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Results for “WIND EFFECT”

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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

The effect of the wind tunnel wall boundary layer on the acoustic testing of propellers

An approximation based on the representation of the boundary layer by lamina of uniform flow with suitable interlayer boundary conditions is shown to be accurate, efficient, and compatible with finite element formulations. The approximation has been implemented using existing codes to produce a model for assessing the suitability of the acoustic environment in a wind tunnel for the acoustic testing of propellers. It is found that, with suitable acoustic treatment and with measurements made near the propeller and well removed from the walls, the free field directivity and level can be reproduced with good fidelity.

Eversman, Walter↗
NASA NTRS1990

Analysis of small-scale rotor hover performance data

Rotor hover-performance data from a 1/6-scale helicopter rotor are analyzed and the data sets compared for the effects of ambient wind, test stand configuration, differing test facilities, and scaling. The data are also compared to full scale hover data. The data exhibited high scatter, not entirely due to ambient wind conditions. Effects of download on the test stand proved to be the most significant influence on the measured data. Small-scale data correlated resonably well with full scale data; the correlation did not improve with Reynolds number corrections.

Kitaplioglu, Cahit↗
NASA NTRS1992

Measurements of the effects of surface winds on ocean currents with a stepped-frequency Alpha K radar system

A frequency-agile C band Alpha K radar system was used to measure ocean surface currents during the SAXON-Chesapeake Light Tower experiment. Surface currents were measured with the radar approximately 80 percent of the time from September 20 to October 14, 1988. These measurements are compared with in situ current and wind probe measurements. The agreement between the radar and current probe measurements are found to be very good during periods when the wind- and wave-driven currents are negligible in the radar-viewing direction. During other times, the radar measurements are approximated by the Weber model.

Popstefanija, Ivan↗
NASA NTRS1992

Mixed convective-dynamic roll vortices and their effects on initial wind and temperature profiles

A new nonlinear 14-coefficient spectral model of two-dimensional shallow Boussinesq flow is developed and used to investigate the onset and development of both dynamically and convectively forced boundary-layer rolls. The model is developed to accept arbitrary basic-state wind profiles as dynamic forcing, using an Ekman profile to provide a means for easy comparison with other studies. The results are qualitatively compared with those of previous theoretical and observational investigations. The rolls are shown to significantly alter the initial wind profile in the sense found by Faller and Kaylor (1967) and Brown (1970), but via a mechanism independent of the Coriolis force.

Haack, Tracy↗
NASA NTRS1991

Mixed convective/dynamic roll vortices and their effects on initial wind and temperature profiles

The onset and development of both dynamically and convectively forced boundary layer rolls are studied with linear and nonlinear analyses of a truncated spectral model of shallow Boussinesq flow. Emphasis is given here on the energetics of the dominant roll modes, on the magnitudes of the roll-induced modifications of the initial basic state wind and temperature profiles, and on the sensitivity of the linear stability results to the use of modified profiles as basic states. It is demonstrated that the roll circulations can produce substantial changes to the cross-roll component of the initial wind profile and that significant changes in orientation angle estimates can result from use of a roll-modified profile in the stability analysis. These results demonstrate that roll contributions must be removed from observed background wind profiles before using them to investigate the mechanisms underlying actual secondary flows in the boundary layer. The model is developed quite generally to accept arbitrary basic state wind profiles as dynamic forcing. An Ekman profile is chosen here merely to provide a means for easy comparison with other theoretical boundary layer studies; the ultimate application of the model is to study observed boundary layer profiles. Results of the analytic stability analysis are validated by comparing them with results from a larger linear model. For an appropriate Ekman depth, a complete set of transition curves is given in forcing parameter space for roll modes driven both thermally and dynamically. Preferred orientation angles, horizontal wavelengths and propagation frequencies, as well as energetics and wind profile modifications, are all shown to agree rather well with results from studies on Ekman layers as well as with studies on near-neutral and convective atmospheric boundary layers.

Haack, Tracy↗
NASA NTRS2011

Effects of Solar Wind Conditions on the Plasma Wake Within a Polar Crater: Preliminary Results

As the solar wind sweeps horizontally past a shadowed lunar crater it simultaneously diffuses toward the surface through an ambipolar process, forming a plasma wake (e.g., Figure 1). Importantly, the resulting electric field structure diverts solar wind protons toward the cold crater floor where they may represent a source of surficial hydrogen. We present a handful of two-dimensional kinetic simulations exploring the range of wake structures and surface particle fluxes possible under various background plasma conditions.

Zimmerman, M. I.↗