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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Boundary-layer and wake measurements on a swept, circulation-control wing

Wind tunnel measurements of boundary layer and wake velocity profiles and surface static pressure distributions are presented for a swept, circulation control wing. The model is an aspect ratio four semispan wing mounted on the tunnel side wall as a sweep angle of 45 deg. A full span, tangetial, rearward blowing, circulation control slot is located ahead of the trailing edge on the upper surface. Flow surveys were obtained at mid-semispan at freestream Mach numbers of 0.425 and 0.70. Boundary layer profiles measured on the forward portions of the wing are approximately streamwise and two dimensional. The flow in the vicinity of the jet exit and in the near wake is highly three dimensional. The jet flow near the slot on the Coanda surface is directed normal to the slot. Near wake surveys show large outboard flows at the center of the wake. At Mach 0.425 and a 5 deg angle of attack, a range of jet blowing rates was found for which an abrupt transition from incipient separation to attached flow occurs in the boundary layer upstream of the slot. The variation in the lower surface separation location with blowing rate was determined from the boundary layer measurements at Mach 0.425.

Spaid, Frank W.↗
DOE OSTI2025

Resolution dependence of the turbulent atmospheric boundary layer in global storm-resolving climate simulations

The current generation of state-of-the-art global climate models are being run at increasingly higher horizontal resolutions, with the goal of resolving organised deep convection explicitly. How a kilometre-scale resolution impacts the representation of the atmospheric boundary layer is, however, not well known. Using statistical analysis on global fields as well as high-frequency data at selected locations, produced with the Integrated Forecasting System (IFS) model for the Next Generation Earth-system Models (nextGEMS) project, we investigate the horizontal resolution dependence of some boundary-layer processes. We find that a change in resolution from 9 to 2.8 km causes no substantial changes to boundary-layer properties and processes at most of the locations studied, although some global changes are detected that indicate circulation changes. Small changes to the boundary-layer depth and structure are found in the Tropics. The short simulation length and lack of data for optimal boundary-layer analysis limits the conclusions, especially in relation to the connection between the boundary layer and the atmosphere general circulation.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1991

A general approach for the prediction of localized instability generation in boundary layer flows

The present approach to the prediction of instability generation that is due to the interaction of freestream disturbances with regions of subscale variations in surface boundary conditions can account for the finite Reynolds number effects, while furnishing a framework for the study of receptivity in compressible flow and in 3D boundary layers. The approach is illustrated for the case of Tollmien-Schlichting wave generation in a Blasius boundary layer, due to the interaction of a freestream acoustic wave with a localized wall inhomogeneity. Results are presented for the generation of viscous and inviscid instabilities in adverse pressure-gradient boundary layers, supersonic boundary layer instabilities, and cross-flow vortex instabilities.

Choudhari, Meelan↗
NASA NTRS1997

Representation of Clear and Cloudy Boundary Layers in Climate Models

The atmospheric general circulation models which are being used as components of climate models rely on their boundary layer parameterizations to produce realistic simulations of the surface turbulent fluxes of sensible heat. moisture. and momentum: of the boundary-layer depth over which these fluxes converge: of boundary layer cloudiness: and of the interactions of the boundary layer with the deep convective clouds that grow upwards from it. Two current atmospheric general circulation models are used as examples to show how these requirements are being addressed: these are version 3 of the Community Climate Model. which has been developed at the U.S. National Center for Atmospheric Research. and the Colorado State University atmospheric general circulation model. The formulations and results of both models are discussed. Finally, areas for future research are suggested.

Randall, D. A.↗
DOE OSTI2022

Direct numerical simulation of hypersonic turbulent boundary layers: effect of spatial evolution and Reynolds number

Direct numerical simulations (DNS) are performed to investigate the spatial evolution of flat-plate zero-pressure-gradient turbulent boundary layers over long streamwise domains ( >300δ i , with δ i the inflow boundary-layer thickness) at three different Mach numbers, 2.5, 4.9 and 10.9, with the surface temperatures ranging from quasiadiabatic to highly cooled conditions. The settlement of turbulence statistics into a fully developed equilibrium state of the turbulent boundary layer has been carefully monitored, either based on the satisfaction of the von Kármán integral equation or by comparing runs with different inflow turbulence generation techniques. The generated DNS database is used to characterize the streamwise evolution of multiple important variables in the high-Mach-number, cold-wall regime, including the skin friction, the Reynolds analogy factor, the shape factor, the Reynolds stresses, and the fluctuating wall quantities. The data confirm the validity of many classic and newer compressibility transformations at moderately high Reynolds numbers (up to friction Reynolds number Re τ ≈1200 ) and show that, with proper scaling, the sizes of the near-wall streaks and superstructures are insensitive to the Mach number and wall cooling conditions. The strong wall cooling in the hypersonic cold-wall case is found to cause a significant increase in the size of the near-wall turbulence eddies (relative to the boundary-layer thickness), which leads to a reduced-scale separation between the large and small turbulence scales, and in turn to a lack of an outer peak in the spanwise spectra of the streamwise velocity in the logarithmic region.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1943

The Effect of Compressibility on the Growth of the Laminar Boundary Layer on Low-Drag Wings and Bodies

The development of the laminar boundary layer in a compressible fluid is considered. Formulas are given for determining the boundary-layer thickness and the ratio of the boundary-layer Reynolds number to the body Reynolds number for airfoils and bodies of revolution. It i s shown that the effect of compressibility will profoundly alter the Reynolds number corresponding to the upper limit of the range of the low-drag coefficients . The available data indicate that for low-drag and high critical compressibility speed airfoils and bodies of revolution, this effect is favorable.

Allen, H. Julian↗
NASA NTRS1979

First results of a study on turbulent boundary layers in oscillating flow with a mean adverse pressure gradient

The development of a turbulent unsteady boundary layer with a mean pressure gradient strong enough to induce separation, in order to complete the extend results obtained for the flat plate configuration is presented. The longitudinal component of the velocity is measured using constant temperature hot wire anemometer. The region where negative velocities exist is investigated with a laser Doppler velocimeter system with BRAGG cells. The boundary layer responds by forced pulsation to the perturbation of potential flow. The unsteady effects observed are very important. The average location of the zero skin friction point moves periodically at the perturbation frequency. Average velocity profiles from different instants in the cycle are compared. The existence of a logarithmic region enables a simple calculation of the maximum phase shift of the velocity in the boundary layer. An attempt of calculation by an integral method of boundary layer development is presented, up to the point where reverse flow starts appearing.

Houdeville, R.↗
NASA NTRS1971

Some characteristics of turbulent boundary layers in rapidly accelerated flows

An analysis of time-mean-turbulent boundary layer velocity profiles measured in a rapidly accelerating flow suggests that the outer region of the velocity profiles consists of essentially inviscid, rotational flow. The extent of this inviscid outer region was observed in some cases to exceed 90 percent of what is ordinarily thought of as the turbulent boundary layer thickness. On the other hand, the inner frictional region of these velocity profiles appears to have turbulent characteristics similar to those of more conventional turbulent boundary layers. Hence, the outer edge boundary condition for this inner region is more properly the external rotational flow region than the free stream.

Brinich, P. F.↗
NASA NTRS1992

Quasi-Coherent Structures In Turbulent Boundary Layers

Two-part report reviews knowledge of coherent structures in turbulent boundary layers. Part I describes processes and status of cooperative project to summarize data from research on boundary-layer turbulence. Part II presents results of study of numerically simulated flat-plate canonical turbulent boundary layer.

Robinson, S. K.↗
NASA NTRS2010

Orbiter Boundary Layer Transition Prediction Tool Enhancements

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

Berry, Scott A.↗
NASA NTRS1993

Coupling of magnetopause-boundary layer to the polar ionosphere

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

Wei, C. Q.↗
NASA NTRS1982

Instability of compressible boundary layers along curved walls with suction or cooling

This paper investigates the effect of suction of the boundary layer and wall cooling on the growth and development of three-dimensional longitudinal vortices over concave walls. The study is carried out for compressible flows for a range of Mach numbers from 0 to 5. Despite indications that small suction or small cooling rates locally reduce the critical Goertler number (destabilize the boundary layer), the overall effect of suction or cooling is to stabilize the boundary layer by reducing the amplitude ratio of the vortices. In case of suction, this becomes more difficult with increasing Mach number unless high suction rates are used. On the other hand, stabilizing the boundary layer with respect to Goertler vortices can hardly be achieved by cooling even when high cooling rates are used.

El-Hady, N. M.↗
NASA NTRS1977

Investigation of supersonic turbulent boundary-layer separation on a compression ramp by an integral method

An investigation was made to determine the feasibility of using a boundary layer integral method to study the separation of a turbulent boundary layer on a two dimensional ramp at supersonic speeds. The numerical calculations were made for a free stream Mach number of 3, a Reynolds number of 10 million, and over a ramp angle range from 0 deg to 30 deg. For ramp angles where no flow separation was indicated, theoretical calculations were in reasonable agreement with experimental data except for a somewhat belated rise in pressure. For larger ramp angles, where separation was present, the investigation produced results that were not in agreement with experiment or with results calculated by time dependent Navier-Stokes methods. This apparently was true because no provision had been made for a proper shock boundary layer interaction where strong normal pressure gradients are induced within the boundary layer under the shock independent of surface curvature effects.

Patel, D. K.↗
NASA NTRS1981

Force and moment, flow-visualization, and boundary-layer tests on a shuttle orbiter model at Mach 6

Force and moment, flow visualization, and boundary layer state tests were conducted using two 0.004 scale shuttle orbiter models. The force and moment tests were conducted for an angle of attack range from 20 to 40 deg and for Reynolds numbers based on reference length from 0.4 million to 3.6 million. Schlieren photographs were obtained for each angle of attack and Reynolds number. The boundary layer state tests, which were conducted using hot film sensors mounted in a separate model, were conducted over the same range of conditions as the force tests. Test results were combined to show that changes in the boundary layer on a typical hypersonic force test model affect measurement of the axial force coefficient and that the state of the local boundary layer is important for interpreting hypersonic aerodynamic test results.

Calloway, R. L.↗
NASA NTRS1986

The influence of free-stream turbulence on separation of turbulent boundary layers in incompressible, two-dimensional flow

Experiments were conducted to determine if free-stream turbulence scale affects separation of turbulent boundary layers. In consideration of possible interrelation between scale and intensity of turbulence, the latter characteristic also was varied and its role was evaluated. Flow over a 2-dimensional airfoil in a subsonic wind tunnel was studied with the aid of hot-wire anemometry, liquid-film flow visualization, a Preston tube, and static pressure measurements. Profiles of velocity, relative turbulence intensity, and integral scale in the boundary layer were measured. Detachment boundary was determined for various angles of attack and free-stream turbulence. The free-stream turbulence intensity and scale were found to spread into the entire turbulent boundary layer, but the effect decreased as the airfoil surface was approached. When the changes in stream turbulence were such that the boundary layer velocity profiles were unchanged, detachment location was not significantly affected by the variations of intensity and scale. Pressure distribution remained the key factor in determining detachment location.

Potter, J. Leith↗
NASA NTRS1980

Low-frequency pressure fluctuations in axisymmetric turbulent boundary layers

Measurements were made of wall pressure fluctuations under a turbulent boundary layer on the fuselage of a sailplane. Experiments with the sailplane offered a noise-free flow with a low free-stream turbulence level. In this environment the wall-pressure spectrum of a turbulent boundary layer with natural transition was found to drop off at low frequencies. Correlations between several wall-mounted microphones revealed that the large-scale motions contribute about 35% to the mean square pressure. Velocity fluctuations at several positions within and outside the boundary layer were measured and correlated with the wall pressure. It seems that the irrotational motions in the turbulent region are primarily responsible for the large-scale wall-pressure fluctuations. A time-lagged conditional correlation of the pressure was introduced to gain further insight into the pressure-producing motions.

Panton, R. L.↗