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1

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

2

Friction of a slider on a granular layer: Nonmonotonic thickness dependence and effect of boundary conditions  

E-print Network

Friction of a slider on a granular layer: Nonmonotonic thickness dependence and effect of boundary the effective friction encountered by a mass sliding on a granular layer as a function of bed thickness and boundary roughness conditions. The observed friction has minima for a small number of layers before

Kudrolli, Arshad

3

Progress in Boundary Layer Control: Robust ReducedOrder Control of SkinFriction Drag  

E-print Network

Progress in Boundary Layer Control: Robust Reduced­Order Control of Skin­Friction Drag by L drag reduction and eventually the flow is relaminarized. \\Lambda Corresponding author: Telephone (310, in other words, to the problem of reducing drag produced by skin friction. ``The skin friction constitutes

Soatto, Stefano

4

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

5

Calculation of skin-friction coefficients for low Reynolds number turbulent boundary layer flows  

Microsoft Academic Search

An analysis is presented of the reliability of various generally accepted empirical expressions for the prediction of the skin-friction coefficient C\\/sub f\\/ of turbulent boundary layers at low Reynolds numbers in zero-pressure-gradient flows on a smooth flat plate. The skin-friction coefficients predicted from these expressions were compared to the skin-friction coefficients of experimental profiles that were determined from a graphical

P. K. Barr

1980-01-01

6

Effect of boundary vibration on the frictional behavior of a dense sheared granular layer  

E-print Network

We report results of 3D Discrete Element Method (DEM) simulations aiming at investigating the role of the boundary vibration in inducing frictional weakening in sheared granular layers. We study the role of different vibration amplitudes applied at various shear stress levels, for a granular layer in the stick-slip regime and in the steady-sliding regime. Results are reported in terms of friction drops and kinetic energy release associated with frictional weakening events. We find that larger vibration amplitude induces larger frictional weakening events. The results show evidence of a threshold below which no induced frictional weakening takes place. Friction drop size is found to be dependent on the shear stress at the time of vibration. A significant increase in the ratio between the number of slipping contacts to the number of sticking contacts in the granular layer is observed for large vibration amplitudes. These vibration-induced contact rearrangements enhance particle mobilization and induces a friction drop and kinetic energy release. This observation provides some insight into the grain-scale mechanisms of frictional weakening by boundary vibration in a dense sheared granular layer. In addition to characterizing the basic physics of vibration induced shear weakening, we are attempting to understand how a fault fails in the earth under seismic wave forcing. This is the well know phenomenon of dynamic earthquake triggering. We believe that the granular physics are key to this understanding.

B. Ferdowsi; M. Griffa; R. A. Guyer; P. A. Johnson; J. Carmeliet

2014-01-24

7

Friction measurement in zero and adverse pressure gradient boundary layer using oil droplet interferometric method  

NASA Astrophysics Data System (ADS)

The oil droplet interferometric technique has been used to investigate the skin friction distribution along a zero and adverse pressure gradient boundary layer developing in the Laboratoire de Mcanique de Lille wind tunnel. This experimental task was a part of the WALLTURB project, funded by the European Community, in order to bring significant progress in the understanding of near wall turbulence in boundary layers. Skin friction values close to 0.01 Pa have been measured with this optical method. A comparison with the results obtained with hot-wire anemometry and macro-PIV demonstrates the great potential of the oil droplet technique.

Pailhas, Guy; Barricau, P.; Touvet, Y.; Perret, L.

2009-08-01

8

Artificially thickened turbulent boundary layers for studying heat transfer and skin friction on rough surfaces  

NASA Astrophysics Data System (ADS)

A technique has been developed to produce artificially thickened boundary layers on a uniformly rough surface which have two-dimensional, equilibrium properties representative of normal behavior at the level of spectra of the longitudinal velocity fluctuations. Skin surface friction coefficients and Stanton numbers are obtained for rough surface boundary layers much thicker than those previously studied. The results provide additional understanding of turbulent shear flow and a basis for testing engineering calculation schemes and design procedures for situations where thick, rough-wall boundary layers are present. The Stanton numbers and skin friction coefficients are shown to be representative of natural behavior because three higher levels of information, as well as the turbulent transport of momentum and heat, are the same as would have existed in naturally developed layers of the same thickness.

Ligrani, P. M.; Moffat, R. J.; Kays, W. M.

1983-06-01

9

Estimation of the Friction Velocity in Stably Stratified Boundary-Layer Flows Over Hills  

Microsoft Academic Search

A method is suggested for the calculation of the friction velocity for stable turbulent boundary-layer flow over hills. The method is tested using a continuous upstream mean velocity profile compatible with the propagation of gravity waves, and is incorporated into the linear model of Hunt, Leibovich and Richards with the modification proposed by Hunt, Richards and Brighton to include the

Jos Luis Argan; Pedro M. A. Miranda; Miguel A. C. Teixeira

2008-01-01

10

Effects of Riblets on Skin Friction in High-Speed Turbulent Boundary Layers  

NASA Technical Reports Server (NTRS)

Direct numerical simulations of spatially developing turbulent boundary layers over riblets are conducted to examine the effects of riblets on skin friction at supersonic speeds. Zero-pressure gradient boundary layers with an adiabatic wall, a Mach number of M1 = 2.5, and a Reynolds number based on momentum thickness of Re = 1720 are considered. Simulations are conducted for boundary-layer flows over a clean surface and symmetric V- groove riblets with nominal spacings of 20 and 40 wall units. The DNS results confirm the few existing experimental observations and show that a drag reduction of approximately 7% is achieved for riblets with proper spacing. The influence of riblets on turbulence statistics is analyzed in detail with an emphasis on identifying the differences, if any, between the drag reduction mechanisms for incompressible and high-speed boundary layers.

Duan, Lian; Choudhari, Meelan M.

2012-01-01

11

Introduction to boundary-layer theory. [viscous friction loss calculation for turbine blade design  

NASA Technical Reports Server (NTRS)

The pressure ratio across a turbine provides a certain amount of ideal energy that is available to the turbine for producing work. The portion of the ideal energy that is not converted to work is considered to be a loss. One of the more important and difficult aspects of turbine design is the prediction of the losses. The primary cause of losses is the boundary layer that develops on the blade and end wall surfaces. Boundary-layer theory is used to calculate the parameters needed to estimate viscous (friction) losses.

Mcnally, W. D.

1973-01-01

12

Estimation of the Friction Velocity in Stably Stratified Boundary-Layer Flows Over Hills  

Microsoft Academic Search

A method is suggested for the calculation of the friction velocity for stable turbulent boundary-layer flow over hills. The\\u000a method is tested using a continuous upstream mean velocity profile compatible with the propagation of gravity waves, and is\\u000a incorporated into the linear model of Hunt, Leibovich and Richards with the modification proposed by Hunt, Richards and Brighton\\u000a to include the

Jos Luis Argan; Pedro M. A. Miranda; Miguel A. C. Teixeira

2009-01-01

13

Skin-friction measurements in a 3-D, supersonic shock-wave/boundary-layer interaction  

NASA Astrophysics Data System (ADS)

An experimental study has been conducted in a three-dimensional, supersonic shockwave/boundary-layer interaction (3-D SW/BLI) with the intent of providing accurate experimental data for turbulence modeling and computational fluid dynamics (CFD) code validation. The experiment was performed in the High Reynolds Channel 1 (HRCI) wind tunnel at NASA Ames Research Center. The test was conducted at a Mach number of M(sub infinity) = 2.89 and at a Reynolds number of Re = 15 x 106/m. The model consisted of a sting-supported cylinder aligned with the tunnel axis and a 20 deg half-angle conical flare offset 1.27 cm from the cylinder centerline. The generated shock system was verified to be steady by schlieren visualization. The highlight of the study was the acquisition of 3-D skin-friction data by a laser interferometric skin friction (LISF) meter. Surface pressure measurements were obtained in 15 deg intervals around the cylinder and flare. Additional measurements included surface oil flow and laser light sheet illumination which were used to document the flow topology. Skin-friction measurements are proving to be a very challenging test of a CFD code predictive capability. However, at the present time there is a very limited amount of accurate skin-friction data in complex flows such as in 3-D SW/BLI. The LISF technique is advantageous as compared to other skin-friction measurement techniques for application in complex flows like the present since it is non-intrusive and is capable of performing measurements in flows with large shear and pressure gradients where the reliability of other techniques is questionable. Thus, the prevent skin-friction data will prove valuable to turbulence modeling and CFD code validation efforts.

Wideman, Jeffrey Kenneth

14

Laser interferometer skin-friction measurements of crossing-shock-wave/turbulent-boundary-layer interactions  

NASA Technical Reports Server (NTRS)

Wall shear stress measurements beneath crossing-shock-wave/turbulent boundary-layer interactions have been made for three interactions of different strengths. The interactions are generated by two sharp fins at symetric angles of attack mounted on a flat plate. The shear stress measurements were made for fin angles of 7 and 11 deg at Mach 3 and 15 deg at Mach 3.85. The measurements were made using a laser interferometer skin-friction meter, a device that determines the wall shear by optically measuring the time rate of thinning of an oil film placed on the test model surface. Results of the measurements reveal high skin-friction coefficients in the vicinity of the fin/plate junction and the presence of quasi-two-dimensional flow separation on the interaction center line. Additionally, two Navier-Stokes computations, one using a Baldwin-Lomax turbulence model and one using a k-epsilon model, are compared with the experimental results for the Mach 3.85, 15-deg interaction case. Although the k-epsilon model did a reasonable job of predicting the overall trend in portions of the skin-friction distribution, neither computation fully captured the physics of the near-surface flow in this complex interaction.

Garrison, T. J.; Settles, G. S.; Narayanswami, N.; Knight, D. D.

1994-01-01

15

Friction of a slider on a granular layer: Non-monotonic thickness dependence and effect of boundary conditions  

E-print Network

We investigate the effective friction encountered by a mass sliding on a granular layer as a function of bed thickness and boundary roughness conditions. The observed friction has minima for a small number of layers before it increases and saturates to a value which depends on the roughness of the sliding surface. We use an index-matched interstitial liquid to probe the internal motion of the grains with fluorescence imaging in a regime where the liquid has no significant effect on the measured friction. The shear profiles obtained as a function of depth show decrease in slip near the sliding surface as the layer thickness is increased. We propose that the friction depends on the degree of grain confinement relative to the sliding surfaces.

Saloome Siavoshi; Ashish V. Orpe; Arshad Kudrolli

2005-12-22

16

A Simple Method for Determining Heat Transfer, Skin Friction, and Boundary-Layer Thickness for Hypersonic Laminar Boundary-Layer Flows in a Pressure Gradient  

NASA Technical Reports Server (NTRS)

A procedure based on the method of similar solutions is presented by which the skin friction, heat transfer, and boundary-layer thickness in a laminar hypersonic flow with pressure gradient may be rapidly evaluated if the pressure distribution is known. This solution, which at present is. restricted to power-law variations of pressure with surface distance, is presented for a wide range of exponents in the power law corresponding to both favorable and adverse pressure gradients. This theory has been compared to results from heat-transfer experiments on blunt-nose flat plates and a hemisphere cylinder at free-stream Mach numbers of 4 and 6.8. The flat-plate experiments included tests made at a Mach number of 6.8 over a range of angle of attack of +/- 10 deg. Reasonable agreement of the experimental and theoretical heat-transfer coefficients has been obtained as well as good correlation of the experimental results over the entire range of angle of attack studied. A similar comparison of theory with experiment was not feasible for boundary-layer-thickness data; however, the hypersonic similarity theory was found to account satisfactorily for the variation in boundary-layer thickness due to local pressure distribution for several sets of measurements.

Bertram, Mitchel H.; Feller, William V.

1959-01-01

17

Turbulent Friction in the Boundary Layer of a Flat Plate in a Two-Dimensional Compressible Flow at High Speeds  

NASA Technical Reports Server (NTRS)

In the present report an investigation is made on a flat plate in a two-dimensional compressible flow of the effect of compressibility and heating on the turbulent frictional drag coefficient in the boundary layer of an airfoil or wing radiator. The analysis is based on the Prandtl-Karman theory of the turbulent boundary later and the Stodola-Crocco, theorem on the linear relation between the total energy of the flow and its velocity. Formulas are obtained for the velocity distribution and the frictional drag law in a turbulent boundary later with the compressibility effect and heat transfer taken into account. It is found that with increase of compressibility and temperature at full retardation of the flow (the temperature when the velocity of the flow at a given point is reduced to zero in case of an adiabatic process in the gas) at a constant R (sub x), the frictional drag coefficient C (sub f) decreased, both of these factors acting in the same sense.

Frankl, F.; Voishel, V.

1943-01-01

18

Direct measurements and analysis of skin friction and cooling downstream of multiple flush-slot injection into a turbulent Mach 6 boundary layer  

NASA Technical Reports Server (NTRS)

Experiments were conducted to determine the reduction in surface skin friction and the effectiveness of surface cooling downstream of one to four successive flush slots injecting cold air at an angle of 10 deg into a turbulent Mach 6 boundary layer. Data were obtained by direct measurement of surface shear and equilibrium temperatures, respectively. Increasing the number of slots decreased the skin friction, but the incremental improvement in skin-friction reduction decreased as the number of slots was increased. Cooling effectiveness was found to improve, for a given total mass injection, as the number of slots was increased from one to four. Comparison with previously reported step-slot data, however, indicated that step slots with tangential injection are more effective for both reducing skin friction and cooling than the present flush-slot configuration. Finite-difference predictions are in reasonable agreement with skin-friction data and with boundary-layer profile data.

Howard, F. G.; Strokowski, A. J.

1978-01-01

19

Laser Interferometer Skin-Friction measurements of crossing-shock wave/turbulent boundary-layer interactions  

NASA Technical Reports Server (NTRS)

Wall shear stress measurements beneath crossingshock wave/turbulent boundary-layer interactions have been made for three interactions of different strengths. The interactions are generated by two sharp fins at symmetric angles of attack mounted on a flat plate. The shear stress measurements were made for fin angles of 7 and 11 degrees at Mach 3 and 15 degrees at Mach 4. The measurements were made using a Laser Interferometer Skin Friction (LISF) meter; a device which determines the wail shear by optically measuring the time rate of thinning of an oil film placed on the test model surface. Results of the measurements reveal high skin friction coefficients in the vicinity of the fin/plate junction and the presence of quasi-two-dimensional flow separation on the interaction centerline. Additionally, two Navier-Stokes computations, one using a Baldwin-Lomax turbulence model and one using a k- model, are compared to the experimental results for the Mach 4, 15 degree interaction case. While the k- model did a reasonable job of predicting the overall trend in portions of the skin friction distribution, neither computation fully captured the physics of the near surface flow in this complex interaction.

Garrison, T. J.; Settles, G. S.

1993-01-01

20

Boundary-layer transition and global skin friction measurement with an oil-fringe imaging technique  

NASA Technical Reports Server (NTRS)

A new oil-fringe imaging system skin friction (FISF) technique to measure skin friction on wind tunnel models is presented. In the method used to demonstrate the technique, lines of oil are applied on surfaces that connect the intended sets of measurement points, and then a wind tunnel is run so that the oil thins and forms interference fringes that are spaced in proportion to local skin friction. After a run the fringe spacings are imaged with a CCD-array digital camera and measured on a computer. Skin friction and transition measurements on a two-dimensional wing are presented and compared with computational predictions.

Monson, Daryl J.; Mateer, George G.; Menter, Florian R.

1993-01-01

21

In-flight compressible turbulent boundary layer measurements on a hollow cylinder at a Mach number of 3.0. [supersonic heat transfer and skin friction  

NASA Technical Reports Server (NTRS)

Skin temperatures, shearing forces, surface static pressures, and boundary layer pitot pressures and total temperatures were measured on a hollow cylinder 3.04 meters long and 0.437 meter in diameter mounted beneath the fuselage of the YF-12A airplane. The data were obtained at a nominal free stream Mach number of 3.0 and at wall-to-recovery temperature ratios of 0.66 to 0.91. The free stream Reynolds number had a minimal value of 4.2 million per meter. Heat transfer coefficients and skin friction coefficients were derived from skin temperature time histories and shear force measurements, respectively. Boundary layer velocity profiles were derived from pitot pressure measurements, and a Reynolds analogy factor of 1.11 was obtained from the measured heat transfer and skin friction data. The skin friction coefficients predicted by the theory of van Driest were in excellent agreement with the measurements. Theoretical heat transfer coefficients, in the form of Stanton numbers calculated by using a modified Reynolds analogy between skin friction and heat transfer, were compared with measured values. The measured velocity profiles were compared to Coles' incompressible law-of-the-wall profile.

Quinn, R. D.; Gong, L.

1978-01-01

22

The behavior of the skin-friction coefficient of a turbulent boundary layer flow over a flat plate with differently configured transverse square grooves  

SciTech Connect

Skin-friction coefficient of turbulent boundary layer flow over a smooth-wall with transverse square grooves was investigated. Four grooved-wall cases were investigated. The four grooved-wall configurations are single 5mm square grooved-wall, and 5mm square grooves spaced 10, 20 and 40 element widths apart in the streamwise direction. Laser-Doppler Anemometer (LDA) was used for the mean velocity and turbulence intensity measurements. The skin-friction coefficient determined from the velocity profile increases sharply just downstream of the groove. This overshoot is followed by an undershoot and then relaxation back to the smooth-wall value. This behavior is observed in most grooved-wall cases. Integrating the skin-friction coefficient in the streamwise direction indicates that there is an increase in the overall drag in all the grooved-wall cases.

Wahidi, R.; Chakroun, W.; Al-Fahed, S. [Faculty of Engineering, Mechanical Engineering, Kuwait University, P.O. Box 5969, 13060 Safat (Kuwait)

2005-11-01

23

Dynamics of the seismogenic layer of Central and East Asia: Fault friction and the role of crustal buoyancies versus boundary conditions  

NASA Astrophysics Data System (ADS)

We present dynamic solutions for the seismogenic layer of the India-Eurasia collision zone. We exploit a forward dynamic modeling approach, where body force distributions, inferred lateral variations in linear effective viscosity, and known far-field velocity boundary conditions are defined. Body forces are the differences in gravity potential energy per unit area (GPE), which are calculated as the depth integral of vertical stress from the surface down to a common depth reference (20 km below sea level). In our models of the seismogenic layer, depth-integrated viscosities are proportional to the assumed long-term friction on faults and inversely proportional to the long-term strain rates. Lateral variations in linear effective viscosity of the modeled layer span over 5 orders of magnitude. The velocity boundary conditions are defined using long-term plate motion estimates. Self-consistent dynamic strain rate tensor solutions to the force-balance equations were solved and tested for best-fit match with kinematic strain rate and velocity fields of central and east Asia defined by a large set of Quaternary fault observations. We investigate models using a range of long-term fault friction coefficients from 0.02 - 1.0 under hydrostatic pore pressure conditions. Assessment of fitness of the dynamic solutions to deformation indicators is evaluated using four measures. The forward dynamic strain rate tensor styles are scored by misfit to the kinematic strain rate tensor styles inferred from Kostrov summation of Quaternary fault observations. The ratio of dynamic strain rates to kinematic model strain rates are compared. Dynamic model velocity fields are scored via reduced chi-square misfit with the long-term kinematic model velocity field defined by Quaternary fault observations. Dynamic model velocity fields are scored via reduced chi-square misfit with GPS velocity observations. Preliminary results indicate that models defined with low fault friction (0.05 < ? < 0.40) achieve a better fit to Quaternary deformation indicators than models with models with high fault friction coefficients. Such models indicate that deviatoric stresses associated with internal crustal buoyancies dominate over deviatoric stresses associated with velocity boundary conditions within the Tibetan Plateau. Conversely, deviatoric stresses associated with boundary conditions dominate over deviatoric stresses associated with internal crustal buoyancies within Tarim Basin and the Tien Shan.

Klein, E. C.; Flesch, L. M.; Holt, W. E.

2009-12-01

24

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

25

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

26

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

27

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

28

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

29

Friction microprobe investigation of particle layer effects on sliding friction  

SciTech Connect

Interfacial particles (third-bodies), resulting from wear or external contamination, can alter and even dominate the frictional behavior of solid-solid sliding in the absence of effective particle removal processes (e.g., lubricant flow). A unique friction microprobe, developed at Oak Ridge National Laboratory, was used to conduct fine- scale friction studies using 1.0 mm diameter stainless steel spheres sliding on several sizes of loose layers of fine aluminum oxide powders on both aluminum and alumina surfaces. Conventional, pin-on-disk experiments were conducted to compare behavior with the friction microprobe results. The behavior of the relatively thick particle layers was found to be independent of the nature of underlying substrate, substantiating previous work by other investigators. The time-dependent behavior of friction, for a spherical macrocontact starting from rest, could generally be represented by a series of five rather distinct phases involving static compression, slider breakaway, transition to steady state, and dynamic layer instability. A friction model for the steady state condition, which incorporates lamellar powder layer behavior, is described.

Blau, P.J.

1993-01-01

30

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

31

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

32

Theory of friction: The role of elasticity in boundary lubrication  

NASA Astrophysics Data System (ADS)

I analyze the sliding motion of an elastic block on a substrate with a layer of lubrication molecules. This model of boundary lubrication illustrates how the surface stress generated by the lubrication layer at the block-substrate interface is transmitted to the upper surface of the block. It shows that it is essential to correctly incorporate the elastic properties of the block and of the substrate; otherwise, incorrect results will result. In light of the theoretical results I discuss the sliding friction measurements of Yoshizawa and Israelachvili.

Persson, B. N. J.

1994-08-01

33

Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. Part 1: Pressure distribution. Part 2: Wall shear stress. Part 3: Simplified formulas for the prediction of surface pressures and skin friction  

NASA Technical Reports Server (NTRS)

An asymptotic description is derived for the interaction between a shock wave and a turbulent boundary layer in transonic flow, for a particular limiting case. The dimensionless difference between the external flow velocity and critical sound speed is taken to be much smaller than one, but large in comparison with the dimensionless friction velocity. The basic results are derived for a flat plate, and corrections for longitudinal wall curvature and for flow in a circular pipe are also shown. Solutions are given for the wall pressure distribution and the shape of the shock wave. Solutions for the wall shear stress are obtained, and a criterion for incipient separation is derived. Simplified solutions for both the wall pressure and skin friction distributions in the interaction region are given. These results are presented in a form suitable for use in computer programs.

Adamson, T. C., Jr.; Liou, M. S.; Messiter, A. F.

1980-01-01

34

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.

35

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

36

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

37

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.

38

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

39

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

40

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

41

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

42

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

43

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

44

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

45

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

46

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

47

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

48

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

49

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

50

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

51

Measurement of Heat Transfer in the Turbulent Boundary Layer on a Flat Plate in a Supersonic Flow and Comparison with Skin Friction Results  

NASA Technical Reports Server (NTRS)

Local heat-transfer rates on the surface of a heated flat plate at zero incidence to an air stream flowing at Mach numbers of 1.69 and 2.27 are presented. The Reynolds number range for both Mach numbers was 1 million to 10 million. Surface temperatures were maintained near recovery temperature. It was found that the variation of heat transfer with Mach number was in agreement with previously reported variations of directly measured skin friction with Mach number on unheated bodies. The variation with Mach number of the average skin coefficient, as determined from impact-pressure surveys, was in agreement with that from other momentum loss measurements but differed from the variation obtained from directly measured skin friction as reported by others. (author)

Pappas, C C

1954-01-01

52

Tribological property of plain bearing with low frictional layer  

Microsoft Academic Search

This paper describes the excellent frictional properties of a newly developed lead-free aluminum alloy bearing with a low frictional layer on its inner surface, which consists of a molybdenum disulfide (MoS2) layer deposited directly without any binders such as resin. The thickness of the layer is in sub-micron levels. This bearing has high potential in reducing the friction losses within

Yukihiko Kagohara; Satoshi Takayanagi; Shigeya Haneda; Masahito Fujita; Yoshiro Iwai

2009-01-01

53

Frictional anisotropy under boundary lubrication: effect of surface texture.  

SciTech Connect

The friction coefficient was measured under boundary lubrication with a ball-on-flat contact configuration in unidirectional sliding. The ball was smooth and hardened 52100 steel. Discs were made from case-carburized and hardened 4620, annealed 1080, and 1018 steels with directionally ground surfaces. A synthetic lubricant of stock polyalphaolefin was used for testing. During testing with each material, a frictional spike was observed whenever the ball slid parallel to the grinding ridge on the disc surface. The average friction coefficient for all tests was about 0.1, which is typical for the boundary lubrication regime. The magnitude of the frictional spikes, which reached as high as a friction coefficient of 0.25, and their persistence depended on the hardness of the disc surface. On the basis of elastohydrodynamic theory, coupled with the observation of severe plastic deformation on the ridges parallel to the sliding direction, the frictional spike could be due to localized plastic deformation on the disc surface at locations of minimal thickness for the lubricant fluid film. This hypothesis was further supported by lack of frictional spikes in tests using discs coated with a thin film of diamond-like carbon, in which plastic deformation is minimal.

Ajayi, O. O.; Erck, R. A.; Lorenzo-Martin, C.; Fenske, G. R.; Energy Systems

2009-06-15

54

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

55

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

56

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

57

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

58

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

59

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

60

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

61

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

62

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

63

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

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

64

Application of algebraic-RNG eddy viscosity model to simulation of transitional boundary layer flow  

NASA Technical Reports Server (NTRS)

An algebraic eddy-viscosity model is derived from the renormalization group (RNG) theory of turbulence. A new length scale, based on boundary layer characteristics (displacement thickness, shape factor), is proposed. The model was applied to transitional boundary layer flow over a flat plate. Integral characteristics, such as the total skin friction coefficient, and mean velocity profile across the boundary layer, are found to be in good agreement with experimental data.

Yakhot, Alexander; Kedar, Omer; Orszag, Steven A.

1992-01-01

65

A conditioned volumetric view of ``superstructure'' events in turbulent boundary layers  

Microsoft Academic Search

A conditionally averaged view of ``superstructure'' type events is presented for the case of zero pressure gradient turbulent boundary layers at friction Reynolds number, Retau 14,00. Detailed boundary layer traverses are acquired above a simultaneously sampled spanwise rake of 10 flush-mounted hot-film sensors, affixed to the tunnel wall with a spanwise spacing of approximately 0.08 boundary layer thicknesses (delta). The

Nicholas Hutchins; Bharathram Ganapathisubramani; Jason Monty; Ivan Marusic; Min Chong

2008-01-01

66

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

67

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.

68

Investigation and modeling of frictional boundary conditions in oblique cutting of aluminum alloys  

NASA Astrophysics Data System (ADS)

Friction at the cutting tool interface has been studied for 60 years, yet an accurate model of friction is largely unavailable, especially in operations such as turning, where the interface is inaccessible due the continuous contact between chip and tool. A historical perspective of friction in turning is provided to better understand the purpose of this thesis. The contradictions arising from different frictional boundary condition assumptions in machining were analyzed. Experimental observations were substantiated in the light of the literature review. Friction conditions at the tool chip interface were found to be more complex than the simple models of seizure followed by sliding, which is accepted in most machining models. This thesis investigated the surface topology of cutting tools in conventional turning operation, which is one of the oldest and common machining processes. Two different aluminum alloys Al-2024 and Al-6061 were used in turning experiments with carbide tools to define the frictional conditions as these alloys exhibited a wide range of frictional contacts at different machining conditions. Experiments were conducted using carbide cutting tools at a range of speeds, feed rates, and depths of cut, which are commonly utilized in industrial applications. The analysis of tool chip interface at microscopic levels revealed further details of seizure and sliding zone formation. Newer techniques developed in microscopy and surface characterization were used to characterize the interface in a non-destructive manner. Scanning electron microscopy (SEM), surface profilometer and laser scanning confocal microscopy (LSCM) techniques helped us in the understanding of the frictional boundaries. Analysis of SEM images obtained by turning experiments revealed three distinct regions whose topology is closely related to turning parameters. These different zones were named as primary sticking zone, sliding zone and secondary sticking zone. Furthermore, with the assistance of a developed computer code, the real area of contact and each different contact area were determined numerically. Therefore, this study is the first attempt in literature both identifies the frictional contact areas and computes their exact numerical values. The SEM backscattering technique showed that the workpiece material behavior is different in the built up edge and sticking areas. This finding was especially used to identify the preliminary and secondary sticking areas. Thus, it has been showed first time that the deposited layers on frictional areas show different material characteristics. With the help of tool surface image analysis, area calculation algorithm, chemical composition identification, and earlier efforts cited in the literature, we proposed a stress-model which accurately predicted experimental normal and shear forces in oblique cutting of aluminum alloys for most tested conditions.

Kilic, Dursun Sedat

69

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

70

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

71

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

72

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

73

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

74

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

75

Frictional rheology of a confined adsorbed polymer layer.  

PubMed

The sliding dynamics of a confined adsorbed polymer layer is investigated at the nanoscale. A combined mechanical and physical approach is used to model the rheology and structure of the adsorbed layer. The confinement at short distances governs the nanotribological behavior of the polymer layer formed close to the surface. It appears that the Amontons' proportionality between frictional and normal stresses does not hold here: the higher the contact pressure, the lower the friction. Besides, the sliding stress is strongly dependent on the velocity: it increases with the sliding velocity. Using a model based on the kinetics of formation and rupture of adhesive bonds between the two shearing surfaces theoretically accounts for the behavior of this system. This approach allows us to correlate the frictional properties to the molecular organization on the surfaces. PMID:19572533

Cayer-Barrioz, Juliette; Mazuyer, Denis; Tonck, Andr; Yamaguchi, Elaine

2009-09-15

76

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

77

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

78

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

79

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

80

Analysis of the stability of stationary boundary friction modes in the framework of a synergetic model  

E-print Network

A synergetic model describing the state of an ultrathin lubricant layer squeezed between two atomically smooth solid surfaces operating in the boundary friction mode has been developed further. To explain the presence of different operation modes of the system for various sets of its main parameters, the mathematical analysis of the synergetic model is carried out. The type of functioning a tribological system is described in accordance with the stability character of singular points, and the diagrams distinguishing various operation modes are obtained. Phase portraits corresponding to different stability types are plotted for all diagram areas. A stick-slip mode of motion that is often observed experimentally is described.

Iakov A. Lyashenko; Nataliia N. Manko

2014-01-17

81

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

82

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

SciTech Connect

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

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

1996-01-01

83

Effect of sulphide layers on the tribological behavior of steels under boundary lubrication conditions  

NASA Astrophysics Data System (ADS)

Sulphide layers were prepared on the surface of AISI 1045 steel by ion sulphurization. The anti-scuffing, friction-reducing, and wear-resistant behavior of these sulphurized surfaces were investigated systematically using a ball-on-disc wear tester with engine oil as a lubricant. SEM, EDX, XPS, and AES were used to examine the morphologies and compositions of wear scars and boundary films. Sulphide layers improved anti-scuffing properties remarkably at low sliding velocities, and exhibited good friction-reducing and wear-resistant effects. During friction the sulphide layer promoted the growth of oxide, and iron sulphide could be decomposed and regenerated to form FeS again on the rubbing surface. An appropriately thick sulphide layer optimizes the sulphur-to-oxygen concentration in the boundary film resulting in the highest load-bearing capacity, and shows that thicker sulphide layers are unnecessary.

Ning, Zhang; Da-Ming, Zhuang; Jia-Jun, Liu; Xiao-Dong, Fang; Ming-Xi, Guan

2001-09-01

84

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

85

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

86

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

87

A fast, uncoupled, compressible, two-dimensional, unsteady boundary layer algorithm with separation for engine inlets  

NASA Technical Reports Server (NTRS)

A finite difference boundary layer algorithm was developed to model viscous effects when an inviscid core flow solution is given. This algorithm solved each boundary layer equation separately, then iterated to find a solution. Solving the boundary layer equations sequentially was 2.4 to 4.0 times faster than solving the boundary layer equations simultaneously. This algorithm used a modified Baldwin-Lomax turbulence model, a weighted average of forward and backward differencing of the pressure gradient, and a backward sweep of the pressure. With these modifications, the boundary layer algorithm was able to model flows with and without separation. The number of grid points used in the boundary layer algorithm affected the stability of the algorithm affected the stability of the algorithm as well as the accuracy of the predictions of friction coefficients and momentum thicknesses. Results of this boundary layer algorithm compared well with experimental observations of friction coefficients and momentum thicknesses. In addition, when used interactively with an inviscid flow algorithm, this boundary layer algorithm corrected for viscous effects to give a good match with experimental observations for pressures in a supersonic inlet.

Roach, Robert L.; Nelson, Chris; Sakowski, Barbara; Darling, Douglas; Van De Wall, Allan G.

1992-01-01

88

A fast, uncoupled, compressible, two-dimensional, unsteady boundary layer algorithm with separation for engine inlets  

NASA Technical Reports Server (NTRS)

A finite difference boundary layer algorithm was developed to model viscous effects when an inviscid core flow solution is given. This algorithm solved each boundary layer equation separately, then iterated to find a solution. Solving the boundary layer equations sequentially was 2.4 to 4.0 times faster than solving the boundary layer equations simultaneously. This algorithm used a modified Baldwin-Lomax turbulence model, a weighted average of forward and backward differencing of the pressure gradient, and a backward sweep of the pressure. With these modifications, the boundary layer algorithm was able to model flows with and without separation. The number of grid points used in the boundary layer algorithm affected the stability of the algorithm as well as the accuracy of the predictions of friction coefficients and momentum thicknesses. Results of this boundary layer algorithm compared well with experimental observations of friction coefficients and momentum thicknesses. In addition, when used interactively with an inviscid flow algorithm, this boundary layer algorithm corrected for viscous effects to give a good match with experimental observations for pressures in a supersonic inlet.

Roach, Robert L.; Nelson, Chris; Sakowski, Barbara; Darling, Douglas; Vandewall, Allan G.

1992-01-01

89

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

90

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

91

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

92

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

93

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

94

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

95

Swept shock/boundary layer interaction experiments in support of CFD code validation  

NASA Technical Reports Server (NTRS)

Research on the topic of shock wave/turbulent boundary layer interaction was carried out. Skin friction and surface pressure measurements in fin-induced, swept interactions were conducted, and heat transfer measurements in the same flows are planned. The skin friction data for a strong interaction case (Mach 4, fin-angles equal 16 and 20 degrees) were obtained, and their comparison with computational results was published. Surface pressure data for weak-to-strong fin interactions were also obtained.

Settles, G. S.; Lee, Y.

1990-01-01

96

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

97

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

98

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

99

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

100

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.

101

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

102

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

103

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

104

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

105

Friction, Frontogenesis, and the Stratification of the Surface Mixed Layer LEIF THOMAS*  

E-print Network

Friction, Frontogenesis, and the Stratification of the Surface Mixed Layer LEIF THOMAS* Department restratification resulting from frontogenesis in regions of confluent flow. Frictional forces acting of friction versus frontogenesis in the restratification of the mixed layer and are tested using numerical

Thompson, Andrew

106

The influence of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients  

NASA Technical Reports Server (NTRS)

The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent boundary layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free-stream, both of which act to improve the transmission of momentum from the free-stream to the boundary layers.

Hoffmann, J. A.; Kassir, S. M.; Larwood, S. M.

1989-01-01

107

Effect of the temperature dependence of the viscosity of pseudoplastic lubricants on the boundary friction regime  

NASA Astrophysics Data System (ADS)

The boundary friction regime appearing between two atomically smooth solid surfaces with an ultrathin lubricating layer between them is considered. The interrupted (stick-slip) regime of motion typical of the boundary lubrication is represented as a first-order phase transition between the structural states of the lubricant. The thermodynamic and shear melting is described. The universal dependence of the viscosity of high-molecular alkanes (lubricants) on the temperature and velocity gradient is taken into account. The dependence of the friction force on the lubricant temperature and the relative shear velocity of the interacting surfaces are analyzed. It is shown that the temperature dependence of the viscosity makes it possible to describe some experimentally observed effects. The possibility of prolonged damped oscillations after lubricant melting prior to the stabilization of the steady-state sliding mode is predicted. In the stick-slip regime in a wide range of parameters, a reversive motion is observed when the upper block moves in both directions after melting.

Lyashenko, I. A.

2013-07-01

108

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

109

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

110

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

111

The Drag in a Navier-Stokes Flow with Friction-Driven Boundary Conditions  

E-print Network

The Drag in a Navier-Stokes Flow with Friction-Driven Boundary Conditions Matthieu Bonnivard Abstract We consider the drag of an obstacle in a Navier-Stokes flow, associated to the friction, they appear as a natural control variable in order to reduce the drag using the effect of micro

Paris-Sud XI, Université de

112

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

113

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

114

Surface documentation of a 3-D supersonic, shock-wave/boundary-layer interaction  

NASA Astrophysics Data System (ADS)

The experimental documentation of a three-dimensional shock-wave/boundary-layer interaction in a nominal Mach 3 flow is presented. The model consisted of a sting-supported cylinder, aligned with the free-stream flow, and a 20 deg half-angle conical flare offset 1.25 cm from the cylinder centerline. Surface oil flow, laser light sheet illumination and schlieren were used to document the flow topology. The data includes surface-pressure and skin-friction measurements. A laser interferometric skin friction instrument was employed to acquire the skin-friction data. Included in the skin-friction data are measurements within separated regions and 3-D measurements in highly-swept regions. The skin-friction data will be particularly valuable to turbulence modeling and computational fluid dynamics validation. A computer diskette supplememnt containing data tables 1-37 is included.

Wideman, Jeffrey K.; Brown, James L.; Miles, John B.; Ozcan, Oktay

1994-06-01

115

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

116

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

117

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 MoninObukhov (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

118

Laminar boundary layer on the moving surface of a rankine oval  

Microsoft Academic Search

A numerical investigation has been made of the laminar boundary layer that arises on the moving surface of a cylindrical body (Rankine oval with relative elongation 4) that moves with constant velocity in an incompressible fluid. The distributions of the frictional stress on the surface of the cylinder for different velocities of the wall motion are found. Numerical integration was

V. M. Zubarev

1984-01-01

119

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

120

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

121

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

122

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.; Lindstrm, E.; Bertelsen, A. F.; Jensen, A.; Laskovski, D.; Slevik, G.

2013-01-01

123

Frictional Figures of Merit for Single Layered Nanostructures  

NASA Astrophysics Data System (ADS)

We determine the frictional figures of merit for a pair of layered honeycomb nanostructures, such as graphane, fluorographene, MoS2 and WO2 moving over each other, by carrying out ab initio calculations of interlayer interaction under constant loading force. Using the Prandtl-Tomlinson model we derive the critical stiffness required to avoid stick-slip behavior. We show that these layered structures have low critical stiffness even under high loading forces due to their charged surfaces repelling each other. The intrinsic stiffness of these materials exceeds critical stiffness and thereby the materials avoid the stick-slip regime and attain nearly dissipationless continuous sliding. Remarkably, tungsten dioxide displays a much better performance relative to others and heralds a potential superlubricant. The absence of mechanical instabilities leading to conservative lateral forces is also confirmed directly by the simulations of sliding layers.

Cahangirov, S.; Ataca, C.; Topsakal, M.; Sahin, H.; Ciraci, S.

2012-03-01

124

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

125

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...

126

The influence of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients  

NASA Technical Reports Server (NTRS)

The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent bounday layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free stream, both of which act to improve the transmission of momentum from the free stream to the boundary layers.

Hoffmann, Jon A.

1988-01-01

127

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

128

Secondary Grtler 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. Grtler instability is one of the many B-L instability mechanisms. Grtler 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, Grtler instability is an important subject in fluid mechanics. In this paper, Grtler 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 Grtler vortices in hypersonic boundary layers. DNS is used to simulate Grtler 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 Grtler vortices are also investigated using DNS. Inflectional profiles develop due to the distortion of the mean flow caused by nonlinear growth of Grtler vortices which induces secondary instability. Secondary instability will be investigated using secondary instability theory and DNS.

Whang, C. W.; Zhong, X.

2000-11-01

129

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

130

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

131

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

132

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

133

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

134

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

135

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

136

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

137

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

138

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

139

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

140

Changes in the turbulent boundary layer structure associated with net drag reduction by outer layer manipulators  

NASA Technical Reports Server (NTRS)

A specially designed wind tunnel was used to examine the effects of tandemly arranged parallel plate manipulators (TAPPMs) on a turbulent boundary-layer structure and the associated drag. Momentum balances, as well as measurements of the local shear stress from the velocity gradient near the wall, were used to obtain the net drag and local skin friction changes. Two TAPPMs, identical except for the thickness of their plates, were used in the study. Results with .003 inch plates were a maximum net drag reduction of 10 percent at 58 beta sub o (using a momentum balance). At 20 beta sub o, simultaneous laser sheet flow visualization and hot-wire anemometry data showed that the Reynolds stress in the large eddies was significantly reduced, as were the streamwise and normal velocity components. Using space-time correlations the reductions were again identified. Furthermore, quantitative flow visualization showed that the outward normal velocity of the inner region was also significantly decreased in the region around 20 beta sub o. However, throughout the first 130 beta sub o, the measured sublayer thickness with the TAPPMs in place was 15 to 20 percent greater. The data showed that the skin friction, as well as the structure of the turbulence, was strongly modified in the first 35 beta sub o, but that they both significantly relaxed toward unmanipulated boundary layer values by 50 beta sub o.

Rashidnia, N.; Falco, R. E.

1987-01-01

141

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.

142

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.

143

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

144

Logarithmic boundary layers in strong Taylor-Couette turbulence.  

PubMed

We provide direct measurements of the boundary layer properties in highly turbulent Taylor-Couette flow up to Re=2106) (Ta=6.210(12)) using high-resolution particle image velocimetry and particle tracking velocimetry. We find that the mean azimuthal velocity profile at the inner and outer cylinder can be fitted by the von Krmn log law u+=1/? lny+ +B. The von Krmn constant ? is found to depend on the driving strength Ta and for large Ta asymptotically approaches ??0.40. The variance profiles of the local azimuthal velocity have a universal peak around y+?12 and collapse when rescaled with the driving velocity (and not with the friction velocity), displaying a log dependence of y+ as also found for channel and pipe flows. PMID:23848878

Huisman, Sander G; Scharnowski, Sven; Cierpka, Christian; Khler, Christian J; Lohse, Detlef; Sun, Chao

2013-06-28

145

Convex curvature effects on the heated turbulent boundary layer  

NASA Technical Reports Server (NTRS)

A convexly curved and isothermally heated wall with a 45-cm radius of curvature is subjected to turbulent boundary layer flow measurements in order to determine wall heat transfer rates and mean velocity and temperature profiles. Significant curvature effects are noted, with Stanton number and skin friction coefficient reductions of 35-40 percent by comparison with flat plate values for the same momentum or enthalpy thickness Reynolds numbers. Profiles of mean velocity and temperature show a more rapid growth of the wake regions, and a shortening of the log-linear region, as a result of curvature. Turbulent Prandtl numbers deduced from the mean temperature profiles under the assumption of a wall thermal law were found to be increased by 40-50 percent by this strong convex curvature.

Simon, T. W.; Moffat, R. J.

1982-01-01

146

Towards Petascale DNS of High Reynolds-Number Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

In flight vehicles, a large portion of fuel consumption is due to skin-friction drag. Reduction of this drag will significantly reduce the fuel consumption of flight vehicles and help our nation to reduce CO 2 emissions. In order to reduce skin-friction drag, an increased understanding of wall-turbulence is needed. Direct numerical simulation (DNS) of spatially developing turbulent boundary layers (SDTBL) can provide the fundamental understanding of wall-turbulence in order to produce models for Reynolds averaged Navier-Stokes (RANS) and large-eddy simulations (LES). DNS of SDTBL over a flat plate at Retheta = 1430 - 2900 were performed. Improvements were made to the DNS code allowing for higher Reynolds number simulations towards petascale DNS of turbulent boundary layers. Mesh refinement and improvements to the inflow and outflow boundary conditions have resulted in turbulence statistics that match more closely to experimental results. The Reynolds stresses and the terms of their evolution equations are reported.

Webster, Keegan R.

147

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.

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

1998-11-01

148

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

149

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

150

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

151

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

152

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

153

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

154

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

155

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

156

Friction  

NSDL National Science Digital Library

This web resource was created as a study in friction by students at an Advanced Mechanics class at Davidson College in Davidson. The resource includes a historical background as well as the various factors that affect friction. The analysis includes sections about Rolling Friction, Velocity Dependence, Stick-Slip mechanism, Adhesion, Wear, Lubrication, Viscosity and Wet vs. Dry Friction.

Conatser, Ryan; Kinnaman, Ben; Lassiter, Mike

2011-04-13

157

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

158

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

159

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

160

The excitation of unstable perturbations in a laminar friction layer  

NASA Technical Reports Server (NTRS)

With the aid of the method of small oscillations which was used successfully in the investigation of the stability of laminar velocity distributions in the presence of two-dimensional perturbations, the excitation of the unstable perturbations for the Hartree velocity distributions occurring in plane boundary-layer flow for decreasing and increasing pressure is calculated as a supplement to a former report. The results of this investigation are to make a contribution toward calculation of the transition point on cylindrical bodies.

Pretsch, Joachim

1952-01-01

161

Singularity Analysis and Boundary Integral Equation Method for Frictional Crack Problems in Two-Dimensional Elasticity  

Microsoft Academic Search

This study investigates the stress singularities in the neighborhood of the tip of a sliding crack with Coulomb-type frictional\\u000a contact surfaces, and applies the boundary integral equation method to solve some frictional crack problems in plane elasticity.\\u000a A universal approach to the determination of the complex order of stress singularity is established analytically by using\\u000a the series expansion of the

K. T. Chau; Y. B. Wang

1998-01-01

162

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

163

The influence of freestream turbulence spectrum on boundary layer transition  

NASA Astrophysics Data System (ADS)

The flow in turbomachines is characterized by a high turbulent activity. Its spectrum frequently reveals energy peaks at privileged frequencies. They generally have an influence upon the boundary layer transition onset. This type of forced transition was studied at the von Karman Institute in a low speed wind tunnel along a flat test surface. Discrete frequency energy peaks were generated into the mainstream flow by acoustic means. The receptivity of the boundary layer flow to the acoustic excitation frequency is put in evidence both by the frequency-dependent transition Reynolds number and the streamwise intermittency factor distributions. The intermittency measurements were performed with the help of a conditional sampling technique; the latter includes a new approach to the positioning of the laminar/turbulent status decision threshold. The growths of selected oscillation modes are compared in a natural and a forced transition situation. A model providing an estimation, within the transition region, of the turbulence level profiles and the skin friction coefficient is proposed.

Costa, Jorge; Arts, Tony

164

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

165

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

166

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

167

Control of Nanoscale Friction on Gold in an Ionic Liquid by a Potential-Dependent Ionic Lubricant Layer  

NASA Astrophysics Data System (ADS)

The lubricating properties of an ionic liquid on gold surfaces can be controlled through application of an electric potential to the sliding contact. A nanotribology approach has been used to study the frictional behavior of 1-butyl-1-methylpyrrolidinium tris(penta?uoroethyl) tri?uorophosphate ([Py1,4]FAP) confined between silica colloid probes or sharp silica tips and a Au(111) substrate using atomic force microscopy. Friction forces vary with potential because the composition of a confined ion layer between the two surfaces changes from cation-enriched (at negative potentials) to anion-enriched (at positive potentials). This offers a new approach to tuning frictional forces reversibly at the molecular level without changing the substrates, employing a self-replenishing boundary lubricant of low vapor pressure.

Sweeney, James; Hausen, Florian; Hayes, Robert; Webber, Grant B.; Endres, Frank; Rutland, Mark W.; Bennewitz, Roland; Atkin, Rob

2012-10-01

168

Control of nanoscale friction on gold in an ionic liquid by a potential-dependent ionic lubricant layer.  

PubMed

The lubricating properties of an ionic liquid on gold surfaces can be controlled through application of an electric potential to the sliding contact. A nanotribology approach has been used to study the frictional behavior of 1-butyl-1-methylpyrrolidinium tris(penta?uoroethyl) tri?uorophosphate ([Py(1,4)]FAP) confined between silica colloid probes or sharp silica tips and a Au(111) substrate using atomic force microscopy. Friction forces vary with potential because the composition of a confined ion layer between the two surfaces changes from cation-enriched (at negative potentials) to anion-enriched (at positive potentials). This offers a new approach to tuning frictional forces reversibly at the molecular level without changing the substrates, employing a self-replenishing boundary lubricant of low vapor pressure. PMID:23102330

Sweeney, James; Hausen, Florian; Hayes, Robert; Webber, Grant B; Endres, Frank; Rutland, Mark W; Bennewitz, Roland; Atkin, Rob

2012-10-12

169

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

170

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

171

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

172

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.

173

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

174

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

175

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

176

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

177

Supersonic and Hypersonic Boundary-Layer Flows  

Microsoft Academic Search

Supersonic and hypersonic numerical research activities of the Lehrstuhl fr Aerodynamik at the Technische Universitt Mnchen\\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

178

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.

179

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

180

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

181

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

182

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

183

Friction and wear characteristics of multi-layer graphene films investigated by atomic force microscopy  

Microsoft Academic Search

Friction and wear characteristics of multi-layer graphene films deposited on a Si substrate by mechanical exfoliation were investigated by atomic force microscopy (AFM). The graphene films consisted of a few layers of carbon basal plane. The number of graphene layers was determined by AFM and Raman spectroscopy. For the AFM friction measurement, loads in the range of ?5 to 30nN

Li-Yu Lin; Dae-Eun Kim; Whan-Kyun Kim; Seong-Chan Jun

2011-01-01

184

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

185

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

186

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

187

ADSORPTION MODELING OF FATTY ESTERS AND OLEIC ESTOLIDES VIA BOUNDARY LUBRICATION COEFFICIENT OF FRICTION MEASUREMENTS  

Technology Transfer Automated Retrieval System (TEKTRAN)

The frictional behaviors of a variety of fatty esters (methyl palmitate (MP), methyl laurate (ML), and 2-ethylhexyl oleate (EHO)) and oleic estolide esters (methyl oleic estolide ester (ME) and 2-ethylhexyl oleic estolide ester (EHE)) as additives in hexadecane have been examined in a boundary lubri...

188

Thermomechanical model with adaptive boundary conditions for friction stir welding of Al 6061  

Microsoft Academic Search

Thermo-mechanical simulation of friction stir welding can predict the transient temperature field, active stresses developed, forces in all the three dimensions and may be extended to determine the residual stress. The thermal stresses constitute a major portion of the total stress developed during the process. Boundary conditions in the thermal modeling of process play a vital role in the final

Vijay Soundararajan; Srdja Zekovic; Radovan Kovacevic

2005-01-01

189

Adsorption Behavior of Heat Modified Soybean Oil via Boundary Lubrication Coefficient of Friction Measurements  

Technology Transfer Automated Retrieval System (TEKTRAN)

The frictional behaviors of soybean oil and heat modified soybean oils with different Gardner scale viscosities as additives in hexadecane have been examined in a boundary lubrication test regime (steel contacts) using Langmuir adsorption model. The free energy of adsorption (delta-Gads) of various...

190

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

191

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

192

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.

193

Near Wall Bubble Transport in a Forced Turbulent Boundary Layer  

NASA Astrophysics Data System (ADS)

Transport of bubbles in turbulent boundary layers remains an area of active research. One of the areas of recent interest is the use of bubbles in skin friction drag reduction. However, for drag reduction to be effective, it seems that bubbles need to be kept in the near wall region, where wall shear stress derives from. Simulating the conditions meaningful to full scale vessels is very difficult in the laboratory due to scaling issues. Towards that end, we have used the idea of forced turbulence to simulate the near wall region. This allows us to inject bubbles into what is effectively the sub-layer, letting us explore bubble transport very close to the wall. We used the hydrogen wire technique to generate bubbles through electrolysis of water. The generating wire was placed at various heights above the wall to measure how transport is affected by injection location. Results indicate that injection at the wall may not be optimal with regards to keeping the bubbles near the wall. The authors would like to thank the Office of Naval Research for their support under Grant No. N00014-00-1-0110.

Jeon, David

2005-11-01

194

Turbulent boundary layer over solid and porous surfaces with small roughness  

NASA Technical Reports Server (NTRS)

Skin friction and profiles of mean velocity, axial and normal turbulence intensity, and Reynolds stress in the untripped boundary layer were measured directly on a large diameter, axisymmetric body with: (1) a smooth, solid surface; (2) a sandpaper-roughened, solid surface; (3) a sintered metal, porous surface; (4) a smooth, perforated titanium surface; (5) a rough solid surface made of fine, diffusion bonded screening, and (6) a rough, porous surface of the same screening. Results obtained for each of these surfaces are discussed. It is shown that a rough, porous wall simply does not influence the boundary layer in the same way as a rough solid wall. Therefore, turbulent transport models for boundary layers over porous surfaces either with or without injection or suction, must include both surface roughness and porosity effects.

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

1982-01-01

195

Assessment of Turbulent Shock-Boundary Layer Interaction Computations Using the OVERFLOW Code  

NASA Technical Reports Server (NTRS)

The performance of two popular turbulence models, the Spalart-Allmaras model and Menter s SST model, and one relatively new model, Olsen & Coakley s Lag model, are evaluated using the OVERFLOWcode. Turbulent shock-boundary layer interaction predictions are evaluated with three different experimental datasets: a series of 2D compression ramps at Mach 2.87, a series of 2D compression ramps at Mach 2.94, and an axisymmetric coneflare at Mach 11. The experimental datasets include flows with no separation, moderate separation, and significant separation, and use several different experimental measurement techniques (including laser doppler velocimetry (LDV), pitot-probe measurement, inclined hot-wire probe measurement, preston tube skin friction measurement, and surface pressure measurement). Additionally, the OVERFLOW solutions are compared to the solutions of a second CFD code, DPLR. The predictions for weak shock-boundary layer interactions are in reasonable agreement with the experimental data. For strong shock-boundary layer interactions, all of the turbulence models overpredict the separation size and fail to predict the correct skin friction recovery distribution. In most cases, surface pressure predictions show too much upstream influence, however including the tunnel side-wall boundary layers in the computation improves the separation predictions.

Oliver, A. B.; Lillard, R. P.; Schwing, A. M.; Blaisdell, G> A.; Lyrintzis, A. S.

2007-01-01

196

Acoustics of friction.  

PubMed

This article presents an overview of the acoustics of friction by covering friction sounds, friction-induced vibrations and waves in solids, and descriptions of other frictional phenomena related to acoustics. Friction, resulting from the sliding contact of solids, often gives rise to diverse forms of waves and oscillations within solids which frequently lead to radiation of sound to the surrounding media. Among the many everyday examples of friction sounds, violin music and brake noise in automobiles represent the two extremes in terms of the sounds they produce and the mechanisms by which they are generated. Of the multiple examples of friction sounds in nature, insect sounds are prominent. Friction also provides a means by which energy dissipation takes place at the interface of solids. Friction damping that develops between surfaces, such as joints and connections, in some cases requires only microscopic motion to dissipate energy. Modeling of friction-induced vibrations and friction damping in mechanical systems requires an accurate description of friction for which only approximations exist. While many of the components that contribute to friction can be modeled, computational requirements become prohibitive for their contemporaneous calculation. Furthermore, quantification of friction at the atomic scale still remains elusive. At the atomic scale, friction becomes a mechanism that converts the kinetic energy associated with the relative motion of surfaces to thermal energy. However, the description of the conversion to thermal energy represented by a disordered state of oscillations of atoms in a solid is still not well understood. At the macroscopic level, friction interacts with the vibrations and waves that it causes. Such interaction sets up a feedback between the friction force and waves at the surfaces, thereby making friction and surface motion interdependent. Such interdependence forms the basis for friction-induced motion as in the case of ultrasonic motors and other examples. Last, when considered phenomenologically, friction and boundary layer turbulence exhibit analogous properties and, when compared, each may provide clues to a better understanding of the other. PMID:12002837

Akay, Adnan

2002-04-01

197

Friction-term response to boundary-condition type in flow models  

USGS Publications Warehouse

The friction-slope term in the unsteady open-channel flow equations is examined using two numerical models based on different formulations of the governing equations and employing different solution methods. The purposes of the study are to analyze, evaluate, and demonstrate the behavior of the term in a set of controlled numerical experiments using varied types and combinations of boundary conditions. Results of numerical experiments illustrate that a given model can respond inconsistently for the identical resistance-coefficient value under different types and combinations of boundary conditions. Findings also demonstrate that two models employing different dependent variables and solution methods can respond similarly for the identical resistance-coefficient value under similar types and combinations of boundary conditions. Discussion of qualitative considerations and quantitative experimental results provides insight into the proper treatment, evaluation, and significance of the friction-slope term, thereby offering practical guidelines for model implementation and calibration.

Schaffranek, R.W.; Lai, C.

1996-01-01

198

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

199

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

200

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

201

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

202

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

203

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

204

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

205

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

206

Reduction of friction and wear by grooves applied on the nanoscale polished surface in boundary lubrication conditions  

PubMed Central

The evolution of a friction surface geometry with initially directed microscale grooves on a nanoscale polished surface in ring-on-block sliding contact is studied experimentally. Reduced wear and friction is observed when the orientation of grooves coincides with the direction of sliding. A new compressive-vacuum hypothesis of friction force nature under a condition of boundary lubrication is proposed, which successfully explains the observed phenomena. Grooves supply lubricant into the contact zone and facilitate its devacuumization, which lead to substantial reduction of surface wear. The obtained results enable developing optimized roughness profiles of friction surfaces to create high-performance durable friction units. PMID:24872807

2014-01-01

207

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

208

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

209

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

210

The Role of Adsorbed Water on the Friction of a Layer of Submicron Particles CHARLES G. SAMMIS,1  

E-print Network

friction with an apparent coefficient near l = 0.6 at low slip speeds to a coefficient near l = 0 layer enables the otherwise rough particles to rotate, the coefficient of friction will drop to l = 0 layer vaporizes, the particles contact and lock, and the coefficient of friction rises to l = 0

Ze'ev, Reches

211

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

212

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

213

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

214

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

215

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

216

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

217

Navier-Stokes equations in 3D thin domains with Navier friction boundary condition  

NASA Astrophysics Data System (ADS)

In this article we study the 3D Navier-Stokes equations with Navier friction boundary condition in thin domains. We prove the global existence of strong solutions to the 3D Navier-Stokes equations when the initial data and external forces are in large sets as the thickness of the domain is small. We generalize the techniques developed to study the 3D Navier-Stokes equations in thin domains, see [G. Raugel, G. Sell, Navier-Stokes equations on thin 3D domains I: Global attractors and global regularity of solutions, J. Amer. Math. Soc. 6 (1993) 503-568; G. Raugel, G. Sell, Navier-Stokes equations on thin 3D domains II: Global regularity of spatially periodic conditions, in: Nonlinear Partial Differential Equations and Their Application, College de France Seminar, vol. XI, Longman, Harlow, 1994, pp. 205-247; R. Temam, M. Ziane, Navier-Stokes equations in three-dimensional thin domains with various boundary conditions, Adv. Differential Equations 1 (1996) 499-546; R. Temam, M. Ziane, Navier-Stokes equations in thin spherical shells, in: Optimization Methods in Partial Differential Equations, in: Contemp. Math., vol. 209, Amer. Math. Soc., Providence, RI, 1996, pp. 281-314], to the Navier friction boundary condition by introducing a new average operator M in the thin direction according to the spectral decomposition of the Stokes operator A. Our analysis hinges on the refined investigation of the eigenvalue problem corresponding to the Stokes operator A with Navier friction boundary condition.

Hu, Changbing

218

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

219

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

220

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

221

A finite-difference outer layer and integral inner layer method for the solution of the turbulent boundary layer equations  

NASA Technical Reports Server (NTRS)

A new turbulent boundary-layer method is developed which models the inner region with the law of the wall while the outer region uses Clauser's eddy viscosity in Matsuno's finite-difference method. The match point between the inner and outer regions as well as the wall shear stress are determined at each marching step during the computation. Results obtained for incompressible, two-dimensional flow over flat plates and ellipses are compared with solutions from a baseline method which uses a finite-difference method for the entire boundary layer. Since the present method used the finite-difference method in the outer region only, the number of grid points required was about half that needed for the baseline method. Accurate displacement and momentum thicknesses were predicted for all cases. Skin friction was predicted well for the flat plate, but the accuracy decreased significantly for the ellipses. Adding a wake functions to the law of the wall allows some of the pressure gradient effect to be taken into account thereby increasing the accuracy of the method.

Barnwell, R. W.; Dejarnette, F. R.; Wahls, R. A.

1987-01-01

222

Three-dimensional boundary layer stability and transition  

NASA Technical Reports Server (NTRS)

Nonparallel and nonlinear stability of a three-dimensional boundary layer, subject to crossflow instability, is investigated using parabolized stability equations (PSEs). Both traveling and stationary disturbances are considered and nonparallel effect on crossflow instability is found to be destabilizing. Our linear PSE results for stationary disturbances agree well with the results from direct solution of Navier-Stokes equations obtained by Spalart (1989). Nonlinear calculations have been carried out for stationary vortices and the computed wall vorticity pattern results in streamwise streaks which resemble remarkably well with the surface oil-flow visualizations in swept-wing experiments. Other features of the stationary vortex development (half-mushroom structure, inflected velocity profiles, vortex doubling, etc.) are also captured in our nonlinear calculations. Nonlinear interaction of the stationary amplitude of the stationary vortex is large as compared to the traveling mode, and the stationary vortex dominates most of the downstream development. When the two modes have the same initial amplitude, the traveling mode dominates the downstream development owing to its higher growth rate, and there is a tendency for the stationary mode to be suppressed. The effect of nonlinear wave development on the skin-friction coefficient is also computed.

Malik, M. R.; Li, F.

1992-01-01

223

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.

224

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

225

Friction  

NSDL National Science Digital Library

This website from Kathleen Cummings Dominguez at the Illinois Institute of Technology provides a lesson plan on the concepts of friction. It describes a lesson plan which will engage students in active classroom learning.

2010-03-17

226

A New View on Origin, Role and Manipulation of Large Scales in Turbulent Boundary Layers  

NASA Technical Reports Server (NTRS)

The potential of passive 'manipulators' for altering the large scale turbulent structures in boundary layers was investigated. Utilizing smoke wire visualization and multisensor probes, the experiment verified that the outer scales could be suppressed by simple arrangements of parallel plates. As a result of suppressing the outer scales in turbulent layers, a decrease in the streamwise growth of the boundary layer thickness was achieved and was coupled with a 30 percent decrease in the local wall friction coefficient. After accounting for the drag on the manipulator plates, the net drag reduction reached a value of 20 percent within 55 boundary layer thicknesses downstream of the device. No evidence for the reoccurrence of the outer scales was present at this streamwise distance thereby suggesting that further reductions in the net drag are attainable. The frequency of occurrence of the wall events is simultaneously dependent on the two parameters, Re2 delta sub 2 and Re sub x. As a result of being able to independently control the inner and outer boundary layer characteristics with these manipulators, a different view of these layers emerged.

Corke, T. C.; Nagib, H. M.; Guezennec, Y. G.

1982-01-01

227

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

228

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

229

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

230

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

231

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

232

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

233

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

234

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

235

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

236

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

237

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

238

Friction  

NASA Astrophysics Data System (ADS)

Friction materials such as disk pads, brake linings, and clutch facings are widely used for automotive applications. Friction materials function during braking due to frictional resistance that transforms kinetic energy into thermal energy. There has been a rudimentary evolution, from materials like leather or wood to asbestos fabric or asbestos fabric saturated with various resins such as asphalt or resin combined with pitch. These efforts were further developed by the use of woven asbestos material saturated by either rubber solution or liquid resin binder and functioned as an internal expanding brake, similar to brake lining system. The role of asbestos continued through the use of chopped asbestos saturated by rubber, but none was entirely successful due to the poor rubber heat resistance required for increased speeds and heavy gearing demands of the automobile industry. The use of phenolic resins as binder for asbestos friction materials provided the necessary thermal resistance and performance characteristics. Thus, the utility of asbestos as the main friction component, for over 100 years, has been significantly reduced in friction materials due to asbestos identity as a carcinogen. Steel and other fibrous components have displaced asbestos in disk pads. Currently, non-asbestos organics are the predominate friction material. Phenolic resins continue to be the preferred binder, and increased amounts are necessary to meet the requirements of highly functional asbestos-free disk pads for the automotive industry. With annual automobile production exceeding 70 million vehicles and additional automobile production occurring in developing countries worldwide and increasing yearly, the amount of phenolic resin for friction material is also increasing (Fig. 14.1). Fig. 14.1 Worldwide commercial vehicle production In recent years, increased fuel efficiency of passenger car is required due to the CO2 emission issue. One of the solutions to improve fuel efficiency is to lower the car body weight. It means that the weight of car components must be decreased. In the case of reduced weight for friction parts, the load applied to the friction parts would be higher (more heat also) and trend would lead to phenolic resins with improved heat resistance.

Matsuo, Yoshihiro; Clarke, Daryl D.; Ozeki, Shinichi

239

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

240

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

241

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

242

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

243

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

244

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

245

Role of friction in pattern formation in oscillated granular layers Sung Joon Moon,* J. B. Swift, and Harry L. Swinney  

E-print Network

Role of friction in pattern formation in oscillated granular layers Sung Joon Moon,* J. B. Swift as there are no elastic grains. Our molecular dynamics simulations reveal that friction is essential for realistic with friction. More importantly, even though square and hexagonal patterns form for a wide range

Texas at Austin. University of

246

Role of friction in pattern formation in oscillated granular layers Sung Joon Moon, # J. B. Swift, and Harry L. Swinney  

E-print Network

Role of friction in pattern formation in oscillated granular layers Sung Joon Moon, # J. B. Swift grains. Our molecular dynamics simu­ lations reveal that friction is essential for realistic modeling at a container acceleration about 30% smaller than that observed in experiments and simulations with friction

Texas at Austin. University of

247

Existence and general decay for nondissipative distributed systems with boundary frictional and memory dampings and acoustic boundary conditions  

NASA Astrophysics Data System (ADS)

In this paper, we study the existence and general energy decay rate of global solutions for nondissipative distributed systems u''-triangle u+h(nabla u)=0 with boundary frictional and memory dampings and acoustic boundary conditions. For the existence of solutions, we prove the global existence of weak solution by using Faedo-Galerkin's method and compactness arguments. For the energy decay rate, we first consider the general nonlinear case of h satisfying a smallness condition and prove the general energy decay rate by using perturbed modified energy method. Then, we consider the linear case of h: {h(nabla u)=-nabla?\\cdotnabla u} and prove the general decay estimates of equivalent energy.

Liu, Wenjun; Chen, Kewang

2014-12-01

248

Friction  

NSDL National Science Digital Library

The representation demonstrates, through an animated, narrated slide-show, how frictional forces, including air resistance, can affect the motion of an object. This resource also includes an interactive test and review of the material. One is also able to download "myskoool" which allows allows one to download lessons to run offline and use anytime.

249

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

250

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 Mkinen; Marcello Fulchignoni

2006-01-01

251

An Experimental Investigation of Forced Mixing of a Turbulent Boundary Layer in an Annular Diffuser. Ph.D. Thesis - Ohio State Univ.; [for boundary layer control  

NASA Technical Reports Server (NTRS)

The forced mixing process of a turbulent boundary layer in an axisymmetric annular diffuser using conventional wing-like vortex generators was studied. Flow field measurements were made at four axial locations downstream of the vortex generators. At each axial location, a total of 25 equally spaced profiles were measured behind three consecutive vortex generators which formed two pairs of vortex generators. Hot film anemometry probes measured the boundary layer turbulence structure at the same locations where pressure measurements were made. Both single and cross film probes were used. The diffuser turbulence data was teken only for a nominal inlet Mach number of 0.3. Three vortex generator configurations were tested. The differences between configurations involved changes in size and relative vortex generator positions. All three vortex generator configurations tested provided increases in diffuser performance. Distinct differences in the boundary layer integral properties and skin friction levels were noted between configurations. The axial turbulence intensity and Reynolds stress profiles measured displayed similarities in trends but differences in levels for the three configurations.

Shaw, R. J.

1979-01-01

252

The friction factor of two-dimensional rough-boundary turbulent soap film flows  

E-print Network

We use momentum transfer arguments to predict the friction factor $f$ in two-dimensional turbulent soap-film flows with rough boundaries (an analogue of three-dimensional pipe flow) as a function of Reynolds number Re and roughness $r$, considering separately the inverse energy cascade and the forward enstrophy cascade. At intermediate Re, we predict a Blasius-like friction factor scaling of $f\\propto\\textrm{Re}^{-1/2}$ in flows dominated by the enstrophy cascade, distinct from the energy cascade scaling of $\\textrm{Re}^{-1/4}$. For large Re, $f \\sim r$ in the enstrophy-dominated case. We use conformal map techniques to perform direct numerical simulations that are in satisfactory agreement with theory, and exhibit data collapse scaling of roughness-induced criticality, previously shown to arise in the 3D pipe data of Nikuradse.

Nicholas Guttenberg; Nigel Goldenfeld

2009-03-25

253

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

254

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

255

The Role of Adsorbed Water on the Friction of a Layer of Submicron Particles  

NASA Astrophysics Data System (ADS)

Anomalously low values of friction observed in layers of submicron particles deformed in simple shear at high slip velocities are explained as the consequence of a one nanometer thick layer of water adsorbed on the particles. The observed transition from normal friction with an apparent coefficient near ?=0.6 at low slip speeds to a coefficient near ?=0.3 at higher slip speeds is attributed to a competition between the time required to extrude the water layer from between neighboring particles in a force chain and the average lifetime of the chain. At low slip speeds the time required for extrusion is less than the average lifetime of a chain so the particles make contact and lock. As slip speed increases, the average lifetime of a chain decreases until it is less than the extrusion time and the particles in a force chain never come into direct contact. If the adsorbed water layer allows the otherwise rough particles to rotate, then the coefficient of friction will drop to ?=0.3 appropriate for rotating spheres. At the highest slip speeds particle temperatures rise above 100 C, the water layer vaporizes, the particles contact and lock, and the coefficient of friction rises to ?=0.6. The observed onset of weakening at slip speeds near 0.001 m/s is consistent with the measured viscosity of a 1nm thick layer of adsorbed water, with a minimum particle radius of about 20 nm, and with reasonable assumptions about the distribution of force chains guided by experimental observation. The reduction of friction and range of velocities over which it occurs decreases with increasing normal stress as predicted by the model. Moreover, the analysis predicts that this high speed weakening mechanism should operate only for particles with radii smaller than about 1 ?m. For larger particles the slip speed required for weakening is so large that frictional heating will evaporate the adsorbed water and weakening will not occur.

Sammis, C. G.; Lockner, D. A.; Reches, Z.

2011-12-01

256

The Role of Adsorbed Water on the Friction of a Layer of Submicron Particles  

NASA Astrophysics Data System (ADS)

Anomalously low values of friction observed in layers of submicron particles deformed in simple shear at high slip velocities are explained as the consequence of a one nanometer thick layer of water adsorbed on the particles. The observed transition from normal friction with an apparent coefficient near ? = 0.6 at low slip speeds to a coefficient near ? = 0.3 at higher slip speeds is attributed to competition between the time required to extrude the water layer from between neighboring particles in a force chain and the average lifetime of the chain. At low slip speeds the time required for extrusion is less than the average lifetime of a chain so the particles make contact and lock. As slip speed increases, the average lifetime of a chain decreases until it is less than the extrusion time and the particles in a force chain never come into direct contact. If the adsorbed water layer enables the otherwise rough particles to rotate, the coefficient of friction will drop to ? = 0.3, appropriate for rotating spheres. At the highest slip speeds particle temperatures rise above 100C, the water layer vaporizes, the particles contact and lock, and the coefficient of friction rises to ? = 0.6. The observed onset of weakening at slip speeds near 0.001 m/s is consistent with the measured viscosity of a 1 nm thick layer of adsorbed water, with a minimum particle radius of approximately 20 nm, and with reasonable assumptions about the distribution of force chains guided by experimental observation. The reduction of friction and the range of velocities over which it occurs decrease with increasing normal stress, as predicted by the model. Moreover, the analysis predicts that this high-speed weakening mechanism should operate only for particles with radii smaller than approximately 1 ?m. For larger particles the slip speed required for weakening is so large that frictional heating will evaporate the adsorbed water and weakening will not occur.

Sammis, Charles G.; Lockner, David A.; Reches, Ze'ev

2011-12-01

257

The role of adsorbed water on the friction of a layer of submicron particles  

USGS Publications Warehouse

Anomalously low values of friction observed in layers of submicron particles deformed in simple shear at high slip velocities are explained as the consequence of a one nanometer thick layer of water adsorbed on the particles. The observed transition from normal friction with an apparent coefficient near ? = 0.6 at low slip speeds to a coefficient near ? = 0.3 at higher slip speeds is attributed to competition between the time required to extrude the water layer from between neighboring particles in a force chain and the average lifetime of the chain. At low slip speeds the time required for extrusion is less than the average lifetime of a chain so the particles make contact and lock. As slip speed increases, the average lifetime of a chain decreases until it is less than the extrusion time and the particles in a force chain never come into direct contact. If the adsorbed water layer enables the otherwise rough particles to rotate, the coefficient of friction will drop to ? = 0.3, appropriate for rotating spheres. At the highest slip speeds particle temperatures rise above 100C, the water layer vaporizes, the particles contact and lock, and the coefficient of friction rises to ? = 0.6. The observed onset of weakening at slip speeds near 0.001 m/s is consistent with the measured viscosity of a 1 nm thick layer of adsorbed water, with a minimum particle radius of approximately 20 nm, and with reasonable assumptions about the distribution of force chains guided by experimental observation. The reduction of friction and the range of velocities over which it occurs decrease with increasing normal stress, as predicted by the model. Moreover, the analysis predicts that this high-speed weakening mechanism should operate only for particles with radii smaller than approximately 1 ?m. For larger particles the slip speed required for weakening is so large that frictional heating will evaporate the adsorbed water and weakening will not occur.

Sammis, Charles G.; Lockner, David A.; Reches, Zeev

2011-01-01

258

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.

259

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

260

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

261

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

262

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

263

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

264

Turbulent boundary layer over solid and porous surfaces with small roughness  

NASA Technical Reports Server (NTRS)

The turbulent boundary layer over a smooth, solid wall is examined along with a sandpaper-roughened, solid wall, and a porous wall. Suitable results are obtained with the smooth, solid wall for the Law of the Wall, the Defect Law, and the axial and turbulence intensities. The logarithmic portion of the Wall Law is shifted in the sandpaper-roughened, solid wall and an increase in the normal turbulence intensity and Reynolds stress is observed. An increase in the local skin friction values and all the turbulence values is found with the porous wall. The influence of a slightly rough, porous wall of sintered metal on the boundary layer is compared with a solid sandpaper-roughened wall in the same nominal K(+) range.

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

1981-01-01

265

Boundary-layer measurements on a high Reynolds number three-element airfoil  

NASA Technical Reports Server (NTRS)

An experimental investigation is being conducted to evaluate the boundary layer associated with a two-dimensional three-element single-flap airfoil at high Reynolds numbers. The present measurements are being made in the Langley Low-Turbulence (centerline turbulence intensity level is 0.034 percent at a Mach number of 0.2 and a total pressure of 60 psia) Pressure Tunnel (LTPT). The LTPT is a closed-circuit wind tunnel with a test section which is 3 ft wide, 7.5 ft high, and 7.5 ft long. Operating total pressure for the LTPT varies from 10 atmospheres to near-vacuum conditions. Tests are being conducted at a Mach number of 0.2 and Reynolds numbers (based on chord length) of 5, 9, and 16 million. Measurements include boundary-layer velocity surveys at several chordwise locations and surface skin-friction measurements using Preston tubes.

Selby, Gregory V.

1992-01-01

266

The Compressible Laminar Boundary Layer with Heat Transfer and Arbitrary Pressure Gradient  

NASA Technical Reports Server (NTRS)

An approximate method for the calculation of the compressible laminar boundary layer with heat transfer and arbitrary pressure gradient, based on Thwaites' correlation concept, is presented. With the definition of dimensionless shear and heat-transfer parameters and an assumed correlation of these parameters in terms of a momentum parameter, a complete system of relations for calculating skin friction and heat transfer results. Knowledge of velocity or temperature profiles is not necessary in using this calculation method. When the method is applied to a convergent-divergent, axially symmetric rocket nozzle, it shows that high rates of heat transfer are obtained at the initial stagnation point and at the throat of the nozzle. Also indicated are negative displacement thicknesses in the convergent portion of the nozzle; these occur because of the high density within the lower portions of the cooled boundary layer. (author)

Cohen, Clarence B; Reshotko, Eli

1956-01-01

267

Investigation of blown boundary layers with an improved wall jet system  

NASA Technical Reports Server (NTRS)

Measurements were made in a two dimensional incompressible wall jet submerged under a thick upstream boundary layer with a zero pressure gradient and an adverse pressure gradient. The measurements included mean velocity and Reynolds stresses profiles, skin friction, and turbulence spectra. The measurements were confined to practical ratios (less than 2) of the jet velocity to the free stream velocity. The wall jet used in the experiments had an asymmetric velocity profile with a relatively higher concentration of momentum away from the wall. An asymmetric jet velocity profile has distinct advantages over a uniform jet velocity profile, especially in the control of separation. Predictions were made using Irwin's (1974) method for blown boundary layers. The predictions clearly show the difference in flow development between an asymmetric jet velocity profile and a uniform jet velocity profile.

Saripalli, K. R.; Simpson, R. L.

1980-01-01

268

Experimental study of boundary layer transition on a heated flat plate  

NASA Technical Reports Server (NTRS)

A detailed investigation to the document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were done in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate, and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for momentum thickness Reynolds number, Re(sub theta) less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length and uniform heat flux. A small dependence of turbulence results on the freestream turbulence intensity was observed.

Sohn, K. H.; Reshotko, E.; Zaman, K. B. M. Q.

1991-01-01

269

Laminar boundary layer on the moving surface of a Rankine oval  

NASA Astrophysics Data System (ADS)

The paper presents a numerical analysis of a laminar boundary layer arising on the surface of a cylindrical body (a Rankine oval with a relative elongation of 4) moving with constant velocity in an incompressible fluid. Distributions of shear stress on the cylinder surface are determined for different velocities of the wall. Numerical integration is used to determine the magnitude of work necessary to overcome friction and pressure drag as well as to calculate the work expended on the motion of the moving cylinder surface. The drag forces in the presence of a separation region are calculated on the assumption that, in this region, the pressure and shear stress on the wall are constant and equal to the corresponding values at the singular point in the solution of the boundary layer equations.

Zubarev, V. M.

1984-06-01

270

Turbulent boundary layer on the moving surface of a 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.

1984-10-01

271

A finite difference method for predicting supersonic turbulent boundary layer flows with tangential slot injection  

NASA Technical Reports Server (NTRS)

An implicit finite difference method has been applied to tangential slot injection into supersonic turbulent boundary layer flows. In addition, the effects induced by the interaction between the boundary layer displacement thickness and the external pressure field are considered. In the present method, three different eddy viscosity models have been used to specify the turbulent momentum exchange. One model depends on the species concentration profile and the species conservation equation has been included in the system of governing partial differential equations. Results are compared with experimental data at stream Mach numbers of 2.4 and 6.0 and with results of another finite difference method. Good agreement was generally obtained for the reduction of wall skin friction with slot injection and with experimental Mach number and pitot pressure profiles. Calculations with the effects of pressure interaction included showed these effects to be smaller than effects of changing eddy viscosity models.

Miner, E. W.; Lewis, C. H.

1972-01-01

272

Study of stirred layers on 316L steel created by friction stir processing  

NASA Astrophysics Data System (ADS)

Nanostructured materials are known to exhibit attractive properties, especially in the mechanical field where high hardness is of great interest. The friction stir process (FSP) is a recent surface engineering technique derived from the friction stir welding method (FSW). In this study, the FSP of an 316L austenitic stainless steel has been evaluated. The treated layers have been characterized in terms of hardness and microstructure and these results have been related to the FSP operational parameters. The process has been analysed using a Response Surface Method (RSM) to enable the stirred layer thickness prediction.

Langlade, C.; Roman, A.; Schlegel, D.; Gete, E.; Folea, M.

2014-08-01

273

A boundary-layer model for Mars - Comparison with Viking lander and entry data  

NASA Astrophysics Data System (ADS)

A 1D boundary-layer model of Mars based on a momentum equation that describes friction, pressure gradient, and Coriolis forces is presented. Frictional forces and convective heating are computed using the level-2 turbulence closure theory of Mellor and Yamada (1974). The model takes into account the radiative effects of CO2 gas and suspended dust particles. Both radiation and convection depend on surface temperatures which are computed from a surface heat budget. Model predictions are compared with available observations from Viking landers. It is concluded that, in general, the model reproduces the basic features of the temperature data. The agreement is particularly good at entry time for the V L-2 site, where the model and observations are within several degrees at all levels for which data are available.

Haberle, R. M.; Houben, H. C.; Hertenstein, R.; Herdtle, T.

1993-06-01

274

Self-adaptive difference method for the effective solution of computationally complex problems of boundary layer theory  

NASA Technical Reports Server (NTRS)

An implicit difference procedure for the solution of equations for a chemically reacting hypersonic boundary layer is described. Difference forms of arbitrary error order in the x and y coordinate plane were used to derive estimates for discretization error. Computational complexity and time were minimized by the use of this difference method and the iteration of the nonlinear boundary layer equations was regulated by discretization error. Velocity and temperature profiles are presented for Mach 20.14 and Mach 18.5; variables are velocity profiles, temperature profiles, mass flow factor, Stanton number, and friction drag coefficient; three figures include numeric data.

Schoenauer, W.; Daeubler, H. G.; Glotz, G.; Gruening, J.

1986-01-01

275

A critical evaluation of invariant second-order closure models for subsonic boundary layers  

NASA Technical Reports Server (NTRS)

Computations based on several second-order turbulence models, including full Reynolds stress and two-equation models, are compared with a number of boundary-layer experiments. In general, the models represent the data reasonably well, with skin friction tending to be somewhat overpredicted in the far downstream region of the adverse pressure gradient experiments. A discussion of the behavior of the ARAP full Reynolds stress model in predicting the components of the Reynolds stress tensor is given. It is concluded that compatibility at the wall may necessitate the use of more than one length scale.

Rubesin, M. W.; Crisalli, A. J.; Acharya, M.; Lanfranco, M. J.

1977-01-01

276

Highly Accurate Solutions of the Blasius and Falkner-Skan Boundary Layer Equations via Convergence Acceleration  

E-print Network

A new highly accurate algorithm for the solution of the Falkner-Skan equation of boundary layer theory is presented. The algorithm, based on a Maclaurin series representation, finds its coefficients from recurrence. In addition, Wynn-epsilon convergence acceleration and continuous analytical continuation enable an accurate evaluation. The most accurate skin friction coefficients (shooting angle) to date are presented along with comparisons to past and present values found in the literature. The algorithm, coded in FORTRAN, uses neither enhanced precision arithmetic beyond quadruple precision nor computer algebra to achieve results in a timely fashion. Key Words: Falkner-Skan flow; Blasius flow; Wynn-epsilon acceleration; Romberg acceleration; Continuous analytical continuation

B. D. Ganapol

2010-06-19

277

The turbulent boundary layer on a porous plate: An experimental study of the fluid mechanics for adverse free stream pressure gradients  

NASA Technical Reports Server (NTRS)

An experimental investigation of transpired turbulent boundary layers in zero and adverse pressure gradients has been carried out. Profiles of: (1) the mean velocity, (2) the three intensities of the turbulent fluctuations, and (3) the Reynolds stress were obtained by hot-wire anemometry. The friction coefficients were measured by using an integrated form of the boundary layer equation to extrapolate the measured shear stress profiles to the wall.

Anderson, P. S.; Kays, W. M.; Moffat, R. J.

1972-01-01

278

Lecture Series "Boundary Layer Theory". Part I - Laminar Flows. Part 1; Laminar Flows  

NASA Technical Reports Server (NTRS)

In the lecture series starting today author want to give a survey of a field of aerodynamics which has for a number of years been attracting an ever growing interest. The subject is the theory of flows with friction, and, within that field, particularly the theory of friction layers, or boundary layers. A great many considerations of aerodynamics are based on the ideal fluid, that is the frictionless incompressibility and fluid. By neglect of compressibility and friction the extensive mathematical theory of the ideal fluid, (potential theory) has been made possible. Actual liquids and gases satisfy the condition of incomressibility rather well if the velocities are not extremely high or, more accurately, if they are small in comparison with sonic velocity. For air, for instance, the change in volume due to compressibility amounts to about 1 percent for a velocity of 60 meters per second. The hypothesis of absence of friction is not satisfied by any actual fluid; however, it is true that most technically important fluids, for instance air and water, have a very small friction coefficient and therefore behave in many cases almost like the ideal frictionless fluid. Many flow phenomena, in particular most cases of lift, can be treated satisfactorily, - that is, the calculations are in good agreement with the test results, -under the assumption of frictionless fluid. However, the calculations with frictionless flow show a very serious deficiency; namely, the fact, known as d'Alembert's paradox, that in frictionless flow each body has zero drag whereas in actual flow each body experiences a drag of greater or smaller magnitude. For a long time the theory has been unable to bridge this gap between the theory of frictionless flow and the experimental findings about actual flow. The cause of this fundamental discrepancy is the viscosity which is neglected in the theory of ideal fluid; however, in spite of its extraordinary smallness it is decisive for the course of the flow phenomena.

Schlichting, H.

1949-01-01

279

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, Anglique (Anglique Pascale)

2006-01-01

280

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

281

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...

282

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

283

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

284

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

285

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

286

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

287

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

288

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

289

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

290

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

291

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

292

Heat Transmission in the Boundary Layer  

NASA Technical Reports Server (NTRS)

In the present paper which deals with the heat transfer between the gas and the wall for large temperature drops and large velocities use is made of the method of Dorodnitsyn of the introduction of a new independent variable, with this difference, however, that the relation between the temperature field (that is, density) and the velocity field in the general case considered is not assumed given but is determined from the solution of the problem. The effect of the compressibility arising from the heat transfer is thus taken into account (at the same time as the effect of the compressibility at the large velocities). A method is given for determining the coefficients of heat transfer and the friction coefficients required in many technical problems for a curved wall in a gas flow at large Mach numbers and temperature drops. The method proposed is applicable both for Prandtl number P = 1 and for P not equal to 1.

Kalikhman, L. E.

1949-01-01

293

FEM simulation on rotating piercing process of double-layer clad sheet with Coulomb friction  

NASA Astrophysics Data System (ADS)

This study proposes a new piercing technology with rotating punch on the double-layer clad sheet; it carries out an FEM simulation on rotating piercing process using DEFORM-3D commercial software. Frictions among the punch, the blank holder, the dies and the double-layer clad sheet material are assumed as Coulomb friction, but can be different. The surface of the inner diameter, the effective stress, the effective strain, velocity field, damage, burr and the shearing force can be determined form the FEM simulation. In this study, effects of various piercing conditions such as the clearance, the punch nose angle, the frictional factor, the rotating angular velocity, the shearing force, and burr on shearing characteristics are explored effectively to realize the feasibility of FEM model.

Tzou, Gow-Yi; Hwang, Yeong-Maw; Teng, Hsiang-Yu

2013-12-01

294

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-Bnard experiment are presented for the Rayleigh number Ra=1.41010. 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-Bnard 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, Andr; Willert, Christian

2014-03-28

295

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

296

Frictional Heating Recoded in Vitrinite Reflectance Within Coal Material Concentrated Layer: the Cretaceous Shimanto Belt  

NASA Astrophysics Data System (ADS)

Frictional heating by faulting is related to effective friction coefficient, displacement, and thickness of fault. Geological records of frictional heating have been measured from some faults by various methods and applied to reconstructions of the fault slip behaviors (i.e., Fulton et al., 2012). Vitrinite reflectance (Ro) is one of the methods to detect the geological records of frictional heating. Vitrinite is a kind of coal maceral. Degree of coalification is related to Ro. In the previous studies, using Ro, frictional heating was identified along some faults including shallow deocollement and mega-splay fault in Nankai trough (Sakaguchi et al., 2011). The similar geological evidence can be observed in exhumed accretionary complexes. In this study, we tried to detect the evidence of frictional heating along minor faults developed in an exhumed accretionary complex using Ro. A coal concentrated layer was found in an exhumed accretionary complex, Shimanto Belt, SW Japan. The thickness of the coal concentrated layer is about 80 cm. Some faults are developed within the coal concentrated layer. Thickness of the faults is about a few mm to 1 cm. The coal concentrated layer is appropriate to examine the distribution of Ro. I measured Ro from samples collected around and outside of the layer. Ro of the sample more than 3cm away from the fault was about 1.0% in average. This value is corresponds the background value in this area. On the other hand, Ro of the samples within 3 cm from the fault shows bimodal distribution in histogram representing 1.0% and 1.2% at the peaks. This higher peak can indicate the frictional heating by faulting. Temperature by frictional heating was estimated from Ro following methods of O'Hara (2004), Fulton et al (2012) and Kitamura et al (2013). O'Hara (2004) set cooling rates as 100c/Ma and 0.035, 1.0c/s. Fulton et al. (2012) calculated temperature evolution at and around a fault on the basis of frictional heating and heat diffusion. Both used the reaction formula by Sweeney and Burnham (1990) to convert the estimated temperature to Ro. Kitamura et al (2013) made a relationship between temperature and Ro directly from friction experiments with temperature monitoring. In the experiments, Ro is significantly higher at a temperature than that from Sweeney and Burnham (1990), suggesting mechanical effects may make the Ro higher. The estimated temperature of host rock and fault in this study using methods of O'Hara (2004), Fulton et al. (2012) and Kitamura et al. (2013) were 146c and 460-540c, 178.5c and 460-510c, and 178.5c and 260c, respectively. In the case of methods of O'Hara (2004) and Fulton et al (2012), 0.2 of friction coefficient with 1m displacement was estimated. At method of Kitamura et al (2013), friction coefficient was calculated as 75% lower with 1m displacement. Very low friction coefficient was estimated at the coal concentrated layer.

Kiyohiko, M.; Hashimoto, Y.; Hirose, T.; Kitamura, M.

2013-12-01

297

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

298

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

299

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

300

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

301

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

302

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

303

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

304

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

305

Experimental study of boundary layer transition with elevated freestream turbulence on a heated flat plate  

NASA Technical Reports Server (NTRS)

A detailed investigation to document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were acquired in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities (TI) from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for R(sub theta) is less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length. The measured laminar value of Reynolds analogy factor was as much as 53 percent higher than the Pr(sup -2/3). A small dependence of turbulent results on TI was observed. Conditional sampling performed in the transitional boundary layer indicated the existence of a near-wall drop in intermittency, pronounced at certain low intermittencies, which is consistent with the cross-sectional shape of turbulent spots observed by others. Non-turbulent intervals were observed to possess large magnitudes of near-wall unsteadiness and turbulent intervals had peak values as much as 50 percent higher than were measured at fully turbulent stations. Non-turbulent and turbulent profiles in transitional boundary layers cannot be simply treated as Blasius and fully turbulent profiles, respectively. The boundary layer spectra indicate predicted selective amplification of T-S waves for TI is approximately 0.4 percent. However, for TI is approximately 0.8 and 1.1 percent, T-S waves are localized very near the wall and do not play a dominant role in transition process.

Sohn, Ki-Hyeon; Reshotko, Eli

1991-01-01

306

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

307

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

308

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

309

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

310

Revisiting Surface Heat-Flux and Temperature Boundary Conditions in Models of Stably Stratified Boundary-Layer Flows  

NASA Astrophysics Data System (ADS)

Two formulations of the surface thermal boundary condition commonly employed in numerical modelling of atmospheric stably stratified surface-layer flows are evaluated using analytical considerations and observational data from the Cabauw site in the Netherlands. The first condition is stated in terms of the surface heat flux and the second is stated in terms of the vertical potential temperature difference. The similarity relationships used to relate the flux and the difference are based on conventional log-linear expressions for vertical profiles of wind velocity and potential temperature. The heat-flux formulation results in two physically meaningful values for the friction velocity with no obvious criteria available to choose between solutions. Both solutions can be obtained numerically, which casts doubt on discarding one of the solutions as was previously suggested based on stability arguments. This solution ambiguity problem is identified as the key issue of the heat-flux condition formulation. In addition, the agreement between the temperature difference evaluated from similarity solutions and their measurement-derived counterparts from the Cabauw dataset appears to be very poor. Extra caution should be paid to the iterative procedures used in the model algorithms realizing the heat-flux condition as they could often provide only partial solutions for the friction velocity and associated temperature difference. Using temperature difference as the lower boundary condition bypasses the ambiguity problem and provides physically meaningful values of heat flux for a broader range of stability condition in terms of the flux Richardson number. However, the agreement between solutions and observations of the heat flux is again rather poor. In general, there is a great need for practicable similarity relationships capable of treating the vertical turbulent transport of momentum and heat under conditions of strong stratification in the surface layer.

Gibbs, Jeremy A.; Fedorovich, Evgeni; Shapiro, Alan

2015-02-01

311

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

312

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

313

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

314

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

315

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

316

Diffusion of drag-reducing polymer solutions within a rough-walled turbulent boundary layer  

NASA Astrophysics Data System (ADS)

The influence of surface roughness on diffusion of wall-injected, drag-reducing polymer solutions within a turbulent boundary layer was studied with a 0.94 m long flat-plate test model at speeds of up to 10.6 m s-1 and Reynolds numbers of up to 9106. The surface was hydraulically smooth, transitionally rough, or fully rough. Mean concentration profiles were acquired with planar laser induced fluorescence, which was the primary flow diagnostic. Polymer concentration profiles with high injection concentrations (?1000 wppm) had the peak concentration shifted away from the wall, which was partially attributed to a lifting phenomenon. The diffusion process was divided into three zonesinitial, intermediate, and final. Studies of polymer injection into a polymer ocean at concentrations sufficient for maximum drag reduction indicated that the maximum initial zone length is of the order of 100 boundary layer thicknesses. The intermediate zone results indicate that friction velocity and roughness height are important scaling parameters in addition to flow and injection conditions. Lastly, the current results were combined with those in Petrie et al. ["Polymer drag reduction with surface roughness in flat-plate turbulent boundary layer flow," Exp. Fluids 35, 8 (2003)] to demonstrate that the influence of polymer degradation increases with increased surface roughness.

Elbing, Brian R.; Dowling, David R.; Perlin, Marc; Ceccio, Steven L.

2010-04-01

317

Numerical simulation of a shock wave/turbulent boundary layer interaction in a duct  

NASA Astrophysics Data System (ADS)

A numerical investigation of the interaction of an incident oblique shock wave with a turbulent duct flow is presented. The investigation consisted of solving the three dimensional, unsteady, compressible, and mass averaged Navier-Stokes equations. An implicit finite volume lower-upper time marching code (RPLUS) has been employed and modified. A three dimensional Baldwin-Lomax turbulence model has been programmed in conjunction with the code. Computed results are obtained at Mach number 2.9 for a turning angle of 12.99 degrees and Reynolds number based on duct width of 1.36 x 10(exp 7). Under various inlet conditions, the results clearly depict the flow characteristics including the shock structure, the separated flow region, the wall pressure distribution, and the skin friction distribution. The findings provide a physical understanding of the three dimensional vortex structure of the flow in a duct in which a shock wave interacts with a turbulent boundary layer. The results show that the ratio of the boundary layer thickness to the duct width is the critical parameter in determining the separation structure. The computational results also show that the corner vortices and center separation structures are closely related. However, the non-uniformities and secondary flows in the approach boundary layer do not change the separation structure qualitatively.

Yang, Wei-Li

318

Hot-Film and Hot-Wire Anemometry for a Boundary Layer Active Flow Control Test  

NASA Technical Reports Server (NTRS)

Unsteady active flow control (AFC) has been used experimentally for many years to minimize bluff-body drag. This technology could significantly improve performance of rotorcraft by cleaning up flow separation. It is important, then, that new actuator technologies be studied for application to future vehicles. A boundary layer wind tunnel was constructed with a 1ft-x-3ft test section and unsteady measurement instrumentation to study how AFC manipulates the boundary layer to overcome adverse pressure gradients and flow separation. This unsteady flow control research requires unsteady measurement methods. In order to measure the boundary layer characteristics, both hot-wire and hot-film Constant Temperature Anemometry is used. A hot-wire probe is mounted in the flow to measure velocity while a hot-film array lays on the test surface to measure skin friction. Hot-film sensors are connected to an anemometer, a Wheatstone bridge circuit with an output that corresponds to the dynamic flow response. From this output, the time varying flow field, turbulence, and flow reversal can be characterized. Tuning the anemometers requires a fan test on the hot-film sensors to adjust each output. This is a delicate process as several variables drastically affect the data, including control resistance, signal input, trim, and gain settings.

Lenahan, Keven C.; Schatzman, David M.; Wilson, Jacob Samuel

2013-01-01

319

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

320

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

321

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

322

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

323

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

324

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

325

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

326

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

327

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

328

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

329

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

330

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

331

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

332

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

333

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

334

Interacting boundary-layer solutions for laminar separated flow past airfoils  

NASA Technical Reports Server (NTRS)

Numerical solutions of the interacting laminar boundary layer equations are presented for two symmetric airfoils at zero incidence: the NACA 0012 and the NACA 66 sub 3-108 airfoils. The potential flow was computed using Carlson's code, and viscous interaction was treated following a Hilbert integral scheme due to Veldman. Effects of various grid parameters are studied, and pressure and skin friction distributions are compared at several Reynolds numbers. For the NACA 0012 airfoil, Reynolds number is varied from a value just below separation (R sub N = 3000) to a value for which extensive separation occurs (R sub N = 100,000). For the 66 sub 3-018 airfoil, results are given at intermediate values (R sub N - 10,000 and 40,000). The method fails to converge for greater values of Reynolds number, corresponding to the development of very thin well separated shear layers where transition to turbulence would occur naturally.

Burggraf, O. R.

1984-01-01

335

Heat transfer and fluid mechanics measurements in transitional boundary layer flows  

NASA Technical Reports Server (NTRS)

Experimental results are presented to document hydrodynamic and thermal development of flat-plate boundary layers undergoing natural transition. Local heat transfer coefficients, skin friction coefficients and profiles of velocity, temperature and Reynolds normal and shear stresses are presented. A case with no transition and transitional cases with 0.68 percent and 2.0 percent free-stream disturbance intensities were investigated. The locations of transition are consistent with earlier data. A late-laminar state with significant levels of turbulence is documented. In late-transitional and early-turbulent flows, turbulent Prandtl number and conduction layer thickness values exceed, and the Reynolds analogy factor is less than, values previously measured in fully turbulent flows.

Wang, T.; Simon, T. W.; Buddhavarapu, J.

1985-01-01

336

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

337

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

338

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

339

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

340

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

341

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

342

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

343

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

344

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

345

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

346

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

347

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

348

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

349

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

350

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

351

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

352

High-speed boundary layer transition induced by a discrete roughness element  

NASA Astrophysics Data System (ADS)

The effect of a hemispherical bump on a Mach 3.37 laminar boundary layer is studied using DNS for three conditions with k/?= 2.54, 0.25 and 0.125, where k is the roughness height. The simulation parameters are based on the experiment by Danehy et. al. (AIAA-2009-394). The flow downstream of the roughness is transitional for all the three conditions accompanied by a rise in skin friction and heat transfer. Upon interaction with the roughness element, the boundary layer separates to form a series of spanwise vortices upstream and a shear layer. These vortices wrap around the roughness to yield a system of streamwise vortices downstream. Perturbation of the shear layer due to the vortices results in the formation of hairpin-shaped vortices further downstream of the roughness. While hairpin vortices were observed in both the center plane and off-symmetry planes on either side for the smallest ? case, they were observed only in the center plane for the other cases.

Iyer, Prahladh; Mahesh, Krishnan

2011-11-01

353

Static friction force between catalyst layer and micro porous layer and its effect on deformations of membrane electrode assemblies under swelling  

NASA Astrophysics Data System (ADS)

Membrane electrode assemblies (MEAs) composed of a Nafion membrane and heat-transferred catalyst layers (CLs) were employed in this study. The deformation of MEAs between micro porous layers (MPLs)/gas diffusion layers (GDLs) was investigated in response to humidity cycles. The MEA deformed into wrinkle shapes at lower contact pressures and exhibited bulge deformation at higher contact pressures. Wrinkles were generated by large in-plane swelling after buckling when swelling could not be restricted by the friction force from MPLs. Next, the static friction coefficient between the MEA and MPL was measured, and a friction mechanism was investigated. The static friction coefficient was 0.43 at the contact pressure of 0.22MPa between the MEA and MPL and increased with the increase in the contact pressure. The surface observation of the MPL after the friction test indicated that a static friction was generated by the contact of the convex MPL and flat CL surface. The static friction force and swelling force were calculated to investigate the effect of the static friction force on the MEA deformation. The static friction force, which was more than 12% of the swelling force, could prevent wrinkles in 33?m thick MEA.

Uchiyama, Tomoaki; Kumei, Hideyuki; Yoshida, Toshihiko; Ishihara, Kazuhiko

2014-12-01

354

Fabrication of Nano-Composite Surface Layers on Aluminium Employing Friction Stir Processing Technique  

SciTech Connect

Al/Al{sub 2}O{sub 3} nano-composite surface layer was fabricated via friction stir processing technique. Commercial AA6082 aluminium alloy extruded bar and nanometric Al{sub 2}O{sub 3} powder were subjected to friction stir processing at a substrate travel speed of 80 mm/min and a tool rotation speed of 1000 rpm using a hardened H-13 tool steel. The grain structure and reinforcement particles were investigated by using optical and scanning electron microscopy. Results show that Al{sub 2}O{sub 3} particles can be more uniformly dispread in aluminium substrate by increasing the number of processing passes. Also, hardness enhancement of the nano-composite surface layer was found. This is attributed to uniform dispersion of Al{sub 2}O{sub 3} particles.

Bozorg, S. F. K.; Zarghani, A. S.; Zarei-Hanzaki, A. [School of Metallurgy and Materials Engineering, Faculty of Engineering, University of Tehran, Tehran, P.O. Box: 14395-553 (Iran, Islamic Republic of)

2010-03-11

355

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

356

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

357

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

358

New concepts on the interfacial friction behavior between flat steel ribbon layers  

SciTech Connect

Flat steel ribbon wound pressure vessels are widely used in chemical, petrochemical, and other industries. However, no satisfactory theoretical formulae are available to estimate the additional strengthening induced by the friction between the layers. Effective normal stress in the ribbon wide direction and shear stress are new concepts for describing such strengthening effect. These concepts are analyzed further to obtain expressions for both axial and circumferential bursting pressure, and stresses of the vessel. Comparison with one set of experimental results shows excellent agreement.

Zheng, J.; Zhu, G. [Zhejiang Univ., Hangzhou (China). Institute of Chemical Machinery and Equipment

1995-11-01

359

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

360

Friction properties of the plate boundary megathrust beneath the frontal wedge near the Japan Trench: an inference from topographic variation  

NASA Astrophysics Data System (ADS)

The 2011 Tohoku-Oki earthquake (Mw 9.0) produced a fault rupture that extended to the toe of the Japan Trench. The deformation and frictional properties beneath the forearc are keys that can help to elucidate this unusual event. In the present study, to investigate the frictional properties of the shallow part of the plate boundary, we applied the critically tapered Coulomb wedge theory to the Japan Trench and obtained the effective coefficient of basal friction and Hubbert-Rubey pore fluid pressure ratio (?) of the wedge beneath the lower slope. We extracted the surface slope angle and dcollement dip angle (which are the necessary topographic parameters for applying the critical taper theory) from seismic reflection and refraction survey data at 12 sites in the frontal wedges of the Japan Trench. We found that the angle between the dcollement and back-stop interface generally decreases toward the north. The measured taper angle and inferred effective friction coefficient were remarkably high at three locations. The southernmost area, which had the highest coefficient of basal friction, coincides with the area where the seamount is colliding offshore of Fukushima. The second area with a high effective coefficient of basal friction coincides with the maximum slip location during the 2011 Tohoku-Oki earthquake. The area of the 2011 earthquake rupture was topographically unique from other forearc regions in the Japan Trench. The strain energy accumulation near the trench axis may have proceeded because of the relatively high friction, and later this caused a large slip and collapse of the wedge. The location off Sanriku, where there are neither seamount collisions nor rupture propagation, also has a high coefficient of basal friction. The characteristics of the taper angle, effective coefficient of basal friction, and pore fluid pressure ratio along the Japan Trench presented herein may contribute to the understanding of the relationship between the geometry of the prism and the potential for generating seismo-tsunamigenic slips.

Koge, Hiroaki; Fujiwara, Toshiya; Kodaira, Shuichi; Sasaki, Tomoyuki; Kameda, Jun; Kitamura, Yujin; Hamahashi, Mari; Fukuchi, Rina; Yamaguchi, Asuka; Hamada, Yohei; Ashi, Juichiro; Kimura, Gaku

2014-12-01

361

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

362

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

363

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

364

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

365

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

366

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

367

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 surfaceincluding moisture availability, albedo, and aerodynamic roughnessas 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

368

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...

369

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

370

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

371

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

372

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

373

On TollmienSchlichting-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

374

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

375

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

376

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

377

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

378

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

379

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

380

Von Krmn'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 Krmn'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 Hgstrm

1985-01-01

381

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

382

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...

383

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

384

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

385

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...

386

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

387

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

388

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

389

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

390

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

391

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

392

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 ...

393

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

394

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

395

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

396

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

397

Synergetic model of boundary friction taking into account spatial nonuniformity of stresses, strain, and temperature  

NASA Astrophysics Data System (ADS)

Spatial nonuniformity of stresses, strain, and temperature of a lubricating layer is taken into account in the context of the synergetic model. We consider the motion of interacting surfaces in opposite directions with identical velocities as well as the situation when the lower surface is rigidly fixed and the upper is displaced with a fixed velocity. In both cases, the spatial profiles of stresses, strains, and temperature are obtained. Allowance for the spatial distribution of the parameters makes it possible to describe the nontrivial non-Newtonian behavior of the effective shear viscosity of the lubricant. The effect of the temperature of the surfaces and the viscosity of the lubricant on the steady-state friction regime is analyzed.

Lyashenko, I. A.; Manko, N. N.

2014-12-01

398

Multiple pass and multiple layer friction stir welding and material enhancement processes  

DOEpatents

Processes for friction stir welding, typically for comparatively thick plate materials using multiple passes and multiple layers of a friction stir welding tool. In some embodiments a first portion of a fabrication preform and a second portion of the fabrication preform are placed adjacent to each other to form a joint, and there may be a groove adjacent the joint. The joint is welded and then, where a groove exists, a filler may be disposed in the groove, and the seams between the filler and the first and second portions of the fabrication preform may be friction stir welded. In some embodiments two portions of a fabrication preform are abutted to form a joint, where the joint may, for example, be a lap joint, a bevel joint or a butt joint. In some embodiments a plurality of passes of a friction stir welding tool may be used, with some passes welding from one side of a fabrication preform and other passes welding from the other side of the fabrication preform.

Feng, Zhili (Knoxville, TN) [Knoxville, TN; David, Stan A. (Knoxville, TN) [Knoxville, TN; Frederick, David Alan (Harriman, TN) [Harriman, TN

2010-07-27

399

Study of nonlinear behaviors and modal reductions for friction destabilized systems. Application to an elastic layer  

NASA Astrophysics Data System (ADS)

As noise reduction tends to be part of environmental directives, predicting squeal noise generated by disc brakes is an important industrial issue. It involves both the transient and stationary nonlinear dynamics of self-excited systems with frictional contact. Time simulation of the phenomenon is an attractive option for reducing experiment costs. However, since such computations using full finite element models of industrial disc brake systems is time-consuming, model reduction has to be performed. In this paper, both the transient and stationary nonlinear behaviors of the friction destabilized system and the effect of dynamical reduction on the nonlinear response of a simple friction destabilized system are carried out. The first part provides a description of the general modeling retained for friction destabilized systems. Then, discretization and solving processes for the stability analysis and the temporal evolution are presented. The third part presents an analysis of a sliding elastic layer for different operating conditions, in order to better understand the nonlinear behavior of such systems. Finally, spatial model reduction is performed with different kinds of reduction bases in order to analyze the different effects of modal reductions. This clearly shows the necessity of including static modes in the reduction basis and that nonlinear interactions between unstable modes are very difficult to represent with reduced bases. Finally, the proposed model and the associated studies are intended to be the benchmark cases for future comparison.

Loyer, A.; Sinou, J.-J.; Chiello, O.; Lorang, X.

2012-02-01

400

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

401

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

402

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

403

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

404

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

405

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

406

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

407

The effects of micro-vortex generators on normal shock wave/boundary layer interactions  

NASA Astrophysics Data System (ADS)

Shock wave/boundary-layer interactions (SWBLIs) are complex flow phenomena that are important in the design and performance of internal supersonic and transonic flow fields such as engine inlets. This investigation was undertaken to study the effects of passive flow control devices on normal shock wave/boundary layer interactions in an effort to gain insight into the physics that govern these complex interactions. The work concentrates on analyzing the effects of vortex generators (VGs) as a flow control method by contributing a greater understanding of the flowfield generated by these devices and characterizing their effects on the SWBLI. The vortex generators are utilized with the goal of improving boundary layer health (i.e., reducing/increasing the boundary-layer incompressible shape factor/skin friction coefficient) through a SWBLI, increasing pressure recovery, and reducing flow distortion at the aerodynamic interface plane while adding minimal drag to the system. The investigation encompasses experiments in both small-scale and large-scale inlet testing, allowing multiple test beds for improving the characterization and understanding of vortex generators. Small-scale facility experiments implemented instantaneous schlieren photography, surface oil-flow visualization, pressure-sensitive paint, and particle image velocimetry to characterize the effects of an array of microramps on a normal shock wave/boundary-layer interaction. These diagnostics measured the time-averaged and instantaneous flow organization in the vicinity of the microramps and SWBLI. The results reveal that a microramp produces a complex vortex structure in its wake with two primary counter-rotating vortices surrounded by a train of Kelvin- Helmholtz (K-H) vortices. A streamwise velocity deficit is observed in the region of the primary vortices in addition to an induced upwash/downwash which persists through the normal shock with reduced strength. The microramp flow control also increased the spanwise-averaged skin-friction coefficient and reduced the spanwise-averaged incompressible shape factor, thereby improving the health of the boundary layer. The velocity in the near-wall region appears to be the best indicator of microramp effectiveness at controlling SWBLIs. Continued analysis of additional micro-vortex generator designs in the small-scale facility revealed reduced separation within a subsonic diffuser downstream of the normal shock wave/boundary layer interaction. The resulting attached flow within the diffuser from the micro-vortex generator control devices reduces shock wave position and pressure RMS fluctuations within the diffuser along with increased pressure recovery through the shock and at the entrance of the diffuser. The largest effect was observed by the micro-vortex generators that produce the strongest streamwise vortices. High-speed pressure measurements also indicated that the vortex generators shift the energy of the pressure fluctuations to higher frequencies. Implementation of micro-vortex generators into a large-scale, supersonic, axisymmetric, relaxed-compression inlet have been investigated with the use of a unique and novel flow-visualization measurement system designed and successfully used for the analysis of both upstream micro-VGs (MVGs) and downstream VGs utilizing surface oil-flow visualization and pressure-sensitive paint measurements. The inlet centerbody and downstream diffuser vortex-generator regions were imaged during wind-tunnel testing internally through the inlet cowl with the diagnostic system attached to the cowl. Surface-flow visualization revealed separated regions along the inlet centerbody for large mass-flow rates without vortex generators. Upstream vortex generators did reduce separation in the subsonic diffuser, and a unique perspective of the flowfield produced by the downstream vortex generators was obtained. In addition, pressure distributions on the inlet centerbody and vortex generators were measured with pressure-sensitive paint. At low mass-flow ratios the onset of buzz occurs in the lar

Herges, Thomas G.

408

Explicit Solvent Simulations of Friction between Brush Layers of Charged and Neutral Bottle-Brush Macromolecules  

SciTech Connect

We study friction between charged and neutral brush layers of bottle-brush macromolecules using molecular dynamics simulations. In our simulations the solvent molecules were treated explicitly. The deformation of the bottle-brush macromolecules under the shear were studied as a function of the substrate separation and shear stress. For charged bottle-brush layers we study effect of the added salt on the brush lubricating properties to elucidate factors responsible for energy dissipation in charged and neutral brush systems. Our simulations have shown that for both charged and neutral brush systems the main deformation mode of the bottle-brush macromolecule is associated with the backbone deformation. This deformation mode manifests itself in the backbone deformation ratio, , and shear viscosity, , to be universal functions of the Weissenberg number W. The value of the friction coefficient, , and viscosity, , are larger for the charged bottle-brush coatings in comparison with those for neutral brushes at the same separation distance, D, between substrates. The additional energy dissipation generated by brush sliding in charged bottle-brush systems is due to electrostatic coupling between bottle-brush and counterion motion. This coupling weakens as salt concentration, cs, increases resulting in values of the viscosity, , and friction coefficient, , approaching corresponding values obtained for neutral brush systems.

Carrillo, Jan-Michael [University of Connecticut] [University of Connecticut; Brown, W Michael [ORNL] [ORNL; Dobrynin, Andrey [University of Connecticut] [University of Connecticut

2012-01-01

409

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

410

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

411

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

412

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

413

Boundary layer heights determinate from Raman multiwavelengths lidar and microwave radiometer measurements  

NASA Astrophysics Data System (ADS)

Planetary boundary layer (PBL) is the lowest part of the troposphere that is directly influenced by friction and solar heating from earth's surface. Accurate determination of the boundary layer heights is critical in understanding the regional air quality. Lidar systems have been widely used to examine the structure and variability of the boundary layer (BL) heights (Brook et al 2000, Talianu et al 2006, Madonna et al, 2011). This paper aims to develop a method of assessing the PBL heights using Raman multi-wavelengths lidar - RALI measurements. RALI system has three elastic (1064nm, 532nm, 355nm) and two Raman (607nm, 387nm) channels. This method is based on the vertical gradient accurate calculation of the ratio between signal collected from elastic and inelastic channels. From 500m up to 10 km this will give information about vertical distributions of aerosols layers. We have chosen to use as method for validation the one described by Stull (Stull 1988) based on virtual potential temperature. The vertical gradient of the virtual potential temperature gives also information about the stability of stratification. Temperature, pressure and humidity profiles provided by the microwave radiometer (collocated with the lidar system) have been used to determine virtual potential temperature profiles. The PBL heights calculated from virtual potential temperature have been compared with PBL heights determinate from lidar data collected before and after sunset measurements, in Magurele (Longitude: 26.029 E, Latitude: 44.348 N, a.s.l: 93m), near Bucharest, June to August 2011. Results from lidar data showed the breakdown of the boundary layer after sunset and is visible on almost every day of measurements. The height of the boundary layer has been determined and lies between 700 and 800 meters during 2011 summer time. These results have been similar with the outputs of the virtual potential temperature method and a good correlation of the two methods has been found. Therefore we validated the method based on Raman multi-wavelength lidar measurements to calculate PBL heights as a reliable and useful tool.

Talianu, C.; Nicolae, D.; Carstea, E.; Belegante, L.

2012-04-01

414

Separated and Recovering Turbulent Boundary Layer Flow Behind a Backward Facing Step For Different Reynolds Numbers  

NASA Technical Reports Server (NTRS)

Experimental results for a two-dimensional separated turbulent boundary layer behind a backward facing step for five different Reynolds numbers are reported. Results are presented in the form of tables, graphs and a floppy disk for an easy access of the data. Reynolds number based on the step height was varied by changing the reference velocity upstream of the step, U(sub o), and the step height, h. Hot-wire measurement techniques were used to measure three Reynolds stresses and four triple-velocity correlations. In addition, surface pressure and skin friction coefficients were measured. All hot-wire measurements were acquired in a measuring domain which excluded recirculating flow region due to the directional insensitivity of hot-wires. The downstream extent of the domain from the step was 51 h for the largest and I 14h for the smallest step height. This significant downstream length permitted extensive study of the flow recovery. Prediction of perturbed flows and their recovery is particularly attractive for popular turbulence models since variations of turbulence length and time scales and flow interactions in different regions are generally inadequately predicted. The data indicate that the flow in the free shear layer region behaves like the plane mixing layer up to about 2/3 of the mean reattachment length when the flow interaction with the wall commences the flow recovery to that of an ordinary turbulent boundary layer structure. These changes of the flow do not occur abruptly with the change of boundary conditions. A reattachment region represents a transitional region where the flow undergoes the most dramatic adjustments to the new boundary conditions. Large eddies, created in the upstream free-shear layer region, are being torn, recirculated, reentrained back into the main stream interacting with the incoming flow structure. It is foreseeable that it is quite difficult to describe the physics of this region in a rational and quantitative manner other than statistical. Downstream of the reattachment point the flow recovers at different rates near the wall, in the newly developing internal boundary layer, and in the outer part of the flow. It appears that Reynolds stresses do not fully recover up to the longest recovery length of 114 h.

Jovic, Srba; Kutler, Paul F. (Technical Monitor)

1994-01-01

415

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

416

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.

417

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

418

Reynolds number and pressure gradient effects on compressible turbulent boundary layers  

NASA Technical Reports Server (NTRS)

A detailed investigation of attached supersonic turbulent boundary layers over an extensive range of Reynolds numbers (12 x 10 to the 6th to 314 x 10 to the 6th) is presented. Experimental measurements were obtained for adverse pressure gradients ranging in magnitude from those of previous investigations to those approaching separation. The measurements include mean values of surface pressure and skin-friction, mean-flow profiles, and profiles of the three turbulent velocity fluctuation components and turbulent shear stress. Numerical solutions, employing three turbulence models of various degrees of complexity have been compared with the details of the measured flow fields. Generally, it was found that the more sophisticated turbulence models are superior to a mixing length model for predicting the Reynolds number and pressure gradient effects. However, some details of the turbulent fluctuations as well as the exact Reynolds number trends indicated by the data were not accurately predicted with any of the turbulence models considered.

Acharya, M.; Kussoy, M. I.; Horstman, C. C.

1978-01-01

419

A novel boundary layer sensor utilizing domain switching in ferroelectric liquid crystals  

NASA Astrophysics Data System (ADS)

This paper describes the design and the principles of operation of a novel sensor for the optical detection of a shear stress field induced by air or gas flow on a rigid surface. The detection relies on the effects of shear-induced optical switching in ferroelectric liquid crystals. It is shown that the method overcomes many of the limitations of similar measuring techniques including those using cholesteric liquid crystals. The present method offers a preferred alternative for flow visualization and skin friction measurements in wind-tunnel experiments on laminar boundary layer transition investigations. A theoretical model for the optical response to shear stress is presented together with a schematic diagram of the experimental setup.

Parmar, D. S.

1991-02-01

420

Computer program for calculation of real gas turbulent boundary layers with variable edge entropy  

NASA Technical Reports Server (NTRS)

A user's manual for a computer program which calculates real gas turbulent boundary layers with variable edge entropy on a blunt cone or flat plate at zero angle of attack is presented. An integral method is used. The method includes the effect of real gas in thermodynamic equilibrium and variable edge entropy. A modified Crocco enthalpy velocity relationship is used for the enthalpy profiles and an empirical correlation of the N-power law profile is used for the velocity profile. The skin-friction-coefficient expressions of Spalding and Chi and Van Driest are used in the solution of the momentum equation and in the heat-transfer predictions that use several modified forms of Reynolds analogy.

Boney, L. R.

1974-01-01

421

Chasing eddies and their wall signature in turbulent boundary layers at Mach 3 through 14  

NASA Astrophysics Data System (ADS)

We use a direct numerical simulation database of turbulent boundary layers,footnotetextMartin, M.P., JFM, vol. 570, pp. 347-364, 2006^,footnotetextMartin, M.P., AIAA Paper 2004-2337^,footnotetextBeekman & Martin, APS DFD08 statistical tools,footnotetextBrown & Thomas, Phys. Fluids, vol. 20, pp 243-251, 1977 scientifically-rooted packet-pattern recognition,footnotetextRinguette, Wu & Martin, JFM, vol. 594, pp. 59-69, 2008 and validated visualization algorithmsfootnotetextO'Farrell, C. Senior Thesis, Princeton University 2008 to identify hairpin packets and their wall signature. We investigate the variation of time scales and length scales associated with coherent structures and the role of hairpin packets on the generation of skin friction, wall-pressure loading and heat transfer.

Beekman, I. B.; Priebe, S.; Martin, M. P.

2009-11-01

422

A novel boundary layer sensor utilizing domain switching in ferroelectric liquid crystals  

NASA Technical Reports Server (NTRS)

This paper describes the design and the principles of operation of a novel sensor for the optical detection of a shear stress field induced by air or gas flow on a rigid surface. The detection relies on the effects of shear-induced optical switching in ferroelectric liquid crystals. It is shown that the method overcomes many of the limitations of similar measuring techniques including those using cholesteric liquid crystals. The present method offers a preferred alternative for flow visualization and skin friction measurements in wind-tunnel experiments on laminar boundary layer transition investigations. A theoretical model for the optical response to shear stress is presented together with a schematic diagram of the experimental setup.

Parmar, D. S.

1991-01-01

423

A hybrid RANS/LES framework to investigate spatially developing turbulent boundary layers  

E-print Network

A hybrid RANS/LES framework is developed based on a recently proposed Improved Delayed Detached Eddy Simulation (IDDES) model combined with a variant of recycling and rescaling method of generating inflow turbulence. This framework was applied to investigate spatially developing flat plate turbulent boundary layer up to momentum thickness Reynolds number, $R_{\\theta} = 31000$ and the results are compared with the available experimental data. Good agreement was obtained for the global quantities such as mean velocity and skin friction at all momentum thickness Reynolds numbers considered. The trends obtained for the Reynolds stress components are in the right direction. At high $R_{\\theta$}, the shear stress distribution shows significant differences close to the wall indicating scope for further improving the near-wall modeling in such methods.

Arolla, Sunil K

2014-01-01

424

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

425

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

426

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

427

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

428

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

429

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

430

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

431

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

432

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

433

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

434

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

435

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

436

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

437

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

438

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

439

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

440

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

441

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. Snchez-Adsuar; J. M. Martn-Martnez

1995-01-01

442

Laboratory simulation of rotating atmospheric boundary layer flows over obstacles  

Microsoft Academic Search

SummaryThe 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'Hires; H. Didelle

1983-01-01

443

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

444

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 advectiondiffusion 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 timespace

G. Chapalain; L. Thais; H. Smaoui

1999-01-01

445

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

446

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. Fredse; B. M. Sumer; E. D. Christensen

2006-01-01