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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The effects of the laminar/turbulent boundary layer states on the development of a plane mixing layer

The effect, of the laminar/turbulent boundary layer state on the mean and rms velocities of a developing plane mixing layer, has been investigated. The maximum Ux/nu allowed by the facility was 6.7 x 100.000; the maximum x station surveyed corresponds to approximately 2000 and 700 initial momentum thicknesses for the laminar and turbulent cases respectively. The use of commonly accepted non-dimensional representations of the data confirm (at least) an approximately self-preserving condition. They also suggest that the effects of the laminar/turbulent initial condition persist in the self-preserving region. A direct comparison of the data reveals that the persistence so observed is illusory. An interpretation of the reason for this misunderstanding is advanced.

Foss, J. F.↗
DOE OSTI2022

SST ..kappa..-..omega.. Simulations of the Atmospheric Boundary Layer Including the Coriolis Effect

For large-scale structures in the atmospheric boundary layer (ABL), the Coriolis effect and near-wall behavior can have a meaningful impact. For example, both the Coriolis effect and blade boundary layer impact how muchpower wind farms produce. RANS simulations of the ABL typically use the ..kappa..-epsilon turbulence model, which has been developed to accurately capture the Coriolis effect but typically does not perform well near walls. The SST ..kappa..-..omega.. turbulence model performs well near walls but does not accurately capture the Coriolis effect. This work modifies SST ..kappa..-..omega.. to accurately model the Coriolis effect. We discuss the similarities and differences in how to modify ..kappa..-epsilon and SST ..kappa..-..omega.. for the Coriolis effect. Finally, we compare ..kappa..-epsilon and SST ..kappa..-..omega.. simulations of the ABL, including the Coriolis effect, with large eddy simulations and measurements.

atmospheric boundary layer↗
NASA NTRS1991

Exploratory study of in-plane streamline curvature effects on a turbulent boundary layer at a Mach number of 3

This report on a program to study in-plane streamline curvature effects in a turbulent boundary layer at a Mach number of 3. The original proposal, for a 3-year program to explore in-plane streamline curvature effects on a supersonic turbulent boundary layer using three-dimensional pressure fields generated by fins and wall geometry, ended after one year. The purpose of these tests was to compare these streamline curvature effects to the more classical two-dimensional curvature generated by wall shape and imposed pressure gradients, previously considered primarily in a plane normal to the floor. The studies were carried out in the Mach number of 3, 8 x 8 inch High Reynolds Number Supersonic Tunnel. The usual surface visualization and mean wall static pressures were supplemented by the use of many small high frequency wall static pressure gauges (Kulites) to get some indication of the amplification of boundary layer disturbances by the in-plane streamline curvature caused by the three-dimensional pressure fields imposed on the boundary layer.

Bogdonoff, Seymour M.↗
NASA NTRS1975

Wall Cooling Effects on Hypersonic Transitional/Turbulent Boundary Layers at High Reynolds Numbers

A 4 degree wedge was used to produce a thick turbulent boundary layer with an edge Mach number of 11. By using a two-dimensional model, the boundary layer was nearly free from upstream history effects associated with nozzle wall turbulent boundary layers. Heat-transfer distributions were used to define regions of laminar, transitional, and turbulent flow at several values of T(sub w)/T(sub t) for an edge unit Reynolds number of 0.47 x lot per cm. Pitot and total temperature profiles and skin-friction measurements were obtained at selected stations along the model. Turbulence parameters (mixing length/sigma and epsilon) were derived from the fully turbulent profiles and used to more completely define the "low Reynolds number" effect. Turbulent Prandtl number distributions are also presented.

Watson, Ralph D.↗
NASA NTRS1990

Effect of nose bluntness on boundary layer stability and transition

The effect of nose bluntness on boundary layer instability is studied theoretically for a Mach 8 flow past a 7 degree semivertex cone. The basic flow is computed by solving the parabolized Navier-Stokes equations. Linear stability analysis of the basic flow reveals that, with small amount of bluntness, the critical Reynolds number for the onset of instability increases by an order of magnitude compared to the sharp cone value. The computed second mode frequencies are also in reasonable agreement with the experimental results. The results are used to explain the effect of unit Reynolds number on transition present in the quiet aeroballistic range data.

Malik, M. R.↗
NASA NTRS1961

Radiation Emission Effects of the Equilibrium Boundary Layer in the Stagnation Region

The laminar compressible boundary layer in chemical equilibrium is analysed to show the effect of emission of radiation by the boundary layer on solutions of the energy equation and on the resulting heat transfer. Solutions are obtained at one flight condition, but for several nose radii, in a regime where absorption is negligible. The consequent effects on heat transfer and boundary-layer thickness are determined. The concept of a separate boundary layer and shock layer is discussed in the light of the results obtained.

Howe, John Thomas↗
NASA NTRS1987

Interplanetary radial cosmic-ray gradients and their implication for a possible large modulation effect at the heliospheric boundary

It is proposed here that a large and time-variable part of the overall 11-year cosmic ray modulation in the heliosphere takes place near the heliosphere boundary itself. This conclusion is reached by examining interplanetary radial gradient measurements which show that out to 30-40 AU this gradient remains nearly independent of heliocentric distance throughout the solar cycle. Properties of the solar wind which suggest that the distance to the pressure balance boundary does not vary by more than + or - 25 percent over the solar cycle are also used in support of the proposal. The importance of the large modulation effect at the boundary could exceed that of interplanetary effects expected from present models.

Webber, W. R.↗
NASA NTRS1985

Viscous dissipation effects on thermophoretically augmented aerosol particle transport across laminar boundary layers

The effect of viscous dissipation on mass transport across nonisothermal low-mass-loading laminar boundary layers of dusty gas is investigated theoretically by means of numerical simulations. The derivation of the model is outlined, and numerical results are presented in extensive graphs and characterized in detail. The dissipation effects are found to be significant, increasing total particle-deposition rates; the intensity of the effects depends on the ratio of wall temperature to mainstream static temperature.

Gokoglu, S. A.↗
NASA NTRS1990

Effect of Suction on Controlling the Secondary Instability of Boundary Layers

The effect of suction on controlling the 3-D secondary instability is investigated for a boundary layer with pressure gradient in the presence of small but finite amplitude Tollmien-Schlichting wave. The focus is on principal parametric resonance responsible for strong growth of subharmonics in low disturbance environment. Calculations are presented for the effect of suction on the onset and amplification of the secondary instability in Blasius and Falkner-Skan flows, as well as its effect on controlling the production of the vortical structure.

El-Hady, Nabil M.↗
NASA NTRS1991

Effect of suction on controlling the secondary instability of boundary layers

The effect of suction on controlling the three-dimensional secondary instability is investigated for a boundary layer with a pressure gradient in the presence of a small but finite-amplitude Tollmien-Schlichting wave. The focus is on the principal parametric resonance responsible for the strong growth of subharmonics in a low disturbance environment. Calculations are presented for the effect of suction on the onset and amplification of the secondary instability in Blasius and Falkner-Skan flows, as well as its effect on controlling the production of the vortical structure.

El-Hady, Nabil M.↗
NASA NTRS1988

Some effects of finite spatial resolution on skin friction measurements in turbulent boundary layers

The effects of finite spatial resolution often cause serious errors in measurements in turbulent boundary layers, with particularly large effects for measurements of fluctuating skin friction and velocities within the sublayer. However, classical analyses of finite spatial resolution effects have generally not accounted for the substantial inhomogeneity and anisotropy of near-wall turbulence. The present study has made use of results from recent computational simulations of wall-bounded turbulent flows to examine spatial resolution effects for measurements made at a wall using both single-sensor probes and those employing two sensing volumes in a V shape. Results are presented to show the effects of finite spatial resolution on a variety of quantitites deduced from the skin friction field.

Westphal, Russell V.↗
NASA NTRS1977

Wall cooling effects on hypersonic transitional/turbulent boundary layers at high Reynolds numbers

The characteristics of a thick hypersonic boundary layer turbulent for a length of 175 cm on a 4 deg sharp wedge were measured. The resulting boundary layer was free from transverse curvature effects and only mildly affected by upstream history effects caused by pressure and wall temperature gradients. Heat-transfer distributions were used to locate regions of laminar, transitional, and turbulent flow at an edge unit Reynolds number of 470,000 cm at wall-to-total temperature ratios from about 0.3 to 1. Wall cooling had little effect on the location of the transition region. Pitot and total temperature profiles and skin-friction measurements were obtained at several locations along the model longitudinal centerline. Mixing length and turbulent Prandtl number distributions were derived from the fully turbulent mean profiles.

Watson, R. D.↗
NASA NTRS1987

The effect of a sector boundary crossing on the cometary dust tail

Recognizing that gains in the cometary dust tail are electrically charged, the effect of an interplanetary sector boundary crossing on grain distribution is studied. Specifically, Halley's comet around the time of encounter by the GIOTTO and VEGA 1 and 2 spacecraft in March 1986 is considered. The smallest dust particles are strongly effected, and the projection of their distributions in a plane containing the sun-comet axis and normal to the orbital plane shows a wavy appearance. Also, since reversals in the interplanetary magnetic field occur with a periodicity of 5 to 10 days, the spacecraft, which follow 3 to 4 days apart, are likely to encounter entirely different dust distributions at the lower end of the mass spectrum.

Horanyi, M.↗