

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...

200

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

201

Tropical boundary layer equilibrium in the last ice age  

NASA Technical Reports Server (NTRS)

A radiative-convective boundary layer model is used to assess the effect of changing sea surface temperature, pressure, wind speed, and the energy export from the tropics on the boundary layer equilibrium equivalent potential temperature. It remains difficult to reconcile the observations that during the last glacial maximum (18,000 yr BP) the snowline on the tropical mountains fell 950 m, while the tropical sea surface temperatures fell only 1-2 K.

Betts, Alan K.; Ridgway, W.

1992-01-01

202

Study of a turbulent boundary layer by laser plane visualization  

NASA Astrophysics Data System (ADS)

Flow visualization was implemented with a laser light plane longitudinal to the flow in wind tunnel experiments. The experimental setup was complemented by wall friction sensors and hot film transducers. The influence of large eddy breakup devices was also tested. The visualization results are in accord with those obtained by FALCO. When manipulating the boundary layer, the results confirm the screen effect played by the wake on the fluid penetration in the inside part of the boundary layer.

Stanislas, M.; Hoyez, M. C.; Pruvost, J.

1988-12-01

203

A note on boundary-layer friction in baroclinic cyclones  

E-print Network

The interaction between extratropical cyclones and the underlying boundary layer has been a topic of recent discussion in papers by Adamson et. al. (2006) and Beare (2007). Their results emphasise different mechanisms through which the boundary layer dynamics may modify the growth of a baroclinic cyclone. By using different sea-surface temperature distributions and comparing the low-level winds, the differences are exposed and both of the proposed mechanisms appear to be acting within a single simulation.

Boutle, I A; Belcher, S E; Plant, R S

2008-01-01

204

Composite Structure of Plumes in Stratus-topped Boundary Layers  

Microsoft Academic Search

Knowledge of convective plumes within the clear convective boundary layer (CBL) is quite advanced owing to direct measurements, tank experiments, and large-eddy simulation studies. As a result, modeling of the CBL is relatively successful. Progress for the stratus-topped boundary layer (STBL), however, is slow. This study compares the plume structure of the surface-heated CBL with that of the cloud-top-cooled STBL

Chin-Hoh Moeng; Ulrich Schumann

1991-01-01

205

Acoustic emissions from unsteady transitional boundary layer flow structures  

Microsoft Academic Search

The acoustic radiation contribution of boundary layer flow structures has long been the subject of debate. The research described critically examines the popular approaches to modeling the radiation mechanisms and attempts to bring some degree of closure to the physical and practical significance of noise and pseudo-noise originating in the laminar-to-turbulent transition zone within a natural boundary layer. This includes

Richard Chostner Marboe

2000-01-01

206

Reynolds Stress Budgets in Couette and Boundary Layer Flows  

Microsoft Academic Search

Reynolds stress budgets for both Couette and boundary layer flows are evaluated and presented. Data are taken from direct\\u000a numerical simulations of rotating and non-rotating plane turbulent Couette flow and turbulent boundary layer with and without\\u000a adverse pressure gradient. Comparison of the total shear stress for the two types of flows suggests that the Couette case\\u000a may be regarded as

Jukka Komminaho; Martin Skote

2002-01-01

207

Turbulence in rough-wall boundary layers: universality issues  

Microsoft Academic Search

Wind tunnel measurements of turbulent boundary layers over three-dimensional rough surfaces have been carried out to determine\\u000a the critical roughness height beyond which the roughness affects the turbulence characteristics of the entire boundary layer.\\u000a Experiments were performed on three types of surfaces, consisting of an urban type surface with square random height elements,\\u000a a diamond-pattern wire mesh and a sand-paper

Mohammad Amir; Ian P. Castro

2011-01-01

208

Flow visualization of shock-boundary layer interaction  

NASA Technical Reports Server (NTRS)

Two and three-dimensional shock-boundary layer interaction data were obtained from supersonic wind tunnel tests. These interactions are studied both with and without boundary layer bleed. The data verify computational fluid dynamic codes. Surface static pressure, pitot pressure, flow angularity, and bleed rates, are studied by flow visualization techniques. Surface oil flow using fluorescent dye and laser sheet using water droplets as the scattering material are used for flow visualization.

Hingst, W. R.; Jurkovich, M.

1982-01-01

209

The axisymmetric boundary layer beneath a Rankine-like vortex  

Microsoft Academic Search

An experimental investigation of the three-dimensional boundary layer induced by a Rankine-like vortex with its axis normal\\u000a to a stationary disk is described. The velocity field through the boundary layer was measured for Reynolds number Re (based on the tangential velocity and radius at the disk edge) ranging from 10?000 to 25?000 at various radial distances\\u000a by means of a

B. C. Khoo; K. S. Yeo; D. F. Lim

1997-01-01

210

Integral-matrix procedure for boundary-layer problems  

NASA Technical Reports Server (NTRS)

Program, BLIMP, provides fast, highly accurate solution to general class of gas-phase boundary layer flow problems encompassing broad range of boundary conditions. Program is capable of obtaining accurate and economical solutions to governing differential equations of momentum, energy, and species.

Gross, K. W.; Evans, R. M.

1977-01-01

211

Inflow Turbulence Generation and Oblique Shock \\/ Turbulent Boundary Layer Interaction  

Microsoft Academic Search

Large-eddy simulation of an oblique shock impinging on a supersonic turbulent boundary layer (M? = 2.28, = 8 , Retheta = 1800, 5100) is carried out with a high-order compact differencing scheme using localized artificial diffusivity for shock capturing. Solution sensitivity is investigated with regards to mesh resolution, spanwise domain, Reynolds number, and inflow turbulence boundary conditions. Through analysis of

Brandon Morgan; Soshi Kawai; Sanjiva Lele

2010-01-01

212

Turbulent boundary layer in high Rayleigh number convection in air.  

PubMed

Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra=1.4×1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re?200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal. PMID:24724653

du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian

2014-03-28

213

Orbiter Boundary Layer Transition Stability Modeling at Flight Entry Conditions  

NASA Technical Reports Server (NTRS)

State of the art boundary layer stability modeling capabilities are increasingly seeing application to entry flight vehicles. With the advent of user friendly and robust implementations of two-dimensional chemical nonequilibrium stability modeling with the STABL/PSE-CHEM software, the need for flight data to calibrate such analyses capabilities becomes more critical. Recent efforts to perform entry flight testing with the Orbiter geometry related to entry aerothermodynamics and boundary layer transition is allowing for a heightened focus on the Orbiter configuration. A significant advancement in the state of the art can likely be achieved by establishing a basis of understanding for the occurrence of boundary layer transition on the Orbiter due to discrete protruding gap fillers and the nominal distributed roughness of the actual thermal protection system. Recent success in demonstrating centerline two-dimensional stability modeling on the centerline of the Orbiter at flight entry conditions provides a starting point for additional investigations. The more detailed paper will include smooth Orbiter configuration boundary layer stability results for several typical orbiter entry conditions. In addition, the numerical modeling approach for establishing the mean laminar flow will be reviewed and the method for determining boundary layer disturbance growth will be overviewed. In addition, if actual Orbiter TPS surface data obtained via digital surface scans become available, it may be possible to investigate the effects of an as-flown flight configuration on boundary layer transition compared to a smooth CAD reference.

Bartkowicz, Matt; Johnson, Heath; Candler, Graham; Campbell, Charles H.

2009-01-01

214

Dense gas boundary layer experiments: Visualization, pressure measurements, concentration evaluation  

SciTech Connect

This technical report describes methods that were applied to investigate turbulent boundary layers generated by inviscid, baroclinic effects. The Cranz-Schardin 24-sparks camera was used to visualize the interactions of a planar shock wave with a Freon R12-layer. The shock propagates more slowly in the Freon layer than in air because of its smaller sound speed. This causes the shock front to be curved and to be reflected between the wall and the layer interface. As a consequence of the reflection process, a series of compression and expansion waves radiate from the layer. Large fluctuations in the streamwise velocity and in pressure develop for about 1 ms. These waves strongly perturb the interface shear layer, which rapidly transitions to a turbulent boundary flow. Pressure measurements showed that the fluctuations in the Freon layer reach a peak pressure 4 times higher than in the turbulent boundary flow. To characterize the preshock Freon boundary layer, concentration measurements were performed with a differential interferometry technique. The refraction index of Freon R12 is so high that Mach-Zehnder interferometry was not successful in these experiments. The evaluation of the concentration profile is described here in detail. Method and results of corresponding LDV measurements under the same conditions are presented in a different report, EMI Report T 9/92. The authors plan to continue the dense gas layer investigations with the gas combination helium/Freon.

Reichenbach, H.; Neuwald, P. [Ernst-Mach-Institut, Freiburg (DE); Kuhl, A.L. [R and D Associates, Los Angeles, CA (United States)

1992-11-01

215

Optimal Control of Shock Wave Turbulent Boundary Layer Interactions Using Micro-Array Actuation  

NASA Technical Reports Server (NTRS)

The intent of this study on micro-array flow control is to demonstrate the viability and economy of Response Surface Methodology (RSM) to determine optimal designs of micro-array actuation for controlling the shock wave turbulent boundary layer interactions within supersonic inlets and compare these concepts to conventional bleed performance. The term micro-array refers to micro-actuator arrays which have heights of 25 to 40 percent of the undisturbed supersonic boundary layer thickness. This study covers optimal control of shock wave turbulent boundary layer interactions using standard micro-vane, tapered micro-vane, and standard micro-ramp arrays at a free stream Mach number of 2.0. The effectiveness of the three micro-array devices was tested using a shock pressure rise induced by the 10 shock generator, which was sufficiently strong as to separate the turbulent supersonic boundary layer. The overall design purpose of the micro-arrays was to alter the properties of the supersonic boundary layer by introducing a cascade of counter-rotating micro-vortices in the near wall region. In this manner, the impact of the shock wave boundary layer (SWBL) interaction on the main flow field was minimized without boundary bleed.

Anderson, Bernhard H.; Tinapple, Jon; Surber, Lewis

2006-01-01

216

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

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

217

Turbulence in a Convective Marine Atmospheric Boundary Layer  

Microsoft Academic Search

The structure and kinetic energy budget of turbulence in the convective marine atmospheric boundary layer as observed by aircraft during a cold air outbreak have been studied using mixed layer scaling. The results are significantly different from those of previous studies under conditions closer to free convection. The normalized turbulent kinetic energy and turbulent transport are about twice those found

Shu-Hsien Chou; David Atlas; Eueng-Nan Yeh

1986-01-01

218

Observational Study of the Atmospheric Boundary Layer over Antarctica  

Microsoft Academic Search

During the austral summer of 1982\\/83, measurements of wind and temperature profiles were made through the atmospheric boundary layer in Adelie Land, East Antarctica, an area known for strong katabatic winds. It was found that a shallow but strong temperature inversion was developed at night, and destroyed during the day, resulting in the development of a well-mixed layer. Wind hodographs

Zbigniew Sorbjan; Yuji Kodama; Gerd Wendler

1986-01-01

219

Basic entrainment equations for the atmospheric boundary layer  

Microsoft Academic Search

The parameterization of penetrative convection and other cases of turbulent entrainment by the atmospheric boundary layer is reviewed in this paper. The conservation equations for a one-layer model of entrainment are straightforward; all modeling problems arise in the context of the parameterization of various terms in the budget of turbulent kinetic energy. There is no consensus in the literature on

H. Tennekes; A. G. M. Driedonks

1981-01-01

220

Multiple paths to subharmonic laminar breakdown in a boundary layer  

NASA Technical Reports Server (NTRS)

Numerical simulations demonstrate that laminar breakdown in a boundary layer induced by the secondary instability of two-dimensional Tollmien-Schlichting waves to three-dimensional subharmonic disturbances need not take the conventional lambda vortex/high-shear layer path.

Zang, Thomas A.; Hussaini, M. Yousuff

1989-01-01

221

Urban air pollution modelling and measurements of boundary layer height  

Microsoft Academic Search

An urban field trial has been undertaken with the aim of assessing the performance of the boundary layer height (BLH) determination of two models: the Met Office Unified Model (UM) and a Gaussian-type plume model, ADMS. Pulsed Doppler lidar data were used to measure mixing layer height and cloud base heights for a variety of meteorological conditions over a 3

F. Davies; D. R. Middleton; K. E. Bozier

2007-01-01

222

EART 265 Lecture Notes: Boundary Layers We're interested here mainly in boundary layers relevant to planets, i.e. those of planetary atmo-  

E-print Network

EART 265 Lecture Notes: Boundary Layers We're interested here mainly in boundary layers relevant to planets, i.e. those of planetary atmo- spheres, oceans and uid cores. Of these, the atmospheric boundary. There is a another class of important boundary layer problems involving aerodynamics of objects moving in uids, i

Nimmo, Francis

223

An experimental study into the effects of streamwise and spanwise acceleration in a turbulent boundary layer  

NASA Astrophysics Data System (ADS)

We compare two turbulent boundary layers produced in a low-speed water channel experiment. Both are subjected to an identical streamwise pressure gradient generated via a lateral contraction of the channel, and an additional spanwise pressure gradient is imposed on one of the layers by curving the contraction walls. Despite a relatively high streamwise acceleration, hot-film probe measurements of the mean-velocity distributions show that the Reynolds number increases whilst the coefficient of friction decreases downstream. Visualization of the viscous layers using hydrogen bubbles reveal an increase in the non-dimensional streak spacing in response to the acceleration. Changes in statistical moments of the streamwise velocity near the wall suggest an increased dominance of high-velocity fluctuations. The near-wall streaks and velocity statistics have little sensitivity to the boundary layer three-dimensionality induced by the spanwise pressure gradient, with the boundary-layer crossflow velocity reaching 11 % that of the local freestream velocity.

Pearce, N. F.; Denissenko, P.; Lockerby, D. A.

2012-12-01

224

An experimental study into the effects of streamwise and spanwise acceleration in a turbulent boundary layer  

NASA Astrophysics Data System (ADS)

We compare two turbulent boundary layers produced in a low-speed water channel experiment. Both are subjected to an identical streamwise pressure gradient generated via a lateral contraction of the channel, and an additional spanwise pressure gradient is imposed on one of the layers by curving the contraction walls. Despite a relatively high streamwise acceleration, hot-film probe measurements of the mean-velocity distributions show that the Reynolds number increases whilst the coefficient of friction decreases downstream. Visualization of the viscous layers using hydrogen bubbles reveal an increase in the non-dimensional streak spacing in response to the acceleration. Changes in statistical moments of the streamwise velocity near the wall suggest an increased dominance of high-velocity fluctuations. The near-wall streaks and velocity statistics have little sensitivity to the boundary layer three-dimensionality induced by the spanwise pressure gradient, with the boundary-layer crossflow velocity reaching 11 % that of the local freestream velocity.

Pearce, N. F.; Denissenko, P.; Lockerby, D. A.

2013-01-01

225

A Numerical Model of the Atmospheric Boundary Layer  

Microsoft Academic Search

A physical model is const.meted for studying the response of the lowest atmo- spheric layers and the underlying soil stratum to incoming solar radiation and other external in- fluences. The model consists of three strata: a soil layer, a surface layer in which the vertical fluxes of heat, momentum, and moisture are constant with height, and an overlying transition layer.

Mariano A. Estoque

1963-01-01

226

Vibrations of plates with clamped and free edges excited by low-speed turbulent boundary layer flow  

Microsoft Academic Search

Plate vibrations due to turbulent boundary layer (TBL) excitation can depend strongly on the plate boundary conditions, especially when the flow convects over the plate at speeds much slower than those of the bending waves in the plate. The vibration response of a TBL excited baffled flat rectangular plate is analyzed with two sets of boundary conditions: (a) all four

S. A. Hambric; Y. F. Hwang; W. K. Bonness

2004-01-01

227

Feasibility study of optical boundary layer transition detection method  

NASA Technical Reports Server (NTRS)

A high sensitivity differential interferometer was developed to locate the region where the boundary layer flow undergoes transition from laminar to turbulent. Two laboratory experimental configurations were used to evaluate the performance of the interferometer: open shear layer, and low speed wind tunnel turbulent spot configuration. In each experiment, small temperature fluctuations were introduced as the signal source. Simultaneous cold wire measurements were compared with the interferometer data. The comparison shows that the interferometer is sensitive to very weak phase variations in the order of 0.001 the laser wavelength. An attempt to detect boundary layer transition over a flat plate at NASA-Langley Unitary Supersonic Wind Tunnel using the interferometer system was performed. The phase variations during boundary layer transition in the supersonic wind tunnel were beyond the minimum signal-to-noise level of the instrument.

Azzazy, M.; Modarress, D.; Trolinger, J. D.

1986-01-01

228

Calculation of three-dimensional compressible turbulent boundary layers  

NASA Technical Reports Server (NTRS)

From comparisons of high speed data with low speed closure procedures using variable mean density, there does not appear to be any appreciable influence of compressibility upon turbulent shear stress modeling in compressible turbulent boundary layers, even for extreme cases such as Mach 14 to 20 with a change in density across the layer of up to a factor of 100. Other evidence of apparent lack of compressibility caused new physics which may alter the shear stress for the compressible boundary layer cases including: (1) fluctuation Mach number was generally less than 1; (2) the shear stress distribution through the boundary layer was not a function of Mach number for zero pressure gradient flows; (3) the Morkovin hypothesis was valid up to Mach 5 (based on fluctuation data); (4) profile N power was not a function of Mach number, at least up to Mach 10; and (5) the nondimensional burst period was approximately the same as that for low speed.

1977-01-01

229

Dense gas boundary layer experiments: Visualization, pressure measurements, concentration evaluation  

Microsoft Academic Search

This technical report describes methods that were applied to investigate turbulent boundary layers generated by inviscid, baroclinic effects. The Cranz-Schardin 24-sparks camera was used to visualize the interactions of a planar shock wave with a Freon R12-layer. The shock propagates more slowly in the Freon layer than in air because of its smaller sound speed. This causes the shock front

H. Reichenbach; P. Neuwald; A. L. Kuhl

1992-01-01

230

The Temporal Behavior of the Atmospheric Boundary Layer in Israel  

Microsoft Academic Search

Upper-air measurements collected for three consecutive years (1987-89) from the Israel Meteorological Service permanent sounding site, in Beit-Dagan, Israel, enabled the temporal behavior of the atmospheric boundary layer over Israel to be characterized. Data analyzed consisted of the layer depth, the thermal gradient within the layer, and occurrence frequency of radiative and elevated inversions. To adequately represent the multiyear seasonal

Uri Dayan; Jacob Rodnizki

1999-01-01

231

The Boundary Layer Late Afternoon and Sunset Turbulence Project  

NASA Astrophysics Data System (ADS)

The BLLAST (Boundary Layer Late Afternoon and Sunset Turbulence) project aims at better understanding the turbulence processes which occur during the transition from a well-mixed convective boundary layer to a residual layer overlying a stabilized nocturnal layer. This phase of the diurnal cycle is challenging from both modeling and observational perspectives: it is transitory, most of the forcings are small or null during the transition and the turbulence regime changes from the fully convective regime of turbulence, close to homogeneous and isotropic, toward more heterogeneous and intermittent turbulence during its decay. Those issues motivated a field campaign that was conducted from 14 June to 8 July 2011 in southern France in complex terrain and consisted of a range of integrated instrument platforms including: full-size aircraft, Remotely Piloted Airplane Systems (RPAS), remote sensing instruments, radiosoundings, tethered balloons, surface flux stations, and various meteorological towers deployed over different surface covers. The boundary layer, from the earth's surface to free troposphere was densely probed during the entire day, with a focus and intense observations from midday until sunset. The field dataset now forms the base of a set of studies utilizing the observations and several types of models including: Large Eddy Simulation, Mesoscale models, forecast models. The presentation will expose an overview of this experiment and of the current observational and modeling studies, with the focus on: the turbulence decay process within the entire boundary layer from surface to the top, the mesoscale forcings of importance during BLLAST, the ability of the forecast models to represent the diurnal cycle, the relevance of the Monin Obukhov similarity theory, and shallow drainage flows. Reference: Lothon M. et al., 2012. The Boundary-Layer Late Afternoon and Sunset Turbulence field experiment, Proc. of the 20th Symposium on Boundary-Layers and Turbulence, 7-13 July, Boston, MA, USA.

Lothon, Marie; Lohou, Fabienne; Darbieu, Clara; Couvreux, Fleur; Pino, David; Blay, Estel; Vila-Guerau de Arellano, Jordi; Pietersen, Henk; Hartogensis, Oscar; Pardyjak, Eric; Alexander, Daniel; Reuder, Joachim; Baaserud, Line; Nilsson, Erik; Jimenez, Maria Antonia; Faloona, Ian; Sastre-Marugan, Mariano; Angevine, Wayne M.; Canut, Guylaine; Bazile, Eric

2014-05-01

232

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

NASA Technical Reports Server (NTRS)

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

Vanness, W.

1978-01-01

233

Surface modes in sheared boundary layers over impedance linings  

NASA Astrophysics Data System (ADS)

Surface modes, being duct modes localized close to the duct wall, are analysed within a lined cylindrical duct with uniform flow apart from a thin boundary layer. As well as full numerical solutions of the Pridmore-Brown equation, simplified mathematical models are given where the duct lining and boundary layer are lumped together and modelled using a single boundary condition (a modification of the Myers boundary condition previously proposed by the author), from which a surface mode dispersion relation is derived. For a given frequency, up to six surface modes are shown to exist, rather than the maximum of four for uniform slipping flow. Not only is the different number and behaviour of surface modes important for frequency-domain mode-matching techniques, which depend on having found all relevant modes during matching, but the thin boundary layer is also shown to lead to different convective and absolute stability than for uniform slipping flow. Numerical examples are given comparing the predictions of the surface mode dispersion relation to full solutions of the Pridmore-Brown equation, and the accuracy with which surface modes are predicted is shown to be significantly increased compared with the uniform slipping flow assumption. The importance of not only the boundary layer thickness but also its profile (tanh or linear) is demonstrated. A Briggs-Bers stability analysis is also performed under the assumption of a mass-spring-damper or Helmholtz resonator impedance model.

Brambley, E. J.

2013-08-01

234

Active Flow Control on a Boundary-Layer-Ingesting Inlet  

NASA Technical Reports Server (NTRS)

Boundary layer ingestion (BLI) is explored as means to improve overall system performance for Blended Wing Body configuration. The benefits of BLI for vehicle system performance benefit are assessed with a process derived from first principles suitable for highly-integrated propulsion systems. This performance evaluation process provides framework within which to assess the benefits of an integrated BLI inlet and lays the groundwork for higher-fidelity systems studies. The results of the system study show that BLI provides a significant improvement in vehicle performance if the inlet distortion can be controlled, thus encouraging the pursuit of active flow control (AFC) as a BLI enabling technology. The effectiveness of active flow control in reducing engine inlet distortion was assessed using a 6% scale model of a 30% BLI offset, diffusing inlet. The experiment was conducted in the NASA Langley Basic Aerodynamics Research Tunnel with a model inlet designed specifically for this type of testing. High mass flow pulsing actuators provided the active flow control. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion was determined by 120 total pressure measurements located at the aerodynamic interface plane. The test matrix was limited to a maximum freestream Mach number of 0.15 with scaled mass flows through the inlet for that condition. The data show that the pulsed actuation can reduce distortion from 29% to 4.6% as measured by the circumferential distortion descriptor DC60 using less than 1% of inlet mass flow. Closed loop control of the actuation was also demonstrated using a sidewall surface static pressure as the response sensor.

Gorton, Susan Althoff; Owens, Lewis R.; Jenkins, Luther N.; Allan, Brian G.; Schuster, Ernest P.

2004-01-01

235

Particle motion in atmospheric boundary layers of Mars and Earth  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

236

Stabilization of boundary layer streaks by plasma actuators  

NASA Astrophysics Data System (ADS)

A flow's transition from laminar to turbulent leads to increased levels of skin friction. In recent years, dielectric barrier discharge actuators have been shown to be able to delay the onset of turbulence in boundary layers. While the laminar to turbulent transition process can be initiated by several different instability mechanisms, so far, only stabilization of the Tollmien-Schlichting path to transition has received significant attention, leaving the stabilization of other transition paths using these actuators less explored. To fill that void, a bi-global stability analysis is used here to examine the stabilization of boundary layer streaks in a laminar boundary layer. These streaks, which are important to both transient and by-pass instability mechanisms, are damped by the addition of a flow-wise oriented plasma body force to the boundary layer. Depending on the magnitude of the plasma actuation, this damping can be up to 25% of the perturbation's kinetic energy. The damping mechanism appears to be due to highly localized effects in the immediate vicinity of the body force, and when examined using a linearized Reynolds-averaged Navier-Stokes energy balance, indicate negative production of the perturbation's kinetic energy. Parametric studies of the stabilization have also been performed, varying the magnitude of the plasma actuator's body force and the spanwise wavenumber of the actuation. Based on these parametric studies, the damping of the boundary layer streaks appears to be linear with respect to the total amount of body force applied to the flow.

Riherd, Mark; Roy, Subrata

2014-03-01

237

Linear and nonlinear PSE for compressible boundary layers  

NASA Technical Reports Server (NTRS)

Compressible stability of growing boundary layers is studied by numerically solving the partial differential equations under a parabolizing approximation. The resulting parabolized stability equations (PSE) account for nonparallel as well as nonlinear effects. Evolution of disturbances in compressible flat-plate boundary layers are studied for freestream Mach numbers ranging from 0 to 4.5. Results indicate that the effect of boundary-layer growth is important for linear disturbances. Nonlinear calculations are performed for various Mach numbers. Two-dimensional nonlinear results using the PSE approach agree well with those from direct numerical simulations using the full Navier-Stokes equations while the required computational time is less by an order of magnitude. Spatial simulation using PSE were carried out for both the fundamental and subharmonic type breakdown for a Mach 1.6 boundary layer. The promising results obtained show that the PSE method is a powerful tool for studying boundary-layer instabilities and for predicting transition over a wide range of Mach numbers.

Chang, Chau-Lyan; Malik, Mujeeb R.; Erlebacher, Gordon; Hussaini, M. Yousuff

1993-01-01

238

Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

239

A second-order bulk boundary-layer model  

NASA Technical Reports Server (NTRS)

Bulk mass-flux models represent the large eddies that are primarily responsible for the turbulent fluxes in the planetary boundary layer as convective circulations, with an associated convective mass flux. In order for such models to be useful, it is necessary to determine the fractional area covered by rising motion in the convective circulations. This fraction can be used as an estimate of the cloud amount, under certain conditions. 'Matching' conditions have been developed that relate the convective mass flux to the ventilation and entrainment mass fluxes. These are based on conservation equations for the scalar means and variances in the entrainment and ventilation layers. Methods are presented to determine both the fractional area covered by rising motion and the convective mass flux. The requirement of variance balance is used to relax the 'well-mixed' assumption. The vertical structures of the mean state and the turbulent fluxes are determined analytically. Several aspects of this simple model's formulation are evaluated using results from large-eddy simulations.

Randall, David A.; Shao, Qingqiu; Moeng, Chin-Hoh

1992-01-01

240

Slow Growth Formulation for DNS of Temporally Evolving Boundary Layers  

NASA Astrophysics Data System (ADS)

A formulation for DNS of temporally evolving boundary layers is developed and demonstrated. The formulation relies on a multiscale approach to account separately for the slow time evolution of statistical averages, and the fast time evolution of turbulent fluctuations. The source terms that arise from the multiscale analysis are modeled assuming a self-similar evolution of the averages. The performance of the formulation is evaluated using DNS of spatially evolving compressible boundary layers. This formulation was developed to provide data for the calibration of turbulence model parameters and enable the quantification of uncertainty due to the models. The extension of this formulation to homogenize spatially evolving boundary layers will also be discussed. This work is supported by the Department of Energy [National Nuclear Security Administration] under Award Number [DE-FC52-08NA28615].

Topalian, Victor; Sahni, Onkar; Oliver, Todd; Moser, Robert

2011-11-01

241

Turbulence in the convective boundary layer observed by microwave interferometry  

SciTech Connect

A 9-antenna, 400 meter microwave interferometer was utilized in SALSA MEX on the San Pedro River area in July and August, 1997, to measure the turbulence in the Convective Boundary Layer. Water vapor has an appreciable index of refraction at radio frequencies around 10 GHz, and acts as a passive tracer of the magnitude and motion of turbulence. The relative phase changes of a signal from a satellite were tracked by an array of 9 antennas, and the phase differences between antennas were then used to derive the turbulence properties of the boundary layer. Preliminary analysis shows clearly different characteristics for the convection activity of the boundary layer between day and night. From the structure function analysis they can see that the turbulence structure starts to decorrelate at scale sizes of 200 meters for a temporal passband around 100 seconds. Derivation of average wind fields is currently in process.

Shao, X.M.; Carlos, R.C.; Kirkland, M.W.

1997-12-01

242

Numerical Simulations of Wake/Boundary Layer Interactions  

NASA Technical Reports Server (NTRS)

Direct and large-eddy simulations of the interaction between the wake of a circular cylinder and a flat-plate boundary layer are conducted. Two Reynolds numbers are examined. The simulations indicate that at the lower Reynolds number the boundary layer is buffeted by the unsteady Karman vortex street shed by the cylinder. The fluctuations, however, cannot be self-sustained due to the low Reynolds-number, and the flow does not reach a turbulent state within the computational domain. In contrast, in the higher Reynolds-number case, boundary-layer fluctuations persist after the wake has decayed (due, in part, to the higher values of the local Reynolds number Re(sub theta) achieved in this case); some evidence could be observed that a self-sustaining turbulence generation cycle was beginning to be established.

Piomelli, Ugo; Choudhari, Meelan M.; Ovchinnikov, Victor; Balaras, Elias

2003-01-01

243

Effect of Blowing on Boundary Layer of Scarf Inlet  

NASA Technical Reports Server (NTRS)

When aircraft operate in stationary or low speed conditions, airflow into the engine accelerates around the inlet lip and pockets of turbulence that cause noise and vibration can be ingested. This problem has been encountered with engines equipped with the scarf inlet, both in full scale and in model tests, where the noise produced during the static test makes it difficult to assess the noise reduction performance of the scarf inlet. NASA Langley researchers have implemented boundary layer control in an attempt to reduce the influence of the flow nonuniformity in a 12-in. diameter model of a high bypass fan engine mounted in an anechoic chamber. Static pressures and boundary layer profiles were measured in the inlet and far field acoustic measurements were made to assess the effectiveness of the blowing treatment. The blowing system was found to lack the authority to overcome the inlet distortions. Methods to improve the implementation of boundary layer control to reduce inlet distortion are discussed.

Gerhold, Carl H.; Clark, Lorenzo R.

2004-01-01

244

Roughness Induced Transition in a Supersonic Boundary Layer  

NASA Technical Reports Server (NTRS)

Direct numerical simulation is used to investigate the transition induced by threedimensional isolated roughness elements in a supersonic boundary layer at a free stream Mach number of 3.5. Simulations are performed for two different configurations: one is a square planform roughness and the other is a diamond planform roughness. The mean-flow calculations show that the roughness induces counter rotating streamwise vortices downstream of the roughness. These vortices persist for a long distance downstream and lift the low momentum fluid from the near wall region and place it near the outer part of the boundary layer. This forms highly inflectional boundary layer profiles. These observations agree with recent experimental observations. The receptivity calculations showed that the amplitudes of the mass-flux fluctuations near the neutral point for the diamond shape roughness are the same as the amplitude of the acoustic disturbances. They are three times smaller for the square shape roughness.

Balakumar, Ponnampalam; Kergerise, Michael A.

2013-01-01

245

Boundary layer integral matrix procedure: Verification of models  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

246

Optical measurements of degradation in aircraft boundary layers  

NASA Technical Reports Server (NTRS)

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

Kelsall, D.

1980-01-01

247

Boundary layer effects on particle impaction and capture  

NASA Technical Reports Server (NTRS)

The inertial impaction and deposition of small particles on larger bodies with viscous boundary layers are considered theoretically, in a detailed comment on a paper by Menguturk et al. (1983). Topics addressed include cushion effects, the dimensionless groups corresponding to the diameter range (3-6 microns) examined by Menguturk et al. in a numerical example, analogous effects of particle-gas energy and mass exchange in boundary layers, and the combined effects of particle inertia and diffusion. It is argued that the inertial effects can be characterized in terms of a body, boundary-layer, or sublayer Stokes number. In a reply by Menguturk et al., the focus is on the application of the theoretical model to the erosion of blade surfaces in large gas turbines; the Stokes number is found to be of limited practical value in these cases, because the particle motion is not primarily normal to the blade surfaces.

Rosner, D. E.; Fernandez De La Mora, J.

1984-01-01

248

Laminar boundary layer instability noise produced by an aerofoil  

NASA Astrophysics Data System (ADS)

When a laminar boundary layer exists on the surface of an aerofoil up to the trailing edge, a tone or a number of tones are sometimes produced. These tones have been the subject of a number of investigations which have proposed a variety of different mechanisms regarding their production. This paper gives a brief overview of the previously proposed mechanisms and then describes the development of a theoretical model to estimate the tone frequencies. The model is validated against a number of well-known published experiments and also against the results of an experimental investigation undertaken by the authors. The model is compared with other models available for predicting laminar boundary layer instability noise and is shown to be accurate and robust. Unlike previous models, which are empirical, the model presented in this paper is purely theoretical and could be used to predict the frequency of laminar boundary layer instability noise produced by an arbitrary aerofoil.

Kingan, Michael J.; Pearse, John R.

2009-05-01

249

Three dimensional boundary layer separation in supersonic flow  

NASA Technical Reports Server (NTRS)

An account is given of a detailed experimental investigation of three dimensional boundary layer separation in supersonic flow. In investigating three dimensional effects on supersonic separation, models were chosen which exhibited departures from two dimensional flow in the simplest way. The plane compression corner was replaced by a plate attached to a swept back wedge formed by two obliquely intersecting planes. Maintaining a constant tunnel Mach number of 2.5, surface pressure measurements were made on these models at static orifices spaced along the centerline and along three parallel lines. The flow parameters in the boundary layer and separated regions adjacent to the model surface were measured by traversing hot wire and pitot probes. The traverses were taken across the boundary layer and reversed flow regions in a direction normal to the body surface; they were made in several vertical planes, including the plane of symmetry.

Bachalo, W. D.; Holt, M.

1976-01-01

250

An investigation of shock/turbulent boundary layer bleed interactions  

NASA Technical Reports Server (NTRS)

A numerical investigation was conducted to determine the effect of bleed on oblique shock wave/turbulent boundary layer interactions. The numerical solution to the compressible Navier-Stokes equations reveal the flow details throughout the interaction zone and inside the normal bleed slot. Results are presented for an incident oblique shock of sufficient strength to cause boundary layer separation in the absence of bleed. Bleed is applied across the shock impingement location over a range of bleed mass flow rates corresponding to different values of plenum pressures. The results indicate a complex flow structure with large variations in both normal and tangential flow velocities across the bleed slot. The flow entrainment into the slot is accompanied by an expansion-compression wave system with a bow shock originating inside the bleed slot. Increasing the bleed mass flow by decreasing the plenum pressure caused an initial decrease then a later increase in the boundary layer momentum and displacement thickness downstream of the interaction.

Hamed, A.; Shih, S. H.; Yeuan, J. J.

1992-01-01

251

Finite volume solution of the compressible boundary-layer equations  

NASA Technical Reports Server (NTRS)

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

Loyd, B.; Murman, E. M.

1986-01-01

252

Sound from boundary layer flow over steps and gaps  

NASA Astrophysics Data System (ADS)

This study is concerned with the radiated sound from boundary layer flows over small forward and backward steps and gap configurations of similar dimension. These measurements were performed in the Virginia Tech Anechoic Wall Jet Facility for step heights that ranged from approximately 10 percent to 100 percent of the incoming boundary layer height. The results show the influence of step height and boundary layer edge velocity on the far-field sound from forward and backward steps. Neither source shows clear dipole directivity and at least the larger step heights considered in this study are shown to not be acoustically compact. A new mixed scaling normalization is proposed for the far-field spectra from both types of step. Backward steps are shown to be much weaker producers of far-field sound than similarly sized forward steps. The implications of this behavior are discussed with respect to the far-field sound measured from various gap flows.

Ryan Catlett, M.; Devenport, William; Glegg, Stewart A. L.

2014-09-01

253

Boundary-Layer Turbulence Over The Nebraska Sandhills  

NASA Astrophysics Data System (ADS)

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 data where horizontal velocity perturbations appear at the same wavelengths as the terrain and variances (normalised by u 2 , where u is the local friction velocity) are significantly enhanced relative to standard flat terrain values. By contrast the vertical velocity variance seems less affected and terrain effects are much less evident in data from the afternoon convective boundary layer.

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

254

Numerical simulation of separated boundary-layer flow  

Microsoft Academic Search

The numerical simulation of time-dependent, 2-D compressible boundary-layer flow containing a region of separation is studied. The separation is generated by the introduction of an adverse pressure gradient along the freestream boundary. In order to validate the numerical method, a low Mach-number laminar separation bubble flow is considered, which enables an extensive comparison with incompressible results. The generation of an

B. Wasistho; B. J. Geurts; J. G. M. Kuerten

1997-01-01

255

Effect of Far-Field Boundary Conditions on Boundary-Layer Transition  

NASA Technical Reports Server (NTRS)

The effect of far-field boundary conditions on the evolution of a finite-amplitude two-dimensional wave in the Blasius boundary layer is assessed. With the use of the parabolized stability equations (PSE) theory for the numerical computations, either asymptotic, Dirichlet, Neumann or mixed boundary conditions are imposed at various distances from the wall. The results indicate that asymptotic and mixed boundary conditions yield the most accurate mean-flow distortion and unsteady instability modes in comparison with the results obtained with either Dirichlet or Neumann conditions.

Bertolotti, Fabio P.; Joslin, Ronald D.

1994-01-01

256

Effect of Far-Field Boundary Conditions on Boundary-Layer Transition  

NASA Technical Reports Server (NTRS)

The effect of far-field boundary conditions on the evolution of a finite-amplitude two-dimensional wave in the Blasius boundary layer is assessed. With the use of the parabolized stability equations (PSE) theory for the numerical computations, either asymptotic, Dirichlet, Neumann or mixed boundary conditions are imposed at various distances from the wall. The results indicate that asymptotic and mixed boundary conditions yield the most accurate mean-flow distortion and unsteady instability modes in comparison with the results obtained with either Dirichlet or Neumann conditions.

Bertolotti, Fabio P.; Joslin, Ronald D.

1995-01-01

257

Second mode interactions in supersonic boundary layers  

NASA Technical Reports Server (NTRS)

The nonlinear evolution of a two-dimensional second mode unstable wave in a Mach 4.5 wall-bounded flow is computed by solving the full time-dependent compressible Navier-Stokes equations. A highly accurate solution is obtained using spectral collocation methods. It is shown that departure from linearity first occurs in the critical layer due to the cubic nonlinearities in the momentum equation. This is a direct result of the large density perturbations in this regime. Time evolution studies of the growth rate as a function of normal distance from the plate suggests that the mode is evolving toward a nonlinear saturated state, and that this problem is possibly amenable to standard weakly nonlinear perturbation methods.

Erlebacher, Gordon; Hussaini, M. Y.

1990-01-01

258

Spectral scales in the atmospheric boundary layer  

NASA Technical Reports Server (NTRS)

Wind data taken from 10 levels between 18 and 305 m were examined to determine the properties of atmospheric turbulence within and above the atmospheric surface layer into the PBL. The samples were averaged over 40 min intervals, with all periods of rain, fog, and other disturbances being eliminated from the 16 days of monitoring. Turbulence spectra were calculated using a fast Fourier transformation. The tower was located in rolling terrain covered with pine forests, waist-high scrub, and cultivated fields. Results are presented for the wavelength and Eulerian length scales, considering the neutral, stable, and unstable PBL. Correlation coefficients were found between velocity fluctuations and wavelengths for the stability classes. Good agreements were found for measured and computed spectra in all but unstable conditions.

Weber, A. H.; Irwin, J. S.; Mathis, J. J., Jr.; Kahler, J. P.; Petersen, W. B.

1982-01-01

259

Secondary instability in boundary-layer flows  

NASA Technical Reports Server (NTRS)

The stability of a secondary Tollmien-Schlichting wave, whose wavenumber and frequency are nearly one half those of a fundamental Tollmien-Schlichting instability wave is analyzed using the method of multiple scales. Under these conditions, the fundamental wave acts as a parametric exciter for the secondary wave. The results show that the amplitude of the fundamental wave must exceed a critical value to trigger this parametric instability. This value is proportional to a detuning parameter which is the real part of k - 2K, where k and K are the wavenumbers of the fundamental and its subharmonic, respectively. For Blasius flow, the critical amplitude is approximately 29% of the mean flow, and hence many other secondary instabilities take place before this parametric instability becomes significant. For other flows where the detuning parameter is small, such as free-shear layer flows, the critical amplitude can be small, thus the parametric instability might play a greater role.

Nayfeh, A. H.; Bozatli, A. N.

1979-01-01

260

Time Scales of the Trade Wind Boundary Layer Adjustment GILLES BELLON  

E-print Network

of the trade wind atmospheric boundary layer to an abrupt sea surface warming is in- vestigated using a large of the boundary layer depth. 1. Introduction The trade wind atmospheric boundary layer can be consideredTime Scales of the Trade Wind Boundary Layer Adjustment GILLES BELLON Centre National de Recherches

Ribes, Aurélien

261

Spectral characteristics of velocity and vorticity fluxes in an unstratified turbulent boundary layer  

E-print Network

with the empirical form found in the atmospheric boundary layer. In the inertial subrange the momentum flux of turbulence spectral properties have been conducted in the atmospheric boundary layer, e.g., the 1968 Kansas spectral properties in the oceanic boundary layer com- pared to studies in the atmospheric boundary layer

Lien, Ren-Chieh

262

De Bilt, 2010 | Technical report; TR-315 Assimilation of Cabauw boundary layer  

E-print Network

;#12;Assimilation of Cabauw boundary layer observations in an atmospheric single-column model using an ensemble the structure and transport properties of the atmospheric boundary layer (ABL). Boundary layer processes have the full atmospheric column over the Netherland of which the atmospheric boundary layer forms the lowest

Stoffelen, Ad

263

Surface heterogeneity effects on regional-scale fluxes in stable boundary layers: surface temperature transitions  

E-print Network

understanding of homogeneous stable boundary layers (SBLs). However, in general, the atmospheric boundary layerSurface heterogeneity effects on regional-scale fluxes in stable boundary layers: surface temperature distributions on regional-scale turbulent fluxes in the stable boundary layer (SBL). Simulations

Stoll, Rob

264

An Innovative Flow-Measuring Device: Thermocouple Boundary Layer Rake  

NASA Technical Reports Server (NTRS)

An innovative flow-measuring device, a thermocouple boundary layer rake, was developed. The sensor detects the flow by using a thin-film thermocouple (TC) array to measure the temperature difference across a heater strip. The heater and TC arrays are microfabricated on a constant-thickness quartz strut with low heat conductivity. The device can measure the velocity profile well into the boundary layer, about 65 gm from the surface, which is almost four times closer to the surface than has been possible with the previously used total pressure tube.

Hwang, Danny P.; Fralick, Gustave C.; Martin, Lisa C.; Wrbanek, John D.; Blaha, Charles A.

2001-01-01

265

Numerical Study of Boundary-Layer in Aerodynamics  

NASA Technical Reports Server (NTRS)

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

Shih, Tom I-P.

1997-01-01

266

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

2010-10-01

267

Solid\\/free-surface juncture boundary layer and wake  

Microsoft Academic Search

The Reynolds-averaged flow for a solid\\/free-surface juncture boundary layer and wake is documented. The three mean-velocity\\u000a components and five of the Reynolds stresses are measured for a surface-piercing flat plate in a towing tank using a laser-Doppler\\u000a velocimeter system for both boundary-layer and wake planes in regions close to the free surface. The experimental method is\\u000a described, including the foil-plate

J. Longo; H. P. Huang; F. Stern

1998-01-01

268

Flow separation in oblique shock wave turbulent boundary layer interactions  

NASA Technical Reports Server (NTRS)

Available experimental data on flow separation in shock wave turbulent boundary layer interactions are reviewed at hypersonic and supersonic speeds in two dimensional and axisymmetric interactions. The conditions leading to flow separation and the subsequent changes in the flow are discussed. The effects of the Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed. Pertinent experimental data for the separated flow characteristics in turbulent boundary layer oblique shock wave interactions are also presented and discussed. Empirical correlations for separated flows are also reviewed.

Hamed, A.

1990-01-01

269

Analytical Model of the Time Developing Turbulent Boundary Layer  

E-print Network

We present an analytical model for the time-developing turbulent boundary layer (TD-TBL) over a flat plate. The model provides explicit formulae for the temporal behavior of the wall-shear stress and both the temporal and spatial distributions of the mean streamwise velocity, the turbulence kinetic energy and Reynolds shear stress. The resulting profiles are in good agreement with the DNS results of spatially-developing turbulent boundary layers at momentum thickness Reynolds number equal to 1430 and 2900. Our analytical model is, to the best of our knowledge, the first of its kind for TD-TBL.

Victor S. L'vov; Anna Pomyalov; Antonino Ferrante; Said Elghobashi

2007-06-04

270

Circulation and boundary layers in differentially heated rotating strarified fluid  

NASA Astrophysics Data System (ADS)

Recent laboratory experiments with rotating stratified water in a cylinder have revealed many of the predictions of linearized, analytic theory. Earlier measurements of the velocity field generated in a cylinder by top heating compared well with theory. Large stratification clearly suppressed Ekman pumping so that the interior velocity field (primarily azimuthal) responded by satisfying no-slip top and bottom boundary conditions without the need for Ekman layers. This interior flow also occupied a boundary layer of greater thickness than the Ekman layer under some conditions. Theory and experiments have now been conducted for sidewall heating. As before, experiment and theory agree well over some parameter ranges. But for some parameters, the flow is unstable. The exact nature of the instability remains poorly understood. The size of one combination of both vertical and horizontal boundary layers is governed by the Rossby radius of deformation multiplied by the square root of the Prandtl number. Sidewall boundary layers and their scales will be reviewed with the present results in mind.

Whitehead, J. A.; Pedlosky, J.

2000-01-01

271

DNS Study on Physics of Late Boundary Layer Transition  

E-print Network

This paper serves as a review of our recent new DNS study on physics of late boundary layer transition. This includes mechanism of the large coherent vortex structure formation, small length scale generation and flow randomization. The widely spread concept vortex breakdown to turbulence,which was considered as the last stage of flow transition, is not observed and is found theoretically incorrect. The classical theory on boundary layer transition is challenged and we proposed a new theory with five steps, i.e. receptivity, linear instability, large vortex formation, small length scale generation, loss of symmetry and randomization to turbulence. We have also proposed a new theory about turbulence generation. The new theory shows that all small length scales (turbulence) are generated by shear layer instability which is produced by large vortex structure with multiple level vortex rings, multiple level sweeps and ejections, and multiple level negative and positive spikes near the laminar sub-layers.Therefore,...

Liu, Chaoqun

2014-01-01

272

Magnetic field maxima in the low latitude boundary layer  

SciTech Connect

The magnetic field often exhibits a maximum in the Earth's low-latitude boundary layer. The authors show examples of this behavior, using data from the AMPTE/IRM spacecraft, and argue that two fundamentally distinct causes exist for the excess field: (1) a depression, within the layer, of the population of medium-energy ions of magnetospheric origin; (2) field curvature effects associated with undulations of the magnetopause itself.

Sonnerup, B. (Dartmouth College, Hannover, NH (United States)); Paschmann, G.; Phan, T.D. (Max-Planck-Institut fuer Extraterrestrische Physik, Garching (Germany)); Luehr, H. (Technische Universitaet, Braunschweig (Germany))

1992-09-04

273

Some Turbulence Characteristics in Stable Atmospheric Boundary Layer Flow  

Microsoft Academic Search

Atmospheric boundary layer measurements during stable and near neutral condition from seven sites in different kinds of terrain have been analyzed in order to find relationships among turbulence parameters.The shape of the spectral and cospectral distributions turned out to be well represented by the universal expressions found for ideal sites.For near neutral conditions in the surface layer w\\/u( increases and

Ann-Sofi Smedman

1991-01-01

274

New aspects of turbulent boundary-layer structure  

Microsoft Academic Search

Using flow visualization techniques and hot wire measurements, the structure of the zero-pressure-gradient turbulent boundary-layer is studied over the Reynolds number range of 500 less than Re sub theta less than 17,500. A section of the turbulent layer, filled with smoke, is illuminated by an intense plane of light, and a low-speed wind tunnel with a very long working section

M. R. Head; P. Bandyopadhyay

1981-01-01

275

Physical description of boundary-layer transition: Experimental evidence  

NASA Technical Reports Server (NTRS)

The problems of understanding the origins of turbulent flow and transition to turbulent flow are the most important unsolved problems of fluid mechanics and aerodynamics. It is well known that the stability, transition, and turbulent characteristics of bounded shear layers are fundamentally different from those of free shear layers. Likewise, the stability, transition, and turbulent characteristics of open systems are fundamentally different from those of closed systems. Because of the influence of indigenous disturbances, surface geometry and roughness, sound, heat transfer, and ablation, it is not possible to develop general prediction schemes for transition location and the nature of turbulent structures in boundary-layer flows. At the present time no mathematical model exists that can predict the transition Reynolds number on a flat plate. The recent progress in this area is encouraging, in that a number of distinct transition mechanisms have been found experimentally. The theoretical work finds them to be amplitude and Reynolds-number dependent. The theory remains rather incomplete with regard to predicting transition. Amplitude and spectral characteristics of the disturbances inside the laminar viscous layer strongly influence which type of transition occurs. The major need in this area is to understand how freestream disturbances are entrained into the boundary layer, i.e., to answer the question of receptivity. We refer receptivity to the mechanism(s) that cause freestream disturbances to enter the boundary layer and create the initial amplitudes for unstable waves.

Saric, William S.

1994-01-01

276

Scaling of heat transfer augmentation due to mechanical distortions in hypervelocity boundary layers  

NASA Astrophysics Data System (ADS)

We examine the response of hypervelocity boundary layers to global mechanical distortions due to concave surface curvature. Surface heat transfer and visual boundary layer thickness data are obtained for a suite of models with different concave surface geometries. Results are compared to predictions using existing approximate methods. Near the leading edge, good agreement is observed, but at larger pressure gradients, predictions diverge significantly from the experimental data. Up to a factor of five underprediction is reported in regions with greatest distortion. Curve fits to the experimental data are compared with surface equations. We demonstrate that reasonable estimates of the laminar heat flux augmentation may be obtained as a function of the local turning angle for all model geometries, even at the conditions of greatest distortion. This scaling may be explained by the application of Lees similarity. As a means of introducing additional local distortions, vortex generators are used to impose streamwise structures into the boundary layer. The response of the large scale vortices to an adverse pressure gradient is investigated. Surface streak evolution is visualized over the different surface geometries using fast response pressure sensitive paint. For a flat plate baseline case, heat transfer augmentation at similar levels to turbulent flow is measured. For the concave geometries, increases in heat transfer by factors up to 2.6 are measured over the laminar values. The scaling of heat transfer with turning angle that is identified for the laminar boundary layer response is found to be robust even in the presence of the imposed vortex structures.

Flaherty, W.; Austin, J. M.

2013-10-01

277

Effects Of Changing Surface Heat Flux On Atmospheric Boundary-Layer Flow Over Flat Terrain  

Microsoft Academic Search

We examine the unsteady response of a neutral atmospheric boundary layer (ABL) of depth h and friction velocity u* when a uniform surface heat flux is applied abruptly or decreased rapidly over a time scale t? less than about h \\/(10u*). Standard Monin–Obukhov (MO) relationships are used for the perturbed eddy viscosity profile in terms of the changes to the

Antony Z. Owinoh; Julian C. R. Hunt; Andrew Orr; Peter Clark; Rupert Klein; H. J. S. Fernando; Frans T. M. Nieuwstadt

2005-01-01

278

On Monin–Obukhov Similarity In The Stable Atmospheric Boundary Layer  

Microsoft Academic Search

Atmospheric measurements from several field experiments have been combined to develop a better understanding of the turbulence structure of the stable atmospheric boundary layer. Fast response wind velocity and temperature data have been recorded using 3-dimensional sonic anemometers, placed at severalheights (˜1 m to 4.3 m) above the ground. The measurements wereused to calculate the standard deviations of the three

Markus Pahlow; Marc B. Parlange; Fernando Porté-Agel

2001-01-01

279

Kinetic Boundary Layers and FluidKinetic Coupling in Semiconductors  

E-print Network

Kinetic Boundary Layers and Fluid­Kinetic Coupling in Semiconductors Pierre Degond 1 and Christian Schmeiser 2 Abstract. The semiconductor Boltzmann equation with elastic collisions as the dominating decomposition approach are presented. Key words: Semiconductor Boltzmann equation, spherical harmonics ex

Schmeiser, Christian

280

Radiation-dominated, relativistic jets and their boundary layers  

NASA Astrophysics Data System (ADS)

The energetics of certain astrophysical jets, such as those launched from the progenitors of long gamma-ray bursts and super-Eddington tidal disruption events, are likely dominated by radiation. In the limit that the outflow is optically thick, the shear boundary layer that develops between the jet and the ambient medium is mediated by radiation viscosity. We use the relativistic equations of radiation hydrodynamics in the viscous limit, accurate to first order in the mean-free path of a photon, to describe the dynamics of the boundary layer. A set of boundary layer equations is derived and we solve them in a self-similar manner, demonstrating in the process how the compressibility of the fluid, the variation of the viscosity coefficient, and the relativistic nature of the velocity affect the structure and dynamics of the boundary layer. We apply the model to the case of Swift J1644+57, the recently-observed, jetted, super-Eddington tidal distruption event, in an attempt to place tighter constraints on the physical characteristics of the jet.

Coughlin, Eric Robert; Begelman, Mitchell C.

2015-01-01

281

Boundary-Layer Meteorology An International Journal of Physical,  

E-print Network

1 23 Boundary-Layer Meteorology An International Journal of Physical, Chemical and Biological and evolution of persistent inversions. It is found that the inversion formed mainly because of the interaction affect human lives and health because the stable air traps air pollutants near the surface and allows

Pu, Zhaoxia

282

ACTIVE FLOW CONTROL ON A BOUNDARY-LAYER-INGESTING INLET  

Microsoft Academic Search

Boundary layer ingestion (BLI) is explored as a means to improve overall system performance for a Blended Wing Body configuration. The benefits of BLI for vehicle system performance benefit are assessed with a process derived from first principles suitable for highly-integrated propulsion systems. This performance evaluation process provides a framework within which to assess the benefits of an integrated BLI

Susan Althoff Gorton; Lewis R. Owens; Luther N. Jenkins; Brian G. Allan; Ernest P. Schuster

283

Boundary layer measurements using hot-film sensors  

NASA Technical Reports Server (NTRS)

Measurements in the aerodynamic boundary layer using heat transfer, hot-film sensors are receiving a significant amount of effort at the Langley Research Center. A description of the basic sensor, the signal conditioning employed, and several manifestations of the sensor are given. Results of a flow reversal sensor development are presented, and future work areas are outlined.

Holmes, Harlan K.; Carraway, Debra L.

1986-01-01

284

Numerical Study of Flat-Plate Boundary Layer Bypass Transition.  

NASA Astrophysics Data System (ADS)

Previous numerical simulations of boundary-layer bypass transition due to free-stream-turbulence (FST) have focused primarily on the transition region itself, using an ad hoc inflow condition downstream of the plate leading edge. This approach involves significant assumptions regarding the spatial evolution of FST and its penetration into the boundary layer. Additionally, the effects of FST length-scale have largely been ignored, which can lead to incorrect decay rates over the boundary layer, making a quantitative comparison with experiments difficult. We present DNS of boundary-layer bypass transition, which addresses some of the above limitations by including the super-elliptic leading edge of the flat-plate model inside the computational domain. The FST is generated upstream of the plate, enabling the leading-edge/FST interaction region to be fully captured in the simulations. The FST also has the same decay rate as in the experiments of Roach and Brierlay (1992), facilitating a direct comparison with the experimental data.

Ovchinnikov, Victor; Piomelli, Ugo; Choudhari, Meelan M.

2004-11-01

285

A sensitivity theory for the equilibrium boundary layer over land  

NASA Astrophysics Data System (ADS)

Due to the intrinsic complexities associated with modeling land-atmosphere interactions, global models typically use elaborate land surface and boundary layer physics parameterizations. Unfortunately, it is difficult to use elaborate models, by themselves, to develop a deeper understanding of how land surface parameters affect the coupled land-atmosphere system. At the same time, it is also increasingly important to gain a deeper understanding of the role of changes in land cover, land use, and ecosystem function as forcings and feedbacks in past and future climate change. To improve the foundation of our understanding, we outline a framework for boundary layer climate sensitivity based on surface energy balance; just as global climate sensitivity is based on top-of-atmosphere energy balance. We develop an analytic theory for the boundary layer climate sensitivity of an idealized model of a diurnally averaged well-mixed boundary layer over land. This analytic sensitivity theory identifies changes in the properties of the land surface—including moisture availability, albedo, and aerodynamic roughness—as forcings, and identifies strong negative feedbacks associated with the surface fluxes of latent and sensible heat. We show that our theory can explain nearly all of the sensitivity of the Betts (2000) full system of equations. Favorable comparison of the theory and the simulation results from a two-column radiative convective model suggests that the theory may be broadly useful for unifying our understanding of how changes in land use or ecosystem function may affect climate change.

Cronin, Timothy W.

2013-12-01

286

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...

287

ON HYDROMAGNETIC STRESSES IN ACCRETION DISK BOUNDARY LAYERS  

SciTech Connect

Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. In order to shed light on physically viable mechanisms for angular momentum transport in this inner disk region, we examine the generation of hydromagnetic stresses and energy density in differentially rotating backgrounds with angular frequencies that increase outward in the shearing-sheet framework. We isolate the modes that are unrelated to the standard MRI and provide analytic solutions for the long-term evolution of the resulting shearing MHD waves. We show that, although the energy density of these waves can be amplified significantly, their associated stresses oscillate around zero, rendering them an inefficient mechanism to transport significant angular momentum (inward). These findings are consistent with the results obtained in numerical simulations of MHD accretion disk boundary layers and challenge the standard assumption of efficient angular momentum transport in the inner disk regions. This suggests that the detailed structure of turbulent MHD accretion disk boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity.

Pessah, Martin E. [Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen O (Denmark); Chan, Chi-kwan, E-mail: mpessah@nbi.dk, E-mail: ckch@nordita.org [NORDITA, Roslagstullsbacken 23, 106 91 Stockholm (Sweden)

2012-05-20

288

Stability of Supersonic Boundary Layers Over Blunt Wedges  

NASA Technical Reports Server (NTRS)

Receptivity and stability of supersonic boundary layers over blunt flat plates and wedges are numerically investigated at a free stream Mach number of 3.5 and at a high Reynolds number of 10(exp 6)/inch. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations using the 5th-order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. Computations are performed for a flat plate with leading edge thicknesses of 0.0001, 0.001, 0.005 and 0.01 inches that give Reynolds numbers based on the leading edge thickness ranging from 1000 to 10000. Calculations are also performed for a wedge of 10 degrees half angle with different leading edge radii 0.001 and 0.01 inches. The linear stability results showed that the bluntness has a strong stabilizing effect on the stability of two-dimensional boundary layers. The transition Reynolds number for a flat plate with a leading edge thickness of 0.01 inches is about 3.5 times larger than it is for the Blasius boundary layer. It was also revealed that boundary layers on blunt wedges are far more stable than on blunt flat plates.

Balakumar, Ponnampalam

2006-01-01

289

Effect of heat transfer on turbulent boundary layers  

NASA Astrophysics Data System (ADS)

We use direct numerical simulation to gather a database of hypersonic turbulent boundary layers at different flow conditions varying heat transfer. A statistical description of the data is given, including the effect of wall-temperature condition on fluctuation levels, Reynolds stresses, energy and vorticity budgets, Reynolds analogies, skin friction, wall- pressure loading, and entrainment. Additionally, the turbulence structure is visualized and characterized.

Beekman, Izaak; Pino Martin, M.

2008-11-01

290

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. PMID:23847738

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

2013-01-01

291

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

292

An analytical model of capped turbulent oscillatory bottom boundary layers  

Microsoft Academic Search

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

Kenji Shimizu

2010-01-01

293

On Tollmien–Schlichting-like waves in streaky boundary layers  

Microsoft Academic Search

The linear stability of the boundary layer developing on a flat plate in the presence of finite-amplitude, steady and spanwise periodic streamwise streaks is investigated. The streak amplitudes considered here are below the threshold for onset of the inviscid inflectional instability of sinuous perturbations. It is found that, as the amplitude of the streaks is increased, the most unstable viscous

Carlo Cossu; Luca Brandt

2004-01-01

294

Turbulence Modulation by MicroParticles in Boundary Layers  

Microsoft Academic Search

Turbulent dispersed flows over boundary layers are crucial in a number of industrial and environmental applications. In most applications, the key information is the spatial distribution of inertial particles, which is known to be highly non-homogeneous and may exhibit a complex pattern driven by the structures of the turbulent flow field. Theoretical and experimental evidence shows that fluid motions in

Maurizio Picciotto; Andrea Giusti; Cristian Marchioli; Alfredo Soldati

295

DNS of Turbulent Boundary Layer Subject Strong Adverse Pressure Gradient  

NASA Astrophysics Data System (ADS)

Direct Numerical Simulations of spatially evolving turbulent boundary layers with prescribed strong adverse pressure gradients are performed. The driven force behind this investigation is to analyze the interaction between the inner and outer layers in adverse pressure gradient with eventual separation. A method for prescribing realistic turbulent velocity inflow boundary conditions is employed. The approach is based on the rescaling-recycling method proposed by Lund et al. (1998) and the dynamic multi- scale method developed recently by Araya et al. (2009). The standard rescaling process requires prior knowledge about how the appropriate velocity and length scales are related between the inlet and recycle stations (e.g. classic scaling laws). Here a dynamic approach is proposed in which such information is deduced dynamically by involving an additional plane located between the inlet and recycle stations. The approach also distinguishes between the inner and outer regions of the boundary layer and enables the use of multiple velocity scales. This flexibility allows applications to boundary layer flows with arbitrary pressure gradients.

Araya, Guillermo; Castillo, Luciano

2010-11-01

296

Detection of boundary-layer transitions in wind tunnels  

NASA Technical Reports Server (NTRS)

Accelerometer replaces stethoscope in technique for detection of laminar-to-turbulent boundary-layer transitions on wind-tunnel models. Technique allows measurements above or below atmospheric pressure because human operator is not required within tunnel. Data may be taken from accelerometer, and pressure transducer simultaneously, and delivered to systems for analysis.

Wood, W. R.; Somers, D. M.

1978-01-01

297

Entrainment effects in the well-mixed atmospheric boundary layer  

Microsoft Academic Search

We discuss the structure and evolution of a cloud-free atmospheric boundary layer (ABL) during daytime over land, starting from a shallow ABL at sunrise and developing into a deep ABL with strong convection in the afternoon. The structure of the turbulence in the lower half of a convective ABL capped by an inversion is reasonably well understood. Less is known

A. G. M. Driedonks; H. Tennekes

1984-01-01

298

A Simulation of the Wangara Atmospheric Boundary Layer Data  

Microsoft Academic Search

Previously, the authors have studied a hierarchy of turbulent boundary layer models, all based on the same closure assumptions for the triple turbulence moments. The models differ in complexity by virtue of a systematic process of neglecting certain of the tendency and diffusion terms in the dynamic equations for the turbulent moments. Based on this work a Level 3 model

Tetsuji Yamada; George Mellor

1975-01-01

299

Von Kármán's Constant in Atmospheric Boundary Layer Flow: Reevaluated  

Microsoft Academic Search

A field experiment has been carried out with the specific objective in mind to determine the value of von Kármán's constant in atmospheric boundary layer flow, and also to investigate its possible dependence on the surface Rossby number Ro0. Data from three field measurement campaigns at Marsta, Sweden, were used in the analysis. Depending on the ground cover: deep snow

Ulf Högström

1985-01-01

300

Current problems in the stratocumulus-topped atmospheric boundary layer  

Microsoft Academic Search

Extended sheets of stratocumulus (Sc) in the upper part of the atmospheric boundary layer (ABL) often occur under appropriate meteorological conditions. These cloud decks are important both in climate studies and in weather forecasting. We review the current knowledge of the turbulent structure of the ABL capped by a cloud deck, in the light of recent observations and model studies.

A. G. M. Driedonks; P. G. Duynkerke

1989-01-01

301

FLUID MODELING OF ATMOSPHERIC DISPERSION IN THE CONVECTIVE BOUNDARY LAYER  

EPA Science Inventory

Study of convective boundary layer (CBL) processes has depended largely upon laboratory analogs for many years. The pioneering work of Willis and Deardorff (1974) and some 35 subsequent papers by the same authors showed that much useful research could be accomplished with a re...

302

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

2007-01-01

303

Atmospheric boundary layer studies in FIFE - Challenges and advances  

NASA Technical Reports Server (NTRS)

A review is presented of a number of other articles concerning the atmospheric boundary layer (ABL) that focus on challenges and progress in experimental design and analysis represented by those studies. The articles address problems posed by the experimental site itself (inhomogeneity of terrain, size, and vegetation) and examine relationships between the ABL and remote sensing measurements.

Kelly, Robert D.

1992-01-01

304

Atmospheric boundary layer evening transitions over West Texas  

Technology Transfer Automated Retrieval System (TEKTRAN)

A systemic analysis of the atmospheric boundary layer behavior during some evening transitions over West Texas was done using the data from an extensive array of instruments which included small and large aperture scintillometers, net radiometers, and meteorological stations. The analysis also comp...

305

Pressure Drag of Obstacles in the Atmospheric Boundary Layer  

Microsoft Academic Search

Pressure drag of obstacles in the atmospheric boundary layer is computed with a mesoscale numerical model of the troposphere. Different parts of the drag can be separated from the numerical results: total pressure drag is determined from the surface pressure distribution, hydrostatic drag from the temperature distribution in the atmosphere, and form drag as a residual. The dependence of the

Stefan Emeis

1990-01-01

306

Fluid-dynamic boundary layers in CFB boilers  

Microsoft Academic Search

The characteristics of the fluid-dynamic boundary layer (FBL) were studied in the 12 MW circulating fluidized bed boiler at Chalmers University of Technology. For a comparison, some additional measurements were made in a 165 MW CFB boiler. The FBL consists mainly of the falling film of particles at the furnace wall. The distance from the wall to the zero net

Wennan Zhang; Filip Johnsson; Bo Leckner

1995-01-01

307

Stability of hypersonic boundary-layer flows with chemistry  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

308

Scaling the Urban Boundary Layer S. E. Belcher & O. Coceal  

E-print Network

, there are applications of urban meteorology, such as modelling urban air quality, that require estimates of the transport for the dynamical effect of urban areas on the atmospheric boundary layer, and one that models the winds actually, (ii) some measures of the winds are resolved within the urban canopy, and finally (iii) the model

Reading, University of

309

Insulating wall boundary layer in a Faraday MHD generator  

Microsoft Academic Search

The velocity profile at the center of the insulating wall in an MHD generator was measured using a dual beam real fringe anemometer system with an argon ion laser. The analytic model involved the computer solution, using finte difference techniques, of the momentum, energy, and electrical equations including MHD effects for the turbulent insulating wall boundary layer. The turbulence model

R. R. Rankin

1978-01-01

310

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 ...

311

On the Effects of Surface Roughness on Boundary Layer Transition  

NASA Technical Reports Server (NTRS)

Surface roughness can influence laminar-turbulent transition in many different ways. This paper outlines selected analyses performed at the NASA Langley Research Center, ranging in speed from subsonic to hypersonic Mach numbers and highlighting the beneficial as well as adverse roles of the surface roughness in technological applications. The first theme pertains to boundary-layer tripping on the forebody of a hypersonic airbreathing configuration via a spanwise periodic array of trip elements, with the goal of understanding the physical mechanisms underlying roughness-induced transition in a high-speed boundary layer. The effect of an isolated, finite amplitude roughness element on a supersonic boundary layer is considered next. The other set of flow configurations examined herein corresponds to roughness based laminar flow control in subsonic and supersonic swept wing boundary layers. A common theme to all of the above configurations is the need to apply higher fidelity, physics based techniques to develop reliable predictions of roughness effects on laminar-turbulent transition.

Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan; Edwards, Jack

2009-01-01

312

Energetic ion composition in the subsolar magnetopause and boundary layer  

Microsoft Academic Search

Energetic ion mass spectrometer data obtained on ISEE 1 have shown that the plasma in the subsolar magnetospheric boundary layer, magnetopause, and adjacent magnetosheath have an ionospheric component (He\\/sup +\\/ and O\\/sup +\\/) in addition to the solar wind component (H\\/sup +\\/ and He\\/sup + +\\/). We have examined in detail nine intervals where the location of the subsolar magnetopause

W.K. Peterson; E. G. Shelley; G. Haerendel; G. Paschmann

1982-01-01

313

Laminar boundary-layer solutions in three dimensions  

NASA Technical Reports Server (NTRS)

As an alternative to pure finite-difference techniques, the Method of Integral Relations (MIR) is formulated for three-dimensional boundary-layer flows with separation, and applied to two problems. The first concerns an incompressible laminar flow over a plate with an attached cylinder, where the potential solution of the flow round the circular cylinder is used as the boundary condition. In the second application the solution to the three-dimensional boundary-layer flow over blunt bodies is discussed and results for an ellipsoid of revolution at 30 deg incidence are presented. In both cases the results are found to be in satisfactory agreement with those obtained by finite-difference methods.

Modarress, D.; Holt, M.

1976-01-01

314

On Supersonic-Inlet Boundary-Layer Bleed Flow  

NASA Technical Reports Server (NTRS)

Boundary-layer bleed in supersonic inlets is typically used to avoid separation from adverse shock-wave/boundary-layer interactions and subsequent total pressure losses in the subsonic diffuser and to improve normal shock stability. Methodologies used to determine bleed requirements are reviewed. Empirical sonic flow coefficients are currently used to determine the bleed hole pattern. These coefficients depend on local Mach number, pressure ratio, hole geometry, etc. A new analytical bleed method is presented to compute sonic flow coefficients for holes and narrow slots and predictions are compared with published data to illustrate the accuracy of the model. The model can be used by inlet designers and as a bleed boundary condition for computational fluid dynamic studies.

Harloff, Gary J.; Smith, Gregory E.

1995-01-01

315

Reply in response to comment by E. W. Hones. [concerning the paper, on hot tenuous plasmas, fireballs, and boundary layers in the earth's magnetotail by Frank, et al.  

NASA Technical Reports Server (NTRS)

Hones 1977 points out the marked disagreement between the plasma flow measurements reported by Frank et al. 1976 and those obtained with the LASL plasma analyzer. He suggests (1) that solar ultraviolet background rates may have been incorrectly accounted for in the computation of proton bulk flows in the magnetotail as reported by Frank et al. 1976 and (2) that bulk flows with substantial speeds, i.e., those speeds greater than 50 km per sec, are seldom encountered in the plasma sheet at geocentric radial distances approx. equal to 35 R sub E. It is demonstrated that such ultraviolet responses were carefully considered by Frank et al. 1976 and thus the conclusion is maintained that bulk flows greater than 50 km per sec frequently occur in the plasma sheet at these radial distances. Further, a direct comparison of the capabilities of the LASL plasma analyzer employed by Hones and of the LEPEDEA Frank et al., 1976 indicates that there are rather severe restrictions on which plasmas in the plasma sheet can be properly measured to gain proton temperatures, number densities and flow velocities with the LASL plasma analyzer.

Frank, L. A.; Decoster, R. J.; Ackerson, K. L.

1977-01-01

316

Some Basic Aspects of Magnetohydrodynamic Boundary-Layer Flows  

NASA Technical Reports Server (NTRS)

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

Hess, Robert V.

1959-01-01

317

Linear segmentation algorithm for detecting layer boundary with lidar.  

PubMed

The automatic detection of aerosol- and cloud-layer boundary (base and top) is important in atmospheric lidar data processing, because the boundary information is not only useful for environment and climate studies, but can also be used as input for further data processing. Previous methods have demonstrated limitations in defining the base and top, window-size setting, and have neglected the in-layer attenuation. To overcome these limitations, we present a new layer detection scheme for up-looking lidars based on linear segmentation with a reasonable threshold setting, boundary selecting, and false positive removing strategies. Preliminary results from both real and simulated data show that this algorithm cannot only detect the layer-base as accurate as the simple multi-scale method, but can also detect the layer-top more accurately than that of the simple multi-scale method. Our algorithm can be directly applied to uncalibrated data without requiring any additional measurements or window size selections. PMID:24216909

Mao, Feiyue; Gong, Wei; Logan, Timothy

2013-11-01

318

Provenance of the K/T boundary layers  

NASA Technical Reports Server (NTRS)

An array of chemical, physical and isotopic evidence indicates that an impact into oceanic crust terminated the Cretaceous Period. Approximately 1500 cu km of debris, dispersed by the impact fireball, fell out globally in marine and nonmarine environments producing a 2 to 4 mm thick layer (fireball layer). In North American locales, the fireball layer overlies a 15 to 25 mm thick layer of similar but distinct composition. This 15 to 25 mm layer (ejecta layer) may represent approximately 1000 cu km of lower energy ejecta from a nearby impact site. Isotopic and chemical evidence supports a mantle provenance for the bulk of the layers. The extraordinary REE pattern of the boundary clays was modelled as a mixture of oceanic crust, mantle, and approximately 10 percent continental material. The results are presented. If the siderophiles of the ejecta layer were derived solely from the mantle, a test may be available to see if the siderophile element anomaly of the fireball layer had an extraterrestrial origin. Radiogenic Os-187 is depleted in the mantle relative to an undifferentiated chondritic source. Os-187/Os-186 ratios of 1.049 and 1.108 were calculated for the ejecta and fireball layers, respectively.

Hildebrand, A. R.; Boynton, W. V.

1988-01-01

319

Surface pressure fluctuations in hypersonic turbulent boundary layers  

NASA Technical Reports Server (NTRS)

The surface pressure fluctuations on a flat plate model at hypersonic Mach numbers of 5.2, 7.4 and 10.4 with an attached turbulent boundary layer were measured using flush mounted small piezoelectric sensors. A high frequency resolution of the pressure field was achieved using specially designed small piezoelectric sensors that had a good frequency response well above 300 KHz. The RMS pressures and non-dimensional energy spectra for all above Mach numbers are presented. The convective velocities, obtained from space time correlation considerations are equal to 0.7 U sub infinity. The results indicate the RMS pressures vary from 5 to 25 percent of the mean static pressures. The ratios of RMS pressure to dynamic pressure are less than the universally accepted subsonic value of 6 x 10/3. The ratio decreases in value as the Mach number or the dynamic pressure is increased. The ratio of RMS pressure to wall shear for Mach number 7.4 satisfies one smaller than or equal to p/tau sub w smaller than or equal to three.

Raman, K. R.

1974-01-01

320

Nonlinear Tollmien-Schlichting/vortex interaction in boundary layers  

NASA Technical Reports Server (NTRS)

The nonlinear reaction between two oblique 3-D Tollmein-Schlichting (TS) waves and their induced streamwise-vortex flow is considered theoretically for an imcompressible boundary layer. The same theory applies to the destabilization of an incident vortex motion by subharmonic TS waves, followed by interaction. The scales and flow structure involved are addressed for high Reynolds numbers. The nonlionear interaction is powerful, starting at quite low amplitudes with a triple-deck structure for the TS waves but a large-scale structure for the induced vortex, after which strong nonlinear amplification occurs. This includes nonparallel-flow effects. The nonlinear interaction is governed by a partial differential system for the vortex flow coupled with an ordinary-differential one for the TS pressure. The solution properties found sometimes produce a breakup within a finite distance and sometimes further downstream, depending on the input amplitudes upstream and on the wave angles, and that then leads to the second stages of interaction associated with higher amplitudes, the main second stages giving either long-scale phenomena significantly affected by nonparallelism or shorter quasi-parallel ones governed by the full nonlinear triple-deck response.

Hall, P.; Smith, F. T.

1988-01-01

321

Footprint characteristics of scalar concentration in the convective boundary layer  

NASA Astrophysics Data System (ADS)

Footprint characteristics for passive scalar concentration in the convective boundary layer (CBL) are investigated. A backward Lagrangian stochastic (LS) dispersion model and a large eddy simulation (LES) model are used in the investigation. Typical characteristics of the CBL and their responses to the surface heterogeneity are resolved from the LES. Then the turbulence fields are used to drive the backward LS dispersion. To remedy the spoiled description of the turbulence near the surface, Monin-Obukhov similarity is applied to the lowest LES level and the surface for the modeling of the backward LS dispersion. Simulation results show that the footprint within approximately 1 km upwind predominates in the total contribution. But influence from farther distances also exists and is even slightly greater than that from closer locations. Surface heterogeneity may change the footprint pattern to a certain degree. A comparison to three analytical models provides a validation of the footprint simulations, which shows the possible influence of along-wind turbulence and the large eddies in the CBL, as well as the surface heterogeneity.

Guo, Xiaofeng; Cai, Xuhui

2005-11-01

322

Nonlinear a Tollmien-Schlichting/vortex interaction in boundary layers  

NASA Technical Reports Server (NTRS)

The nonlinear reaction between two oblique three-dimensional Tollmien-Schlichting (TS) waves and their induced streamwise-vortex flow is considered theoretically for an incompressible boundary layer. The same theory applies to the destabilization of an incident vortex motion by subharmonic TS waves, followed by interaction. The scales and flow structure involved are addressed for high Reynolds numbers. The nonlinear interaction is powerful, starting at quite low amplitudes with a triple-deck structure for the TS waves but a large-scale structure for the induced vortex, after which strong nonlinear amplification occurs. This includes nonparallel-flow effects. The nonlinear interaction is governed by a partial differential system for the vortex flow coupled with an ordinary-differential one for the TS pressure. The solution properties found sometimes produce a breakup within a finite distance and sometimes further downstream, depending on the input amplitudes upstream and on the wave angles, and that then leads to the second stages of interaction associated with higher amplitudes, the main second stages giving either long-scale phenomena significantly affected by nonparallelism or shorter quasi-parallel ones governed by the full nonlinear triple-deck response.

Hall, P.; Smith, F. T.

1989-01-01

323

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

NASA Technical Reports Server (NTRS)

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

Tetervin, Neal; Lin, Chia Chiao

1951-01-01

324

Hypersonic Turbulent Boundary-Layer and Free Sheer Database Datasets  

NASA Technical Reports Server (NTRS)

A critical assessment and compilation of data are presented on attached hypersonic turbulent boundary layers in pressure gradients and compressible turbulent mixing layers. Extensive searches were conducted to identify candidate experiments, which were subjected to a rigorous set of acceptance criteria. Accepted datasets are both tabulated and provided in machine-readable form. The purpose of this database effort is to make existing high quality data available in detailed form for the turbulence-modeling and computational fluid dynamics communities. While significant recent data were found on the subject of compressible turbulent mixing, the available boundary-layer/pressure-gradient experiments are all older ones of which no acceptable data were found at hypersonic Mach numbers.

Settles, Gary S.; Dodson, Lori J.

1993-01-01

325

Turbulent boundary layer on a convex, curved surface  

NASA Technical Reports Server (NTRS)

The effects of strong convex curvature on boundary layer turbulence were investigated. The data gathered on the behavior of Reynolds stress suggested the formulation of a simple turbulence model. Three sets of data were taken on two separate facilities. Both rigs had flow from a flat surface, over a convex surface with 90 deg of turning, and then onto a flat recovery surface. The geometry was adjusted so that, for both rigs, the pressure gradient along the test surface was zero - thus avoiding any effects of streamwise acceleration on the wall layers. Results show that after a sudden introduction of curvature, the shear stress in the outer part of the boundary layer is sharply diminished and is even slightly negative near the edge. The wall shear also drops off quickly downstream. In contrast, when the surface suddenly becomes flat again, the wall shear and shear stress profiles recover very slowly towards flat wall conditions.

Gillis, J. C.; Johnston, J. P.; Kays, W. M.; Moffat, R. J.

1980-01-01

326

Beam stresses induced by a turbulent boundary layer and simulated with a reverberant acoustic field  

NASA Technical Reports Server (NTRS)

Unsteady pressure fluctuations are a feature of the flow field of an airplane or a space vehicle in atmospheric flight. Undesirable effects of these fluctuations range from internal (cabin) noise to structural fatigue and damage of avionic and ordnance systems. The integrity to withstand these fluctuating loads is established through reverberant room acoustical qualification testing. The purpose of this paper is to develop a methodology of simulating turbulent boundary layer fluctuating pressure loading for a simply supported beam with a reverberant acoustic field. This goal was accomplished using normal mode vibration analysis. The main results were developed in terms of dimensionless quantities such as turbulent boundary layer spectrums, reverberant acoustical field simulation spectrums, and stress response spectrums with parameters: dimensionless fundamental frequency, Mach number, and relative boundary layer displacement thickness.

Schutzenhofer, L. A.

1981-01-01

327

Observed bottom boundary layer transport and uplift on the continental shelf adjacent to a western boundary current  

NASA Astrophysics Data System (ADS)

boundary currents strongly influence the dynamics on the adjacent continental shelf and in particular the cross-shelf transport and uplift through the bottom boundary layer. Four years of moored in situ observations on the narrow southeastern Australian shelf (in water depths of between 65 and 140 m) were used to investigate bottom cross-shelf transport, both upstream (30°S) and downstream (34°S) of the separation zone of the East Australian Current (EAC). Bottom transport was estimated and assessed against Ekman theory, showing consistent results for a number of different formulations of the boundary layer thickness. Net bottom cross-shelf transport was onshore at all locations. Ekman theory indicates that up to 64% of the transport variability is driven by the along-shelf bottom stress. Onshore transport in the bottom boundary layer was more intense and frequent upstream than downstream, occurring 64% of the time at 30°S. Wind-driven surface Ekman transport estimates did not balance the bottom cross-shelf flow. At both locations, strong variability was found in bottom water transport at periods of approximately 90-100 days. This corresponds with periodicity in EAC fluctuations and eddy shedding as evidenced from altimeter observations, highlighting the EAC as a driver of variability in the continental shelf waters. Ocean glider and HF radar observations were used to identify the bio-physical response to an EAC encroachment event, resulting in a strong onshore bottom flow, the uplift of cold slope water, and elevated coastal chlorophyll concentrations.

Schaeffer, A.; Roughan, M.; Wood, J. E.

2014-08-01

328

DNS of laminar/turbulent boundary layer transition induced by solid obstacles  

NASA Astrophysics Data System (ADS)

Direct numerical simulation is used to investigate how boundary layer transition is affected by the shape and size of an isolated obstacle whose size is of the order of the boundary layer thickness. The Navier-Stokes equations are discretized by means of an energy-conserving second-order staggered finite-difference method, and the geometrical complexity associated with the obstacle is handled through the immersed-boundary technique. A series of simulations have been performed by varying: i) the obstacle shape (cylinders and prisms with rectangular and triangular base); ii) the roughness height (as a fraction of the boundary layer thickness); iii) the width of the obstacle; iv) the Reynolds number of the incoming boundary layer. We have monitored the vorticity dynamics of the structures which are shed past the obstacle, and observed the concurrence of two mechanisms which promote transition to turbulence, namely the unsteady shear layer separation at the top edge of the obstacle, and the regeneration of quasi-streamwise vortices at the sides of the obstacle. The validity of semi-empirical transition criteria based on a suitably defined roughness Reynolds number will also be discussed, and associated with the physical mechanisms responsible for the self-sustainment of the disturbances.

Orlandi, Paolo; Bernardini, Matteo; Pirozzoli, Sergio

2011-11-01

329

Hypersonic Boundary Layer Stability over a Flared Cone in a Quiet Tunnel  

NASA Technical Reports Server (NTRS)

Hypersonic boundary layer measurements were conducted over a flared cone in a quiet wind tunnel. The flared cone was tested at a freestream unit Reynolds number of 2.82x106/ft in a Mach 6 flow. This Reynolds number provided laminar-to-transitional flow over the model in a low-disturbance environment. Point measurements with a single hot wire using a novel constant voltage anemometry system were used to measure the boundary layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the laminar-to-transitional state of the boundary layer and to identify instability modes. Results suggest that the second mode disturbances were the most unstable and scaled with the boundary layer thickness. The integrated growth rates of the second mode compared well with linear stability theory in the linear stability regime. The second mode is responsible for transition onset despite the existence of a second mode sub-harmonic. The sub-harmonic wavelength also scales with the boundary layer thickness. Furthermore, the existence of higher harmonics of the fundamental suggests that non-linear disturbances are not associated with high free stream disturbance levels.

Lachowicz, Jason T.; Chokani, Ndaona; Wilkinson, Stephen P.

1996-01-01

330

Hypersonic Boundary Layer Stability Experiments in a Quiet Wind Tunnel with Bluntness Effects  

NASA Technical Reports Server (NTRS)

Hypersonic boundary layer measurements over a flared cone were conducted in a Mach 6 quiet wind tunnel at a freestream unit Reynolds number of 2.82 million/ft. This Reynolds number provided laminar-to-transitional flow over the cone model in a low-disturbance environment. Four interchangeable nose-tips, including a sharp-tip, were tested. Point measurements with a single hot-wire using a novel constant voltage anemometer were used to measure the boundary layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the transitional state of the boundary layer and to identify instability modes. Results suggest that second mode disturbances were the most unstable and scaled with the boundary layer thickness. The second mode integrated growth rates compared well with linear stability theory in the linear stability regime. The second mode is responsible for transition onset despite the existence of a second mode subharmonic. The subharmonic disturbance wavelength also scales with the boundary layer thickness. Furthermore, the existence of higher harmonics of the fundamental suggests that nonlinear disturbances are not associated with 'high' free stream disturbance levels. Nose-tip radii greater than 2.7% of the base radius completely stabilized the second mode.

Lachowicz, Jason T.; Chokani, Ndaona

1996-01-01

331

Impact Wind Farms on the Marine Atmospheric Boundary Layer  

NASA Astrophysics Data System (ADS)

We introduce a new, validated wind farm parametrization (Explicit Wake Parametrization, EWP) which is based on the assumption that the downstream propagation of a single turbine wake can be described by a turbulent diffusion process. Thus, the downstream velocity deficit distribution can be described explicitly. Additionally, it allows us to take into account turbine interactions, making it possible to determine the unresolved turbine hub height velocities. Both the EWP wind farm parametrization and the wind farm scheme available in the Weather Research & Forecasting Model (WRF) have been validated against in situ measurements from Horns Rev I (A large offshore wind farm consisting of 80 2MW turbines situated near the west coast of Denmark). The main quantities of interest are the thrust applied to the flow, a consequence of the energy extracted by the wind turbines which determines mainly the wind farm wake extension (around 50 km for Horns Rev I) and the vertical velocity deficit distribution. Results show that the thrust in the WRF-WF scheme is overestimated inside the wind farm. We noticed that the velocity deficit propagates from the first turbine-containing-grid-cell up to the boundary layer top, which is in contrast to the theoretical expected expansion (confirmed by turbulence resolving models and wind tunnel results). The vertical expansion of the velocity deficit is a consequence of the additional turbulence source term in the WRF-WF scheme. The EWP scheme estimates the total amount of thrust correctly and is also able to follow the reduced thrust downstream since it considers the turbine interaction. From the good agreement with the far wake measurement, we can conclude that the formulation of the sub grid scale vertical extension of the velocity deficit must be correct. We will present results from WRF simulations in which we analyze the atmospheric response within the wake of wind farms resulting from the energy extraction of wind turbines. We place hypotetical wind farms in offshore areas with good wind resources near California. The wind farm sizes are choosen to be comparable to present ones errected in the European North Sea. Of particular interest is the influence of wind farms on the persistent stratocumulus clouds of the California coastal region, the thermal stratification of the boundary layer and wind stress changes due to reduced wind speeds near the surface. Although no wind farms are presently constructed along the Californian coast, fast and steady wind speeds makes it an attractive region for future offshore wind farms, especially if the first floating turbines near the coast of Norway are proven to be a success.

Volker, P.; Capps, S. B.; Huang, H. J.; Sun, F.; Badger, J.; Hahmann, A.

2012-12-01

332

The role of chemical boundary layers in regulating the thickness of continental and oceanic thermal boundary layers  

Microsoft Academic Search

An important feature of continents and oceans is that they are underlain by chemically distinct mantle, made intrinsically buoyant and highly viscous by melt depletion and accompanying dehydration, respectively. Of interest here are the influences of these preexisting chemical boundary layers on small-scale convective processes (as opposed to large-scale processes, which govern the drift of continents and the eventual fate

Cin-Ty Aeolus Lee; Adrian Lenardic; Catherine M. Cooper; Fenglin Niu; Alan Levander

2005-01-01

333

Influences on the Height of the Stable Boundary Layer as seen in Large-Eddy Simulations  

SciTech Connect

Numerical weather prediction (NWP) models and atmospheric dispersion models rely on parameterizations of planetary boundary layer height. In the case of a stable boundary layer, errors in boundary layer height estimation can result in gross errors in boundary-layer evolution and in prediction of turbulent mixing within the boundary layer. We use large-eddy simulations (LES) of moderately stable boundary layers to characterize the effects of various physical processes on stable boundary layers. The stable boundary layer height is assumed to be a function of surface friction velocity, geostrophic wind, Monin-Obukhov length, and the strength of the temperature inversion atop the stable boundary layer. This temperature inversion induces gravity waves with a frequency determined by the strength of the temperature inversion.

Kosovic, B; Lundquist, J K

2004-03-29

334

BLSTA: A boundary layer code for stability analysis  

NASA Technical Reports Server (NTRS)

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

Wie, Yong-Sun

1992-01-01

335

Boundary-Layer Meteorol (2010) 134:367-386 DOI 10.1007/s10546-009-9452-9  

E-print Network

· Synoptically-forced boundary layer 1 Introduction The atmospheric boundary layers is typically thought of underBoundary-Layer Meteorol (2010) 134:367-386 DOI 10.1007/s10546-009-9452-9 The Moist Boundary Layer layer in this transport. We expand a conceptual model of dry boundary-layer structure under synoptic

Reading, University of

336

Turbulence spectra of the FIRE stratocumulus-topped boundary layers  

NASA Technical Reports Server (NTRS)

There are at least four physical phenomena which contribute to the FIRE boundary layer turbulence spectra: boundary layer spanning eddies resulting from buoyant and mechanical production of turbulent kinetic energy (the microscale subrange); inertial subrange turbulence which cascades this energy to smaller scales; quasi-two dimensional mesoscale variations; and gravity waves. The relative contributions of these four phenomena to the spectra depend on the altitude of observation and variable involved (vertical velocity, temperature and moisture spectra are discussed). The physical origins of these variations in relative contribution are discussed. As expected from the theory (Kaimal et al., 1976), mixed layer scaling of the spectra (i.e., nondimensionalizing wavelength by Z(sub i) and spectral density by Z(sub i) and the dissipation rates) is successful for the microscale subrange and inertial subrange but not for the mesoscale subrange. The most striking feature of the normalized vertical velocity spectra is the lack of any significant mesoscale contribution. The spectral peak results from buoyant and mechanical production on scales similar to the boundary layer depth. The decrease in spectral density at larger scales results from the suppression of vertical velocity perturbations with large horizontal scales by the shallowness of the atmosphere. The spectral density also decreases towards smaller scales following the well known inertial subrange slope. There is a significant variation in the shape of the normalized spectra with height.

Young, G. S.; Nucciarone, J. J.; Albrecht, Bruce A.

1990-01-01

337

Polymer Effects on Heat Transport in Laminar Boundary Layer Flow  

E-print Network

We consider a laminar Blasius boundary-layer flow above a slightly heated horizontal plate and study the effect of polymer additives on the heat transport. We show that the action of the polymers can be understood as a space-dependent effective viscosity that first increases from the zero-shear value then decreases exponentially back to the zero-shear value as one moves away from the boundary. We find that with such an effective viscosity, both the horizontal and vertical velocities near the plate are decreased thus leading to an increase in the friction drag and a decrease in the heat transport in the flow.

Roberto Benzi; Emily S. C. Ching; Vivien W. S. Chu

2011-04-21

338

Numerical Simulation of a Spatially Evolving Supersonic Turbulent Boundary Layer  

NASA Technical Reports Server (NTRS)

The results from direct numerical simulations of a spatially evolving, supersonic, flat-plate turbulent boundary-layer flow, with free-stream Mach number of 2.25 are presented. The simulated flow field extends from a transition region, initiated by wall suction and blowing near the inflow boundary, into the fully turbulent regime. Distributions of mean and turbulent flow quantities are obtained and an analysis of these quantities is performed at a downstream station corresponding to Re(sub x)= 5.548 x10(exp 6) based on distance from the leading edge.

Gatski, T. B.; Erlebacher, G.

2002-01-01

339

Post-doctoral position in atmospheric boundary layer dynamics Analysis of BLLAST field experiment  

E-print Network

Post-doctoral position in atmospheric boundary layer dynamics Analysis of BLLAST field experiment. Background: The international BLLAST project (Boundary Layer Late Afternoon and Sunset Turbulence, http the daytime well-mixed, convective boundary layer (CBL), decays to an intermittently turbulent "residual layer

340

Snodar: a new instrument to measure the height of the boundary layer on the Antarctic plateau  

E-print Network

of the atmospheric boundary layer at Dome A and Dome C on the Antarctic plateau. Snodar, or Surface layer Non of the atmospheric boundary layer (ABL) over the Antarctic plateau is of interest to meteorologists, atmosphericSnodar: a new instrument to measure the height of the boundary layer on the Antarctic plateau Colin

Ashley, Michael C. B.

341

Local and Bi-Global Stability Analysis of a Plasma Actuated Boundary Layer  

E-print Network

Local and Bi-Global Stability Analysis of a Plasma Actuated Boundary Layer Mark Riherd and Subrata discharge actuators on a laminar, zero pressure gradi- ent boundary layer. Both methods indicate layer. The general behavior of boundary layer stabilization is consistent with experimental results

Roy, Subrata

342

Nonlinear Interaction of Frequency-Detuned Modes in Boundary Layers  

NASA Technical Reports Server (NTRS)

The present critical-layer asymptotic analysis for the nonlinear interaction of frequency-detuned modes in boundary-layer transition indicates that the interaction between a plane mode at the fundamental frequency and a pair of symmetrical oblique waves at the near-subharmonic frequency amplifies another pair of symmetrical oblique waves at the 'mirror frequency'. This type of interaction is stronger in the frequency-detuned case than the resonant triad case, and leads to a sharp drop in the oblique waves' peak with small detuning.

Mankbadi, Reda R.

1993-01-01

343

Atmospheric tides on Venus. III - The planetary boundary layer  

NASA Technical Reports Server (NTRS)

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

Dobrovolskis, A. R.

1983-01-01

344

Spatial simulation of boundary layer instability - Effects of surface roughness  

NASA Technical Reports Server (NTRS)

The effects of an isolated, two-dimensional roughness element on the spatial development of instability waves in boundary layers are investigated by numerically integrating the two-dimensional, time-dependent, incompressible Navier-Stokes equations, using a finite difference/Chebyshev discretization. It is shown that (high) inviscid frequencies have higher growth rates than Tollmien-Schlichting frequencies, indicating that disturbances growing in the separation zone are controlled by the inviscid instability of the shear layer at the edge of the separation zone.

Danabasoglu, G.; Bringen, S.; Streett, C. L.

1993-01-01

345

Boundary layer integral matrix procedure code modifications and verifications  

NASA Technical Reports Server (NTRS)

A summary of modifications to Aerotherm's Boundary Layer Integral Matrix Procedure (BLIMP) code is presented. These modifications represent a preliminary effort to make BLIMP compatible with other JANNAF codes and to adjust the code for specific application to rocket nozzle flows. Results of the initial verification of the code for prediction of rocket nozzle type flows are discussed. For those cases in which measured free stream flow conditions were used as input to the code, the boundary layer predictions and measurements are in excellent agreement. In two cases, with free stream flow conditions calculated by another JANNAF code (TDK) for use as input to BLIMP, the predictions and the data were in fair agreement for one case and in poor agreement for the other case. The poor agreement is believed to result from failure of the turbulent model in BLIMP to account for laminarization of a turbulent flow. Recommendations for further code modifications and improvements are also presented.

Evans, R. M.; Morse, H. L.

1974-01-01

346

Excitation of Crossflow Instabilities in a Swept Wing Boundary Layer  

NASA Technical Reports Server (NTRS)

The problem of crossflow receptivity is considered in the context of a canonical 3D boundary layer (viz., the swept Hiemenz boundary layer) and a swept airfoil used recently in the SWIFT flight experiment performed at Texas A&M University. First, Hiemenz flow is used to analyze localized receptivity due to a spanwise periodic array of small amplitude roughness elements, with the goal of quantifying the effects of array size and location. Excitation of crossflow modes via nonlocalized but deterministic distribution of surface nonuniformity is also considered and contrasted with roughness induced acoustic excitation of Tollmien-Schlichting waves. Finally, roughness measurements on the SWIFT model are used to model the effects of random, spatially distributed roughness of sufficiently small amplitude with the eventual goal of enabling predictions of initial crossflow disturbance amplitudes as functions of surface roughness parameters.

Carpenter, Mark H.; Choudhari, Meelan; Li, Fei; Streett, Craig L.; Chang, Chau-Lyan

2010-01-01

347

Effects of surface wave breaking on the oceanic boundary layer  

NASA Astrophysics Data System (ADS)

Existing laboratory studies suggest that surface wave breaking may exert a significant impact on the formation and evolution of oceanic surface boundary layer, which plays an important role in the ocean-atmosphere coupled system. However, present climate models either neglect the effects of wave breaking or treat them implicitly through some crude parameterization. Here we use a one-dimensional ocean model (General Ocean Turbulence Model, GOTM) to investigate the effects of wave breaking on the oceanic boundary layer on diurnal to seasonal time scales. First a set of idealized experiments are carried out to demonstrate the basic physics and the necessity to include wave breaking. Then the model is applied to simulating observations at the northern North Sea and the Ocean Weather Station Papa, which shows that properly accounting for wave breaking effects can improve model performance and help it to successfully capture the observed upper ocean variability.

He, Hailun; Chen, Dake

2011-04-01

348

Atmospheric surface and boundary layers of the Amazon Basin  

NASA Technical Reports Server (NTRS)

Three phases of work were performed: design of and preparation for the Amazon Boundary Layer Experiment (ABLE 2-A); execution of the ABLE 2-A field program; and analysis of the ABLE 2-A data. Three areas of experiment design were dealt with: surface based meteorological measurements; aircraft missions; and project meteorological support. The primary goal was to obtain a good description of the structure of the atmosphere immediately above the rain forest canopy (top of canopy to a few thousand meters), to describe this region during the growing daytime phase of the boundary layer; and to examine the nighttime stratified state. A secondary objective was to examine the role that deep convective storms play in the vertical transport of heat, water vapor, and other trace gases. While significant progress was made, much of the analysis remains to be done.

Garstang, Michael

1987-01-01

349

Finite-element numerical modeling of atmospheric turbulent boundary layer  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

350

Atmospheric boundary layer modification in the marginal ice zone  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

351

Nonparallel instability of supersonic and hypersonic boundary layers  

NASA Technical Reports Server (NTRS)

Multiple scaling technique is used to examine the nonparallel instability of supersonic and hypersonic boundary-layer flows to three dimensional (first mode) and two dimensional (second mode) disturbances. The method is applied to the flat plate boundary layer for a range of Mach numbers from 0 to 10. Growth rates of disturbances are calculated based on three different criteria: following the maximum of the mass-flow disturbance, using an integral of the disturbance kinetic energy, and using the integral of the square of the mass-flow amplitude. By following the maximum of the mass-flow disturbance, the calculated nonparallel growth rates are in good quantitative agreement with the experimental results at Mach number 4.5.

El-Hady, Nabil M.

1991-01-01

352

Nonlinear spectral dynamics of hypersonic laminar boundary layer flow  

NASA Astrophysics Data System (ADS)

The nonlinear interactions of the instability modes in a hypersonic laminar boundary layer undergoing natural transition are examined using bispectral analysis. The data are from an experiment of a boundary layer flow on a cooled-wall cone in a low-level free-stream disturbance hypersonic wind tunnel, and thus, the bispectral measurements are a good representation of the natural transition processes. The bispectral analysis shows that in the initial stages of transition the dominant nonlinear interaction is forcing by the fundamental to generate a harmonic. Subsequently, mutual forcing of the fundamental and harmonic yield a second harmonic. Difference interactions within the band of unstable disturbances centered on the fundamental and harmonic also generate a low frequency nonlinear interaction. At high amplitudes of the fundamental and harmonic a nonlinear interaction characterized by a low frequency modulation of the fundamental and harmonic then follows. This nonlinear interaction is then the most dominant and precedes the breakdown of the laminar flow.

Chokani, Ndaona

1999-12-01

353

Benthic boundary layer processes in the Lower Florida Keys  

USGS Publications Warehouse

This special issue of Geo-Marine Letters, "Benthic Boundary Layer Processes in the Lower Florida Keys," includes 12 papers that present preliminary results from the Key West Campaign. The Dry Tortugas and Marquesas Keys test sites were selected by a group of 115 scientists and technicians to study benthic boundary layer processes in a carbonate environment controlled by bioturbation and biogeochemical processes. Major activities included remote sediment classification; high-frequency acoustic scattering experiments; sediment sampling for radiological, geotechnical, biological, biogeochemical, physical, and geoacoustic studies; and hydrodynamic studies using an instrumented tetrapod. All these data are being used to improve our understanding of the effects of environmental processes on sediment structure and behavior.

Lavoie, D.L.; Richardson, M.D.; Holmes, C.

1997-01-01

354

Turbulent boundary layer at moving surface of cylindrical body  

NASA Astrophysics Data System (ADS)

An analysis is made of the two dimensional turbulent boundary on the moving surface of a cylindrical body (a Rankine oval with an aspect ratio of 4) moving at constant velocity in an incompressible fluid. A numerical simulation is used in which the boundary layer is divided in accordance with a two layer model into inner and outer regions, for which different expressions for the turbulent transport coefficients are employed. The following integral characteristics are determined for the body: the work of the friction force as the body moves; the work expended on the motion of its surface; and (for separated flow) the work of the pressure force. These characteristics are compared with corresponding integral characteristics obtained for laminar flow, on the moving surface of a flat plate, and on a wing of infinite span whose contour is a Rankine oval.

Zubarev, V. M.

1986-02-01

355

Investigation of Turbulent Boundary-Layer Separation Using Laser Velocimetry  

NASA Technical Reports Server (NTRS)

Boundary-layer measurements realized by laser velocimetry are presented for a Much 2.9, two-dimensional, shock-wave/turbulent boundary-layer interaction containing an extensive region of separated flow. Mean velocity and turbulent intensity profiles were obtained from upstream of the interaction zone to downstream of the mean reattachment point. The superiority of the laser velocimeter technique over pressure sensors in turbulent separated flows is demonstrated by a comparison of the laser velocimeter data with results obtained from local pilot and static pressure measurements for the same flow conditions. The locations of the mean separation and reattachment points as deduced from the mean velocity measurements are compared to oil-now visualization results. Representative velocity probability density functions obtained in the separated now region are also presented. Critical to the success of this investigation were: the use of Bragg cell frequency shifting and artificial seeding of the now with submicron light-scattering particles.

Modarress, D.; Johnson, D. A.

1979-01-01

356

Inverse boundary-layer technique for airfoil design  

NASA Technical Reports Server (NTRS)

A description is presented of a technique for the optimization of airfoil pressure distributions using an interactive inverse boundary-layer program. This program allows the user to determine quickly a near-optimum subsonic pressure distribution which meets his requirements for lift, drag, and pitching moment at the desired flow conditions. The method employs an inverse turbulent boundary-layer scheme for definition of the turbulent recovery portion of the pressure distribution. Two levels of pressure-distribution architecture are used - a simple roof top for preliminary studies and a more complex four-region architecture for a more refined design. A technique is employed to avoid the specification of pressure distributions which result in unrealistic airfoils, that is, those with negative thickness. The program allows rapid evaluation of a designed pressure distribution off-design in Reynolds number, transition location, and angle of attack, and will compute an airfoil contour for the designed pressure distribution using linear theory.

Henderson, M. L.

1979-01-01

357

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

358

Numerical solution of the resistive magnetohydrodynamic boundary-layer equations  

SciTech Connect

Three different techniques are presented for numerical solution of the equations governing the boundary layer of resistive magnetohydrodynamic tearing and interchange instabilities in toroidal geometry. Excellent agreement among these methods and with analytical results provides confidence in the correctness of the results. Solutions obtained in regimes where analytical medthods fail indicate a new scaling for the tearing mode as well as the existence of a new regime of stability.

Glasser, A.H.; Jardin, S.C.; Tesauro, G.

1983-10-01

359

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

360

Laboratory simulation of rotating atmospheric boundary layer flows over obstacles  

Microsoft Academic Search

Summary  The present study fits in the frame of a research program concerning in general the dynamics of airflow in the atmospheric\\u000a boundary layer and in particular the influence of terrestrial rotation on the movements of air masses interacting with natural\\u000a extended obstacles (mountains). The experiment has been performed by the method of hydraulic simulation, using schematic models\\u000a at reduced scale

S. Alessio; L. Briatore; A. Longhetto; G. Chabert D'Hières; H. Didelle

1983-01-01

361

Analysis of Coherent Structures Within the Atmospheric Boundary Layer  

Microsoft Academic Search

Large-eddy simulation has become an important tool for the study of the atmospheric boundary layer. However, since large-eddy\\u000a simulation does not simulate small scales, which do interact to some degree with large scales, and does not explicitly resolve\\u000a the viscous sublayer, it is reasonable to ask if these limitations affect significantly the ability of large-eddy simulation\\u000a to simulate large-scale coherent

J. Huang; M. Cassiani; J. D. Albertson

2009-01-01

362

Modeling of a tidal bottom boundary layer with suspended sediment  

Microsoft Academic Search

A one-dimensional model of the vertical exchange of suspended sediment in a tidal boundary layer is proposed. The model includes two linearized momentum equations for the horizontal velocity components and a series of advection–diffusion equations for concentrations of suspended sediment of specific size. Turbulence generated at the sea-bed is computed with the aid of a two-equation closure describing the time–space

G. Chapalain; L. Thais; H. Smaoui

1999-01-01

363

LASTRAC.3d: Transition Prediction in 3D Boundary Layers  

NASA Technical Reports Server (NTRS)

Langley Stability and Transition Analysis Code (LASTRAC) is a general-purpose, physics-based transition prediction code released by NASA for laminar flow control studies and transition research. This paper describes the LASTRAC extension to general three-dimensional (3D) boundary layers such as finite swept wings, cones, or bodies at an angle of attack. The stability problem is formulated by using a body-fitted nonorthogonal curvilinear coordinate system constructed on the body surface. The nonorthogonal coordinate system offers a variety of marching paths and spanwise waveforms. In the extreme case of an infinite swept wing boundary layer, marching with a nonorthogonal coordinate produces identical solutions to those obtained with an orthogonal coordinate system using the earlier release of LASTRAC. Several methods to formulate the 3D parabolized stability equations (PSE) are discussed. A surface-marching procedure akin to that for 3D boundary layer equations may be used to solve the 3D parabolized disturbance equations. On the other hand, the local line-marching PSE method, formulated as an easy extension from its 2D counterpart and capable of handling the spanwise mean flow and disturbance variation, offers an alternative. A linear stability theory or parabolized stability equations based N-factor analysis carried out along the streamline direction with a fixed wavelength and downstream-varying spanwise direction constitutes an efficient engineering approach to study instability wave evolution in a 3D boundary layer. The surface-marching PSE method enables a consistent treatment of the disturbance evolution along both streamwise and spanwise directions but requires more stringent initial conditions. Both PSE methods and the traditional LST approach are implemented in the LASTRAC.3d code. Several test cases for tapered or finite swept wings and cones at an angle of attack are discussed.

Chang, Chau-Lyan

2004-01-01

364

Large Eddy Simulation of the ventilated wave boundary layer  

Microsoft Academic Search

A Large Eddy Simulation (LES) of (1) a fully developed turbulent wave boundary layer and (2) case 1 subject to ventilation (i.e., suction and injection varying alternately in phase) has been performed, using the Smagorinsky subgrid-scale model to express the subgrid viscosity. The model was found to reproduce experimental results well. However, in case 1, the near-bed ensemble averaged velocity

I. P. Lohmann; J. Fredsøe; B. M. Sumer; E. D. Christensen

2006-01-01

365

Vortex/boundary-layer interactions: Data report, volume 1  

NASA Technical Reports Server (NTRS)

This report summarizes the work done under NASA Grant NAGw-581, Vortex/Boundary Layer Interactions. The experimental methods are discussed in detail and numerical results are presented, but are not fully interpreted. This report should be useful to anyone who wishes to make further use of the data (available on floppy disc or magnetic tape) for the development of turbulence models or the validation of predictive methods. Journal papers are in course of preparation.

Cutler, A. D.; Bradshaw, P.

1987-01-01

366

A pulsed CO2 Doppler lidar for boundary layer monitoring  

NASA Technical Reports Server (NTRS)

A monostatic, master oscillator power amplifier (MOPA), CO2 pulsed Doppler lidar was constructed and tested. The system is compact (120 x 60 cm), operates at high pulse repetition rates (greater than 1 kHz) and is intended for simultaneous Doppler/Differential Absorption Lidar (DIAL) monitoring of the planetary boundary layer. Details of the system design, hard target calibrations, and aerosol returns are presented.

Pearson, Guy N.

1992-01-01

367

Turbulence observations of the nearshore wave bottom boundary layer  

Microsoft Academic Search

Field observations of turbulence and sediment suspension in the nearshore wave bottom boundary layer obtained during the Duck94 field experiment on the North Carolina coast showed the generation of near-bed turbulence to be highly intermittent. The intermittent nature of the flow was examined by applying homogeneous isotropic turbulence laws over small windows of data. The time-varying estimates of turbulent kinetic

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

2006-01-01

368

Streamline-curvature effect in three-dimensional boundary layers  

NASA Technical Reports Server (NTRS)

The effect of including wall and streamline curvature terms in swept-wing boundary-layer stability calculations is studied. The linear disturbance equations are cast on a fixed, body-intrinsic, curvilinear coordinate system. Those nonparallel terms which contribute mainly to the streamline-curvature effect are retained in this formulation and approximated by their local finite-difference values. Convex-wall curvature has a stabilizing effect, while streamline curvature is destabilizing if the curvature exceeds a critical value.

Reed, Helen L.; Lin, Ray-Sing; Petraglia, Media M.

1992-01-01

369

System identification and control of a turbulent boundary layer  

NASA Astrophysics Data System (ADS)

An experimental investigation is made into the active control of the near-wall region of a turbulent boundary layer using a linear feed-forward control algorithm. A wall-based detection scheme is described which effectively detects coherent structures and predicts downstream flow behavior. A simple demonstration, using three wall-based sensors and a single actuator, achieves a maximum of 31% reduction in urms and 17% reduction in prms.

Rathnasingham, Ruben; Breuer, Kenneth S.

1997-07-01

370

A kappa-epsilon calculation of transitional boundary layers  

NASA Technical Reports Server (NTRS)

A recently proposed kappa-epsilon model for low Reynolds number turbulent flows was modified by introducing a new damping function f(sub mu). The modified model is used to calculate the transitional boundary layer over a flat plate with different freestream turbulence levels. It is found that the model could mimic the transitional flow. However, the predicted transition is found to be sensitive to the initial conditions.

Yang, Z.; Shih, T. H.

1992-01-01

371

Boundary Layer Transition Experiments in Support of the Hypersonics Program  

NASA Technical Reports Server (NTRS)

Two experimental boundary layer transition studies in support of fundamental hypersonics research are reviewed. The two studies are the HyBoLT flight experiment and a new ballistic range effort. Details are provided of the objectives and approach associated with each experimental program. The establishment of experimental databases from ground and flight are to provide better understanding of high-speed flows and data to validate and guide the development of simulation tools.

Berry, Scott A.; Chen, Fang-Jenq; Wilder, Michael C.; Reda, Daniel C.

2007-01-01

372

Numerical simulation of shock/turbulent boundary layer interaction  

NASA Technical Reports Server (NTRS)

Most flows of aerodynamic interest are compressible and turbulent. However, our present knowledge on the structures and mechanisms of turbulence is mostly based on incompressible flows. In the present work, compressibility effects in turbulent, high-speed, boundary layer flows are systematically investigated using the Direct Numerical Simulation (DNS) approach. Three-dimensional, time-dependent, fully nonlinear, compressible Navier-Stokes equations were numerically integrated by high-order finite-difference methods; no modeling for turbulence is used during the solution because the available resolution is sufficient to capture the relevant scales. The boundary layer problem deals with fully-turbulent compressible flows over flat geometries. Apart from its practical relevance to technological flows, turbulent compressible boundary layer flow is the simplest experimentally realizable turbulent compressible flow. Still, measuring difficulties prohibit a detailed experimental description of the flow, especially in the near-wall region. DNS studies provide a viable means to probe the physics of compressible turbulence in this region. The focus of this work is to explore the paths of energy transfer through which compressible turbulence is sustained. The structural similarities and differences between the incompressible and compressible turbulence are also investigated. The energy flow patterns or energy cascades are found to be directly related to the evolution of vortical structures which are generated in the near-wall region. Near-wall structures, and mechanisms which are not readily accessible through physical experiments are analyzed and their critical role on the evolution and the behavior of the flow is documented extensively.

Biringen, Sedat; Hatay, Ferhat F.

1993-01-01

373

Non-methane hydrocarbons in the Arctic boundary layer  

NASA Astrophysics Data System (ADS)

C 2-C 7 non-methane hydrocarbons were measured in clean maritime boundary layer air at latitudes between 53°N and 81°N. Measurements were made as part of the Arctic ice and environmental variability cruise aboard RRS James Clark Ross using a high sensitivity automated gas chromatography system. The data were collected during summer 1999, a period of continuous Arctic sunlight. Hydrocarbons of anthropogenic origin were observed to decrease in concentration with increasing latitude, a combination of dispersion and extensive atmospheric chemical processing. At high latitudes, low boundary layer conditions were common and species of exclusively anthropogenic origin reached highly stable although non-zero values (e.g. acetylene 27.8±2.4 pptV). A number of hydrocarbons believed to be of oceanic origin showed wide variability in these regions of atmospheric boundary layer stability (average ethene=37.2±20.9 pptV), highlighting inhomogeneity in the ocean to atmosphere flux rates. Whilst substantial increases in biological activity and productivity in the marginal ice zone have been previously reported, no evidence for increased biogenic hydrocarbon emissions were observed during this cruise. Removal mechanisms for atmospheric hydrocarbons were generally dominated by OH chemistry. Under clean maritime conditions the observed iso-/ n pentane and butane ratios were in good agreement with published sea-fluxes. Using the relative ratios of iso-/ n-butane and iso-butane/propane, there was evidence of significant chlorine atom chemistry at these high latitudes.

Hopkins, J. R.; Jones, I. D.; Lewis, A. C.; McQuaid, J. B.; Seakins, P. W.

374

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

375

Turbulent boundary layer over porous surfaces with different surface geometries  

NASA Technical Reports Server (NTRS)

The turbulent boundary layer over three porous walls with different surface geometries was studied in order to investigate the individual influences of porosity and small roughness, as well as their combined effects, on turbulent boundary layer behavior. The tests were conducted in a 2 m x 2 m tunnel on a large axisymmetric model at speeds corresponding to Re(L) = 5,000,000-6,000,000. The development of the turbulent boundary layer was compared for that of sintered metal, bonded screening, and perforated sheet and then to that for the flow over a solid smooth wall and a solid, sand-roughened wall. The comparisons reveal that the effect of porosity is to shift the logarithmic region of the wall law down by a certain amount from the solid wall results and to increase the skin friction values by about 30-40%. The downward shift of the logarithmic region of the wall law and the increase of the skin friction value by the combined effects of small roughness and porosity are found to be roughly the sum of their individual effects.

Kong, F. Y.; Schetz, J. A.

1982-01-01

376

Vortex Generator Induced Flow in a High Re Boundary Layer  

NASA Astrophysics Data System (ADS)

Stereoscopic Particle Image Velocimetry measurements have been conducted in cross-planes behind three different geometries of Vortex Generators (VGs) in a high Reynolds number boundary layer. The VGs have been mounted in a cascade producing counter-rotating vortices and the downstream flow development was examined. Three VG geometries were investigated: rectangular, triangular and cambered. The various VG geometries tested are seen to produce different impacts on the boundary layer flow. Helical symmetry of the generated vortices is confirmed for all investigated VG geometries in this high Reynolds number boundary layer. From the parameters resulting from this analysis, it is observed at the most upstream measurement position that the rectangular and triangular VGs produce vortices of similar size, strength and velocity induction whilst the cambered VGs produce smaller and weaker vortices. Studying the downstream development in the ensemble and spanwise averaged measurements, it is observed that the impact from the rectangular and triangular VGs differs. For the rectangular VGs, self-similarity in the streamwise component was confirmed.

Velte, C. M.; Braud, C.; Coudert, S.; Foucaut, J.-M.

2014-12-01

377

Numerical Investigation of a Fuselage Boundary Layer Ingestion Propulsion Concept  

NASA Technical Reports Server (NTRS)

In the present study, a numerical assessment of the performance of fuselage boundary layer ingestion (BLI) propulsion techniques was conducted. This study is an initial investigation into coupling the aerodynamics of the fuselage with a BLI propulsion system to determine if there is sufficient potential to warrant further investigation of this concept. Numerical simulations of flow around baseline, Boundary Layer Controlled (BLC), and propelled boundary layer controlled airships were performed. Computed results showed good agreement with wind tunnel data and previous numerical studies. Numerical simulations and sensitivity analysis were then conducted on four BLI configurations. The two design variables selected for the parametric study of the new configurations were the inlet area and the inlet to exit area ratio. Current results show that BLI propulsors may offer power savings of up to 85% over the baseline configuration. These interim results include the simplifying assumption that inlet ram drag is negligible and therefore likely overstate the reduction in power. It has been found that inlet ram drag is not negligible and should be included in future analysis.

Elmiligui, Alaa A.; Fredericks, William J.; Guynn, Mark D.; Campbell, Richard L.

2013-01-01

378

Improving Subtropical Boundary Layer Cloudiness in the 2011 NCEP GFS  

SciTech Connect

The current operational version of National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) shows significant low cloud bias. These biases also appear in the Coupled Forecast System (CFS), which is developed from the GFS. These low cloud biases degrade seasonal and longer climate forecasts, particularly of short-wave cloud radiative forcing, and affect predicted sea surface temperature. Reducing this bias in the GFS will aid the development of future CFS versions and contributes to NCEP's goal of unified weather and climate modelling. Changes are made to the shallow convection and planetary boundary layer parameterisations to make them more consistent with current knowledge of these processes and to reduce the low cloud bias. These changes are tested in a single-column version of GFS and in global simulations with GFS coupled to a dynamical ocean model. In the single-column model, we focus on changing parameters that set the following: the strength of shallow cumulus lateral entrainment, the conversion of updraught liquid water to precipitation and grid-scale condensate, shallow cumulus cloud top, and the effect of shallow convection in stratocumulus environments. Results show that these changes improve the single-column simulations when compared to large eddy simulations, in particular through decreasing the precipitation efficiency of boundary layer clouds. These changes, combined with a few other model improvements, also reduce boundary layer cloud and albedo biases in global coupled simulations.

Fletcher, J. K.; Bretherton, Christopher S.; Xiao, Heng; Sun, Ruiyu N.; Han, J.

2014-09-23

379

Thermocapillary Bubble Migration: Thermal Boundary Layers for Large Marangoni Numbers  

NASA Technical Reports Server (NTRS)

The migration of an isolated gas bubble in an immiscible liquid possessing a temperature gradient is analyzed in the absence of gravity. The driving force for the bubble motion is the shear stress at the interface which is a consequence of the temperature dependence of the surface tension. The analysis is performed under conditions for which the Marangoni number is large, i.e. energy is transferred predominantly by convection. Velocity fields in the limit of both small and large Reynolds numbers are used. The thermal problem is treated by standard boundary layer theory. The outer temperature field is obtained in the vicinity of the bubble. A similarity solution is obtained for the inner temperature field. For both small and large Reynolds numbers, the asymptotic values of the scaled migration velocity of the bubble in the limit of large Marangoni numbers are calculated. The results show that the migration velocity has the same scaling for both low and large Reynolds numbers, but with a different coefficient. Higher order thermal boundary layers are analyzed for the large Reynolds number flow field and the higher order corrections to the migration velocity are obtained. Results are also presented for the momentum boundary layer and the thermal wake behind the bubble, for large Reynolds number conditions.

Balasubramaniam, R.; Subramanian, R. S.

1996-01-01

380

The nonlinear development of Gortler vortices in growing boundary layers  

NASA Technical Reports Server (NTRS)

The development of Gortler vortices in boundary layers over curved walls in the nonlinear regime is investigated. The growth of the boundary layer makes a parallel flow analysis impossible except in the high wavenumber regime so in general the instability equations must be integrated numerically. Here the spanwise dependence of the basic flow is described using Fourier series expansion whilst the normal and streamwise variations are taken into account using finite differences. The calculations suggest that a given disturbance imposed at some position along the wall will eventually reach a local equilibrium state essentially independent of the initial conditions. In fact, the equilibrium state reached is qualitatively similar to the large amplitude high wave-number solution described asymptotically by Hall (1982). In general, it is found that the nonlinear interactions are dominated by a mean field type of interaction between the mean flow and the fundamental. Thus, even though higher harmonics of the fundamental are necessarily generated, most of the disturbance energy is confined to the mean flow correction and the fundamental. A major result of the calculations is finding that the downstream velocity field develops a strongly inflection character as the flow moves downstream. The latter result suggests that the major effect of Gortler vortices on boundary layers of practical importance might be to make them highly receptive to rapidly growing Rayleigh modes of instability.

Hall, Philip

1986-01-01

381

Physical processes within the nocturnal stratus-topped boundary layer  

SciTech Connect

Within the stratus-topped boundary layer many physical processes are involved: longwave radiation cooling, entrainment, latent heating, surface heating, solar heating, drizzling, etc. How all processes combine to maintain the turbulence within the stratus-topped boundary layer remains an unsolved problem. The large-eddy simulation technique is used to examine the first four physical processes mentioned. First, the contribution of each physical process to the thermodynamic differences between the updraft and downdraft branches of turbulent circulations is examined through a conditional sampling. Second, these mean thermodynamic differences are shown to express well the vertical distributions of heat and moisture fluxes within stratus-topped boundary layers. These provide a method to validate the process-partitioning technique. (This technique assumes that the net flux profile can be partitioned into different component-flux profiles according to physical processes and that each partitioned component flux is linear in height.) In this paper, the heat and moisture fluxes are process partitioned, and each component flux is found to contribute to the net flux in a way that is consistent with its corresponding process contribution to the mean thermodynamic differences between updrafts and downdrafts. Also, the net flux obtained by summing all component fluxes agrees well with that obtained directly from the large-eddy simulations.

Moeng, C.H.; Shen, S. (National Center for Atmospheric Research, Boulder, CO (United States)); Randall, D.A. (Colorado State Univ., Fort Collins (United States))

1992-12-15

382

Improving subtropical boundary layer cloudiness in the 2011 NCEP GFS  

NASA Astrophysics Data System (ADS)

The current operational version of National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) shows significant low cloud bias. These biases also appear in the Coupled Forecast System (CFS), which is developed from the GFS. These low cloud biases degrade seasonal and longer climate forecasts, particularly of short-wave cloud radiative forcing, and affect predicted sea surface temperature. Reducing this bias in the GFS will aid the development of future CFS versions and contributes to NCEP's goal of unified weather and climate modelling. Changes are made to the shallow convection and planetary boundary layer parameterisations to make them more consistent with current knowledge of these processes and to reduce the low cloud bias. These changes are tested in a single-column version of GFS and in global simulations with GFS coupled to a dynamical ocean model. In the single-column model, we focus on changing parameters that set the following: the strength of shallow cumulus lateral entrainment, the conversion of updraught liquid water to precipitation and grid-scale condensate, shallow cumulus cloud top, and the effect of shallow convection in stratocumulus environments. Results show that these changes improve the single-column simulations when compared to large eddy simulations, in particular through decreasing the precipitation efficiency of boundary layer clouds. These changes, combined with a few other model improvements, also reduce boundary layer cloud and albedo biases in global coupled simulations.

Fletcher, J. K.; Bretherton, C. S.; Xiao, H.; Sun, R.; Han, J.

2014-09-01

383

Review of Orbiter Flight Boundary Layer Transition Data  

NASA Technical Reports Server (NTRS)

In support of the Shuttle Return to Flight program, a tool was developed to predict when boundary layer transition would occur on the lower surface of the orbiter during reentry due to the presence of protuberances and cavities in the thermal protection system. This predictive tool was developed based on extensive wind tunnel tests conducted after the loss of the Space Shuttle Columbia. Recognizing that wind tunnels cannot simulate the exact conditions an orbiter encounters as it re-enters the atmosphere, a preliminary attempt was made to use the documented flight related damage and the orbiter transition times, as deduced from flight instrumentation, to calibrate the predictive tool. After flight STS-114, the Boundary Layer Transition Team decided that a more in-depth analysis of the historical flight data was needed to better determine the root causes of the occasional early transition times of some of the past shuttle flights. In this paper we discuss our methodology for the analysis, the various sources of shuttle damage information, the analysis of the flight thermocouple data, and how the results compare to the Boundary Layer Transition prediction tool designed for Return to Flight.

Mcginley, Catherine B.; Berry, Scott A.; Kinder, Gerald R.; Barnell, maria; Wang, Kuo C.; Kirk, Benjamin S.

2006-01-01

384

Görtler instability of the axisymmetric boundary layer along a cone  

NASA Astrophysics Data System (ADS)

Exact partial differential equations are derived to describe Görtler instability, caused by a weakly concave wall, of axisymmetric boundary layers with similar velocity profiles that are decomposed into a sequence of ordinary differential systems on the assumption that the solution can be expanded into inverse powers of local Reynolds number. The leading terms of the series solution are determined by solving a non-parallel version of Görtler’s eigenvalue problem and lead to a neutral stability curve and finite values of critical Görtler number and wave number for stationary and longitudinal vortices. Higher-order terms of the series solution indicate Reynolds-number dependence of Görtler instability and a limited validity of Görtler’s approximation based on the leading terms only. The present formulation is simply applicable to two-dimensional boundary layers of similar profiles, and critical Görtler number and wave number of the Blasius boundary layer on a flat plate are given by G2c = 1.23 and ?2c = 0.288, respectively, if the momentum thickness is chosen as the reference length.

ITOH, Nobutake

2014-10-01

385

LES and DNS of Shock-Boundary Layer Interactions.  

NASA Astrophysics Data System (ADS)

Large-eddy simulations (LES) of an incident oblique shock wave interacting with a flat-plate supersonic turbulent boundary layer at various flow/shock conditions are performed and the results are compared with the direct numerical simulation (DNS) data. The objectives are to evaluate the performance of compressible subgrid-scale (SGS) models in shock-turbulence flow regions and to study the effects of shock angle, Mach number and other parameters on the shock-boundary layer interactions. The filtered compressible Navier-Stokes equations are solved with a seventh-order Monotonicity-Preserving scheme for the Euler fluxes and a sixth-order compact scheme for the viscous terms. Comparison of DNS and LES results reveal the significance of the SGS model in supersonic boundary layer flow, particularly in the shock-turbulence regions. Due to its excessive dissipative nature, the standard Smagorinsky and gradient type models are found to predict a significantly larger mean separation bubble size when compared to the DNS data. In contrast, the predicted results by the scale-similarity, mixed or dynamic Smagorinsky models are found to be in reasonably good agreement with the DNS. Similar trends are observed for all the major flow variables. In general, the dynamic models, though computationally expensive, are found to generate better results when compared to other models.

Jammalamadaka, Avinash; Li, Zhaorui; Jaberi, Farhad

2009-11-01

386

Coupled wake boundary layer model of wind-farms  

E-print Network

We present and test a coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a wind-farm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall wind-farm boundary layer structure. The wake expansion/superposition model captures the effect of turbine positioning, while the top-down portion adds the interaction between the wind-turbine wakes and the atmospheric boundary layer. Each portion of the model requires specification of a parameter that is not known a-priori. For the wake model the wake expansion coefficient is required, while the top-down model requires an effective span-wise turbine spacing within which the model's momentum balance is relevant. The wake expansion coefficient is obtained by matching the predicted mean velocity at the turbine from both approaches, while the effective span-wise turbine spacing depends on turbine positioning and thus can be determined from the wake expansion...

Stevens, Richard J A M; Meneveau, Charles

2014-01-01

387

Multi-dimensional Longwave Forcing of Boundary Layer Cloud Systems  

SciTech Connect

The importance of multi-dimensional (MD) longwave radiative effects on cloud dynamics is evaluated in a large eddy simulation (LES) framework employing multi-dimensional radiative transfer (Spherical Harmonics Discrete Ordinate Method —SHDOM). Simulations are performed for a case of unbroken, marine boundary layer stratocumulus and a broken field of trade cumulus. “Snapshot” calculations of MD and IPA (independent pixel approximation —1D) radiative transfer applied to LES cloud fields show that the total radiative forcing changes only slightly, although the MD effects significantly modify the spatial structure of the radiative forcing. Simulations of each cloud type employing MD and IPA radiative transfer, however, differ little. For the solid cloud case, relative to using IPA, the MD simulation exhibits a slight reduction in entrainment rate and boundary layer TKE relative to the IPA simulation. This reduction is consistent with both the slight decrease in net radiative forcing and a negative correlation between local vertical velocity and radiative forcing, which implies a damping of boundary layer eddies. Snapshot calculations of the broken cloud case suggest a slight increase in radiative cooling, though few systematic differences are noted in the interactive simulations. We attribute this result to the fact that radiative cooling is a relatively minor contribution to the total energetics. For the cloud systems in this study, the use of IPA longwave radiative transfer is sufficiently accurate to capture the dynamical behavior of BL clouds. Further investigations are required in order to generalize this conclusion for other cloud types and longer time integrations. 1

Mechem, David B.; Kogan, Y. L.; Ovtchinnikov, Mikhail; Davis, Anthony B; Evans, K. F.; Ellingson, Robert G.

2008-12-20

388

Minnowbrook II 1997 Workshop on Boundary Layer Transition in Turbomachines  

NASA Technical Reports Server (NTRS)

The volume contains materials presented at the Minnowbrook II - 1997 Workshop on Boundary Layer Transition in Turbomachines, held at Syracuse University Minnowbrook Conference Center, New York, on September 7-10, 1997. The workshop followed the informal format at the 1993 Minnowbrook I workshop, focusing on improving the understanding of late stage (final breakdown) boundary layer transition, with the engineering application of improving design codes for turbomachinery in mind. Among the physical mechanisms discussed were hydrodynamic instabilities, laminar to turbulent transition, bypass transition, turbulent spots, wake interaction with boundary layers, calmed regions, and separation, all in the context of flow in turbomachinery, particularly in compressors and high and low pressure turbines. Results from experiments, DNS, computation, modeling and theoretical analysis were presented. Abstracts and copies of viewgraphs, a specifically commissioned summation paper prepared after the workshop, and a transcript of the extensive working group reports and discussions are included in this volume. They provide recommendations for future research and clearly highlight the need for continued vigorous research in the technologically important area of transition in turbomachines.

LaGraff John E. (Editor); Ashpis, David E. (Editor)

1998-01-01

389

Surface-cooling effects on compressible boundary-layer instability  

NASA Technical Reports Server (NTRS)

The influence of surface cooling on compressible boundary layer instability is discussed theoretically for both viscous and inviscid modes, at high Reynolds numbers. The cooling enhances the surface heat transfer and shear stress, creating a high heat transfer sublayer. This has the effect of distorting and accentuating the viscous Tollmien-Schlichting modes to such an extent that their spatial growth rates become comparable with, and can even exceed, the growth rates of inviscid modes, including those found previously. This is for moderate cooling, and it applies at any Mach number. In addition, the moderate cooling destabilizes otherwise stable viscous or inviscid modes, in particular triggering outward-traveling waves at the edge of the boundary layer in the supersonic regime. Severe cooling is also discussed as it brings compressible dynamics directly into play within the viscous sublayer. All the new cooled modes found involve the heat transfer sublayer quite actively, and they are often multi-structured in form and may be distinct from those observed in previous computational and experimental investigations. The corresponding nonlinear processes are also pointed out with regard to transition in the cooled compressible boundary layer. Finally, comparisons with Lysenko and Maslov's (1984) experiments on surface cooling are presented.

Seddougui, Sharon O.; Bowles, R. I.; Smith, F. T.

1990-01-01

390

Boundary-layer equations in generalized curvilinear coordinates  

NASA Technical Reports Server (NTRS)

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

Panaras, Argyris G.

1987-01-01

391

Advanced boundary layer transition measurement methods for flight applications  

NASA Technical Reports Server (NTRS)

In modern laminar flow flight research, it is important to understand the specific cause(s) of laminar to turbulent boundary-layer transition. Such information is crucial to the exploration of the limits of practical application of laminar flow for drag reduction on aircraft. The transition modes of interest in current flight investigations include the viscous Tollmien-Schlichting instability, the inflectional instability at laminar separation, and the crossflow inflectional instability, as well as others. This paper presents the results to date of research on advanced devices and methods used for the study of laminar boundary-layer transition phenomena in the flight environment. Recent advancements in the development of arrayed hot-film devices and of a new flow visualization method are discussed. Arrayed hot-film devices have been designed to detect the presence of laminar separation, and of crossflow vorticity. The advanced flow visualization method utilizes color changes in liquid-crystal coatings to detect boundary-layer transition at high altitude flight conditions. Flight and wind tunnel data are presented to illustrate the design and operation of these advanced methods. These new research tools provide information on disturbance growth and transition mode which is essential to furthering our understanding of practical design limits for applications of laminar flow technology.

Holmes, B. J.; Croom, C. C.; Gail, P. D.; Manuel, G. S.; Carraway, D. L.

1986-01-01

392

Atmospheric Boundary Layer of a pasture site in Amazônia  

NASA Astrophysics Data System (ADS)

A great effort has been made by the community of micrometeorology and planetary boundary layer for a better description of the properties of the Atmospheric Boundary Layer (ABL), such as its height, thermodynamics characteristics and its time evolution. This work aims to give a review of the main characteristics of Atmospheric Boundary Layer over a pasture site in Amazonia. The measurements dataset was carried out from 3 different LBA field campaigns: RBLE 3 (during the dry season from 1993), RaCCI (during the dry-to-wet transition season from 2002) and WetAMC (during the wet season from 1999), collected with tethered balloon, radiosondes and eddy correlation method in a pasture site in the southwestern Amazonia. Different techniques and instruments were used to estimate the AB?s properties. During the daytime, it was possible to observe that there is an abrupt growth of the Convective Boundary Layer (CBL) between 08 and 11 LT, with a stationary pattern between 14 and 17 LT. The maximum heights at late afternoon were around 1600 m during the dry season, whilst the wet season it only reached 1000 m. This is due to the lower surface turbulent sensible heat flux as the soil is wetter and the partition of energy is completely different between wet to the dry season. For the transition period (RaCCI 2002), it was possible to analyze and compare several estimates from different instruments and methods. It showed that the parcel method overestimates the heights of all measurements (mainly at 14 LT) due to the high incidence of solar radiation and superadiabatic gradients. The profile and Richardson number methods gave results very similar to estimate the height of the CBL. The onset of the Nocturnal Boundary Layer (NBL) occurs before the sunset (18 LT) and its height is reasonable stable during the night (typical values around 180-250 m). An alternative method (Vmax) which used the height of the maximum windspeed derived from a SODAR instrument during RaCCI 2002 was proposed and it showed to be satisfactory comparing with the others methods. Besides that, it has the advantage to have measurements each 30 min.

Trindade de Araújo Tiburtino Neves, Theomar; Fisch, Gilberto; Raasch, Siegfried

2013-04-01

393

Numerical analysis of a weighted-residual integral boundary-layer model for nonlinear  

E-print Network

Numerical analysis of a weighted-residual integral boundary-layer model for nonlinear dynamics-01.html #12;Numerical analysis of a weighted-residual integral boundary-layer model for nonlinear dynamics

Rimon, Elon

394

Effects of passive porous walls on hypersonic boundary layers  

NASA Astrophysics Data System (ADS)

We consider the effect of a passive porous wall on the first mode of a hypersonic boundary layer on a sharp slender cone. A theoretical stability analysis is used for large Mach number and large Reynolds number which includes the effect of curvature and of the attached shock. The formulation considers the scales appropriate to the first mode which is associated with Tollmien- Schlichting waves and this results in a triple-deck structure. The flow in the hypersonic boundary layer is coupled to the flow in the porous layer. We consider the porous layer on the cone surface to be a sheet perforated with cylindrical blind holes of equal spacingfootnotetextFedorov, A. V., Malmuth, N. D., Rasheed, A. and Hornung, H. G. AIAA J. 39, 605 (2001).. The linear stability analysis results in an eigenrelation, relating the streamwise wavenumber and the frequency of the disturbances. Neutral solutions will be presented, indicating a destabilizing efect of the porous wall. Spatial growth rates obtained will demonstrate that the porous wall leads to a significant increase in disturbance growth rates. In addition, the effect of nonlinearity is considered.

Stephen, Sharon; Michael, Vipin

2009-11-01

395

Turbulent Thermal Convection under Modified Boundary Conditions: An Experimental Study of Heat Transport and Boundary Layers  

NASA Astrophysics Data System (ADS)

In this thesis three sets of experiments of turbulent Rayleigh-B e nard convection with modified boundary conditions are presented. The first set of measurements were made in cylindrical cells with aspect ratio one and with various combinations of smooth and rough plates in the form of regularly-arrayed pyramids. The experimental results suggest that the Nu -- Ra relationship can be represented by the combination of two power laws, corresponding to the bulk dominant regime (exponent=1/2) and boundary layer dominant one (exponent=1/4) of the Grossmann-Lohse model. The behaviors of the coefficients of the two power laws suggest that the roughness of the plate can enhance the contribution of bulk and push the system to change from the boundary dominant state to bulk dominant state. A further examination of the individual plates reveal that the heat transport properties of smooth plates are insensitive to the surface and boundary conditions of the other plate of the same cell, whether smooth or rough, or whether under constant flux or constant temperature. The heat transport properties of the rough plates, on the other hand, appear to depend on surface and boundary conditions of the other plate of the same cell. In the second set of experiments we study the effect of polymer additives in two Rayleigh-Be nard convection cells, one with smooth top and bottom plates and the other with rough top and bottom plates. For the cell with smooth plates, a reduction of the measured Nusselt number (Nu) was observed. Furthermore, the amount of Nu reduction increases with increasing polymer concentration (c), reaching ~ 12% for c = 120 ppm and an apparent level-off thereafter. For the cell with rough plates, however, an enhancement (~ 4%) of Nu was observed when the polymer concentration is greater than 120 ppm. The third set of experiments investigates the properties of the velocity boundary layer in turbulent Rayleigh-Bénard convection in a cylindrical cell when it is tilted with respect to gravity. It is found that at small tilt angles (theta ? 1°), the measured viscous boundary layer thickness delta v scales with the Reynolds number Re with an exponent close to that for a Prandtl-Blasius laminar boundary layer. For larger tilt angles, the scaling exponent of deltav with Re decreases with theta. The normalized mean horizontal velocity profiles measured at the same tilt angle but with different Ra are found to have an invariant shape. But for different tilt angles, the shape of the normalized profiles is different.

Wei, Ping

396

Interaction between the atmospheric and oceanic boundary layers  

NASA Technical Reports Server (NTRS)

The two-layer system of an atmosphere over water bodies is reduced to a single-layer problem. Values of the interfacial quantities, such as the friction velocity, the surface velocity, the angles, alpha and beta, between the surface shear stress and the geostrophic wind velocity and the surface wind velocity, respectively, and the surface roughness, all of which depend upon external parameters, such as the geostrophic wind and stratifications, are obtained. The geostrophic drag coefficient, the geostrophic wind coefficient, and the angles alpha, and beta, of the turbulent flow at the sea-air interface are functions of a dimensionless number, mfG/kg, with S sub 1 and S sub 2 as two free stratification parameters. The surface roughness is uniquely determined from the geostrophic wind rather than from the wind profile in the boundary layer.

Yeh, G.-T.

1974-01-01

397

A complex-lamellar description of boundary layer transition  

NASA Astrophysics Data System (ADS)

Flow transition is important, in both practical and phenomenological terms. However, there is currently no method for identifying the spatial locations associated with transition, such as the start and end of intermittency. The concept of flow stability and experimental correlations have been used, however, flow stability only identifies the location where disturbances begin to grow in the laminar flow and experimental correlations can only give approximations as measuring the start and end of intermittency is difficult. Therefore, the focus of this work is to construct a method to identify the start and end of intermittency, for a natural boundary layer transition and a separated flow transition. We obtain these locations by deriving a complex-lamellar description of the velocity field that exists between a fully laminar and fully turbulent boundary condition. Mathematically, this complex-lamellar decomposition, which is constructed from the classical Darwin-Lighthill-Hawthorne drift function and the transport of enstrophy, describes the flow that exists between the fully laminar Pohlhausen equations and Prandtl's fully turbulent one seventh power law. We approximate the difference in enstrophy density between the boundary conditions using a power series. The slope of the power series is scaled by using the shape of the universal intermittency distribution within the intermittency region. We solve the complex-lamellar decomposition of the velocity field along with the slope of the difference in enstrophy density function to determine the location of the laminar and turbulent boundary conditions. Then from the difference in enstrophy density function we calculate the start and end of intermittency. We perform this calculation on a natural boundary layer transition over a flat plate for zero pressure gradient flow and for separated shear flow over a separation bubble. We compare these results to existing experimental results and verify the accuracy of our transition model.

Kolla, Maureen Louise

398

Ground-based remote sensing of the atmospheric boundary layer: 25 years of progress  

Microsoft Academic Search

The role of ground-based remote sensors in boundary-layer research is reviewed, emphasizing the contributions of radars, sodars, and lidars. The review begins with a brief comparison of the state of remote sensors in boundary-layer research 25 years ago with its present-day status. Next, a summary of the current capabilities of remote sensors for boundary-layer studies demonstrates that for boundary-layer depth

J. M. Wilczak; E. E. Gossard; W. D. Neff; W. L. Eberhard

1996-01-01

399

Numerical simulations of spatially developing, accelerating boundary layers  

NASA Astrophysics Data System (ADS)

We present the results of direct and large-eddy simulations of spatially developing boundary layers subjected to favorable pressure gradient, strong enough to cause reversion of the flow towards a quasi-laminar state. The numerical results compare well with experimental data. Visualization of the flow structures shows the well-known stabilization of the streaks, the re-orientation of outer layer vortices in the streamwise direction, and the appearance of turbulent spots in the re-transition region. Both instantaneous visualizations and turbulent statistics highlight the significant damping of wall-normal and spanwise fluctuations. The fast component of the pressure fluctuations appears to be the main driver of this process, contributing to reduce pressure fluctuations and, as a consequence, the energy redistribution term in the Reynolds stress budgets. The streamwise stresses, in whose budget a separate production term plays a role, do not decay but remain frozen at their upstream value. The decrease of wall-normal and spanwise fluctuations appears to be the main cause of the inner-layer stabilization, by disrupting the generation and subsequent growth of streaks, consistent with various models of the turbulence-generation cycle proposed in the literature. The outer layer seems to play a passive role in this process. The stretching and reorientation of the outer-layer vortices results in a more orderly and organized structure; since fewer ejections occur, the inner layer does not break this re-organization, which is maintained until re-transition begins.

Piomelli, Ugo; Yuan, Junlin

2013-10-01

400

Adaptive nonlinear polynomial neural networks for control of boundary layer/structural interaction  

NASA Technical Reports Server (NTRS)

The acoustic pressures developed in a boundary layer can interact with an aircraft panel to induce significant vibration in the panel. Such vibration is undesirable due to the aerodynamic drag and structure-borne cabin noises that result. The overall objective of this work is to develop effective and practical feedback control strategies for actively reducing this flow-induced structural vibration. This report describes the results of initial evaluations using polynomial, neural network-based, feedback control to reduce flow induced vibration in aircraft panels due to turbulent boundary layer/structural interaction. Computer simulations are used to develop and analyze feedback control strategies to reduce vibration in a beam as a first step. The key differences between this work and that going on elsewhere are as follows: that turbulent and transitional boundary layers represent broadband excitation and thus present a more complex stochastic control scenario than that of narrow band (e.g., laminar boundary layer) excitation; and secondly, that the proposed controller structures are adaptive nonlinear infinite impulse response (IIR) polynomial neural network, as opposed to the traditional adaptive linear finite impulse response (FIR) filters used in most studies to date. The controllers implemented in this study achieved vibration attenuation of 27 to 60 dB depending on the type of boundary layer established by laminar, turbulent, and intermittent laminar-to-turbulent transitional flows. Application of multi-input, multi-output, adaptive, nonlinear feedback control of vibration in aircraft panels based on polynomial neural networks appears to be feasible today. Plans are outlined for Phase 2 of this study, which will include extending the theoretical investigation conducted in Phase 2 and verifying the results in a series of laboratory experiments involving both bum and plate models.

Parker, B. Eugene, Jr.; Cellucci, Richard L.; Abbott, Dean W.; Barron, Roger L.; Jordan, Paul R., III; Poor, H. Vincent

1993-01-01

401

Low heat conduction in white dwarf boundary layers?  

E-print Network

X-ray spectra of dwarf novae in quiescence observed by Chandra and XMM-Newton provide new information on the boundary layers of their accreting white dwarfs. Comparison of observations and models allows us to extract estimates for the thermal conductivity in the accretion layer and reach conclusions on the relevant physical processes. We calculate the structure of the dense thermal boundary layer that forms under gravity and cooling at the white dwarf surface on accretion of gas from a hot tenuous ADAF-type coronal inflow. The distribution of density and temperature obtained allows us to calculate the strength and spectrum of the emitted X-ray radiation. They depend strongly on the values of thermal conductivity and mass accretion rate. We apply our model to the dwarf nova system VW Hyi and compare the spectra predicted for different values of the thermal conductivity with the observed spectrum. We find a significant deviation for all values of thermal conductivity that are a sizable fraction of the Spitzer conductivity. A good fit arises however for a conductivity of about 1% of the Spitzer value. This also seems to hold for other dwarf nova systems in quiescence. We compare this result with thermal conduction in other astrophysical situations. The highly reduced thermal conductivity in the boundary layer requires magnetic fields perpendicular to the temperature gradient. Locating their origin in the accretion of magnetic fields from the hot ADAF-type coronal flow we find that dynamical effects of these fields will lead to a spatially intermittent, localized accretion geometry at the white dwarf surface.

F. K. Liu; F. Meyer; E. Meyer-Hofmeister; V. Burwitz

2008-03-13

402

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

403

NUMERICAL MODEL OF A NON-STEADY ATMOSPHERIC PLANETARY BOUNDARY LAYER, BASED ON SIMILARITY  

E-print Network

NUMERICAL MODEL OF A NON-STEADY ATMOSPHERIC PLANETARY BOUNDARY LAYER, BASED ON SIMILARITY THEORY S November, 1991) Abstract. A numerical model of a non-stationary atmospheric planetary boundary layer (PBL boundary layer (PBL) subjected to diurnal variations. The typical pattern of diurnal changes

Fedorovich, Evgeni

404

Thickness of the Atmospheric Boundary Layer Above Dome A, Antarctica, during 2009  

E-print Network

Thickness of the Atmospheric Boundary Layer Above Dome A, Antarctica, during 2009 C. S. BONNER,1 M thick (Marks et al. 1999; Travouillon et al. 2003). The atmospheric boundary layer is the lowest region continuously turbulent over its entire depth (Stull 1988). The atmospheric boundary layer can extend up

Ashley, Michael C. B.

405

Large-Scale Atmospheric Forcing by Southeast Pacific Boundary-Layer Clouds: A Regional Model Study  

E-print Network

Large-Scale Atmospheric Forcing by Southeast Pacific Boundary-Layer Clouds: A Regional Model Study the radiative effect of boundary layer clouds over the Southeast Pacific on large-scale atmosphere circulation of the equator, and marine boundary layer stratocumulus clouds to the south. In a sensitivity experiment

Xie, Shang-Ping

406

Spatial statistics of marine boundary layer clouds Gregory M. Lewis1  

E-print Network

and Atmospheric Dynamics: Boundary layer processes; 3359 Meteorology and Atmospheric Dynamics: Radiative processesSpatial statistics of marine boundary layer clouds Gregory M. Lewis1 The Fields Institute, Toronto. Szczodrak (2004), Spatial statistics of marine boundary layer clouds, J. Geophys. Res., 109, D04104, doi:10

Lewis, Greg

407

Journal of the Atmospheric Sciences Comments on "Symmetric and Asymmetric Structures of Hurricane Boundary Layer in  

E-print Network

Boundary Layer in Coupled Atmosphere-Wave-Ocean Models and Observations" --Manuscript Draft-- Manuscript symmetric and asymmetric hurricane boundary-layer structures in a fully coupled atmosphere-28 wave Number: Full Title: Comments on "Symmetric and Asymmetric Structures of Hurricane Boundary Layer

Smith, Roger K.

408

Boundary-Layer Meteorol DOI 10.1007/s10546-014-9914-6  

E-print Network

Stochastic Model for Turbulent Dispersion in Atmospheric Boundary-Layer and Canopy Flows Tomer Duman for the highly inhomogeneous case of canopy flow. Application of this model to atmospheric boundary-layer). For atmospheric boundary-layer (ABL) flows, intermittency in can play a significant role, where the ratio between

Katul, Gabriel

409

Atmospheric Boundary Layer Studies with Unified RANS-LES and Dynamic LES Methods  

E-print Network

Atmospheric Boundary Layer Studies with Unified RANS-LES and Dynamic LES Methods Michael to neutrally stratified atmospheric boundary layer (NABL) simulations. The advantages of dynamic LES methods and dynamic methods to turbulent boundary-layer turbulence studies relevant to wind energy applications

Heinz, Stefan

410

Atmospheric sounding over the winter Kuroshio Extension: Effect of surface stability on atmospheric boundary layer structure  

E-print Network

: Effect of surface stability on atmospheric boundary layer structure, Geophys. Res. Lett., 33, L04703, doi the Pacific equatorial front [Hashizume et al., 2002] show marked changes in atmospheric boundary layer (ABL boundary layer structure Hiroki Tokinaga,1,2 Youichi Tanimoto,3,4 Masami Nonaka,5 Bunmei Taguchi,6 Tomohiro

Xie, Shang-Ping

411

Atmospheric Environment 40 (2006) 5057 Trace-gas mixing in isolated urban boundary layers  

E-print Network

Atmospheric Environment 40 (2006) 50­57 Trace-gas mixing in isolated urban boundary layers: Results. Keywords: Air pollution; CO; Ozone; Noy; Mixing; Convective atmospheric boundary layer 1. Introduction Luke over the full depth of growing convective atmospheric boundary layers (CABLs) have been scarce

412

Large-Scale Atmospheric Forcing by Southeast Pacific Boundary Layer Clouds: A Regional Model Study*  

E-print Network

Large-Scale Atmospheric Forcing by Southeast Pacific Boundary Layer Clouds: A Regional Model Study the radiative effect of boundary layer clouds over the southeast Pacific on large-scale atmosphere circulation of the equator, and marine boundary layer stratocumulus clouds to the south. In a sensitivity experiment

Wang, Yuqing

413

www.risoe.dk High Meteorology: Wind throughout the boundary-layer  

E-print Network

www.risoe.dk High Meteorology: Wind throughout the boundary-layer Sven-Erik Gryning, Hans E Monin-Obukhov wind profiles planetary boundary layer only, constant flux and based on Businger (-1 MOLzx -= #12;EWEC 06, Athens Monin-Obukhov wind profiles planetary boundary layer only, constant flux

414

BOUNDARY LAYER (BL) THERMAL EDDIES OVER A PINE FOREST FROM CARES 2010  

E-print Network

BOUNDARY LAYER (BL) THERMAL EDDIES OVER A PINE FOREST FROM CARES 2010 Gunnar Senum and Stephen instruments provide two independents means of measuring the vertical velocity of the boundary layer sampled, which was a ARRA purchase. The UHSAS measured the boundary- layer aerosol particle concentration from 55

415

Computation of three-dimensional mixed convective boundary layer flow  

NASA Technical Reports Server (NTRS)

The paper presents the numerical solution of heat and mass transfer during cross-flow (orthogonal) mixed convection. In this class of flow, a buoyancy-driven transport in the vertical direction and a forced convective flow in the horizontal direction results in a three-dimensional boundary layer structure adjacent to the plate. The rates of heat and mass transfer are determined by a combined influence of the two transport processes. The equations for the conservation of mass, momentum, energy, and species concentration were solved along with appropriate boundary conditions to determine the distributions of velocity components, temperature, and concentration across the thickness of the boundary layer at different locations on the plate. Results were expressed in dimensionless form using Reynolds number, Richardson number for heat transfer, Richardson number for mass transfer, Prandtl number, and Schmidt number as parameters. It was found that the transport is dominated by buoyancy at smaller vertical locations and at larger distances away from the forced convection leading edge. Effects of forced convection appeared to be very strong at smaller horizontal distances from the leading edge. The cross stream forced convection enhanced the rate of heat and mass transfer by a very significant amount.

Gadepalli, Prashandt; Rahman, Muhammad M.

1995-01-01

416

Damping Tollmien-Schlichting waves in a boundary layer using plasma actuators  

NASA Astrophysics Data System (ADS)

The response of a zero pressure gradient boundary layer modified by flow-wise oriented momentum injection similar to that of a plasma actuator is calculated using a two-dimensional (bi-global) stability analysis. It is found that the addition of momentum into the boundary layer has a significant impact on Tollmien-Schlichting waves, which may be damped by up to two orders of magnitude. Changes to the exponential growth rate of the perturbations are also measured. These stabilizing effects are largely due to the momentum addition modifying the downstream boundary layer profiles, but localized stabilization effects are also noted. The relative stabilization of the TS wave appears to be a linear function with respect to the ratio of the plasma-induced wall jet velocity under quiescent conditions and the free-stream velocity for lower levels of plasma actuation (i.e. velocity ratios less than 0.1). For higher levels of plasma actuation, the relative stabilization of the TS wave appears to be exponential with respect to the total momentum addition to the boundary layer by the plasma actuator.

Riherd, Mark; Roy, Subrata

2013-12-01

417

Role of the residual layer and large-scale subsidence on the development and evolution of the convective boundary layer  

NASA Astrophysics Data System (ADS)

Observations, mixed-layer theory and the Dutch Large-Eddy Simulation model (DALES) are used to analyze the dynamics of the boundary layer during an intensive operational period (1 July 2011) of the Boundary Layer Late Afternoon and Sunset Turbulence campaign. Continuous measurements made by remote sensing and in situ instruments in combination with radio soundings, and measurements done by remotely piloted aircraft systems and two manned aircrafts probed the vertical structure and the temporal evolution of the boundary layer during the campaign. The initial vertical profiles of potential temperature, specific humidity and wind, and the temporal evolution of the surface heat and moisture fluxes prescribed in the models runs are inspired by some of these observations. The research focuses on the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer. By using DALES, we show the importance of the dynamics of the boundary layer during the previous night in the development of the boundary layer at the morning. DALES numerical experiments including the residual layer are capable of modeling the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. These simulations show a large increase of the entrainment buoyancy flux when the residual layer is incorporated into the mixed layer. We also examine how the inclusion of the residual layer above a shallow convective boundary layer modifies the turbulent kinetic energy budget. Large-scale subsidence mainly acts when the boundary layer is fully developed, and, for the studied day, it is necessary to be considered to reproduce the afternoon observations. Finally, we also investigate how carbon dioxide (CO2) mixing ratio stored the previous night in the residual layer plays a fundamental role in the evolution of the CO2 mixing ratio during the following day.

Blay-Carreras, E.; Pino, D.; Vilà-Guerau de Arellano, J.; van de Boer, A.; De Coster, O.; Darbieu, C.; Hartogensis, O.; Lohou, F.; Lothon, M.; Pietersen, H.

2014-05-01

418

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

419

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

NASA Technical Reports Server (NTRS)

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

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

1951-01-01

420

Dynamical Properties of Vortex Furrows in Transitioning Boundary Layers  

NASA Astrophysics Data System (ADS)

A vortex filament simulation of the spatially growing transitional boundary layer reveals the presence of low speed streaks underlying furrow-like streamwise oriented folds in the surface vorticity layer (AIAA J. Vol. 48, 2010; Proc. ETC13, 2011). The putative hairpin vortices and packets widely observed in boundary layers are found to be an illusion created by assigning the status of structure to the visualized form of regions of rotational motion created by the vortex furrows. Thus, at best, hairpins roughly describe the shape taken by that part of the vorticity within the furrows that directly causes rotation while ignoring the ``invisible'' and considerable non-rotational part. The life history of the furrows is discussed here including a description of how they grow and the dynamics of the vorticity field within them. Long lived furrows represent ``factories'' within which initially spanwise vorticity progresses from arch to either one or two-lobed mushroom-like structures in a continuous stream. Furrows grow by this same process. At the heart of the furrow phenomenon is a self-reinforcing process by which streamwise vorticity begets more streamwise vorticity.

Bernard, Peter

2011-11-01

421

Determining Boundary-Layer Height from Aircraft Measurements  

NASA Astrophysics Data System (ADS)

The height of the atmospheric boundary layer (ABL) is an important variable in both observational studies and model simulations. The most commonly used measurement for obtaining ABL height is a rawinsonde profile. Mesoscale or regional scale models use a bulk Richardson number based on profiles of the forecast variables. Here we evaluate the limitations of several frequently-used approaches for defining ABL height from a single profile, and identify the optimal threshold value for each method if profiles are the only available measurements. Aircraft measurements from five field projects are used, representing a variety of ABL conditions including stable, convective, and cloud-topped boundary layers over different underlying surfaces. ABL heights detected from these methods were validated against the `true' value determined from aircraft soundings, where ABL height is defined as the top of the layer with significant turbulence. A detection rate was defined to denote how often the ABL height was correctly diagnosed with a particular method. The results suggest that the temperature gradient method provides the most reasonable estimates, although the detection rate and suitable detection criteria vary for different types of ABL. The Richardson number method, on the other hand, is in most cases inadequate or inferior to the other methods that were tried. The optimal range of the detection criteria is given for all ABL types examined in this study.

Dai, C.; Wang, Q.; Kalogiros, J. A.; Lenschow, D. H.; Gao, Z.; Zhou, M.

2014-09-01

422

The boundary layer beneath a Rankine-like vortex  

NASA Astrophysics Data System (ADS)

The three-dimensional boundary layer (BL) arising beneath a Rankine-like vortex (RLV) in a rotating right circular cylinder with a stationary horizontal base is investigated experimentally, using water as the working fluid and a dual-beam forward-scattering LDV apparatus with an He-Ne laser to determine BL and RLV velocity profiles. The theoretical background, boundary conditions, and experimental setup are described in detail, and the results for the outer flow and BL are presented in graphs. The BL is found to be laminar at disk-edge Reynolds number Re = 5000, transitional at Re = 10,000, and turbulent (over some parts of the disk) at Re = 15,000 or higher. The effectiveness of an outer-flow radial pressure gradient in stabilizing the BL at Re = 10,000-30,000 is shown to decrease with increasing Re.

Phillips, W. R. C.; Khoo, B. C.

1987-05-01

423

Tollmien-Schlichting/vortex interactions in compressible boundary layer flows  

NASA Technical Reports Server (NTRS)

The weakly nonlinear interaction of oblique Tollmien-Schlichting waves and longitudinal vortices in compressible, high Reynolds number, boundary-layer flow over a flat plate is considered for all ranges of the Mach number. The interaction equations comprise of equations for the vortex which is indirectly forced by the waves via a boundary condition, whereas a vortex term appears in the amplitude equation for the wave pressure. The downstream solution properties of interaction equations are found to depend on the sign of an interaction coefficient. Compressibility is found to have a significant effect on the interaction properties; principally through its impact on the waves and their governing mechanism, the triple-deck structure. It is found that, in general, the flow quantities will grow slowly with increasing downstream co-ordinate; i.e. in general, solutions do not terminate in abrupt, finite-distance 'break-ups'.

Blackaby, Nicholas D.

1993-01-01

424

Noise of a turbulent boundary layer flow over smooth and rough plates at low mach numbers  

Microsoft Academic Search

The spectral levels of the quadrupole noise generated by a boundary layer flow over a smooth surface are calculated. Explicit\\u000a dependences of the noise levels on the Reynolds number are obtained for the low-frequency and high-frequency ranges. It is\\u000a shown that the logarithmic zone of the velocity profile is responsible for the region of the quadrupole noise spectrum with\\u000a a

A. V. Smol’yakov

2001-01-01

425

Observed covariance between ecosystem carbon exchange and atmospheric boundary layer dynamics at a site in northern Wisconsin  

E-print Network

Observed covariance between ecosystem carbon exchange and atmospheric boundary layer dynamics 2004; published 17 April 2004. [1] Ecosystem CO2 exchange and atmosphere boundary layer (ABL) mixing interactions; 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 3322 Meteorology

Collett Jr., Jeffrey L.

426

Interaction of a Boundary Layer with a Turbulent Wake  

NASA Technical Reports Server (NTRS)

The objective of this grant was to study the transition mechanisms on a flat-plate boundary layer interacting with the wake of a bluff body. This is a simplified configuration presented and designed to exemplify the phenomena that occur in multi-element airfoils, in which the wake of an upstream element impinges on a downstream one. Some experimental data is available for this configuration at various Reynolds numbers. The first task carried out was the implementation and validation of the immersed-boundary method. This was achieved by performing calculations of the flow over a cylinder at low and moderate Reynolds numbers. The low-Reynolds number results are discussed, which is enclosed as Appendix A. The high-Reynolds number results are presented in a paper in preparation for the Journal of Fluid Mechanics. We performed calculations of the wake-boundary-layer interaction at two Reynolds numbers, Re approximately equal to 385 and 1155. The first case is discussed and a comparison of the two calculations is reported. The simulations indicate that at the lower Reynolds number the boundary layer is buffeted by the unsteady Karman vortex street shed by the cylinder. This is shown: long streaky structures appear in the boundary layer in correspondence of the three-dimensionalities in the rollers. The fluctuations, however, cannot be self-sustained due to the low Reynolds-number, and the flow does not reach a turbulent state within the computational domain. In contrast, in the higher Reynolds-number case, boundary-layer fluctuations persist after the wake has decayed (due, in part, to the higher values of the local Reynolds number Re achieved in this case); some evidence could be observed that a self-sustaining turbulence generation cycle was beginning to be established. A third simulation was subsequently carried out at a higher Reynolds number, Re=3900. This calculation gave results similar to those of the Re=l155 case. Turbulence was established at fairly low Reynolds number, as a consequence of the high level of the free-stream perturbation. An instantaneous flow visualization for that case is shown. A detailed examination of flow statistics in the transitional and turbulent regions, including the evolution of the turbulent kinetic energy (TKE) budget and frequency spectra showed the formation and evolution of turbulent spots characteristic of the bypass transition mechanism. It was also observed that the turbulent eddies achieved an equilibrium, fully developed turbulent states first, as evidenced by the early agreement achieved by the terms in the TKE budget with those observed in turbulent flows. Once a turbulent Reynolds stress profile had been established, the velocity profile began to resemble a turbulent one, first in the inner region and later in the outer region of the wall layer. An extensive comparison of the three cases, including budgets, mean velocity and Reynolds stress profiles and flow visualization, is included. The results obtained are also presented.

Piomelli, Ugo

2004-01-01

427

The interaction of synthetic jets with turbulent boundary layers  

NASA Astrophysics Data System (ADS)

In recent years, a promising approach to the control of wall bounded as well as free shear flows, using synthetic jet (oscillatory jet with zero-net-mass-flux) actuators, has received a great deal of attention. A variety of impressive flow control results have been achieved experimentally by many researchers including the vectoring of conventional propulsive jets, modification of aerodynamic characteristics of bluff bodies, control of lift and drag of airfoils, reduction of skin-friction of a flat plate boundary layer, enhanced mixing in circular jets, and control of external as well as internal flow separation and of cavity oscillations. More recently, attempts have been made to numerically simulate some of these flowfields. Numerically several of the above mentioned flow fields have been simulated primarily by employing the Unsteady Reynolds-Averaged Navier Stokes (URANS) equations with a turbulence model and a limited few by Direct Numerical Simulation (DNS). In simulations, both the simplified boundary conditions at the exit of the jet as well as the details of the cavity and lip have been included. In this dissertation, I describe the results of simulations for several two- and three-dimensional flowfields dealing with the interaction of a synthetic jet with a turbulent boundary layer and control of separation. These simulations have been performed using the URANS equations in conjunction with either one- or a two-equation turbulence model. 2D simulations correspond to the experiments performed by Honohan at Georgia Tech. and 3D simulations correspond to the CFD validation test cases proposed in the NASA Langley Research Center Workshop---"CFD Validation of Synthetic Jets and Turbulent Separation Control" held at Williamsburg VA in March 2004. The sources of uncertainty due to grid resolution, time step, boundary conditions, turbulence modeling etc. have been examined during the computations. Extensive comparisons for various flow variables are made with the experimental data; fair agreement is obtained.

Cui, Jing

428

Infrared Imaging of Boundary Layer Transition Flight Experiments  

NASA Technical Reports Server (NTRS)

The Hypersonic Thermodynamic Infrared Measurement (HYTHIRM) project is presently focused on near term support to the Shuttle program through the development of an infrared imaging capability of sufficient spatial and temporal resolution to augment existing on-board Orbiter instrumentation. Significant progress has been made with the identification and inventory of relevant existing optical imaging assets and the development, maturation, and validation of simulation and modeling tools for assessment and mission planning purposes, which were intended to lead to the best strategies and assets for successful acquisition of quantitative global surface temperature data on the Shuttle during entry. However, there are longer-term goals of providing global infrared imaging support to other flight projects as well. A status of HYTHIRM from the perspective of how two NASA-sponsored boundary layer transition flight experiments could benefit by infrared measurements is provided. Those two flight projects are the Hypersonic Boundary layer Transition (HyBoLT) flight experiment and the Shuttle Boundary Layer Transition Flight Experiment (BLT FE), which are both intended for reducing uncertainties associated with the extrapolation of wind tunnel derived transition correlations for flight application. Thus, the criticality of obtaining high quality flight data along with the impact it would provide to the Shuttle program damage assessment process are discussed. Two recent wind tunnel efforts that were intended as risk mitigation in terms of quantifying the transition process and resulting turbulent wedge locations are briefly reviewed. Progress is being made towards finalizing an imaging strategy in support of the Shuttle BLT FE, however there are no plans currently to image HyBoLT.

Berry, Scott A.; Horvath, Thomas J., Jr.; Schwartz, Richard; Ross, Martin; Anderson, Brian; Campbell, Charles H.

2008-01-01

429

Laser Doppler velocimeter measurements of boundary layer velocity and turbulent intensities in Mach 2.5 flow  

NASA Technical Reports Server (NTRS)

In recent years, the interest in developing a high-speed civil transport has increased. This has led to an increase in research activity on compressible supersonic flows, in particular the boundary layer. The structure of subsonic boundary layers has been extensively documented using conditional sampling techniques which exploit the knowledge of both u and v velocities. Researchers using these techniques have been able to explore some of the complex three-dimensional motions which are responsible for Reynolds stress production and transport in the boundary layer. As interest in turbulent structure has grown to include supersonic flows, a need for simultaneous multicomponent velocity measurements in these flows has developed. The success of conditional analysis in determining the characteristics of coherent motions and structures in the boundary layer relies on accurate, simultaneous measurement of two instantaneous velocity components.

Sewell, Jesse; Chew, Larry

1994-01-01

430

A High-Lift Building Block Flow: Turbulent Boundary Layer Relaminarization  

NASA Technical Reports Server (NTRS)

A working wind tunnel test facility has been constructed at the University of Notre Dame's Hessert Center. The relaminarization test facility has been constructed in the 1.5m x 1.5m (5ft x 5 ft) atmospheric wind tunnel and generates a Re(theta)=4694 turbulent boundary layer in nominally zero-pressure gradient before it is exposed to the Case #1 pressure gradient (K approximately equal to 4.2 x 10(exp -6), which is believed to be sufficient to achieve relaminarization. Future work to be conducted will include measuring the response of the turbulent boundary layer to the favorable pressure gradients created in the test facility and documenting this response in order to understand the underlying flow physics responsible for relaminarization. It is the goal of this research to have a better understanding of accelerated turbulent boundary layers which will aid in the development of future flow diagnostic utilities to be implemented in applied aerodynamic research.

Bourassa, Corey; Thomas, Flint O.; Nelson, Robert C.

2001-01-01

431

Effects of compressibility on boundary-layer turbulence  

NASA Technical Reports Server (NTRS)

A series of turbulence measurements in a subsonic compressible turbulent boundary-layer flow in the Mach number range of 0.1 to 0.7 is described. Measurements include detailed surveys of the turbulence intensities and Reynolds shear stresses, and other quantities such as the turbulent kinetic energy. These data are examined to bring out the effects of compressibility and show that the stream-wise and transverse fluctuations and the turbulent shear stress follow a universal scaling law. A preliminary attempt is made to examine some of the assumptions made in turbulence models commonly used in numerical codes for the calculation of compressible flows.

Acharya, M.

1976-01-01

432

Turbulent boundary-layer control with plasma spanwise travelling waves  

NASA Astrophysics Data System (ADS)

Arrays of dielectric-barrier-discharge plasma actuators have been designed to generate spanwise travelling waves in the turbulent boundary layer for possible skin-friction drag reductions. Particle image velocimetry was used to elucidate the modifications to turbulence structures created by the plasma spanwise travelling waves. It has been observed that the plasma spanwise travelling waves amalgamated streamwise vortices, lifting low-speed fluid from the near-wall region up and around the peripheries of their cores to form wide ribbons of low-speed streamwise velocity within the viscous sublayer.

Whalley, Richard D.; Choi, Kwing-So

2014-08-01

433

Aerodynamic heating for gaps in laminar and transitional boundary layers  

NASA Technical Reports Server (NTRS)

The presence of gaps, slots, and/or steps in a surface may significantly perturb a supersonic boundary layer. The paper discusses heat-transfer distributions for a variety of gap configurations which were obtained by placing instrumented inserts in a flat-plate structural carrier. The data were obtained in a 3.50 foot hypersonic wind tunnel at a freestream Mach number of 5.10 over a range of Reynolds number from 2,570,000 to 8,110,000. The variables of the test program included the freestream Reynolds number and the gap configuration, e.g., width, depth, step height, number, and orientation.

Bertin, J. J.; Goodrich, W. D.

1980-01-01

434

Regional scale evaporation and the atmospheric boundary layer  

NASA Technical Reports Server (NTRS)

In this review we briefly summarize some current models of evaporation and the atmospheric boundary layer (ABL) and discuss new experimental and computational oppurtunities that may aid our understanding of evaporation at these larger scales. In particular, consideration is given to remote sensing of the atmosphere, computational fluid dynamics and the role numerical models can play in understanding land-atmosphere interactions. These powerful modeling and measurement tools are allowing us to visualize and study spatial and temporal scales previously untouched, thereby increasing the oppurtunities to improve our understanding of land-atmosphere interaction.

Parlange, Marc B.; Eichinger, William E.; Albertson, John D.

1995-01-01

435

End-wall boundary layer prediction for axial compressors  

NASA Technical Reports Server (NTRS)

An integral boundary layer procedure has been developed for the computation of viscous and secondary flows along the annulus walls of an axial compressor. The procedure is an outgrowth and extension of the pitch-averaged methods of Mellor and Horlock. In the present work secondary flow theory is used to develop approximations for the velocity profiles inside a rotating blade row and for the blade force deficit terms in the momentum integral equations. The computer code based on this procedure has been iteratively coupled to a quasi-one-dimensional model for the external inviscid flow. Computed results are compared with measurements in a compressor cascade.

Sockol, P. M.

1978-01-01

436

End-wall boundary layer prediction for axial compressors  

NASA Technical Reports Server (NTRS)

An integral boundary layer procedure was developed for the computation of viscous and secondary flows along the annulus walls of an axial compressor. The procedure is an outgrowth and extension of the pitch-averaged methods of Mellor and Horlock. In the present work secondary flow theory is used to develop approximations for the velocity profiles inside a rotating blade row and for the blade force deficit terms in the momentum integral equations. The computer code based on this procedure was iteratively coupled to a quasi-one-dimensional model for the external inviscid flow. Computed results are compared with measurements in a compressor cascade.

Sockol, P. M.

1978-01-01

437

Measurements of a supersonic turbulent boundary layer with mass addition  

NASA Astrophysics Data System (ADS)

Boundary-layer measurements were carried out on two 8-deg sphere-cones with mass addition at a Mach Number of 2.5 and a freestream Reynolds Number of 8.86 million/m). These cones were fabricated from two different grades of porous materials. Measurements were made with two-dimensional LDV, from which the mean velocity, turbulence intensities, Reynolds stresses, eddy viscosity and mixing length were determined. Measurements were carried out for four different mass-addition rates at two stations on the model. Air was used as the injection gas.

Yanta, William J.; Collier, Arnold S.; Smith, Timothy S.

1989-01-01

438

Direct simulation of a turbulent oscillating boundary layer  

NASA Technical Reports Server (NTRS)

The turbulent boundary layer driven by a freestream velocity that varies sinusoidally in time around a zero mean is considered. The flow has a rich behavior including strong pressure gradients, inflection points, and reversal. A theory for the velocity and stress profiles at high Reynolds number is formulated. Well-resolved direct Navier-Stokes simulations are conducted over a narrow range of Reynolds numbers, and the results are compared with the theoretical predictions. The flow is also computed over a wide range of Reynolds numbers using a new algebraic turbulence model; the results are compared with the direct simulations and the theory.

Spalart, Philippe R.; Baldwin, Barrett S.

1987-01-01

439

Free-stream disturbances, continuous eigenfunctions, boundary-layer instability and transition  

NASA Technical Reports Server (NTRS)

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

Salwen, H.

1980-01-01

440

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

NASA Technical Reports Server (NTRS)

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

Grosch, C. E.

1980-01-01

441

Entry and acceleration of He(+) in the low latitude boundary layer  

NASA Technical Reports Server (NTRS)

AMPTE/CCE He(+) and H(+) observations in the magnetosphere, low latitude boundary layer, and magnetosheath reveal that cold plasmaspheric He(+) distributions from the outer magnetosphere convect into the low latitude boundary layer. In the boundary layer, the cold He(+) is accelerated and heated to a few keV. The data are resolved in sufficient detail to show that the process of pickup of the cold He(+) distribution in the boundary layer H(+) flow may not be adequate to explain the observed He(+) distributions in the boundary layer.

Fuselier, S. A.; Peterson, W. K.; Klumpar, D. M.; Shelly, E. G.

1989-01-01

442

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

443

Aerodynamic Models for Hurricanes III. Modeling hurricane boundary layer  

E-print Network

The third paper of the series (see previous ones in Refs.[1-2]) discusses basic physicalprocesses in the (quasi-) steady hurricane boundary layer (HBL), develops an approximate airflow model, establishes the HBL structure, and presents integral balance relations for dynamic and thermodynamic variables in HBL. Models of evaporation and condensation are developed, where the condensation is treated similarly to the slow combustion theory. A turbulent approximation for the lower sub-layer of HBL is applied to the sea-air interaction to establish the observed increase in angular momentum in the outer region of HBL.A closed set of balance relations has been obtained. Simple analytical solution of the set yields expressions for the basic dynamic variables - maximal tangential and radial velocities in hurricane, maximal vertical speed in eye wall, the affinity speed of hurricane travel, and the maximal temperature increase after condensation. Estimated values of the variables seem to be realistic. An attempt is also ...

Leonov, Arkady I

2008-01-01

444

DOI 10.1007/s10546-005-4735-2 Boundary-Layer Meteorology (2006) 118: 169187 Springer 2006  

E-print Network

-number boundary layers, such as the atmospheric boundary layer, is the spec- ification of the surface boundary-tunnel study. Keywords: Aerodynamic roughness length, Atmospheric boundary layer, Large-eddy simula- tionDOI 10.1007/s10546-005-4735-2 Boundary-Layer Meteorology (2006) 118: 169­187 © Springer 2006 EFFECT

Stoll, Rob

445

Onset of new particle formation in boundary layer  

NASA Astrophysics Data System (ADS)

At this moment, the mechanisms of atmospheric new particle formation (NPF), and the vapors participating in this process are not truly understood. Especially, in which part of the atmosphere the NPF takes place, is still an open question. To detect directly the very first steps of NPF in the atmosphere, we measured these chemical and physical processes within the Planetary Boundary Layer (PBL). We used airborne Zeppelin and Cessna measurements, and ground based in-situ measurements. Using Zeppelin, we focused on the time of the development of the PBL (altitudes up to 1 km) from sunrise until noon to measure vertical profiles of aerosol particles and chemical compounds. This is also the time when NPF typically occurs at ground level. On summer 2012, Zeppelin was measuring nucleation occurring in the polluted Po Valley area, Northern Italy, especially over the San Pietro Capofiume field site. A year later, Zeppelin had a spring campaign in boreal forest area, close to Hyytiälä field site in Southern Finland. During both campaigns, we aimed on measuring the vertical and the horizontal extension for NPF events using an instrumented Zeppelin. The vertical profile measurements represent the particle and gas concentrations in the lower parts of the atmosphere: the residual layer, the nocturnal boundary layer, and the PBL. At the same time, the ground based measurements records present conditions in the surface layer. The key instruments to measure the onset of NPF were an Atmospheric Pressure interface Time-Of-Flight mass spectrometer (APi-TOF), a Particle Size Magnifier (PSM), and a Neutral cluster and Air Ion Spectrometer (NAIS). These instruments are able to measure particles at the size range ~1-2 nm where atmospheric nucleation and cluster activation takes place. The onset of NPF was usually observed onboard Zeppelin when it was measuring inside the rising mixed layer which is connected to the surface layer by effective vertical mixing. The newly formed, subsequently growing, particles were observed to be homogeneously distributed inside the mixed layer. These measurements are part of the PEGASOS project which aims to quantify the magnitude of regional to global feedbacks between the atmospheric chemistry and physics, and thus quantify the changing climate.

Manninen, Hanna E.; Lampilahti, Janne; Mirme, Sander; Nieminen, Tuomo; Ehn, Mikael; Pullinen, Iida

2014-05-01

446

Long-term Observations of the Convective Boundary Layer Using Insect Radar Returns at the SGP ARM Climate Research Facility  

SciTech Connect

A long-term study of the turbulent structure of the convective boundary layer (CBL) at the U.S. Department of Energy Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) Climate Research Facility is presented. Doppler velocity measurements from insects occupying the lowest 2 km of the boundary layer during summer months are used to map the vertical velocity component in the CBL. The observations cover four summer periods (2004-08) and are classified into cloudy and clear boundary layer conditions. Profiles of vertical velocity variance, skewness, and mass flux are estimated to study the daytime evolution of the convective boundary layer during these conditions. A conditional sampling method is applied to the original Doppler velocity dataset to extract coherent vertical velocity structures and to examine plume dimension and contribution to the turbulent transport. Overall, the derived turbulent statistics are consistent with previous aircraft and lidar observations. The observations provide unique insight into the daytime evolution of the convective boundary layer and the role of increased cloudiness in the turbulent budget of the subcloud layer. Coherent structures (plumes-thermals) are found to be responsible for more than 80% of the total turbulent transport re