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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Jet engine exhaust noise due to rough combustion and nonsteady aerodynamic sources

Internal sources are accounted for in terms of fluctuations of mass and momentum at the nozzle exit plane. At low Mach numbers, mass flow fluctuations generated at the exit plane by acoustic resonant type fluctuations inside the engine are found to be dominant. In the subsonic Mach number range between 0.3 and 0.5, exit plane mass flow fluctuations at frequencies characteristic of turbulence become most dominant. Above Mach 0.5, the turbulent momentum fluctuations at the exit plane become dominant, and the jet contribution is not found significant at subsonic speeds.

Plett, E. G.↗
NASA NTRS1974

Rough surface scattering based on facet model

A model for the radar return from bare ground was developed to calculate the radar cross section of bare ground and the effect of the frequency averaging on the reduction of the variance of the return. It is shown that, by assuming that the distribution of the slope to be Gaussian and that the distribution of the length of the facet to be in the form of the positive side of a Gaussian distribution, the results are in good agreement with experimental data collected by an 8- to 18-GHz radar spectrometer system. It is also shown that information on the exact correlation length of the small structure on the ground is not necessary; an effective correlation length may be calculated based on the facet model and the wavelength of the incident wave.

Khamsi, H. R.↗
NASA NTRS1976

Surface roughness estimation at three points on the lunar surface using 23-CM monostatic radar

Differences in quasi-specular scattering by the lunar surface have been observed at 23-cm wavelength by using earth-based radar. By taking advantage of libration, three subradar points were isolated, and distinct scattering laws were identified for terrain near Hipparchus, Sinus Medii, and the crater Schroeter F. Interpretations of lunar radar data should henceforth incorporate a recognition that these variations take place. Unidirectional rms surface slope estimates of 6-8 deg in the Central Highlands and 4-5 deg in old mare are appropriate to horizontal scales of 100 m.

Simpson, R. A.↗
NASA NTRS1977

Effects of surface cooling and of roughness on the heating (including transition) to the windward plane-of-symmetry of the shuttle orbiter

The theoretical heat-transfer distributions are compared with experimental heat-transfer distributions obtained in Tunnel B at AEDC using a 0.0175 scale model of the space shuttle orbiter configuration for which the first 80% of the windward surface was roughened by a simulated tile misalignment. The theoretical solutions indicate that thinning the boundary layer by surface cooling increased the nondimensionalized value of the local heat-transfer coefficient. Tile misalignment did not significantly affect the heat-transfer rate in regions where the boundary layer was either laminar or turbulent.

Bertin, J. J.↗
NASA NTRS1977

An experimental study of the atmospheric boundary layer modified by a change in surface roughness and surface temperature

Turbulent flow, resembling an on-shore flow from the ocean crossing the beach at an oblique angle, is investigated. Measurements of this flow have been taken at high sample rates and include measurements at various heights, high enough to describe the portion of the mean wind and temperature profiles and fluxes that are of interest for the solution of practical engineering problems. These problems could include air pollution (fumigation and plume trapping), operation of low flying aircraft, crop-spraying and crop-dusting operations.

Tieleman, H. W.↗
NASA NTRS1976

Creative revision - From rough draft to published paper

The process of revising a technical or scientific paper can be performed more efficiently by the people involved (author, co-author, supervisor, editor) when the revision is controlled by breaking it into a series of steps. The revision process recommended here is based on the levels-of-edit concept that resulted from a study of the technical editorial function at the Jet Propulsion Laboratory of the California Institute of Technology. Types of revision discussed are Substantive, Policy, Language, Mechanical Style, Format, Integrity, and Copy Clarification.

Buehler, M. F.↗
NASA NTRS1979

Influence of corrugation-roughness shape on aerodynamic heating in thick turbulent boundary layers

The results of an experimental program to evaluate the effects of wave shape on heat transfer and pressure distributions of corrugation roughened flat plates in thick turbulent boundary layers are presented. The wave shaping effects studied were wavelength, wave amplitude, and wave radius. The experimental program consisted of tests in the sidewall boundary layer of the Langley Continuous Flow Hypersonic Tunnel at a Mach number of 10.3 and Reynolds numbers from 1.3 to 8.2 x 10 to the 6th per meter. The effects of wave shape are analyzed, correlated and compared with previous data obtained in both thick and thin boundary layers. The correlations include the effects of a large range of geometric, inviscid flow, internal boundary layer, and bulk boundary layer parameters in supersonic and hypersonic flow.

Brandon, H. J.↗
NASA NTRS1979

Microwave backscatter dependence on surface roughness, soil moisture, and soil texture. II - Vegetation-covered soil

Results are presented for an experimental investigation to determine the relationship between radar backscatter coefficient (sigma) and soil moisture for vegetation-covered soil. These results extend a previous report which showed the experimental relationship between sigma and soil moisture for bare soil. It is shown that the highest correlation between sigma and soil moisture is 0.92 for the combined response of four crop types measured at 4.25 GHz, 10 deg incidence angle, and HH polarization. Radar look direction, relative to the crop row direction, is shown to have an insignificant effect on soil-moisture estimation if the radar frequency is higher than 4 GHz. The dependence on soil type can be minimized by expressing soil moisture in units of percent of field capacity. The possibility of using a single radar for measuring soil moisture for both bare and vegetated fields is demonstrated with a linear estimation algorithm having an experimental correlation coefficinet of 0.8.

Ulaby, F. T.↗
NASA NTRS1980

Determining sea-ice boundaries and ice roughness using GEOS-3 altimeter data

The GEOS-3 satellite and radar altimeter instrumentation are described, detailing the ice boundary discrimination technique utilized and presenting an analyses of the GEOS-3 data with respect to satellite visual and IR imagery. A brief description of the GEOS-3 real time data system is also given.

Dwyer, R. E.↗
NASA NTRS1983

Synthetic aperture radar observation of ocean roughness from rolls in an unstable marine boundary layer

Simultaneous synthetic aperture radar (SAR) and cloud photographic observations of the Atlantic Ocean off the coast of Florida were made from a high-altitude aircraft when there was an unstable marine boundary layer. The synthetic aperture radar images show unusual kilometer-sized features on the ocean surface which are related to clouds. The ocean near shore was cloud-free and had no radar features, while from 30 to 330 km offshore there were clouds and prominent kilometer-sized features in the SAR image. These radar features are most prominent when the radar was looking upwind, are less prominent when the radar was looking downwind, and disappear entirely when the radar was looking crosswind. Since ocean radar echo strengths are believed to be controlled primarily by ocean waves satisfying the Bragg relation, these radar features most likely resulted from local enhancements of short gravity waves with 17- to 34-cm wavelengths, which in turn are surface expressions of roll convections in a kilometer-thick unstable marine boundary layer.

Thompson, T. W.↗
NASA NTRS1985

Detecting Cracks in Rough Metal Surfaces

Test based on eddy-current probe technique identifies cracks in swaged metals. Hinged collar with spring-loaded latch holds probe in place on part tested. For repeated measurements on same or similar parts, collar loosened and moved to various measuring positions. Method suitable for many kinds of metal parts, including swaged fittings, tubing, and pipes. Used for rapid crack/no-crack determinations in suspect parts already installed.

Zuver, N. T.↗