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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 235 records · Page 13

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NASA NTRS1986

Comparison of reflectivity and wind profiles measured on 46.8 MHz and 430 MHz at the Arecibo Observatory

Comparisons of troposphere and stratosphere radar experiments at ultrahigh frequency (UHF) and very high frequency (VHF) were done at the Arecibo Observatory in April 1980 with the 430 MHz and 46.8 MHz radar. The velocity profiles measured on both frequencies with the Doppler beam swinging mode were compared. In general, the velocity profiles were equivalent. The VHF profile, however, shows more fluctuations with height than the UHF profile, although the latter was recorded with 150 m resolution instead of 300 m resolution on VHF.

Rottger, J.↗

NASA NTRS1974

Theoretical study of the effects of refraction on the noise produced by turbulence in jets

The production of noise by turbulence in jets is an extremely complex problem. One aspect of that problem, the transmission of acoustic disturbances from the interior of the jet through the mean velocity profile and into the far field is studied. The jet (two-dimensional or circular cylindrical) is assumed infinitely long with mean velocity profile independent of streamwise location. The noise generator is a sequence of transient sources drifting with the surrounding fluid and confined to a short length of the jet.

Graham, E. W.↗

NASA NTRS1984

Real jet effects on dual jets in a crossflow

A 6-ft by 6-ft wind tunnel section was modification to accommodate the 7-ft wide NASA dual-jet flate model in an effort to determine the effects of nonuniform and/or noncircular jet exhaust profiles on the pressure field induced on a nearby surface. Tests completed yield surface pressure measurements for a 90 deg circular injector producing exit profiles representative of turbofan nozzles (such as the TF-34 nozzle). The measurements were obtained for both tandem and side-by-side jet configurations, jet spacing of S/D =2, and velocity ratios of R=2.2 and 4.0. Control tests at the same mass flow rate but with uniform exit velocity profiles were also conducted, for comparison purposes. Plots for 90 deg injection and R=2.2 show that the effects of exit velocity profile nonuniformity are quite significant.

Schetz, J. A.↗

NASA NTRS1980

Coannular jets - Are they really quiet and why

The noise reductions from both normal- and inverted-velocity-profile (IVP) shock-free coannular jets are critically assessed on the basis of existing data. The fully mixed equivalent (FMEQ) single jet, defined as having a uniform exit profile and the same thrust, mass flow rate and exit area as the coannular jet, is used throughout as the reference for noise comparisons. It is shown that uninverted-velocity-profile coannular jets are consistently noisier than FMEQ jets, whereas IVP jets are slightly quieter. The practical implications are discussed in detail. The 'inverted velocity' effects are isolated experimentally from the 'inverted temperature' effects and the resulting noise reductions or increases are explained by using the measurements of mean flow, turbulence structure, and source location in coannular jets.

Tanna, H. K.↗

NASA NTRS1979

Low-Reynolds-number turbulent boundary layers

A test facility operating at substantially reduced pressures is described and shown to be suitable when used with an open-circuit turbulent boundary layer wind tunnel. The facility is capable of producing flows with momentum Reynolds number in the range 200-10,000 by varying the ambient pressure. At low-Reynolds-number flows the pressure is low enough to allow the tunnel to operate with large values of freestream speed. The tunnel's reliability is verified by examining flows where momentum Reynolds number is greater than 1200. The results skin friction coefficients, wake parameters, and basic velocity profiles - consistently agreed with well-established data. For momentum Reynolds number from 600 through 1200 the resulting data indicate that the 'universal velocity profile' is accurate and correctly describes the mean flow properties. For Reynolds number from 425 through 600, the viscous sublayer in this range can no longer maintain its characteristic size.

White, B. R.↗

NASA NTRS1986

An experimental study of the aerodynamics of a NACA 0012 airfoil with a simulated glaze ice accretion

An experimental study was conducted in the Ohio State University subsonic wind tunnel to measure the detailed aerodynamic characteristics of an airfoil with a simulated glaze ice accretion. A NACA 0012 model with interchangeable leading edges and pressure taps every one percent chord was used. Surface pressure and wake data were taken on the airfoil clean, with forced transition and with a simulated glaze ice shape. Lift and drag penalties due to the ice shape were found and the surface pressure clearly showed that large separation bubbles were present. Both total pressure and split-film probes were used to measure velocity profiles, both for the clean model and for the model with a simulated ice accretion. A large region of flow separation was seen in the velocity profiles and was correlated to the pressure measurements. Clean airfoil data were found to compare well to existing airfoil analysis methods.

Bragg, M. B.↗

NASA NTRS1979

Generalized velocities in the outer region of hypersonic turbulent boundary layers

An attempt is made to show that the outer portion of the velocity profile of hypersonic turbulent boundary layers can be transformed so that the constants determined by a best fit to the law of the wake are in reasonable agreement with the wake constant for incompressible boundary layers at the same Reynolds number. Both y transformations (where y is distance from the surface) and velocity transformations produce velocity profiles which, with the proper choice of wall shear stress to give shear velocity, can be reduced to the incompressible law of the wall.

Watson, R. D.↗

NASA NTRS1981

Unsteady boundary-layer injection

The boundary-layer equations for two-dimensional incompressible flow are integrated numerically for the flow over a flat plate and a Howarth body. Injection is introduced either impulsively or periodically along a narrow strip. Results indicate that injection perpendicular to the wall is transmitted instantly across the boundary layer and has little effect on the velocity profile parallel to the wall. The effect is a little more noticeable for flows with adverse pressure gradients. Injection parallel to the wall results in fuller velocity profiles. Parallel and oscillatory injection appears to influence the mean. The amplitude of oscillation decreases with distance from the injection strip but further downstream it increases again in a manner reminiscent of an unstable process.

Telionis, D. P.↗

NASA NTRS1984

The forward-reverse shock pair at large heliocentric distances

An unsteady one-dimensional numerical magnetohydrodynamic (MHD) model is developed in order to study the essential physical processes involved in the development of the forward-reverse shock pair in the heliosphere. In the model, MHD shocks are treated as boundary surfaces which divide the domain of interest in the r-t plane into several flow regions. The positions of the shock boundary surfaces between two neighboring flow regions are determined by shock speed. On the basis of integrations of the model, it is found that the strong MHD disturbances generated in a corotating interaction region (CIR) propagate at a fast speed relative to the moving material, and that the wave propagation speed is greater in CIR than in its surroundings. This causes disturbances in CIR to pile up and form a shock pair. The newly formed shock pair will in turn propagate outward from the leading edge to interact with ambient rarefaction regions. This interaction accounts for the double sawtooth configuration observed in velocity profiles of shock pairs. It is also demonstrated that the merging of two shocks produces a stronger shock and constant surface on its backside. Computer generated velocity profiles based on the model are presented.

Whang, Y. C.↗

NASA NTRS1985

Semiempirical method of determining flow coefficients for pitot rake mass flow rate measurements

Flow coefficients applicable to area-weighted pitot rake mass flow rate measurements are presented for fully developed, turbulent flow in an annulus. A turbulent velocity profile is generated semiempirically for a given annulus hub-to-tip radius ratio and integrated numerically to determine the ideal mass flow rate. The calculated velocities at each probe location are then summed, and the flow rate as indicated by the rake is obtained. The flow coefficient to be used with the particular rake geometry is subsequently obtained by dividing the ideal flow rate by the rake-indicated flow rate. Flow coefficients ranged from 0.903 for one probe placed at a radius dividing two equal areas to 0.984 for a 10-probe area-weighted rake. Flow coefficients were not a strong function of annulus hub-to-tip radius ratio for rakes with three or more probes. The semiempirical method used to generate the turbulent velocity profiles is described in detail.

Trefny, C. J.↗

NASA NTRS1977

Calculation of turbulent boundary layers with tangential slot injection

Paper describes a numerical calculation scheme for tangential slot injection (wall-wake) flows; application of the scheme over a wide range of flow conditions indicates increased accuracy compared to previous work. Predictions from the numerical code were in good agreement with experiment (velocity profile, skin-friction, and effectiveness data) for low- and high-speed flows. To achieve improved accuracy, modifications in the turbulence modeling, compared to previous research, were necessary for the imbedded shear layer region in the near field and for the wall region near shear layer impingement. Anomalous behavior was noted for far field experimental velocity profiles in low-speed flow when the slot-to-free stream velocity ratio was near one

Cary, A. M., Jr.↗

NASA NTRS1985

Detailed measurements of the flowfield in the vicinity of an airfoil with glaze ice

An experimental study has been conducted in the OSU subsonic tunnel to measure the characteristics of the separation bubble on an airfoil with glaze ice. A measured glaze ice accretion on a NACA 0012 airfoil was simulated in wood for this dry tunnel test. The 21 inch chord model was pressure belted and the ice shape internally tapped to obtain surface pressures, lift and moment coefficients. A wake survey probe was used to obtain airfoil drag. The separation bubble was explored by measuring the time averaged velocities using a split film probe. The probe was positioned using a computer controlled two-dimensional traversing system. In this paper, airfoil lift, drag, and moment coefficient data are compared for the airfoil with and without glaze ice. Velocity profiles in the separation bubble are presented for several chordwise stations at three angles of attack. The ice shape caused a severe lift and drag penalty. The velocity profiles show clearly the large bubble geometry, regions of reversed flow, and bubble reattachment.

Bragg, M. B.↗

NASA NTRS1985

Momentum-dependent diffusive particle acceleration in modified shock fronts

In the presently derived analytic solutions of the steady transport equation for diffusive particle acceleration in a modified, planar shock front having free escape boundaries, the fluid velocity profile through the shock transition decreases monotonically between the upstream and downstream boundaries. The spatial diffusion coefficient's spatial dependence is linked to that of the fluid velocity profile. Attention is given to the solution corresponding to monoenergetic particle injection at the shock front, with free particle escape at finite distances both upstream and downstream of the shock. The accelerated particle spectrum is dominated at high energies by an exponential cutoff, due to the competition between acceleration by the first-order Fermi mechanism and particle loss through the free escape boundaries.

Webb, G. M.↗

NASA NTRS1974

Attenuation characteristics of nonlinear pressure waves propagating in pipes

A series of experiments was conducted to investigate temporal and spatial velocity distributions of fluid flow in 3-in. open-end pipes of various lengths up to 210 ft, produced by the propagation of nonlinear pressure waves of various intensities. Velocity profiles across each of five sections along the pipes were measured as a function of time with the use of hot-film and hot-wire anemometers for two pressure waves produced by a piston. Peculiar configurations of the velocity profiles across the pipe section were noted, which are uncommon for steady pipe flow. Theoretical consideration was given to this phenomenon of higher velocity near the pipe wall for qualitative confirmation. Experimentally time-dependent velocity distributions along the pipe axis were compared with one-dimensional theoretical results obtained by the method of characteristics with or without diffusion term for the purpose of determining the attenuation characteristics of the nonlinear wave propagation in the pipes.

Shih, C. C.↗

NASA NTRS1981

Interaction of eddies and mean zonal flow on Jupiter as inferred from Voyager 1 and 2 images

Voyagers 1 and 2 narrow angle frames are used to obtain displacements of features at resolutions of 130 km over time intervals of 1 Jovian rotation. It is shown that the mean zonal velocity profile does not change by a measurable amount between Voyagers 1 and 2, which is consistent with previous observations. It is also shown that the curvature of the velocity profile vanes varies with latitudes in the range from -3 beta to +2 beta. The barotropic stability criterion is violated at 10 latitudes between + and - 60 deg, and the rate of conversion of eddy kinetic energy into zonal mean kinetic energy is in the range from 1.5 to 3.0 per sq Wm for a layer 2.5 bar deep. The rate of energy conversion is more than 10% of the total infrared heat flux for Jupiter, as compared to the earth where it is only 0.1% of the infrared, which suggests that the two planets possess fundamentally different thermomechanical energy cycles.

Ingersoll, A. P.↗

NASA NTRS1985

A study of laminar separation bubble in the concave region of an airfoil using laser velocimetry

Laser velocimetry (LV) was used to study the nature of laminar separation bubbles in the concave region of a 1.83-meter airfoil model which was tested in the NASA Langley Low Turbulence Pressure Tunnel. Three component, coincident data from LV measurements including histograms of particle velocity, mean velocity profiles, turbulence intensity, and Reynolds stresses within the shear layer were used to determine the locations of laminar separation, transition, and turbulent reattachment. boundary-layer parameters determined from velocity profiles were used to compare the results with existing empirical relations for describing the laminar separation bubble.

Mangalam, S. M.↗

NASA NTRS1985

A Study of Laminar Separation Bubble in the Concave Region of an Airfoil Using Laser Velocimetry

Laser velocimetry (LV) was used to study the nature of laminar separation bubbles in the concave region of a 1.83-meter airfoil model which was tested in the NASA Langley Low Turbulence Pressure Tunnel. Three component, coincident data from LV measurements including histograms of particle velocity, mean velocity profiles, turbulence intensity, and Reynolds stresses within the shear layer were used to determine the locations of laminar separation, transition, and turbulent reattachment. Boundary-layer parameters determined from velocity profiles were used to compare the results with existing empirical relations for describing the laminar separation bubble.

Mangalam, Sivaramakrishnan↗

NASA NTRS1988

Line variability and the broad emission line region of quasi-stellar objects. III - Line profiles and velocity field

Spectroscopic data were used to derive significant information about the broad emission line regions (BELRs) of QSOs. It is found that, if the light-crossing time of the whole BELR is significantly larger than the separation between observations, then an apparent asymmetry in line profiles and time development of both line fluxes and profiles would be expected. The lack of such confirmed developments suggests that a major part of the BELR in these QSOs is not considerably larger than one light-month. In one case, the net change is found to be narrower than the static part of H-beta. This may imply that the inner parts of the BELR have a smaller velocity dispersion. A redshift of about 700 km/s relative to the narrow forbidden O III is found in the QSO 0026+129. This sets an upper limit to the central mass as 6 x 10 to the 9th solar if the size of the BELR is not larger than five light-months.

Zheng, Wei↗