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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Effects of velocity profile on boundary-layer shielding

A simple uniform flow boundary-layer model is used to study the effects on the acoustic field at the aircraft fuselage of placing Large Eddy Break Up devices in the boundary layer. The introduction of velocity defects into the boundary layer is shown to enhance boundary-layer shielding. Furthermore, shielding improvements are found to occur by moving the velocity defect further from the wall, by increasing its extent within the boundary layer, and by decreasing the minimum velocity in the defect.

Mcaninch, Gerry L.↗
NASA NTRS1982

Three-dimensional flow field in the tip region of a compressor rotor passage. I - Mean velocity profiles and annulus wall boundary layer

A rotating three-sensor, hot-wire probe has been used along with rotor blade static pressure measurements to investigate the complex inviscid and viscid effects in the annulus wall flowfield, including the three components of mean velocity, turbulence intensity, and turbulence stress inside the rotor blade passage. It is found that the tip leakage flow originates near quarter-chord, with peak values occurring near mid-chord. The leakage flow, which is in the form of a jet within the blade row, is augmented by the blade rotation and travels further away from the suction surface than that observed in stationary blade rows and cascades. This leakage flow tends to roll up between the mid-passage and the pressure surface near the tip region; the vortex formation does not occur within the passage in this particular case.

Lakshminarayana, B.↗
NASA NTRS1979

A method for predicting the noise levels of coannular jets with inverted velocity profiles

A coannular jet was equated with a single stream equivalent jet with the same mass flow, energy, and thrust. The acoustic characteristics of the coannular jet were then related to the acoustic characteristics of the single jet. Forward flight effects were included by incorporating a forward exponent, a Doppler amplification factor, and a Strouhal frequency shift. Model test data, including 48 static cases and 22 wind tunnel cases, were used to evaluate the prediction method. For the static cases and the low forward velocity wind tunnel cases, the spectral mean square pressure correlation coefficients were generally greater than 90 percent, and the spectral sound pressure level standard deviation were generally less than 3 decibels. The correlation coefficient and the standard deviation were not affected by changes in equivalent jet velocity. Limitations of the prediction method are also presented.

Russell, J. W.↗
NASA NTRS1975

A wall-wake velocity profile for turbulent compressible boundary layers with heat transfer

A modified form of the wall-wake profile which is applicable to flows with heat transfer is presented. The modified profile takes into account the effect of a turbulent Prandtl number; it was found to provide a good representation of the experimental data from several sources. The C sub f values which are determined by a least squares fit of the profile to the data agree well with values which were measured by the floating element technique.

Sun, C. C.↗
NASA NTRS1975

Wall-wake velocity profile for compressible non-adiabatic flows

A form of the wall-wake profile, which is applicable to flows with heat transfer, and for which a variation in y = O at y = delta, was suggested. The modified profile, which takes into account the effect of turbulent Prandtl number, was found to provide a good representation of experimental data for a wide range numbers and heat transfer. The Cf values which are determined by a least squares fit of the profile to the data agree well with values which were measured by the floating element technique. In addition, the values of delta determined by the fit correspond more closely to the outer edge of the viscous flow region than those obtained with earlier versions of the wall-wake profile.

Sun, C. C.↗
NASA NTRS1980

Measurements of the sampling volume of an infrared laser doppler velocimeter for the study of feasibility of simultaneous three-dimensional velocity profile mapping

High resolution incoherent mapping of the sampling volume was performed to determine the three dimensional profile of the volume of the beam from which information can be obtained by scattering. The incoherent sampling volume of the infrared laser Doppler velocimeter was found to be heavily dependent upon the configuration of the outgoing laser beam. In general when only half the beam is allowed to focus at the focal plane, the x, y traverses indicate a broader beam with nominal side lobes. However, if the total beam is permitted to impinge on the focal plane there is substantial narrowing of the beam with increased maximum intensity and an increase in side lobes. The double maximum indicated by the coherent sampling volume appears to be an artifact of the scanning process not a fundamental entity of the sampling volume.

Bond, R. L.↗
NASA NTRS1981

The effect of inflow velocity profiles on the performance of supersonic ejector nozzles

The design of supersonic nozzles is becoming increasingly complex as conflicting requirements for low noise, higher efficiency, and wider operating range are driving the designer toward more variable geometry and multiple stream flows. Analysis techniques must be modified and expanded to take into account these additional complexities and still retain the rapid computational rate necessary for optimization and design studies. A nozzle analysis must handle more flow streams, more complex geometries, and more highly distorted initial profiles. This paper discusses some modifications to a method for calculating the performance characteristics of supersonic ejector nozzles and demonstrates the improvement in results the modifications provide.

Bishop, A. R.↗
NASA NTRS1986

Synoptic Gulf Stream velocity profiles through simultaneous inversion of hydrographic and acoustic Doppler data

Data from a shipborne acoustic profiling device have been combined with conductivity, temperature, depth/O2 sections across the Gulf Stream to form estimates of the absolute flow fields. The procedure for the combination was a form of inverse method. The results suggest that at the time of the observations (June 1982) the net Gulf Stream transport off Hatteras was 107 + or - 11 Sv and that across a section near 72.5 W it had increased to 125 + or - 6 Sv. The transport of the deep western boundary current was 9 + or - 3 Sv. For comparison purposes an inversion was done using the hydrographic/O2 data alone as in previously published results and obtained qualitative agreement with the combined inversion. Inversion of the acoustic measurements alone, when corrected for instrument biases, leaves unacceptably large mass transport residuals in the deep water.

Joyce, T. M.↗
NASA NTRS1987

Fermi acceleration at shocks with arbitrary velocity profiles

Diffusive particle acceleration in modified shock fronts is considered. A method by means of which to obtain the resulting particle spectrum for an arbitrary flow profile is outlined; this method is based on a reformulation of the transport equation as a nonlinear first-order equation. Besides the shape of the flow profile, the spectral index of particles depends on the Peclet number of the shock. Results are given for some sample profiles.

Schneider, Peter↗
NASA NTRS1988

Velocity profile similarity for viscous flow development along a longitudinally slotted wind-tunnel wall

A discussion of the flow field measurements on the slot centerline of two different longitudinally slotted wind-tunnel walls is presented. The longitudinal and transverse components of these data are then transformed using the concept of flow similarity to demonstrate the applicability of the technique to the development of the viscous shear flow along and through a slotted wall. Results are presented showing the performance of the similarity transformations with variations in tunnel station, Mach number, and airfoil-induced curvature of the tunnel free stream.

Everhart, Joel L.↗