ON AERODYNAMIC AND BOUNDARY LAYER RESISTANCES WITHIN DRY DEPOSITION MODELS
There have been many empirical parameterizations for the aerodynamic and boundary layer resistances proposed in the literature, e.g. those of the Meyers Multi-Layer Deposition Model (MLM) used with the nation-wide dry deposition network. Many include arbitrary constants or par...
Boundary-layer transition over aerodynamically-significant rotating bodies
NASA Astrophysics Data System (ADS)
Garrett, Stephen; Hussain, Zahir; Barrow, Alistair; Towers, Paul
2010-11-01
For practical reasons rotating-disk flow has served as the foremost model problem for studying transition in fully 3D incompressible boundary layers for over six decades and has a huge body of associated literature. However, continuing developments in spinning projectiles and aeroengines has led to the need to understand the onset of transition over rotating cones and spheroids as objects in their own right. Although numerous experimental observations have been published, these geometries received only little theoretical attention prior to 2002 when Garrett and co-workers commenced their work. In this paper we give a comparative study of the instability characteristics of the flows over these distinct geometries, discussing their similarities and differences with each other and the rotating-disk paradigm. The rotating-cone flow in particular is found to demonstrate significantly different characteristics as the half-angle is reduced below 40degs. This observation has led to the hypothesis and ultimate identification of an alternative instability mode which is expected to dominate for slender cones. Theoretical studies using numerical and asymptotic techniques are discussed. Comparisons are made to existing experimental data, and in many cases excellent agreement is observed for measurable properties. Where close agreement is not seen, we discuss possible reasons why.
Interaction of aerodynamic noise with laminar boundary layers in supersonic wind tunnels
NASA Technical Reports Server (NTRS)
Schopper, M. R.
1984-01-01
The interaction between incoming aerodynamic noise and the supersonic laminar boundary layer is studied. The noise field is modeled as a Mach wave radiation field consisting of discrete waves emanating from coherent turbulent entities moving downstream within the supersonic turbulent boundary layer. The individual disturbances are likened to miniature sonic booms and the laminar boundary layer is staffed by the waves as the sources move downstream. The mean, autocorrelation, and power spectral density of the field are expressed in terms of the wave shapes and their average arrival rates. Some consideration is given to the possible appreciable thickness of the weak shock fronts. The emphasis in the interaction analysis is on the behavior of the shocklets in the noise field. The shocklets are shown to be focused by the laminar boundary layer in its outer region. Borrowing wave propagation terminology, this region is termed the caustic region. Using scaling laws from sonic boom work, focus factors at the caustic are estimated to vary from 2 to 6 for incoming shocklet strengths of 1 to .01 percent of the free stream pressure level. The situation regarding experimental evidence of the caustic region is reviewed.
NASA Astrophysics Data System (ADS)
Sun, Quan; Cui, Wei; Li, Ying-Hong; Cheng, Bang-Qin; Jin, Di; Li, Jun
2014-07-01
The potential of controlling shockwave—boundary layer interactions (SWBLIs) in air by plasma aerodynamic actuation is demonstrated. Experiments are conducted in a Mach 3 in-draft air tunnel. The separation-inducing shock is generated with a diamond-shaped shockwave generator located on the wall opposite to the surface electrodes, and the flow properties are studied with schlieren imaging and static wall pressure probes. The measurements show that the separation phenomenon is weakened with the plasma aerodynamic actuation, which is observed to have significant control authority over the interaction. The main effect is the displacement of the reflected shock. Perturbations of incident and reflected oblique shocks interacting with the separation bubble in a rectangular cross section supersonic test section are produced by the plasma actuation. This interaction results in a reduction of the separation bubble size, as detected by phase-lock schlieren images. The measured static wall pressure also shows that the separation-inducing shock is restrained. Our results suggest that the boundary layer separation control through heating is the primary control mechanism.
Aerodynamic wake study: oscillating model wind turbine within a turbulent boundary layer
NASA Astrophysics Data System (ADS)
Feist, Christopher J.
An experimental investigation on the aerodynamic wake behind a pitching and/or heaving model wind turbine was performed. The study was split into two quasi-coupled phases; the first phase characterized the motion of an offshore floating wind turbine subjected to linear wave forcing, the second phase replicated specific motion cases, which were driven by results from phase I, on a model wind turbine within a turbulent boundary layer. Wake measurements were made in an effort to quantify fluctuations in the flow associated with the motion of the turbine. Weak differences were observed in the mean, streamwise velocity and turbulent fluctuations between the static and oscillating turbine cases. These weak differences were a result of opposing trends in the velocity quantities based on turbine motion phases. The wake oscillations created by the turbine motion was characteristic of a 2D wave (with convection in the x plane and amplitude in the z plane) with a relatively small amplitude as compared to urms..
NASA Technical Reports Server (NTRS)
Avery, D. E.
1978-01-01
An experimental heat-transfer investigation was conducted on two staggered arrays of metallic tiles in laminar and turbulent boundary layers. This investigation was conducted for two purposes. The impingement heating distribution where flow in a longitudinal gap intersects a transverse gap and impinges on a downstream blocking tile was defined. The influence of tile and gap geometries was analyzed to develop empirical relationships for impingement heating in laminar and turbulent boundary layers. Tests were conducted in a high temperature structures tunnel at a nominal Mach number of 7, a nominal total temperature of 1800 K, and free-stream unit Reynolds numbers from 1.0 x 10 million to 4.8 x 10 million per meter. The test results were used to assess the impingement heating effects produced by parameters that include gap width, longitudinal gap length, slope of the tile forward-facing wall, boundary-layer displacement thickness, Reynolds number, and local surface pressure.
NASA Astrophysics Data System (ADS)
Aleshin, B. S.; Khomich, V. Yu.; Chernyshev, S. L.
2016-12-01
The results of investigations on the possibility of an electrohydrodynamic force effect on a gas flow implemented with the help of a barrier discharge are presented. A new method of controlling the laminar flow around a base with suppression of instabilities of the incoming flow due to electrohydrodynamic force action on the boundary layer near the forward edge of a swept wing is proposed. An efficient multidischarge actuator system is developed and created for active control of aerodynamic flows with induced-air-flow characteristics exceeding the world analogues.
Characterization of Aerodynamic Performance of Boundary-Layer-Ingesting Inlet Under Crosswind
NASA Technical Reports Server (NTRS)
Liou, Meng-Sing; Lee, Byung Joon
2012-01-01
NASA has been studying future transport concepts, envisioned to be technically realizable in the timeframe of 2020-2030, to meet environmental and performance goals. One concept receiving considerable interest involves a propulsion system embedded into a hybrid wing-body aircraft. While offering significant advantages in fuel savings and noise reduction by this concept, there are several technical challenges that are not encountered in the current fleet and must be overcome so as to deliver target performance and operability. One of these challenges is associated with an inlet system that ingests a significantly thick boundary layer, developing along the wing-body surface, into a serpentine diffuser before the flow meeting fan blades. The flow is subject to considerable total pressure loss and distorted at the fan face, much more significantly than in the inlet system of conventional aircraft. In our previous studies [1, 2], we have shown that through innovative design changes on the airframe surface, it is possible to simultaneously increase total pressure recovery and decrease distortion in the flow, without resorting to conventional penalty-ridden flow control concepts, such as vortex generator or boundary layer bleeding/suction. In the current study, we are interested in understanding the following issues: how the embedded propulsion system performs under a crosswind condition by studying in detail the flow characteristics of two inlets, the baseline and another optimized previously under the cruise condition. With the insight, it is hoped that it can help in the follow-on study by devising effective strategies to minimize flow distortion arising from the integration of an embedded-engine system into an airframe to the level acceptable to the operation and fuel consumption before 2030. To achieve these demanding goals, non-conventional concepts are called for; but technology gap is too big that it requires evolutionary approach by focusing various concepts and
Defraeye, Thijs; Blocken, Bert; Koninckx, Erwin; Hespel, Peter; Carmeliet, Jan
2010-08-26
This study aims at assessing the accuracy of computational fluid dynamics (CFD) for applications in sports aerodynamics, for example for drag predictions of swimmers, cyclists or skiers, by evaluating the applied numerical modelling techniques by means of detailed validation experiments. In this study, a wind-tunnel experiment on a scale model of a cyclist (scale 1:2) is presented. Apart from three-component forces and moments, also high-resolution surface pressure measurements on the scale model's surface, i.e. at 115 locations, are performed to provide detailed information on the flow field. These data are used to compare the performance of different turbulence-modelling techniques, such as steady Reynolds-averaged Navier-Stokes (RANS), with several k-epsilon and k-omega turbulence models, and unsteady large-eddy simulation (LES), and also boundary-layer modelling techniques, namely wall functions and low-Reynolds number modelling (LRNM). The commercial CFD code Fluent 6.3 is used for the simulations. The RANS shear-stress transport (SST) k-omega model shows the best overall performance, followed by the more computationally expensive LES. Furthermore, LRNM is clearly preferred over wall functions to model the boundary layer. This study showed that there are more accurate alternatives for evaluating flow around bluff bodies with CFD than the standard k-epsilon model combined with wall functions, which is often used in CFD studies in sports.
NASA Astrophysics Data System (ADS)
deGraffenried, Albert L.
2002-07-01
The paper presents a derivation showing the propagation mechanisms fundamental to the growth of the laminar aerodynamic boundary layer. The molecular mechanisms basic to such growth are those presented by James Clerk Maxwell in his classic derivation of mu, the viscosity of a gas, based on the Kinetic Theory of Gases. Maxwell's derivation is modified by moving the scene of the analysis from a free-stream location (where he assumes a linear velocity gradient) to a location immediately adjacent an infinite flat plate, using an unknown velocity profile. Gas, initially quiescent above the flat plate, suddenly jumps to velocity U0 at time t=0+. The resultant growth of a boundary-layer velocity profile, vx)(y,t, is solved for in the following manner: a. Phi-up, the stream momentum crossing an element of area, da=dxdz per second per square centimeter, in an upward (+y) direction, is found by integrating through all volume below da, using an unknown velocity profile, vx)(y,t. Similarly, Phi-down, the stream momentum crossing da in a downward (-y) direction is found by integrating through all volume above da. The net stream momentum, Phy(y) equals Phi-up minus Phi-down. The acceleration, dvx/dt of an element of mass dm, equal to rho times dxdydz is set equal to minus the partial of Phi with respect to y, the net momentum-flux gradient, based on Newton's Law. In cylindrical coordinates, azimuth angle gamma is promptly integrated out. Elevation angle theta is integrated-out numerically, using a short BASIC program on a PC. Separation of Variables is assumed, specifically, vx)(y,t may be set equal to f1(y)f2(t), thus producing two separate integro-differential equations which are each set equal to a common constant, -Beta2. LaPlace transforming these two equations into the sy and st domains, applying the Method of Partial Fractions to the sy equation, the FORM of the solution is found, viz., exponential and hyperbolic functions. Boundary conditions are satisfied in order to
A fast and accurate method to predict 2D and 3D aerodynamic boundary layer flows
NASA Astrophysics Data System (ADS)
Bijleveld, H. A.; Veldman, A. E. P.
2014-12-01
A quasi-simultaneous interaction method is applied to predict 2D and 3D aerodynamic flows. This method is suitable for offshore wind turbine design software as it is a very accurate and computationally reasonably cheap method. This study shows the results for a NACA 0012 airfoil. The two applied solvers converge to the experimental values when the grid is refined. We also show that in separation the eigenvalues remain positive thus avoiding the Goldstein singularity at separation. In 3D we show a flow over a dent in which separation occurs. A rotating flat plat is used to show the applicability of the method for rotating flows. The shown capabilities of the method indicate that the quasi-simultaneous interaction method is suitable for design methods for offshore wind turbine blades.
Steady incompressible variable thickness shear layer aerodynamics
NASA Technical Reports Server (NTRS)
Chi, M. R.
1976-01-01
A shear flow aerodynamic theory for steady incompressible flows is presented for both the lifting and non lifting problems. The slow variation of the boundary layer thickness is considered. The slowly varying behavior is treated by using multitime scales. The analysis begins with the elementary wavy wall problem and, through Fourier superpositions over the wave number space, the shear flow equivalents to the aerodynamic transfer functions of classical potential flow are obtained. The aerodynamic transfer functions provide integral equations which relate the wall pressure and the upwash. Computational results are presented for the pressure distribution, the lift coefficient, and the center of pressure travel along a two dimensional flat plate in a shear flow. The aerodynamic load is decreased by the shear layer, compared to the potential flow. The variable thickness shear layer decreases it less than the uniform thickness shear layer based upon equal maximum shear layer thicknesses.
Boundary Layer Control on Airfoils.
ERIC Educational Resources Information Center
Gerhab, George; Eastlake, Charles
1991-01-01
A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)
The atmospheric boundary layer
Garratt, J.R.
1992-01-01
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.
NASA Technical Reports Server (NTRS)
Rumsey, Charles B.; Lee, Dorothy B.
1961-01-01
Measurements of aerodynamic heat transfer have been made at several stations on the 15 deg total-angle conical nose of a rocket-propelled model in free flight at Mach numbers up to 5.2. Data are presented for a range of local Mach number just outside the boundary layer from 1.40 to 4.65 and a range of local Reynolds number from 3.8 x 10(exp 6) to 46.5 x 10(exp 6), based on length from the nose tip to a measurement station. Laminar, transitional, and turbulent heat-transfer coefficients were measured. The laminar data were in agreement with laminar theory for cones, and the turbulent data agreed well with turbulent theory for cones using Reynolds number based on length from the nose tip. At a nearly constant ratio of wall to local static temperature of 1.2 the Reynolds number of transition increased from 14 x 10(exp 6) to 30 x 10(exp 6) as Mach number increased from 1.4 to 2.9 and then decreased to 17 x 10(exp 6) as Mach number increased to 3.7. At Mach numbers near 3.5, transition Reynolds numbers appeared to be independent of skin temperature at skin temperatures very cold with respect to adiabatic wall temperature. The transition Reynolds number was 17.7 x 10(exp 6) at a condition of Mach number and ratio of wall to local static temperature near that for which three-dimensional disturbance theory has been evaluated and has predicted laminar boundary-layer stability to very high Reynolds numbers (approximately 10(exp 12)).
The Atmospheric Boundary Layer
ERIC Educational Resources Information Center
Tennekes, Hendrik
1974-01-01
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)
NASA Technical Reports Server (NTRS)
Rumsey, Charles B.; Lee, Dorothy B.
1961-01-01
Measurements of aerodynamic heat transfer have been made at six stations on the 40-inch-long 10 deg. total-angle conical nose of a rocket- propelled model which was flight tested at Mach numbers up to 5.9. are presented for a range of local Mach number just outside the bound- ary layer on the cone from 1.57 to 5.50, and a range of local Reynolds number from 6.6 x 10(exp 6) to 55.2 x 10(exp 6) based on length from the nose tip.
Boundary Layer Theory. Part 1; Laminar Flows
NASA Technical Reports Server (NTRS)
Schlichting, H.
1949-01-01
The purpose of this presentation is to give you 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. As you know, a great many considerations of aerodynamics are based on the so-called ideal fluid, that is, the frictionless incompressible fluid. By neglect of compressibility and friction the extensive mathematical theory of the ideal fluid (potential theory) has been made possible.
NASA Technical Reports Server (NTRS)
Magliozzi, B.; Hanson, D. B.
1991-01-01
An analysis of tone noise propagation through a boundary layer and fuselage scattering effects was derived. This analysis is a three dimensional and the complete wave field is solved by matching analytical expressions for the incident and scattered waves in the outer flow to a numerical solution in the boundary layer flow. The outer wave field is constructed analytically from an incident wave appropriate to the source and a scattered wave in the standard Hankel function form. For the incident wave, an existing function - domain propeller noise radiation theory is used. In the boundary layer region, the wave equation is solved by numerical methods. The theoretical analysis is embodied in a computer program which allows the calculation of correction factors for the fuselage scattering and boundary layer refraction effects. The effects are dependent on boundary layer profile, flight speed, and frequency. Corrections can be derived for any point on the fuselage, including those on the opposite side from the source. The theory was verified using limited cases and by comparing calculations with available measurements from JetStar tests of model prop-fans. For the JetStar model scale, the boundary layer refraction effects produce moderate fuselage pressure reinforcements aft of and near the plane of rotation and significant attenuation forward of the plane of rotation at high flight speeds. At lower flight speeds, the calculated boundary layer effects result in moderate amplification over the fuselage area of interest. Apparent amplification forward of the plane of rotation is a result of effective changes in the source directivity due to boundary layer refraction effects. Full scale effects are calculated to be moderate, providing fuselage pressure amplification of about 5 dB at the peak noise location. Evaluation using available noise measurements was made under high-speed, high-altitude flight conditions. Comparisons of calculations made of free field noise, using a
Boundary layer simulator improvement
NASA Technical Reports Server (NTRS)
Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.
1989-01-01
Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.
Lear jet boundary layer/shear layer laser propagation experiments
NASA Technical Reports Server (NTRS)
Gilbert, K.
1980-01-01
Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.
Boundary layer simulator improvement
NASA Technical Reports Server (NTRS)
Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.
1984-01-01
High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.
Electromagnetic precipitation and ducting of particles in turbulent boundary layers
NASA Technical Reports Server (NTRS)
Davey, K. R.; Melcher, J. R.
1980-01-01
A method for analyzing magnetic migration of particles in turbulent flows is applied to the prediction of particle trajectories and densities in turbulent aerodynamic boundary layers. Results for conditions typical of aircraft with 30-40 micron particles indicate a large upstream collection and a 5% loss of particles during one pass through the boundary layer. The capacity of the magnetic field to achieve a balance with turbulent diffusion in confining the particles to the boundary layer is discussed.
NASA Technical Reports Server (NTRS)
Deveikis, William D.; Walker, Robert W.
1961-01-01
A wind-tunnel investigation was made to determine heat-transfer distributions on three steel sphere-ellipsoid bodies with surface roughnesses of 5, 100, and 200 microinches. Tests were conducted in the Langley 9- by 6-foot thermal structures tunnel at a Mach number of 3.0, free-stream Reynolds numbers (based on model spherical diameter) of 4.25 x 10(exp 6) and 2.76 x l0(exp 6), and at a stagnation temperature of 650 F. Pressure distributions were obtained also on a fourth model. The results indicated that the combination of surface roughness and boundary-layer cooling tended to promote early transition and nullify the advantages attributable to the blunt shape of the model for reducing local temperatures. Good correlation between experimental heating rates and those calculated from laminar theory was achieved up to the start of boundary-layer transition. The correlation also was good with the values predicted by turbulent theory for surface stations downstream from the 45 deg. station.
Boundary layer transition studies
NASA Technical Reports Server (NTRS)
Watmuff, Jonathan H.
1995-01-01
A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated
Boundary layer transition studies
NASA Astrophysics Data System (ADS)
Watmuff, Jonathan H.
1995-02-01
A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated
NASA Astrophysics Data System (ADS)
Finson, M. L.; Clarke, A. S.; Wu, P. K. S.
1981-01-01
A Reynolds stress model for turbulent boundary layers is used to study surface roughness effects on skin friction and heat transfer. The issues of primary interest are the influence of roughness character (element shape and spacing) and the nature of roughness effects at high Mach numbers. Computations based on the model compare satisfactorily with measurements from experiments involving variations in roughness character, in low speed and modestly supersonic conditions. The more limited data base at hypersonic Mach numbers is also examined with reasonable success, although no quantitative explanation is offered for the reduction of heat transfer with increasing roughness observed by Holden at Me -9.4. The present calculations indicate that the mean velocity is approximately uniform over much of the height range below the tops of the elements, y less than or equal to k. With this constant (roughness velocity,) it is simple to estimate the form drag on the elements. This roughness velocity has been investigated by systematically exercising the present model over ranges of potential parameters. The roughness velocity is found to be primarily a function of the projected element frontal area per unit surface area, thus providing a new and simple method for predicting roughness character effects. The model further suggests that increased boundary layer temperatures should be generated by roughness at high edge Mach numbers, which would tend to reduce skin friction and heat transfer, perhaps below smooth wall levels.
Aerodynamic noise emission from turbulent shear layers.
NASA Technical Reports Server (NTRS)
Pao, S. P.
1973-01-01
The Phillips (1960) convected wave equation is employed in this paper to study aerodynamic noise emission processes in subsonic and supersonic shear layers. The wave equation in three spatial dimensions is first reduced to an ordinary differential equation by Fourier transformation and then solved via the WKBJ method. Three typical solutions are required for discussions in this paper. The current results are different from the classical conclusions. The effects of refraction, convection, Mach-number dependence and temperature dependence of turbulent noise emission are analyzed in the light of solutions to the Phillips equation.
High speed propeller acoustics and aerodynamics - A boundary element approach
NASA Technical Reports Server (NTRS)
Farassat, F.; Myers, M. K.; Dunn, M. H.
1989-01-01
The Boundary Element Method (BEM) is applied in this paper to the problems of acoustics and aerodynamics of high speed propellers. The underlying theory is described based on the linearized Ffowcs Williams-Hawkings equation. The surface pressure on the blade is assumed unknown in the aerodynamic problem. It is obtained by solving a singular integral equation. The acoustic problem is then solved by moving the field point inside the fluid medium and evaluating some surface and line integrals. Thus the BEM provides a powerful technique in calculation of high speed propeller aerodynamics and acoustics.
Boundary-Layer-Ingesting Inlet Flow Control
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.
2008-01-01
An experimental study was conducted to provide the first demonstration of an active flow control system for a flush-mounted inlet with significant boundary-layer-ingestion in transonic flow conditions. The effectiveness of the flow control in reducing the circumferential distortion at the engine fan-face location was assessed using a 2.5%-scale model of a boundary-layer-ingesting offset diffusing inlet. The inlet was flush mounted to the tunnel wall and ingested a large boundary layer with a boundary-layer-to-inlet height ratio of 35%. Different jet distribution patterns and jet mass flow rates were used in the inlet to control distortion. A vane configuration was also tested. Finally a hybrid vane/jet configuration was tested leveraging strengths of both types of devices. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow rates through the duct and the flow control actuators. The distortion and pressure recovery were measured at the aerodynamic interface plane. The data show that control jets and vanes reduce circumferential distortion to acceptable levels. The point-design vane configuration produced higher distortion levels at off-design settings. The hybrid vane/jet flow control configuration reduced the off-design distortion levels to acceptable ones and used less than 0.5% of the inlet mass flow to supply the jets.
NASA Astrophysics Data System (ADS)
Costigliola, V.
2010-09-01
It has long been known that specific atmospheric processes, such as weather and longer-term climatic fluctuations, affect human health. The biometeorological literature refers to this relationship as meteorotropism, defined as a change in an organism that is correlated with a change in atmospheric conditions. Plenty of (patho)physiological functions are affected by those conditions - like the respiratory diseases - and currently it is difficult to put any limits for pathologies developed in reply. Nowadays the importance of atmospheric boundary layer and health is increasingly recognised. A number of epidemiologic studies have reported associations between ambient concentrations of air pollution, specifically particulate pollution, and adverse health effects, even at the relatively low concentrations of pollution found. Since 1995 there have been over twenty-one studies from four continents that have explicitly examined the association between ambient air pollutant mixes and daily mortality. Statistically significant and positive associations have been reported in data from various locations around the world, all with varying air pollutant concentrations, weather conditions, population characteristics and public health policies. Particular role has been given to atmospheric boundary layer processes, the impact of which for specific patient-cohort is, however, not well understood till now. Assessing and monitoring air quality are thus fundamental to improve Europe's welfare. One of current projects run by the "European Medical Association" - PASODOBLE will develop and demonstrate user-driven downstream information services for the regional and local air quality sectors by combining space-based and in-situ data with models in 4 thematic service lines: - Health community support for hospitals, pharmacies, doctors and people at risk - Public information for regions, cities, tourist industry and sporting event organizers - Compliance monitoring support on particulate
Modeling the urban boundary layer
NASA Technical Reports Server (NTRS)
Bergstrom, R. W., Jr.
1976-01-01
A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and boundary problems, (5) nocturnal boundary layer, and (6) verification of models.
Approximation theory for boundary layer suction through individual slits
NASA Technical Reports Server (NTRS)
Walz, A.
1979-01-01
The basic concepts of influencing boundary layers are summarized, especially the prevention of flow detachment and the reduction of frictional resistance. A mathematical analysis of suction through a slit is presented with two parameters, for thickness and for shape of the boundary layer, being introduced to specify the flow's velocity profile behind the slit. An approximation of the shape parameter produces a useful formula, which can be used to determine the most favorable position of the slit. An aerodynamic example is given.
Flow unsteadiness effects on boundary layers
NASA Technical Reports Server (NTRS)
Murthy, Sreedhara V.
1989-01-01
The development of boundary layers at high subsonic speeds in the presence of either mass flux fluctuations or acoustic disturbances (the two most important parameters in the unsteadiness environment affecting the aerodynamics of a flight vehicle) was investigated. A high quality database for generating detailed information concerning free-stream flow unsteadiness effects on boundary layer growth and transition in high subsonic and transonic speeds is described. The database will be generated with a two-pronged approach: (1) from a detailed review of existing literature on research and wind tunnel calibration database, and (2) from detailed tests in the Boundary Layer Apparatus for Subsonic and Transonic flow Affected by Noise Environment (BLASTANE). Special instrumentation, including hot wire anemometry, the buried wire gage technique, and laser velocimetry were used to obtain skin friction and turbulent shear stress data along the entire boundary layer for various free stream noise levels, turbulence content, and pressure gradients. This database will be useful for improving the correction methodology of applying wind tunnel test data to flight predictions and will be helpful for making improvements in turbulence modeling laws.
The plasma sheet boundary layer
NASA Technical Reports Server (NTRS)
Eastman, T. E.; Frank, L. A.; Peterson, W. K.; Lennartsson, W.
1984-01-01
A spatially distinct, temporally variable, transition region between the magnetotail lobes and the central plasma sheet designated the plasma sheet boundary layer has been identified from a survey of particle spectra and three-dimensional distributions as sampled by the ISEE 1 LEPEDEA. The instrumentation and data presentation are described, and the signatures of the magnetotail plasma regimes are presented and discussed for the central plasma sheet and lobe and the plasma sheet boundary layer. Comparisons of plasma parameters and distribution fucntions are made and the evolution of ion velocity distributions within the plasma sheet boundary layer is discussed. The spatial distribution of the plasma sheet boundary layer is considered and ion composition measurements are presented.
Removing Boundary Layer by Suction
NASA Technical Reports Server (NTRS)
Ackeret, J
1927-01-01
Through the utilization of the "Magnus effect" on the Flettner rotor ship, the attention of the public has been directed to the underlying physical principle. It has been found that the Prandtl boundary-layer theory furnishes a satisfactory explanation of the observed phenomena. The present article deals with the prevention of this separation or detachment of the flow by drawing the boundary layer into the inside of a body through a slot or slots in its surface.
Physics of magnetospheric boundary layers
NASA Technical Reports Server (NTRS)
Cairns, Iver H.
1995-01-01
This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.
Physics of magnetospheric boundary layers
NASA Technical Reports Server (NTRS)
Cairns, I. H.
1993-01-01
The central ideas of this grant are that the magnetospheric boundary layers link disparate regions of the magnetosphere together, and the global behavior of the magnetosphere can be understood only by understanding the linking mechanisms. Accordingly the present grant includes simultaneous research on the global, meso-, and micro-scale physics of the magnetosphere and its boundary layers. These boundary layers include the bow shock, magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical and simulation projects have been performed on these subjects, as well as comparison of theoretical results with observational data. Very good progress has been made, with four papers published or in press and two additional papers submitted for publication during the six month period 1 June - 30 November 1993. At least two projects are currently being written up. In addition, members of the group have given papers at scientific meetings. The further structure of this report is as follows: section two contains brief accounts of research completed during the last six months, while section three describes the research projects intended for the grant's final period.
Stability of Boundary Layer Flow.
1980-03-01
and Teske (1975). We can conclude (as in the case of ducting) that theoretical models of boundary layer structure and associated radar structure...FI33 (Secret). Hitney, (1978) "Surface Duct Effects," Naval Ocean Systems Center, San Diego, Calif., Report No. TD144. Lewellen, W. S., and M. E. Teske
Boundary-Layer-Ingesting Inlet Flow Control
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.
2006-01-01
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.
Boundary-Layer-Ingesting Inlet Flow Control
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.
2006-01-01
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.
Three-Dimensional Boundary Layers.
1985-02-01
sketched in figure 1 . The model design is des- • cribed in more detail in reference 2. At measuring station 1 the turbulent boundary layer is very...layer methods are increasingly important as their use for design purposes increases. Specific recommendations for future work include the following. 1 ...MEMBERS M. 1 ’Ing. G&n C.Cap~lier Prof. Dr. Jr. J.L. van Ingen Directeur de l’A~rodynamique Department of Aerospace B.P. 72 Engineering% ONERA Delf
Boundary layer receptivity and control
NASA Technical Reports Server (NTRS)
Hill, D. C.
1993-01-01
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
Multi-colored layers for visualizing aerodynamic flow effects
NASA Technical Reports Server (NTRS)
Jensen, Ronald N. (Inventor)
1991-01-01
A method is provided for visualizing aerodynamic flow effects on a test surface. First, discrete quantities of a sublimating chemical such as naphthalene are distinctively colored via appropriate dyes or paints. Next, a uniform layer of the sublimating chemical having a particular color is applied to the test surface. This layer is covered with a second uniform layer of a different colored sublimating chemical, and so on until a composite of multi-colored layers is formed having a discrete thickness. Friction caused by an airflow results in the distinctly colored layers being removed in proportion to such aerodynamic flow characteristics as velocity and temperature, resulting in a multi-colored portrait which approximates the air flow on the underlying test surface.
Boundary conditions for direct computation of aerodynamic sound generation
NASA Technical Reports Server (NTRS)
Colonius, Tim; Lele, Sanjiva K.; Moin, Parviz
1992-01-01
A numerical scheme suitable for the computation of both the near field acoustic sources and the far field sound produced by turbulent free shear flows utilizing the Navier-Stokes equations is presented. To produce stable numerical schemes in the presence of shear, damping terms must be added to the boundary conditions. The numerical technique and boundary conditions are found to give stable results for computations of spatially evolving mixing layers.
Optical measurements of degradation in aircraft boundary layers
NASA Technical Reports Server (NTRS)
Kelsall, D.
1980-01-01
Visible wavelength measurements of the degradation of optical beams when transmitted through the thin aerodynamic boundary layers around an aircraft are reviewed. The measured results indicated degradation levels for the KC-135 airplanes between 0.10 to 0.13 lambda increasing to 0.18 lambda (rms wavefront distortion). For the Lear Jet, degradation with a 25 mm diameter optics was roughly 0.07 lambda. The corresponding infinite aperture degradation levels are also calculated. The corresponding measured correlation lengths of roughly 12 mm for the KC-135 aircraft and 6 mm for the Lear Jet scale to roughly 20 and 25 mm, respectively, for infinite apertures. These boundary layer correlation lengths do not appear to reflect the different boundary layer thicknesses on the two different aircraft.
Method for laminar boundary layer transition visualization in flight
NASA Technical Reports Server (NTRS)
Holmes, Bruce J. (Inventor); Gall, Peter D. (Inventor)
1988-01-01
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.
Boundary Layer Heights from CALIOP
NASA Astrophysics Data System (ADS)
Kuehn, R.; Ackerman, S. A.; Holz, R.; Roubert, L.
2012-12-01
This work is focused on the development of a planetary boundary layer (PBL) height retrieval algorithm for CALIOP and validation studies. Our current approach uses a wavelet covariance transform analysis technique to find the top of the boundary layer. We use the methodology similar to that found in Davis et. al. 2000, ours has been developed to work with the lower SNR data provided by CALIOP, and is intended to work autonomously. Concurrently developed with the CALIOP algorithm we will show results from a PBL height retrieval algorithm from profiles of potential temperature, these are derived from Aircraft Meteorological DAta Relay (AMDAR) observations. Results from 5 years of collocated AMDAR - CALIOP retrievals near O'Hare airport demonstrate good agreement between the CALIOP - AMDAR retrievals. In addition, because we are able to make daily retrievals from the AMDAR measurements, we are able to observe the seasonal and annual variation in the PBL height at airports that have sufficient instrumented-aircraft traffic. Also, a comparison has been done between the CALIOP retrievals and the NASA Langley airborne High Spectral Resolution Lidar (HSRL) PBL height retrievals acquired during the GoMACCS experiment. Results of this comparison, like the AMDAR comparison are favorable. Our current work also involves the analysis and verification of the CALIOP PBL height retrieval from the 6 year CALIOP global data set. Results from this analysis will also be presented.
Nonequilibrium chemistry boundary layer integral matrix procedure
NASA Technical Reports Server (NTRS)
Tong, H.; Buckingham, A. C.; Morse, H. L.
1973-01-01
The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the boundary layer.
Vortex boundary-layer interactions
NASA Technical Reports Server (NTRS)
Bradshaw, P.
1986-01-01
Parametric studies to identify a vortex generator were completed. Data acquisition in the first chosen configuration, in which a longitudinal vortex pair generated by an isolated delta wing starts to merge with a turbulent boundary layer on a flat plate fairly close to the leading edge is nearly completed. Work on a delta-wing/flat-plate combination, consisting of a flow visualization and hot wire measurements taken with a computer controlled traverse gear and data logging system were completed. Data taking and analysis have continued, and sample results for another cross stream plane are presented. Available data include all mean velocity components, second order mean products of turbulent fluctuations, and third order mean products. Implementation of a faster data logging system was accomplished.
Boundary layer theory and subduction
Fowler, A.C.
1993-12-01
Numerical models of thermally activated convective flow in Earth`s mantle do not resemble active plate tectonics because of their inability to model successfully the process of subduction, other than by the inclusion of artificial weak zones. Here we show, using a boundary layer argument, how the `rigid lid` style of convection favored by thermoviscous fluids leads to lithospheric stresses which may realistically exceed the yield stress and thus cause subduction ot occur through the visoc-plastic failure of lithospheric rock. An explicit criterion for the failure of the lid is given, which is sensitive to the internal viscosity eta(sub a) below the lid. For numbers appropriate to Earth`s mantle, this criterion is approximately eta(sub a) greater than 10(exp 21) Pa s.
Outer layer effects in wind-farm boundary layers: Coriolis forces and boundary layer height
NASA Astrophysics Data System (ADS)
Allaerts, Dries; Meyers, Johan
2015-11-01
In LES studies of wind-farm boundary layers, scale separation between the inner and outer region of the atmospheric boundary layer (ABL) is frequently assumed, i.e., wind turbines are presumed to fall within the inner layer and are not affected by outer layer effects. However, modern wind turbine and wind farm design tends towards larger rotor diameters and farm sizes, which means that outer layer effects will become more important. In a prior study, it was already shown for fully-developed wind farms that the ABL height influences the power performance. In this study, we use the in-house LES code SP-Wind to investigate the importance of outer layer effects on wind-farm boundary layers. In a suite of LES cases, the ABL height is varied by imposing a capping inversion with varying inversion strengths. Results indicate the growth of an internal boundary layer (IBL), which is limited in cases with low inversion layers. We further find that flow deceleration combined with Coriolis effects causes a change in wind direction throughout the farm. This effect increases with decreasing boundary layer height, and can result in considerable turbine wake deflection near the end of the farm. The authors are supported by the ERC (ActiveWindFarms, grant no: 306471). Computations were performed on VSC infrastructiure (Flemish Supercomputer Center), funded by the Hercules Foundation and the Flemish Government-department EWI.
Microgravity Effects on Plant Boundary Layers
NASA Technical Reports Server (NTRS)
Stutte, Gary; Monje, Oscar
2005-01-01
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.
Microgravity Effects on Plant Boundary Layers
NASA Astrophysics Data System (ADS)
Stutte, Gary; Monje, Oscar
2005-08-01
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.
Unified Parameterization of the Marine Boundary Layer
2010-09-30
information if it does not display a currently valid OMB control number. 1. REPORT DATE 2010 2 . REPORT TYPE 3. DATES COVERED 00-00-2010 to 00-00-2010...boundary layer closure for the convective boundary layer 2 . An EDMF approach to the vertical transport of TKE in convective boundary layers 3. EDMF in...4 implementation and extension to shallow cumulus parameterization is in progress. 2 An integrated TKE-based eddy-diffusivity/mass-flux
Development of perturbations in the boundary layer
NASA Technical Reports Server (NTRS)
Dovgal, A. V.; Kachanov, Y. S.; Kozlov, V. V.; Levchenko, V. Y.; Maksimov, V. P.
1986-01-01
The transition of laminar flows into turbulent flows in a boundary layer is discussed. The individual aspects of the transition process, observed under controllable model conditions are examined. The aspect of this problem, namely the development or excitation of the natural oscillations in the boundary layer, the so-called Tollmin-Schlichting waves is covered. Three types of excitation of these waves are considered: (1) distributed generation throughout the boundary layer; (2) generation in the vicinity of the forward edge of a model, having either a sharp edge or an edge with a large radius or curvature, and (3) generation in a developed boundary layer by means of a focused effect.
Relationship between the free shear layer, the wingtip vortex and aerodynamic efficiency
NASA Astrophysics Data System (ADS)
Gunasekaran, Sidaard
The overarching objective of this experimental investigation is to explore the relationship between the aerodynamic efficiency of the wing and its turbulent wake (both the free shear layer and the wingtip vortex). Recent evidence of unique turbulent signatures in the free shear layer of a turbulent generator provided the motivation behind this research. The balance of induced drag and the parasite drag was hypothesized to be mirrored in the properties of the wingtip vortex and the free shear layer respectively expanding from classical theoretical descriptions. Experimental investigations were focused on the wake of wings to understand this balance in the parasite and the induced drag and to explore the use of the properties in the turbulent wake to increase the aerodynamic efficiency of the wing. Because of the highly complex nature of the wake, the research is broken down into several individual sub-studies which explore a) the relationship between the aerodynamic efficiency and the free shear layer, b) the relationship between the aerodynamic efficiency and the wingtip vortex, and c) the relationship between the free shear layer and the wingtip vortex and their correlation to the aerodynamic efficiency. Particle Image Velocimetry (PIV) was used to measure the velocity in the wake of an SD 7003 wall-to-wall model and an AR 4 flat plate with and without a spanwise boundary layer trip in the Horizontal Free Surface Water Tunnel (HFWT) at the Air Force Research Labs (AFRL) and in the Low Speed Wind Tunnel at the University of Dayton (UD-LSWT). The results from experimental investigations were Reynolds decomposed to study the mean and fluctuating quantities in the wake of the wing. The initial prediction of these quantities in the wake of SD 7003 wall-to-wall model and AR 4 flat plate were made using the existing momentum deficit and Reynolds stress models (which are derived from simplified Navier-Stokes equations). Even though the momentum deficit model yielded a
The Martian Atmospheric Boundary Layer
NASA Astrophysics Data System (ADS)
Petrosyan, A.; Galperin, B.; Larsen, S. E.; Lewis, S. R.; Määttänen, A.; Read, P. L.; Renno, N.; Rogberg, L. P. H. T.; Savijärvi, H.; Siili, T.; Spiga, A.; Toigo, A.; Vázquez, L.
2011-09-01
The planetary boundary layer (PBL) represents the part of the atmosphere that is strongly influenced by the presence of the underlying surface and mediates the key interactions between the atmosphere and the surface. On Mars, this represents the lowest 10 km of the atmosphere during the daytime. This portion of the atmosphere is extremely important, both scientifically and operationally, because it is the region within which surface lander spacecraft must operate and also determines exchanges of heat, momentum, dust, water, and other tracers between surface and subsurface reservoirs and the free atmosphere. To date, this region of the atmosphere has been studied directly, by instrumented lander spacecraft, and from orbital remote sensing, though not to the extent that is necessary to fully constrain its character and behavior. Current data strongly suggest that as for the Earth's PBL, classical Monin-Obukhov similarity theory applies reasonably well to the Martian PBL under most conditions, though with some intriguing differences relating to the lower atmospheric density at the Martian surface and the likely greater role of direct radiative heating of the atmosphere within the PBL itself. Most of the modeling techniques used for the PBL on Earth are also being applied to the Martian PBL, including novel uses of very high resolution large eddy simulation methods. We conclude with those aspects of the PBL that require new measurements in order to constrain models and discuss the extent to which anticipated missions to Mars in the near future will fulfill these requirements.
Cyclone separator having boundary layer turbulence control
Krishna, Coimbatore R.; Milau, Julius S.
1985-01-01
A cyclone separator including boundary layer turbulence control that is operable to prevent undue build-up of particulate material at selected critical areas on the separator walls, by selectively varying the fluid pressure at those areas to maintain the momentum of the vortex, thereby preventing particulate material from inducing turbulence in the boundary layer of the vortical fluid flow through the separator.
Turbulent boundary-layer control with plasma actuators.
Choi, Kwing-So; Jukes, Timothy; Whalley, Richard
2011-04-13
This paper reviews turbulent boundary-layer control strategies for skin-friction reduction of aerodynamic bodies. The focus is placed on the drag-reduction mechanisms by two flow control techniques-spanwise oscillation and spanwise travelling wave, which were demonstrated to give up to 45 per cent skin-friction reductions. We show that these techniques can be implemented by dielectric-barrier discharge plasma actuators, which are electric devices that do not require any moving parts or complicated ducting. The experimental results show different modifications to the near-wall structures depending on the control technique.
Structure of relaminarizing turbulent boundary layers
NASA Astrophysics Data System (ADS)
Ramesh, O.; Patwardhan, Saurabh
2014-11-01
Relaminarization of a turbulent boundary layer in a strongly accelerated flow has received a great attention in recent times. It has been found that such relaminarization is a general and regularly occurring phenomenon in the leading-edge region of a swept wing of an airplane (van Dam et al., 1993). In this work, we investigate the effect of initial Reynolds number on the process of relaminarization in turbulent boundary layers. The experimental and numerical investigation of relaminarizing turbulent boundary layers undergoing same history reveals that the boundary layer with higher initial Reynolds number relaminarizes at a lower pressure gradient value compared to the one with lower Reynolds number. This effect can be explained on the inviscid theory proposed earlier in the literature. Further, various parameter criteria proposed to predict relaminarization, are assessed and the structure of relaminarizing boundary layers is investigated. A mechanism for stabilization of near-wall low speed streaks is proposed.
Aerodynamically-driven condensate layer thickness distributions on isothermal cylindrical surfaces
NASA Technical Reports Server (NTRS)
Rosner, D. E.; Gunes, D.; Nazih-Anous, N.
1983-01-01
A simple yet rather general mathematical model is presented for predicting the distribution of condensate layer thickness when aerodynamic shear is the dominant mechanism of liquid flow along the surface. The Newtonian condensate film is treated using well-known thin-layer (lubrication theory) approximations, and condensate supply is taken to be the result of either convective diffusion or inertial impaction. Illustrative calculations for a circular cylinder in a crossflow at Re = 100,000 reveal the consequences of alternate condensate arrival mechanisms and the existence of thicker reverse-flow films behind the position of gas boundary-layer separation. The present formulation is readily generalized to include transient liquid layer flows on noncircular objects of variable surface temperature, as encountered in turbine-blade materials testing or operation.
Aerodynamically-driven condensate layer thickness distributions on isothermal cylindrical surfaces
NASA Astrophysics Data System (ADS)
Rosner, D. E.; Gunes, D.; Nazih-Anous, N.
A simple yet rather general mathematical model is presented for predicting the distribution of condensate layer thickness when aerodynamic shear is the dominant mechanism of liquid flow along the surface. The Newtonian condensate film is treated using well-known thin-layer (lubrication theory) approximations, and condensate supply is taken to be the result of either convective diffusion or inertial impaction. Illustrative calculations for a circular cylinder in a crossflow at Re = 100,000 reveal the consequences of alternate condensate arrival mechanisms and the existence of thicker reverse-flow films behind the position of gas boundary-layer separation. The present formulation is readily generalized to include transient liquid layer flows on noncircular objects of variable surface temperature, as encountered in turbine-blade materials testing or operation.
LDV measurements of turbulent baroclinic boundary layers
Neuwald, P.; Reichenbach, H.; Kuhl, A.L.
1993-07-01
Described here are shock tube experiments of nonsteady, turbulent boundary layers with large density variations. A dense-gas layer was created by injecting Freon through the porous floor of the shock tube. As the shock front propagated along the layer, vorticity was created at the air-Freon interface by an inviscid, baroclinic mechanism. Shadow-schlieren photography was used to visualize the turbulent mixing in this baroclinic boundary layer. Laser-Doppler-Velocimetry (LDV) was used to measure the streamwise velocity histories at 14 heights. After transition, the boundary layer profiles may be approximated by a power-law function u {approximately} u{sup {alpha}} where {alpha} {approx_equal} 3/8. This value lies between the clean flat plate value ({alpha} = 1/7) and the dusty boundary layer value ({alpha} {approx_equal} 0.7), and is controlled by the gas density near the wall.
Calculation methods for compressible turbulent boundary layers
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.
1976-01-01
Calculation procedures for non-reacting compressible two- and three-dimensional turbulent boundary layers were reviewed. Integral, transformation and correlation methods, as well as finite difference solutions of the complete boundary layer equations summarized. Alternative numerical solution procedures were examined, and both mean field and mean turbulence field closure models were considered. Physics and related calculation problems peculiar to compressible turbulent boundary layers are described. A catalog of available solution procedures of the finite difference, finite element, and method of weighted residuals genre is included. Influence of compressibility, low Reynolds number, wall blowing, and pressure gradient upon mean field closure constants are reported.
Application of the controlled boundary layer concept for the wall interference reduction
NASA Astrophysics Data System (ADS)
Ivanov, A. I.; Kursakov, I. A.; Streltsov, E. V.
2016-10-01
Traditional boundaries of transonic wind tunnels (perforated and slotted walls) have some disadvantages that do not allow to completely remove wall interference on all main aerodynamic characteristics. This article focuses on the results of implementation of new boundary condition based, in general, on the idea of jet boundaries. Authors examine the implementation of the controlled boundary layer on solid walls, which characteristics were artificially increased with the aim of near-wall spoiler grid mounted at the test section entrance. The analysis underlines significant decreasing of wall interference on all main aerodynamic characteristics, including lift coefficient and pitching moment coefficient. We conclude that realization of the controlled boundary layer might become simple and rather effective method of wall-interference reduction.
F-16XL ship #1 - CAWAP boundary layer rakes and hot film on left wing
NASA Technical Reports Server (NTRS)
1996-01-01
This photo shows the boundary layer hot film and the boundary layer rakes on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.
Boundary-layer control for drag reduction
NASA Technical Reports Server (NTRS)
Harvey, William D.
1988-01-01
Although the number of possible applications of boundary-layer control is large, a discussion is given only of those that have received the most attention recently at NASA Langley Research Center to improve airfoil drag characteristics. This research concerns stabilizing the laminar boundary layer through geometric shaping (natural laminar flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (laminar flow control, LFC) either through discrete slots or a perforated surface. At low Reynolds numbers, a combination of shaping and forced transition has been used to achieve the desired run of laminar flow and control of laminar separation. In the design of both natural laminar flow and laminar flow control airfoils and wings, boundary layer stability codes play an important role. A discussion of some recent stability calculations using both incompressible and compressible codes is given.
Boundary-layer stability and airfoil design
NASA Technical Reports Server (NTRS)
Viken, Jeffrey K.
1986-01-01
Several different natural laminar flow (NLF) airfoils have been analyzed for stability of the laminar boundary layer using linear stability codes. The NLF airfoils analyzed come from three different design conditions: incompressible; compressible with no sweep; and compressible with sweep. Some of the design problems are discussed, concentrating on those problems associated with keeping the boundary layer laminar. Also, there is a discussion on how a linear stability analysis was effectively used to improve the design for some of the airfoils.
Solute boundary layer on a rotating crystal
NASA Astrophysics Data System (ADS)
Povinelli, Michelle L.; Korpela, Seppo A.; Chait, Arnon
1994-11-01
A perturbation analysis has been carried out for the solutal boundary layer next to a rotating crystal. Our aim is to extend the classical results of Burton, Prim and Slicher [1] in order to obtain higher order terms in asymptotic expansions for the concentration field and boundary-layer thickness. Expressions for the effective segregation coefficient are directly obtained from the concentration solution in the two limits that correspond to weak and strong rotation.
The Ocean Boundary Layer beneath Hurricane Frances
NASA Astrophysics Data System (ADS)
Dasaro, E. A.; Sanford, T. B.; Terrill, E.; Price, J.
2006-12-01
The upper ocean beneath the peak winds of Hurricane Frances (57 m/s) was measured using several varieties of air-deployed floats as part of CBLAST. A multilayer structure was observed as the boundary layer deepened from 20m to 120m in about 12 hours. Bubbles generated by breaking waves create a 10m thick surface layer with a density anomaly, due to the bubbles, of about 1 kg/m3. This acts to lubricate the near surface layer. A turbulent boundary layer extends beneath this to about 40 m depth. This is characterized by large turbulent eddies spanning the boundary layer. A stratified boundary layer grows beneath this reaching 120m depth. This is characterized by a gradient Richardson number of 1/4, which is maintained by strong inertial currents generated by the hurricane, and smaller turbulent eddies driven by the shear instead of the wind and waves. There is little evidence of mixing beneath this layer. Heat budgets reveal the boundary layer to be nearly one dimensional through much of the deepening, with horizontal and vertical heat advection becoming important only after the storm had passed. Turbulent kinetic energy measurements support the idea of reduced surface drag at high wind speeds. The PWP model correctly predicts the degree of mixed layer deepening if the surface drag is reduced at high wind speed. Overall, the greatest uncertainty in understanding the ocean boundary layer at these extreme wind speeds is a characterization of the near- surface processes which govern the air-sea fluxes and surface wave properties.
General fuselage coordinates for the calculation of three-dimensional boundary layers
NASA Astrophysics Data System (ADS)
Hoeld, R.
1986-07-01
A programming package for the numerical calculation of three-dimensional boundary layers in aerodynamics was developed. It is suited for sub-, trans-, and supersonic flows. The fundamentals of general boundary layer coordinates and boundary layer theory are presented. The boundary layer calculation package consists of several programs, allowing a flexible application. Emphasis is placed on the control and the presentation of the results, facilitating the recognition and elimination of errors. A calculation network, adapted to the flow pattern about the body, was developed, with a view to the parabolic character of the boundary layer-equations. The developed program version was tested on a rotation ellipsoid; the calculated results agree with experimental results for an angle of attack of 0 deg, but differ substantially for increasing angles.
NASA Technical Reports Server (NTRS)
Avery, D. E.
1985-01-01
The heat transfer to simulated shuttle thermal protection system tiles was investigated experimentally by using a highly instrumented metallic thin wall tile arranged with other metal tiles in a staggered tile array. Cold wall heating rate data for laminar and turbulent flow were obtained in the Langley 8 foot high Temperature Tunnel at a nominal Mach number of 7, a nominal total temperature of 3300R, a free stream unit Reynolds number from 3.4 x 10 sup 5 to 2.2 10 sup 6 per foot, and a free stream dynamic pressure from 2.1 to 9.0 psia. Experimental data are presented to illustrate the effects of flow angularity and gap width on both local peak heating and overall heating loads. For the conditions of the present study, the results show that localized and total heating are sensitive to changes in flow angle only for the test conditions of turbulent boundary layer flow with high kinetic energy and that a flow angle from 30 deg to 50 deg will minimize the local heating.
Characteristic boundary conditions for three-dimensional transonic unsteady aerodynamics
NASA Technical Reports Server (NTRS)
Whitlow, W., Jr.
1984-01-01
Characteristic far-field boundary conditions for the three-dimensional unsteady transonic small disturbance potential equation have been developed. The boundary conditions were implemented in the XTRAN3S finite difference code and tested for a flat plate rectangular wing with a pulse in angle of attack; the freestream Mach number was 0.85. The calculated force response shows that the characteristic boundary conditions reduce disturbances that are reflected from the computational boundaries.
NASA Technical Reports Server (NTRS)
Horstman, Raymond H.
1992-01-01
Aerodynamic flow achieved by adding fixed fairings to butterfly valve. When valve fully open, fairings align with butterfly and reduce wake. Butterfly free to turn, so valve can be closed, while fairings remain fixed. Design reduces turbulence in flow of air in internal suction system. Valve aids in development of improved porous-surface boundary-layer control system to reduce aerodynamic drag. Applications primarily aerospace. System adapted to boundary-layer control on high-speed land vehicles.
Modeling the summertime Arctic cloudy boundary layer
Curry, J.A.; Pinto, J.O.; McInnes, K.L.
1996-04-01
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.
Alpha models and boundary-layer turbulence
NASA Astrophysics Data System (ADS)
Cheskidov, Alexey
We study boundary-layer turbulence using the Navier-Stokes-alpha model obtaining an extension of the Prandtl equations for the averaged flow in a turbulent boundary layer. In the case of a zero pressure gradient flow along a flat plate, we derive a nonlinear fifth-order ordinary differential equation, an extension of the Blasius equation. We study it analytically and prove the existence of a two-parameter family of solutions satisfying physical boundary conditions. From this equation we obtain a theoretical prediction of the skin-friction coefficient in a wide range of Reynolds numbers based on momentum thickness, and deduce the maximal value of the skin-friction coefficient in the turbulent boundary layer. The two-parameter family of solutions to the equation matches experimental data in the transitional boundary layers with different free stream turbulence intensity. A one-parameter sub-family of solutions, obtained using our skin-friction coefficient law, matches experimental data in the turbulent boundary layer for moderately large Reynolds numbers.
Numerical Investigation of a Fuselage Boundary Layer Ingestion Propulsion Concept
NASA Technical Reports Server (NTRS)
Elmiligui, Alaa A.; Fredericks, William J.; Guynn, Mark D.; Campbell, Richard L.
2013-01-01
In the present study, a numerical assessment of the performance of fuselage boundary layer ingestion (BLI) propulsion techniques was conducted. This study is an initial investigation into coupling the aerodynamics of the fuselage with a BLI propulsion system to determine if there is sufficient potential to warrant further investigation of this concept. Numerical simulations of flow around baseline, Boundary Layer Controlled (BLC), and propelled boundary layer controlled airships were performed. Computed results showed good agreement with wind tunnel data and previous numerical studies. Numerical simulations and sensitivity analysis were then conducted on four BLI configurations. The two design variables selected for the parametric study of the new configurations were the inlet area and the inlet to exit area ratio. Current results show that BLI propulsors may offer power savings of up to 85% over the baseline configuration. These interim results include the simplifying assumption that inlet ram drag is negligible and therefore likely overstate the reduction in power. It has been found that inlet ram drag is not negligible and should be included in future analysis.
Numerical simulation of shock/turbulent boundary layer interaction
NASA Technical Reports Server (NTRS)
Biringen, Sedat; Hatay, Ferhat F.
1993-01-01
Most flows of aerodynamic interest are compressible and turbulent. However, our present knowledge on the structures and mechanisms of turbulence is mostly based on incompressible flows. In the present work, compressibility effects in turbulent, high-speed, boundary layer flows are systematically investigated using the Direct Numerical Simulation (DNS) approach. Three-dimensional, time-dependent, fully nonlinear, compressible Navier-Stokes equations were numerically integrated by high-order finite-difference methods; no modeling for turbulence is used during the solution because the available resolution is sufficient to capture the relevant scales. The boundary layer problem deals with fully-turbulent compressible flows over flat geometries. Apart from its practical relevance to technological flows, turbulent compressible boundary layer flow is the simplest experimentally realizable turbulent compressible flow. Still, measuring difficulties prohibit a detailed experimental description of the flow, especially in the near-wall region. DNS studies provide a viable means to probe the physics of compressible turbulence in this region. The focus of this work is to explore the paths of energy transfer through which compressible turbulence is sustained. The structural similarities and differences between the incompressible and compressible turbulence are also investigated. The energy flow patterns or energy cascades are found to be directly related to the evolution of vortical structures which are generated in the near-wall region. Near-wall structures, and mechanisms which are not readily accessible through physical experiments are analyzed and their critical role on the evolution and the behavior of the flow is documented extensively.
NASA Technical Reports Server (NTRS)
Mikic, Gregor Veble; Stoll, Alex; Bevirt, JoeBen; Grah, Rok; Moore, Mark D.
2016-01-01
Theoretical and numerical aspects of aerodynamic efficiency of propulsion systems are studied. Focus is on types of propulsion that closely couples to the aerodynamics of the complete vehicle. We discuss the effects of local flow fields, which are affected both by conservative flow acceleration as well as total pressure losses, on the efficiency of boundary layer immersed propulsion devices. We introduce the concept of a boundary layer retardation turbine that helps reduce skin friction over the fuselage. We numerically investigate efficiency gains offered by boundary layer and wake interacting devices. We discuss the results in terms of a total energy consumption framework and show that efficiency gains offered depend on all the elements of the propulsion system.
Streamline curvature effects on turbulent boundary layers
NASA Technical Reports Server (NTRS)
Wilcox, D. C.; Chambers, T. L.
1976-01-01
A theoretical tool has been developed for predicting, in a nonempirical manner, effects of streamline curvature and coordinate-system rotation on turbulent boundary layers. The second-order closure scheme developed by Wilcox and Traci has been generalized for curved streamline flow and for flow in a rotating coordinate system. A physically based straightforward argument shows that curvature/rotation primarily affects the turbulent mixing energy; the argument yields suitable curvature/rotation terms which are added to the mixing-energy equation. Singular-perturbation solutions valid in the wall layer of a curved-wall boundary layer and a fully developed rotating channel flow demonstrate that, with the curvature/rotation terms, the model predicts the curved-wall and the rotating coordinate system laws of the wall. Results of numerical computations of curved-wall boundary layers and of rotating channel flow show that curvature/rotation effects can be computed accurately with second-order closure.
NASA Astrophysics Data System (ADS)
Fernholz, H. H.; Krause, E.
Papers are presented on recent research concerning three-dimensional turbulent boundary layers. Topics examined include experimental techniques in three-dimensional turbulent boundary layers, turbulence measurements in ship-model flow, measurements of Reynolds-stress profiles in the stern region of a ship model, the effects of crossflow on the vortex-layer-type three-dimensional flow separation, and wind tunnel investigations of some three-dimensional separated turbulent boundary layers. Also examined are three-dimensional boundary layers in turbomachines, the boundary layers on bodies of revolution spinning in axial flows, the effect on a developed turbulent boundary layer of a sudden local wall motion, three-dimensional turbulent boundary layer along a concave wall, the numerical computation of three-dimensional boundary layers, a numerical study of corner flows, three-dimensional boundary calculations in design aerodynamics, and turbulent boundary-layer calculations in design aerodynamics. For individual items see A83-47012 to A83-47036
The Kinematics of Turbulent Boundary Layer Structure
NASA Technical Reports Server (NTRS)
Robinson, Stephen Kern
1991-01-01
The long history of research into the internal structure of turbulent boundary layers has not provided a unified picture of the physics responsible for turbulence production and dissipation. The goals of the present research are to: (1) define the current state of boundary layer structure knowledge; and (2) utilize direct numerical simulation results to help close the unresolved issues identified in part A and to unify the fragmented knowledge of various coherent motions into a consistent kinematic model of boundary layer structure. The results of the current study show that all classes of coherent motion in the low Reynolds number turbulent boundary layer may be related to vortical structures, but that no single form of vortex is representative of the wide variety of vortical structures observed. In particular, ejection and sweep motions, as well as entrainment from the free-streem are shown to have strong spatial and temporal relationships with vortical structures. Disturbances of vortex size, location, and intensity show that quasi-streamwise vortices dominate the buffer region, while transverse vortices and vortical arches dominate the wake region. Both types of vortical structure are common in the log region. The interrelationships between the various structures and the population distributions of vortices are combined into a conceptual kinematic model for the boundary layer. Aspects of vortical structure dynamics are also postulated, based on time-sequence animations of the numerically simulated flow.
Turbulent Spots Inside the Turbulent Boundary Layer
NASA Astrophysics Data System (ADS)
Skarda, Jinhie; Wu, Xiaohua; Moin, Parviz; Lozano-Duran, Adrian; Wallace, James; Hickey, Jean-Pierre
2016-11-01
We present evidence that the buffer region of the canonical turbulent boundary layer is populated by locally generated turbulent spots, which cause strong indentations on the near-wall low-momentum streaks. This evidence is obtained from a spatially-developing direct numerical simulation carrying the inlet Blasius boundary layer through a bypass transition to the turbulent boundary layer state over a moderate Reynolds number range. The turbulent spots are structurally analogous to their transitional counter-parts but without any direct causality connection. High-pass filtered time-history records are used to calculate the period of turbulent spot detection and this period is compared to the boundary layer bursting period reported in hot-wire experiments. The sensitivity of the results to parameters such as the high pass filter frequency and the amplitude discriminator level is examined. The characteristics of these turbulent spots are also quantified using a spatial connectivity based conditional sampling technique. This evidence seems to be at odds with the notion that the buffer region is dominated by quasi-streamwise vortices, and contributes to the potential unification of the studies on near-wall turbulent boundary layer dynamics.
Boundary Layer Cloudiness Parameterizations Using ARM Observations
Bruce Albrecht
2004-09-15
This study used DOE ARM data and facilities to: (1) study macroscopic properties of continental stratus clouds at SGP and the factors controlling these properties, (2) develop a scientific basis for understanding the processes responsible for the formation of boundary layer clouds using ARM observations in conjunction with simple parametric models and LES, and (3) evaluate cumulus cloud characteristics retrieved from the MMCR operating at TWP-Nauru. In addition we have used high resolution 94 GHz observations of boundary layer clouds and precipitation to: (1) develop techniques for using high temporal resolution Doppler velocities to study large-eddy circulations and turbulence in boundary layer clouds and estimate the limitations of using current and past MMCR data for boundary layer cloud studies, (2) evaluate the capability and limitations of the current MMCR data for estimating reflectivity, vertical velocities, and spectral under low- signal-to-noise conditions associated with weak no n-precipitating clouds, (3) develop possible sampling modes for the new MMCR processors to allow for adequate sampling of boundary layer clouds, and (4) retrieve updraft and downdraft structures under precipitating conditions.
High enthalpy hypersonic boundary layer flow
NASA Technical Reports Server (NTRS)
Yanow, G.
1972-01-01
A theoretical and experimental study of an ionizing laminar boundary layer formed by a very high enthalpy flow (in excess of 12 eV per atom or 7000 cal/gm) with allowance for the presence of helium driver gas is described. The theoretical investigation has shown that the use of variable transport properties and their respective derivatives is very important in the solution of equilibrium boundary layer equations of high enthalpy flow. The effect of low level helium contamination on the surface heat transfer rate is minimal. The variation of ionization is much smaller in a chemically frozen boundary layer solution than in an equilibrium boundary layer calculation and consequently, the variation of the transport properties in the case of the former was not essential in the integration. The experiments have been conducted in a free piston shock tunnel, and a detailed study of its nozzle operation, including the effects of low levels of helium driver gas contamination has been made. Neither the extreme solutions of an equilibrium nor of a frozen boundary layer will adequately predict surface heat transfer rate in very high enthalpy flows.
KC-135 aero-optical turbulent boundary layer/shear layer experiment revisited
NASA Astrophysics Data System (ADS)
Craig, J.; Allen, C.
1987-05-01
The aero-optical effects associated with propagating a laser beam through both an aircraft turbulent boundary layer and artificially generated shear layers are examined. The data present comparisons from observed optical performance with those inferred from aerodynamic measurements of unsteady density and correlation lengths within the same random flow fields. Using optical instrumentation with tens of microsecond temporal resolution through a finite aperture, optical performance degradation was determined and contrasted with the infinite aperture time averaged aerodynamic measurement. In addition, the optical data were artificially clipped to compare to theoretical scaling calculations. Optical instrumentation consisted of a custom Q switched Nd:Yag double pulsed laser, and a holographic camera which recorded the random flow field in a double pass, double pulse mode. Aerodynamic parameters were measured using hot film anemometer probes and a five hole pressure probe. Each technique is described with its associated theoretical basis for comparison. The effects of finite aperture and spatial and temporal frequencies of the random flow are considered.
KC-135 aero-optical turbulent boundary layer/shear layer experiment revisited
NASA Technical Reports Server (NTRS)
Craig, J.; Allen, C.
1987-01-01
The aero-optical effects associated with propagating a laser beam through both an aircraft turbulent boundary layer and artificially generated shear layers are examined. The data present comparisons from observed optical performance with those inferred from aerodynamic measurements of unsteady density and correlation lengths within the same random flow fields. Using optical instrumentation with tens of microsecond temporal resolution through a finite aperture, optical performance degradation was determined and contrasted with the infinite aperture time averaged aerodynamic measurement. In addition, the optical data were artificially clipped to compare to theoretical scaling calculations. Optical instrumentation consisted of a custom Q switched Nd:Yag double pulsed laser, and a holographic camera which recorded the random flow field in a double pass, double pulse mode. Aerodynamic parameters were measured using hot film anemometer probes and a five hole pressure probe. Each technique is described with its associated theoretical basis for comparison. The effects of finite aperture and spatial and temporal frequencies of the random flow are considered.
NASA Technical Reports Server (NTRS)
Mack, L. M.
1967-01-01
The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the boundary layer which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.
Longitudinal vortices in concave surface boundary layer
NASA Astrophysics Data System (ADS)
Crane, R. I.,; Winoto, S. H.
1980-01-01
Local measurements of mean and fluctuating velocity by laser anemometer were made inside the developing concave surface boundary layer in a free surface water channel at Reynolds numbers up to 16000. Concave surface radius was 3.5 times channel width and the ratio of spanwise mean boundary layer thickness to surface radius ranged between 0.03 and 0.11. Systems of longtitudinal vortices developed without artificial triggering. Vortex wavelength varied across the span by as much as a factor of 2, but mean wavelength was typically 1.3 times the boundary layer thickness and did not vary significantly in the flow direction. Continuous vortex growth at Reynolds number = 9800 contrasted with apparent breakup of the vortices at Reynolds number = 16000.
NASA Astrophysics Data System (ADS)
Suzuki, Kojiro; Abe, Takashi
1995-03-01
The boundary-layer transition on the EXPRESS reentry capsule at transonic and supersonic speeds is studied experimentally by the wind tunnel tests. For the diagnostic of the turbulent transition of the boundary layer, the China-clay method is used. The experimental results clarify that when the freestream Mach number increases, the transition point moves downstream on the body surface and the distance between the beginning of the transition and its completion to the fully turbulent flow becomes larger. The effects of the freestream Mach number on the location of the boundary-layer transition are described successfully in terms of two nondimensional quantities, that is, the transition Reynolds number and the local Mach number at the boundary-layer edge. The oil-flow pictures reveal that in the transonic regime, the separation bubble is formed at the junction between the blunt nose and the conical part of the body and therefore the transition begins behind the reattachment point of the separation bubble. The effects of the turbulent transition on the aerodynamic characteristics of the reentry body are investigated by using the technique of the boundary-layer trip and the experimental results show that the aerodynamic characteristics of the EXPRESS reentry vehicle are not sensitive to the boundary-layer transition.
NASA Technical Reports Server (NTRS)
Braun, Scott A.; Tao, Wei-Kuo
1999-01-01
The MM5 mesoscale model is used to simulate Hurricane Bob (1991) using grids nested to high resolution (4 km). Tests are conducted to determine the sensitivity of the simulation to the available planetary boundary layer parameterizations, including the bulk-aerodynamic, Blackadar, Medium-RanGe Forecast (MRF) model, and Burk-Thompson boundary-layer schemes. Significant sensitivity is seen, with minimum central pressures varying by up to 17 mb. The Burk-Thompson and bulk-aerodynamic boundary-layer schemes produced the strongest storms while the MRF scheme produced the weakest storm. Precipitation structure of the simulated hurricanes also varied substantially with the boundary layer parameterizations. Diagnostics of boundary-layer variables indicated that the intensity of the simulated hurricanes generally increased as the ratio of the surface exchange coefficients for heat and momentum, C(sub h)/C(sub M), although the manner in which the vertical mixing takes place was also important. Findings specific to the boundary-layer schemes include: 1) the MRF scheme produces mixing that is too deep and causes drying of the lower boundary layer in the inner-core region of the hurricane; 2) the bulk-aerodynamic scheme produces mixing that is probably too shallow, but results in a strong hurricane because of a large value of C(sub h)/C(sub M) (approximately 1.3); 3) the MRF and Blackadar schemes are weak partly because of smaller surface moisture fluxes that result in a reduced value of C(sub h)/C(sub M) (approximately 0.7); 4) the Burk-Thompson scheme produces a strong storm with C(sub h)/C(sub M) approximately 1; and 5) the formulation of the wind-speed dependence of the surface roughness parameter, z(sub 0), is important for getting appropriate values of the surface exchange coefficients in hurricanes based upon current estimates of these parameters.
Boundary-Layer Code For Supersonic Combustion
NASA Technical Reports Server (NTRS)
Pinckney, S. Z.; Walton, J. T.
1994-01-01
HUD is integral computer code based on Spaulding-Chi method for predicting development of boundary layers in laminar, transitional, and turbulent regions of flows on two-dimensional or axisymmetric bodies. Approximates nonequilibrium velocity profiles as well as local surface friction in presence of pressure gradient. Predicts transfer of heat in turbulent boundary layer in presence of high axial presure gradient. Provides for pressure gradients both normal and lateral to surfaces. Also used to estimate requirements for cooling scramjet engines. Because of this capability, HUD program incorporated into several scramjet-cycle-performance-analysis codes, including SCRAM (ARC-12338) and SRGULL (LEW-15093). Written in FORTRAN 77.
Glancing shock wave-turbulent boundary layer interaction with boundary layer suction
NASA Technical Reports Server (NTRS)
Barnhart, P. J.; Greber, I.; Hingst, W. R.
1988-01-01
Tests conducted to ascertain the stagnation pressure and flow angularity profiles of a turbulent boundary layer subjected to boundary layer suction (BLS) as it crosses a glancing sidewall shock wave have determined that the boundary layer does not separate upon crossing the shock wave. Without BLS, the upstream influence of the shock wave-induced wall static pressure rise was extensive, of the order of four bloundary layer thicknesses; for the same case, with suction, the extent of upstream influence was 50 percent lower. In addition, flow angularities at the wall were found to be smaller with suction than without it.
Calculation methods for compressible turbulent boundary layers, 1976
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.
1977-01-01
Equations and closure methods for compressible turbulent boundary layers are discussed. Flow phenomena peculiar to calculation of these boundary layers were considered, along with calculations of three dimensional compressible turbulent boundary layers. Procedures for ascertaining nonsimilar two and three dimensional compressible turbulent boundary layers were appended, including finite difference, finite element, and mass-weighted residual methods.
Boundary-layer theory for blast waves
NASA Technical Reports Server (NTRS)
Kim, K. B.; Berger, S. A.; Kamel, M. M.; Korobeinikov, V. P.; Oppenheim, A. K.
1975-01-01
It is profitable to consider the blast wave as a flow field consisting of two regions: the outer, which retains the properties of the inviscid solution, and the inner, which is governed by flow equations including terms expressing the effects of heat transfer and, concomitantly, viscosity. The latter region thus plays the role of a boundary layer. Reported here is an analytical method developed for the study of such layers, based on the matched asymptotic expansion technique combined with patched solutions.
Inclusion of Separation in Integral Boundary Layer Methods
NASA Astrophysics Data System (ADS)
Wallace, Brodie; O'Neill, Charles
2016-11-01
An integral boundary layer (IBL) method coupled with a potential flow solver quickly allows simulating aerodynamic flows, allowing for aircraft geometries to be rapidly designed and optimized. However, most current IBL methods lack the ability to accurately model three-dimensional separated flows. Various IBL equations and closure relations were investigated in an effort to develop an IBL capable of modeling separation. Solution techniques, including a Newton's method and the inverse matrix solving program GMRES, as well as methods for coupling an IBL with a potential flow solver were also investigated. Results for two-dimensional attached flow as well as methods for expanding an IBL to model three-dimensional separation are presented. Funding from NSF REU site Grant EEC 1358991 is greatly appreciated.
Boundary-layer-ingesting inlet flow control system
NASA Technical Reports Server (NTRS)
Owens, Lewis R. (Inventor); Allan, Brian G. (Inventor)
2010-01-01
A system for reducing distortion at the aerodynamic interface plane of a boundary-layer-ingesting inlet using a combination of active and passive flow control devices is disclosed. Active flow control jets and vortex generating vanes are used in combination to reduce distortion across a range of inlet operating conditions. Together, the vortex generating vanes can reduce most of the inlet distortion and the active flow control jets can be used at a significantly reduced control jet mass flow rate to make sure the inlet distortion stays low as the inlet mass flow rate varies. Overall inlet distortion, measured and described as average SAE circumferential distortion descriptor, was maintained at a value of 0.02 or less. Advantageous arrangements and orientations of the active flow control jets and the vortex generating vanes were developed using computational fluid dynamics simulations and wind tunnel experimentations.
Vortex unwinding in a turbulent boundary layer
NASA Technical Reports Server (NTRS)
Mcginley, Catherine B.; Beeler, George B.
1987-01-01
The vortex unwinding method is used as a tool in performing vortex cancellation in a turbulent boundary layer. Sufficient reduction in the isotach variation was achieved to verify the usefulness of this technique, for the cases of both wall turbulence control and horseshoe vortex alleviation. More detailed measurements of vortex strength and position improve the optimization process and increase the amount of vortex unwinding.
Astrophysical Boundary Layers: A New Picture
NASA Astrophysics Data System (ADS)
Belyaev, Mikhail; Rafikov, Roman R.; Mclellan Stone, James
2016-04-01
Accretion is a ubiquitous process in astrophysics. In cases when the magnetic field is not too strong and a disk is formed, accretion can proceed through the mid plane all the way to the surface of the central compact object. Unless that compact object is a black hole, a boundary layer will be formed where the accretion disk touches its surfaces. The boundary layer is both dynamically and observationally significant as up to half of the accretion energy is dissipated there.Using a combination of analytical theory and computer simulations we show that angular momentum transport and accretion in the boundary layer is mediated by waves. This breaks with the standard astrophysical paradigm of an anomalous turbulent viscosity that drives accretion. However, wave-mediated angular momentum transport is a natural consequence of "sonic instability." The sonic instability, which we describe analytically and observe in our simulations, is a close cousin of the Papaloizou-Pringle instability. However, it is very vigorous in the boundary layer due to the immense radial velocity shear present at the equator.Our results are applicable to accreting neutron stars, white dwarfs, protostars, and protoplanets.
The structure of APG turbulent boundary layers
NASA Astrophysics Data System (ADS)
Gungor, Ayse G.; Maciel, Yvan; Simens, Mark P.; Soria, Julio
2013-11-01
A boundary layer under influence of a strong APG is studied using DNS. Transition to turbulence is triggered using a trip wire which is modelled using the immersed boundary method. The Reynolds number close to the exit of the numerical domain is Reθ = 2175 and the shape-factor H = 2 . 5 . Two dimensional two-point spatial correlation functions are obtained in this region and close to the transition region. Cvu with a reference point close to the transition region shows a flow periodicity until Reθ ~ 1600 . This periodicity is related to the shear layer instability of the separation bubble created as a result of the APG. The Cvv and Cww correlations obtained far from the transition region at Reθ = 2175 and at y / δ = 0 . 4 coincide with results obtained for a ZPG boundary layer. Implying that the structure of the v , w fluctuations is the same as in ZPG. However, Cuu indicates that the structure of the u fluctuation in an APG boundary layer is almost twice as short as the ZPG structures. The APG structures are also less correlated with the flow at the wall. The near wall structure of strong APG flows is different from ZPG flows in that streaks are much shorter or absent. Funded in part by ITU, NSERC of Canada, ARC Discovery Grant, and Multiflow program of the ERC.
Planetary Boundary Layer from AERI and MPL
Sawyer, Virginia
2014-02-13
The distribution and transport of aerosol emitted to the lower troposphere is governed by the height of the planetary boundary layer (PBL), which limits the dilution of pollutants and influences boundary-layer convection. Because radiative heating and cooling of the surface strongly affect the PBL top height, it follows diurnal and seasonal cycles and may vary by hundreds of meters over a 24-hour period. The cap the PBL imposes on low-level aerosol transport makes aerosol concentration an effective proxy for PBL height: the top of the PBL is marked by a rapid transition from polluted, well-mixed boundary-layer air to the cleaner, more stratified free troposphere. Micropulse lidar (MPL) can provide much higher temporal resolution than radiosonde and better vertical resolution than infrared spectrometer (AERI), but PBL heights from all three instruments at the ARM SGP site are compared to one another for validation. If there is agreement among them, the higher-resolution remote sensing-derived PBL heights can accurately fill in the gaps left by the low frequency of radiosonde launches, and thus improve model parameterizations and our understanding of boundary-layer processes.
Boundary Layer Transition on X-43A
NASA Technical Reports Server (NTRS)
Berry, Scott; Daryabeigi, Kamran; Wurster, Kathryn; Bittner, Robert
2008-01-01
The successful Mach 7 and 10 flights of the first fully integrated scramjet propulsion systems by the Hyper-X (X-43A) program have provided the means with which to verify the original design methodologies and assumptions. As part of Hyper-X s propulsion-airframe integration, the forebody was designed to include a spanwise array of vortex generators to promote boundary layer transition ahead of the engine. Turbulence at the inlet is thought to provide the most reliable engine design and allows direct scaling of flight results to groundbased data. Pre-flight estimations of boundary layer transition, for both Mach 7 and 10 flight conditions, suggested that forebody boundary layer trips were required to ensure fully turbulent conditions upstream of the inlet. This paper presents the results of an analysis of the thermocouple measurements used to infer the dynamics of the transition process during the trajectories for both flights, on both the lower surface (to assess trip performance) and the upper surface (to assess natural transition). The approach used in the analysis of the thermocouple data is outlined, along with a discussion of the calculated local flow properties that correspond to the transition events as identified in the flight data. The present analysis has confirmed that the boundary layer trips performed as expected for both flights, providing turbulent flow ahead of the inlet during critical portions of the trajectory, while the upper surface was laminar as predicted by the pre-flight analysis.
Nonlinear Transient Growth and Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Paredes, Pedro; Choudhari, Meelan M.; Li, Fei
2016-01-01
Parabolized stability equations (PSE) are used in a variational approach to study the optimal, non-modal disturbance growth in a Mach 3 at plate boundary layer and a Mach 6 circular cone boundary layer. As noted in previous works, the optimal initial disturbances correspond to steady counter-rotating streamwise vortices, which subsequently lead to the formation of streamwise-elongated structures, i.e., streaks, via a lift-up effect. The nonlinear evolution of the linearly optimal stationary perturbations is computed using the nonlinear plane-marching PSE for stationary perturbations. A fully implicit marching technique is used to facilitate the computation of nonlinear streaks with large amplitudes. To assess the effect of the finite-amplitude streaks on transition, the linear form of plane- marching PSE is used to investigate the instability of the boundary layer flow modified by spanwise periodic streaks. The onset of bypass transition is estimated by using an N- factor criterion based on the amplification of the streak instabilities. Results show that, for both flow configurations of interest, streaks of sufficiently large amplitude can lead to significantly earlier onset of transition than that in an unperturbed boundary layer without any streaks.
Flow visualization of turbulent boundary layer structure
NASA Astrophysics Data System (ADS)
Head, M. R.; Bandyopadhyay, P.
1980-01-01
The results from flow visualization experiments performed using an argon-ion laser to illuminate longitudinal and transverse sections of the smoke filled boundary layer in zero pressure gradient are discussed. Most of the experiments were confined to the range 600 Re sub theta 10,000. Results indicate that the boundary layer consists almost exclusively of vortex loops or hairpins, some of which may extend through the complete boundary layer thickness and all of which are inclined at a more or less constant characteristic angle of approximately 45 deg to the wall. Since the cross-stream dimensions of the hairpins appear to scale roughly with the wall variables U sub tau and nu, while their length is limited only by the boundary layer thickness, there are very large scale effects on the turbulence structure. At high Reynolds numbers (Re sub theta = 10,000) there is little evidence of large-scale coherent motions, other than a slow overturning of random agglomerations of the hairpins just mentioned.
2007 Program of Study: Boundary Layers
2008-06-01
of boundary layer flows Jan Zika , University of New South Wales ..................................................................143 Double...Angel Ruiz-Angulo Caltech Henrik van Lengerich Cornell University Andrew Wells University of Cambridge Jan Zika University of New South Wales Staff...Gallet, Frederic Laliberte, Henrik van Lengerich, Jan Zika , Iva Kavcic. Second row (L/R): Ed Spiegel (standing), Charles Doering, Willem Malkus, Vitalii
Orbiter Boundary Layer Transition Prediction Tool Enhancements
NASA Technical Reports Server (NTRS)
Berry, Scott A.; King, Rudolph A.; Kegerise, Michael A.; Wood, William A.; McGinley, Catherine B.; Berger, Karen T.; Anderson, Brian P.
2010-01-01
Updates to an analytic tool developed for Shuttle support to predict the onset of boundary layer transition resulting from thermal protection system damage or repair are presented. The boundary layer transition tool is part of a suite of tools that analyze the local aerothermodynamic environment to enable informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each d agmea site or repair, the expected time (and thus Mach number) of transition onset is predicted to help define proper environments for use in subsequent thermal and stress analysis of the thermal protection system and structure. The boundary layer transition criteria utilized within the tool were updated based on new local boundary layer properties obtained from high fidelity computational solutions. Also, new ground-based measurements were obtained to allow for a wider parametric variation with both protuberances and cavities and then the resulting correlations were calibrated against updated flight data. The end result is to provide correlations that allow increased confidence with the resulting transition predictions. Recently, a new approach was adopted to remove conservatism in terms of sustained turbulence along the wing leading edge. Finally, some of the newer flight data are also discussed in terms of how these results reflect back on the updated correlations.
Separation behavior of boundary layers on three-dimensional wings
NASA Technical Reports Server (NTRS)
Stock, H. W.
1981-01-01
An inverse boundary layer procedure for calculating separated, turbulent boundary layers at infinitely long, crabbing wing was developed. The procedure was developed for calculating three dimensional, incompressible turbulent boundary layers was expanded to adiabatic, compressible flows. Example calculations with transsonic wings were made including viscose effects. In this case an approximated calculation method described for areas of separated, turbulent boundary layers, permitting calculation of this displacement thickness. The laminar boundary layer development was calculated with inclined ellipsoids.
Numerical methods for hypersonic boundary layer stability
NASA Technical Reports Server (NTRS)
Malik, M. R.
1990-01-01
Four different schemes for solving compressible boundary layer stability equations are developed and compared, considering both the temporal and spatial stability for a global eigenvalue spectrum and a local eigenvalue search. The discretizations considered encompass: (1) a second-order-staggered finite-difference scheme; (2) a fourth-order accurate, two-point compact scheme; (3) a single-domain Chebychev spectral collocation scheme; and (4) a multidomain spectral collocation scheme. As Mach number increases, the performance of the single-domain collocation scheme deteriorates due to the outward movement of the critical layer; a multidomain spectral method is accordingly designed to furnish superior resolution of the critical layer.
Active Flow Control on a Boundary-Layer-Ingesting Inlet
NASA Technical Reports Server (NTRS)
Gorton, Susan Althoff; Owens, Lewis R.; Jenkins, Luther N.; Allan, Brian G.; Schuster, Ernest P.
2004-01-01
Boundary layer ingestion (BLI) is explored as means to improve overall system performance for Blended Wing Body configuration. The benefits of BLI for vehicle system performance benefit are assessed with a process derived from first principles suitable for highly-integrated propulsion systems. This performance evaluation process provides framework within which to assess the benefits of an integrated BLI inlet and lays the groundwork for higher-fidelity systems studies. The results of the system study show that BLI provides a significant improvement in vehicle performance if the inlet distortion can be controlled, thus encouraging the pursuit of active flow control (AFC) as a BLI enabling technology. The effectiveness of active flow control in reducing engine inlet distortion was assessed using a 6% scale model of a 30% BLI offset, diffusing inlet. The experiment was conducted in the NASA Langley Basic Aerodynamics Research Tunnel with a model inlet designed specifically for this type of testing. High mass flow pulsing actuators provided the active flow control. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion was determined by 120 total pressure measurements located at the aerodynamic interface plane. The test matrix was limited to a maximum freestream Mach number of 0.15 with scaled mass flows through the inlet for that condition. The data show that the pulsed actuation can reduce distortion from 29% to 4.6% as measured by the circumferential distortion descriptor DC60 using less than 1% of inlet mass flow. Closed loop control of the actuation was also demonstrated using a sidewall surface static pressure as the response sensor.
Wing flutter boundary prediction using unsteady Euler aerodynamic method
NASA Technical Reports Server (NTRS)
Lee-Rausch, Elizabeth M.; Batina, John T.
1993-01-01
Modifications to an existing 3D implicit upwind Euler/Navier-Stokes code for the aeroelastic analysis of wings are described. These modifications include the incorporation of a deforming mesh algorithm and the addition of the structural equations of motion for their simultaneous time-integration with the governing flow equations. The paper gives a brief description of these modifications and presents unsteady calculations which check the modifications to the code. Euler flutter results for an isolated 45 deg swept-back wing are compared with experimental data for seven freestream Mach numbers which define the flutter boundary over a range of Mach number from 0.499 to 1.14. These comparisons show good agreement in flutter characteristics for freestream Mach numbers below unity. For freestream Mach numbers above unity, the computed aeroelastic results predict a premature rise in the flutter boundary as compared with the experimental boundary. Steady and unsteady contours of surface Mach number and pressure are included to illustrate the basic flow characteristics of the time-marching flutter calculations and to aid in identifying possible causes for the premature rise in the computational flutter boundary.
Wing flutter boundary prediction using an unsteady Euler aerodynamic method
NASA Technical Reports Server (NTRS)
Lee-Rausch, Elizabeth M.; Batina, John T.
1993-01-01
Modifications to an existing three-dimensional, implicit, upwind Euler/Navier-Stokes code (CFL3D Version 2.1) for the aeroelastic analysis of wings are described. These modifications, which were previously added to CFL3D Version 1.0, include the incorporation of a deforming mesh algorithm and the addition of the structural equations of motion for their simultaneous time-integration with the government flow equations. The paper gives a brief description of these modifications and presents unsteady calculations which check the modifications to the code. Euler flutter results for an isolated 45 degree swept-back wing are compared with experimental data for seven freestream Mach numbers which define the flutter boundary over a range of Mach number from 0.499 to 1.14. These comparisons show good agreement in flutter characteristics for freestream Mach numbers below unity. For freestream Mach numbers above unity, the computed aeroelastic results predict a premature rise in the flutter boundary as compared with the experimental boundary. Steady and unsteady contours of surface Mach number and pressure are included to illustrate the basic flow characteristics of the time-marching flutter calculations and to aid in identifying possible causes for the premature rise in the computational flutter boundary.
INDIVIDUAL TURBULENT CELL INTERACTION: BASIS FOR BOUNDARY LAYER ESTABLISHMENT
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...
Thermal instability of forced convection boundary layers
NASA Astrophysics Data System (ADS)
Chen, K.; Chen, M. M.
1981-11-01
The thermal instability of forced convection boundary layers with non-zero streamwise pressure gradient is examined. An analysis is carried out for the family of Falkner-Skan flows, and only the streamwise buoyancy generated instability for fluid layers with shear at low Reynolds number are considered. When the wedge angle is equal to one, the perturbation equations based on the boundary layer equations are identical to the exact perturbation equations for the stagnation flow. Calculated critical Rayleigh numbers and wave numbers are found to be independent of wedge angle in the limiting case of infinite Prandtl number, and results are compared with previous experimental results by Gilpin et al. (1978), showing good agreement.
Bursting frequency prediction in turbulent boundary layers
LIOU,WILLIAM W.; FANG,YICHUNG
2000-02-01
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.
Flowfield Measurements Inside a Boundary-Layer Bleed Slot
NASA Technical Reports Server (NTRS)
Davis, D. O.; Willis, B. P.; Hingst, W. R.
1996-01-01
An experimental investigation was conducted to determine the flowfield inside a bleed slot used to control an oblique shock-wave and turbulent boundary-layer interaction. The slot was oriented normal to the primary flow direction and had a width of 1.0 cm (primary flow direction) and a length of 2.54 cm and spanned 16.5 cm. The approach boundary layer upstream of the interaction was nominally 3.0 cm thick. Two operating conditions were studied: M = 1.98 with a shock generator deflection angle of 6 deg and M = 2.46 with a shock generator deflection angle of 8 deg. Measurements include surface and flowfield static pressure, pitot pressure, and total mass flow through the slot. The results show that despite an initially two-dimensional interaction for the zero-bleed-flow case, the slot does not remove mass uniformly in the spanwise direction. Inside the slot, the flow is characterized bv two separation regions, which significantly reduce the effective flow area. The upper separation region acts as an aerodynamic throat, resulting in supersonic flow through much of the slot.
Characterization of structural response to hypersonic boundary-layer transition
Riley, Zachary B.; Deshmukh, Rohit; Miller, Brent A.; ...
2016-05-24
The inherent relationship between boundary-layer stability, aerodynamic heating, and surface conditions makes the potential for interaction between the structural response and boundary-layer transition an important and challenging area of study in high-speed flows. This paper phenomenologically explores this interaction using a fundamental two-dimensional aerothermoelastic model under the assumption of an aluminum panel with simple supports. Specifically, an existing model is extended to examine the impact of transition onset location, transition length, and transitional overshoot in heat flux and fluctuating pressure on the structural response of surface panels. Transitional flow conditions are found to yield significantly increased thermal gradients, and theymore » can result in higher maximum panel temperatures compared to turbulent flow. Results indicate that overshoot in heat flux and fluctuating pressure reduces the flutter onset time and increases the strain energy accumulated in the panel. Furthermore, overshoot occurring near the midchord can yield average temperatures and peak displacements exceeding those experienced by the panel subject to turbulent flow. Lastly, these results suggest that fully turbulent flow does not always conservatively predict the thermo-structural response of surface panels.« less
Characterization of structural response to hypersonic boundary-layer transition
Riley, Zachary B.; Deshmukh, Rohit; Miller, Brent A.; McNamara, Jack J.; Casper, Katya M.
2016-05-24
The inherent relationship between boundary-layer stability, aerodynamic heating, and surface conditions makes the potential for interaction between the structural response and boundary-layer transition an important and challenging area of study in high-speed flows. This paper phenomenologically explores this interaction using a fundamental two-dimensional aerothermoelastic model under the assumption of an aluminum panel with simple supports. Specifically, an existing model is extended to examine the impact of transition onset location, transition length, and transitional overshoot in heat flux and fluctuating pressure on the structural response of surface panels. Transitional flow conditions are found to yield significantly increased thermal gradients, and they can result in higher maximum panel temperatures compared to turbulent flow. Results indicate that overshoot in heat flux and fluctuating pressure reduces the flutter onset time and increases the strain energy accumulated in the panel. Furthermore, overshoot occurring near the midchord can yield average temperatures and peak displacements exceeding those experienced by the panel subject to turbulent flow. Lastly, these results suggest that fully turbulent flow does not always conservatively predict the thermo-structural response of surface panels.
The Effect of Nonlinear Critical Layers on Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Goldstein, Marvin E.
1995-01-01
Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear and spatially growing instability waves evolve downstream in nominally two-dimensional and spanwise periodic 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 an appropriate superposition of linear instability waves. The amplitudes of these waves are determined by either a single integro-differential equation or by a pair of integro-differential equations with quadratic to quartic-type nonlinearities.
Characteristics of Boundary Layer Transition in a Multi-Stage Low-Pressure Turbine
NASA Technical Reports Server (NTRS)
Wisler, Dave; Halstead, David E.; Okiishi, Ted
2007-01-01
An experimental investigation of boundary layer transition in a multi-stage turbine has been completed using surface-mounted hot-film sensors. Tests were carried out using the two-stage Low Speed Research Turbine of the Aerodynamics Research Laboratory of GE Aircraft Engines. Blading in this facility models current, state-of-the-art low pressure turbine configurations. The instrumentation technique involved arrays of densely-packed hot-film sensors on the surfaces of second stage rotor and nozzle blades. The arrays were located at mid-span on both the suction and pressure surfaces. Boundary layer measurements were acquired over a complete range of relevant Reynolds numbers. Data acquisition capabilities provided means for detailed data interrogation in both time and frequency domains. Data indicate that significant regions of laminar and transitional boundary layer flow exist on the rotor and nozzle suction surfaces. Evidence of relaminarization both near the leading edge of the suction surface and along much of the pressure surface was observed. Measurements also reveal the nature of the turbulent bursts occuring within and between the wake segments convecting through the blade row. The complex character of boundary layer transition resulting from flow unsteadiness due to nozzle/nozzle, rotor/nozzle, and nozzle/rotor wake interactions are elucidated using these data. These measurements underscore the need to provide turbomachinery designers with models of boundary layer transition to facilitate accurate prediction of aerodynamic loss and heat transfer.
HIFiRE-5 Boundary Layer Transition and HIFiRE-1 Shock Boundary Layer Interaction
2015-10-01
For this work, new capabilities in ground test and in flight data analysis were developed. Also, as a necessary precursor to wind tunnel tests on...necessary precursor to wind tunnel tests on boundary layer transition on the leeside of a cone at angle of attack, extensive computations were undertaken...analysis of the HIFiRE-1 shock boundary layer interaction experiment was completed. Tests at the Purdue University Mach 6 quiet wind tunnel demonstrated a
The interaction of synthetic jets with turbulent boundary layers
NASA Astrophysics Data System (ADS)
Cui, Jing
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
Influence of Mach Number and Incoming Boundary Layer on Shock Boundary Layer Interaction
NASA Astrophysics Data System (ADS)
Stab, Ilona; Threadgill, James; Little, Jesse
2016-11-01
Wall pressure fluctuations, schlieren imaging, oil flow visualization and PIV measurements have been performed on the shock boundary layer interaction (SBLI) formed by a 10° compression ramp. The incoming Mach number and boundary layer characteristics are varied to examine their influence on the SBLI. Focus is placed on understanding the effect of these parameters on the structure and unsteadiness of the resultant interaction. Lower Mach numbers M = 2 . 3 (δ0 = 1 . 7 mm , θ = 0 . 29 mm , Reθ = 3115 , H = 1 . 4) and M = 3 (δ0 = 1 . 3 mm , θ = 0 . 25 mm , Reθ = 1800 , H = 1 . 8) show a turbulent or transitional approach boundary layer with no apparent separation at the ramp. Mach 4 has a large separated region which is seemingly a result of a now laminar or transitional approach boundary layer. Pulsations in the separated region correspond to the expected low frequency SBLI dynamics showing a broad peak around a Strouhal number of St = fLint /U∞ = 0 . 27 which is lower than the characteristic frequency of the turbulent boundary layer. Additional results examining the influence of boundary layer modifications (e.g. sweep) and wind tunnel side-walls are also included. Supported by Raytheon Missile Systems.
Boundary layer transition detection by luminescence imaging
NASA Technical Reports Server (NTRS)
Mclachlan, B. G.; Bell, J. H.; Gallery, J.; Gouterman, M.; Callis, J.
1993-01-01
In recent experiments we have demonstrated the feasibility of a new approach to boundary layer transition detection. This new approach employs the temperature dependence of certain photoluminescent materials in the form of a surface coating or 'paint' to detect the change in heat transfer characteristics that accompany boundary layer transition. The feasibility experiments were conducted for low subsonic to transonic Mach numbers on two-dimensional airfoil and flat plate configurations. Paint derived transition locations were determined and compared to those obtained from Preston pressure probe measurements. Artificial heating of the models was used to obtain transition temperature signatures suitable for the instrumentation available to us. Initial estimates show, however, that passive kinetic heating at high Mach numbers is a promising alternative.
Analytic prediction for planar turbulent boundary layers
NASA Astrophysics Data System (ADS)
Chen, Xi; She, Zhen-Su
2016-11-01
Analytic predictions of mean velocity profile (MVP) and streamwise ( x) development of related integral quantities are presented for flows in channel and turbulent boundary layer (TBL), based on a symmetry analysis of eddy length and total stress. Specific predictions include the relations for momentum Reynolds number ( Re θ) with friction Re τ and streamwise Re x : Re θ ≈ 3.27 Re τ, and Re x / Re θ = 4.94 [(ln Re θ + 1.88)2 + 1]; the streamwise development of the friction velocity u τ: U e / u τ ≈ 2.22ln Re x + 2.86 - 3.83ln(ln Re x ), and of the boundary layer thickness δ e : x/δ e ≈ 7.27ln Re x -5.18-12.52ln(ln Re x ), which are fully validated by recent reliable data.
Analytic prediction for planar turbulent boundary layers
NASA Astrophysics Data System (ADS)
She, Zhen-Su; Chen, Xi
2016-11-01
Analytic predictions of mean velocity profile (MVP) and streamwise (x) development of related integral quantities are presented for flows in channel and turbulent boundary layer (TBL), based on a symmetry analysis of eddy length and total stress. Specific predictions include the relations for momentum Reynolds number (Reθ) with friction Reτ and streamwise Rex : Reθ 3 . 27 Reτ and Rex / Reθ = 4 . 94 [(lnReθ + 1 . 88) 2 + 1 ] ; the streamwise development of the friction velocityuτ: Ue /uτ 2 . 22 lnRex + 2 . 86 - 3 . 83 ln (lnRex) , and of the boundary layer thickness δe: x /δe 7 . 27 lnRex - 5 . 18 - 12 . 52 ln (lnRex) , which are fully validated by recent reliable data.
Turbulent shear stresses in compressible boundary layers
NASA Technical Reports Server (NTRS)
Laderman, A. J.; Demetriades, A.
1979-01-01
Hot-wire anemometer measurements of turbulent shear stresses in a Mach 3 compressible boundary layer were performed in order to investigate the effects of heat transfer on turbulence. Measurements were obtained by an x-probe in a flat plate, zero pressure gradient, two dimensional boundary layer in a wind tunnel with wall to freestream temperature ratios of 0.94 and 0.71. The measured shear stress distributions are found to be in good agreement with previous results, supporting the contention that the shear stress distribution is essentially independent of Mach number and heat transfer for Mach numbers from incompressible to hypersonic and wall to freestream temperature ratios of 0.4 to 1.0. It is also found that corrections for frequency response limitations of the electronic equipment are necessary to determine the correct shear stress distribution, particularly at the walls.
BOREAS AFM-6 Boundary Layer Height Data
NASA Technical Reports Server (NTRS)
Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)
2000-01-01
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).
Turbulent boundary layer over flexible plates
NASA Astrophysics Data System (ADS)
Rostami, Parand; Ioppolo, Tindaro
2016-11-01
This research describes the structure of a turbulent boundary layer flow with a zero pressure gradient over elastic plates. The elastic plates made of a thin aluminum sheets with thickness between 50 and 500 microns were placed on the floor of a subsonic wind tunnel and exposed to a turbulent boundary layer flow with a free stream velocity between 20m/s and 100m/s. The ceiling of the test section of the wind tunnel is adjustable so that a nearly zero pressure gradient is obtained in the test section. Hot-wire anemometry was used to measure the velocity components. Mean, fluctuating velocities and Reynolds stresses will be presented and compared with the values of a rigid plate.
Boundary Layer Control for Hypersonic Airbreathing Vehicles
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Nowak, Robert J.; Horvath, Thomas J.
2004-01-01
Active and passive methods for tripping hypersonic boundary layers have been examined in NASA Langley Research Center wind tunnels using a Hyper-X model. This investigation assessed several concepts for forcing transition, including passive discrete roughness elements and active mass addition (or blowing), in the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air Tunnels. Heat transfer distributions obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the Hyper-X nominal Mach 7 flight test-point of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For passive roughness, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The passive roughness study resulted in a swept ramp configuration, scaled to be roughly 0.6 of the calculated boundary layer thickness, being selected for the Mach 7 flight vehicle. For the active blowing study, the manifold pressure was systematically varied (while monitoring the mass flow) for each configuration to determine the jet penetration height, with schlieren, and transition movement, with the phosphor system, for comparison to the passive results. All the blowing concepts tested, which included various rows of sonic orifices (holes), two- and three-dimensional slots, and random porosity, provided transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model surface static pressure, which is adequate to ensure sonic jets. The present results indicate that the jet penetration height for blowing was roughly half the height required with passive roughness elements for an equivalent amount of transition movement.
Boundary Layer Transition Results From STS-114
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J.; Cassady, Amy M.; Kirk, Benjamin S.; Wang, K. C.; Hyatt, Andrew J.
2006-01-01
The tool for predicting the onset of boundary layer transition from damage to and/or repair of the thermal protection system developed in support of Shuttle Return to Flight is compared to the STS-114 flight results. The Boundary Layer Transition (BLT) Tool is part of a suite of tools that analyze the aerothermodynamic environment of the local thermal protection system to allow informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each damage site or repair, the expected time of transition onset is predicted to help determine the proper aerothermodynamic environment to use in the subsequent thermal and stress analysis of the local structure. The boundary layer transition criteria utilized for the tool was developed from ground-based measurements to account for the effect of both protuberances and cavities and has been calibrated against flight data. Computed local boundary layer edge conditions provided the means to correlate the experimental results and then to extrapolate to flight. During STS-114, the BLT Tool was utilized and was part of the decision making process to perform an extravehicular activity to remove the large gap fillers. The role of the BLT Tool during this mission, along with the supporting information that was acquired for the on-orbit analysis, is reviewed. Once the large gap fillers were removed, all remaining damage sites were cleared for reentry as is. Post-flight analysis of the transition onset time revealed excellent agreement with BLT Tool predictions.
Off-Body Boundary-Layer Measurement Techniques Development for Supersonic Low-Disturbance Flows
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Kegerise, Michael A.; Wilkinson, Stephen P.
2011-01-01
Investigations were performed to develop accurate boundary-layer measurement techniques in a Mach 3.5 laminar boundary layer on a 7 half-angle cone at 0 angle of attack. A discussion of the measurement challenges is presented as well as how each was addressed. A computational study was performed to minimize the probe aerodynamic interference effects resulting in improved pitot and hot-wire probe designs. Probe calibration and positioning processes were also developed with the goal of reducing the measurement uncertainties from 10% levels to less than 5% levels. Efforts were made to define the experimental boundary conditions for the cone flow so comparisons could be made with a set of companion computational simulations. The development status of the mean and dynamic boundary-layer flow measurements for a nominally sharp cone in a low-disturbance supersonic flow is presented.
Entropy production in relativistic jet boundary layers
NASA Astrophysics Data System (ADS)
Kohler, Susanna; Begelman, Mitchell C.
2015-01-01
Hot relativistic jets, passing through a background medium with a pressure gradient p ∝ r-η where 2 < η ≤ 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 η = 8/3. Here, we demonstrate that models with η < 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.
The role of nonlinear critical layers in boundary layer transition
NASA Technical Reports Server (NTRS)
Goldstein, M.E.
1995-01-01
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.
Roughness Characterization of and Turbulent Boundary Layer Flow over flat Snow Surfaces
NASA Astrophysics Data System (ADS)
Gromke, C.; Guala, M.; Manes, C.; Walter, B.; Lehning, M.
2009-12-01
The surface roughness is essential for all turbulent exchange processes within the lower part of the atmospheric boundary layer. Consequently, a proper representation of the surfaces roughness is needed in every mathematical description of near surface mass-, energy- and momentum exchange processes. Considering the vertical mean velocity profile of turbulent boundary layer flow, this is done by assigning an aerodynamic roughness length z0 to the surface. We followed two procedures to describe the roughness of freshly fallen snow surfaces. First, photographs of snow surfaces have been taken and evaluated using digital image analysis giving snow surface contour line coordinates. Applying structure functions to the snow surface coordinates and statistical fitting procedures, resulted in classes of surface characteristic length scales and scaling exponents. These results allow to identify the deposition process of snow fall as scaling exponents corresponded to that of Ballistic Deposition. Moreover, the resulting characteristic length scales can be assigned to typical particle size and aggregation size length scales consistent with results found by Lowe et al. (2007) and Manes et al. (2008). Second, aerodynamic roughness lengths z0 have been estimated from log-law fitting of velocity profiles over the snow surfaces measured in the SLF cold atmospheric boundary layer wind tunnel. The aerodynamic roughness lengths found are in general agreement with available literature data and suggest the presence of aerodynamically rough regimes with flow independent z0. In the synthesis of both approaches, we found evidence for a linear relationship between one class of surface characteristic length scales, which is associated with typical snow particle sizes, and aerodynamic roughness lengths z0. The correlation with the aggregation length scale is weaker for the few (4) samples analyzed thus far. The relatively weak pronounced scale separation between particle and aggregation size
The Lowest Atmosphere: Atmospheric Boundary Layer Including Atmospheric Surface Layer.
1996-04-01
troposphere" as a result of frictional forces. A good definition of the atmospheric boundary layer (ABL) (provided to me by the late Dr. Rudy...wind extends light flag. Raises dust and loose paper; small branches are moved. Small trees in leaf begin to sway; crested wavelets form on inland...Calm. Sea like a mirror. Light air Ripples like scales, no foam crest. Light breeze Small wavelets ; crests have glassy appearance, do not break
Parameterization of continental boundary layer clouds
NASA Astrophysics Data System (ADS)
Zhu, Ping; Zhao, Wei
2008-05-01
Large eddy simulations (LESs) of continental boundary layer clouds (BLCs) observed at the southern Great Plains (SGP) are used to study issues associated with the parameterization of sub-grid BLCs in large scale models. It is found that liquid water potential temperature θl and total specific humidity qt, which are often used as parameterization predictors in statistical cloud schemes, do not share the same probability distribution in the cloud layer with θl skewed to the left (negatively skewed) and qt skewed to the right (positively skewed). The skewness and kurtosis change substantially in time and space when the development of continental BLCs undergoes a distinct diurnal variation. The wide range of skewness and kurtosis of θl and qt can hardly be described by a single probability distribution function. To extend the application of the statistical cloud parameterization approach, this paper proposes an innovative cloud parameterization scheme that uses the boundary layer height and the lifting condensation level as the primary parameterization predictors. The LES results indicate that the probability distribution of these two quantities is relatively stable compared with that of θl and qt during the diurnal variation and nearly follows a Gaussian function. Verifications using LES output and the observations collected at the Atmospheric Radiation Measurement (ARM) Climate Research Facility (ARCF) SGP site indicate that the proposed scheme works well to represent continental BLCs.
Aerosol fluxes in the marine boundary layer
NASA Astrophysics Data System (ADS)
Petelski, Tomasz; Zieliński, Tymon; Makuch, Przemysław; Kowalczyk, Jakub; Ponczkowska, Agnieszka; Drozdowska, Violetta; Piskozub, Jacek
2010-05-01
We present aerosol emission fluxes and concentrations calculated from in-situ measurement in the Nordic Sea from R/V Oceania. We compare vertical fluxes calculated with the eddy correlation and gradient methods. We use the results to test the hypothesis that marine aerosol emitted from the sea surface helps to clear the boundary layer from other aerosol particles. As the emitted droplets do not dry out in the highly humid surface layer air and because of their sizes most of them are deposited quickly at the sea surface. Therefore marine aerosol has many features of rain meaning that the deposition in the marine boundary layer in high wind events is controlled not only by the "dry" processes but also by the "wet" scavenging. We have estimated the effectiveness of the process using our own measurements of vertical aerosol fluxes in the Nordic Seas. This process could explain observed phenomenon of lower Arctic aerosol optical thickness (AOT) when the air masses moved over open sea than over sea-ice. We show a negative correlation between the sea-ice coverage in the seas adjacent to Svalbard and monthly AOT values in Ny Alesund.
Acoustic radar investigations of boundary layer phenomena
NASA Technical Reports Server (NTRS)
Marks, J. R.
1974-01-01
A comparison is made between acoustic radar echoes and conventional meteorological data obtained from the WKY tower, for the purpose of better understanding the relationships between acoustic radar echoes and boundary layer processes. Two thunderstorm outflow cases are presented and compared to both acoustic radar data and Charba's gust front model. The acoustic radar echoes reveal the boundary between warm and cold air and other areas of mixing and strong thermal gradient quite well. The thunderstorm outflow of 27 June 1972 is found to compare with in most respects to Charba's gust front model. The major difference is the complete separation of the head from the main body of cold air, probably caused by erosion of the area behind the head by mixing with the ambient air. Two cases of nocturnal inversions caused by advection of warmer air aloft are presented. It is found that areas of turbulent mixing or strong thermal gradient can be identified quite easily in the acoustic radar record.
Flow Quality and Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Watmuff, Jonathan H; Tobak, M.; Davis, Sanford S. (Technical Monitor)
1997-01-01
The widely held view is that transition to turbulence in the Blasius boundary layer occurs via amplification and eventual nonlinear breakdown of initially small amplitude instabilities i.e. Tollmien-Schlichting (TS) waves. However this scenario is only observed for low amplitude free-stream turbulence levels, i.e. u/U < 0.1%. Bypass of linear TS instability mechanism occurs for higher EST levels, yet considerable differences exist between the few experiments carefully designed to assess the effect of EST on transition. The consensus is that EST leads to longitudinal streaks that form near the leading edge in the boundary layer . These streaks appeal to be regions of concentrated streamwise vorticity and they are often referred to as Klebanoff modes. The importance of mean flow free-stream nonuniformity (FSN) is not as widely appreciated as EST for characterizing wind tunnel flow quality. Here it is shown that, although the v like generated by a d=50micron wire located upstream of the contraction (Re(sub d)=6.6, x/d=45,000) is immeasurably small by the time it interacts with the leading edge in the test section, it is responsible for generation of a pair of weak streamwise vortices in the boundary layer downstream. The characteristics of these wake-induced vortices and their effect on TS waves are demonstrated. Small remnant FSN variations are also shown to exist downstream of a turbulence grid. The question arises Are the adverse effects introduced by the turbulence grid caused by FST or by small remnant FSN variations?
NASA Astrophysics Data System (ADS)
Im, Seongkyun; di Cristina, Giovanni; Do, Hyungrok
2016-11-01
Boundary layer separations induced by shockwave boundary layer interaction at various contraction ratios were investigated at a Mach 4.5 flow. Stagnation pressure and temperature condition of 10 bars and 295 K were used, and a high-speed schlieren system visualized the flow features. A shockwave generator with 12 degree wedge generated an impinging shockwave onto a laminar boundary layer on a flat plate. The contraction ratio of the flow was varied by changing the distance between the shockwave generator and the flat plate. The location of the shockwave impingement was fixed while the contraction ratios were changed. Flow visualization showed that the flow separation and its size were influenced by the contraction ratio although overall flow features were similar. At higher contraction ratio, stronger impinging shockwave and more severe flow separation were observed.
Heterogeneous Vapor Condensation in Boundary Layers
Bonilla, L. L.; Carpio, A.; Neu, J. C.
2008-09-01
We consider heterogeneous condensation of vapors mixed with a carrier gas in stagnation point boundary layer flow near a cold wall in the presence of solid particles much larger than the mean free path of vapor particles. The supersaturated vapor condenses on the particles by diffusion, particles and droplets are thermophoretically attracted to the wall. We sketch three asymptotic theories of the condensation process, calculate the flow-induced shift in the dew point interface, vapor density profile and deposition rates at the wall, and compare them to direct numerical simulation.
NASA Technical Reports Server (NTRS)
Lee, Jong-Hun
1993-01-01
The basic governing equations for the second-order three-dimensional hypersonic thermal and chemical nonequilibrium boundary layer are derived by means of an order-of-magnitude analysis. A two-temperature concept is implemented into the system of boundary-layer equations by simplifying the rather complicated general three-temperature thermal gas model. The equations are written in a surface-oriented non-orthogonal curvilinear coordinate system, where two curvilinear coordinates are non-orthogonial and a third coordinate is normal to the surface. The equations are described with minimum use of tensor expressions arising from the coordinate transformation, to avoid unnecessary confusion for readers. The set of equations obtained will be suitable for the development of a three-dimensional nonequilibrium boundary-layer code. Such a code could be used to determine economically the aerodynamic/aerothermodynamic loads to the surfaces of hypersonic vehicles with general configurations. In addition, the basic equations for three-dimensional stagnation flow, of which solution is required as an initial value for space-marching integration of the boundary-layer equations, are given along with the boundary conditions, the boundary-layer parameters, and the inner-outer layer matching procedure. Expressions for the chemical reaction rates and the thermodynamic and transport properties in the thermal nonequilibrium environment are explicitly given.
Sound radiation due to boundary layer transition
NASA Technical Reports Server (NTRS)
Wang, Meng
1993-01-01
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.
Aero-Optical Turbulent Boundary Layer/Shear Layer Experiment On The KC-135 Aircraft Revisited
NASA Astrophysics Data System (ADS)
Craig, James E.; Allen, C.
1985-06-01
This paper examines the aero-optical effects associated with propagating a laser beam through both an aircraft turbulent boundary layer and artificially generated shear layers. The data present comparisons of observed optical performances with those inferred from aerodynamic measurements of unsteady density and correlation lengths within the same random flow fields. Using optical instrumentation with tens of microseconds temporal resolution through a finite aperture, optical performance degradation was determined and contrasted with the infinite-aperture, time-averaged aerodynamic measurement. In addition, the optical data were artificially clipped to compare to theoretical scaling calculations. Optical instrumentation consisted of a custom Q-switched Nd:YAG double-pulsed laser and a holographic camera that recorded the random flow field in a double-pass, double-pulse mode. Aero-dynamic parameters were measured using hot film anemometer probes and a five-hole pressure probe. Each technique is described with its associated theo-retical basis for comparison. The effects of finite aperture and spatial and temporal frequencies of the random flow are considered. The results presented represent five flights flown at altitudes from 1.8 km to 10.7 km and at Mach numbers from 0.32 to 0.79. Single-pass phase deviations for the boundary layer were from 0.06 to 0.17 waves (at X = 0.53 ;Am) with piston and tilt components removed. Measured phase deviations for the artificially induced shear flows were from 0.10 to 0.279 waves (at X = 0.53 /um) with piston and tilt components removed. However, when low order aberrations through coma were removed, the remaining deviations were only 0.09 to 0.18 waves. This resulted in a 33 to 250% increase in the Strehl ratio at the 14 cm optical aperture. It was further shown that the low order aberrations corresponded to the longer wavelengths in the random flow, and these waves propagated with a longer characteristic time than the higher order
NASA Astrophysics Data System (ADS)
Schobeiri, M. T.; Pappu, K.
The results from an experimental investigation of unsteady boundary layer behavior on a linear turbine cascade are presented in this paper. To perform a detailed study on unsteady cascade aerodynamics and heat transfer, a new large-scale, high-subsonic research facility for simulating the periodic unsteady flow has been developed. It is capable of sequentially generating up to four different unsteady inlet flow conditions that lead to four different passing frequencies, wake structures, and freestream turbulence intensities. For a given Reynolds number, two different unsteady wake formations are utilized. Detailed unsteady boundary layer velocity. turbulence intensity, and pressure measurements are performed along the suction and pressure surfaces of one blade. The results display the transition and development of the boundary layer, ensemble-averaged velocity, and turbulence intensity.
NASA Technical Reports Server (NTRS)
Ball, J. W.; Lindahl, R. H.
1976-01-01
The purpose of the test was to investigate the nature of the Orbiter boundary layer characteristics at angles of attack from -4 to 32 degrees at a Mach number of 4.6. The effect of large grit, employed as transition strips, on both the nature of the boundary layer and the force and moment characteristics were investigated along with the effects of large negative elevon deflection on lee side separation. In addition, laminar and turbulent boundary layer separation phenomena which could cause asymmetric flow separation were investigated.
Sound Radiation from a Turbulent Boundary Layer
NASA Technical Reports Server (NTRS)
Laufer, J.
1961-01-01
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.
X-33 Hypersonic Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J.; Hollis, Brian R.; Thompson, Richard A.; Hamilton, H. Harris, II
1999-01-01
Boundary layer and aeroheating characteristics of several X-33 configurations have been experimentally examined in the Langley 20-Inch Mach 6 Air Tunnel. Global surface heat transfer distributions, surface streamline patterns, and shock shapes were measured on 0.013-scale models at Mach 6 in air. Parametric variations include angles-of-attack of 20-deg, 30-deg, and 40-deg; Reynolds numbers based on model length of 0.9 to 6.6 million; and body-flap deflections of 0, 10 and 20-deg. The effects of discrete and distributed roughness elements on boundary layer transition, which included trip height, size, location, and distribution, both on and off the windward centerline, were investigated. The discrete roughness results on centerline were used to provide a transition correlation for the X-33 flight vehicle that was applicable across the range of reentry angles of attack. The attachment line discrete roughness results were shown to be consistent with the centerline results, as no increased sensitivity to roughness along the attachment line was identified. The effect of bowed panels was qualitatively shown to be less effective than the discrete trips; however, the distributed nature of the bowed panels affected a larger percent of the aft-body windward surface than a single discrete trip.
Optimal Growth in Hypersonic Boundary Layers
NASA Technical Reports Server (NTRS)
Paredes, Pedro; Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan
2016-01-01
The linear form of the parabolized linear stability equations is used in a variational approach to extend the previous body of results for the optimal, nonmodal disturbance growth in boundary-layer flows. This paper investigates the optimal growth characteristics in the hypersonic Mach number regime without any high-enthalpy effects. The influence of wall cooling is studied, with particular emphasis on the role of the initial disturbance location and the value of the spanwise wave number that leads to the maximum energy growth up to a specified location. Unlike previous predictions that used a basic state obtained from a self-similar solution to the boundary-layer equations, mean flow solutions based on the full Navier-Stokes equations are used in select cases to help account for the viscous- inviscid interaction near the leading edge of the plate and for the weak shock wave emanating from that region. Using the full Navier-Stokes mean flow is shown to result in further reduction with Mach number in the magnitude of optimal growth relative to the predictions based on the self-similar approximation to the base flow.
Helical mode breakdown in transitional boundary layers
NASA Astrophysics Data System (ADS)
Bose, Rikhi; Durbin, Paul
2016-11-01
Results of direct numerical simulation of transition to turbulence in adverse pressure gradient boundary layers beneath free-stream turbulence will be presented. Instability waves are excited spontaneously and may be identified when intensity of free-stream turbulence (Tu) is sufficiently low. At very low Tu 0 . 1 % , secondary instability of the TS waves and at high Tu > 2 % , conventional bypass mechanisms trigger turbulent spot formation. At low Tu 1 % transition proceeds through formation of helical modes. Helical structures as in n = 1 instability modes of axisymmetric wakes and jets are clearly identifiable in visualizations of isosurfaces of stream-wise perturbation velocity. Helical modes also trigger transition at same level of Tu in zero pressure gradient boundary layers as well, provided that the inlet disturbances include a low amplitude time-periodic unstable TS wave. This indicates that these secondary instability modes might arise due to interaction of Klebanoff streaks and instability waves. Characteristically, the helical modes are inner instability modes. This work was supported by NSF Grant CBET-1228195. Computer time was provided by the Extreme Science and Engineering Discovery Environment (XSEDE).
Soot profiles in boundary-layer flames
Beier, R.A.; Pagni, P.J.
1981-12-01
Carbon particulate volume fractions and approximate particle size distributions are measured in a free laminar combusting boundary layer for liquid hydrocarbon fuels (n-heptane, iso-octane, cyclohexane, cyclohexene, toluene) and polymethylmethacrylate (PMMA). A multiwavelength laser transmission technique determines a most probable radius and the total particle concentration, which are two parameters in an assumed form for the size distribution. In the combusting boundary layer, a sooting region exists between the pyrolyzing fuel surface and the flame zone. The liquid fuel soot volume fractions, f/sub v/, range from f/sub v/ approx. 10/sup -7/ for n-heptane, a paraffin, to f/sub v approx. 10/sup -5/ for toluene, an aromatic. The PMMA volume fractions, f/sub v/ approx. 5 X 10/sup -7/, are approximately the same as the values previously reported for pool fires. The soot volume fractions increase with height; convection of carbon particles downstream widens the soot region with height. For all fuels tested, the most probable radius is between 20 nm and 50 nm, and it changes only slightly with height and distance from the fuel surface.
Boundary Layer Transition Flight Experiment Overview
NASA Technical Reports Server (NTRS)
Berger, Karen T.; Anderson, Brian P.; Campbell, Charles H.; Garske, Michael T.; Saucedo, Luis A.; Kinder, Gerald R.; Micklos, Ann M.
2011-01-01
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.
Aerodynamic Applications of Boundary Layer Control Using Embedded Streamwise Vortices
2003-07-01
presents results of calculated diameters dd of droplets depending on the correlation between the consumption of gas Qgp and liquid phases Qlp= 0.37 g/s as...dimensions can be made even less provided that volatile substances are used. Table 9.1.1 d2, mm 4.0 3.0 4.0 3.0 4.0 d1, mm 0.8 0.8 2.0 2.0 1.2 Qgp , g
Nanoscale Hot-Wire Probes for Boundary-Layer Flows
NASA Technical Reports Server (NTRS)
Tedjojuwono, Ken T.; Herring, Gregory C.
2003-01-01
Hot-wire probes having dimensions of the order of nanometers have been proposed for measuring temperatures (and possibly velocities) in boundary-layer flows at spatial resolutions much finer and distances from walls much smaller than have been possible heretofore. The achievable resolutions and minimum distances are expected to be of the order of tens of nanometers much less than a typical mean free path of a molecule and much less than the thickness of a typical flow boundary layer in air at standard temperature and pressure. An additional benefit of the small scale of these probes is that they would perturb the measured flows less than do larger probes. The hot-wire components of the probes would likely be made from semiconducting carbon nanotubes or ropes of such nanotubes. According to one design concept, a probe would comprise a single nanotube or rope of nanotubes laid out on the surface of an insulating substrate between two metallic wires. According to another design concept, a nanotube or rope of nanotubes would be electrically connected and held a short distance away from the substrate surface by stringing it between two metal electrodes. According to a third concept, a semiconducting nanotube or rope of nanotubes would be strung between the tips of two protruding electrodes made of fully conducting nanotubes or ropes of nanotubes. The figure depicts an array of such probes that could be used to gather data at several distances from a wall. It will be necessary to develop techniques for fabricating the probes. It will also be necessary to determine whether the probes will be strong enough to withstand the aerodynamic forces and impacts of micron-sized particles entrained in typical flows of interest.
NASA Technical Reports Server (NTRS)
Chan, William Machado; Pandya, Shishir Ashok; Rogers, Stuart E.
2013-01-01
Recent developments on the automation of the X-rays approach to hole-cutting in over- set grids is further improved. A fast method to compute an auxiliary wall-distance function used in providing a rst estimate of the hole boundary location is introduced. Subsequent iterations lead to automatically-created hole boundaries with a spatially-variable o set from the minimum hole. For each hole boundary location, an averaged cell attribute measure over all fringe points is used to quantify the compatibility between the fringe points and their respective donor cells. The sensitivity of aerodynamic loads to di erent hole boundary locations and cell attribute compatibilities is investigated using four test cases: an isolated re-entry capsule, a two-rocket con guration, the AIAA 4th Drag Prediction Workshop Common Research Model (CRM), and the D8 \\Double Bubble" subsonic aircraft. When best practices in hole boundary treatment are followed, only small variations in integrated loads and convergence rates are observed for different hole boundary locations.
F-16XL ship #1 - CAWAP boundary layer rakes and hot film on left wing
NASA Technical Reports Server (NTRS)
1996-01-01
This photo shows the boundary layer hot film and the boundary layer rakes on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.
Wake Dynamics in the Atmospheric Boundary Layer Over Complex Terrain
NASA Astrophysics Data System (ADS)
Markfort, Corey D.
The goal of this research is to advance our understanding of atmospheric boundary layer processes over heterogeneous landscapes and complex terrain. The atmospheric boundary layer (ABL) is a relatively thin (˜ 1 km) turbulent layer of air near the earth's surface, in which most human activities and engineered systems are concentrated. Its dynamics are crucially important for biosphere-atmosphere couplings and for global atmospheric dynamics, with significant implications on our ability to predict and mitigate adverse impacts of land use and climate change. In models of the ABL, land surface heterogeneity is typically represented, in the context of Monin-Obukhov similarity theory, as changes in aerodynamic roughness length and surface heat and moisture fluxes. However, many real landscapes are more complex, often leading to massive boundary layer separation and wake turbulence, for which standard models fail. Trees, building clusters, and steep topography produce extensive wake regions currently not accounted for in models of the ABL. Wind turbines and wind farms also generate wakes that combine in complex ways to modify the ABL. Wind farms are covering an increasingly significant area of the globe and the effects of large wind farms must be included in regional and global scale models. Research presented in this thesis demonstrates that wakes caused by landscape heterogeneity must be included in flux parameterizations for momentum, heat, and mass (water vapor and trace gases, e.g. CO2 and CH4) in ABL simulation and prediction models in order to accurately represent land-atmosphere interactions. Accurate representation of these processes is crucial for the predictions of weather, air quality, lake processes, and ecosystems response to climate change. Objectives of the research reported in this thesis are: 1) to investigate turbulent boundary layer adjustment, turbulent transport and scalar flux in wind farms of varying configurations and develop an improved
Chemistry of a polluted cloudy boundary layer
NASA Technical Reports Server (NTRS)
Jacob, Daniel J.; Gottlieb, Elaine W.; Prather, Michael J.
1989-01-01
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.
Persistent Structures in the Turbulent Boundary Layer
NASA Technical Reports Server (NTRS)
Palumbo, Dan; Chabalko, Chris
2005-01-01
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.
Modelling of the Evolving Stable Boundary Layer
NASA Astrophysics Data System (ADS)
Sorbjan, Zbigniew
2014-06-01
A single-column model of the evolving stable boundary layer (SBL) is tested for self-similar properties of the flow and effects of ambient forcing. The turbulence closure of the model is diagnostic, based on the K-theory approach, with a semi-empirical form of the mixing length, and empirical stability functions of the Richardson number. The model results, expressed in terms of local similarity scales, are universal functions, satisfied in the entire SBL. Based on similarity expression, a realizability condition is derived for the minimum allowable turbulent heat flux in the SBL. Numerical experiments show that the development of "horse-shoe" shaped, fixed-elevation hodographs in the interior of the SBL around sunrise is controlled by effects imposed by surface thermal forcing.
Helical modes in boundary layer transition
NASA Astrophysics Data System (ADS)
Bose, Rikhi; Durbin, Paul A.
2016-11-01
Observations are presented to show that in an adverse pressure gradient boundary layer, beneath free-stream turbulence, the interaction between Klebanoff streaks and naturally arising instability waves leads to helical disturbances which break down to form turbulent spots. This occurs under low to moderate levels, 1%-2%, of free-stream turbulence. At high levels of free-stream turbulence, conventional bypass mechanisms are seen. The helical structures are clearly identifiable in visualizations of isosurfaces of streamwise perturbation velocity. A direct numerical simulation also was performed in zero pressure gradient, with a time-periodic Tollmien-Schlichting wave eigenfunction at the inlet. Again, under a moderate level of free-stream turbulence, helices were observed, and found to trigger transition. Their wave speed is on the order of 1/2 U∞ , so helical breakdown can be viewed as a type of inner mode, secondary instability.
Linear Controllers for Turbulent Boundary Layers
NASA Astrophysics Data System (ADS)
Lim, Junwoo; Kim, John; Kang, Sung-Moon; Speyer, Jason
2000-11-01
Several recent studies have shown that controllers based on a linear system theory work surprisingly well in turbulent flows, suggesting that a linear mechanism may play an important role even in turbulent flows. It has been also shown that non-normality of the linearized Navier-Stokes equations is an essential characteristic in the regeneration of near-wall turbulence structures in turbulent boundary layers. A few controllers designed to reduce the role of different linear mechanisms, including that to minimize the non-normality of the linearized Navier-Stokes equations, have been developed and applied to a low Reynolds nubmer turbulent channel flow. A reduced-order model containing the most controllable and observables modes is derived for each system. Other existing control schemes, such as Choi et al's opposition control, have been examined from the point of a linear system control. Further discussion on controller design, such as choice of cost function and other control parameters, will be presented.
Acoustics of laminar boundary layers breakdown
NASA Technical Reports Server (NTRS)
Wang, Meng
1994-01-01
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.
Some measurements in synthetic turbulent boundary layers
NASA Astrophysics Data System (ADS)
Savas, O.
1980-01-01
Synthetic turbulent boundary layers are examined which were constructed on a flat plate by generating systematic moving patterns of turbulent spots in a laminar flow. The experiments were carried out in a wind tunnel at a Reynolds number based on plate length of 1,700,000. Spots were generated periodically in space and time near the leading edge to form a regular hexagonal pattern. The disturbance mechanism was a camshaft which displaced small pins momentarily into the laminar flow at frequencies up to 80 Hz. The main instrumentation was a rake of 24 hot wires placed across the flow in a line parallel to the surface. The main measured variable was local intermittency; i.e., the probability of observing turbulent flow at a particular point in space and time. The results are reported in x-t diagrams showing the evolution of various synthetic flows along the plate. The dimensionless celerity or phase velocity of the large eddies is found to be 0.88, independent of eddy scale. All patterns with sufficiently small scales eventually showed loss of coherence as they moved downstream. A novel phenomenon called eddy transposition was observed in several flows which contained appreciable laminar regions. The large eddies shifted in formation to new positions, intermediate to their original ones, while preserving their hexagonal pattern. The present results, together with some empirical properties of a turbulent spot, are used to estimate the best choice of scales for constructing a synthetic boundary layer suitable for detailed study. The values recommended are: spanwise scale/thickness = 2.5, streamwise scale/thickness = 8.
Active Boundary Layer Trip for Supersonic Flows
NASA Astrophysics Data System (ADS)
Schloegel, F.; Panigua, G.; Tirtey, S.
2009-01-01
The last decade has been full of excitement and success for the hypersonic community thanks to various Scramjet ground tests and launches. These studies have shown promising potentials but the viability to perform commercial flights at Mach 8 is still to be demonstrated. An ideal Scramjet is one which is capable of self- starting over a wide range of angles of attack and Mach number. The Scramjet designer has to ensure that the boundary layer over the inlet ramp is fully turbulent where shocks impact, hence reducing the risks of chocked flow conditions. Most studies have issued the efficiency of roughness trip to trigger the boundary layer transition. At hypersonic speed, heat transfer and drag dramatically increase resulting in skin friction averaging at 40% of the overall drag. This study investigates the possibility of triggering transition using perpendicular air jets on a flat plate place in a hypersonic cross-flow. Experiments were conducted in the von Karman Institute hypersonic blow down wind tunnel H3. This facility is mounted with a Mach 6 contoured nozzles and provides flows with Reynolds number in the range of 10x106/m to 30x106/m. The model consist of a flat plate manufactured with a built -in settling chamber, equipped with a pressure tap and a thermocouple to monitor the jet conditions. A first flat plate was manufactured with a black-coated Plexiglas top, for surface heat transfer measurement using an infrared camera. On the second model, a Upilex sheet equipped with 32 thin film gages was glued, time dependent heat transfer measurements up to 60kHz. The jet injection conditions have been varied and a Mach number of 5.5 kept constant. The flow topology was investigated using fast schlieren techniques and oil flow, in order to gain a better understanding.
Large Eddy Simulation of Transitional Boundary Layer
NASA Astrophysics Data System (ADS)
Sayadi, Taraneh; Moin, Parviz
2009-11-01
A sixth order compact finite difference code is employed to investigate compressible Large Eddy Simulation (LES) of subharmonic transition of a spatially developing zero pressure gradient boundary layer, at Ma = 0.2. The computational domain extends from Rex= 10^5, where laminar blowing and suction excites the most unstable fundamental and sub-harmonic modes, to fully turbulent stage at Rex= 10.1x10^5. Numerical sponges are used in the neighborhood of external boundaries to provide non-reflective conditions. Our interest lies in the performance of the dynamic subgrid scale (SGS) model [1] in the transition process. It is observed that in early stages of transition the eddy viscosity is much smaller than the physical viscosity. As a result the amplitudes of selected harmonics are in very good agreement with the experimental data [2]. The model's contribution gradually increases during the last stages of transition process and the dynamic eddy viscosity becomes fully active and dominant in the turbulent region. Consistent with this trend the skin friction coefficient versus Rex diverges from its laminar profile and converges to the turbulent profile after an overshoot. 1. Moin P. et. al. Phys Fluids A, 3(11), 2746-2757, 1991. 2. Kachanov Yu. S. et. al. JFM, 138, 209-247, 1983.
Three-dimensional turbulent boundary layers in turbomachines
NASA Astrophysics Data System (ADS)
Lakshminarayana, B.
Turbulent shear layers in turbomachines are compared with turbulent boundary layers on airfoils. The effects of turbulent boundary layers on turbomachine performance (rotating blade, stator blade, end wall, annulus wall, rotating hub) are listed. Generalized equations; momentum integral techniques; velocity profile models; and skin friction stress calculation are summarized.
Improved Boundary Layer Depth Retrievals from MPLNET
NASA Technical Reports Server (NTRS)
Lewis, Jasper R.; Welton, Ellsworth J.; Molod, Andrea M.; Joseph, Everette
2013-01-01
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.
Acoustic sounding in the planetary boundary layer
NASA Technical Reports Server (NTRS)
Kelly, E. H.
1974-01-01
Three case studies are presented involving data from an acoustic radar. The first two cases examine data collected during the passage of a mesoscale cold-air intrusion, probably thunderstorm outflow, and a synoptic-scale cold front. In these studies the radar data are compared to conventional meteorological data obtained from the WKY tower facility for the purpose of radar data interpretation. It is shown that the acoustic radar echoes reveal the boundary between warm and cold air and other areas of turbulent mixing, regions of strong vertical temperature gradients, and areas of weak or no wind shear. The third case study examines the relationship between the nocturnal radiation inversion and the low-level wind maximum or jet in the light of conclusions presented by Blackadar (1957). The low-level jet is seen forming well above the top of the inversion. Sudden rapid growth of the inversion occurs which brings the top of the inversion to a height equal that of the jet. Coincident with the rapid growth of the inversion is a sudden decrease in the intensity of the acoustic radar echoes in the inversion layer. It is suggested that the decrease in echo intensity reveals a decrease in turbulent mixing in the inversion layer as predicted by Blackadar. It is concluded that the acoustic radar can be a valuable tool for study in the lower atmosphere.
CFL3D Contribution to the AIAA Supersonic Shock Boundary Layer Interaction Workshop
NASA Technical Reports Server (NTRS)
Rumsey, Christopher L.
2010-01-01
This paper documents the CFL3D contribution to the AIAA Supersonic Shock Boundary Layer Interaction Workshop, held in Orlando, Florida in January 2010. CFL3D is a Reynolds-averaged Navier-Stokes code. Four shock boundary layer interaction cases are computed using a one-equation turbulence model widely used for other aerodynamic problems of interest. Two of the cases have experimental data available at the workshop, and two of the cases do not. The effect of grid, flux scheme, and thin-layer approximation are investigated. Comparisons are made to the available experimental data. All four cases exhibit strong three-dimensional behavior in and near the interaction regions, resulting from influences of the tunnel side-walls.
Shock Wave Turbulent Boundary Layer Interaction in Hypersonic Flow
1975-06-01
An examination and correlation of skin friction heat transfer and pressure measurements in laminar, transitional and turbulent boundary layers on...and heat transfer measurements made In turbulent boundary layers DO 1 JAN 73 W3 EDITION OF 1 NOV 65 IS OBSOLETE ’ / Unclassified SECURITY...Eckert. The Van Driest II method is in best overall agreement with the measurements . From 50 to 100 boundary layer thicknesses are
Boundary Layer Transition Flight Experiment Implementation on OV-103
NASA Technical Reports Server (NTRS)
Spanos, Theodoros A.
2009-01-01
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.
Development of a laminar boundary layer behind a suction point
NASA Technical Reports Server (NTRS)
Wuest, Walter
1952-01-01
A theoretical investigation is made of the development of a laminar boundary layer behind a suction slot that is assumed to cut off part of the boundary layer without exerting any sink effect. The development, which is approximate, is based on the heat conduction equation. The heat conduction equation enters the analysis through a linearization of the Prandtl-Mises form of the boundary-layer equation.
NASA Astrophysics Data System (ADS)
Nowotarski, Christopher J.
Nearly all previous numerical simulations of supercell thunderstorms have neglected surface uxes of heat, moisture, and momentum as well as horizontal inhomogeneities in the near-storm environment from resulting dry boundary layer convection. This investigation uses coupled radiation and land-surface schemes within an idealized cloud model to identify the effects of organized boundary layer convection in the form of horizontal convective rolls (HCRs) on the strength, structure, and evolution of simulated supercell thunderstorms. The in uence of HCRs and the importance of their orientation relative to storm motion is tested by comparing simulations with a convective boundary layer (CBL) against those with a horizontally homogeneous base state having the same mean environment. The impact of anvil shading on the CBL is tested by comparing simulations with and without the effects of clouds in the radiative transfer scheme. The results of these simulations indicate that HCRs provide a potentially important source of environmental vertical vorticity in the sheared, near-storm boundary layer. These vorticity perturbations are amplified both beneath the main supercell updraft and along the trailing out ow boundary, leading to the formation of occasionally intense misovortices. HCRs perpendicular to storm motion are found to have a detrimental effect on the strength and persistence of the lowlevel mesocyclone, particularly during its initial development. Though the mean environment is less supportive of low-level rotation with a wind profile conducive to HCRs oriented parallel to storm motion, such HCRs are found to often enhance the low-level mesocyclone circulation. When anvil shading is included, stabilization results in generally weaker low-level mesocyclone circulation, regardless of HCR orientation. Moreover, HCRs diminish in the near-storm environment such that the effects of HCRs on the supercell are mitigated. HCRs are also shown to be a necessary condition for the
NASA Astrophysics Data System (ADS)
Jacob, Chinthaka; Anderson, William
2017-01-01
Aeolian erosion of flat, arid landscapes is induced (and sustained) by the aerodynamic surface stress imposed by flow in the atmospheric surface layer. Conceptual models typically indicate that sediment mass flux, Q (via saltation or drift), scales with imposed aerodynamic stress raised to some exponent, n, where n > 1. This scaling demonstrates the importance of turbulent fluctuations in driving aeolian processes. In order to illustrate the importance of surface-stress intermittency in aeolian processes, and to elucidate the role of turbulence, conditional averaging predicated on aerodynamic surface stress has been used within large-eddy simulation of atmospheric boundary-layer flow over an arid, flat landscape. The conditional-sampling thresholds are defined based on probability distribution functions of surface stress. The simulations have been performed for a computational domain with ≈ 25 H streamwise extent, where H is the prescribed depth of the neutrally-stratified boundary layer. Thus, the full hierarchy of spatial scales are captured, from surface-layer turbulence to large- and very-large-scale outer-layer coherent motions. Spectrograms are used to support this argument, and also to illustrate how turbulent energy is distributed across wavelengths with elevation. Conditional averaging provides an ensemble-mean visualization of flow structures responsible for erosion `events'. Results indicate that surface-stress peaks are associated with the passage of inclined, high-momentum regions flanked by adjacent low-momentum regions. Fluid in the interfacial shear layers between these adjacent quasi-uniform momentum regions exhibits high streamwise and vertical vorticity.
On the dynamic behavior of composite panels under turbulent boundary layer excitations
NASA Astrophysics Data System (ADS)
Ciappi, E.; De Rosa, S.; Franco, F.; Vitiello, P.; Miozzi, M.
2016-03-01
In this work high Mach number aerodynamic and structural measurements acquired in the CIRA (Italian Aerospace Research Center) transonic wind tunnel and the models used to analyze the response of composite panels to turbulent boundary layer excitation are presented. The two investigated panels are CFRP (Carbon Fiber-Reinforced Polymer) composite plates and their lay-up is similar to configurations used in aeronautical structures. They differ only for the presence of an embedded viscoelastic layer. The experimental set-up has been designed to reproduce a pressure fluctuations field beneath a turbulent boundary layer as close as possible to those in flight. A tripping system, specifically conceived to this aim for this facility, has been used to generate thick turbulent boundary layers at Mach number values ranging between 0.4 and 0.8. It is shown that the designed setup provides a realistic representation of full scale size pressure spectra in the frequency range of interest for the noise component inside the fuselage, generated by turbulent boundary layer. The significant role of the viscoelastic layer at reducing panel's response is detailed and discussed. Finally, it is demonstrated that at high Mach number the aeroelastic effect cannot be neglected when analyzing the panel response, especially when composite materials are considered.
Incorporation of the planetary boundary layer in atmospheric models
NASA Technical Reports Server (NTRS)
Moeng, Chin-Hoh; Wyngaard, John; Pielke, Roger; Krueger, Steve
1993-01-01
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.
Control of the Transitional Boundary Layer
NASA Astrophysics Data System (ADS)
Belson, Brandt A.
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
Boundary layer problem on a hyperbolic system arising from chemotaxis
NASA Astrophysics Data System (ADS)
Hou, Qianqian; Wang, Zhi-An; Zhao, Kun
2016-11-01
This paper is concerned with the boundary layer problem for a hyperbolic system transformed via a Cole-Hopf type transformation from a repulsive chemotaxis model with logarithmic sensitivity proposed in [23,34] modeling the biological movement of reinforced random walkers which deposit a non-diffusible (or slowly moving) signal that modifies the local environment for succeeding passages. By prescribing the Dirichlet boundary conditions to the transformed hyperbolic system in an interval (0 , 1), we show that the system has the boundary layer solutions as the chemical diffusion coefficient ε → 0, and further use the formal asymptotic analysis to show that the boundary layer thickness is ε 1 / 2. Our work justifies the boundary layer phenomenon that was numerically found in the recent work [25]. However we find that the original chemotaxis system does not possess boundary layer solutions when the results are reverted to the pre-transformed system.
Forced unsteady deceleration of a turbulent boundary layer from a temporal perspective
NASA Technical Reports Server (NTRS)
Brereton, G. J.
1992-01-01
The behavior of a turbulent boundary layer which has been subjected to a local ramp-like deceleration in the external velocity field, which leads to forced separation, has been studied experimentally. The data of this study are re-interpreted in light of more recent findings concerning the temporal nature of boundary layer turbulence in the presence of forced unsteady shear. In particular, the robustness of the near-wall turbulent motions to organized deformation is recognized. Their resilence during unsteady shearing action promotes continued efficient turbulent mixing and rapid redistribution of turbulent kinetic energy during forced transients. In aerodynamic problems, the rapid nature of the adjustment of the turbulence field to a new temporal boundary condition necessitates equally rapid remedial measures to be taken if means of control/prevention of forced unsteady separation are to be deployed to maximum effect. This requirement suggests exploration of the use of simple, real-time statistical forecasting techniques, based upon time-series analysis of easily-measurable features of the flow, to help assure timely deployment of mechanisms of boundary-layer control. This paper focuses upon the nature of turbulence in boundary layers undergoing forced deceleration which would lead to separation. A preliminary form of a forecasting model is presented and evaluated. Using observations of the previous two large eddies passing a detector, it forecasts the behavior of the future large eddy rather well.
Forced unsteady deceleration of a turbulent boundary layer from a temporal perspective
NASA Astrophysics Data System (ADS)
Brereton, G. J.
1992-03-01
The behavior of a turbulent boundary layer which has been subjected to a local ramp-like deceleration in the external velocity field, which leads to forced separation, has been studied experimentally. The data of this study are re-interpreted in light of more recent findings concerning the temporal nature of boundary layer turbulence in the presence of forced unsteady shear. In particular, the robustness of the near-wall turbulent motions to organized deformation is recognized. Their resilence during unsteady shearing action promotes continued efficient turbulent mixing and rapid redistribution of turbulent kinetic energy during forced transients. In aerodynamic problems, the rapid nature of the adjustment of the turbulence field to a new temporal boundary condition necessitates equally rapid remedial measures to be taken if means of control/prevention of forced unsteady separation are to be deployed to maximum effect. This requirement suggests exploration of the use of simple, real-time statistical forecasting techniques, based upon time-series analysis of easily-measurable features of the flow, to help assure timely deployment of mechanisms of boundary-layer control. This paper focuses upon the nature of turbulence in boundary layers undergoing forced deceleration which would lead to separation. A preliminary form of a forecasting model is presented and evaluated. Using observations of the previous two large eddies passing a detector, it forecasts the behavior of the future large eddy rather well.
Turbulence in the Stable Atmospheric Boundary Layer
NASA Astrophysics Data System (ADS)
Fernando, Harindra; Kit, Eliezer; Conry, Patrick; Hocut, Christopher; Liberzon, Dan
2016-11-01
During the field campaigns of the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program, fine-scale measurements of turbulence in the atmospheric boundary layer (ABL) were made using a novel sonic and hot-film anemometer dyad (a combo probe). A swath of scales, from large down to Kolmogorov scales, was covered. The hot-film was located on a gimbal within the sonic probe volume, and was automated to rotate in the horizontal plane to align with the mean flow measured by sonic. This procedure not only helped satisfy the requirement of hot-film alignment with the mean flow, but also allowed in-situ calibration of hot-films. This paper analyzes a period of nocturnal flow that was similar to an idealized stratified parallel shear flow. Some new phenomena were identified, which included the occurrence of strong bursts in the velocity records indicative of turbulence generation at finer scales that are not captured by conventional sonic anemometers. The spectra showed bottleneck effect, but its manifestation did not fit into the framework of previous bottleneck-effect theories and was unequivocally related to bursts of turbulence. The measurements were also used to evaluate the energetics of stratified shear flows typical of the environment. ONR # N00014-11-1-0709; NSF # AGS-1528451; ISF 408/15.
Effect of sound on boundary layer stability
NASA Technical Reports Server (NTRS)
Saric, William S. (Principal Investigator); Spencer, Shelly Anne
1993-01-01
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-travelling, 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 modelling are observed.
Effect of sound on boundary layer stability
NASA Technical Reports Server (NTRS)
Saric, William S.; Spencer, Shelly Anne
1993-01-01
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.
Green House Gases Flux Model in Boundary Layer
NASA Astrophysics Data System (ADS)
Nurgaliev, Ildus
Analytical dynamic model of the turbulent flux in the three-layer boundary system is presented. Turbulence is described as a presence of the non-zero vorticity. The generalized advection-diffusion-reaction equation is derived for an arbitrary number of components in the flux. The fluxes in the layers are objects for matching requirements on the boundaries between the layers. Different types of transport mechanisms are dominant on the different levels of the layers.
F-16XL ship #1 - CAWAP boundary layer hot film, left wing
NASA Technical Reports Server (NTRS)
1996-01-01
This photo shows the boundary layer hot film on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. Hot film is used to measure temperature changes on a surface. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.
Parametric investigation of boundary layer control using triangular micro vortex generators
NASA Astrophysics Data System (ADS)
Bagheri, Milad; Muslmani, Motassem Al; Masood, Asad; Khosravi, Mahmood; Atef Mahmoud, Mohamed; Cardoz, Aniket; Akkuwari, Abdulrahman; Alanezi, Yusuf; Kim, Young
2014-03-01
Improving the aerodynamic performance of an airfoil is one of the primary interests of the Aerodynamicists. Such performance improvement can be achieved using passive or active flow control devices. One of such passive devices having a compact size along with an effective performance is the Micro Vortex Generators (MVGs). A special type of MVGs, which has been recently introduced in the aerospace industry, is "Triangular Shape" MVGs and its impact on aerodynamic characteristics is the main interest of this study. This study will compare the effects of various configurations through which delay of the flow separation using boundary layer control will be analysed by experimental and theoretical approach. The experimental investigations have been conducted using subsonic wind tunnel and the theoretical analysis using ANSYS® 13.0 FLUENT of which the final results are compared with each other.
Approach to Modeling Boundary Layer Ingestion using a Fully Coupled Propulsion-RANS Model
NASA Technical Reports Server (NTRS)
Gray, Justin; Martins, Joaquim R. R.
2017-01-01
Although boundary layer ingestion (BLI), or wake ingestion, is commonly applied in marine propulsion applications, it has not yet seen wide-spread adoption in aircraft applications. However, recent studies have predicted that BLI offers a potential for a 10 reduction in aircraft fuel burn, even on a fairly traditional aircraft configuration. This dramatic reduction in fuel burn is achieved via tight integration of the propulsion system and airframe aerodynamics, but actually realizing such large performance gains will require modifying the aircraft design process to account for this integration. Traditionally, in aircraft design, the airframe and the propulsion system are designed separately and then the engine sizing is managed with a rubber-engine approach. This works when the propulsion system is placed in the free-stream air, away from the aerodynamic influence of the airframe, and it is reasonable to assume that small changes to either system won't have a strong impact on the other.
Modeling coupled aerodynamics and vocal fold dynamics using immersed boundary methods.
Duncan, Comer; Zhai, Guangnian; Scherer, Ronald
2006-11-01
The penalty immersed boundary (PIB) method, originally introduced by Peskin (1972) to model the function of the mammalian heart, is tested as a fluid-structure interaction model of the closely coupled dynamics of the vocal folds and aerodynamics in phonation. Two-dimensional vocal folds are simulated with material properties chosen to result in self-oscillation and volume flows in physiological frequency ranges. Properties of the glottal flow field, including vorticity, are studied in conjunction with the dynamic vocal fold motion. The results of using the PIB method to model self-oscillating vocal folds for the case of 8 cm H20 as the transglottal pressure gradient are described. The volume flow at 8 cm H20, the transglottal pressure, and vortex dynamics associated with the self-oscillating model are shown. Volume flow is also given for 2, 4, and 12 cm H2O, illustrating the robustness of the model to a range of transglottal pressures. The results indicate that the PIB method applied to modeling phonation has good potential for the study of the interdependence of aerodynamics and vocal fold motion.
Aerodynamic Analyses Requiring Advanced Computers, Part 1
NASA Technical Reports Server (NTRS)
1975-01-01
Papers are presented which deal with results of theoretical research on aerodynamic flow problems requiring the use of advanced computers. Topics discussed include: viscous flows, boundary layer equations, turbulence modeling and Navier-Stokes equations, and internal flows.
A study of methods to investigate nozzle boundary layer transition
NASA Astrophysics Data System (ADS)
Pauley, Laura L.
1991-05-01
To further investigate nozzle flow, numerical computations are employed. The computations produce complete flow velocity and temperature fields within the nozzle. As a check, these results can be compared with experimental data at the wall. Once an accurate numerical scheme has been validated, it can be used as a design tool to predict the performance of other nozzle designs without the cost of experimental testing. Typically, the numerical analysis assumes either a laminar boundary layer or a fully turbulent boundary layer which is steady and two-dimensional. Boundary layer transition is not considered. Computing both the completely laminar boundary layer and the completely turbulent boundary layer conditions gives the minimum and maximum wall heat flux possible for a specified geometry. When the experimental heat flux measurements lie between these two values, the nature of the boundary layer is unknown. The boundary layer may have transitioned from laminar to turbulent; three-dimensional structures may be present in the boundary layer, or the inlet flow conditions may not be correctly specified in the computation.
Turbulence Modeling for Shock Wave/Turbulent Boundary Layer Interactions
NASA Technical Reports Server (NTRS)
Lillard, Randolph P.
2011-01-01
Accurate aerodynamic computational predictions are essential for the safety of space vehicles, but these computations are of limited accuracy when large pressure gradients are present in the flow. The goal of the current project is to improve the state of compressible turbulence modeling for high speed flows with shock wave / turbulent boundary layer interactions (SWTBLI). Emphasis will be placed on models that can accurately predict the separated region caused by the SWTBLI. These flows are classified as nonequilibrium boundary layers because of the very large and variable adverse pressure gradients caused by the shock waves. The lag model was designed to model these nonequilibrium flows by incorporating history effects. Standard one- and two-equation models (Spalart Allmaras and SST) and the lag model will be run and compared to a new lag model. This new model, the Reynolds stress tensor lag model (lagRST), will be assessed against multiple wind tunnel tests and correlations. The basis of the lag and lagRST models are to preserve the accuracy of the standard turbulence models in equilibrium turbulence, when the Reynolds stresses are linearly related to the mean strain rates, but create a lag between mean strain rate effects and turbulence when nonequilibrium effects become important, such as in large pressure gradients. The affect this lag has on the results for SWBLI and massively separated flows will be determined. These computations will be done with a modified version of the OVERFLOW code. This code solves the RANS equations on overset grids. It was used for this study for its ability to input very complex geometries into the flow solver, such as the Space Shuttle in the full stack configuration. The model was successfully implemented within two versions of the OVERFLOW code. Results show a substantial improvement over the baseline models for transonic separated flows. The results are mixed for the SWBLI assessed. Separation predictions are not as good as the
Transonic Shock-Wave/Boundary-Layer Interactions on an Oscillating Airfoil
NASA Technical Reports Server (NTRS)
Davis, Sanford S.; Malcolm, Gerald N.
1980-01-01
Unsteady aerodynamic loads were measured on an oscillating NACA 64A010 airfoil In the NASA Ames 11 by 11 ft Transonic Wind Tunnel. Data are presented to show the effect of the unsteady shock-wave/boundary-layer interaction on the fundamental frequency lift, moment, and pressure distributions. The data show that weak shock waves induce an unsteady pressure distribution that can be predicted quite well, while stronger shock waves cause complex frequency-dependent distributions due to flow separation. An experimental test of the principles of linearity and superposition showed that they hold for weak shock waves while flows with stronger shock waves cannot be superimposed.
Symmetries in Turbulent Boundary Layer Flows
NASA Technical Reports Server (NTRS)
Oberlack, M.
1996-01-01
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.
Aeolian Sand Transport by Boundary Layer Turbulence
NASA Astrophysics Data System (ADS)
Baas, A. C.
2007-12-01
The erratic and intermittent nature of wind-driven sand transport challenges our current transport models, which lack physical mechanisms for explaining and taking into account this spatio-temporal variability. This paper presents a collective overview of results from investigations into the nature of spatio-temporal variability in sand transport generally, and the formation and behaviour of aeolian streamers specifically. This includes three principal studies. First, the results of field investigations into the formation and behaviour of aeolian streamers in coastal and desert environments, where spatio-temporal transport variability and associated turbulence characteristics were assessed with an extensive instrument array. Streamers were measured with a transverse array of Safires, while the wind field and associated turbulent structures were monitored with cup-anemometry and a rake of hot-film probes. Second, these field data were used to assess the statistical trends in transport variability as a function of spanwise scale of measurement and the temporal scale of time-averaging transport rates. Third, spectral wavelet analysis of high-frequency collocated wind speed (hot- film probes) and transport flux (Safires) time-series revealed distinct forcing-response regimes at different temporal scales. The transitions between these regimes and their ranges compare favourably with physically meaningful scales, such as the minimum temporal scale of saltation response to wind speed fluctuations, and the integral time-scale of the observed internal boundary layer turbulence dynamics. The paper concludes with a tentative conceptual framework that attempts to integrate the results and insights from these studies towards an improved understanding of aeolian sediment transport processes.
Destiny of earthward streaming plasma in the plasmasheet boundary layer
NASA Technical Reports Server (NTRS)
Green, J. L.; Horwitz, J. L.
1986-01-01
The dynamics of the earth's magnetotail have been investigated, and it has become clear that the plasmasheet boundary layer field lines map into the Region I Field-Aligned Currents (FAC) of the auroral zone. It is pointed out that the role of earthward streaming ions in the plasmasheet boundary layer may be of fundamental importance in the understanding of magnetotail dynamics, auroral zone physics, and especially for ionospheric-magnetospheric interactions. The present paper has the objective to evaluate propagation characteristics for the earthward streaming ions observed in the plasmasheet boundary layer. An investigation is conducted of the propagation characteristics of protons in the plasmasheet boundary layer using independent single particle dynamics, and conclusions are discussed. The density of earthward streaming ions found in the plasmasheet boundary layer should include the ring current as well as the auroral zone precipitaiton and inner plasmasheet regions of the magnetosphere.
Dynamic behavior of an unsteady trubulent boundary layer
NASA Technical Reports Server (NTRS)
Parikh, P. G.; Reynolds, W. C.; Jayaramen, R.; Carr, L. W.
1981-01-01
Experiments on an unsteady turbulent boundary layer are reported in which the upstream portion of the flow is steady (in the mean) and in the downstream region, the boundary layer sees a linearly decreasing free stream velocity. This velocity gradient oscillates in time, at frequencies ranging from zero to approximately the bursting frequency. For the small amplitude, the mean velocity and mean turbulence intensity profiles are unaffected by the oscillations. The amplitude of the periodic velocity component, although as much as 70% greater than that in the free stream for very low frequencies, becomes equal to that in the free stream at higher frequencies. At high frequencies, both the boundary layer thickness and the Reynolds stress distribution across the boundary layer become frozen. The behavior at higher amplitude is quite similar. At sufficiently high frequencies, the boundary layer thickness remains frozen at the mean value over the oscillation cycle, even though flow reverses near the wall during a part of the cycle.
On an Asymptotically Consistent Unsteady Interacting Boundary Layer
NASA Technical Reports Server (NTRS)
Bartels, Robert E.
2007-01-01
This paper develops the asymptotic matching of an unsteady compressible boundary layer to an inviscid flow. Of particular importance is the velocity injection or transpiration boundary condition derived by this theory. It is found that in general the transpiration will contain a slope of the displacement thickness and a time derivative of a density integral. The conditions under which the second term may be neglected, and its consistency with the established results of interacting boundary layer are discussed.
Towards improving efficiency of control for blowing into a boundary layer through a permeable wall
NASA Astrophysics Data System (ADS)
Fomin, V. M.; Kornilov, V. I.; Boiko, A. V.
2016-08-01
The results of experimental and numerical investigations of the efficiency of control by an incompressible turbulent boundary layer with the help air blowing through a permeable wall fabricated with maintenance of most of the necessary requirements for the quality and configuration of microapertures and having a low effective roughness are analyzed. Various cases of modeling the process of air blowing into the boundary layer through a specified hi-tech finely perforated surface are considered, and the data for average parameters and characteristics of turbulence of the flow types under investigation are presented. A substantial decrease in the skin-friction coefficient along the model length, which can achieve 90% with increasing the blowing coefficient, is shown. The estimate of the energy consumption for the process of blowing under terrestrial conditions testifies to the high potential of this method of control capable to provide 4-5% gain in the total aerodynamic drag of a simple modeling configuration.
Flight experience with a pivoting traversing boundary-layer probe
NASA Technical Reports Server (NTRS)
Montoya, L. C.; Brauns, D. A.; Cissell, R. E.
1974-01-01
A pivoting traversing boundary layer probe was evaluated in flight on an F-104 airplane. The evaluation was performed at free stream Mach numbers from 0.8 to 2.0. The unit is described, and operating problems and their solutions are discussed. Conventional boundary layer profiles containing variations in flow angle within the viscous layer are shown for free stream Mach numbers of 0.8, 1.6, and 2.0. Although the unit was not optimized for size and weight, it successfully measured simultaneously flow angularity, probe height, and pitot pressure through the boundary layer.
NASA Technical Reports Server (NTRS)
Deutsch, Steven; Zierke, William C.
1987-01-01
A one-component laser Doppler velocimeter (LDV) has been used to measure the two-dimensional, periodic flow field about a double circular arc, compressor blade in cascade. Eleven boundary layer profiles were taken on both the pressure and suction surfaces of the blade, and two were taken in the near wake. In this part of the study, the LDV system is described and the suction surface flow field is documented. The suction surface profiles appear to separate both at the leading edge and again somewhat beyond midchord; the leading edge separation apparently reattaches by 2.6 percent chord.
An Equation for the Mean Velocity Distribution of Boundary Layers
NASA Technical Reports Server (NTRS)
Sandborn, V. A.
1959-01-01
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.
Boundary Layer Rolls Observed Above and Below a Jet in a Marine Boundary Layer
NASA Astrophysics Data System (ADS)
Foster, R. C.; Emmitt, G. D.; Godwin, K.; Greco, S.
2013-12-01
We have flown a coherent Doppler wind lidar (DWL) on the Cirpas Twin Otter off the California coast near Monterey since 2003. One scientific purpose of these flights is to understand the relationship between the turbulent fluxes measured on the aircraft or on other platforms and the observed structure of the marine boundary layer (MBL). Two common features are found in the MBL flow: (1) a strong jet at approximately 200 m above the sea surface; and (2) organized large eddies (OLE) in the form of roll vortices that are approximately aligned along the mean wind direction. On two flights (April 13, 2007 and September 30, 2012), the DWL data indicated that roll OLE existed simultaneously both above and below the jet. The DWL winds suggest that the OLE in these layers are sometimes independent and sometimes connected. Standard flux data are obtained on the Twin Otter at flight level, which is nominally 300 m. The 10 Hz wind and temperature data exhibit variability at spatial scales corresponding to the OLE wavelength. We have constructed a nonlinear theoretical model that includes triad wave-wave interactions to test the hypothesis that rolls could form both above and below the jet. This model shows that this is possible and that the rolls in the two layers could have unique characteristics compared to standard boundary layer rolls. The model further shows that the rolls above and below the jet are due to separate instabilities that interact. This is consistent with the observations of both connected and independent OLE above and below the jet. Contrast-enhanced DWL line-of-sight winds. Jet maximum 200 m below aircraft. Typical resonant triad solution for rolls above and below a PBL jet.
On Reflection of Shock Waves from Boundary Layers
NASA Technical Reports Server (NTRS)
Liepmann, H W; Roshko, A; Dhawan, S
1952-01-01
Measurements are presented at Mach numbers from about 1.3 to 1.5 of reflection characteristics and the relative upstream influence of shock waves impinging on a flat surface with both laminar and turbulent boundary layers. The difference between impulse and step waves is discussed and their interaction with the boundary layer is compared. General considerations on the experimental production of shock waves from wedges and cones and examples of reflection of shock waves from supersonic shear layers are also presented.
On the theory of laminar boundary layers involving separation
NASA Technical Reports Server (NTRS)
Von Karman, TH; Millikan, C
1934-01-01
This paper presents a mathematical discussion of the laminar boundary layer, which was developed with a view of facilitating the investigation of those boundary layers in particular for which the phenomenon of separation occurs. The treatment starts with a slight modification of the form of the boundary layer equation first published by Von Mises. Two approximate solutions of this equation are found, one of which is exact at the outer edge of the boundary layer while the other is exact at the wall. The final solution is obtained by joining these two solutions at the inflection points of the velocity profiles. The final solution is given in terms of a series of universal functions for a fairly broad class of potential velocity distributions outside of the boundary layer. Detailed calculations of the boundary layer characteristics are worked out for the case in which the potential velocity is a linear function of the distance from the upstream stagnation point. Finally, the complete separation point characteristics are determined for the boundary layer associated with a potential velocity distribution made up of two linear functions of the distance from the stagnation point. It appears that extensions of the detailed calculations to more complex potential flows can be fairly easily carried out by using the explicit formulae given in the paper. (author)
Spatial Linear Instability of Confluent Wake/Boundary Layers
NASA Technical Reports Server (NTRS)
Liou, William W.; Liu, Feng-Jun; Rumsey, C. L. (Technical Monitor)
2001-01-01
The spatial linear instability of incompressible confluent wake/boundary layers is analyzed. The flow model adopted is a superposition of the Blasius boundary layer and a wake located above the boundary layer. The Orr-Sommerfeld equation is solved using a global numerical method for the resulting eigenvalue problem. The numerical procedure is validated by comparing the present solutions for the instability of the Blasius boundary layer and for the instability of a wake with published results. For the confluent wake/boundary layers, modes associated with the boundary layer and the wake, respectively, are identified. The boundary layer mode is found amplified as the wake approaches the wall. On the other hand, the modes associated with the wake, including a symmetric mode and an antisymmetric mode, are stabilized by the reduced distance between the wall and the wake. An unstable mode switching at low frequency is observed where the antisymmetric mode becomes more unstable than the symmetric mode when the wake velocity defect is high.
The aerodynamics of small Reynolds numbers
NASA Technical Reports Server (NTRS)
Schmitz, F. W.
1980-01-01
Aerodynamic characteristics of wing model gliders and bird wings in particular are discussed. Wind tunnel measurements and aerodynamics of small Reynolds numbers are enumerated. Airfoil behavior in the critical transition from laminar to turbulent boundary layer, which is more important to bird wing models than to large airplanes, was observed. Experimental results are provided, and an artificial bird wing is described.
NASA Technical Reports Server (NTRS)
Krueger, W.
1947-01-01
Calculations and test results are given about the feed-power requirement of airplanes with boundary-layer control. Curves and formulas for the rough estimate of pressure-loss and feed-power requirement are set up for the investigated arrangements which differ structurally and aerodynamically. According to these results the feed power for three different designs is calculated at the end of the report.
Shock wave-boundary layer interactions in rarefied gas flows
NASA Technical Reports Server (NTRS)
Bird, G. A.
1991-01-01
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.
Further Improvements to Nozzle Boundary Layer Calculations in BLIMPJ
NASA Technical Reports Server (NTRS)
Praharaj, S. C.; Gross, Klaus W.
1989-01-01
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.
Structure of turbulence in three-dimensional boundary layers
NASA Technical Reports Server (NTRS)
Subramanian, Chelakara S.
1993-01-01
This report provides an overview of the three dimensional turbulent boundary layer concepts and of the currently available experimental information for their turbulence modeling. It is found that more reliable turbulence data, especially of the Reynolds stress transport terms, is needed to improve the existing modeling capabilities. An experiment is proposed to study the three dimensional boundary layer formed by a 'sink flow' in a fully developed two dimensional turbulent boundary layer. Also, the mean and turbulence field measurement procedure using a three component laser Doppler velocimeter is described.
Formation of pre-sheath boundary layers in electronegative plasmas
Vitello, P., LLNL
1998-05-01
In electronegative plasmas Coulomb scattering between positive and negative ions can lead to the formation of a pre-sheath boundary layer containing the bulk of the negative ions. The negative ion boundary layer forms when momentum transfer from positive to negative ions dominates the negative ion acceleration from the electric field. This condition is met in Inductively Coupled Plasma reactors that operate at low pressure and high plasma density. Simulations of the GEC reactor for Chlorine and Oxygen chemistries using the INDUCT95 2D model are presented showing the pre-sheath boundary layer structure as a function of applied power and neutral pressure.
Stable Boundary Layer Education (STABLE) Final Campaign Summary
Turner, David D.
2016-03-01
The properties of, and the processes that occur in, the nocturnal stable boundary layer are not well understood, making it difficult to represent adequately in numerical models. The nocturnal boundary layer often is characterized by a temperature inversion and, in the Southern Great Plains region, a low-level jet. To advance our understanding of the nocturnal stable boundary layer, high temporal and vertical resolution data on the temperature and wind properties are needed, along with both large-eddy simulation and cloud-resolving modeling.
Effects of Interaction Between Normal Shock and Boundary Layer
NASA Technical Reports Server (NTRS)
Donaldson, Coleman duP.
1944-01-01
A discussion of the interaction between normal shocks and boundary layers on the basis of experimental evidence obtained in studies of supersonic flows in passages is given. The investigation was made as a result of the inability of the existing normal-shock theory to explain phenomena involving normal shocks that occurred in the presence of boundary layers. Assumptions with regard to the character of the effects of interaction between boundary layer and normal shock are proposed; these assumptions seem to give good agreement with certain experimental results.
The Effects of Rotation on Boundary Layers in Turbomachine Rotors
NASA Technical Reports Server (NTRS)
Johnston, J. P.
1974-01-01
The boundary layers in turbomachine rotors are subject to Coriolis forces which can (1) contribute directly to the development of secondary flows and (2) indirectly influence the behavior of boundary layers by augmentation and/or suppression of turbulence production in the boundary layers on blades. Both these rotation-induced phenomena are particularly important in the development of understanding of flow and loss mechanisms in centrifugal and mixed flow machines. The primary objective of this paper is to review the information available on these effects.
Structure of the zero-pressure-gradient turbulent boundary layer.
Barenblatt, G I; Chorin, A J; Hald, O H; Prostokishin, V M
1997-07-22
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.
A Diagnostic Diagram to Understand the Marine Atmospheric Boundary Layer at High Wind Speeds
NASA Astrophysics Data System (ADS)
Kettle, Anthony
2014-05-01
Engineering and Industrial Aerodynamics, 57, 97-100, 1995). In the Froya study, plots on axes of wind speed and air-sea temperature difference provided an effective method to 'fingerprint' atmospheric conditions and summarize large segments of the data. The increasing numbers of offshore meteorological masts associated with the offshore wind industry are amenable to a similar approach to understand the main characteristics of the boundary layer. In this presentation, the Froya diagnostic figure is used interpret data from the FINO1 platform in the North Sea and understand boundary layer dynamics at high wind speeds.
Size distributions of boundary-layer clouds
Stull, R.; Berg, L.; Modzelewski, H.
1996-04-01
Scattered fair-weather clouds are triggered by thermals rising from the surface layer. Not all surface layer air is buoyant enough to rise. Also, each thermal has different humidities and temperatures, resulting in interthermal variability of their lifting condensation levels (LCL). For each air parcel in the surface layer, it`s virtual potential temperature and it`s LCL height can be computed.
NASA Technical Reports Server (NTRS)
Eastman, Timothy E.
1995-01-01
Evidence for the probable existence of magnetospheric boundary layers was first presented by Hones, et al. (1972), based on VELA satellite plasma observations (no magnetic field measurements were obtained). This magnetotail boundary layer is now known to be the tailward extension of the high-latitude boundary layer or plasma mantle (first uniquely identified using HEOS 2 plasma and field observations by Rosenbauer et al., 1975) and the low-latitude boundary layer (first uniquely identified using IMP 6 plasma and field observations by Eastman et al., 1976). The magnetospheric boundary layer is the region of magnetosheath-like plasma located Earthward of, but generally contiguous with the magnetopause. This boundary layer is typically identified by comparing low-energy (less than 10 keV) ion spectra across the magnetopause. Low-energy electron measurements are also useful for identifying the boundary layer because the shocked solar wind or magnetosheath has a characteristic spectral signature for electrons as well. However, there are magnetopause crossings where low-energy electrons might suggest a depletion layer outside the magnetopause even though the traditional field-rotation signature indicates that this same region is a boundary layer Earthward of the current layer. Our analyses avoided crossings which exhibit such ambiguities. Pristine magnetopause crossings are magnetopause crossings for which the current layer is well defined and for which there is no adjoining magnetospheric boundary layer as defined above. Although most magnetopause models to date apply to such crossings, few comparisons between such theory and observations of pristine magnetopause crossings have been made because most crossings have an associated magnetospheric boundary layer which significantly affects the applicable boundary conditions for the magnetopause current layer. Furthermore, almost no observational studies of magnetopause microstructure have been done even though key
NASA Technical Reports Server (NTRS)
Liou, May-Fun; Lee, Byung Joon
2013-01-01
It is known that the adverse effects of shock wave boundary layer interactions in high speed inlets include reduced total pressure recovery and highly distorted flow at the aerodynamic interface plane (AIP). This paper presents a design method for flow control which creates perturbations in geometry. These perturbations are tailored to change the flow structures in order to minimize shock wave boundary layer interactions (SWBLI) inside supersonic inlets. Optimizing the shape of two dimensional micro-size bumps is shown to be a very effective flow control method for two-dimensional SWBLI. In investigating the three dimensional SWBLI, a square duct is employed as a baseline. To investigate the mechanism whereby the geometric elements of the baseline, i.e. the bottom wall, the sidewall and the corner, exert influence on the flow's aerodynamic characteristics, each element is studied and optimized separately. It is found that arrays of micro-size bumps on the bottom wall of the duct have little effect in improving total pressure recovery though they are useful in suppressing the incipient separation in three-dimensional problems. Shaping sidewall geometry is effective in re-distributing flow on the side wall and results in a less distorted flow at the exit. Subsequently, a near 50% reduction in distortion is achieved. A simple change in corner geometry resulted in a 2.4% improvement in total pressure recovery.
Energy efficient engine, low-pressure turbine boundary layer program
NASA Technical Reports Server (NTRS)
Gardner, W. B.
1981-01-01
A study was conducted to investigate development of boundary layers under the influence of velocity distributions simulating the suction side of two state-of-the-art turbine airfoils: a forward loaded airfoil (squared-off design) and an aft loaded airfoil (aft-loaded design). These velocity distributions were simulated in a boundary layer wind tunnel. Detailed measurements of boundary layer mean velocity and turbulence intensity profiles were obtained for an inlet turbulence level of 2.4 percent and an exit Reynolds number of 800,000. Flush-mounted hot film probes identified the boundary layer transition regimes in the adverse pressure gradient regions for both velocity distributions. Wall intermittency data showed good agreement with the correlations of Dhawan and Narasimha for the intermittency factor distribution in transitional flow regimes.
Impact of incident Mach wave on supersonic boundary layer
NASA Astrophysics Data System (ADS)
Vaganov, A. V.; Ermolaev, Yu. G.; Kolosov, G. L.; Kosinov, A. D.; Panina, A. V.; Semionov, N. V.; Yatskikh, A. A.
2016-01-01
Results of an experimental study of the excitation of high-intensity disturbances by a weak external shock wave in laminar boundary layer on flat-plate models with sharp and blunted leading edges at M = 2.5 are reported. The field of disturbances produced by a 2D sticker in turbulent boundary layer on the wall of wind-tunnel test section in the free stream is shown to have the form of an N-wave. It is found that, on the blunted plate, the intensity of pulsations produced by weak external shock waves in boundary layer several times exceeds the intensity of pulsations produced in boundary layer on the model with a sharp leading edge.
Calculations of unsteady turbulent boundary layers with flow reversal
NASA Technical Reports Server (NTRS)
Nash, J. F.; Patel, V. C.
1975-01-01
The results are presented of a series of computational experiments aimed at studying the characteristics of time-dependent turbulent boundary layers with embedded reversed-flow regions. A calculation method developed earlier was extended to boundary layers with reversed flows for this purpose. The calculations were performed for an idealized family of external velocity distributions, and covered a range of degrees of unsteadiness. The results confirmed those of previous studies in demonstrating that the point of flow reversal is nonsingular in a time-dependent boundary layer. A singularity was observed to develop downstream of reversal, under certain conditions, accompanied by the breakdown of the boundary-layer approximations. A tentative hypothesis was advanced in an attempt to predict the appearance of the singularity, and is shown to be consistent with the calculated results.
A compressible boundary layer algorithm for use with SINDA '85
NASA Technical Reports Server (NTRS)
Sakowski, Barbara; Darling, Douglas; Vandewall, Allan
1992-01-01
It is useful to interface a high-speed-flow solution and SINDA to analyze the thermal behavior of systems that include both conduction and high speed flows. When interfacing a high-speed-flow solution to SINDA, it may be necessary to include the viscous effects in the energy equations. Boundary layer effects of interest include heat transfer coefficients (including convection and viscous dissipation) and friction coefficients. To meet this need, a fast, uncoupled, compressible, two-dimensional, boundary layer algorithm was developed that can model flows with and without separation. This algorithm was used as a subroutine with SINDA. Given the core flow properties and the wall heat flux from SINDA, the boundary layer algorithm returns a wall temperature to SINDA and boundary layer algorithm are iterated until they predict the same wall temperature.
Interacting turbulent boundary layer over a wavy wall
NASA Technical Reports Server (NTRS)
Polak, A.; Werle, M. J.
1977-01-01
The two dimensional supersonic flow of a thick turbulent boundary layer over a train of relatively small wave-like protuberances is considered. The flow conditions and the geometry are such that there exists a strong interaction between the viscous and inviscid flow. The problem cannot be solved without inclusion of interaction effects due to the occurrence of the separation singularity in classical boundary layer methods. The interacting boundary layer equations are solved numerically using a time-like relaxation method with turbulence effects represented by the inclusion of the eddy viscosity model. Results are presented for flow over a train of up to six waves for Mach numbers of 10 and 32 million/meter, and wall temperature rations (T sub w/T sub 0) of 0.4 and 0.8. Limited comparisons with independent experimental and analytical results are also given. Detailed results on the influence of small protuberances on surface heating by boundary layers are presented.
Experimental measurements of unsteady turbulent boundary layers near separation
NASA Technical Reports Server (NTRS)
Simpson, R. L.
1982-01-01
Investigations conducted to document the behavior of turbulent boundary layers on flat surfaces that separate due to adverse pressure gradients are reported. Laser and hot wire anemometers measured turbulence and flow structure of a steady free stream separating turbulent boundary layer produced on the flow of a wind tunnel section. The effects of sinusoidal and unsteadiness of the free stream velocity on this separating turbulent boundary layer at a reduced frequency were determined. A friction gage and a thermal tuft were developed and used to measure the surface skin friction and the near wall fraction of time the flow moves downstream for several cases. Abstracts are provided of several articles which discuss the effects of the periodic free stream unsteadiness on the structure or separating turbulent boundary layers.
The current structure of stratified tidal planetary boundary layer flow
Myrhaug, D.; Slaattelid, O.H.
1995-12-31
The paper presents the bottom shear stress and velocity profiles in stratified tidal planetary boundary layer flow by using similarity theory. For a given seabed roughness length, free stream current velocity components, frequency of tidal oscillation, Coriolis parameter and stratification parameter the maximum bottom shear stress is determined for flow conditions in the rough, smooth and transitional smooth-to-rough turbulent regime. Further, the direction of the bottom shear stress and the velocity profiles are given. Comparison is made with data from field measurements of time-independent as well as tidal planetary boundary layer flow for neutral conditions, and the agreement between the predictions and the data is generally good. Further, an example of application for stable stratification is given, and qualitatively the predictions show, as expected, that the bottom shear stress and the thickness of the boundary layer become smaller for stable than for neutral stratification. Other features of the tidal planetary boundary layer flow are also discussed.
Accretion disc boundary layers around pre-main-sequence stars.
NASA Astrophysics Data System (ADS)
Godon, P.
1996-04-01
One-dimensional time-dependent calculations of geometrically thin accretion disc boundary layers in pre-main-sequence stars are carried out for mass-accretion rates in the range M˙ = 5×10-7 to 10-4 Msunyr-1, α = 0.005-0.3 and different inner boundary conditions on the temperature. Two kinds of solution are obtained: those with a distinct thermal boundary layer (BL) component and those without a thermal boundary layer. For M˙ up to ≍10-5Msunyr-1, and for a α > αcritic ≍ 0.04, solutions with a thermal BL are obtained. For M˙ ≍ 10-4Msunyr-1 or for α < αcritic solutions without a thermal BL are obtained. The inner boundary condition Fr = σTeff4 leads to hotter solutions and higher threshold values αcritic while the no-flux boundary condition dT/dr=0 leads to cooler solutions. For a very low mass-accretion rate (M˙ ≍ 5×10-7Msunyr-1), the temperature in the disc drops below 104K and the ionization front is adjacent to the outer edge of the hot thermal boundary layer. In the vicinity of the ionization front, the medium becomes slightly optically thin. For a very high mass accretion rate, advection of energy (ζ = Ladv/Lacc ≍ 0.1-0.2) from the boundary layer into the inner boundary becomes important, and the boundary layer luminosity is only a fraction of its expected value.
An analytic study of nonsteady two-phase laminar boundary layer around an airfoil
NASA Technical Reports Server (NTRS)
Hsu, Yu-Kao
1989-01-01
Recently, NASA, FAA, and other organizations have focused their attention upon the possible effects of rain on airfoil performance. Rhode carried out early experiments and concluded that the rain impacting the aircraft increased the drag. Bergrum made numerical calculation for the rain effects on airfoils. Luers and Haines did an analytic investigation and found that heavy rain induces severe aerodynamic penalties including both a momentum penalty due to the impact of the rain and a drag and lift penalty due to rain roughening of the airfoil and fuselage. More recently, Hansman and Barsotti performed experiments and declared that performance degradation of an airfoil in heavy rain is due to the effective roughening of the surface by the water layer. Hansman and Craig did further experimental research at low Reynolds number. E. Dunham made a critical review for the potential influence of rain on airfoil performance. Dunham et al. carried out experiments for the transport type airfoil and concluded that there is a reduction of maximum lift capability with increase in drag. There is a scarcity of published literature in analytic research of two-phase boundary layer around an airfoil. Analytic research is being improved. The following assumptions are made: the fluid flow is non-steady, viscous, and incompressible; the airfoil is represented by a two-dimensional flat plate; and there is only a laminar boundary layer throughout the flow region. The boundary layer approximation is solved and discussed.
Transport Processes in the Coastal Atmospheric Boundary Layer
2016-06-07
coastlines or boundary layer processes at the coast. The transported constituents may be properties of the marine boundary layer, e.g. humidity, air ... pollution or aerosols, the latter both of natural and man-made origin. In particular I am interested in the cross-coast mixing potential. By this I mean...speed maximas. Also some properties of the coastal marine air , e.g. the presence of aerosol and low clouds, are detrimental to remote sensing based on
Tropical boundary layer equilibrium in the last ice age
NASA Technical Reports Server (NTRS)
Betts, Alan K.; Ridgway, W.
1992-01-01
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.
Acoustic sources in the low Mach number turbulent boundary layer
NASA Technical Reports Server (NTRS)
Hardin, Jay C.
1991-01-01
The sources of sound production in a low Mach number turbulent boundary layer are examined. The sources are shown to be quadrupole in nature and to result from supersonically convecting wave-number components of the fluctuating Reynolds' normal stresses. The primary Tollmien-Schlichting instability of the boundary layer is found to radiate no sound. Analysis of various vortical phenomena suggests that the primary source is the process of formation of horseshoe vortices, with viscous sublayer bursts a possible secondary source.
Computation of Three-Dimensional Boundary Layers Including Separation
1987-02-01
such boundary layers, the x-dependence is eliminated, so the integral equations give algebraic relationships between CE and the boundary layer...this way, the equations are transformed in a set of algebraic equations. One of the rules to construct a correct numerical approximation is the...to explain a departure from the isotropic eddy viscosity. The modelling of transport equations is often simplified to give the so-called algebraic
Wave phenomena in a high Reynolds number compressible boundary layer
NASA Technical Reports Server (NTRS)
Bayliss, A.; Maestrello, L.; Parikh, P.; Turkel, E.
1985-01-01
Growth of unstable disturbances in a high Reynolds number compressible boundary layer is numerically simulated. Localized periodic surface heating and cooling as a means of active control of these disturbances is studied. It is shown that compressibility in itself stabilizes the flow but at a lower Mach number, significant nonlinear distortions are produced. Phase cancellation is shown to be an effective mechanism for active boundary layer control.
Turbulent oceanic western-boundary layers at low latitude
NASA Astrophysics Data System (ADS)
Quam Cyrille Akuetevi, Cataria; Wirth, Achim
2013-04-01
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).
Adaptive nonlinear polynomial neural networks for control of boundary layer/structural interaction
NASA Technical Reports Server (NTRS)
Parker, B. Eugene, Jr.; Cellucci, Richard L.; Abbott, Dean W.; Barron, Roger L.; Jordan, Paul R., III; Poor, H. Vincent
1993-01-01
The acoustic pressures developed in a boundary layer can interact with an aircraft panel to induce significant vibration in the panel. Such vibration is undesirable due to the aerodynamic drag and structure-borne cabin noises that result. The overall objective of this work is to develop effective and practical feedback control strategies for actively reducing this flow-induced structural vibration. This report describes the results of initial evaluations using polynomial, neural network-based, feedback control to reduce flow induced vibration in aircraft panels due to turbulent boundary layer/structural interaction. Computer simulations are used to develop and analyze feedback control strategies to reduce vibration in a beam as a first step. The key differences between this work and that going on elsewhere are as follows: that turbulent and transitional boundary layers represent broadband excitation and thus present a more complex stochastic control scenario than that of narrow band (e.g., laminar boundary layer) excitation; and secondly, that the proposed controller structures are adaptive nonlinear infinite impulse response (IIR) polynomial neural network, as opposed to the traditional adaptive linear finite impulse response (FIR) filters used in most studies to date. The controllers implemented in this study achieved vibration attenuation of 27 to 60 dB depending on the type of boundary layer established by laminar, turbulent, and intermittent laminar-to-turbulent transitional flows. Application of multi-input, multi-output, adaptive, nonlinear feedback control of vibration in aircraft panels based on polynomial neural networks appears to be feasible today. Plans are outlined for Phase 2 of this study, which will include extending the theoretical investigation conducted in Phase 2 and verifying the results in a series of laboratory experiments involving both bum and plate models.
Boundary layer effects on liners for aircraft engines
NASA Astrophysics Data System (ADS)
Gabard, Gwénaël
2016-10-01
The performance of acoustic treatments installed on aircraft engines is strongly influenced by the boundary layer of the grazing flow on the surface of the liner. The parametric study presented in this paper illustrates the extent of this effect and identifies when it is significant. The acoustic modes of a circular duct with flow are calculated using a finite difference method. The parameters are representative of the flow conditions, liners and sound fields found in current turbofan engines. Both the intake and bypass ducts are considered. Results show that there is a complex interplay between the boundary layer thickness, the direction of propagation and the liner impedance and that the boundary layer can have a strong impact on liner performance for typical configurations (including changes of the order of 30 dB on the attenuation of modes associated with tonal fan noise). A modified impedance condition including the effect of a small but finite boundary layer thickness is considered and compared to the standard Myers condition based on an infinitely thin boundary layer. We show how this impedance condition can be implemented in a mode calculation method by introducing auxiliary variables. This condition is able to capture the trends associated with the boundary layer effects and in most cases provides improved predictions of liner performance.
Turbulent Boundary Layer in High Rayleigh Number Convection in Air
NASA Astrophysics Data System (ADS)
du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian
2014-03-01
Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra =1.4×1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re ≈200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal.
Dense gas boundary layer experiments: Visualization, pressure measurements, concentration evaluation
Reichenbach, H.; Neuwald, P.; Kuhl, A.L.
1992-11-01
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.
Boundary Layer Flow Over a Moving Wavy Surface
NASA Astrophysics Data System (ADS)
Hendin, Gali; Toledo, Yaron
2016-04-01
Boundary Layer Flow Over a Moving Wavy Surface Gali Hendin(1), Yaron Toledo(1) January 13, 2016 (1)School of Mechanical Engineering, Tel-Aviv University, Israel Understanding the boundary layer flow over surface gravity waves is of great importance as various atmosphere-ocean processes are essentially coupled through these waves. Nevertheless, there are still significant gaps in our understanding of this complex flow behaviour. The present work investigates the fundamentals of the boundary layer air flow over progressive, small-amplitude waves. It aims to extend the well-known Blasius solution for a boundary layer over a flat plate to one over a moving wavy surface. The current analysis pro- claims the importance of the small curvature and the time-dependency as second order effects, with a meaningful impact on the similarity pattern in the first order. The air flow over the ocean surface is modelled using an outer, inviscid half-infinite flow, overlaying the viscous boundary layer above the wavy surface. The assumption of a uniform flow in the outer layer, used in former studies, is now replaced with a precise analytical solution of the potential flow over a moving wavy surface with a known celerity, wavelength and amplitude. This results in a conceptual change from former models as it shows that the pressure variations within the boundary layer cannot be neglected. In the boundary layer, time-dependent Navier-Stokes equations are formulated in a curvilinear, orthogonal coordinate system. The formulation is done in an elaborate way that presents additional, formerly neglected first-order effects, resulting from the time-varying coordinate system. The suggested time-dependent curvilinear orthogonal coordinate system introduces a platform that can also support the formulation of turbulent problems for any surface shape. In order to produce a self-similar Blasius-type solution, a small wave-steepness is assumed and a perturbation method is applied. Consequently, a
High-order Finite Element Analysis of Boundary Layer Flows
NASA Astrophysics Data System (ADS)
Zhang, Alvin; Sahni, Onkar
2014-11-01
Numerical analysis of boundary layer flows requires careful approximations, specifically the use of a mesh with layered and graded elements near the (viscous) walls. This is referred to as a boundary layer mesh, which for complex geometries is composed of triangular elements on the walls that are inflated or extruded into the volume along the wall-normal direction up to a desired height while the rest of the domain is filled with unstructured tetrahedral elements. Linear elements with C0 inter-element continuity are employed and in some situations higher order C0 elements are also used. However, these elements only enforce continuity whereas high-order smoothness is not attained as will be the case with C1 inter-element continuity and higher. As a result, C0 elements result in a poor approximation of the high-order boundary layer behavior. To achieve greater inter-element continuity in boundary layer region, we employ B-spline basis functions along the wall-normal direction (i.e., only in the layered portion of the mesh). In the rest of the fully unstructured mesh, linear or higher order C0 elements are used as appropriate. In this study we demonstrate the benefits of finite-element analysis based on such higher order and continuity basis functions for boundary layer flows.
Application of a Reynolds stress model to separating boundary layers
NASA Technical Reports Server (NTRS)
Ko, Sung HO
1993-01-01
Separating turbulent boundary layers occur in many practical engineering applications. Nonetheless, the physics of separation/reattachment of flows is poorly understood. During the past decade, various turbulence models were proposed and their ability to successfully predict some types of flows was shown. However. prediction of separating/reattaching flows is still a formidable task for model developers. The present study is concerned with the process of separation from a smooth surface. Features of turbulent separating boundary layers that are relevant to modeling include the following: the occurrence of zero wall shear stress, which causes breakdown of the boundary layer approximation; the law of the wall not being satisfied in the mean back flow region; high turbulence levels in the separated region; a significant low-frequency motion in the separation bubble; and the turbulence structure of the separated shear layer being quite different from that of either the mixing layers or the boundary layers. These special characteristics of separating boundary layers make it difficult for simple turbulence models to correctly predict their behavior.
Matching boundary layer and inviscid flowfields at hypersonic speeds
NASA Astrophysics Data System (ADS)
Harwell, Karen Elizabeth
2000-10-01
Boundary layer equations are developed and incorporated into an implicit finite-difference technique solving non-similar, axi-symmetric boundary layer equations for both laminar and turbulent flow. The new equations match all the boundary layer properties with the variation of the inviscid solution near the edge, except for the normal velocity. In this way entropy layer swallowing effects are automatically included in the solution. The method also incorporates more inviscid flowfield information into the boundary layer solution than other methods at a negligible increase in run-time. Results show that the new technique can provide improved heating rates and skin friction predictions for preliminary design of vehicles where shear layers and entropy layer swallowing are important. Solutions are presented for three sphere-cone configurations at high Mach number and comparisons are made with the SABLE boundary layer code, Navier-Stokes solutions, and Viscous Shock Layer solutions. Use of a new L'Hopital rule-based inviscid velocity gradient provides better prediction of stagnation-point heating rates. Heating rates are predicted more accurately in both the nose region and areas near the sphere-cone juncture than SABLE's final iteration. Shear stress results are also improved in the sphere-cone juncture area. The new technique's impact is seen readily in cases where the inviscid flowfield experiences velocity and enthalpy gradients near the wall. Little effect was seen on cases where the inviscid velocity ratios at the boundary layer edge was less than 1.5 and the enthalpy ratio greater than 0.9.
NASA Technical Reports Server (NTRS)
Oliver, A. B.; Lillard, R. P.; Blaisdell, G. A.; Lyrintizis, A. S.
2006-01-01
The capability of the OVERFLOW code to accurately compute high-speed turbulent boundary layers and turbulent shock-boundary layer interactions is being evaluated. Configurations being investigated include a Mach 2.87 flat plate to compare experimental velocity profiles and boundary layer growth, a Mach 6 flat plate to compare experimental surface heat transfer,a direct numerical simulation (DNS) at Mach 2.25 for turbulent quantities, and several Mach 3 compression ramps to compare computations of shock-boundary layer interactions to experimental laser doppler velocimetry (LDV) data and hot-wire data. The present paper describes outlines the study and presents preliminary results for two of the flat plate cases and two small-angle compression corner test cases.
Funazaki, K.
1996-04-01
As the second part of the study, detailed hot-wire anemometry measurements of wake-affected boundary layers on the flat plate are made. These measurements are organized in order, first, to check the standpoint of the modeling of the wake-induced transition proposed in Part 1, and second, to observe wake-boundary layer interaction in detail from a viewpoint of direct and indirect effect of the wake passage upon turbulent spot generation within the boundary layer, as described by Walker (1993). The validity of the presumed state of the wake-affected boundary layer in the distance-time domain, which constitutes the basis of the transition model, is confirmed to great extent. However, it is also found that the criterion for the onset of the wake-induced transition adopted in Part 1 should be reconsidered. Some successful attempts are therefore made to specify the transition onset.
The separated turbulent boundary layer over a wavy wall
NASA Technical Reports Server (NTRS)
Polak, A.; Werle, M. J.
1977-01-01
A study and application of the fourth order spline collocation procedure, numerical solution of boundary layer like differential equations, is presented. A simple inversion algorithm for the simultaneous solution of the resulting difference equations is given. Particular attention is focused on the boundary condition representation for the spline second derivative approximations. Solutions using the spline procedure, as well as the three point finite difference method, are presented for several model problems in order to assess and improve the spline numerical scheme. Application of the resulting algorithm to the incompressible laminar self similar boundary layer equations is presented.
Review of Research on Low-Profile Vortex Generators to Control Boundary-Layer Separation
NASA Technical Reports Server (NTRS)
Lin, John C.
2002-01-01
An in-depth review of boundary-layer flow-separation control by a passive method using low-profile vortex generators is presented. The generators are defined as those with a device height between 10% and 50% of the boundary layer thickness. Key results are presented for several research efforts, all of which were performed within the past decade and a half where the majority of these works emphasize experimentation with some recent efforts on numerical simulations. Topics of discussion consist of both basic fluid dynamics and applied aerodynamics research. The fluid dynamics research includes comparative studies on separation control effectiveness as well as device-induced vortex characterization and correlation. The comparative studies cover the controlling of low-speed separated flows in adverse pressure gradient and supersonic shock-induced separation. The aerodynamics research includes several applications for aircraft performance enhancement and covers a wide range of speeds. Significant performance improvements are achieved through increased lift and/or reduced drag for various airfoils-low-Reynolds number, high-lift, and transonic-as well as highly swept wings. Performance enhancements for non-airfoil applications include aircraft interior noise reduction, inlet flow distortion alleviation inside compact ducts, and a more efficient overwing fairing. The low-profile vortex generators are best for being applied to applications where flow-separation locations are relatively fixed and the generators can be placed reasonably close upstream of the separation. Using the approach of minimal near-wall proturbances through substantially reduced device height, these devices can produce streamwise vortices just strong enough to overcome the separation without unnecessarily persisting within the boundary layer once the flow-control objective is achieved. Practical advantages of low-profile vortex generators, such as their inherent simplicity and low device drag, are
Inviscid/Boundary-Layer Aeroheating Approach for Integrated Vehicle Design
NASA Technical Reports Server (NTRS)
Lee, Esther; Wurster, Kathryn E.
2017-01-01
A typical entry vehicle design depends on the synthesis of many essential subsystems, including thermal protection system (TPS), structures, payload, avionics, and propulsion, among others. The ability to incorporate aerothermodynamic considerations and TPS design into the early design phase is crucial, as both are closely coupled to the vehicle's aerodynamics, shape and mass. In the preliminary design stage, reasonably accurate results with rapid turn-representative entry envelope was explored. Initial results suggest that for Mach numbers ranging from 9-20, a few inviscid solutions could reasonably sup- port surface heating predictions at Mach numbers variation of +/-2, altitudes variation of +/-10 to 20 kft, and angle-of-attack variation of +/- 5. Agreement with Navier-Stokes solutions was generally found to be within 10-15% for Mach number and altitude, and 20% for angle of attack. A smaller angle-of-attack increment than the 5 deg around times for parametric studies and quickly evolving configurations are necessary to steer design decisions. This investigation considers the use of an unstructured 3D inviscid code in conjunction with an integral boundary-layer method; the former providing the flow field solution and the latter the surface heating. Sensitivity studies for Mach number, angle of attack, and altitude, examine the feasibility of using this approach to populate a representative entry flight envelope based on a limited set of inviscid solutions. Each inviscid solution is used to generate surface heating over the nearby trajectory space. A subset of a considered in this study is recommended. Results of the angle-of-attack sensitivity studies show that smaller increments may be needed for better heating predictions. The approach is well suited for application to conceptual multidisciplinary design and analysis studies where transient aeroheating environments are critical for vehicle TPS and thermal design. Concurrent prediction of aeroheating
Boundary Layer Parameterization for a Global Spectral Model
1991-01-27
assume an upside down structure with the main source of shear generation occurring near the top of the surface invesion layer (Mahrt, 1985). The local...1980: The structure of a fair weather boundary layer Nkcho!ls, S. based on the results of several inasuarement strategies . Mon. Wea. Rev., 108, 349-364
An experimental investigation of turbulent boundary layers along curved surfaces
NASA Technical Reports Server (NTRS)
So, R. M. C.; Mellor, G. L.
1972-01-01
A curved wall tunnel was designed, and an equilibrium turbulent boundary layer was set up on the straight section preceding the curved test section. Turbulent boundary layer flows with uniform and adverse pressure distributions along convex and concave walls were investigated. Hot-wire measurements along the convex surface indicated that turbulent mixing between fluid layers was very much reduced. However, the law of the wall held and the skin friction, thus determined, correlated well with other measurements. Hot-wire measurements along the concave test wall revealed a system of longitudinal vortices inside the boundary layer and confirmed that concave curvature enhances mixing. A self-consistent set of turbulent boundary layer equations for flows along curved surfaces was derived together with a modified eddy viscosity. Solution of these equations together with the modified eddy viscosity gave results that correlated well with the present data on flows along the convex surface with arbitrary pressure distribution. However, it could only be used to predict the mean characteristics of the flow along concave walls because of the existence of the system of longitudinal vortices inside the boundary layer.
A numerical investigation of boundary layer quasi-equilibrium
NASA Astrophysics Data System (ADS)
Thayer-Calder, K.; Randall, David
2015-01-01
Despite the large energy input from surface evaporation, the moist static energy (MSE) of the tropical boundary layer remains relatively constant on large spatial and temporal scales due to lifting of vapor by cloudy updrafts and the addition of dry air from the layers above. Arakawa and Schubert (1974) suggested that drying is due mainly to clear-air turbulent entrainment between cloudy updrafts, while Raymond (1995) described drying due mainly to convective downdrafts. We used cloud-resolving numerical simulations to investigate the transport of MSE into the boundary layer and found turbulent entrainment between clouds to be the dominant process.
Numerical Studies of Boundary-Layer Receptivity
NASA Technical Reports Server (NTRS)
Reed, Helen L.
1995-01-01
Direct numerical simulations (DNS) of the acoustic receptivity process on a semi-infinite flat plate with a modified-super-elliptic (MSE) leading edge are performed. The incompressible Navier-Stokes equations are solved in stream-function/vorticity form in a general curvilinear coordinate system. The steady basic-state solution is found by solving the governing equations using an alternating direction implicit (ADI) procedure which takes advantage of the parallelism present in line-splitting techniques. Time-harmonic oscillations of the farfield velocity are applied as unsteady boundary conditions to the unsteady disturbance equations. An efficient time-harmonic scheme is used to produce the disturbance solutions. Buffer-zone techniques have been applied to eliminate wave reflection from the outflow boundary. The spatial evolution of Tollmien-Schlichting (T-S) waves is analyzed and compared with experiment and theory. The effects of nose-radius, frequency, Reynolds number, angle of attack, and amplitude of the acoustic wave are investigated. This work is being performed in conjunction with the experiments at the Arizona State University Unsteady Wind Tunnel under the direction of Professor William Saric. The simulations are of the same configuration and parameters used in the wind-tunnel experiments.
Measured Boundary Layer Transition and Rotor Hover Performance at Model Scale
NASA Technical Reports Server (NTRS)
Overmeyer, Austin D.; Martin, Preston B.
2017-01-01
An experiment involving a Mach-scaled, 11:08 f t: diameter rotor was performed in hover during the summer of 2016 at NASA Langley Research Center. The experiment investigated the hover performance as a function of the laminar to turbulent transition state of the boundary layer, including both natural and fixed transition cases. The boundary layer transition locations were measured on both the upper and lower aerodynamic surfaces simultaneously. The measurements were enabled by recent advances in infrared sensor sensitivity and stability. The infrared thermography measurement technique was enhanced by a paintable blade surface heater, as well as a new high-sensitivity long wave infrared camera. The measured transition locations showed extensive amounts, x=c>0:90, of laminar flow on the lower surface at moderate to high thrust (CT=s > 0:068) for the full blade radius. The upper surface showed large amounts, x=c > 0:50, of laminar flow at the blade tip for low thrust (CT=s < 0:045). The objective of this paper is to provide an experimental data set for comparisons to newly developed and implemented rotor boundary layer transition models in CFD and rotor design tools. The data is expected to be used as part of the AIAA Rotorcraft SimulationWorking Group
Computational Assessment of the Benefits of Boundary Layer Ingestion for the D8 Aircraft
NASA Technical Reports Server (NTRS)
Pandya, Shishir A.; Uranga, Alejandra
2013-01-01
To substantially reduce the fuel burn of future commercial transportation aircraft, the boundary layer ingestion idea is investigated. The idea is that an engine placed in the wake of the aircraft it is propelling is more efficient than a conventional engine placement under the wing or on pods mounted to the rear of the fuselage. The top, rear of the fuselage is thus designed to act as a diffuser such that the engines can be placed there with a minimal nacelle. The boundary layer thickens over the rear of the fuselage such that a large portion of it is ingested by the fan. To assess whether the boundary layer ingesting (BLI) engine placement is indeed advantageous, a study of the nacelle aerodynamics is carried out using Overflow, a viscous CFD flow solver that uses overset meshes. The computed forces and moments are compared to a wind tunnel experiment for validation. Some aspects of the design are verified using the simulation results. Finally, the effect of the nacelle placement is assessed by comparing the BLI nacelle configuration to a podded nacelle configuration and to the unpowered (without nacelles) aircraft.
A High-Lift Building Block Flow: Turbulent Boundary Layer Relaminarization
NASA Technical Reports Server (NTRS)
Bourassa, Corey; Thomas, Flint O.; Nelson, Robert C.
2001-01-01
A working wind tunnel test facility has been constructed at the University of Notre Dame's Hessert Center. The relaminarization test facility has been constructed in the 1.5m x 1.5m (5ft x 5 ft) atmospheric wind tunnel and generates a Re(theta)=4694 turbulent boundary layer in nominally zero-pressure gradient before it is exposed to the Case #1 pressure gradient (K approximately equal to 4.2 x 10(exp -6), which is believed to be sufficient to achieve relaminarization. Future work to be conducted will include measuring the response of the turbulent boundary layer to the favorable pressure gradients created in the test facility and documenting this response in order to understand the underlying flow physics responsible for relaminarization. It is the goal of this research to have a better understanding of accelerated turbulent boundary layers which will aid in the development of future flow diagnostic utilities to be implemented in applied aerodynamic research.
Boundary Layer CO2 budgets at long timescales
NASA Astrophysics Data System (ADS)
Williams, I. N.; Riley, W. J.; Berry, J. A.; Torn, M. S.; Biraud, S.
2009-12-01
This study demonstrates a strong timescale dependence of boundary layer entrainment and storage in six years of high frequency observations from the U.S. Southern Great Plains Atmospheric Radiation Measurement Climate Research Facility. A scalar conservation equation was applied to aircraft and tower CO2 measurements, soundings, eddy covariance fluxes, cloud radar, and mesoscale model analyses, over a range of timescales from diurnal to annual. Entrainment fluxes and storage become order of magnitude smaller than large-scale vertical and horizontal advection at seasonal and longer timescales and order of magnitude larger than advection at diurnal and shorter timescales. The results are compactly summarized in terms of a dimensionless number involving a residence time calculated from large-scale (vertical) wind velocity and boundary layer depth. This number provides a useful metric for determining the validity of equilibrium boundary layer theory versus traditional boundary layer budgets. The implication of this study for annual mean surface flux inversions is that large scale transport and convective cloud mass fluxes are more likely sources of transport model error than high frequency fluctuations (i.e. diurnal) in boundary layer concentrations and depth. The implication for field studies of boundary layer scalar budgets is that the results of any one study are relevant only in the context of the timescale over which the measurements were sampled or averaged. This timescale dependence is also seen over a wider range of meteorological conditions and surface vegetation types at measurements sites across the Northern Hemisphere. We conclude that the relevant physics associated with boundary layer scalar budgets are a function of the time scale of interest.
Shock-like structures in the tropical cyclone boundary layer
NASA Astrophysics Data System (ADS)
Williams, Gabriel J.; Taft, Richard K.; McNoldy, Brian D.; Schubert, Wayne H.
2013-06-01
This paper presents high horizontal resolution solutions of an axisymmetric, constant depth, slab boundary layer model designed to simulate the radial inflow and boundary layer pumping of a hurricane. Shock-like structures of increasing intensity appear for category 1-5 hurricanes. For example, in the category 3 case, the u>(∂u/∂r>) term in the radial equation of motion produces a shock-like structure in the radial wind, i.e., near the radius of maximum tangential wind the boundary layer radial inflow decreases from approximately 22 m s-1 to zero over a radial distance of a few kilometers. Associated with this large convergence is a spike in the radial distribution of boundary layer pumping, with updrafts larger than 22 m s-1 at a height of 1000 m. Based on these model results, it is argued that observed hurricane updrafts of this magnitude so close to the ocean surface are attributable to the dry dynamics of the frictional boundary layer rather than moist convective dynamics. The shock-like structure in the boundary layer radial wind also has important consequences for the evolution of the tangential wind and the vertical component of vorticity. On the inner side of the shock the tangential wind tendency is essentially zero, while on the outer side of the shock the tangential wind tendency is large due to the large radial inflow there. The result is the development of a U-shaped tangential wind profile and the development of a thin region of large vorticity. In many respects, the model solutions resemble the remarkable structures observed in the boundary layer of Hurricane Hugo (1989).
Theory of the low-latitude boundary layer
NASA Technical Reports Server (NTRS)
Sonnerup, B. U. OE.
1980-01-01
A one-dimensional steady state fluid mechanical model is developed of the low-latitude plasma boundary layer inside the dawn and dusk magnetopause. Momentum transfer in the layer is produced by viscosity and/or mass diffusion. Coupling to the ionosphere is achieved via field-aligned currents, the magnitude of which is limited by parallel potential drops. These currents flow into and out of the ionosphere in the manner described by Iijima and Potemra. The higher-latitude (region 1) currents are associated with the boundary layer proper, while the lower-latitude (region 2) ones are associated with a region of sunward return flow adjacent to the boundary layer. The parallel potential drops have a magnitude of typically 2-3 kV and a north-south extent of 100-200 km. The calculated potential profile corresponds reasonably well to observed inverted V precipitation events.
Feasibility study of optical boundary layer transition detection method
NASA Technical Reports Server (NTRS)
Azzazy, M.; Modarress, D.; Trolinger, J. D.
1986-01-01
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.
Direct Numerical Simulations of Very Stable Atmospheric Boundary Layers
2012-01-10
Ekman boundary layers. Very high resolution, three-dimensional, time-dependent simulations are carried out on computational grids of the order of...turbulent Ekman layers", Annual Meeting of the Division of Fluid Dynamics of the American Physical Society, Long Beach. O Flores and JJ Riley. August...September, 2011. "DNS of a strati ed Ekman layer with a capping inversion", 13th European Turbulence Conference, Warsaw, Poland. Number of
Nature, theory and modelling of geophysical convective planetary boundary layers
NASA Astrophysics Data System (ADS)
Zilitinkevich, Sergej
2015-04-01
Geophysical convective planetary boundary layers (CPBLs) are still poorly reproduced in oceanographic, hydrological and meteorological models. Besides the mean flow and usual shear-generated turbulence, CPBLs involve two types of motion disregarded in conventional theories: 'anarchy turbulence' comprised of the buoyancy-driven plumes, merging to form larger plumes instead of breaking down, as postulated in conventional theory (Zilitinkevich, 1973), large-scale organised structures fed by the potential energy of unstable stratification through inverse energy transfer in convective turbulence (and performing non-local transports irrespective of mean gradients of transporting properties). C-PBLs are strongly mixed and go on growing as long as the boundary layer remains unstable. Penetration of the mixed layer into the weakly turbulent, stably stratified free flow causes turbulent transports through the CPBL outer boundary. The proposed theory, taking into account the above listed features of CPBL, is based on the following recent developments: prognostic CPBL-depth equation in combination with diagnostic algorithm for turbulence fluxes at the CPBL inner and outer boundaries (Zilitinkevich, 1991, 2012, 2013; Zilitinkevich et al., 2006, 2012), deterministic model of self-organised convective structures combined with statistical turbulence-closure model of turbulence in the CPBL core (Zilitinkevich, 2013). It is demonstrated that the overall vertical transports are performed mostly by turbulence in the surface layer and entrainment layer (at the CPBL inner and outer boundaries) and mostly by organised structures in the CPBL core (Hellsten and Zilitinkevich, 2013). Principal difference between structural and turbulent mixing plays an important role in a number of practical problems: transport and dispersion of admixtures, microphysics of fogs and clouds, etc. The surface-layer turbulence in atmospheric and marine CPBLs is strongly enhanced by the velocity shears in
The Boundary Layer Late Afternoon and Sunset Turbulence Project
NASA Astrophysics Data System (ADS)
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
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
Diamagnetic boundary layers - A kinetic theory. [for collisionless magnetized plasmas
NASA Technical Reports Server (NTRS)
Lemaire, J.; Burlaga, L. F.
1976-01-01
A kinetic theory is presented for boundary layers associated with MHD tangential 'discontinuities' in a collisionless magnetized plasma, such as those observed in the solar wind. The theory consists of finding self-consistent solutions of Vlasov's equation and Maxwell's equation for stationary one-dimensional boundary layers separating two Maxwellian plasma states. Layers in which the current is carried by electrons are found to have a thickness of the order of a few electron gyroradii, but the drift speed of the current-carrying electrons is found to exceed the Alfven speed, and accordingly such layers are not stable. Several types of layers in which the current is carried by protons are discussed; in particular, cases are considered in which the magnetic-field intensity, direction, or both, changed across the layer. In every case, the thickness was of the order of a few proton gyroradii, and the field changed smoothly, although the characteristics depended somewhat on the boundary conditions. The drift speed was always less than the Alfven speed, consistent with stability of such structures. These results are consistent with observations of boundary layers in the solar wind near 1 AU.
Vortex Generators to Control Boundary Layer Interactions
NASA Technical Reports Server (NTRS)
Babinsky, Holger (Inventor); Loth, Eric (Inventor); Lee, Sang (Inventor)
2014-01-01
Devices for generating streamwise vorticity in a boundary includes various forms of vortex generators. One form of a split-ramp vortex generator includes a first ramp element and a second ramp element with front ends and back ends, ramp surfaces extending between the front ends and the back ends, and vertical surfaces extending between the front ends and the back ends adjacent the ramp surfaces. A flow channel is between the first ramp element and the second ramp element. The back ends of the ramp elements have a height greater than a height of the front ends, and the front ends of the ramp elements have a width greater than a width of the back ends.
Shannon, H.D.; Young, G.S.; Yates, M.; Fuller, Mark R.; Seegar, W.
2003-01-01
An examination of boundary-layer meteorological and avian aerodynamic theories suggests that soaring birds can be used to measure the magnitude of vertical air motions within the boundary layer. These theories are applied to obtain mixed-layer normalized thermal updraft intensity over both flat and complex terrain from the climb rates of soaring American white pelicans and from diagnostic boundary-layer model-produced estimates of the boundary-layer depth zi and the convective velocity scale w*. Comparison of the flatland data with the profiles of normalized updraft velocity obtained from previous studies reveals that the pelican-derived measurements of thermal updraft intensity are in close agreement with those obtained using traditional research aircraft and large eddy simulation (LES) in the height range of 0.2 to 0.8 zi. Given the success of this method, the profiles of thermal vertical velocity over the flatland and the nearby mountains are compared. This comparison shows that these profiles are statistically indistinguishable over this height range, indicating that the profile for thermal updraft intensity varies little over this sample of complex terrain. These observations support the findings of a recent LES study that explored the turbulent structure of the boundary layer using a range of terrain specifications. For terrain similar in scale to that encountered in this study, results of the LES suggest that the terrain caused less than an 11% variation in the standard deviation of vertical velocity.
Surface modes in sheared boundary layers over impedance linings
NASA Astrophysics Data System (ADS)
Brambley, E. J.
2013-08-01
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.
An investigation of streaklike instabilities in laminar boundary layer flames
NASA Astrophysics Data System (ADS)
Miller, Colin; Finney, Mark; Forthofer, Jason; McAllister, Sara; Gollner, Michael
2016-11-01
Observations of coherent structures in boundary layer flames, particularly wildland fires, motivated an investigation on flame instabilities within a boundary layer. This experimental study examined streaklike structures in a stationary diffusion flame stabilized within a laminar boundary layer. Flame streaks were found to align with pre-existing velocity perturbations, enabling stabilization of these coherent structures. Thermocouple measurements were used to quantify streamwise amplification of flame streaks. Temperature mapping indicated a temperature rise in the flame streaks, while the region in between these streaks, the trough, decreased in temperature. The heat flux to the surface was measured with a total heat flux gauge, and the heat flux below the troughs was found to be higher at all measurement locations. This was likely a function of the flame standoff distance, and indicated that the flame streaks were acting to modify the spanwise distribution of heat flux. Instabilities in boundary layer combustion can have an effect on the spanwise distribution of heat transfer. This finding has significant implications for boundary layer combustion, indicating that instantaneous properties can vary significantly in a three-dimensional flow field.
Particle motion in atmospheric boundary layers of Mars and Earth
NASA Technical Reports Server (NTRS)
White, B. R.; Iversen, J. D.; Greeley, R.; Pollack, J. B.
1975-01-01
To study the eolian mechanics of saltating particles, both an experimental investigation of the flow field around a model crater in an atmospheric boundary layer wind tunnel and numerical solutions of the two- and three-dimensional equations of motion of a single particle under the influence of a turbulent boundary layer were conducted. Two-dimensional particle motion was calculated for flow near the surfaces of both Earth and Mars. For the case of Earth both a turbulent boundary layer with a viscous sublayer and one without were calculated. For the case of Mars it was only necessary to calculate turbulent boundary layer flow with a laminar sublayer because of the low values of friction Reynolds number; however, it was necessary to include the effects of slip flow on a particle caused by the rarefied Martian atmosphere. In the equations of motion the lift force functions were developed to act on a single particle only in the laminar sublayer or a corresponding small region of high shear near the surface for a fully turbulent boundary layer. The lift force functions were developed from the analytical work by Saffman concerning the lift force acting on a particle in simple shear flow.
Linear and nonlinear PSE for compressible boundary layers
NASA Technical Reports Server (NTRS)
Chang, Chau-Lyan; Malik, Mujeeb R.; Erlebacher, Gordon; Hussaini, M. Yousuff
1993-01-01
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.
The inner core thermodynamics of the tropical cyclone boundary layer
NASA Astrophysics Data System (ADS)
Williams, Gabriel J.
2016-10-01
Although considerable progress has been made in understanding the inner-core dynamics of the tropical cyclone boundary layer (TCBL), our knowledge of the inner-core thermodynamics of the TCBL remains limited. In this study, the inner-core budgets of potential temperature (θ), specific humidity ( q), and reversible equivalent potential temperature (θ _e) are examined using a high-resolution multilevel boundary layer model. The potential temperature budgets show that the heat energy is dominated by latent heat release in the eyewall, evaporative cooling along the outer edge of the eyewall, and upward surface fluxes of sensible and latent heat from the underlying warm ocean. It is shown that the vertical θ advection overcompensates the sum of radial advective warming from the boundary layer outflow jet and latent heating for the development of cooling in the eyewall within the TCBL. The moisture budgets show the dominant upward transport of moisture in the eyewall updrafts, partly by the boundary-layer outflow jet from the bottom eye region, so that the eyewall remains nearly saturated. The θ _e budgets reveal that the TCBL is maintained thermodynamically by the upward surface flux of higher-θ _e air from the underlying warm ocean, the radial transport of low-θ _e air from the outer regions of the TCBL, and the dry adiabatic cooling associated by eyewall updrafts. These results underscore the significance of vertical motion and the location of the boundary layer outflow jet in maintaining the inner core thermal structure of the TCBL.
A simplified Reynolds stress model for unsteady turbulent boundary layers
NASA Technical Reports Server (NTRS)
Fan, Sixin; Lakshminarayana, Budugur
1993-01-01
A simplified Reynolds stress model has been developed for the prediction of unsteady turbulent boundary layers. By assuming that the net transport of Reynolds stresses is locally proportional to the net transport of the turbulent kinetic energy, the time dependent full Reynolds stress model is reduced to a set of ordinary differential equations. These equations contain only time derivatives and can be readily integrated in a time dependent boundary layer or Navier-Stokes code. The turbulent kinetic energy and dissipation rate needed for the model are obtained by solving the k-epsilon equations. This simplified Reynolds stress turbulence model (SRSM) does not use the eddy viscosity assumption, which may not be valid for unsteady turbulent flows. The anisotropy of both the steady and the unsteady turbulent normal stresses can be captured by the SRSM model. Through proper damping of the shear stresses, the present model can be used in the near wall region of turbulent boundary layers. This model has been validated against data for steady and unsteady turbulent boundary layers, including periodic turbulent boundary layers subjected to a mean adverse pressure gradient. For the cases tested, the predicted unsteady velocity and turbulent stress components agree well with the experimental data. Comparison between the predictions from the SRSM model and a k-epsilon model is also presented.
Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.; Smeltzer, Stanley S., III
2000-01-01
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.
Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.; Smeltzer, Stanley S., III
2000-01-01
An analytical, parametric study of the attenuation of bending boundary layers or edge effects in balanced and unbalanced, symmetrically and unsymmetrically laminated thin cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize and quantify the effects of laminate orthotropy and laminate anisotropy on the bending boundary-layer decay length in a very general and encompassing manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all the laminate constructions considered, the results show that the differences between results that were obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that in some cases neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and in other cases it results in an overestimation.
NASA Technical Reports Server (NTRS)
Vanness, W.
1978-01-01
A summary report of boundary layer studies is presented. Preliminary results of experimental measurements show that: (1) A very thin layer (approximately 0.4 mm) of the boundary layer seems to be accelerated; (2) the static pressure of the outer flow does not remain exactly constant through the boundary layer; and (3) an oncoming boundary layer which is already turbulent at the suction point can again become laminar behind this point without being completely sucked off.
Interferometric data for a shock-wave/boundary-layer interaction
NASA Technical Reports Server (NTRS)
Dunagan, Stephen E.; Brown, James L.; Miles, John B.
1986-01-01
An experimental study of the axisymmetric shock-wave / boundary-layer strong interaction flow generated in the vicinity of a cylinder-cone intersection was conducted. The study data are useful in the documentation and understanding of compressible turbulent strong interaction flows, and are part of a more general effort to improve turbulence modeling for compressible two- and three-dimensional strong viscous/inviscid interactions. The nominal free stream Mach number was 2.85. Tunnel total pressures of 1.7 and 3.4 atm provided Reynolds number values of 18 x 10(6) and 36 x 10(6) based on model length. Three cone angles were studied giving negligible, incipient, and large scale flow separation. The initial cylinder boundary layer upstream of the interaction had a thickness of 1.0 cm. The subsonic layer of the cylinder boundary layer was quite thin, and in all cases, the shock wave penetrated a significant portion of the boundary layer. Owing to the thickness of the cylinder boundary layer, considerable structural detail was resolved for the three shock-wave / boundary-layer interaction cases considered. The primary emphasis was on the application of the holographic interferometry technique. The density field was deduced from an interferometric analysis based on the Able transform. Supporting data were obtained using a 2-D laser velocimeter, as well as mean wall pressure and oil flow measurements. The attached flow case was observed to be steady, while the separated cases exhibited shock unsteadiness. Comparisons with Navier-Stokes computations using a two-equation turbulence model are presented.
Spectral scales in the atmospheric boundary layer
NASA Technical Reports Server (NTRS)
Weber, A. H.; Irwin, J. S.; Mathis, J. J., Jr.; Kahler, J. P.; Petersen, W. B.
1982-01-01
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.
Stability of the Boundary Layer and the Spot
NASA Technical Reports Server (NTRS)
Wygnanski, I.
2007-01-01
The similarity among turbulent spots observed in various transition experiments, and the rate in which they contaminate the surrounding laminar boundary layer is only cursory. The shape of the spot depends on the Reynolds number of the surrounding boundary layer and on the pressure gradient to which it and the surrounding laminar flow are exposed. The propagation speeds of the spot boundaries depend, in addition, on the location from which the spot originated and do not simply scale with the local free stream velocity. The understanding of the manner in which the turbulent manner in which the turbulent spot destabilizes the surrounding, vortical fluid is a key to the understanding of the transition process. We therefore turned to detailed observations near the spot boundaries in general and near the spanwise tip of the spot in particular.
Churchfield, M. J.; Michalakes, J.; Vanderwende, B.; Lee, S.; Sprague, M. A.; Lundquist, J. K.; Moriarty, P. J.
2013-10-01
Wind plant aerodynamics are directly affected by the microscale weather, which is directly influenced by the mesoscale weather. Microscale weather refers to processes that occur within the atmospheric boundary layer with the largest scales being a few hundred meters to a few kilometers depending on the atmospheric stability of the boundary layer. Mesoscale weather refers to large weather patterns, such as weather fronts, with the largest scales being hundreds of kilometers wide. Sometimes microscale simulations that capture mesoscale-driven variations (changes in wind speed and direction over time or across the spatial extent of a wind plant) are important in wind plant analysis. In this paper, we present our preliminary work in coupling a mesoscale weather model with a microscale atmospheric large-eddy simulation model. The coupling is one-way beginning with the weather model and ending with a computational fluid dynamics solver using the weather model in coarse large-eddy simulation mode as an intermediary. We simulate one hour of daytime moderately convective microscale development driven by the mesoscale data, which are applied as initial and boundary conditions to the microscale domain, at a site in Iowa. We analyze the time and distance necessary for the smallest resolvable microscales to develop.
Hypersonic flow separation in shock wave boundary layer interactions
NASA Technical Reports Server (NTRS)
Hamed, A.; Kumar, Ajay
1992-01-01
An assessment is presented for the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists mainly of two dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the subsequent changes in the flow empirical correlations for incipient separation are reviewed. The effects of the Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed. The pertinent experimental data for the separated flow characteristics in separated turbulent boundary layer shock interaction are also presented and discussed.
Atmospheric boundary layer processes during a total solar eclipse
SethuRaman, S.; Prabhu, A.; Narahari Rao, K.; Narasimha, R.
1980-01-01
The total solar eclipse that occurred over the southern part of India on February 16, 1980, gave a unique opportunity to study the earth's atmospheric boundary layer. The meteorological experiments during the 1980 solar eclipse were conducted at Raichur, India (16/sup 0/12'N, 77/sup 0/21'E) located in the state of Karnataka, approximately 400-m above sea level. The main objective was to determine the changes in the earth's atmosphere during and immediately after the eclipse. The goal was to study the changes in the momentum and heat fluxes in the boundary layer due to the eclipse. Measurements were made for 2 days prior to and 1 day after the day of the eclipse to determine background characteristics of the boundary layer which might be site-dependent.
Bypass transition and spot nucleation in boundary layers
NASA Astrophysics Data System (ADS)
Kreilos, Tobias; Khapko, Taras; Schlatter, Philipp; Duguet, Yohann; Henningson, Dan S.; Eckhardt, Bruno
2016-08-01
The spatiotemporal aspects of the transition to turbulence are considered in the case of a boundary-layer flow developing above a flat plate exposed to free-stream turbulence. Combining results on the receptivity to free-stream turbulence with the nonlinear concept of a transition threshold, a physically motivated model suggests a spatial distribution of spot nucleation events. To describe the evolution of turbulent spots a probabilistic cellular automaton is introduced, with all parameters directly obtained from numerical simulations of the boundary layer. The nucleation rates are then combined with the cellular automaton model, yielding excellent quantitative agreement with the statistical characteristics for different free-stream turbulence levels. We thus show how the recent theoretical progress on transitional wall-bounded flows can be extended to the much wider class of spatially developing boundary-layer flows.
Effect of bulk viscosity on a hypersonic boundary layer
NASA Astrophysics Data System (ADS)
Emanuel, George
1992-03-01
The bulk viscosity mu(b) is generally set equal to zero (Stokes' hypothesis). For certain gases, such as CO2, mu(b)/mu exceeds 1000, where mu is the shear viscosity. In this circumstance, the bulk viscosity may substantially alter a hypersonic boundary layer. A general, nonsimilar, laminar, boundary-layer formulation is provided in which the bulk viscosity terms are included as a correction. To obtain explicit results, flow over a flat plate is considered. In addition to the heat transfer, the transverse pressure gradient inside the boundary layer is not zero, whereas the skin friction is unaltered by the bulk viscosity. This analysis is relevant to aerogravity-assisted maneuvers in planetary atmospheres that largely consist of CO2.
Effect of bulk viscosity on a hypersonic boundary layer
NASA Astrophysics Data System (ADS)
Emanuel, George
1992-03-01
The bulk viscosity μb is generally set equal to zero (Stokes' hypothesis). For certain gases, such as CO2, μb/μ exceeds 103, where μ is the shear viscosity. In this circumstance, the bulk viscosity may substantially alter a hypersonic boundary layer. A general, nonsimilar, laminar, boundary-layer formulation is provided in which the bulk viscosity terms are included as a correction. To obtain explicit results, flow over a flat plate is considered. In addition to the heat transfer, the transverse pressure gradient inside the boundary layer is not zero, whereas the skin friction is unaltered by the bulk viscosity. This analysis is relevant to aerogravity-assisted maneuvers in planetary atmospheres that largely consist of CO2.
Spatial Optimal Disturbances in Three-Dimensional Boundary Layers
NASA Astrophysics Data System (ADS)
Tempelmann, David; Hanifi, Ardeshir; Henningson, Dan S.
A parabolised set of equations is used to compute spatial optimal disturbances in Falkner-Skan-Cooke boundary layers. These disturbances associated with maximum energy growth initially take the form of vortices which are tilted against the direction of the mean crossflow shear. They evolve into bended streaks while traveling downstream and finally into crossflow disturbances when entering the supercritical domain of the boundary layer. Two physical mechanisms, namely the lift-up and the Orr-mechanism, can be identified as being responsible for nonmodal growth in three-dimensional boundary layers. A parametric study is presented where, amongst others, the influences of pressure gradient and sweep angle on optimal growth are investigated. It turns out that substantial disturbance growth is already found in regions of the flow where modal disturbances are damped.
Effects of forebody geometry on subsonic boundary-layer stability
NASA Technical Reports Server (NTRS)
Dodbele, Simha S.
1990-01-01
As part of an effort to develop computational techniques for design of natural laminar flow fuselages, a computational study was made of the effect of forebody geometry on laminar boundary layer stability on axisymmetric body shapes. The effects of nose radius on the stability of the incompressible laminar boundary layer was computationally investigated using linear stability theory for body length Reynolds numbers representative of small and medium-sized airplanes. The steepness of the pressure gradient and the value of the minimum pressure (both functions of fineness ratio) govern the stability of laminar flow possible on an axisymmetric body at a given Reynolds number. It was found that to keep the laminar boundary layer stable for extended lengths, it is important to have a small nose radius. However, nose shapes with extremely small nose radii produce large pressure peaks at off-design angles of attack and can produce vortices which would adversely affect transition.
Interacting turbulent boundary layer over a wavy wall
NASA Technical Reports Server (NTRS)
Polak, A.; Werle, M. J.
1977-01-01
This paper is concerned with the two-dimensional supersonic flow of a thick turbulent boundary layer over a train of relatively small wave-like protuberances. The flow conditions and the geometry are such that there exists a strong interaction between the viscous and inviscid flow. The problem cannot be solved without inclusion of interaction effects due to the occurrence of the separation singularity in classical boundary layer methods. Here the interacting boundary layer equations are solved numerically using a time-like relaxation method with turbulence effects represented by the inclusion of the eddy viscosity model of Cebeci and Smith. Results are presented for flow over a train of up to six waves for Mach numbers of 2.5 and 3.5, Reynolds numbers of 10,000,000/m and 32,000,000/m, and wall temperature ratios of 0.4 and 0.8. Limited comparisons with independent experimental and analytical results are also given.
Supersonic separated turbulent boundary - layer over a wavy wall
NASA Technical Reports Server (NTRS)
Polak, A.; Werle, M. J.
1977-01-01
A prediction method is developed for calculating distributions of surface heating rates, pressure and skin friction over a wavy wall in a two-dimensional supersonic flow. Of particular interest is the flow of thick turbulent boundary layers. The surface geometry and the flow conditions considered are such that there exists a strong interaction between the viscous and inviscid flow. First, using the interacting turbulent boundary layer equations, the problem is formulated in physical coordinates and then a reformulation of the governing equations in terms of Levy-Lees variables is given. Next, a numerical scheme for solving interacting boundary layer equations is adapted. A number of modifications which led to the improvement of the numerical algorithm are discussed. Finally, results are presented for flow over a train of up to six waves at various flow conditions.
Lag model for turbulent boundary layers over rough bleed surfaces
NASA Astrophysics Data System (ADS)
Lee, J.; Sloan, M. L.; Paynter, G. C.
1994-07-01
Boundary-layer mass removal (bleed) through spanwise bands of holes on a surface is used to prevent or control separation and to stabilize the normal shock in supersonic inlets. The addition of a transport equation lag relationship for eddy viscosity to the rough wall algebraic turbulence model of Cebeci and Chang was found to improve agreement between predicted and measured mean velocity distributions downstream of a bleed band. The model was demonstrated for a range of bleed configurations, bleed rates, and local freestream Mach numbers. In addition, the model was applied to the boundary-layer development over acoustic lining materials for the inlets and nozzles of commercial aircraft. The model was found to yield accurate results for integral boundary-layer properties unless there was a strong adverse pressure gradient.
The analysis of a nonsimilar laminar boundary layer
NASA Technical Reports Server (NTRS)
Stalmach, D. D.; Bertin, J. J.
1978-01-01
A computer code is described which yields accurate solutions for a broad range of laminar, nonsimilar boundary layers, providing the inviscid flow field is known. The boundary layer may be subject to mass injection for perfect-gas, nonreacting flows. If no mass injection is present, the code can be used with either perfect-gas or real-gas thermodynamic models. Solutions, ranging from two-dimensional similarity solutions to solutions for the boundary layer on the Space Shuttle Orbiter during reentry conditions, have been obtained with the code. Comparisons of these solutions, and others, with solutions presented in the literature; and with solutions obtained from other codes, demonstrate the accuracy of the present code.
Simple turbulence models and their application to boundary layer separation
NASA Technical Reports Server (NTRS)
Wadcock, A. J.
1980-01-01
Measurements in the boundary layer and wake of a stalled airfoil are presented in two coordinate systems, one aligned with the airfoil chord, the other being conventional boundary layer coordinates. The NACA 4412 airfoil is studied at a single angle of attack corresponding to maximum lift, the Reynolds number based on chord being 1.5 x 10 to the 6th power. Turbulent boundary layer separation occurred at the 85 percent chord position. The two-dimensionality of the flow was documented and the momentum integral equation studied to illustrate the importance of turbulence contributions as separation is approached. The assumptions of simple eddy-viscosity and mixing-length turbulence models are checked directly against experiment. Curvature effects are found to be important as separation is approached.
Finite volume solution of the compressible boundary-layer equations
NASA Technical Reports Server (NTRS)
Loyd, B.; Murman, E. M.
1986-01-01
A box-type finite volume discretization is applied to the integral form of the compressible boundary layer equations. Boundary layer scaling is introduced through the grid construction: streamwise grid lines follow eta = y/h = const., where y is the normal coordinate and h(x) is a scale factor proportional to the boundary layer thickness. With this grid, similarity can be applied explicity to calculate initial conditions. The finite volume method preserves the physical transparency of the integral equations in the discrete approximation. The resulting scheme is accurate, efficient, and conceptually simple. Computations for similar and non-similar flows show excellent agreement with tabulated results, solutions computed with Keller's Box scheme, and experimental data.
Numerical Simulations of Wake/Boundary Layer Interactions
NASA Technical Reports Server (NTRS)
Piomelli, Ugo; Choudhari, Meelan M.; Ovchinnikov, Victor; Balaras, Elias
2003-01-01
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.
Separation criteria for three-dimensional boundary-layer calculations
NASA Astrophysics Data System (ADS)
Raven, H. C.
1984-04-01
The behavior of the numerical solution of the boundary-layer equations for 3D viscous flow around streamlined objects in the vicinity of separation-line singularities is investigated. The turbulent boundary layer on a 35-deg swept wing of infinite span is analyzed using the finite-difference-method boundary-layer program described by Raven (1980) and a spanwise-marching approach. A discontinuity in the displacement thickness and other characteristics at the separation line is shown to produce a forbidden region within which the calculated results are grid dependent and may be physically meaningless. The use of local grid refinement to evaluate separation singularities and identify erroneous results is recommended.
Boundary layer effects on particle impaction and capture
NASA Technical Reports Server (NTRS)
Rosner, D. E.; Fernandez De La Mora, J.
1984-01-01
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.
High-enthalpy shock/boundary-layer interaction on a double wedge
NASA Astrophysics Data System (ADS)
Davis, Jean-Paul
1999-11-01
Interaction between a shock wave and a boundary layer at a compression corner can produce a region of separated flow. The length of separation is important in determining aerodynamic forces, and the heat transfer at reattachment is important for the design of thermal protection systems. The effects of high-enthalpy flow on these phenomenon, particularly separation length, are not well known. Experiments to measure separation length and reattachment heating are performed in the T5 Hypervelocity Shock Tunnel using nitrogen test gas and a double-wedge geometry which allows greater control over local flow conditions at separation and, at high incidence angle, may produce real-gas effects due to dissociation behind the leading shock. Local external flow conditions were found by computational reconstruction of the inviscid nonequilibrium flow field.Application of results from asymptotic theory to a simple model for separation leads to a new scaling parameter which approximately accounts for wall temperature effects on separation length for a laminar nonreacting boundary layer and extends previous results to arbitrary viscosity law. A. classification is introduced which divides mechanisms for real-gas effects into those acting internal and external to viscous regions of the flow, with internal mechanisms further subdivided into those arising upstream and downstream of separation. Application of the ideal dissociating gas model to a scaling law based on local external flow parameters and a nonreacting boundary layer shows that external mechanisms due to dissociation decrease separation length at low incidence but depend on the free-stream dissociation at high incidence, and have only a small effect on peak heating. A limited numerical study of reacting boundary layers shows that internal mechanisms due to recombination in the upstream boundary layer cause a slight decrease in separation length and a large increase in heat flux relative to a nonreacting boundary layer with
Instability of a Supersonic Boundary-Layer with Localized Roughness
NASA Technical Reports Server (NTRS)
Marxen, Olaf; Iaccarino, Gianluca; Shaqfeh, Eric S. G.
2010-01-01
A localized 3-D roughness causes boundary-layer separation and (weak) shocks. Most importantly, streamwise vortices occur which induce streamwise (low U, high T) streaks. Immersed boundary method (volume force) suitable to represent roughness element in DNS. Favorable comparison between bi-global stability theory and DNS for a "y-mode" Outlook: Understand the flow physics (investigate "z-modes" in DNS through sinuous spanwise forcing, study origin of the beat in DNS).
Unsteady turbulent boundary layers in swimming rainbow trout.
Yanase, Kazutaka; Saarenrinne, Pentti
2015-05-01
The boundary layers of rainbow trout, Oncorhynchus mykiss, swimming at 1.02±0.09 L s(-1) (mean±s.d., N=4), were measured by the particle image velocimetry (PIV) technique at a Reynolds number of 4×10(5). The boundary layer profile showed unsteadiness, oscillating above and beneath the classical logarithmic law of the wall with body motion. Across the entire surface regions that were measured, local Reynolds numbers based on momentum thickness, which is the distance that is perpendicular to the fish surface through which the boundary layer momentum flows at free-stream velocity, were greater than the critical value of 320 for the laminar-to-turbulent transition. The skin friction was dampened on the convex surface while the surface was moving towards a free-stream flow and increased on the concave surface while retreating. These observations contradict the result of a previous study using different species swimming by different methods. Boundary layer compression accompanied by an increase in local skin friction was not observed. Thus, the overall results may not support absolutely the Bone-Lighthill boundary layer thinning hypothesis that the undulatory motions of swimming fish cause a large increase in their friction drag because of the compression of the boundary layer. In some cases, marginal flow separation occurred on the convex surface in the relatively anterior surface region, but the separated flow reattached to the fish surface immediately downstream. Therefore, we believe that a severe impact due to induced drag components (i.e. pressure drag) on the swimming performance, an inevitable consequence of flow separation, was avoided.
Additive thermochemical effects in turbulent erosive boundary layers
Buckingham, A.C.; Levatin, J.L.
1983-01-18
Previously obtained interior ballistics and wall boundary layer modeling results indicate that significant reduction in erosive heating can be expected when finely divided particles are dispersed through the propellant combustion flow field. Attention was first placed on the particle size influences, together with particle dispersal dynamics in both turbulent combustion core flow and the erosive wall boundary layer region. Submicron thermochemically inert particles were predicted to disperse readily to the near wall region where they were then entrained in the boundary layer. This was estimated to substantially reduce the predicted erosive heat and mass transfer and experimentally confirmed. Examination of the time-averaged turbulent boundary layer macrostructure changes indicated that inertial influences were primarily responsible for this reduction in erosive heating to gun barrel walls. The boundary layers were thickened by the additives and erosive diffusion gradients were correspondingly reduced. The isolated inertial mechanisms are now understood but are difficult to apply in general dimensional analysis scaling or in analytical heat transfer correlation predictions. Three major factors which contribute to these difficulties are: time dependence of both developing mean flow and particle field; turbulence-particle interactions; and thermochemical heat release and exchange between reactive gas components and particles, particles and wall surface, and reactive gas and wall surface. To help illustrate the influence of thes mechanisms and provide a basis for prediction, the influence of submicron additives in unsteady turbulent boundary layer growth and interaction regions adjacent to a model of a chemically active metallic (steel) surface are examined. Equilibrium chemistry is assumed for all phases.
Direct numerical simulation of turbulent boundary layer with constant thickness
NASA Astrophysics Data System (ADS)
Yao, Yichen; Xu, Chunxiao; Huang, Weixi
2016-11-01
Direct numerical simulation is performed to turbulent boundary layer (TBL) with constant thickness at Reθ = 1420 . Periodic boundary condition is applied in the streamwise direction, and a mean body force equivalent to the convection term in the mean momentum equation is imposed in this direction. The body force is calculated using the published TBL data of Schlatter and Orlu (2010) at Reθ = 1420 . The presently simulated TBL is compared with the conventional TBL and turbulent channel flow at the prescribed Reynolds number. The turbulent statistics agrees well with that of Schlatter and Orlu (2010). The pre-multiplied energy spectra in current simulation also present high similarity with the conventional TBL, while differ obviously with those in turbulent channel. The successful replication of turbulent boundary in the current simulation provides an alternative method for boundary layer simulation with much less computational cost. Meanwhile, in aspect of both turbulent statistics and flow structures, the current results indicate that the differences between turbulent channel and boundary layer flow mainly caused by the discrepancy in driving force distribution rather than the periodic boundary restriction. National Natural Science Foundation of China (Project No. 11490551, 11472154, 11322221, 11132005).
Numerical Modeling of the Evolving Stable Boundary Layer
NASA Astrophysics Data System (ADS)
Sorbjan, Z.
2013-12-01
A single-column model of the evolving stable boundary layer is tested for the consistency of turbulence parameterization, self-similar properties of the flow, and effects of ambient forcing. The turbulence closure of the model is based on the K-theory approach, with stability functions based on empirical data, and a semi-empirical form of the mixing length. The model has one internal, governing stability parameter, the Richardson number Ri, which dynamically adjusts to the boundary conditions and to external forcing. Model results, expressed in terms of local similarity scales, are universal functions of the Richardson number, i.e. they are satisfied in the entire stable boundary layer, for all instants of time, and all kinds of external forcing. Based on similarity expression, a realizability condition is derived for the minimum turbulent heat flux in the stable boundary layer. Numerical experiments show that the development of 'horse-shoe' shaped, 'fixed-elevation' wind hodographs in the interior of the stable boundary layer are solely caused by effects imposed by surface thermal forcing, and are not related to the inertial oscillation mechanism.
An Innovative Flow-Measuring Device: Thermocouple Boundary Layer Rake
NASA Technical Reports Server (NTRS)
Hwang, Danny P.; Fralick, Gustave C.; Martin, Lisa C.; Wrbanek, John D.; Blaha, Charles A.
2001-01-01
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.
Non-Equilibrium Effects on Hypersonic Turbulent Boundary Layers
NASA Astrophysics Data System (ADS)
Kim, Pilbum
Understanding non-equilibrium effects of hypersonic turbulent boundary layers is essential in order to build cost efficient and reliable hypersonic vehicles. It is well known that non-equilibrium effects on the boundary layers are notable, but our understanding of the effects are limited. The overall goal of this study is to improve the understanding of non-equilibrium effects on hypersonic turbulent boundary layers. A new code has been developed for direct numerical simulations of spatially developing hypersonic turbulent boundary layers over a flat plate with finite-rate reactions. A fifth-order hybrid weighted essentially non-oscillatory scheme with a low dissipation finite-difference scheme is utilized in order to capture stiff gradients while resolving small motions in turbulent boundary layers. The code has been validated by qualitative and quantitative comparisons of two different simulations of a non-equilibrium flow and a spatially developing turbulent boundary layer. With the validated code, direct numerical simulations of four different hypersonic turbulent boundary layers, perfect gas and non-equilibrium flows of pure oxygen and nitrogen, have been performed. In order to rule out uncertainties in comparisons, the same inlet conditions are imposed for each species, and then mean and turbulence statistics as well as near-wall turbulence structures are compared at a downstream location. Based on those comparisons, it is shown that there is no direct energy exchanges between internal and turbulent kinetic energies due to thermal and chemical non-equilibrium processes in the flow field. Instead, these non-equilibria affect turbulent boundary layers by changing the temperature without changing the main characteristics of near-wall turbulence structures. This change in the temperature induces the changes in the density and viscosity and the mean flow fields are then adjusted to satisfy the conservation laws. The perturbation fields are modified according to
Turbulent boundary layer on perforated surfaces with vector injection
NASA Astrophysics Data System (ADS)
Eroshenko, V. M.; Zaichik, L. I.; Klimov, A. A.; Ianovskii, L. S.; Kondratev, V. I.
1980-10-01
The paper presents an experimental investigation of a turbulent boundary layer on perforated plates with uniform vector injection at various angles to gas flow. It was shown that with strong injection at angles oriented in the flow direction the intensity of turbulent pulsation is decreased, while injection at angles in the opposite direction increase the intensity. A relationship was established between the critical parameters of the boundary layer injection angles; it was concluded that the asymptotic theory of Kutateladze and Leontiev can be used for determining the coefficient of friction of vector injection.
Carbon vaporization into a nonequilibrium, stagnation-point boundary layer
NASA Technical Reports Server (NTRS)
Suzuki, T.
1978-01-01
The heat transfer to the stagnation point of an ablating carbonaceous heat shield, where both the gas-phase boundary layer and the heterogeneous surface reactions are not in chemical equilibrium, is examined. Specifically, the nonequilibrium changes in the mass fraction profiles of carbon species calculated for frozen flow are studied. A set of equations describing the steady-state, nonequilibrium laminar boundary layer in the axisymmetric stagnation region, over an ablating graphite surface, is solved, with allowance for the effects of finite rate of carbon vaporization.
Optimal disturbances and bypass transition in boundary layers
NASA Astrophysics Data System (ADS)
Andersson, Paul; Berggren, Martin; Henningson, Dan S.
1999-01-01
Streamwise streaks are ubiquitous in transitional boundary layers, particularly when subjected to high levels of free-stream turbulence. Using the steady boundary-layer approximation, the upstream disturbances experiencing maximum spatial energy growth are numerically calculated. The calculations use techniques commonly employed when solving optimal-control problems for distributed parameter systems. The calculated optimal disturbances consist of streamwise vortices developing into streamwise streaks. The maximum spatial energy growth was found to scale linearly with the distance from the leading edge. Based on these results, a simple model for prediction of transition location is proposed. Available experiments have been used to correlate the single constant appearing in the model.
Characteristics of turbulence in boundary layer with zero pressure gradient
NASA Technical Reports Server (NTRS)
Klebanoff, P S
1955-01-01
The results of an experimental investigation of a turbulent boundary layer with zero pressure gradient are presented. Measurements with the hot-wire anemometer were made of turbulent energy and turbulent shear stress, probability density and flattening factor of u-fluctuation (fluctuation in x-direction), spectra of turbulent energy and shear stress, and turbulent dissipation. The importance of the region near the wall and the inadequacy of the concept of local isotropy are demonstrated. Attention is given to the energy balance and the intermittent character of the outer region of the boundary layer. Also several interesting features of the spectral distribution of the turbulent motions are discussed.
Lower Atmospheric Boundary Layer Experiment (LABLE) Final Campaign Report
Klein, P; Bonin, TA; Newman, JF; Turner, DD; Chilson, P; Blumberg, WG; Mishra, S; Wainwright, CE; Carney, M; Jacobsen, EP; Wharton, S
2015-11-01
The Lower Atmospheric Boundary Layer Experiment (LABLE) included two measurement campaigns conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site in Oklahoma during 2012 and 2013. LABLE was designed as a multi-phase, low-cost collaboration among the University of Oklahoma, the National Severe Storms Laboratory, Lawrence Livermore National Laboratory, and the ARM program. A unique aspect was the role of graduate students in LABLE. They served as principal investigators and took the lead in designing and conducting experiments using different sampling strategies to best resolve boundary-layer phenomena.
The high-order statistics of APG turbulent boundary layers
NASA Astrophysics Data System (ADS)
Maciel, Yvan; Gungor, Ayse G.; Simens, Mark P.; Soria, Julio
2013-11-01
One and two-point statistics are presented from a new direct numerical simulation of an adverse pressure gradient boundary layer, at Reθ = 250 - 2175 , in which the transition to turbulence is triggered by a trip wire which is modeled using the immersed boundary method. Mean velocity results in the attached turbulent region do not show log law profiles. Departure from the law of the wall occurs throughout the inner region. The production and Reynolds stress peaks move to roughly the middle of the boundary layer. The profiles of the uv correlation factor reveal that de-correlation between u and v takes place throughout the boundary layer, but especially near the wall, as the mean velocity defect increases. The non-dimensional stress ratios and quadrant analysis of uv indicate changes to the turbulence structure. The structure parameter is low, similar to equilibrium APG flows and mixing layers in the present flow and seems to be decreasing as the mean velocity defect increases. The statistics of the upper half of the APG flow show resemblance with results for a mixing layer. Funded in part by ITU, NSERC of Canada, ARC Discovery Grant, and Multiflow program of the ERC.
Magnetic field maxima in the low latitude boundary layer
NASA Technical Reports Server (NTRS)
Sonnerup, B.; Paschmann, G.; Phan, T.-D.; Luehr, H.
1992-01-01
The magnetic field often exhibits a maximum in the earth's low-latitude boundary layer. Examples of this behavior are shown using data from the AMPTE/IRM spacecraft, and it is argued 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 and (2) field curvature effects associated with undulations of the magnetopause itself.
Giant aeolian dune size determined by the average depth of the atmospheric boundary layer.
Andreotti, Bruno; Fourrière, Antoine; Ould-Kaddour, Fouzia; Murray, Brad; Claudin, Philippe
2009-02-26
Depending on the wind regime, sand dunes exhibit linear, crescent-shaped or star-like forms resulting from the interaction between dune morphology and sand transport. Small-scale dunes form by destabilization of the sand bed with a wavelength (a few tens of metres) determined by the sand transport saturation length. The mechanisms controlling the formation of giant dunes, and in particular accounting for their typical time and length scales, have remained unknown. Using a combination of field measurements and aerodynamic calculations, we show here that the growth of aeolian giant dunes, ascribed to the nonlinear interaction between small-scale superimposed dunes, is limited by the confinement of the flow within the atmospheric boundary layer. Aeolian giant dunes and river dunes form by similar processes, with the thermal inversion layer that caps the convective boundary layer in the atmosphere acting analogously to the water surface in rivers. In both cases, the bed topography excites surface waves on the interface that in turn modify the near-bed flow velocity. This mechanism is a stabilizing process that prevents the scale of the pattern from coarsening beyond the resonant condition. Our results can explain the mean spacing of aeolian giant dunes ranging from 300 m in coastal terrestrial deserts to 3.5 km. We propose that our findings could serve as a starting point for the modelling of long-term evolution of desert landscapes under specific wind regimes.
Giant aeolian dune size determined by the average depth of the atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Claudin, P.; Fourrière, A.; Andreotti, B.; Murray, A. B.
2009-12-01
Depending on the wind regime, sand dunes exhibit linear, crescent-shaped or star-like forms resulting from the interaction between dune morphology and sand transport. Small-scale dunes form by destabilization of the sand bed with a wavelength (a few tens of metres) determined by the sand transport saturation length. The mechanisms controlling the formation of giant dunes, and in particular accounting for their typical time and length scales, have remained unknown. Using a combination of field measurements and aerodynamic calculations, we show here that the growth of aeolian giant dunes, ascribed to the nonlinear interaction between small-scale superimposed dunes, is limited by the confinement of the flow within the atmospheric boundary layer. Aeolian giant dunes and river dunes form by similar processes, with the thermal inversion layer that caps the convective boundary layer in the atmosphere acting analogously to the water surface in rivers. In both cases, the bed topography excites surface waves on the interface that in turn modify the near-bed flow velocity. This mechanism is a stabilizing process that prevents the scale of the pattern from coarsening beyond the resonant condition. Our results can explain the mean spacing of aeolian giant dunes ranging from 300 m in coastal terrestrial deserts to 3.5 km. We propose that our findings could serve as a starting point for the modelling of long-term evolution of desert landscapes under specific wind regimes.
Experimental study of three shock wave/turbulent boundary layer interactions
NASA Technical Reports Server (NTRS)
Smits, Alexander J.; Muck, Kin-Choong
1987-01-01
The paper presents a systematic study of the supersonic flow of a turbulent boundary layer over several compression-corner models. The wind tunnel and the compression-corner models (ramps fitted with aerodynamic fences to minimize three-dimensional effects) were identical with those used by Settles et al. (1979); constant-temperature hot-wire anemometry was used for the mass-flow measurements. The turning angles used for the compression corners were 8, 16, and 20 deg. In all three flow cases, the shock wave/turbulent flow interaction did amplify the turbulent stresses dramatically, with amplification increasing with increasing turning angle. However, different stress components were amplified by different amounts.
MEMS flexible thermal flow sensor for measurement of boundary layer separation
NASA Astrophysics Data System (ADS)
Yu, Jui-Ming; Leu, Tzong-Shyng; Miau, Jiun-Jih; Chen, Shih-Jiun
2016-05-01
Micro-electro-mechanical systems (MEMS) thermal flow sensors featured with high spatial resolutions, fast frequency response and minimal interference with fluid flow have been applied widely in boundary-layer studies and aerodynamic flow sensing and control due to the inherent outstanding performances. In this study, MEMS thermal flow sensors were designed and fabricated on a flexible skin using the MEMS technology. The dimension of a single sensing element was 200 μm × 260 μm, which had a resistance of about 200 Ω after annealing. By configuring thermal flow sensors in either a single thermal flow sensor and a thermal tuft sensor, separation points of a two-dimensional (2D) LS(1) 0417 airfoil at various angles of attack could be precisely detected. The experimental results show good agreement with the hot wire sensor and particle traced flow visualization in detecting the separation point on the suction surface of the airfoil.
Designing and Testing a Blended Wing Body with Boundary Layer Ingestion Nacelles
NASA Technical Reports Server (NTRS)
Carter, Melissa B.; Campbell, Richard L.; Pendergraft, Odis C.; Underwood, Pamela J.; Friedman, Douglas M.; Serrano, Leonel
2006-01-01
A knowledge-based aerodynamic design method coupled with an unstructured grid Navier-Stokes flow solver was used to improve the propulsion/airframe integration for a Blended Wing Body with boundary-layer ingestion nacelles. A new zonal design capability was used that significantly reduced the time required to achieve a successful design for each nacelle and the elevon between them. A wind tunnel model was built with interchangeable parts reflecting the baseline and redesigned configurations and tested in the National Transonic Facility (NTF). Most of the testing was done at the cruise design conditions (Mach number = 0.85, Reynolds number = 75 million). In general, the predicted improvements in forces and moments as well as the changes in wing pressures between the baseline and redesign were confirmed by the wind tunnel results. The effectiveness of elevons between the nacelles was also predicted surprisingly well considering the crudeness in the modeling of the control surfaces in the flow code.
A General-Coordinate Formulation For Boundary-Layer Flow
NASA Technical Reports Server (NTRS)
Steger, Joseph L.; Van Dalsem, William R.; Panaras, Argyris G.; Rao, K. V.
1991-01-01
Formulation for solution of equations of boundary-layer flow in general body-fitted curvilinear coordinates retains velocities in Cartesian coordinates. Increases stability of numerical simulations by avoiding coordinate source terms. In formulation, curvilinear coordinates do not have to be orthogonal, and much of software developed previously for use in numerical simulations of flow based on Navier-Stokes equations used.
FLUID MODELING OF ATMOSPHERIC DISPERSION IN THE CONVECTIVE BOUNDARY LAYER
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...
Turbulent boundary layer measurements over high-porosity surfaces
NASA Astrophysics Data System (ADS)
Efstathiou, Christoph; Luhar, Mitul
2016-11-01
Porous surfaces are ubiquitous across a variety of turbulent boundary layer flows of scientific and engineering interest. While turbulent flows over smooth and rough walls have been studied extensively, experimental measurements over porous walls have thus far focused on packed beds, which are limited in porosity (Φ = 0 . 3 - 0 . 5) by their geometry. The current project seeks to address this limitation. A two-component laser doppler velocimeter (LDV) is used to generate velocity measurements in turbulent boundary layer flows over commercially available reticulated foams and 3D-printed porous media at Reynolds number Reθ 3000 - 4000 . Smooth wall profiles for mean and turbulent quantities are compared to data over substrates with porosity Φ > 0 . 8 and average pore sizes in the range 0.4-2.5mm (corresponding to 8 - 50 viscous units). Previous analytical and simulation efforts indicate that the effects of porous substrates on boundary layer flows depend on a modified Reynolds number defined using the length scale √{ κ}, where κ is substrate permeability. A custom permeameter is currently being developed to estimate κ for the substrates tested in the boundary layer experiments.
Turbulent Boundary Layer on a Cylinder in Axial Flow
1988-09-29
wall- norma 6caling or Rao’s wall-normal scaling. Other measurements of the mean velocity in a cylindrical boundary layer should be mentioned for...located near the wall at three azimuthal locations that wre 900 apa ,-t and at several streamwise spacings for flow conditions resulting in 8/a=8
Stability of Supersonic Boundary Layers Over Blunt Wedges
NASA Technical Reports Server (NTRS)
Balakumar, Ponnampalam
2006-01-01
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.
Three dimensional boundary layers on submarine conning towers and rudders
NASA Astrophysics Data System (ADS)
Gleyzes, C.
1988-01-01
Solutions for the definition of grids adapted to the calculation of three-dimensional boundary layers on submarine conning towers and on submarine rudders and fins are described. The particular geometry of such bodies (oblique shaped hull, curved fins) required special adaptations. The grids were verified on examples from a test basin.
ON HYDROMAGNETIC STRESSES IN ACCRETION DISK BOUNDARY LAYERS
Pessah, Martin E.; Chan, Chi-kwan E-mail: ckch@nordita.org
2012-05-20
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.
Passive hypervelocity boundary layer control using an ultrasonically absorptive surface
NASA Astrophysics Data System (ADS)
Rasheed, Adam
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 would damp the second mode (Mack mode). The cone used in the experiments was constructed with a smooth surface on half the cone (to serve as a control) and an acoustically absorptive porous surface on the other half. It was instrumented with flush-mounted thermocouples to detect the transition location. Test gases investigated included nitrogen and carbon dioxide at Mach 5 with specific reservoir enthalpy ranging from 1.3 MJ/kg to 13.0 MJ/kg and reservoir pressure ranging from 9.0 MPa to 50.0 MPa. Detailed comparisons were performed to insure that previous results obtained in similar boundary layer transition experiments (on a regular smooth surface) were reproduced and the results were extended to examine the effects of the porous surface. These experiments indicated that the porous surface was highly effective in delaying transition provided that the hole size was significantly smaller than the viscous length scale.
Passive hypervelocity boundary layer control using an acoustically absortive surface
NASA Astrophysics Data System (ADS)
Rasheed, Adam
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 would damp the second mode (Mack mode). The cone used in the experiments was constructed with a smooth surface on half the cone (to serve as a control) and an acoustically absorptive porous surface on the other half. It was instrumented with flush-mounted thermocouples to detect the transition location. Test gases investigated included nitrogen and carbon dioxide at M = 5 with specific reservoir enthalpy ranging from 1.3 MJ/kg to 13.0 MJ/kg and reservoir pressure ranging from 9.0 MPa to 50.0 MPa. Detailed comparisons were performed to insure that previous results obtained in similar boundary layer transition experiments (on a regular smooth surface) were reproduced and the results were extended to examine the effects of the porous surface. These experiments indicated that the porous surface was highly effective in delaying transition provided that the hole size was significantly smaller than the viscous length scale.
Stability of the laminar boundary layer for an imperfect gas
NASA Astrophysics Data System (ADS)
Gasperas, G.
The linear perturbation equations are derived for the general case of a compressible imperfect gas characterized by an equation of state utilizing a compressibility factor. The specific case of the Beattie-Bridgeman gas is chosen for calculation. Amplification curves calculated using the Beattie-Bridgeman equation of state for two representative flat plate boundary layers are presented.
Determination of Stability and Translation in a Boundary Layer
NASA Technical Reports Server (NTRS)
Crepeau, John; Tobak, Murray
1996-01-01
Reducing the infinite degrees of freedom inherent in fluid motion into a manageable number of modes to analyze fluid motion is presented. The concepts behind the center manifold technique are used. Study of the Blasius boundary layer and a precise description of stability within the flow field are discussed.
Boundary-Layer Receptivity and Integrated Transition Prediction
NASA Technical Reports Server (NTRS)
Chang, Chau-Lyan; Choudhari, Meelan
2005-01-01
The adjoint parabold stability equations (PSE) formulation is used to calculate the boundary layer receptivity to localized surface roughness and suction for compressible boundary layers. Receptivity efficiency functions predicted by the adjoint PSE approach agree well with results based on other nonparallel methods including linearized Navier-Stokes equations for both Tollmien-Schlichting waves and crossflow instability in swept wing boundary layers. The receptivity efficiency function can be regarded as the Green's function to the disturbance amplitude evolution in a nonparallel (growing) boundary layer. Given the Fourier transformed geometry factor distribution along the chordwise direction, the linear disturbance amplitude evolution for a finite size, distributed nonuniformity can be computed by evaluating the integral effects of both disturbance generation and linear amplification. The synergistic approach via the linear adjoint PSE for receptivity and nonlinear PSE for disturbance evolution downstream of the leading edge forms the basis for an integrated transition prediction tool. Eventually, such physics-based, high fidelity prediction methods could simulate the transition process from the disturbance generation through the nonlinear breakdown in a holistic manner.
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...
Turbulent Boundary Layers on a Systematically Varied Rough Wall
2009-01-01
Aeronaut. Sci. 21, 91 1954. 47I. P. Castro, “Rough-wall boundary layers: Mean flow universality,” J. Fluid Mech. 585, 469 2007. 48P. S. Granville ...Properties of d- and k-type roughness in turbulent channel flow,” Phys. Fluids 19, 125101 2007. 50D. H. Wood and R. A. Antonia, “Measurements in a
Laminarization of Turbulent Boundary Layer on Flexible and Rigid Surfaces
NASA Technical Reports Server (NTRS)
Maestrello, Lucio
2001-01-01
An investigation of the control of turbulent boundary layer flow over flexible and rigid surfaces downstream of a concave-convex geometry has been made. The concave-convex curvature induces centrifugal forces and a pressure gradient on the growth of the turbulent boundary layer. The favorable gradient is not sufficient to overcome the unfavorable; thus, the net effect is a destabilizing, of the flow into Gortler instabilities. This study shows that control of the turbulent boundary layer and structural loading can be successfully achieved by using localized surface heating because the subsequent cooling and geometrical shaping downstream over a favorable pressure gradient is effective in laminarization of the turbulence. Wires embedded in a thermally insulated substrate provide surface heating. The laminarized velocity profile adjusts to a lower Reynolds number, and the structure responds to a lower loading. In the laminarization, the turbulent energy is dissipated by molecular transport by both viscous and conductivity mechanisms. Laminarization reduces spanwise vorticity because of the longitudinal cooling gradient of the sublayer profile. The results demonstrate that the curvature-induced mean pressure gradient enhances the receptivity of the flow to localized surface heating, a potentially viable mechanism to laminarize turbulent boundary layer flow; thus, the flow reduces the response of the flexible structure and the resultant sound radiation.
Receptivity of Supersonic Boundary Layers to Acoustic Disturbances
NASA Technical Reports Server (NTRS)
Malik, Mujeeb R.; Balakumar, P.
2005-01-01
Boundary layer receptivity to two-dimensional slow and fast acoustic waves is investigated by solving Navier-Stokes equations for Mach 4.5 flow over a flat plate with a finite-thickness leading edge. Higher order spatial and temporal schemes are employed to obtain the solution whereby the flat-plate leading edge region is resolved by providing a sufficiently refined grid. The results show that the instability waves are generated in the leading edge region and that the boundary-layer is much more receptive to slow acoustic waves (by almost a factor of 20) as compared to the fast waves. Hence, this leading-edge receptivity mechanism is expected to be more relevant in the transition process for high Mach number flows. The effect of acoustic wave incidence angle is also studied and it is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases by more than a factor of 4 when the incidence angle is increased from 0 to 45 deg. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle. The effect of leading-edge thickness is also studied and bluntness is found to stabilize the boundary layer. The relative significance of fast acoustic waves is enhanced in the presence of bluntness.
NASA Astrophysics Data System (ADS)
Gorlé, C.; van Beeck, J.; Rambaud, P.; Van Tendeloo, G.
When considering the modelling of small particle dispersion in the lower part of the Atmospheric Boundary Layer (ABL) using Reynolds Averaged Navier Stokes simulations, the particle paths depend on the velocity profile and on the turbulence kinetic energy, from which the fluctuating velocity components are derived to predict turbulent dispersion. It is therefore important to correctly reproduce the ABL, both for the velocity profile and the turbulence kinetic energy profile. For RANS simulations with the standard k- ɛ model, Richards and Hoxey (1993. Appropriate boundary conditions for computational wind engineering models using the k-ɛ turbulence model. Journal of Wind Engineering and Industrial Aerodynamics 46-47, 145-153.) proposed a set of boundary conditions which result in horizontally homogeneous profiles. The drawback of this method is that it assumes a constant profile of turbulence kinetic energy, which is not always consistent with field or wind tunnel measurements. Therefore, a method was developed which allows the modelling of a horizontally homogeneous turbulence kinetic energy profile that is varying with height. By comparing simulations performed with the proposed method to simulations performed with the boundary conditions described by Richards and Hoxey (1993. Appropriate boundary conditions for computational wind engineering models using the k-ɛ turbulence model. Journal of Wind Engineering and Industrial Aerodynamics 46-47, 145-153.), the influence of the turbulence kinetic energy on the dispersion of small particles over flat terrain is quantified.
Fifty Years of Boundary-Layer Theory and Experiment
NASA Technical Reports Server (NTRS)
Dryden, Hugh L.
1955-01-01
The year 1954 marked the 50th anniversary of the Prandtl boundary-layer theory from which we may date the beginning of man's understanding of the dynamics of real fluids. A backward look at this aspect of the history of the last 50 years may be instructive. This paper (1) attempts to compress the events of those 50 years into a few thousand words, to tell in this brief space the interesting story of the development of a new concept, its slow acceptance and growth, its spread from group to group within its country of origin, and its diffusion to other countries of the world. The original brief paper of Prandtl (2) was presented at the Third International Mathematical Congress at Heidelberg in 1904 and published in the following year. It was an attempt to explain the d'Alembert paradox, namely, that the neglect of the small friction of air in the theory resulted in the prediction of zero resistance to motion. Prandtl set himself the task of computing the motion of a fluid of small friction, so small that its effect could be neglected everywhere except where large velocity differences were present or a cumulative effect of friction occurred This led to the concept of boundary layer, or transition layer, near the wall of a body immersed in a fluid stream in which the velocity rises from zero to the free-stream value. It is interesting that Prandtl used the term Grenzsehicht (boundary layer) only once and the term Ubergangsschicht (transition layer) seven times in the brief article. Later writers also used Reibungsschicht (friction layer), but most writers today use Grenzschicht (boundary layer).
Pressure Fluctuations Induced by a Hypersonic Turbulent Boundary Layer
NASA Technical Reports Server (NTRS)
Duan, Lian; Choudhari, Meelan M.; Zhang, Chao
2016-01-01
Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a spatially-developed Mach 5.86 turbulent boundary layer. The unsteady pressure field is analyzed at multiple wall-normal locations, including those at the wall, within the boundary layer (including inner layer, the log layer, and the outer layer), and in the free stream. The statistical and structural variations of pressure fluctuations as a function of wall-normal distance are highlighted. Computational predictions for mean velocity pro les and surface pressure spectrum are in good agreement with experimental measurements, providing a first ever comparison of this type at hypersonic Mach numbers. The simulation shows that the dominant frequency of boundary-layer-induced pressure fluctuations shifts to lower frequencies as the location of interest moves away from the wall. The pressure wave propagates with a speed nearly equal to the local mean velocity within the boundary layer (except in the immediate vicinity of the wall) while the propagation speed deviates from the Taylor's hypothesis in the free stream. Compared with the surface pressure fluctuations, which are primarily vortical, the acoustic pressure fluctuations in the free stream exhibit a significantly lower dominant frequency, a greater spatial extent, and a smaller bulk propagation speed. The freestream pressure structures are found to have similar Lagrangian time and spatial scales as the acoustic sources near the wall. As the Mach number increases, the freestream acoustic fluctuations exhibit increased radiation intensity, enhanced energy content at high frequencies, shallower orientation of wave fronts with respect to the flow direction, and larger propagation velocity.
On Supersonic-Inlet Boundary-Layer Bleed Flow
NASA Technical Reports Server (NTRS)
Harloff, Gary J.; Smith, Gregory E.
1995-01-01
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.
Modeling Disturbance Dynamics in Transitional and Turbulent Boundary Layers
NASA Technical Reports Server (NTRS)
Grosch, C. E.; Gatski, T. B. (Technical Monitor)
2002-01-01
The dynamics of an ensemble of linear disturbances in boundary-layer flows at various Reynolds numbers is studied through an analysis of the transport equations for the mean disturbance kinetic energy and energy dissipation rate. Effects of adverse and favorable pressure-gradients on the disturbance dynamics are also included in the analysis. Unlike the fully turbulent regime where nonlinear phase scrambling of the fluctuations affects the flow field even in proximity to the wall, the early stage transition regime fluctuations studied here are influenced across the boundary layer by the solid boundary. In addition, the dominating dynamics in the disturbance kinetic energy equation is governed by the energy production, pressure-transport and viscous diffusion - also in contrast to the fully turbulent regime. For the disturbance dissipation rate, a dynamic balance exists between the destruction and diffusion of dissipation.
Linear and nonlinear stability of the Blasius boundary layer
NASA Technical Reports Server (NTRS)
Bertolotti, F. P.; Herbert, TH.; Spalart, P. R.
1992-01-01
Two new techniques for the study of the linear and nonlinear instability in growing boundary layers are presented. The first technique employs partial differential equations of parabolic type exploiting the slow change of the mean flow, disturbance velocity profiles, wavelengths, and growth rates in the streamwise direction. The second technique solves the Navier-Stokes equation for spatially evolving disturbances using buffer zones adjacent to the inflow and outflow boundaries. Results of both techniques are in excellent agreement. The linear and nonlinear development of Tollmien-Schlichting (TS) waves in the Blasius boundary layer is investigated with both techniques and with a local procedure based on a system of ordinary differential equations. The results are compared with previous work and the effects of non-parallelism and nonlinearity are clarified. The effect of nonparallelism is confirmed to be weak and, consequently, not responsible for the discrepancies between measurements and theoretical results for parallel flow.
Anomalous plasma diffusion and the magnetopause boundary layer
NASA Technical Reports Server (NTRS)
Treumann, Rudolf A.; Labelle, James; Haerendel, Gerhard; Pottelette, Raymond
1992-01-01
An overview of the current state of anomalous diffusion research at the magnetopause and its role in the formation of the magnetopause boundary layer is presented. Plasma wave measurements in the boundary layer indicate that most of the relevant unstable wave modes contribute negligibly to the diffusion process at the magnetopause under magnetically undisturbed northward IMF conditions. The most promising instability is the lower hybrid drift instability, which may yield diffusion coefficients of the right order if the highest measured wave intensities are assumed. It is concluded that global stationary diffusion due to wave-particle interactions does not take place at the magnetopause. Microscopic wave-particle interaction and anomalous diffusion may contribute to locally break the MD frozen-in conditions and help in transporting large amounts of magnetosheath plasma across the magnetospheric boundary.
Effective Receptivity Prediction in Three--Dimensional Boundary Layers
NASA Astrophysics Data System (ADS)
Dobrinsky, Alex Y.; Collis, S. Scott
2002-11-01
While the Parabolized Stability Equations (PSE) have been used in the past to study stability and receptivity of boundary layers, it is unclear how effective they are in the highly nonparallel three-dimensional boundary-layers that occur near the leading edge of swept wings. In this talk, we compare results obtained using Direct Numerical Simulation (DNS) with predictions based on PSE for Hiemenz flow subject to wall boundary excitations. After establishing the validity of PSE for stability prediction, we evaluate the Adjoint Parabolized Stability Equations (APSE) for receptivity prediction in Hiemenz flow by comparing with both adjoint Navier--Stokes and DNS as well as results from prior investigations. Along the way, we highlight some important implementational issues of the APSE method necessary to obtain correct receptivity predictions and conclude with general recommendations of when and how PSE and APSE methods should be used to yield accurate receptivity results.
Boundary layer flow visualisation patterns on a riblet surface
NASA Astrophysics Data System (ADS)
Clark, D. G.
Boundary layer flow visualization methods, developed at Queen Mary and Westfield College, have been applied to a riblet surface. The results reveal cellular crossflows developing in the grooves between the riblets. These local flor regimes appear to have little direct effect on the flow in the wall layers immediately adjacent to them. Qualitatively, the behavior of the wall layers appears to be that which would be expected if a virtual surface existed at a level slightly above the riblet tops, but a tendency for the origin of longitudinal eddy pairs to become anchored to the top of a riblet is noted.
NASA Astrophysics Data System (ADS)
Song, Jiyun; Wang, Zhi-Hua
2016-05-01
Urban land-atmosphere interactions can be captured by numerical modeling framework with coupled land surface and atmospheric processes, while the model performance depends largely on accurate input parameters. In this study, we use an advanced stochastic approach to quantify parameter uncertainty and model sensitivity of a coupled numerical framework for urban land-atmosphere interactions. It is found that the development of urban boundary layer is highly sensitive to surface characteristics of built terrains. Changes of both urban land use and geometry impose significant impact on the overlying urban boundary layer dynamics through modification on bottom boundary conditions, i.e., by altering surface energy partitioning and surface aerodynamic resistance, respectively. Hydrothermal properties of conventional and green roofs have different impacts on atmospheric dynamics due to different surface energy partitioning mechanisms. Urban geometry (represented by the canyon aspect ratio), however, has a significant nonlinear impact on boundary layer structure and temperature. Besides, managing rooftop roughness provides an alternative option to change the boundary layer thermal state through modification of the vertical turbulent transport. The sensitivity analysis deepens our insight into the fundamental physics of urban land-atmosphere interactions and provides useful guidance for urban planning under challenges of changing climate and continuous global urbanization.
NASA Technical Reports Server (NTRS)
Oeztuerk, B; Schobeiri, M. T.; Ashpis, David E.
2005-01-01
The paper experimentally and theoretically studies the effects of periodic unsteady wake flow and aerodynamic characteristics on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experiments were carried out at Reynolds number of 110,000 (based on suction surface length and exit velocity). For one steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, intermittency behaviors were experimentally and theoretically investigated. The current investigation attempts to extend the intermittency unsteady boundary layer transition model developed in previously to the LPT cases, where separation occurs on the suction surface at a low Reynolds number. The results of the unsteady boundary layer measurements and the intermittency analysis were presented in the ensemble-averaged and contour plot forms. The analysis of the boundary layer experimental data with the flow separation, confirms the universal character of the relative intermittency function which is described by a Gausssian function.
Shock-boundary layer interaction and transonic flutter
NASA Astrophysics Data System (ADS)
Tumkur Karnick, Pradeepa; Venkatraman, Kartik
2012-11-01
The transonic flutter dip of an aeroelastic system is primarily caused by compressibility of the flowing fluid. Viscous effects are not dominant in the pre-transonic dip region. In fact, an Euler solver can predict this flutter boundary with considerable accuracy. However with an increase in Mach number the shock moves towards the trailing edge causing shock induced separation. This shock-boundary layer interaction changes the flutter boundary in the transonic and post-transonic dip region significantly. We discuss the effect of viscosity in changing the flutter boundary in the post-transonic dip region using a RANS solver coupled to a two-degree of freedom model of the structural dynamics of a wing.
Some Basic Aspects of Magnetohydrodynamic Boundary-Layer Flows
NASA Technical Reports Server (NTRS)
Hess, Robert V.
1959-01-01
An appraisal is made of existing solutions of magnetohydrodynamic boundary-layer equations for stagnation flow and flat-plate flow, and some new solutions are given. Since an exact solution of the equations of magnetohydrodynamics requires complicated simultaneous treatment of the equations of fluid flow and of electromagnetism, certain simplifying assumptions are generally introduced. The full implications of these assumptions have not been brought out properly in several recent papers. It is shown in the present report that for the particular law of deformation which the magnetic lines are assumed to follow in these papers a magnet situated inside the missile nose would not be able to take up any drag forces; to do so it would have to be placed in the flow away from the nose. It is also shown that for the assumption that potential flow is maintained outside the boundary layer, the deformation of the magnetic lines is restricted to small values. The literature contains serious disagreements with regard to reductions in heat-transfer rates due to magnetic action at the nose of a missile, and these disagreements are shown to be mainly due to different interpretations of reentry conditions rather than more complicated effects. In the present paper the magnetohydrodynamic boundary-layer equation is also expressed in a simple form that is especially convenient for physical interpretation. This is done by adapting methods to magnetic forces which in the past have been used for forces due to gravitational or centrifugal action. The simplified approach is used to develop some new solutions of boundary-layer flow and to reinterpret certain solutions existing in the literature. An asymptotic boundary-layer solution representing a fixed velocity profile and shear is found. Special emphasis is put on estimating skin friction and heat-transfer rates.
The influence of bulges on boundary-layer instability
NASA Astrophysics Data System (ADS)
Elli, S.; Vandam, C. P.
Local disturbances caused by a spanwise surface corrugation affect the position of the boundary-layer transition, and so the drag, of an object. This premature transition from laminar to turbulent flow is often associated with a separation of the laminar boundary-layer from its surface. Also the roughness-induced separation bubble provides an important link between the pressure and velocity fluctuations in the environment and the development of the disturbance in the laminar boundary-layer, i.e., the receptivity problem. To investigate the influence of a laminar separation bubble on boundary-layer instability, a separated flow generated by a velocity gradient over a flat plate was analyzed by direct numerical simulation using finite-difference solutions of the Navier-Stokes equations. The bubble acts as a strong amplifier of the instability waves and a highly nonlinear flow field is shown to develop downstream of the bubble. Consequently, the results of the direct numerical simulation differ noticeably from those of the classical linear stability theory proving the fact that the nonparallel effects together with the nonlinear interactions are crucial to this flow development. In the present paper, the effect of physical perturbations such as humps and hollows on boundary-layer instability is analyzed. This problem has been considered theoretically by several researchers (e.g., Nayfeh et al., 1987 and 1990; Cebeci et al., 1988). They used linear stability theory in their approach which does not include the nonparallel nor the nonlinear effects. Therefore, to account for these important effects in studying flow over humps and hollows the direct simulation technique is being implemented in generalized coordinates.
Minimum Wind Dynamic Soaring Trajectories under Boundary Layer Thickness Limits
NASA Astrophysics Data System (ADS)
Bousquet, Gabriel; Triantafyllou, Michael; Slotine, Jean-Jacques
2015-11-01
Dynamic soaring is the flight technique where a glider, either avian or manmade, extracts its propulsive energy from the non-uniformity of horizontal winds. Albatrosses have been recorded to fly an impressive 5000 km/week at no energy cost of their own. In the sharp boundary layer limit, we show that the popular image, where the glider travels in a succession of half turns, is suboptimal for travel speed, airspeed, and soaring ability. Instead, we show that the strategy that maximizes the three criteria simultaneously is a succession of infinitely small arc-circles connecting transitions between the calm and windy layers. The model is consistent with the recordings of albatross flight patterns. This lowers the required wind speed for dynamic soaring by over 50% compared to previous beliefs. In the thick boundary layer limit, energetic considerations allow us to predict a minimum wind gradient necessary for sustained soaring consistent with numerical models.
Turbulent boundary layer on a convex, curved surface
NASA Technical Reports Server (NTRS)
Gillis, J. C.; Johnston, J. P.; Kays, W. M.; Moffat, R. J.
1980-01-01
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.
Buoyancy effects in an unstably stratified turbulent boundary layer flow
NASA Astrophysics Data System (ADS)
Li, Dong; Luo, Kun; Fan, Jianren
2017-01-01
Direct numerical simulation has been performed to investigate the effect of buoyancy on an unstably stratified turbulent boundary layer with the Oberbeck-Boussinesq approximation. The simulation results show that the mean values of the streamwise velocity and scalar fields are increased in the near-wall region but decreased in the outer layer under the effect of buoyancy, which leads to significant increases in the skin-friction drag and heat transfer. In addition, it is found that the unstable thermal stratification results in large increases in the intensities of the near-wall streamwise vortices and high- and low-speed streaks, and a reduction in the mean diameter of the vortical structures. Moreover, the turbulent coherent structures become less organized due to the stratification effect. With respect to the neutral boundary layer flow, the outer vortical structures tend to bias the direction of the principal extensional strain towards the vertical plane in the unstably stratified flow.
Provenance of the K/T boundary layers
NASA Technical Reports Server (NTRS)
Hildebrand, A. R.; Boynton, W. V.
1988-01-01
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.
Investigations on entropy layer along hypersonic hyperboloids using a defect boundary layer
NASA Technical Reports Server (NTRS)
Brazier, J. P.; Aupoix, B.; Cousteix, J.
1992-01-01
A defect approach coupled with matched asymptotic expansions is used to derive a new set of boundary layer equations. This method ensures a smooth matching of the boundary layer with the inviscid solution. These equations are solved to calculate boundary layers over hypersonic blunt bodies involving the entropy gradient effect. Systematic comparisons are made for both axisymmetric and plane flows in several cases with different Mach and Reynolds numbers. After a brief survey of the entropy layer characteristics, the defect boundary layer results are compared with standard boundary layer and full Navier-Stokes solutions. The entropy gradient effects are found to be more important in the axisymmetric case than in the plane one. The wall temperature has a great influence on the results through the displacement effect. Good predictions can be obtained with the defect approach over a cold wall in the nose region, with a first order solution. However, the defect approach gives less accurate results far from the nose on axisymmetric bodies because of the thinning of the entropy layer.
Behaviour of Atmospheric Boundary Layer Height at Dome C, Antarctica
NASA Astrophysics Data System (ADS)
Pietroni, I.; Argentini, S.
2009-09-01
The Antarctic Atmospheric Boundary Layer presents characteristics which are substantially different from the mid-latitudes ABLs. On the Antarctic plateau two different extreme situations are observed. During the summer a mixing height develops during the warmer hours of the day although the sensible heat flux is reduced compared to that at mid-latitudes. During the winter a long lived stable boundary layer is continuously present, the residual layer is never observed, consequently the inversion layer is connected at the free atmosphere. To understand the stable ABL process the STABLEDC (Study of the STAble Boundary Layer Environmental at Dome C) experimental field was held at Concordia, the French Italian plateau station at Dome C, during 2005. In the same period the RMO (Routine Measurements Observations) started. The data included turbulence data at the surface, temperature profiles by a microwave profiler (MTP-5P), a mini-sodar and radio-soundings. In this work we will show the results of a comparison of the ABL height at Concordia (3233 m a.s.l) during the summer and the winter using direct measurements and parameterization. The winter ABL height was estimated directly using experimental data (radio-soundings and radiometer temperature and wind velocity profiles) and different methods proposed in literature. The stable ABL height was also estimated using the formulation proposed by Zilitinkevich et al. (2007) for the long-lived stable boundary layer. The correlation of ABL height with the temperature and wind speed is also shown. The summer mixing height was instead estimated by mini-sodar data and compared with the height given by the model suggested by Batchvarova and Gryning (1991) which use as input the turbulence data.
On buffer layers as non-reflecting computational boundaries
NASA Technical Reports Server (NTRS)
Hayder, M. Ehtesham; Turkel, Eli L.
1996-01-01
We examine an absorbing buffer layer technique for use as a non-reflecting boundary condition in the numerical simulation of flows. One such formulation was by Ta'asan and Nark for the linearized Euler equations. They modified the flow inside the buffer zone to artificially make it supersonic in the layer. We examine how this approach can be extended to the nonlinear Euler equations. We consider both a conservative and a non-conservative form modifying the governing equations in the buffer layer. We compare this with the case that the governing equations in the layer are the same as in the interior domain. We test the effectiveness of these buffer layers by a simulation of an excited axisymmetric jet based on a nonlinear compressible Navier-Stokes equations.
NASA Astrophysics Data System (ADS)
Grosvenor, A. D.; Zheltovodov, A. A.; Matheson, M. A.; Sailer, L. M.; Krzysztopik, M.; Gutzwiller, D. P.
2013-06-01
A set of Reynolds-averaged Navier-Stokes (RANS) computations with turbulence closure provided by the Spalart-Allmaras (SA) model have been carried out for prediction of shock-induced three-dimensional (3D) turbulent separated flows. The experimental data for different aerodynamic test configurations have been used for assessing credibility of the numerical method employed. Particularly, shock wave / turbulent boundary layer interactions (SWTBLI) in the vicinity of an asymmetric sharp double-fin (DF) with different (7° and 11°) deflection angles mounted on a flat plate and two conically sharp cylindrical bodies at varying interbody distances and nose cone angles 60° and 40° mounted over a flat plate at freestream Mach number 4, as well as a transonic fan stage operating in the near-stall regime are considered. The gas dynamic structure and topology of 3D separated flows, surface flow patterns, and pressure distributions as well as body aerodynamic force prediction are analyzed. A transonic fan stage operating in the near-stall regime and a possibility of applying flow control is investigated. High Performance Computing was employed to make high resolution computations of these flows possible, and advanced 3D visualization techniques were employed in order to improve understanding of the separating flow phenomena.
NASA Technical Reports Server (NTRS)
Tetervin, Neal; Lin, Chia Chiao
1951-01-01
A general integral form of the boundary-layer equation, valid for either laminar or turbulent incompressible boundary-layer flow, is derived. By using the experimental finding that all velocity profiles of the turbulent boundary layer form essentially a single-parameter family, the general equation is changed to an equation for the space rate of change of the velocity-profile shape parameter. The lack of precise knowledge concerning the surface shear and the distribution of the shearing stress across turbulent boundary layers prevented the attainment of a reliable method for calculating the behavior of turbulent boundary layers.
Control of a shock wave-boundary layer interaction using localized arc filament plasma actuators
NASA Astrophysics Data System (ADS)
Webb, Nathan Joseph
Supersonic flight is currently possible, but expensive. Inexpensive supersonic travel will require increased efficiency of high-speed air entrainment, an integral part of air-breathing propulsion systems. Although mixed compression inlet geometry can significantly improve entrainment efficiency, numerous Shock Wave-Boundary Layer Interactions (SWBLIs) are generated in this configuration. The boundary layer must therefore develop through multiple regions of adverse pressure gradient, causing it to thicken, and, in severe cases, separate. The associated increase in unsteadiness can have adverse effects on downstream engine hardware. The most severe consequence of these interactions is the increased aerodynamic blockage generated by the thickened boundary layer. If the increase is sufficient, it can choke the flow, causing inlet unstart, and resulting in a loss of thrust and high transient forces on the engine, airframe, and aircraft occupants. The potentially severe consequences associated with SWBLIs require flow control to ensure proper operation. Traditionally, boundary layer bleed has been used to control the interaction. Although this method is effective, it has inherent efficiency penalties. Localized Arc Filament Plasma Actuators (LAFPAs) are designed to generate perturbations for flow control. Natural flow instabilities act to amplify certain perturbations, allowing the LAFPAs to control the flow with minimal power input. LAFPAs also have the flexibility to maintain control over a variety of operating conditions. This work seeks to examine the effectiveness of LAFPAs as a separation control method for an oblique, impinging SWBLI. The low frequency unsteadiness in the reflected shock was thought to be the natural manifestation of a Kelvin-Helmholtz instability in the shear layer above the separation region. The LAFPAs were therefore placed upstream of the interaction to allow their perturbations to convect to the receptivity region (near the shear layer origin
BLSTA: A boundary layer code for stability analysis
NASA Technical Reports Server (NTRS)
Wie, Yong-Sun
1992-01-01
A computer program is developed to solve the compressible, laminar boundary-layer equations for two-dimensional flow, axisymmetric flow, and quasi-three-dimensional flows including the flow along the plane of symmetry, flow along the leading-edge attachment line, and swept-wing flows with a conical flow approximation. The finite-difference numerical procedure used to solve the governing equations is second-order accurate. The flow over a wide range of speed, from subsonic to hypersonic speed with perfect gas assumption, can be calculated. Various wall boundary conditions, such as wall suction or blowing and hot or cold walls, can be applied. The results indicate that this boundary-layer code gives velocity and temperature profiles which are accurate, smooth, and continuous through the first and second normal derivatives. The code presented herein can be coupled with a stability analysis code and used to predict the onset of the boundary-layer transition which enables the assessment of the laminar flow control techniques. A user's manual is also included.
LES of a Stratified Boundary Layer under an Oscillating Current
NASA Astrophysics Data System (ADS)
Gayen, Bishakhdatta; Sarkar, Sutanu; Taylor, John
2008-11-01
A numerical study based on large-eddy simulation (LES) is performed in the case of an oscillating tidal flow with a uniform ambient stratification. Here, the Reynolds number Reδ=U0δs/ν=1790 (U0= maximum amplitude of the outer flow, δs= √2 ν/φ is the Stokes layer thickness, ν is the kinematic viscosity of the fluid and φ the angular frequency of the oscillatory current), and N∞^2/2̂= 500 where N∞ is the buoyancy frequency of the overlying stratified layer. Turbulence appears at a tidal phase of approximately π/4 and is sustained throughout the deceleration phase (π/2<φtd<π, 3π/2<φtd<2π). Production of turbulence is confined to the the wall region and, for stratified flow, in the mixed layer between the wall and the thermocline. For both the stratified and unstratified cases, there is a log layer over a significant extent of the tidal cycle. Our unstratified flow results are verified against the numerical simulations of Salon et ; al (2007) %. JFM, 2007, vol 570, 253-296 and experimental data of Jensen et ; al. (1987). %JFM, 1987, vol 206, 256-297. In the presence of stratification, the boundary layer height decreases substantially and the wall shear stress increases slightly with respect to the unstratified case. Stratification effects on boundary layer turbulence and on the thermal field including the formation and collapse of the thermocline will be discussed.
Boundary-layer model of pattern formation in solidification
NASA Technical Reports Server (NTRS)
Ben-Jacob, E.; Goldenfeld, N.; Langer, J. S.; Schon, G.
1984-01-01
A model of pattern formation in crystal growth is proposed, and its analytic properties are investigated. The principal dynamical variables in this model are the curvature of the solidification front and the thickness (or heat content) of a thermal boundary layer, both taken to be functions of position along the interface. This model is mathematically much more tractable than the realistic, fully nonlocal version of the free-boundary problem, and still recaptures many of the features that seem essential for studying dendritic behavior, for example. Preliminary numerical solutions produce snowflakelike patterns similar to those seen in nature.
Numerical Simulation of a Spatially Evolving Supersonic Turbulent Boundary Layer
NASA Technical Reports Server (NTRS)
Gatski, T. B.; Erlebacher, G.
2002-01-01
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.
Edge Plasma Boundary Layer Generated By Kink Modes in Tokamaks
L.E. Zakharov
2010-11-22
This paper describes the structure of the electric current generated by external kink modes at the plasma edge using the ideally conducting plasma model. It is found that the edge current layer is created by both wall touching and free boundary kink modes. Near marginal stability, the total edge current has a universal expression as a result of partial compensation of the δ-functional surface current by the bulk current at the edge. The resolution of an apparent paradox with the pressure balance across the plasma boundary in the presence of the surface currents is provided.
Turbulence spectra of the FIRE stratocumulus-topped boundary layers
NASA Technical Reports Server (NTRS)
Young, G. S.; Nucciarone, J. J.; Albrecht, Bruce A.
1990-01-01
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.
Small-scale behavior in distorted turbulent boundary layers at low Reynolds number
NASA Astrophysics Data System (ADS)
Saddoughi, Seyed G.
1994-12-01
During the last three years we have conducted high- and low-Reynolds-number experiments, including hot-wire measurements of the velocity fluctuations, in the test-section-ceiling boundary layer of the 80- by 120-foot Full-Scale Aerodynamics Facility at NASA Ames Research Center, to test the local-isotropy predictions of Kolmogorov's universal equilibrium theory. This hypothesis, which states that at sufficiently high Reynolds numbers the small-scale structures of turbulent motions are independent of large-scale structures and mean deformations, has been used in theoretical studies of turbulence and computational methods such as large-eddy simulation; however, its range of validity in shear flows has been a subject of controversy. The present experiments were planned to enhance our understanding of the local-isotropy hypothesis. Our experiments were divided into two sets. First, measurements were taken at different Reynolds numbers in a plane boundary layer, which is a 'simple' shear flow. Second, experiments were designed to address this question: will our criteria for the existence of local isotropy hold for 'complex' nonequilibrium flows in which extra rates of mean strain are added to the basic mean shear?
LDV measurement of boundary layer on rotating blade surface in wind tunnel
NASA Astrophysics Data System (ADS)
Maeda, Takao; Kamada, Yasunari; Murata, Junsuke; Suzuki, Daiki; Kaga, Norimitsu; Kagisaki, Yosuke
2014-12-01
Wind turbines generate electricity due to extracting energy from the wind. The rotor aerodynamics strongly depends on the flow around blade. The surface flow on the rotating blade affects the sectional performance. The wind turbine surface flow has span-wise component due to span-wise change of airfoil section, chord length, twisted angle of blade and centrifugal force on the flow. These span-wise flow changes the boundary layer on the rotating blade and the sectional performance. Hence, the thorough understanding of blade surface flow is important to improve the rotor performance. For the purpose of clarification of the flow behaviour around the rotor blade, the velocity in the boundary layer on rotating blade surface of an experimental HAWT was measured in a wind tunnel. The velocity measurement on the blade surface was carried out by a laser Doppler velocimeter (LDV). As the results of the measurement, characteristics of surface flow are clarified. In optimum tip speed operation, the surface flow on leading edge and r/R=0.3 have large span-wise velocity which reaches 20% of sectional inflow velocity. The surface flow inboard have three dimensional flow patterns. On the other hand, the flow outboard is almost two dimensional in cross sectional plane.
Diagnostics of boundary layer transition by shear stress sensitive liquid crystals
NASA Astrophysics Data System (ADS)
Shapoval, E. S.
2016-10-01
Previous research indicates that the problem of boundary layer transition visualization on metal models in wind tunnels (WT) which is a fundamental question in experimental aerodynamics is not solved yet. In TsAGI together with Khristianovich Institute of Theoretical and Applied Mechanics (ITAM) a method of shear stress sensitive liquid crystals (LC) which allows flow visualization was proposed. This method allows testing several flow conditions in one wind tunnel run and does not need covering the investigated model with any special heat-insulating coating which spoils the model geometry. This coating is easily applied on the model surface by spray or even by brush. Its' thickness is about 40 micrometers and it does not spoil the surface quality. At first the coating obtains some definite color. Under shear stress the LC coating changes color and this change is proportional to shear stress. The whole process can be visually observed and during the tests it is recorded by camera. The findings of the research showed that it is possible to visualize boundary layer transition, flow separation, shock waves and the flow image on the whole. It is possible to predict that the proposed method of shear stress sensitive liquid crystals is a promise for future research.
Design and Evaluation of a New Boundary-Layer Rake for Flight Testing
NASA Technical Reports Server (NTRS)
Bui, Trong T.; Oates, David L.; Gonsalez, Jose C.
2000-01-01
A new boundary-layer rake has been designed and built for flight testing on the NASA Dryden Flight Research Center F-15B/Flight Test Fixture. A feature unique to this rake is its curved body, which allows pitot tubes to be more densely clustered in the near-wall region than conventional rakes allow. This curved rake design has a complex three-dimensional shape that requires innovative solid-modeling and machining techniques. Finite-element stress analysis of the new design shows high factors of safety. The rake has passed a ground test in which random vibration measuring 12 g rms was applied for 20 min in each of the three normal directions. Aerodynamic evaluation of the rake has been conducted in the NASA Glenn Research Center 8 x 6 Supersonic Wind Tunnel at Mach 0-2. The pitot pressures from the new rake agree with conventional rake data over the range of Mach numbers tested. The boundary-layer profiles computed from the rake data have been shown to have the standard logarithmic-law profile. Skin friction values computed from the rake data using the Clauser plot method agree with the Preston tube results and the van Driest II compressible skin friction correlation to approximately +/-5 percent.
Small-scale behavior in distorted turbulent boundary layers at low Reynolds number
NASA Technical Reports Server (NTRS)
Saddoughi, Seyed G.
1994-01-01
During the last three years we have conducted high- and low-Reynolds-number experiments, including hot-wire measurements of the velocity fluctuations, in the test-section-ceiling boundary layer of the 80- by 120-foot Full-Scale Aerodynamics Facility at NASA Ames Research Center, to test the local-isotropy predictions of Kolmogorov's universal equilibrium theory. This hypothesis, which states that at sufficiently high Reynolds numbers the small-scale structures of turbulent motions are independent of large-scale structures and mean deformations, has been used in theoretical studies of turbulence and computational methods such as large-eddy simulation; however, its range of validity in shear flows has been a subject of controversy. The present experiments were planned to enhance our understanding of the local-isotropy hypothesis. Our experiments were divided into two sets. First, measurements were taken at different Reynolds numbers in a plane boundary layer, which is a 'simple' shear flow. Second, experiments were designed to address this question: will our criteria for the existence of local isotropy hold for 'complex' nonequilibrium flows in which extra rates of mean strain are added to the basic mean shear?
Effect of wakes from moving upstream rods on boundary layer separation from a high lift airfoil
NASA Astrophysics Data System (ADS)
Volino, Ralph J.
2011-11-01
Highly loaded airfoils in turbines allow power generation using fewer airfoils. High loading, however, can cause boundary layer separation, resulting in reduced lift and increased aerodynamic loss. Separation is affected by the interaction between rotating blades and stationary vanes. Wakes from upstream vanes periodically impinge on downstream blades, and can reduce separation. The wakes include elevated turbulence, which can induce transition, and a velocity deficit, which results in an impinging flow on the blade surface known as a ``negative jet.'' In the present study, flow through a linear cascade of very high lift airfoils is studied experimentally. Wakes are produced with moving rods which cut through the flow upstream of the airfoils, simulating the effect of upstream vanes. Pressure and velocity fields are documented. Wake spacing and velocity are varied. At low Reynolds numbers without wakes, the boundary layer separates and does not reattach. At high wake passing frequencies separation is largely suppressed. At lower frequencies, ensemble averaged velocity results show intermittent separation and reattachment during the wake passing cycle. Supported by NASA.
Observations and Modelling of the Atmospheric Boundary Layer Over Sea-Ice in a Svalbard Fjord
NASA Astrophysics Data System (ADS)
Mäkiranta, Eeva; Vihma, Timo; Sjöblom, Anna; Tastula, Esa-Matti
2011-07-01
Sonic anemometer and profile mast measurements made in Wahlenbergfjorden, Svalbard Arctic archipelago, in May 2006 and April 2007 were employed to study the atmospheric boundary layer over sea-ice. The turbulent surface fluxes of momentum and sensible heat were calculated using eddy correlation and gradient methods. The results showed that the literature-based universal functions underestimated turbulent mixing in strongly stable conditions. The validity of the Monin-Obukhov similarity theory was questionable for cross-fjord flow directions and in the presence of mesoscale variability or topographic effects. The aerodynamic roughness length showed a dependence on the wind direction. The mean roughness length for along-fjord wind directions was (2.4 ± 2.6) × 10-4 m, whereas that for cross-fjord directions was (5.4 ± 2.8) × 10-3 m. The thermal stratification and turbulent fluxes were affected by the synoptic situation with large differences between the 2 years. Channelling effects and drainage flows occurred especially during a weak large-scale flow. The study periods were simulated applying the Weather Research and Forecasting (WRF) model with 1-km horizontal resolution in the finest domain. The results for the 2-m air temperature and friction velocity were good, but the model failed to reproduce the spatial variability in wind direction between measurement sites 3 km apart. The model suggested that wind shear above the stable boundary layer provided a non-local source for the turbulence observed.
Acoustic Radiation From a Mach 14 Turbulent Boundary Layer
NASA Technical Reports Server (NTRS)
Zhang, Chao; Duan, Lian; Choudhari, Meelan M.
2016-01-01
Direct numerical simulations (DNS) are used to examine the turbulence statistics and the radiation field generated by a high-speed turbulent boundary layer with a nominal freestream Mach number of 14 and wall temperature of 0:18 times the recovery temperature. The flow conditions fall within the range of nozzle exit conditions of the Arnold Engineering Development Center (AEDC) Hypervelocity Tunnel No. 9 facility. The streamwise domain size is approximately 200 times the boundary-layer thickness at the inlet, with a useful range of Reynolds number corresponding to Re 450 ?? 650. Consistent with previous studies of turbulent boundary layer at high Mach numbers, the weak compressibility hypothesis for turbulent boundary layers remains applicable under this flow condition and the computational results confirm the validity of both the van Driest transformation and Morkovin's scaling. The Reynolds analogy is valid at the surface; the RMS of fluctuations in the surface pressure, wall shear stress, and heat flux is 24%, 53%, and 67% of the surface mean, respectively. The magnitude and dominant frequency of pressure fluctuations are found to vary dramatically within the inner layer (z/delta 0.< or approx. 0.08 or z+ < or approx. 50). The peak of the pre-multiplied frequency spectrum of the pressure fluctuation is f(delta)/U(sub infinity) approx. 2.1 at the surface and shifts to a lower frequency of f(delta)/U(sub infinity) approx. 0.7 in the free stream where the pressure signal is predominantly acoustic. The dominant frequency of the pressure spectrum shows a significant dependence on the freestream Mach number both at the wall and in the free stream.
Transitional boundary layers in low-Prandtl-number convection
NASA Astrophysics Data System (ADS)
Schumacher, Jörg; Bandaru, Vinodh; Pandey, Ambrish; Scheel, Janet D.
2016-12-01
The boundary layer structure of the velocity and temperature fields in turbulent Rayleigh-Bénard flows in closed cylindrical cells of unit aspect ratio is revisited from a transitional and turbulent viscous boundary layer perspective. When the Rayleigh number is large enough, the dynamics at the bottom and top plates can be separated into an impact region of downwelling plumes, an ejection region of upwelling plumes, and an interior region away from the side walls. The latter is dominated by the shear of the large-scale circulation (LSC) roll, which fills the whole cell and continuously varies its orientation. The working fluid is liquid mercury or gallium at a Prandtl number Pr=0.021 for Rayleigh numbers 3 ×105≤Ra≤4 ×108 . The generated turbulent momentum transfer corresponds to macroscopic flow Reynolds numbers with 1.8 ×103≤Re≤4.6 ×104 . In highly resolved spectral element direct numerical simulations, we present the mean profiles of velocity, Reynolds stress, and temperature in inner viscous units and compare our findings with convection experiments and channel flow data. The complex three-dimensional and time-dependent structure of the LSC in the cell is compensated by a plane-by-plane symmetry transformation which aligns the horizontal velocity components and all its derivatives with the instantaneous orientation of the LSC. As a consequence, the torsion of the LSC is removed, and a streamwise direction in the shear flow can be defined. It is shown that the viscous boundary layers for the largest Rayleigh numbers are highly transitional and obey properties that are directly comparable to transitional channel flows at friction Reynolds numbers Reτ≲102 . The transitional character of the viscous boundary layer is also underlined by the strong enhancement of the fluctuations of the wall stress components with increasing Rayleigh number. An extrapolation of our analysis data suggests that the friction Reynolds number Reτ in the velocity boundary
Boundary-Value Problem for Two-Dimensional Fluctuations in Boundary Layers
1985-07-01
inviscid analysis by P. Durbin "Distortion of turbulence by a constant-shear layer adjacent to a wall," private communication (1977). (l.2e) 2-D...vortices near a boundary," ~ of the Americ~ p ~ ~ , Volume 20, Number 9 (November 1975). 21. Hultgren, Lennart S. and Gustavsson, L. Hakan, " Algebraic
NASA Astrophysics Data System (ADS)
Denison, Marie F. C.
The reduction of drag and aerodynamic heating caused by boundary layer transition is of central interest for the development of hypersonic vehicles. Receptivity to flow perturbation in the form of Tollmien-Schlichting (TS) wave growth often determines the first stage of the transition process, which can be delayed by depositing specific excitations into the boundary layer. Weakly ionized Dielectric Barrier Discharge (DBD) actuators are being investigated as possible sources of such excitations, but little is known today about their interaction with high-speed flows. In this framework, the first part of the thesis is dedicated to a receptivity study of laminar compressible boundary layers over a flat plate by linear stability analysis following an adjoint operator formulation, under DBD representative excitations assumed independent of flow conditions. The second part of the work concentrates on the development of a coupled plasma-Navier and Stokes solver targeted at the study of supersonic flow and compressibility effects on DBD forcing and non-parallel receptivity. The linear receptivity study of quasi-parallel compressible flows reveals several interesting features such as a significant shift of the region of maximum receptivity deeper into the flow at high Mach number and strong wave amplitude reduction compared to incompressible flows. The response to DBD relevant excitation distributions and to variations of the base flow conditions and system length scales follows these trends. Observed absolute amplitude changes and relative sensitivity modifications between source types are related to the evolution of the offset between forcing peak profile and relevant adjoint mode maximum. The analysis highlights the crucial importance of designing and placing the actuator in a way that matches its force field to the position of maximum boundary layer receptivity for the specific flow conditions of interest. In order to address the broad time and length scale spectrum
The boundary layer over turbine blade models with realistic rough surfaces
NASA Astrophysics Data System (ADS)
McIlroy, Hugh M., Jr.
The impact of turbine blade surface roughness on aerodynamic performance and heat loads is well known. Over time, as the turbine blades are exposed to heat loads, the external surfaces of the blades become rough. Also, for film-cooled blades, surface degradation can have a significant impact on film-cooling effectiveness. Many studies have been conducted on the effects of surface degradation/roughness on engine performance but most investigations have modeled the rough surfaces with uniform or two-dimensional roughness patterns. The objective of the present investigation is to conduct measurements that will reveal the influence of realistic surface roughness on the near-wall behavior of the boundary layer. Measurements have been conducted at the Matched-Index-of-Refraction (MIR) Facility at the Idaho National Engineering and Environmental Laboratory with a laser Doppler velocimeter. A flat plate model of a turbine blade has been developed that produces a transitional boundary layer, elevated freestream turbulence and an accelerating freestream in order to simulate conditions on the suction side of a high-pressure turbine blade. Boundary layer measurements have been completed over a smooth plate model and over a model with a strip of realistic rough surface. The realistic rough surface was developed by scaling actual turbine blade surface data that was provided by U.S. Air Force Research Laboratory. The results indicate that bypass transition occurred very early in the flow over the model and that the boundary layer remained unstable throughout the entire length of the test plate; the boundary layer thickness and momentum thickness Reynolds numbers increased over the rough patch; and the shape factor increased over the rough patch but then decreased downstream of the patch relative to the smooth plate case; in the rough patch case the flow experienced two transition reversals with laminar-like behavior achieved by the end of the test plate; streamwise turbulence
Simulation and optimal control of wind-farm boundary layers
NASA Astrophysics Data System (ADS)
Meyers, Johan; Goit, Jay
2014-05-01
In large wind farms, the effect of turbine wakes, and their interaction leads to a reduction in farm efficiency, with power generated by turbines in a farm being lower than that of a lone-standing turbine by up to 50%. In very large wind farms or `deep arrays', this efficiency loss is related to interaction of the wind farms with the planetary boundary layer, leading to lower wind speeds at turbine level. Moreover, for these cases it has been demonstrated both in simulations and wind-tunnel experiments that the wind-farm energy extraction is dominated by the vertical turbulent transport of kinetic energy from higher regions in the boundary layer towards the turbine level. In the current study, we investigate the use of optimal control techniques combined with Large-Eddy Simulations (LES) of wind-farm boundary layer interaction for the increase of total energy extraction in very large `infinite' wind farms. We consider the individual wind turbines as flow actuators, whose energy extraction can be dynamically regulated in time so as to optimally influence the turbulent flow field, maximizing the wind farm power. For the simulation of wind-farm boundary layers we use large-eddy simulations in combination with actuator-disk and actuator-line representations of wind turbines. Simulations are performed in our in-house pseudo-spectral code SP-Wind that combines Fourier-spectral discretization in horizontal directions with a fourth-order finite-volume approach in the vertical direction. For the optimal control study, we consider the dynamic control of turbine-thrust coefficients in an actuator-disk model. They represent the effect of turbine blades that can actively pitch in time, changing the lift- and drag coefficients of the turbine blades. Optimal model-predictive control (or optimal receding horizon control) is used, where the model simply consists of the full LES equations, and the time horizon is approximately 280 seconds. The optimization is performed using a
Numerical Simulation of Boundary Layer Ingesting (BLI) Inlet-Fan Interaction
NASA Technical Reports Server (NTRS)
Giuliani, James; Chen, Jen-Ping; Beach, Timothy; Bakhle, Milind
2014-01-01
Future civil transport designs may incorporate engine inlets integrated into the body of the aircraft to take advantage of efficiency increases due to weight and drag reduction. Additional increases in engine efficiency are predicted if the inlet ingests the lower momentum boundary layer flow. Previous studies have shown, however, that efficiency benefits of Boundary Layer Ingesting (BLI) ingestion are very sensitive to the magnitude of fan and duct losses, and blade structural response to the non-uniform flow field that results from a BLI inlet has not been studied in-depth. This paper presents an effort to extend the modeling capabilities of an existing rotating turbomachinery unsteady analysis code to include the ability to solve the external and internal flow fields of a BLI inlet. The TURBO code has been a successful tool in evaluating fan response to flow distortions for traditional engine/inlet integrations, such as the development of rotating stall and inlet distortion through compressor stages. This paper describes the first phase of an effort to extend the TURBO model to calculate the external and inlet flowfield upstream of fan so that accurate pressure distortions that result from BLI configurations can be computed and used to analyze fan aerodynamics and structural response. To validate the TURBO program modifications for the BLI flowfield, experimental test data obtained by NASA for a flushmounted S-duct with large amounts of boundary layer ingestion was modeled. Results for the flow upstream and in the inlet are presented and compared to experimental data for several high Reynolds number flows to validate the modifications to the solver. Quantitative data is presented that indicates good predictive capability of the model in the upstream flow. A representative fan is attached to the inlet and results are presented for the coupled inlet/fan model. The impact on the total pressure distortion at the AIP after the fan is attached is examined.
Boundary layer ozone - An airborne survey above the Amazon Basin
NASA Technical Reports Server (NTRS)
Gregory, Gerald L.; Browell, Edward V.; Warren, Linda S.
1988-01-01
Ozone data obtained over the forest canopy of the Amazon Basin during July and August 1985 in the course of NASA's Amazon Boundary Layer Experiment 2A are discussed, and ozone profiles obtained during flights from Belem to Tabatinga, Brazil, are analyzed to determine any cross-basin effects. The analyses of ozone data indicate that the mixed layer of the Amazon Basin, for the conditions of undisturbed meteorology and in the absence of biomass burning, is a significant sink for tropospheric ozone. As the coast is approached, marine influences are noted at about 300 km inland, and a transition from a forest-controlled mixed layer to a marine-controlled mixed layer is noted.
NASA Technical Reports Server (NTRS)
Blumberg, Dan G.; Greeley, Ronald
1992-01-01
The part of the troposphere influenced by the surface of the earth is termed the atmospheric boundary layer. Flow within this layer is influenced by the roughness of the surface; rougher surfaces induce more turbulence than smoother surfaces and, hence, higher atmospheric transfer rates across the surface. Roughness elements also shield erodible particles, thus decreasing the transport of windblown particles. Therefore, the aerodynamic roughness length (z(sub 0)) is an important parameter in aeolian and atmospheric boundary layer processes as it describes the aerodynamic properties of the underlying surface. z(sub 0) is assumed to be independent of wind velocity or height, and dependent only on the surface topography. It is determined using in situ measurements of the wind speed distribution as a function of height. For dry, unvegetated soils the intensity of the radar backscatter (sigma(sup 0)) is affected primarily by surface roughness at a scale comparable with the radar wavelength. Thus, both wind and radar respond to surface roughness variations on a scale of a few meters or less. Greeley showed the existence of a correlation between z(sub 0) and sigma(sup 0). This correlation was based on measurements over lava flows, alluvial fans, and playas in the southwest deserts of the United States. It is shown that the two parameters behave similarly also when there are small changes over a relatively homogeneous surface.
Lumley decomposition of turbulent boundary layer at high Reynolds numbers
NASA Astrophysics Data System (ADS)
Tutkun, Murat; George, William K.
2017-02-01
The decomposition proposed by Lumley in 1966 is applied to a high Reynolds number turbulent boundary layer. The experimental database was created by a hot-wire rake of 143 probes in the Laboratoire de Mécanique de Lille wind tunnel. The Reynolds numbers based on momentum thickness (Reθ) are 9800 and 19 100. Three-dimensional decomposition is performed, namely, proper orthogonal decomposition (POD) in the inhomogeneous and bounded wall-normal direction, Fourier decomposition in the homogeneous spanwise direction, and Fourier decomposition in time. The first POD modes in both cases carry nearly 50% of turbulence kinetic energy when the energy is integrated over Fourier dimensions. The eigenspectra always peak near zero frequency and most of the large scale, energy carrying features are found at the low end of the spectra. The spanwise Fourier mode which has the largest amount of energy is the first spanwise mode and its symmetrical pair. Pre-multiplied eigenspectra have only one distinct peak and it matches the secondary peak observed in the log-layer of pre-multiplied velocity spectra. Energy carrying modes obtained from the POD scale with outer scaling parameters. Full or partial reconstruction of turbulent velocity signal based only on energetic modes or non-energetic modes revealed the behaviour of urms in distinct regions across the boundary layer. When urms is based on energetic reconstruction, there exists (a) an exponential decay from near wall to log-layer, (b) a constant layer through the log-layer, and (c) another exponential decay in the outer region. The non-energetic reconstruction reveals that urms has (a) an exponential decay from the near-wall to the end of log-layer and (b) a constant layer in the outer region. Scaling of urms using the outer parameters is best when both energetic and non-energetic profiles are combined.
Instability of a Local Downflow in a Turbulent Boundary Layer
NASA Astrophysics Data System (ADS)
Lundgren, Thomas
2006-11-01
In the laminar Hiemenz stagnation point flow a downflow produces a straining flow along the boundary. This flow is unstable (Hammerlin,1955) with neutral eigensolution consisting of alternating sign vortex cells of uniform strength along the flow direction. Low-speed and high-speed streaks at the cell boundaries increase in amplitude in the flow direction. In the turbulent problem a local downflow is envisioned to be caused by large scale structures in the outer part of the boundary layer. The Reynolds-averaged equations were employed with an eddy viscosity which depens only on the distance from the wall. The resulting equations are unstable to longitudinal vortices with a structure similar to the Hiemenz neutral egensolutin, with a continuous spectrum of the spanwise wavenumber. It is found that the wavenumber must be smaller than a critical value which depends on the local strainrate. In general when the downflow is weaker the critical wavenuber is smaller (streak spacing larger).
Entropy generation in the viscous parts of turbulent boundary layers
Donald M. McEligot; Edmund J. Walsh; Eckart Laurien; Philippe R. Spalart
2008-06-01
The local (pointwise) entropy generation rate per unit volume S is a key to improving many energy processes and applications. Consequently, in the present study, the objectives are to examine the effects of Reynolds number and favorable streamwise pressure gradients on entropy generation rates across turbulent boundary layers on flat plates and—secondarily—to assess a popular approximate technique for their evaluation. About two-thirds or more of the entropy generation occurs in the viscous part, known as the viscous layer. Fundamental new results for entropy generation in turbulent boundary layers are provided by extending available direct numerical simulations. It was found that, with negligible pressure gradients, results presented in wall coordinates are predicted to be near “universal” in the viscous layer. This apparent universality disappears when a significant pressure gradient is applied; increasing the pressure gradient decreases the entropy generation rate. Within the viscous layer, the approximate evaluation of S differs significantly from the “proper” value but its integral, the entropy generation rate per unit surface area S, agrees within 5% at its edge.
Boundary-layer turbulence as a kangaroo process
NASA Astrophysics Data System (ADS)
Dekker, H.; de Leeuw, G.; Maassen van den Brink, A.
1995-09-01
A nonlocal mixing-length theory of turbulence transport by finite size eddies is developed by means of a novel evaluation of the Reynolds stress. The analysis involves the contruct of a sample path space and a stochastic closure hypothesis. The simplifying property of exhange (strong eddies) is satisfied by an analytical sampling rate model. A nonlinear scaling relation maps the path space onto the semi-infinite boundary layer. The underlying near-wall behavior of fluctuating velocities perfectly agrees with recent direct numerical simulations. The resulting integro-differential equation for the mixing of scalar densities represents fully developed boundary-layer turbulence as a nondiffusive (Kubo-Anderson or kangaroo) type of stochastic process. The model involves a scaling exponent ɛ (with ɛ-->∞ in the diffusion limit). For the (partly analytical) solution for the mean velocity profile, excellent agreement with the experimental data yields ɛ~=0.58.
Direct Numerical Simulations of Sound-Orifice-Boundary Layer Interaction
NASA Astrophysics Data System (ADS)
Zhang, Qi; Bodony, Daniel
2015-11-01
We report on a series of direct numerical simulations (DNS) of the interaction of a monochromatic incident acoustic field with a cavity-backed circular orifice in the presence of laminar and turbulent boundary layers of freestream Mach number 0.5 and momentum thickness Reynolds number 2,300, with application to acoustic liners. The simulations show that the addition of the orifice increases the drag and can induce laminar-to-turbulent transition at sufficiently high acoustic levels. Furthermore, the sound-orifice-boundary layer system support three distinct timescales whose spatial distributions change with the phase of the incident sound. Details of the near-orifice interaction are studied to create a model of the orifice discharge coefficient that is part of a time-domain, nonlinear reduced-order model (ROM) for the liner impedance. Comparisons between the ROM-predicted and DNS-measured near-orifice flow and acoustic impedance are given.
Temporally optimized spanwise vorticity sensor measurements in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Morrill-Winter, C.; Klewicki, J.; Baidya, R.; Marusic, I.
2015-12-01
Multi-element hot-wire anemometry was used to measure spanwise vorticity fluctuations in turbulent boundary layers. Smooth wall boundary layer profiles, with very good spatial and temporal resolution, were acquired over a Kármán number range of 2000-12,700 at the Melbourne Wind Tunnel at the University of Melbourne and the University of New Hampshire's Flow Physics Facility. A custom hot-wire probe was necessary to simultaneously obtain velocity and spanwise vorticity measurements centered at a fixed point in space. A custom calibration/processing scheme was developed to utilize single-wall-parallel wires to optimize the accuracy of the measured wall-normal velocity fluctuations derived from the sensor's ×-array.
Turbulence structures in a strongly decelerated boundary layer
NASA Astrophysics Data System (ADS)
Gungor, Ayse G.; Maciel, Yvan; Simens, Mark P.
2014-11-01
The characteristics of three-dimensional intense Reynolds shear stress structures (Qs) are presented from a direct numerical simulation of an adverse pressure gradient boundary layer at Reθ = 1500 -2175. The intense Q2 (ejections) and Q4 (sweeps) structures separate into two groups: wall-attached and wall-detached structures. In the region where turbulent activity is maximal, between 0 . 2 δ and 0 . 6 δ , 94 % of the structures are detached structures. In comparison to canonical wall flows, the large velocity defect turbulent boundary layers are less efficient in extracting turbulent energy from the mean flow. There is, furthermore, much less turbulence activity and less velocity coherence near the wall. Additionally, the wall-detached structures are more frequent and carry a much larger amount of Reynolds shear stress. Funded in part by ITU, NSERC of Canada, and Multiflow program of the ERC.
Investigation of Turbulent Boundary-Layer Separation Using Laser Velocimetry
NASA Technical Reports Server (NTRS)
Modarress, D.; Johnson, D. A.
1979-01-01
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.
Inverse boundary-layer technique for airfoil design
NASA Technical Reports Server (NTRS)
Henderson, M. L.
1979-01-01
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.
Evaporation estimates using weather station data and boundary layer theory
NASA Astrophysics Data System (ADS)
Gentine, P.; Chhang, A.; Rigden, A.; Salvucci, G.
2016-11-01
Global estimates of evapotranspiration remain a challenge. In this study, we show that the daily course of air temperature and specific humidity available at routine weather stations can be used to estimate evapotranspiration and the evaporative fraction, the ratio of latent heat flux to available energy at the surface. Indeed, the diurnal increase in air temperature reflects the magnitude of the sensible heat flux and the increase of specific humidity after sunrise reflects the amplitude of evapotranspiration. The method is physically constrained and based on the budget of heat and moisture in the boundary layer. Unlike land surface-based estimates, the proposed boundary layer estimate does not rely on ad hoc surface resistance parameterizations (e.g., Penman-Monteith). The proposed methodology can be applied to data collected at weather stations to estimate evapotranspiration and evaporative fraction under cloudy conditions and in the pre-remote sensing era.
Influence of localised double suction on a turbulent boundary layer
NASA Astrophysics Data System (ADS)
Oyewola, O.; Djenidi, L.; Antonia, R. A.
2007-07-01
The effects of localised suction applied through a pair of porous wall strips on a turbulent boundary layer have been quantified through the measurements of mean velocity and Reynolds stresses. The results indicate that the use of second strip extends the pseudo-relaminarisation zone but also reduces the overshoot in the longitudinal and normal r.m.s. velocities. While the minimum r.m.s. occurs at x/δo=3.0 (one strip) and x/δo=12 (two strips), the reduction observed for the latter case is larger. Relative to no suction, the turbulence level is modified by suction and the effect is enhanced with double suction. This increased effectiveness reflects the fact that the second strip acts on a boundary layer whose near-wall active motion has been seriously weakened by the first strip.
A review of unsteady turbulent boundary-layer experiments
NASA Technical Reports Server (NTRS)
Carr, L. W.
1981-01-01
The essential results of a comprehensive review of existing unsteady turbulent boundary-layer experiments are presented. Different types of unsteady flow facilities are described, and the related unsteady turbulent boundary-layer experiments are cataloged and discussed. The measurements that were obtained in the various experiments are described, and a complete list of experimental results is presented. All the experiments that measured instantaneous values of velocity, turbulence intensity, or turbulent shear stress are identified, and the availability of digital data is indicated. The results of the experiments are analyzed, and several significant trends are identified. An assessment of the available data is presented, delineating gaps in the existing data, and indicating where new or extended information is needed. Guidelines for future experiments are included.
Atmospheric surface and boundary layers of the Amazon Basin
NASA Technical Reports Server (NTRS)
Garstang, Michael
1987-01-01
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.
Excitation of Crossflow Instabilities in a Swept Wing Boundary Layer
NASA Technical Reports Server (NTRS)
Carpenter, Mark H.; Choudhari, Meelan; Li, Fei; Streett, Craig L.; Chang, Chau-Lyan
2010-01-01
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.
Flight Experiment Verification of Shuttle Boundary Layer Transition Prediction Tool
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Berger, Karen T.; Horvath, Thomas J.; Wood, William A.
2016-01-01
Boundary layer transition at hypersonic conditions is critical to the design of future high-speed aircraft and spacecraft. Accurate methods to predict transition would directly impact the aerothermodynamic environments used to size a hypersonic vehicle's thermal protection system. A transition prediction tool, based on wind tunnel derived discrete roughness correlations, was developed and implemented for the Space Shuttle return-to-flight program. This tool was also used to design a boundary layer transition flight experiment in order to assess correlation uncertainties, particularly with regard to high Mach-number transition and tunnel-to-flight scaling. A review is provided of the results obtained from the flight experiment in order to evaluate the transition prediction tool implemented for the Shuttle program.
Boundary layer integral matrix procedure code modifications and verifications
NASA Technical Reports Server (NTRS)
Evans, R. M.; Morse, H. L.
1974-01-01
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.
Optimal disturbances in boundary layers subject to streamwise pressure gradient
NASA Technical Reports Server (NTRS)
Ashpis, David E.; Tumin, Anatoli
2003-01-01
An analysis of the optimal non-modal growth of perturbations in a boundary layer in the presence of a streamwise pressure gradient is presented. The analysis is based on PSE equations for an incompressible fluid. Examples with Falkner-Scan profiles indicate that a favorable pressure gradient decreases the non-modal growth, while an unfavorable pressure gradient leads to an increase of the amplification. It is suggested that the transient growth mechanism be utilized to choose optimal parameters of tripping elements on a low-pressure turbine (LPT) airfoil. As an example, a boundary layer flow with a streamwise pressure gradient corresponding to the pressure distribution over a LPT airfoil is considered. It is shown that there is an optimal spacing of the tripping elements and that the transient growth effect depends on the starting point.
Characteristics of Mach 10 transitional and turbulent boundary layers
NASA Technical Reports Server (NTRS)
Watson, R. D.
1978-01-01
Measurements of the mean flow properties of transitional and turbulent boundary layers in helium on 4 deg and 5 deg wedges were made for flows with edge Mach numbers from 9.5 to 11.3, ratios of wall temperature to total temperature of 0.4 to 0.95, and maximum length Reynolds numbers of one hundred million. The data include pitot and total temperature surveys and measurements of heat transfer and surface shear. In addition, with the assumption of local similarity, turbulence quantities such as the mixing length were derived from the mean flow profiles. Low Reynolds number and precursor transition effects were significant factors at these test conditions and were included in finite difference boundary layer predictions.
Works on theory of flapping wing. [considering boundary layer
NASA Technical Reports Server (NTRS)
Golubev, V. V.
1980-01-01
It is shown mathematically that taking account of the boundary layer is the only way to develop a theory of flapping wings without violating the basic observations and mathematics of hydromechanics. A theory of thrust generation by flapping wings can be developed if the conventional downstream velocity discontinuity surface is replaced with the observed Karman type vortex streets behind a flapping wing. Experiments show that the direction of such vortices is the reverse of that of conventional Karman streets. The streets form by breakdown of the boundary layer. Detailed analysis of the movements of certain birds and insects during flight 'in place' is fully consistent with this theory of the lift, thrust and drag of flapping wings. Further directions for research into flight with flapping wings are indicated.
Modeling roughness effects in turbulent boundary layers using elliptic relaxation
NASA Astrophysics Data System (ADS)
George, Jacob; de Simone, Alejandro; Iaccarino, Gianluca; Jimenez, Javier
2010-11-01
We present results from the efforts towards modeling roughness in turbulent boundary layers using elliptic relaxation. This scheme, included in the v^2-f model and first formulated by Durbin (1993, JFM, vol. 249, p.465) for smooth-walls, uses an elliptic partial differential equation to incorporate near-wall turbulence anisotropy and non-local pressure-strain effects. The use of the elliptic PDE is extended to model roughness effects in various transitionally-rough and fully-rough boundary layers consisting of a uniform and sparse distribution of cylinders for which experimental data is available. The roughness effects are incorporated through the elliptic PDE by including the length and time scales that the roughness imposes upon the flow, which the experiment has shown to be constant within the rough-walls. Further modeling of roughness effects is considered by altering the source terms in the elliptic PDE.
Optimal control of wind turbines in a turbulent boundary layer
NASA Astrophysics Data System (ADS)
Yilmaz, Ali Emre; Meyers, Johan
2016-11-01
In recent years, optimal control theory was combined with large-eddy simulations to study the optimal control of wind farms and their interaction with the atmospheric boundary layer. The individual turbine's induction factors were dynamically controlled in time with the aim of increasing overall power extraction. In these studies, wind turbines were represented using an actuator disk method. In the current work, we focus on optimal control on a much finer mesh (and a smaller computational domain), representing turbines with an actuator line method. Similar to Refs., optimization is performed using a gradient-based method, and gradients are obtained employing an adjoint formulation. Different cases are investigated, that include a single and a double turbine case both with uniform inflow, and with turbulent-boundary-layer inflow. The authors acknowledge support from the European Research Council (FP7-Ideas, Grant No. 306471).
Construction of a Non-Equilibrium Thermal Boundary Layer Facility
NASA Astrophysics Data System (ADS)
Biles, Drummond; Ebadi, Alireza; Ma, Allen; White, Christopher
2015-11-01
A thermally conductive, electrically heated wall-plate forming the bottom wall of a wind tunnel has been constructed and validation tests have been performed. The wall-plate is a sectioned wall design, where each section is independently heated and controlled. Each section consists of an aluminum 6061 plate, an array of resistive heaters affixed to the bottom of the aluminum plate, and a calcium silicate holder used for thermal isolation. Embedded thermocouples in the aluminum plates are used to monitor the wall temperature and for feedback control of wall heating. The wall-plate is used to investigate thermal transport in both equilibrium and non-equilibrium boundary layers. The non-equilibrium boundary layer flow investigated is oscillatory flow produced by a rotor-stator mechanism placed downstream of the test section of the wind tunnel.
Planetary boundary layer dynamics over the Amazon rain forest
NASA Astrophysics Data System (ADS)
Pereiradeoliveira, Amauri
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 forest. A linear model was applied to identify the horizontal extent of these circulations and an associated perturbation pressure gradient consistent with the observations. A second order closure model was used to simulate changes in the PBL caused by the thermal circulation. Good agreement with the observations was obtained when the forcing was a horizontal pressure gradient equal to 0.5 mb/100km of limited vertical extent. The dynamics of the equatorial PBL was shown to be plausibly explained using a hypothesis of a river breeze circulation.
Boundary layer energization by means of optimized vortex generators
NASA Technical Reports Server (NTRS)
Barber, T. J.; Mounts, J. S.; Mccormick, D. C.
1993-01-01
A three-dimensional, multi-block, multi-zone, Euler analysis has been developed and applied to analyze the flow processes induced by a lateral array of low profile vortex generators (VG). These vortex generators have been shown to alleviate boundary layer separation through the generation of streamwise vorticity. The analysis has been applied to help develop improved VG configurations in an efficient manner. Special attention has been paid to determining the accuracy requirements of the solver for calculations in which vortical mechanisms are dominant. The analysis has been used to assess the effectiveness or boundary layer energization capacity of different VG's, including the effect of scale and shape variation. Finally, the analysis has been validated through comparisons with experimental data obtained in a large-scale low-speed wind tunnel.
Leading-edge effects on boundary-layer receptivity
NASA Technical Reports Server (NTRS)
Gatski, Thomas B.; Kerschen, Edward J.
1990-01-01
Numerical calculations are presented for the incompressible flow over a parabolic cylinder. The computational domain extends from a region upstream of the body downstream to the region where the Blasius boundary-layer solution holds. A steady mean flow solution is computed and the results for the scaled surface vorticity, surface pressure and displacement thickness are compared to previous studies. The unsteady problem is then formulated as a perturbation solution starting with and evolving from the mean flow. The response to irrotational time harmonic pulsation of the free-stream is examined. Results for the initial development of the velocity profile and displacement thickness are presented. These calculations will be extended to later times to investigate the initiation of instability waves within the boundary-layer.
Possibilities for drag reduction by boundary layer control
NASA Technical Reports Server (NTRS)
Naiman, I.
1946-01-01
The mechanics of laminar boundary layer transition are reviewed. Drag possibilities for boundary layer control are analyzed using assumed conditions of transition Reynolds number, inlet loss, number of slots, blower efficiency, and duct losses. Although the results of such analysis are highly favorable, those obtained by experimental investigations yield conflicting results, showing only small gains, and sometimes losses. Reduction of this data indicates that there is a lower limit to the quantity of air which must be removed at the slot in order to stabilize the laminar flow. The removal of insufficient air permits transition to occur while the removal of excessive amounts of air results in high power costs, with a net drag increases. With the estimated value of flow coefficient and duct losses equal to half the dynamic pressure, drag reductions of 50% may be obtained; with twice this flow coefficient, the drag saving is reduced to 25%.
NASA Technical Reports Server (NTRS)
Berrier, Bobby L.; Carter, Melissa B.; Allan, Brian G.
2005-01-01
An experimental investigation of a flush-mounted, S-duct inlet with large amounts of boundary layer ingestion has been conducted at Reynolds numbers up to full scale. The study was conducted in the NASA Langley Research Center 0.3-Meter Transonic Cryogenic Tunnel. In addition, a supplemental computational study on one of the inlet configurations was conducted using the Navier-Stokes flow solver, OVERFLOW. Tests were conducted at Mach numbers from 0.25 to 0.83, Reynolds numbers (based on aerodynamic interface plane diameter) from 5.1 million to 13.9 million (full-scale value), and inlet mass-flow ratios from 0.29 to 1.22, depending on Mach number. Results of the study indicated that increasing Mach number, increasing boundary layer thickness (relative to inlet height) or ingesting a boundary layer with a distorted profile decreased inlet performance. At Mach numbers above 0.4, increasing inlet airflow increased inlet pressure recovery but also increased distortion. Finally, inlet distortion was found to be relatively insensitive to Reynolds number, but pressure recovery increased slightly with increasing Reynolds number.This CD-ROM supplement contains inlet data including: Boundary layer data, Duct static pressure data, performance-AIP (fan face) data, Photos, Tunnel wall P-PTO data and definitions.
NASA Astrophysics Data System (ADS)
Kim, C. K.; Kleissl, J. P.; Sahu, D. K.; Ghonima, M. S.
2015-12-01
Accurate forecasts of solar irradiance are required for electric utilities to economically integrate substantial amounts of solar power into their power generation portfolios. A common shortcoming of numerical weather models is the prediction of marine boundary layer clouds such as over the California coast as boundary layer processes are not resolved well. There are two turbulence parameterizations employed in the Weather Research and Forecasting model. The MYNN scheme is based on the turbulent kinetic energy that is explicit calculated in the model while the YSU scheme produces the exchange coefficients based on K-profiles for unstable and stable conditions. The microphysical and dynamical characteristics of marine boundary layer clouds are compared between two turbulence parameterizations and then sensitivity tests are conducted to enhance the exchange coefficients for momentum and heat. The results from the simulations show that increasing the exchange coefficient leads to enhanced vertical mixing and a deeper mixed layer over both sea and land surfaces. In this condition, clouds become deeper increasing cloud lifetime and reducing surface irradiance. These changes will reduce the bias of day-ahead solar forecasting over coastal California.
Grey zone simulations of the morning convective boundary layer development
NASA Astrophysics Data System (ADS)
Efstathiou, G. A.; Beare, R. J.; Osborne, S.; Lock, A. P.
2016-05-01
Numerical simulations of two cases of morning boundary layer development are conducted to investigate the impact of grid resolution on mean profiles and turbulent kinetic energy (TKE) partitioning from the large eddy simulation (LES) to the mesoscale limit. Idealized LES, using the 3-D Smagorinsky scheme, is shown to be capable of reproducing the boundary layer evolution when compared against measurements. However, increasing grid spacing results in the damping of resolved TKE and the production of superadiabatic temperature profiles in the boundary layer. Turbulence initiation is significantly delayed, exhibiting an abrupt onset at intermediate resolutions. Two approaches, the bounding of vertical diffusion coefficient and the blending of the 3-D Smagorinsky with a nonlocal 1D scheme, are used to model subgrid diffusion at grey zone resolutions. Simulations are compared against the coarse-grained fields from the validated LES results for each case. Both methods exhibit particular strengths and weaknesses, indicating the compromise that needs to be made currently in high-resolution numerical weather prediction. The blending scheme is able to reproduce the adiabatic profiles although turbulence is underestimated in favor of the parametrized heat flux, and the spin-up of TKE remains delayed. In contrast, the bounding approach gives an evolution of TKE that follows the coarse-grained LES very well, relying on the resolved motions for the nonlocal heat flux. However, bounding gives unrealistic static instability in the early morning temperature profiles (similar to the 3-D Smagorinsky scheme) because model dynamics are unable to resolve TKE when the boundary layer is too shallow compared to the grid spacing.
Vortex/boundary-layer interactions: Data report, volume 1
NASA Technical Reports Server (NTRS)
Cutler, A. D.; Bradshaw, P.
1987-01-01
This report summarizes the work done under NASA Grant NAGw-581, Vortex/Boundary Layer Interactions. The experimental methods are discussed in detail and numerical results are presented, but are not fully interpreted. This report should be useful to anyone who wishes to make further use of the data (available on floppy disc or magnetic tape) for the development of turbulence models or the validation of predictive methods. Journal papers are in course of preparation.
Vortex/boundary-layer interactions: Data report, volume 2
NASA Technical Reports Server (NTRS)
Cutler, A. D.; Bradshaw, P.
1987-01-01
This report summarizes the work done under NASA grant NAGw-581, Vortex/Boundary-Layer Interactions, to date. The experimental methods are discussed in detail and the results presented as a large number of figures, but are not fully interpreted. This report should be useful to anyone who wishes to make further use of the data (available on floppy disc or magnetic tape) for the development of turbulence models or the validation of predictive methods. Journal papers are in preparation.
Study of EM Signals Propagation Through Marine Atmospheric Boundary Layer
2002-09-30
transmision properties. REFERENCES Barrick, D.E., and Weber, B.L., ’On the nonlinear theory for gravity waves on the ocean’s surface. Part II...and Friehe C., 2000. Boundary-Layer Meteorology, 97, 293-307. Ishimaru, A. 1978, Wave propagation and scattering in random media . Academic Press...Irvine. Rytov, S. M., Y. A. Kravtsov, and V. I. Tatarskii: 1987, Principles of statistical radiophysics 4: Wave propagation through random media
Study of Vortices Embedded in Boundary Layers with Film Cooling.
1987-03-01
Turbine parts may be protected from heat loads resulting from exposure to gas at high temperatures by using a coolant within turbine passages and along...then protects metal surfaces by forming a protective insulating film between the blades and the mainstream, and by acting as a heat sink. The flow...boundary layer. In order to understand the effects that this complex flow field has upon heat transfer, vortex characteristics and their interaction with
Partially exposed polymer dispersed liquid crystals for boundary layer investigations
NASA Technical Reports Server (NTRS)
Parmar, Devendra S.; Singh, Jag J.
1992-01-01
A new configuration termed partially exposed polymer dispersed liquid crystal in which the liquid crystal microdroplets dispersed in a rigid polymer matrix are partially entrapped on the free surface of the thin film deposited on a glass substrate is reported. Optical transmission characteristics of the partially exposed polymer dispersed liquid crystal thin film in response to an air flow induced shear stress field reveal its potential as a sensor for gas flow and boundary layer investigations.
Boundary layer elasto-optic switching in ferroelectric liquid crystals
NASA Technical Reports Server (NTRS)
Parmar, D. S.
1992-01-01
The first experimental observation of a change in the director azimuthal angle due to applied shear stress is reported in a sample configuration involving a liquid-crystal-coated top surface exposed directly to gas flow. The electrooptic response caused by the shear stress is large, fast, and reversible. These findings are relevant to the use of liquid crystals in boundary layer investigations on wind tunnel models.
Turbulent Boundary Layer Thickness Estimation Method and Apparatus
2003-04-02
correlation coefficient is computed with measured data from the recorded voltage. A laboratory non- dimensional value of the correlation coefficient is independently determined from laboratory data. The real non-dimensional value is compared with the laboratory non-dimensional value to obtain a boundary layer thickness having a value which minimizes a difference between the values of the real non-dimensional value and the laboratory non-dimensional
SCALING OF THE ANOMALOUS BOOST IN RELATIVISTIC JET BOUNDARY LAYER
Zenitani, Seiji; Hesse, Michael; Klimas, Alex
2010-04-01
We investigate the one-dimensional interaction of a relativistic jet and an external medium. Relativistic magnetohydrodynamic simulations show an anomalous boost of the jet fluid in the boundary layer, as previously reported. We describe the boost mechanism using an ideal relativistic fluid and magnetohydrodynamic theory. The kinetic model is also examined for further understanding. Simple scaling laws for the maximum Lorentz factor are derived, and verified by the simulations.
Boundary Layer Transition Experiments in Support of the Hypersonics Program
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Chen, Fang-Jenq; Wilder, Michael C.; Reda, Daniel C.
2007-01-01
Two experimental boundary layer transition studies in support of fundamental hypersonics research are reviewed. The two studies are the HyBoLT flight experiment and a new ballistic range effort. Details are provided of the objectives and approach associated with each experimental program. The establishment of experimental databases from ground and flight are to provide better understanding of high-speed flows and data to validate and guide the development of simulation tools.
Aerosol-Cloud-Drizzle-Turbulence Interactions in Boundary Layer Clouds
2012-09-30
provide a means for evaluating and developing parameterizations for models that predict cloud microphysical processes. Observations of the...observed during BACEX was associated with African dust above the boundary layer. On two days when convection was completely suppressed, an African... dust event associated with record Aerosol Optical Depths (AODs) for Barbados during this time of the year was observed. The vertical structure of the
Investigation of the Turbulence Producing Structures in the Boundary Layer
1991-07-15
34 . I, IS ieq/noni fCg of M na emE-t Ind Sudag". 0 8ew Or% Aodu tiOm Prole" (0704411), W.ash gon. OC 20SO3. ... RT DATE 3. REPORT TYPE AND DATE...Spalart, P.R., Spatial Character and Time Evolution of Coherent Structures in a Numerically Simulated Boundary Layer, AIAA 88-3577, 19884 ak Robinson
Linear stability theory and three-dimensional boundary layer transition
NASA Technical Reports Server (NTRS)
Spall, Robert E.; Malik, Mujeeb R.
1992-01-01
The viewgraphs and discussion of linear stability theory and three dimensional boundary layer transition are provided. The ability to predict, using analytical tools, the location of boundary layer transition over aircraft-type configurations is of great importance to designers interested in laminar flow control (LFC). The e(sup N) method has proven to be fairly effective in predicting, in a consistent manner, the location of the onset of transition for simple geometries in low disturbance environments. This method provides a correlation between the most amplified single normal mode and the experimental location of the onset of transition. Studies indicate that values of N between 8 and 10 correlate well with the onset of transition. For most previous calculations, the mean flows were restricted to two-dimensional or axisymmetric cases, or have employed simple three-dimensional mean flows (e.g., rotating disk, infinite swept wing, or tapered swept wing with straight isobars). Unfortunately, for flows over general wing configurations, and for nearly all flows over fuselage-type bodies at incidence, the analysis of fully three-dimensional flow fields is required. Results obtained for the linear stability of fully three-dimensional boundary layers formed over both wing and fuselage-type geometries, and for both high and low speed flows are discussed. When possible, transition estimates form the e(sup N) method are compared to experimentally determined locations. The stability calculations are made using a modified version of the linear stability code COSAL. Mean flows were computed using both Navier Stokes and boundary-layer codes.
Numerical Simulation of Transition in Hypersonic Boundary Layers
2011-02-01
T∗∞=103.6K, flat plate. . . . . . . . . 139 6.1 Boundary layer edge Reynolds number as a function of downstream posi- tion for the computed baseflow...200 7.1 Computational domain used for Temporal Direct Numerical Simulations. 205 7.2 Comparison of base flow profiles at downstream location...the computational methods used for all direct numerical simulations (DNS) discussed in this report are presented. The results for a flat plate (Chapter
Aerosol-Cloud-Drizzle-Turbulence Interactions in Boundary Layer Clouds
2013-09-30
understanding of the effects of aerosol-cloud interactions and drizzle and entrainment processes in boundary layer clouds for the purpose of developing...thickness, cloud turbulence intensity, and aerosols on precipitation production; 4) study the processing of aerosols by cloud processes ; 5) explore mass...drizzle processes to the artificial introduction of CCN and giant nuclei under differing aerosol backgrounds. In addition, a set of aerosol and cloud
Lecture Series. Boundary Layer Theory. Part 1. Laminar Flows
1949-04-01
conditions =: p ’ =0 The solution found by series development can be found in the thesis of Hiemenz (reference 10), compare table 1*. The velocity...Boundary Layer on the Cylinder (symmetrical case) The integration method of Blasius given in the previous section was used by Hiemenz (thesis G6ttingen...the differential equations (9.33) are best obtained by numerical integration. The functions f, and f3 were already calculated by Hiemenz (reference
Navier-Stokes Simulation of Boundary-Layer Transition
1990-05-01
AUTHOITY 3 DISTRIBUTION/AVAILABILITY OF REPORT Approved for publlo release, distri but ion unmlioe4 ’ AD-A226 351 5 . MONITORING ORGANIZATION REPORT NUMBER...ARJSR 87-0237, "Navier-Stokes Simulation of Boundary-Layer Transition" escrs. 5 w ccessful efforts to computationally model the receptivity of the...3.1 Basic-State Results........................................ 4 3.2 Unsteady-Disturbance Results................................. 5 3.3 Conclusions
A Review of Unsteady Turbulent Boundary-Layer Experiments.
1981-06-01
thickness. A good example of this phenomenon is shown in Fig. 17, from Houdeville et al. (1976). Here the adverse pressure gradient has combined with...e) When existing data are plotted using the dimensionless frequency, S , quasisteady results occur for only a small range of amplitude or frequency...Houdeville, R.; Raynaud , M.: Oscillating turbulent boundary layer with strong mean pressure gradient. Presented at 2nd Symposium on Turbulent Shear
Evolution and formation of shear layers in a developing turbulent boundary layer
NASA Astrophysics Data System (ADS)
Lee, Junghoon; Monty, Jason; Hutchins, Nicholas
2016-11-01
The evolution and formation mechanism of shear layers in the outer region of a turbulent boundary layer are investigated using time-resolved PIV datasets of a developing turbulent boundary layer from inception at the trip up to Reτ = 3000 . An analysis of a sequence of instantaneous streamwise velocity fluctuation fields reveals that strong streamwise velocity gradients are prevalent along interfaces where low- and high-speed regions interact. To provide an insight on how such regions are associated with the formation of shear layers in the outer regions, we compute conditional averages of streamwise velocity fluctuations based on a strong shear layer. Our results reveal that one possible mechanism for the generation of shear layers in the outer region is due to the mismatch in the convection velocities between low- and high-speed regions. The results also indicate that the angle of the inclined shear layer is developing in time. In addition, the conditionally averaged velocity fluctuations exhibit a local instability along these shear layers, leading to a shear layer roll-up event as the layers evolve in time. Based on these findings, we propose a conceptual model which describes dynamic interactions of shear layers and their associated large-scale coherent motions. The authors wish to acknowledge the financial support of the Australian Research Council.
Cloud-Scale Numerical Modeling of the Arctic Boundary Layer
NASA Technical Reports Server (NTRS)
Krueger, Steven K.
1998-01-01
The interactions between sea ice, open ocean, atmospheric radiation, and clouds over the Arctic Ocean exert a strong influence on global climate. Uncertainties in the formulation of interactive air-sea-ice processes in global climate models (GCMs) result in large differences between the Arctic, and global, climates simulated by different models. Arctic stratus clouds are not well-simulated by GCMs, yet exert a strong influence on the surface energy budget of the Arctic. Leads (channels of open water in sea ice) have significant impacts on the large-scale budgets during the Arctic winter, when they contribute about 50 percent of the surface fluxes over the Arctic Ocean, but cover only 1 to 2 percent of its area. Convective plumes generated by wide leads may penetrate the surface inversion and produce condensate that spreads up to 250 km downwind of the lead, and may significantly affect the longwave radiative fluxes at the surface and thereby the sea ice thickness. The effects of leads and boundary layer clouds must be accurately represented in climate models to allow possible feedbacks between them and the sea ice thickness. The FIRE III Arctic boundary layer clouds field program, in conjunction with the SHEBA ice camp and the ARM North Slope of Alaska and Adjacent Arctic Ocean site, will offer an unprecedented opportunity to greatly improve our ability to parameterize the important effects of leads and boundary layer clouds in GCMs.
Thermocapillary Bubble Migration: Thermal Boundary Layers for Large Marangoni Numbers
NASA Technical Reports Server (NTRS)
Balasubramaniam, R.; Subramanian, R. S.
1996-01-01
The migration of an isolated gas bubble in an immiscible liquid possessing a temperature gradient is analyzed in the absence of gravity. The driving force for the bubble motion is the shear stress at the interface which is a consequence of the temperature dependence of the surface tension. The analysis is performed under conditions for which the Marangoni number is large, i.e. energy is transferred predominantly by convection. Velocity fields in the limit of both small and large Reynolds numbers are used. The thermal problem is treated by standard boundary layer theory. The outer temperature field is obtained in the vicinity of the bubble. A similarity solution is obtained for the inner temperature field. For both small and large Reynolds numbers, the asymptotic values of the scaled migration velocity of the bubble in the limit of large Marangoni numbers are calculated. The results show that the migration velocity has the same scaling for both low and large Reynolds numbers, but with a different coefficient. Higher order thermal boundary layers are analyzed for the large Reynolds number flow field and the higher order corrections to the migration velocity are obtained. Results are also presented for the momentum boundary layer and the thermal wake behind the bubble, for large Reynolds number conditions.
Using UAV's to Measure the Urban Boundary Layer
NASA Astrophysics Data System (ADS)
Jacob, R. L.; Sankaran, R.; Beckman, P. H.
2015-12-01
The urban boundary layer is one of the most poorly studied regions of the atmospheric boundary layer. Since a majority of the world's population now lives in urban areas, it is becoming a more important region to measure and model. The combination of relatively low-cost unmanned aerial vehicles and low-cost sensors can together provide a new instrument for measuring urban and other boundary layers. We have mounted a new sensor and compute platform called Waggle on an off-the-shelf XR8 octo-copter from 3DRobotics. Waggle consists of multiple sensors for measuring pressure, temperature and humidity as well as trace gases such as carbon monoxide, nitrogen dioxide, sulfur dioxide and ozone. A single board computer running Linux included in Waggle on the UAV allows in-situ processing and data storage. Communication of the data is through WiFi or 3G and the Waggle software can save the data in case communication is lost during flight. The flight pattern is a deliberately simple vertical ascent and descent over a fixed location to provide vertical profiles and so flights can be confined to urban parks, industrial areas or the footprint of a single rooftop. We will present results from test flights in urban and rural areas in and around Chicago.
Improving Subtropical Boundary Layer Cloudiness in the 2011 NCEP GFS
Fletcher, J. K.; Bretherton, Christopher S.; Xiao, Heng; Sun, Ruiyu N.; Han, J.
2014-09-23
The current operational version of National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) shows significant low cloud bias. These biases also appear in the Coupled Forecast System (CFS), which is developed from the GFS. These low cloud biases degrade seasonal and longer climate forecasts, particularly of short-wave cloud radiative forcing, and affect predicted sea surface temperature. Reducing this bias in the GFS will aid the development of future CFS versions and contributes to NCEP's goal of unified weather and climate modelling. Changes are made to the shallow convection and planetary boundary layer parameterisations to make them more consistent with current knowledge of these processes and to reduce the low cloud bias. These changes are tested in a single-column version of GFS and in global simulations with GFS coupled to a dynamical ocean model. In the single-column model, we focus on changing parameters that set the following: the strength of shallow cumulus lateral entrainment, the conversion of updraught liquid water to precipitation and grid-scale condensate, shallow cumulus cloud top, and the effect of shallow convection in stratocumulus environments. Results show that these changes improve the single-column simulations when compared to large eddy simulations, in particular through decreasing the precipitation efficiency of boundary layer clouds. These changes, combined with a few other model improvements, also reduce boundary layer cloud and albedo biases in global coupled simulations.
Impinging Turbulent Boundary Layer Influence on Horseshoe Vortex Periodicity
NASA Astrophysics Data System (ADS)
Smith, Charles; Sabatino, Daniel
2000-11-01
The spatial-temporal flow-field and associated surface heat transfer for a turbulent juncture flow were experimentally examined in a water channel using PIV and thermochromic liquid crystals. Turbulent boundary layer "burst" events, which have been previously described as hairpin vortex "packets," are shown to interact and periodically strengthen the juncture-region horseshoe vortex (HV). This strengthening of the HV precipitates its movement upstream and toward the surface. This process that induces the ejection of a secondary vortex, which weakens the HV, with the strengthen-ejection-weakening cycle repeating quasi-periodically. The dominant period of motion for the HV correlates closely to the impinging turbulent boundary layer bursting frequency. This vortex-bursting interaction is responsible for the elevated endwall surface heat transfer upstream of the corner vortex region. The temporal endwall surface heat transfer behavior for a linear turbine cascade juncture was also determined to be essentially the same as that for a simple bluff body, with the impinging boundary layer bursting frequency again being the controlling parameter.
Some characteristics of bypass transition in a heated boundary layer
NASA Technical Reports Server (NTRS)
Sohn, K. H.; Obrien, J. E.; Reshotko, E.
1989-01-01
Experimental measurements of both mean and conditionally sampled characteristics of laminar, transitional and low Reynolds number turbulent boundary layers on a heated flat plate are presented. Measurements were obtained in air over a range of freestream turbulence intensities from 0.3 percent to 6 percent with a freestream velocity of 30.5 m/s and zero pressure gradient. Conditional sampling performed in the transitional boundary layers indicate the existence of a near-wall drop in intermittency, especially pronounced at low intermittencies. Nonturbulent intervals were observed to possess large levels of low-frequency unsteadiness, and turbulent intervals had peak intensities as much as 50 percent higher than were measured at fully turbulent stations. Heat transfer results were consistent with results of previous researchers and Reynolds analogy factors were found to be well predicted by laminar and turbulent correlations which accounted for unheated starting length. A small dependence of the turbulent Reynolds analogy factors on freestream turbulence level was observed. Laminar boundary layer spectra indicated selective amplification of unstable frequencies. These instabilities appear to play a dominant role in the transition process only for the lowest freestream turbulence level studied, however.
Linear stability of three-dimensional boundary layers
NASA Astrophysics Data System (ADS)
Gaponov, S. A.; Smorodskii, B. V.
2008-03-01
Stability of compressible three-dimensional boundary layers on a swept wing model is studied within the framework of the linear theory. The analysis based on the approximation of local self-similarity of the mean flow was performed within the Falkner-Skan-Cooke solution extended to compressible flows. The calculated characteristics of stability for a subsonic boundary layer are found to agree well with the measured results. In the case of a supersonic boundary layer, the results calculated for a Mach number M = 2 are also in good agreement with the measured spanwise scales of nonstationary vortices of the secondary flow. The calculated growth rates of disturbances, however, are substantially different from the measured values. This difference can be attributed to a high initial amplitude of disturbances generated in the experiment, which does not allow the linear stability theory to be applied. The evolution of natural disturbances with moderate amplitudes is fairly well predicted by the theory. The effect of compressibility on crossflow instability modes is demonstrated to be insignificant.
Physical processes within the nocturnal stratus-topped boundary layer
Moeng, C.H.; Shen, S. ); Randall, D.A. )
1992-12-15
Within the stratus-topped boundary layer many physical processes are involved: longwave radiation cooling, entrainment, latent heating, surface heating, solar heating, drizzling, etc. How all processes combine to maintain the turbulence within the stratus-topped boundary layer remains an unsolved problem. The large-eddy simulation technique is used to examine the first four physical processes mentioned. First, the contribution of each physical process to the thermodynamic differences between the updraft and downdraft branches of turbulent circulations is examined through a conditional sampling. Second, these mean thermodynamic differences are shown to express well the vertical distributions of heat and moisture fluxes within stratus-topped boundary layers. These provide a method to validate the process-partitioning technique. (This technique assumes that the net flux profile can be partitioned into different component-flux profiles according to physical processes and that each partitioned component flux is linear in height.) In this paper, the heat and moisture fluxes are process partitioned, and each component flux is found to contribute to the net flux in a way that is consistent with its corresponding process contribution to the mean thermodynamic differences between updrafts and downdrafts. Also, the net flux obtained by summing all component fluxes agrees well with that obtained directly from the large-eddy simulations.
An analytical model of capped turbulent oscillatory bottom boundary layers
NASA Astrophysics Data System (ADS)
Shimizu, Kenji
2010-03-01
An analytical model of capped turbulent oscillatory bottom boundary layers (BBLs) is proposed using eddy viscosity of a quadratic form. The common definition of friction velocity based on maximum bottom shear stress is found unsatisfactory for BBLs under rotating flows, and a possible extension based on turbulent kinetic energy balance is proposed. The model solutions show that the flow may slip at the top of the boundary layer due to capping by the water surface or stratification, reducing the bottom shear stress, and that the Earth's rotation induces current and bottom shear stress components perpendicular to the interior flow with a phase lag (or lead). Comparisons with field and numerical experiments indicate that the model predicts the essential characteristics of the velocity profiles, although the agreement is rather qualitative due to assumptions of quadratic eddy viscosity with time-independent friction velocity and a well-mixed boundary layer. On the other hand, the predicted linear friction coefficients, phase lead, and veering angle at the bottom agreed with available data with an error of 3%-10%, 5°-10°, and 5°-10°, respectively. As an application of the model, the friction coefficients are used to calculate e-folding decay distances of progressive internal waves with a semidiurnal frequency.
Turbulence and mixing in the stable atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Yagüe, C.; Morales, G.; Terradellas, E.; Cuxart, J.
2003-04-01
Transport and mixing in the Stable Atmospheric Boundary Layer is not well understood yet. However this is an important feature in atmospheric pollution as well as in other environmental studies. A Stable Atmospheric Boundary Layer Experiment in Spain (SABLES98) took place from the 10th to the 28th of September 1998. Two masts (100 m and 10 m) were instrumented with five sonic anemometers, 14 thermocouples, 8 cup anemometers, vanes,radiometers, etc. In addition, a sodar, a tethered balloon and a triangular array of cup anemometers were operating during the campaign. The experiment showed three different regimes, being specially interesting the one between 14th and 21st of September where stable and very stable conditions were present. In this work we present the behaviour of turbulent and stability parameters at several heights. The different evolutions of the Nocturnal Boundary Layer and the main parameters that controle its behaviour are discussed.The influence of internal gravity waves and their interaction with turbulence is also studied using wavelets.
Improving Wind-Ramp Forecasts in the Stable Boundary Layer
NASA Astrophysics Data System (ADS)
Jahn, David E.; Takle, Eugene S.; Gallus, William A.
2017-02-01
The viability of wind-energy generation is dependent on highly accurate numerical wind forecasts, which are impeded by inaccuracies in model representation of boundary-layer processes. This study revisits the basic theory of the Mellor, Yamada, Nakanishi, and Niino (MYNN) planetary boundary-layer parametrization scheme, focusing on the onset of wind-ramp events related to nocturnal low-level jets. Modifications to the MYNN scheme include: (1) calculation of new closure parameters that determine the relative effects of turbulent energy production, dissipation, and redistribution; (2) enhanced mixing in the stable boundary layer when the mean wind speed exceeds a specified threshold; (3) explicit accounting of turbulent potential energy in the energy budget. A mesoscale model is used to generate short-term (24 h) wind forecasts for a set of 15 cases from both the U.S.A. and Germany. Results show that the new set of closure parameters provides a marked forecast improvement only when used in conjunction with the new mixing length formulation and only for cases that are originally under- or over-forecast (10 of the 15 cases). For these cases, the mean absolute error (MAE) of wind forecasts at turbine-hub height is reduced on average by 17%. A reduction in MAE values on average by 26% is realized for these same cases when accounting for the turbulent potential energy together with the new mixing length. This last method results in an average reduction by at least 13% in MAE values across all 15 cases.
Manipulation of Turbulent Boundary Layers Using Synthetic Jets
NASA Astrophysics Data System (ADS)
Berger, Zachary; Gomit, Guillaume; Lavoie, Philippe; Ganapathisubramani, Bharath
2015-11-01
This work focuses on the application of active flow control, in the form of synthetic jet actuators, of turbulent boundary layers. An array of 2 synthetic jets are oriented in the spanwise direction and located approximately 2.7 meters downstream from the leading edge of a flat plate. Actuation is applied perpendicular to the surface of the flat plate with varying blowing ratios and reduced frequencies (open-loop). Two-component large window particle image velocimetry (PIV) was performed at the University of Southampton, in the streamwise-wall-normal plane. Complementary stereo PIV measurements were performed at the University of Toronto Institute for Aerospace Studies (UTIAS), in the spanwise-wall-normal plane. The freestream Reynolds number is 3x104, based on the boundary layer thickness. The skin friction Reynolds number is 1,200 based on the skin friction velocity. The experiments at Southampton allow for the observation of the control effects as the flow propagates downstream. The experiments at UTIAS allow for the observation of the streamwise vorticity induced from the actuation. Overall the two experiments provide a 3D representation of the flow field with respect to actuation effects. The current work focuses on the comparison of the two experiments, as well as the effects of varying blowing ratios and reduced frequencies on the turbulent boundary layer. Funded Supported by Airbus.
Effect of thermally induced perturbation in supersonic boundary layers
NASA Astrophysics Data System (ADS)
Yan, Hong; Gaitonde, Datta
2010-06-01
This paper investigates the mechanism of steady and unsteady thermal perturbation (also denoted as thermal bump) in a Mach 1.5 flat plate boundary layer. A high-fidelity upwind-biased third-order Roe scheme is used with the compressive van Leer harmonic limiter on a suitably refined mesh. The study consists of two parts. In the first part, the effects of the steady and pulsed thermal bumps are explored. It is shown that the finite-span thermal bumps generate streamwise vortices. With steady heating, the disturbance decays downstream. However, when the thermal bump is pulsed, vortex shedding is observed and the streamwise vortical disturbance grows with downstream distance, consistent with linear stability analysis. The integrated disturbance energy indicates that streamwise kinetic disturbance energy growth dominates over those associated with other two velocity and thermodynamic components. The second part of this paper explores the physical consequences of the nonlinear dynamics between the vortices produced by the pulsed bump and the compressible boundary layer. The resulting three-dimensional flow distortion generates hairpin structures which are aligned in the streamwise direction, suggesting that the transition process bears some similarity to K-type breakdown. The arrangement of these vortices is connected to the low-speed streaks observed in the evolving boundary layer. The shape factor, velocity, and Reynolds stress profiles suggest that the perturbed flow shows initiation of transition to turbulence, but remains transitional at the end of the plate.
RANS Modeling of Benchmark Shockwave / Boundary Layer Interaction Experiments
NASA Technical Reports Server (NTRS)
Georgiadis, Nick; Vyas, Manan; Yoder, Dennis
2010-01-01
This presentation summarizes the computations of a set of shock wave / turbulent boundary layer interaction (SWTBLI) test cases using the Wind-US code, as part of the 2010 American Institute of Aeronautics and Astronautics (AIAA) shock / boundary layer interaction workshop. The experiments involve supersonic flows in wind tunnels with a shock generator that directs an oblique shock wave toward the boundary layer along one of the walls of the wind tunnel. The Wind-US calculations utilized structured grid computations performed in Reynolds-averaged Navier-Stokes mode. Three turbulence models were investigated: the Spalart-Allmaras one-equation model, the Menter Shear Stress Transport wavenumber-angular frequency two-equation model, and an explicit algebraic stress wavenumber-angular frequency formulation. Effects of grid resolution and upwinding scheme were also considered. The results from the CFD calculations are compared to particle image velocimetry (PIV) data from the experiments. As expected, turbulence model effects dominated the accuracy of the solutions with upwinding scheme selection indicating minimal effects.!
Review of Orbiter Flight Boundary Layer Transition Data
NASA Technical Reports Server (NTRS)
Mcginley, Catherine B.; Berry, Scott A.; Kinder, Gerald R.; Barnell, maria; Wang, Kuo C.; Kirk, Benjamin S.
2006-01-01
In support of the Shuttle Return to Flight program, a tool was developed to predict when boundary layer transition would occur on the lower surface of the orbiter during reentry due to the presence of protuberances and cavities in the thermal protection system. This predictive tool was developed based on extensive wind tunnel tests conducted after the loss of the Space Shuttle Columbia. Recognizing that wind tunnels cannot simulate the exact conditions an orbiter encounters as it re-enters the atmosphere, a preliminary attempt was made to use the documented flight related damage and the orbiter transition times, as deduced from flight instrumentation, to calibrate the predictive tool. After flight STS-114, the Boundary Layer Transition Team decided that a more in-depth analysis of the historical flight data was needed to better determine the root causes of the occasional early transition times of some of the past shuttle flights. In this paper we discuss our methodology for the analysis, the various sources of shuttle damage information, the analysis of the flight thermocouple data, and how the results compare to the Boundary Layer Transition prediction tool designed for Return to Flight.
The nonlinear development of Gortler vortices in growing boundary layers
NASA Technical Reports Server (NTRS)
Hall, Philip
1986-01-01
The development of Gortler vortices in boundary layers over curved walls in the nonlinear regime is investigated. The growth of the boundary layer makes a parallel flow analysis impossible except in the high wavenumber regime so in general the instability equations must be integrated numerically. Here the spanwise dependence of the basic flow is described using Fourier series expansion whilst the normal and streamwise variations are taken into account using finite differences. The calculations suggest that a given disturbance imposed at some position along the wall will eventually reach a local equilibrium state essentially independent of the initial conditions. In fact, the equilibrium state reached is qualitatively similar to the large amplitude high wave-number solution described asymptotically by Hall (1982). In general, it is found that the nonlinear interactions are dominated by a mean field type of interaction between the mean flow and the fundamental. Thus, even though higher harmonics of the fundamental are necessarily generated, most of the disturbance energy is confined to the mean flow correction and the fundamental. A major result of the calculations is finding that the downstream velocity field develops a strongly inflection character as the flow moves downstream. The latter result suggests that the major effect of Gortler vortices on boundary layers of practical importance might be to make them highly receptive to rapidly growing Rayleigh modes of instability.
The nonlinear development of Goertler vortices in growing boundary layers
NASA Technical Reports Server (NTRS)
Hall, Philip
1988-01-01
The development of Goertler vortices in boundary layers over curved walls in the nonlinear regime is investigated. The growth of the boundary layer makes a parallel flow analysis impossible except in the high wavenumber regime so in general the instability equations must be integrated numerically. Here the spanwise dependence of the basic flow is described using Fourier series expansion while the normal and streamwise variations are taken into account using finite differences. The calculations suggest that a given disturbance imposed at some position along the wall will eventually reach a local equilibrium state essentially independent of the initial conditions. In fact, the equilibrium state reached is qualitatively similar to the large amplitude high wave-number solution described asymptotically by Hall (1982). In general, it is found that the nonlinear interactions are dominated by a mean field type of interaction between the mean flow and the fundamental. Thus, even though higher harmonics of the fundamental are necessarily generated, most of the disturbance energy is confined to the mean flow correction and the fundamental. A major result of the calculations is finding that the downstream velocity field develops a strongly inflectional character as the flow moves downstream. The latter result suggests that the major effect of Goertler vortices on boundary layers of practical importance might be to make them highly receptive to rapidly growing Rayleigh modes of instability.
Minnowbrook II 1997 Workshop on Boundary Layer Transition in Turbomachines
NASA Technical Reports Server (NTRS)
LaGraff John E. (Editor); Ashpis, David E. (Editor)
1998-01-01
The volume contains materials presented at the Minnowbrook II - 1997 Workshop on Boundary Layer Transition in Turbomachines, held at Syracuse University Minnowbrook Conference Center, New York, on September 7-10, 1997. The workshop followed the informal format at the 1993 Minnowbrook I workshop, focusing on improving the understanding of late stage (final breakdown) boundary layer transition, with the engineering application of improving design codes for turbomachinery in mind. Among the physical mechanisms discussed were hydrodynamic instabilities, laminar to turbulent transition, bypass transition, turbulent spots, wake interaction with boundary layers, calmed regions, and separation, all in the context of flow in turbomachinery, particularly in compressors and high and low pressure turbines. Results from experiments, DNS, computation, modeling and theoretical analysis were presented. Abstracts and copies of viewgraphs, a specifically commissioned summation paper prepared after the workshop, and a transcript of the extensive working group reports and discussions are included in this volume. They provide recommendations for future research and clearly highlight the need for continued vigorous research in the technologically important area of transition in turbomachines.
Nonlinear stability and control of three-dimensional boundary layers
NASA Astrophysics Data System (ADS)
Janke, Erik
The linear and nonlinear evolution of steady and traveling disturbances in three-dimensional incompressible boundary layer flows is studied using Parabolized Stability Equations (PSE). Extensive primary stability analyses for the model problems of Swept Hiemenz flow and the DLR Transition experiment on a swept flat plate are performed first. Second, and building upon these results, detailed secondary instability studies based on both the classical Floquet Theory and a novel approach that uses the nonlinear PSE are conducted. The investigations reveal a connection of unstable secondary eigenvalues to both the linear eigenvalue spectrum of the undisturbed mean flow and the continuous spectrum, as well as the existence of an absolute instability in the region of nonlinear amplitude saturation. Third, a passive technique for boundary layer transition control using leading edge roughness is examined utilizing a newly developed implicit solution method for the nonlinear PSE. The results confirm experimental observations and indicate possible means of delaying transition on swept wings. In the present work, both the solution of the boundary layer equations for the mean flow and the explicit PSE solver are based on a fourth-order-accurate compact scheme formulation in body-oriented coordinates. In the secondary instability analysis, the Implicitly Restarted Arnoldi Method is applied.
Improved Inlet Noise Attenuation by Alteration of Boundary Layer Profiles
NASA Technical Reports Server (NTRS)
Mani, Ramani; Luedke, Jon; Jones, Michael G.; Nark, Douglas M.
2004-01-01
Acoustic liners are an essential component of technology used to reduce aircraft engine noise. Flow affects attenuation due to the liner in several ways, one of which is that boundary layers adjacent to the liner refract the sound. In the case of inlet noise, the boundary layer causes sound to be refracted away from the liner, thus degrading attenuation. A concept to improve attenuation by the liner by alteration of inlet boundary layer profiles is presented. The alteration of profiles is achieved by inlet blowing. Computational fluid dynamics and duct mode propagation theory for ducts carrying a parallel sheared flow have been used to design experiments to explore such a possibility in the NASA Langley Research Center Grazing Incidence Tube using an inlet blowing scheme developed at General Electric Global Research. The effects of inlet blowing on two liner configurations were evaluated. Calculated results will be shown for blowing ratios (injected flow/duct flow) of approximately 12% and frequencies up to 3 kHz. These results emphasize changes of attenuation achieved by blowing for the two liners. Experimental results of measured flow profiles (with and without blowing) in the Grazing Incidence Tube, and of corresponding changes in attenuation by the liner due to blowing will be presented.
Study of the morning transition of the atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Sastre, M.; Yagüe, C.; Maqueda, G.; Viana, S.
2009-04-01
In this work it will be analyzed the main physical processes related to the transition of the Atmospheric Boundary Layer (ABL) that takes place from the last hours of the night until the first hours of the morning. In order to achieve that, it will be used data from field campaigns which took place in the Research Centre for the Lower Atmosphere (CIBA), especially those gathered in the campaign carried out in June, 2008 where information was obtained from a 10m height mast provided with temperature, wind speed and direction, and moisture sensors at several levels. Also a sonic anemometer (20 Hz sampling rate) at 10m was available. The database is complemented by a triangle of microbarometers installed next to the surface, and another two microbarometers placed in a 100m meteorological tower at 50 and 100m respectively. A GRIMM particle monitor (MODEL 365), which can be used to continuously measure each six seconds simultaneously the PM10, PM2.5 and PM1 values, was also available to evaluate the degree of mixing taking place near the surface. The thermodynamic characteristics of the first hundreds of meters remain registered from information obtained with a tethered balloon and with a RASS-SODAR. The main turbulent and stability parameters, as well as coherent structures present in the Nocturnal Boundary Layer are studied in connection to their influence in the developing of the next Convective Boundary Layer.
Boundary Layer Transition in the NTF: HSR Experience and Plans
NASA Technical Reports Server (NTRS)
Owens, Lewis R., Jr.; Wahls, Richard A.; Hamner, Marvine P.
1999-01-01
Efforts towards understanding boundary layer transition characteristics on a High Speed Civil Transport (HSCT)-class configuration in the National Transonic Facility (NTF) are ongoing. The majority of the High Speed Research (HSR) data base in the NTF has free transition on the wing, even at low Reynolds numbers (Rn) attainable in conventional facilities. Limited data has been obtained and is described herein showing the effects of a conventional, Braslow method based wing boundary-layer trip on drag. Comparisons are made using force data polars and surface flow visualization at selected angles-of-attack and Mach number. Minimum drag data obtained in this study suggest that boundary layer transition occurred very near the wing leading edge by a chord Rn of 30 million. Sublimating chemicals were used in the air mode of operation only at low Rn and low angles-of-attack with no flap deflections; sublimation results suggest that the forebody and outboard wing panel are the only regions with significant laminar flow. The process and issues related to the sublimating chemical technique as applied in the NTF are discussed. Beyond the existing experience, status of efforts to develop a production transition detection system applicable to both air and cryogenic nitrogen environments is presented.
Turbulent thermal boundary layers subjected to severe acceleration
NASA Astrophysics Data System (ADS)
Araya, Guillermo; Castillo, Luciano
2013-11-01
Favorable turbulent boundary layers are flows of great importance in industry. Particularly, understanding the mechanisms of quasi-laminarization by means of a very strong favorable streamwise pressure gradient is indeed crucial in drag reduction and energy management applications. Furthermore, due to the low Reynolds numbers involved in the quasi-laminarization process, abundant experimental investigation can be found in the literature for the past few decades. However, several grey zones still remain unsolved, principally associated with the difficulties that experiments encounter as the boundary layer becomes smaller. In addition, little attention has been paid to the heat transfer in a quasi-laminarization process. In this investigation, DNS of spatially-developing turbulent thermal boundary layers with prescribed very strong favorable pressure gradients (K = 4 × 10-6) are performed. Realistic inflow conditions are prescribed based on the Dynamic Multi-scale Approach (DMA) [Araya et al. JFM, Vol. 670, pp. 581-605, 2011]. In this sense the flow carries the footprint of turbulence, particularly in the streamwise component of the Reynolds stresses.
Advanced boundary layer transition measurement methods for flight applications
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Croom, C. C.; Gail, P. D.; Manuel, G. S.; Carraway, D. L.
1986-01-01
In modern laminar flow flight research, it is important to understand the specific cause(s) of laminar to turbulent boundary-layer transition. Such information is crucial to the exploration of the limits of practical application of laminar flow for drag reduction on aircraft. The transition modes of interest in current flight investigations include the viscous Tollmien-Schlichting instability, the inflectional instability at laminar separation, and the crossflow inflectional instability, as well as others. This paper presents the results to date of research on advanced devices and methods used for the study of laminar boundary-layer transition phenomena in the flight environment. Recent advancements in the development of arrayed hot-film devices and of a new flow visualization method are discussed. Arrayed hot-film devices have been designed to detect the presence of laminar separation, and of crossflow vorticity. The advanced flow visualization method utilizes color changes in liquid-crystal coatings to detect boundary-layer transition at high altitude flight conditions. Flight and wind tunnel data are presented to illustrate the design and operation of these advanced methods. These new research tools provide information on disturbance growth and transition mode which is essential to furthering our understanding of practical design limits for applications of laminar flow technology.
Receptivity of Hypersonic Boundary Layers to Acoustic and Vortical Disturbances
NASA Technical Reports Server (NTRS)
Balakamar, P.; Kegerise, Michael A.
2011-01-01
Boundary layer receptivity to two-dimensional acoustic disturbances at different incidence angles and to vortical disturbances is investigated by solving the Navier-Stokes equations for Mach 6 flow over a 7deg half-angle sharp-tipped wedge and a cone. Higher order spatial and temporal schemes are employed to obtain the solution. The results show that the instability waves are generated in the leading edge region and that the boundary layer is much more receptive to slow acoustic waves as compared to the fast waves. It is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases when the incidence angle is increased from 0 to 30 degrees. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle. The maximum receptivity is obtained when the wave incident angle is about 20 degrees. Vortical disturbances also generate unstable second modes, however the receptivity coefficients are smaller than that for the acoustic waves. Vortical disturbances first generate the fast acoustic modes and they switch to the slow mode near the continuous spectrum.
NASA Technical Reports Server (NTRS)
Deutsch, Steven; Zierke, William C.
1987-01-01
A one-component laser Doppler velocimeter (LDV) has been used to measure the two-dimensional periodic flow field about a double circular arc, compressor blade in cascade. Eleven boundary layer profiles were taken on both the pressure and suction surfaces of the blade, and two profiles were taken in the near wake. In this part of the study, the detailed LDV studies are described. The measurements indicate that the onset of transition occurs near 60 percent chord. The lack of a logarithmic region in the data measured at 97.9 percent chord indicates that transition is not complete. The thin laminar boundary layers near the leading edge led to some measurement problems, characterized by large turbulence intensities, in using the LDV.
Impact of Boundary Layer Processes on Carbon Budgets
NASA Astrophysics Data System (ADS)
McGrath-Spangler, E. L.; Denning, A.
2011-12-01
Previous work has shown the importance of turbulent mixing within the planetary boundary layer (PBL) and entrainment at the top of this layer for the carbon budget. In addition to the impact of carbon flux dilution by a deeper mixing layer, the modification to the vegetative environment at the land surface by PBL processes greatly impacts the vegetative response. Plants adapt to warmer, drier conditions by adjusting fluxes of carbon and water vapor in order to minimize transpiration while also maximizing carbon assimilation. However, a lot of work remains to be done in order to better simulate PBL processes and depth. Relatively few observations exist of PBL depth and even fewer exist of the processes at the PBL top. PBL depth can be estimated using the backscatter from the LIDAR onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. Using an automated method, millions of estimates can be derived to which model results can be compared. Using these estimates as well as carbon dioxide (CO2) observations from a network of towers throughout the continental United States and southern Canada, simulations from a coupled ecosystem-atmosphere model are evaluated using various strengths of an entrainment parameterization. This analysis sheds some light on the spatial heterogeneity of boundary layer processes and the influence on surface carbon fluxes and the carbon budget.
Velocity-vorticity correlation structures in compressible turbulent boundary layer
NASA Astrophysics Data System (ADS)
Chen, Jun; Li, Shi-Yao; She, Zhen-Su
2016-11-01
A velocity-vorticity correlation structure (VVCS) analysis is applied to analyze data of 3-dimensional (3-D) direct numerical simulations (DNS), to investigate the quantitative properties of the most correlated vortex structures in compressible turbulent boundary layer (CTBL) at Mach numbers, Ma = 2 . 25 and 6 . 0 . It is found that the geometry variation of the VVCS closely reflects the streamwise development of CTBL. In laminar region, the VVCS captures the instability wave number of the boundary layer. The transition region displays a distinct scaling change of the dimensions of VVCS. The developed turbulence region is characterized by a constant spatial extension of the VVCS. For various Mach numbers, the maximum correlation coefficient of the VVCS presents a clear multi-layer structure with the same scaling laws as a recent symmetry analysis proposed to quantifying the sublayer, the log-layer, and the wake flow. A surprising discovery is that the wall friction coefficient, Cf, holds a "-1"-power law of the wall normal distance of the VVCS, ys. This validates the speculation that the wall friction is determined by the near-wall coherent structure, which clarifies the correlation between statistical structures and the near-wall dynamics. Project 11452002 and 11172006 supported by National Natural Science Foundation of China.
Lecture Series "Boundary Layer Theory". Part I - Laminar Flows. Part 1; Laminar Flows
NASA Technical Reports Server (NTRS)
Schlichting, H.
1949-01-01
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
NASA Technical Reports Server (NTRS)
Spina, Eric F.
1995-01-01
The primary objective in the two research investigations performed under NASA Langley sponsorship (Turbulence measurements in hypersonic boundary layers using constant temperature anemometry and Reynolds stress measurements in hypersonic boundary layers) has been to increase the understanding of the physics of hypersonic turbulent boundary layers. The study began with an extension of constant-temperature thermal anemometry techniques to a Mach 11 helium flow, including careful examinations of hot-wire construction techniques, system response, and system calibration. This was followed by the application of these techniques to the exploration of a Mach 11 helium turbulent boundary layer (To approximately 290 K). The data that was acquired over the course of more than two years consists of instantaneous streamwise mass flux measurements at a frequency response of about 500 kHz. The data are of exceptional quality in both the time and frequency domain and possess a high degree of repeatability. The data analysis that has been performed to date has added significantly to the body of knowledge on hypersonic turbulence, and the data reduction is continuing. An attempt was then made to extend these thermal anemometry techniques to higher enthalpy flows, starting with a Mach 6 air flow with a stagnation temperature just above that needed to prevent liquefaction (To approximately 475 F). Conventional hot-wire anemometry proved to be inadequate for the selected high-temperature, high dynamic pressure flow, with frequent wire breakage and poor system frequency response. The use of hot-film anemometry has since been investigated for these higher-enthalpy, severe environment flows. The difficulty with using hot-film probes for dynamic (turbulence) measurements is associated with construction limitations and conduction of heat into the film substrate. Work continues under a NASA GSRP grant on the development of a hot film probe that overcomes these shortcomings for hypersonic
NASA Astrophysics Data System (ADS)
Derjaguin, B. V.
1992-05-01
This article, mentioning the influence of surface forces on the formation and the properties of diffuse adsorption layers on the boundary of solution-substrate, is mainly about the influence of surface forces on the structure and properties of boundary layers of the liquid. It deals with the phenomena of formation of homogeneous liquid crystalline layers of nonmesogenic liquids, boundary phases and the properties of boundary nonhomogeneous layers of water and alcohols. In the conclusion the data on surface forces are given with the radius of action up to 100 μm, which are generated by leucocytes of blood plasma with the addition of a concentrated salt solution.
Instabilities in compressible attachment-line boundary layers
NASA Astrophysics Data System (ADS)
Le Duc, Anne; Sesterhenn, Jörn; Friedrich, Rainer
2006-04-01
The hydrodynamic stability of the weakly compressible attachment-line boundary layer, with a sweep Mach number ranging from 0.1 to 1.3, is studied using a temporal compressible direct numerical simulation. A flow impinging non-normally onto an infinitely extended flat plate was computed. This complements the study of Hall et al. [Proc. R. Soc. London, Ser. A 395, 229 (1984)] who investigated the linear stability of an incompressible attachment-line boundary layer under the assumption of Görtler-Hämmerlin perturbation modes. In the present work, the base flow is modeled starting from the incompressible swept Hiemenz flow. Using Rayleigh-Jansen Mach number expansions, we obtain a family of base flows parameterized with the sweep Mach number ranging from 0.1 to 1.3. The Reynolds number of the simulation is higher than the incompressible critical Reynolds number, and the plate is adiabatic. Small purely vortical stochastic perturbations are inserted in the boundary layer and followed in time. For Mach numbers up to 0.3, developed velocity and pressure modes are similar to the ones assumed by Görtler and Hämmerlin. The chordwise dependencies of the temperature mode are presented. When increasing the Mach number, the structure of the modes changes; for high Mach numbers, a significantly slower decay of the eigenfunction with wall-normal distance is observed. Above M =0.5, the perturbations are exponentially decaying. This demonstrates the strong stabilizing effect of compressibility in the moderate Mach regime. Furthermore, for the same base flow, a higher exponential growth rate of the perturbation is obtained, if an isothermal wall boundary condition is applied instead of an adiabatic one.
A complex-lamellar description of boundary layer transition
NASA Astrophysics Data System (ADS)
Kolla, Maureen Louise
Flow transition is important, in both practical and phenomenological terms. However, there is currently no method for identifying the spatial locations associated with transition, such as the start and end of intermittency. The concept of flow stability and experimental correlations have been used, however, flow stability only identifies the location where disturbances begin to grow in the laminar flow and experimental correlations can only give approximations as measuring the start and end of intermittency is difficult. Therefore, the focus of this work is to construct a method to identify the start and end of intermittency, for a natural boundary layer transition and a separated flow transition. We obtain these locations by deriving a complex-lamellar description of the velocity field that exists between a fully laminar and fully turbulent boundary condition. Mathematically, this complex-lamellar decomposition, which is constructed from the classical Darwin-Lighthill-Hawthorne drift function and the transport of enstrophy, describes the flow that exists between the fully laminar Pohlhausen equations and Prandtl's fully turbulent one seventh power law. We approximate the difference in enstrophy density between the boundary conditions using a power series. The slope of the power series is scaled by using the shape of the universal intermittency distribution within the intermittency region. We solve the complex-lamellar decomposition of the velocity field along with the slope of the difference in enstrophy density function to determine the location of the laminar and turbulent boundary conditions. Then from the difference in enstrophy density function we calculate the start and end of intermittency. We perform this calculation on a natural boundary layer transition over a flat plate for zero pressure gradient flow and for separated shear flow over a separation bubble. We compare these results to existing experimental results and verify the accuracy of our transition
Boundary Layer Control in Pipes through Strong Injection
Yeung, William Chor-Chun; Holt, Maurice
1982-01-01
In coal gasification, oxidation and sulfidization cause serious pipe corrosion. This study attempts to determine the feasibility of reducing such corrosion by injecting steam at pipe entry to modify the boundary-layer gas composition along pipe walls. The injection will form a thin layer on the inner wall, preventing, for a time, contact with the corrosive gases. (Turbulence will eventually force diffusion through the protective layer.) The gas products are assumed to be hydrogen sulfide and steam. The Method of Integral Relations is used to obtain the numerical solutions to the governing equations. Finally, with several different injectant lengths and velocities, the concentration of H_{2}S along the pipe wall is calculated and is found low enough to prevent corrosion.
Grain-boundary layering transitions and phonon engineering
NASA Astrophysics Data System (ADS)
Rickman, J. M.; Harmer, M. P.; Chan, H. M.
2016-09-01
We employ semi-grand canonical Monte Carlo simulation to investigate layering transitions at grain boundaries in a prototypical binary alloy. We demonstrate the existence of such transitions among various interfacial states and examine the role of elastic fields in dictating state equilibria. The results of these studies are summarized in the form of diagrams that highlight interfacial state coexistence in this system. Finally, we examine the impact of layering transitions on the phononic properties of the system, as given by the specific heat and, by extension, the thermal conductivity. Thus, it is suggested that by inducing interfacial layering transitions via changes in temperature or pressure, one can thereby engineer thermodynamic and transport properties in materials.
Saarenrinne, Pentti
2016-01-01
ABSTRACT The boundary layers of rainbow trout, Oncorhynchus mykiss [0.231±0.016 m total body length (L) (mean±s.d.); N=6], swimming at 1.6±0.09 L s−1 (N=6) in an experimental flow channel (Reynolds number, Re=4×105) with medium turbulence (5.6% intensity) were examined using the particle image velocimetry technique. The tangential flow velocity distributions in the pectoral and pelvic surface regions (arc length from the rostrum, lx=71±8 mm, N=3, and lx=110±13 mm, N=4, respectively) were approximated by a laminar boundary layer model, the Falkner−Skan equation. The flow regime over the pectoral and pelvic surfaces was regarded as a laminar flow, which could create less skin-friction drag than would be the case with turbulent flow. Flow separation was postponed until vortex shedding occurred over the posterior surface (lx=163±22 mm, N=3). The ratio of the body-wave velocity to the swimming speed was in the order of 1.2. This was consistent with the condition of the boundary layer laminarization that had been confirmed earlier using a mechanical model. These findings suggest an energy-efficient swimming strategy for rainbow trout in a turbulent environment. PMID:27815242
Direct numerical simulation of a separated turbulent boundary layer
NASA Astrophysics Data System (ADS)
Na, Y.; Moin, P.
1998-09-01
A separated turbulent boundary layer over a flat plate was investigated by direct numerical simulation of the incompressible Navier Stokes equations. A suction-blowing velocity distribution was prescribed along the upper boundary of the computational domain to create an adverse-to-favourable pressure gradient that produces a closed separation bubble. The Reynolds number based on inlet free-stream velocity and momentum thickness is 300. Neither instantaneous detachment nor reattachment points are fixed in space but fluctuate significantly. The mean detachment and reattachment locations determined by three different definitions, i.e. (i) location of 50% forward flow fraction, (ii) mean dividing streamline ([psi]=0), (iii) location of zero wall-shear stress ([tau]w=0), are in good agreement. Instantaneous vorticity contours show that the turbulent structures emanating upstream of separation move upwards into the shear layer in the detachment region and then turn around the bubble. The locations of the maximum turbulence intensities as well as Reynolds shear stress occur in the middle of the shear layer. In the detached flow region, Reynolds shear stresses and their gradients are large away from the wall and thus the largest pressure fluctuations are in the middle of the shear layer. Iso-surfaces of negative pressure fluctuations which correspond to the core region of the vortices show that large-scale structures grow in the shear layer and agglomerate. They then impinge on the wall and subsequently convect downstream. The characteristic Strouhal number St=f[delta]*in/U0 associated with this motion ranges from 0.0025 to 0.01. The kinetic energy budget in the detachment region is very similar to that of a plane mixing layer.
A numerical-physical planetary boundary layer model
NASA Astrophysics Data System (ADS)
Padro, Jacob
1983-07-01
A numerical-physical model for the planetary boundary layer has been formulated for the purpose of predicting the winds, temperatures and humidities in the lowest 1600 m of the atmosphere. An application of the model to the synoptic situation of 30 August, 1972, demonstrates its ability to produce useful forecasts for a period of 24 h. Results are illustrated in terms of horizontal maps and time-height sections of winds and temperatures. The model is divided in the vertical direction into three layers that are governed, respectively, by different physical formulations. At the lowest level, which is the surface of the earth, forecasts of temperature and humidity are computed from empirical relations. In the first layer, the surface layer, application is made of the similarity theories of Monin-Obukhov, Monin-Kazanski and Businger’s form of the universal functions. The second layer, the Ekman layer, is 1550 m deep and is governed by diagnostic momentum and time-dependent thermodynamic and humidity equations. External input to the model are large-scale pressure gradients and middle-level cloudiness. Cressman’s objective analysis procedure is applied to conventional surface and upper air data over a horizontal region of about 2500 km by 2500 km, centered about Lake Ontario. With a grid distance of 127 km and a time interval of 30 min, the computer time required on Control Data Cyber 76 for a 24 h forecast for the case study is less than two minutes.
Visualization of Hypersonic Flat-Plate Boundary Layer in Shock Tunnel
NASA Astrophysics Data System (ADS)
Zhang, Qinghu; Yi, Shihe; Zhi, Chen; Zhu, Yangzh; Yu, Wu
In order to design the future aerospace vehicles, it is essential to experimentally investigate the hypersonic boundary layer [1]. Many aspects of hypersonic turbulent boundary layer and transition process are poorly understood.
Computation of three-dimensional mixed convective boundary layer flow
NASA Technical Reports Server (NTRS)
Gadepalli, Prashandt; Rahman, Muhammad M.
1995-01-01
The paper presents the numerical solution of heat and mass transfer during cross-flow (orthogonal) mixed convection. In this class of flow, a buoyancy-driven transport in the vertical direction and a forced convective flow in the horizontal direction results in a three-dimensional boundary layer structure adjacent to the plate. The rates of heat and mass transfer are determined by a combined influence of the two transport processes. The equations for the conservation of mass, momentum, energy, and species concentration were solved along with appropriate boundary conditions to determine the distributions of velocity components, temperature, and concentration across the thickness of the boundary layer at different locations on the plate. Results were expressed in dimensionless form using Reynolds number, Richardson number for heat transfer, Richardson number for mass transfer, Prandtl number, and Schmidt number as parameters. It was found that the transport is dominated by buoyancy at smaller vertical locations and at larger distances away from the forced convection leading edge. Effects of forced convection appeared to be very strong at smaller horizontal distances from the leading edge. The cross stream forced convection enhanced the rate of heat and mass transfer by a very significant amount.
The effects of external conditions in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Brzek, Brian G.
The effects of multiple external conditions on turbulent boundary layers were studied in detail. These external conditions include: surface roughness, upstream turbulence intensity, and pressure gradient. Furthermore, the combined effects of these conditions show the complicated nature of many realistic flow conditions. It was found that the effects of surface roughness are difficult to generalize, given the importance of so many parameters. These parameters include: roughness geometry, roughness regime, roughness height to boundary layer thickness, (k/delta), roughness parameter, ( k+), Reynolds number, and roughness function (Delta B+). A further complication, is the difficulty in computing the wall shear stress, tauw/rho. For the sand grain type roughness, the mean velocity and Reynolds stresses were studied in inner and outer variables, as well as, boundary layer parameters, anisotropy tensor, production term, and viscous stress and form drag contributions. To explore the effects of roughness and Reynolds number dependence in the boundary layer, a new experiment was carefully designed to properly capture the x-dependence of the single-point statistics. It was found that roughness destroys the viscous layer near the wall, thus, reducing the contribution of the viscous stress in the wall region. As a result, the contribution in the skin friction due to form drag increases, while the viscous stress decreases. This yields Reynolds number invariance in the skin friction, near-wall roughness parameters, and inner velocity profiles as k + increases into the fully rough regime. However, in the transitionally rough regime, (i.e., 5 < k+ < 70), it was found that these parameters are functions of both Reynolds number and roughness. For the sand grain type roughnesses, only the Zagarola and Smits scaling, Uinfinitydelta*/delta, is able to remove the effects of roughness and Reynolds number from the velocity profiles in outer variables, provided there is no freestream
NASA Technical Reports Server (NTRS)
Betts, Alan K.; Albrecht, Bruce A.
1987-01-01
An analysis of FGGE dropwindsonde data using conserved thermodynamic variables shows mixing line structures for the convective boundary layer over the equatorial Pacific. Deeper boundary layers show a double structure. Reversals of the gradients of mixing ratio and equivalent potential temperature above the boundary-layer top are present in all the averages and suggest that the origin of the air sinking into the boundary layer needs further study.
Characteristics of convective boundary layer over the Arabian sea region
Parasnis, S.S.
1996-12-31
The Convective Boundary Layer (CBL) over the oceanic regions plays an important role in regulating the transport of energy and moisture upward into the atmosphere from the surface. CBL structure over the Arabian sea region has been explored using the aerological soundings at two ships viz. SHIRSHOV (12.5{degrees}N, 68{degrees}E ) and OKEAN (14.5{degrees} N, 66{degrees} E) during MONSOON-77. Conserved variable analysis of the mean data sets obtained during the period of 29 June - 16 July, 1977 revealed salient features of the CBL over these regions. The vertical gradients of saturation point parameters viz. virtual potential temperature ({Theta}{sub v}), equivalent potential temperature ({Theta}{sub e}), saturated equivalent potential temperature ({Theta}{sub es}), saturation pressure deficit (P*) and the mixing ratio (q) were used to characterize the different sublayers such as subcloud layer, cloud layer and inversion/stable layer. The mean cloud base was around 950 hPa and the subcloud layer has nearly constant {Theta}{sub v}. The moist layer was associated with unstable {Theta}{sub es} with nearly constant value of P* ({approximately} -40 hPa). This cloud layer was capped by the stable (over OKEAN). The {Theta}{sub e} minimum over OKEAN was observed at 650 hPa (50 hPa above the CBL top) indicating that at some time the convection had reached deeper levels. The {Theta}{sub e} -q diagrams showed a characteristic mixing line up through the cloud and stable layer to the top of CBL. The low level stability analysis using the {Theta}{sub e} and {Theta}{sub es} profiles indicated conditions favorable for shallow convection over OKEAN and for deep convection over SHIRSHOV. The above characteristic features could be attributed to the prevailing weather conditions at OKEAN and SHIRSHOV. The results are discussed.
Non-uniqueness in wakes and boundary layers
NASA Astrophysics Data System (ADS)
Smith, F. T.
1984-01-01
In streamlined flow past a flat plate aligned with a uniform stream, it is shown that (a) the Goldstein near-wake and (b) the Blasius boundary layer are nonunique solutions locally for the classical boundary layer equations, whereas (c) the Rott-Hakkinen (1965) very-near-wake appears to be unique. In each of (a) and (b) an alternative solution exists, which has reversed flow and which apparently cannot be discounted on immediate grounds. So, depending mainly on how the alternatives for (a), (b) develop downstream, the symmetric flow at high Reynolds numbers could have two, four or more steady forms. Concerning nonstreamlined flow, for example past a bluff obstacle, new similarity forms are described for the pressure-free viscous symmetric closure of a predominantly slender long wake beyond a large-scale separation. Features arising include nonuniqueness, singularities and algebraic behavior, consistent with nonentraining shear layers with algebraic decay. Nonuniqueness also seems possible in reattachment onto a solid surface and for nonsymmetric or pressure-controlled flows including the wake of a symmetric cascade.
Cloud-Scale Numerical Modeling of the Arctic Boundary Layer
NASA Technical Reports Server (NTRS)
Kruegen, Steven K.; Delnore, Victor E. (Technical Monitor)
2002-01-01
The research objective of this NASA grant-funded project was to determine in detail how large-scale processes. in combination with cloud-scale radiative, microphysical, and dynamical processes, govern the formation and multi-layered structure of Arctic stratus clouds. This information will be useful for developing and improving 1D (one dimensional) boundary layer models for the Arctic. Also, to quantitatively determine the effects of leads on the large-scale budgets of sensible heat, water vapor, and condensate in a variety of Arctic winter conditions. This information will be used to identify the most important lead-flux processes that require parameterization in climate models. Our approach was to use a high-resolution numerical model, the 2D (two dimensional) University of Utah Cloud Resolving Model (UU CRM), and its 1D version, the University of Utah Turbulence Closure Model (UU TCM), a boundary layer model based on third-moment turbulence closure, as well as a large-eddy simulation (LES) model originally developed by C.H. Moeng.
Vertical ozone characteristics in urban boundary layer in Beijing.
Ma, Zhiqiang; Xu, Honghui; Meng, Wei; Zhang, Xiaoling; Xu, Jing; Liu, Quan; Wang, Yuesi
2013-07-01
Vertical ozone and meteorological parameters were measured by tethered balloon in the boundary layer in the summer of 2009 in Beijing, China. A total of 77 tethersonde soundings were taken during the 27-day campaign. The surface ozone concentrations measured by ozonesondes and TEI 49C showed good agreement, albeit with temporal difference between the two instruments. Two case studies of nocturnal secondary ozone maxima are discussed in detail. The development of the low-level jet played a critical role leading to the observed ozone peak concentrations in nocturnal boundary layer (NBL). The maximum of surface ozone was 161.7 ppbv during the campaign, which could be attributed to abundant precursors storage near surface layer at nighttime. Vertical distribution of ozone was also measured utilizing conventional continuous analyzers on 325-m meteorological observation tower. The results showed the NBL height was between 47 and 280 m, which were consistent with the balloon data. Southerly air flow could bring ozone-rich air to Beijing, and the ozone concentrations exceeded the China's hourly ozone standard (approximately 100 ppb) above 600 m for more than 12 h.
LAMINAR TRANSITIONAL AND TURBULENT BOUNDARY LAYERS FOR COMPRESSIBLE AXISYMMETRIC FLOW
NASA Technical Reports Server (NTRS)
Albers, J. A.
1994-01-01
This is a finite-difference program for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to a fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain factors of arbitrary Reynolds number, free-stream Mach number, free stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile. This program has been implemented on the IBM 7094/7044 Direct Couple System. This program is written in FORTRAN IV and was developed in 1974.
An algebraic way to compute boundary layer's sizes
NASA Astrophysics Data System (ADS)
GRENIER, E.
2001-05-01
The aim of the talk is to describe a simple way to recover the classical boundary layers' sizes in rotating fluids and MHD problems, to derive there equations and to simply investigate some of there stability property. This gives a new view on classical Fourier Laplace methods, using modern mathematical tools (pseudodifferential operators) adapted to complex geometries (spheres, between two spheres, non flat boundaries), and greatly simplifies the classical derivations of Proudman and Stewartson (rotating fluids between two spheres), Hartmann... We will give a special stress on equatorial singularities and on the various sizes which appear near the equator, both with and without the magnetic field and make a short review of the mathematical (partial differential equation's type) literature on the subject.
Nonlinear spatial evolution of inviscid instabilities on hypersonic boundary layers
NASA Technical Reports Server (NTRS)
Wundrow, David W.
1996-01-01
The spatial development of an initially linear vorticity-mode instability on a compressible flat-plate boundary layer is considered. The analysis is done in the framework of the hypersonic limit where the free-stream Mach number M approaches infinity. Nonlinearity is shown to become important locally, in a thin critical layer, when sigma, the deviation of the phase speed from unity, becomes o(M(exp -8/7)) and the magnitude of the pressure fluctuations becomes 0(sigma(exp 5/2)M(exp 2)). The unsteady flow outside the critical layer takes the form of a linear instability wave but with its amplitude completely determined by the nonlinear flow within the critical layer. The coupled set of equations which govern the critical-layer dynamics reflect a balance between spatial-evolution, (linear and nonlinear) convection and nonlinear vorticity-generation terms. The numerical solution to these equations shows that nonlinear effects produce a dramatic reduction in the instability-wave amplitude.
Interaction of a Boundary Layer with a Turbulent Wake
NASA Technical Reports Server (NTRS)
Piomelli, Ugo
2004-01-01
The objective of this grant was to study the transition mechanisms on a flat-plate boundary layer interacting with the wake of a bluff body. This is a simplified configuration presented and designed to exemplify the phenomena that occur in multi-element airfoils, in which the wake of an upstream element impinges on a downstream one. Some experimental data is available for this configuration at various Reynolds numbers. The first task carried out was the implementation and validation of the immersed-boundary method. This was achieved by performing calculations of the flow over a cylinder at low and moderate Reynolds numbers. The low-Reynolds number results are discussed, which is enclosed as Appendix A. The high-Reynolds number results are presented in a paper in preparation for the Journal of Fluid Mechanics. We performed calculations of the wake-boundary-layer interaction at two Reynolds numbers, Re approximately equal to 385 and 1155. The first case is discussed and a comparison of the two calculations is reported. The simulations indicate that at the lower Reynolds number the boundary layer is buffeted by the unsteady Karman vortex street shed by the cylinder. This is shown: long streaky structures appear in the boundary layer in correspondence of the three-dimensionalities in the rollers. The fluctuations, however, cannot be self-sustained due to the low Reynolds-number, and the flow does not reach a turbulent state within the computational domain. In contrast, in the higher Reynolds-number case, boundary-layer fluctuations persist after the wake has decayed (due, in part, to the higher values of the local Reynolds number Re achieved in this case); some evidence could be observed that a self-sustaining turbulence generation cycle was beginning to be established. A third simulation was subsequently carried out at a higher Reynolds number, Re=3900. This calculation gave results similar to those of the Re=l155 case. Turbulence was established at fairly low
NASA Astrophysics Data System (ADS)
Marzooqi, Mohamed Al; Basha, Ghouse; Ouarda, Taha B. M. J.; Armstrong, Peter; Molini, Annalisa
2014-05-01
Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature in the boundary layer over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main features however, desert ABLs present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as the transport of dust and pollutants, and turbulent fluxes of momentum, heat and water vapor in hyper-arid regions. In this study, we analyze a continuous record of observations of the atmospheric boundary layer (ABL) height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4oN, 54.6o E, Abu Dhabi, United Arab Emirates), starting March 2013. We compare different methods for the estimation of the ABL height from Ceilometer data such as, classic variance-, gradient-, log gradient- and second derivation-methods as well as recently developed techniques such as the Bayesian Method and Wavelet covariance transform. Our goal is to select the most suited technique for describing the climatology of the ABL in desert environments. Comparison of our results with radiosonde observations collected at the nearby airport of Abu Dhabi indicate that the WCT and the Bayesian method are the most suitable tools to accurately identify the ABL height in all weather conditions. These two methods are used for the definition of diurnal and seasonal climatologies of the boundary layer conditional to different atmospheric stability classes.
Spherical bubble motion in a turbulent boundary layer
NASA Astrophysics Data System (ADS)
Felton, Keith; Loth, Eric
2001-09-01
Monodisperse dilute suspensions of spherical air bubbles in a tap-water turbulent vertical boundary layer were experimentally studied to note their motion and distribution. Bubbles with diameters of 0.37-1.2 mm were injected at various transverse wall-positions for free-stream velocities between 0.4 and 0.9 m/s. The bubbles were released from a single injector at very low frequencies such that two-way coupling and bubble-bubble interaction were negligible. The experimental diagnostics included ensemble-averaged planar laser intensity profiles for bubble concentration distribution, as well as Cinematic Particle Image Velocimetry with bubble tracking for bubble hydrodynamic forces. A variety of void distributions within the boundary layer were found. For example, there was a tendency for bubbles to collect along the wall for higher Stokes number conditions, while the lower Stokes number conditions produced Gaussian-type profiles throughout the boundary layer. In addition, three types of bubble trajectories were observed—sliding bubbles, bouncing bubbles, and free-dispersion bubbles. Instantaneous liquid forces acting on individual bubbles in the turbulent flow were also obtained to provide the drag and lift coefficients (with notable experimental uncertainty). These results indicate that drag coefficient decreases with increasing Reynolds number as is conventionally expected but variations were observed. In general, the instantaneous drag coefficient (for constant bubble Reynolds number) tended to be reduced as the turbulence intensity increased. The averaged lift coefficient is higher than that given by inviscid theory (and sometimes even that of creeping flow theory) and tends to decrease with increasing bubble Reynolds number.
Planetary Boundary Layer Dynamics over Reno, Nevada in Summer
NASA Astrophysics Data System (ADS)
Liming, A.; Sumlin, B.; Loria Salazar, S. M.; Holmes, H.; Arnott, W. P.
2014-12-01
Quantifying the height of the planetary boundary layer (PBL) is important to understand the transport behavior, mixing, and surface concentrations of air pollutants. In Reno, NV, located in complex, mountainous terrain with high desert climate, the daytime boundary layer can rise to an estimated 3km or more on a summer day due to surface heating and convection. The nocturnal boundary layer, conversely, tends to be much lower and highly stable due to radiative cooling from the surface at night and downslope flow of cool air from nearby mountains. With limited availability of radiosonde data, current estimates of the PBL height at any given time or location are potentially over or underestimated. To better quantify the height and characterize the PBL physics, we developed portable, lightweight sensors that measure CO2 concentrations, temperature, pressure, and humidity every 5 seconds. Four of these sensors are used on a tethered balloon system to monitor CO2 concentrations from the surface up to 300m. We will combine this data with Radio Acoustic Sounding System (RASS) data that measures vertical profiles of wind speed, temperature, and humidity from 40m to 400m. This experiment will characterize the diurnal evolution of CO2 concentrations at multiple heights in the PBL, provide insight into PBL physics during stability transition periods at sunrise and sunset, and estimate the nighttime PBL depth during August in Reno. Further, we expect to gain a better understanding of the impact of mixing volume changes (i.e., PBL height) on air quality and pollution concentrations in Reno. The custom portable sensor design will also be presented. It is expected that these instruments can be used for indoor or outdoor air quality studies, where lightness, small size, and battery operation can be of benefit.
Infrared Imaging of Boundary Layer Transition Flight Experiments
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J., Jr.; Schwartz, Richard; Ross, Martin; Anderson, Brian; Campbell, Charles H.
2008-01-01
The Hypersonic Thermodynamic Infrared Measurement (HYTHIRM) project is presently focused on near term support to the Shuttle program through the development of an infrared imaging capability of sufficient spatial and temporal resolution to augment existing on-board Orbiter instrumentation. Significant progress has been made with the identification and inventory of relevant existing optical imaging assets and the development, maturation, and validation of simulation and modeling tools for assessment and mission planning purposes, which were intended to lead to the best strategies and assets for successful acquisition of quantitative global surface temperature data on the Shuttle during entry. However, there are longer-term goals of providing global infrared imaging support to other flight projects as well. A status of HYTHIRM from the perspective of how two NASA-sponsored boundary layer transition flight experiments could benefit by infrared measurements is provided. Those two flight projects are the Hypersonic Boundary layer Transition (HyBoLT) flight experiment and the Shuttle Boundary Layer Transition Flight Experiment (BLT FE), which are both intended for reducing uncertainties associated with the extrapolation of wind tunnel derived transition correlations for flight application. Thus, the criticality of obtaining high quality flight data along with the impact it would provide to the Shuttle program damage assessment process are discussed. Two recent wind tunnel efforts that were intended as risk mitigation in terms of quantifying the transition process and resulting turbulent wedge locations are briefly reviewed. Progress is being made towards finalizing an imaging strategy in support of the Shuttle BLT FE, however there are no plans currently to image HyBoLT.
Shock Train/Boundary-Layer Interaction in Rectangular Scramjet Isolators
NASA Astrophysics Data System (ADS)
Geerts, Jonathan Simon
Numerous studies of the dual-mode scramjet isolator, a critical component in preventing inlet unstart and/or vehicle loss by containing a collection of flow disturbances called a shock train, have been performed since the dual-mode propulsion cycle was introduced in the 1960s. Low momentum corner flow and other three-dimensional effects inherent to rectangular isolators have, however, been largely ignored in experimental studies of the boundary layer separation driven isolator shock train dynamics. Furthermore, the use of two dimensional diagnostic techniques in past works, be it single-perspective line-of-sight schlieren/shadowgraphy or single axis wall pressure measurements, have been unable to resolve the three-dimensional flow features inside the rectangular isolator. These flow characteristics need to be thoroughly understood if robust dual-mode scramjet designs are to be fielded. The work presented in this thesis is focused on experimentally analyzing shock train/boundary layer interactions from multiple perspectives in aspect ratio 1.0, 3.0, and 6.0 rectangular isolators with inflow Mach numbers ranging from 2.4 to 2.7. Secondary steady-state Computational Fluid Dynamics studies are performed to compare to the experimental results and to provide additional perspectives of the flow field. Specific issues that remain unresolved after decades of isolator shock train studies that are addressed in this work include the three-dimensional formation of the isolator shock train front, the spatial and temporal low momentum corner flow separation scales, the transient behavior of shock train/boundary layer interaction at specific coordinates along the isolator's lateral axis, and effects of the rectangular geometry on semi-empirical relations for shock train length prediction. (Abstract shortened by ProQuest.).
Orbiter Entry Aeroheating Working Group Viscous CFD Boundary Layer Transition Trailblazer Solutions
NASA Technical Reports Server (NTRS)
Wood, William A.; Erickson, David W.; Greene, Francis A.
2007-01-01
Boundary layer transition correlations for the Shuttle Orbiter have been previously developed utilizing a two-layer boundary layer prediction technique. The particular two-layer technique that was used is limited to Mach numbers less than 20. To allow assessments at Mach numbers greater than 20, it is proposed to use viscous CFD to the predict boundary layer properties. This report addresses if the existing Orbiter entry aeroheating viscous CFD solutions, which were originally intended to be used for heat transfer rate predictions, adequately resolve boundary layer edge properties and if the existing two-layer results could be leveraged to reduce the number of needed CFD solutions. The boundary layer edge parameters from viscous CFD solutions are extracted along the wind side centerline of the Space Shuttle Orbiter at reentry conditions, and are compared with results from the two-layer boundary layer prediction technique. The differences between the viscous CFD and two-layer prediction techniques vary between Mach 6 and 18 flight conditions and Mach 6 wind tunnel conditions, and there is not a straightforward scaling between the viscous CFD and two-layer values. Therefore: it is not possible to leverage the existing two-layer Orbiter flight boundary layer data set as a substitute for a viscous CFD data set; but viscous CFD solutions at the current grid resolution are sufficient to produce a boundary layer data set suitable for applying edge-based boundary layer transition correlations.
Kubo-Anderson Mixing in the Turbulent Boundary Layer
NASA Astrophysics Data System (ADS)
Dekker, H.; de Leeuw, G.; Brink, A. Maassen Van Den
A novel ab initio analysis of the Reynolds stress is presented in order to model non-local turbulence transport. The theory involves a sample path space and a stochastic hypothesis. A scaling relation maps the path space onto the boundary layer. Analytical sampling rates are shown to model mixing by exchange. Nonlocal mixing involves a scaling exponent ɛ≈0.58 (ɛ→∞ in the diffusion limit). The resulting transport equation represents a nondiffusive (Kubo-Anderson or kangaroo) type stochastic process.
Turbulence modeling in shock wave/turbulent boundary layer interactions
NASA Technical Reports Server (NTRS)
Smits, A. J.
1992-01-01
The research performed was an experimental program to help develop turbulence models for shock wave boundary layer interactions. The measurements were taken in a Mach 3, 16 deg compression corner interaction, at a unit Reynolds number of 63 x 10(exp 6)/m. The data consisted of heat transfer data taken upstream and downstream of the interaction, hot wire measurements of the instantaneous temperature and velocity fluctuations to verify the Strong Reynolds Analogy, and single- and double-pulsed Rayleigh scattering images to study the development of the instantaneous shock/turbulence interaction.
Hot wire anemometry in compressible turbulent boundary layers
NASA Astrophysics Data System (ADS)
1981-11-01
Hot-wire anemometry in compressible flow was studied. New techniques for the measurement of turbulence in compressible flows with thermal sensors are described. The greatest amount of information about fluctuating flow variables as achieved using the newly developed sensors and techniques in conjunction with the classical hot-wire mode diagram method. It was found that the hot wire has no fundamental handicap for accurate high speed turbulence measurements in non-separated boundary layers outside the immediate wall region. It was also known that extreme overheating of a supported sensors leads to advantages in simplicity and accuracy of measurements of turbulent fluctuations over the full Mach number range.
Boundary Layer Measurements in Complex Terrain: Innsbruck-Box
NASA Astrophysics Data System (ADS)
Stiperski, I.; Rotach, M. W.; Gohm, A.
2012-04-01
Planetary boundary layers in complex terrain remain one of the major challenges of today's boundary layer research. Our current knowledge of the characteristics of the turbulence structure and exchange processes in truly complex topography remains limited. Not only is there no suitable theory, it is not known if all the relevant processes such a theory should explain are accounted for. Meanwhile, the increasing resolution of both numerical weather prediction and regional climate models demands precisely such information for improving model performance. Except for a few recent field campaigns, limited both in time and focus, no measurement platform in highly complex terrain is available to date that would be able to provide a complete dataset of boundary layer information in sufficient complexity, resolution and covering all regimes of interest both for model validation and resolving the remaining scientific questions. The Dynamic Meteorology Group of the Institute of Meteorology and Geophysics, University of Innsbruck is presently setting up such a 'reference box', which aims to fill in this gap. It will consist of a combination of high-resolution long-term turbulence observations in an area in the vicinity of Innsbruck (hence the 'Innsbruck-Box') and high-resolution numerical modeling. Whereas the data provided by measurements will allow for improvements in process understanding and model validation, the numerical modeling will be used to fill the data gaps in areas where no measurements are possible or the current measurement techniques are inadequate. Also, numerical experiments using idealized terrain or settings can be performed in order to test hypotheses deduced from the observations. The Innsbruck-Box is designed to be a long-term reference platform for studying boundary layer processes in highly complex terrain with an integrated measurement approach. Sites are located in the Inn-Valley, an approximately East-West oriented valley in western Austria
Fluid Mechanics and Heat Transfer in Transitional Boundary Layers
NASA Technical Reports Server (NTRS)
Wang, Ting
2007-01-01
Experiments have been performed to investigate the effects of elevated free-stream turbulence and streamwise acceleration on flow and thermal structures in transitional boundary layers. The free-stream turbulence ranges from 0.5 to 6.4% and the streamwise acceleration ranges from K = 0 to 0.8 x 10(exp -6). The onset of transition, transition length and the turbulent spot formation rate are determined. The statistical results and conditionally sampled results of th streamwise and cross-stream velocity fluctuations, temperature fluctuations, Reynolds stress and Reynolds heat fluxes are presented.
Streaming effect of wall oscillation to boundary layer separation
NASA Technical Reports Server (NTRS)
Wu, X. H.; Wu, J. Z.; Wu, J. M.
1991-01-01
This paper presents a preliminary theoretical result on the time averaged streaming effect of local forcing excitation to the boundary layer separation from smooth surface. The problem is formulated as a periodic disturbance to a basic steady breakaway separating flow, for which the data are taken from a numerical triple-deck solution. The ratio of Strouhal number St and Reynolds number Re plays an important role, both being assumed sufficiently high. The analytical and numerical results show that this streaming effect is quite strong at proper values of St/Re exp 1/4, which may delay or even suppress the separation.
Asymptotically optimal unsaturated lattice cubature formulae with bounded boundary layer
Ramazanov, M D
2013-07-31
This paper describes a new algorithm for constructing lattice cubature formulae with bounded boundary layer. These formulae are unsaturated (in the sense of Babenko) both with respect to the order and in regard to the property of asymptotic optimality on W{sub 2}{sup m}-spaces, m element of (n/2,∞). Most of the results obtained apply also to W{sub 2}{sup μ}(R{sup n})-spaces with a hypoelliptic multiplier of smoothness μ. Bibliography: 6 titles.
Fluid-membrane tethers: Minimal surfaces and elastic boundary layers
NASA Astrophysics Data System (ADS)
Powers, Thomas R.; Huber, Greg; Goldstein, Raymond E.
2002-04-01
Thin cylindrical tethers are common lipid bilayer membrane structures, arising in situations ranging from micromanipulation experiments on artificial vesicles to the dynamic structure of the Golgi apparatus. We study the shape and formation of a tether in terms of the classical soap-film problem, which is applied to the case of a membrane disk under tension subject to a point force. A tether forms from the elastic boundary layer near the point of application of the force, for sufficiently large displacement. Analytic results for various aspects of the membrane shape are given.
NASA Astrophysics Data System (ADS)
Dehghan Manshadi, Mojtaba; Rabani, Ramin
2016-10-01
Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the practicability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disintegrates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17 % occurs with a triangular shape, while the maximum increase in aerodynamic efficiency (lift-to-drag ratio) of around 10 % happens with a rectangular shape at an angle of attack of 2.26°.
Free-stream disturbances, continuous eigenfunctions, boundary-layer instability and transition
NASA Technical Reports Server (NTRS)
Salwen, H.
1980-01-01
A rational foundation is provided for the application of the linear stability theory of parallel shear flows to transition prediction. An explicit method is given for carrying out the necessary calculations. The expansions are shown to be complete. Sample calculations show that a typical boundary layer is very sensitive to vorticity disturbance in the inner boundary layer near the critical layer. Vorticity disturbances three or four boundary layer thicknesses above the boundary are nearly uncoupled from the boundary layer, in that the amplitudes of the discrete Tollmein-Schlichting waves are an extremely small fraction of the amplitude of the disturbance.
NASA Technical Reports Server (NTRS)
Cebeci, T.; Carr, L. W.
1981-01-01
A procedure which solves the governing boundary layer equations within Keller's box method was developed for calculating unsteady laminar flows with flow reversal. This method is extended to turbulent boundary layers with flow reversal. Test cases are used to investigate the proposition that unsteady turbulent boundary layers also remain free of singularities. Turbulent flow calculations are performed. The governing equations for both models are solved. As in laminar flows, the unsteady turbulent boundary layers are free from singularities, but there is a clear indication of rapid thickening of the boundary layer with increasing flow reversal. Predictions of both turbulence models are the same for all practical purposes.
Free-stream disturbance, continuous Eigenfunctions, boundary-layer instability and transition
NASA Technical Reports Server (NTRS)
Grosch, C. E.
1980-01-01
A rational foundation is presented for the application of the linear shear flows to transition prediction, and an explicit method is given for carrying out the necessary calculations. The expansions used are shown to be complete. Sample calculations show that a typical boundary layer is very sensitive to vorticity disturbances in the inner boundary layer, near the critical layer. Vorticity disturbances three or four boundary layer thicknesses above the boundary are nearly uncoupled from the boundary layer in that the amplitudes of the discrete Tollmien-Schlicting waves are an extremely small fraction of the amplitude of the disturbance.
Surface boundary layer turbulence in the Southern ocean
NASA Astrophysics Data System (ADS)
Merrifield, Sophia; St. Laurent, Louis; Owens, Breck; Naveira Garabato, Alberto
2015-04-01
Due to the remote location and harsh conditions, few direct measurements of turbulence have been collected in the Southern Ocean. This region experiences some of the strongest wind forcing of the global ocean, leading to large inertial energy input. While mixed layers are known to have a strong seasonality and reach 500m depth, the depth structure of near-surface turbulent dissipation and diffusivity have not been examined using direct measurements. We present data collected during the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) field program. In a range of wind conditions, the wave affected surface layer (WASL), where surface wave physics are actively forcing turbulence, is contained to the upper 15-20m. The lag-correlation between wind stress and turbulence shows a strong relationship up to 6 hours (˜1/2 inertial period), with the winds leading the oceanic turbulent response, in the depth range between 20-50m. We find the following characterize the data: i) Profiles that have a well-defined hydrographic mixed layer show that dissipation decays in the mixed layer inversely with depth, ii) WASLs are typically 15 meters deep and 30% of mixed layer depth, iii) Subject to strong winds, the value of dissipation as a function of depth is significantly lower than predicted by theory. Many dynamical processes are known to be missing from upper-ocean parameterizations of mixing in global models. These include surface-wave driven processes such as Langmuir turbulence, submesocale frontal processes, and nonlocal representations of mixing. Using velocity, hydrographic, and turbulence measurements, the existence of coherent structures in the boundary layer are investigated.
NASA Technical Reports Server (NTRS)
Yates, E. Carson, Jr.; Desmarais, Robert N.
1990-01-01
The technique of implicit differentiation has been used in combination with linearized lifting-surface theory to derive analytical expressions for aerodynamic sensitivities (i.e., rates of change of lifting pressures with respect to general changes in aircraft geometry, including planform variations) for steady or oscillating planar or nonplanar lifting surfaces in subsonic, sonic, or supersonic flow. The geometric perturbation is defined in terms of a single variable, and the user need only provide simple expressions or similar means for defining the continuous or discontinuous global or local perturbation of interest. Example expressions are given for perturbations of the sweep, taper, and aspect ratio of a wing with trapezoidal semispan planform. The present process appears to be readily adaptable to more general surface-panel methods.
Optimizing EDMF parameterization for stratocumulus-topped boundary layer
NASA Astrophysics Data System (ADS)
Jones, C. R.; Bretherton, C. S.; Witek, M. L.; Suselj, K.
2014-12-01
We present progress in the development of an Eddy Diffusion / Mass Flux (EDMF) turbulence parameterization, with the goal of improving the representation of the cloudy boundary layer in NCEP's Global Forecast System (GFS), as part of a multi-institution Climate Process Team (CPT). Current GFS versions substantially under-predict cloud amount and cloud radiative impact over much of the globe, leading to large biases in the surface and top of atmosphere energy budgets. As part of the effort to correct these biases, the CPT is developing a new EDMF turbulence scheme for GFS, in which local turbulent mixing is represented by an eddy diffusion term while nonlocal shallow convection is represented by a mass flux term. The sum of both contributions provides the total turbulent flux. Our goal is for this scheme to more skillfully simulate cloud radiative properties without negatively impacting other measures of weather forecast skill. One particular challenge faced by an EDMF parameterization is to be able to handle stratocumulus regimes as well as shallow cumulus regimes. In order to isolate the behavior of the proposed EDMF parameterization and aid in its further development, we have implemented the scheme in a portable MATLAB single column model (SCM). We use this SCM framework to optimize the simulation of stratocumulus cloud top entrainment and boundary layer decoupling.
Nonmethane hydrocarbons in Southern Ocean boundary layer air
NASA Astrophysics Data System (ADS)
Lewis, Alastair C.; Carpenter, Lucy J.; Pilling, Michael J.
2001-03-01
Measurements at the remote marine boundary layer station of Cape Grim, Northwest Tasmania, allow study of the unperturbed background atmosphere. Here we present a continuous data series of nonmethane hydrocarbons (NMHCs), measured in situ and with high sensitivity during the Second Southern Ocean Photochemistry Experiment (SOAPEX 2) during austral summer 1999. Air masses arriving at Cape Grim originate from the Australian continent, Tasmania, and Southern Ocean and Antarctic regions. In Southern Ocean marine boundary layer (MBL) air, C2 and C3 alkanes show a highly uniform abundance (ethane 142±11.9 parts per trillion by volume (pptv), propane 8.9±1.7 pptv) at around 4 times lower concentrations than encountered in unpolluted Northern Hemisphere MBL air. The presence of shorter-lived NMHCs in marine air indicates sources of both C4-C6 alkanes and several alkenes in the Southern Ocean. The alkane isomer distributions and abundances are in broad agreement with literature sea-air flux rates. In dynamically stable maritime air, midday maxima in ethene, propene, and isoprene concentrations of a few pptv indicate photochemically driven sources very near to the sea surface. Despite their high reactivity, the impact of these oceanic alkenes on local OH concentrations in remote MBL air is not significant. However, the abundance of isoprene in marine air may significantly elevate formaldehyde above that generated by methane oxidation.
Sonic eddy model of the turbulent boundary layer
NASA Astrophysics Data System (ADS)
Breidenthal, Robert; Dintilhac, Paul; Williams, Owen
2016-11-01
A model of the compressible turbulent boundary layer is proposed. It is based on the notion that turbulent transport by an eddy requires that information of nonsteady events propagates across the diameter of that eddy during one rotation period. The finite acoustic signaling speed then controls the turbulent fluxes. As a consequence, the fluxes are limited by the largest eddies that satisfies this requirement. Therefore "sonic eddies" with a rotational Mach number of about unity would determine the skin friction, which is predicted to vary inversely with Mach number. This sonic eddy model contrasts with conventional models that are based on the energy equation and variations in the density. The effect of density variations is known to be weak in free shear flows, and the sonic eddy model assumes the same for the boundary layer. In general, Mach number plays two simultaneous roles in compressible flow, one related to signaling and the other related to the energy equation. The predictions of the model are compared with experimental data and DNS results from the literature.
Retrievals of boundary layer methane and isotope fractionation on Titan
NASA Astrophysics Data System (ADS)
Adamkovics, Mate; Lora, Juan M.; Mitchell, Jonathan L.
2016-10-01
The amount of methane in the boundary layer on Titan is an interesting diagnostic of whether or not it might be seeping out of the regolith. We know that kinetic fractionation of methane isotopes can be diagnostic of evaporation at the surface and condensation in the atmosphere. If a parcel is constrained to follow a moist adiabat while condensation occurs, we can predict the amount of fractionation that is expected (Ádámkovics & Mitchell, 2016). We will present our most recent efforts to measure boundary layer methane abundance and isotopic composition, which include our recently published Keck NIRSPAO observations from 17 July 2014 (Ádámkovics et al., 2016), as well as preliminary results from follow-up measurements made on 15 May 2016. Our measurements are tantalizingly close to being able to distinguish between different hydrological parameterizations of the polar regions in the Titan Atmospheric Model (Lora & Ádámkovics, 2016). We will discuss the systematic uncertainties that can be evaluated with the combination of these two datasets and the prospects for exceptionally high S/N observations via particularly deep integrations over multiple nights.
Using GPS Radio Occultation to study polar boundary layer properties
NASA Astrophysics Data System (ADS)
Ganeshan, M.; Wu, D. L.
2015-12-01
The sensitivity of GPS RO refractivity to moisture and temperature variations in polar regions is explored using radiosonde observations from the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment. A retrieval algorithm for the boundary layer inversion height and surface-based inversion (SBI) frequency is developed for dry atmospheric conditions (total precipitable water < 3.6 mm) that typically exist during polar winter, as well as in high-latitude, elevated regions such as eastern Antarctica and central Greenland. The algorithm is applied to the high-resolution refractivity profiles obtained over the polar Arctic region using the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) dataset for the period 2006-2013. The method is found useful for capturing the spatiotemporal variability in Arctic inversion properties. For the Arctic Ocean, the spatial patterns show a minimum inversion height (maximum SBI frequency) over the ice-covered Pacific sector similar to that observed in past studies. Monthly evolution of the inversion characteristics suggests a surface temperature control in the multi-year sea ice region, with the peak in SBI frequency occurring during the transition period from winter to spring. For central Greenland, the seasonal peak in SBI frequency occurs during winter. The diurnal variability in SBI frequency is forced mainly by solar heating, consistent with past observations. Despite some limitations, the RO refractivity profile is found quite useful for monitoring the Arctic boundary layer, and is able to capture the interannual variability of inversion characteristics.
Experimental Study of Unsteady Separation in a Laminar Boundary Layer
NASA Astrophysics Data System (ADS)
Bonacci, Andrew; Lang, Amy; Wahidi, Redha; Santos, Leo
2016-11-01
Separation, caused by an adverse pressure gradient, can be a major problem to aircraft. Reversing flow occurs in separated regions and an investigation of how this backflow forms is of interest due to the fact that this could be used as a means of initiating flow control. Specifically, backflow can bristle shark scales which may be linked to a passive, flow actuated separation control mechanism. An experiment was conducted in a water tunnel to replicate separation, with a focus on the reversing flow development near the wall within a laminar boundary layer. Using a rotating cylinder, an adverse pressure gradient was induced creating a separated region over a flat plate. In this experiment the boundary layer grows to sizes great enough that the scale of the flow is increased, making it more measurable to DPIV. In the future, this research can be utilized to better understand flow control mechanisms such as those enabled by shark skin. Funding from Army Research Office and NSF REU site Grant EEC 1358991 is greatly appreciated.