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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Coma Morphology Due to an Extended Active Region and Implications for the Spin State of Comet Hale-Bopp

We show that the circular character of continuum structures observed in the coma of comet Hale-Bopp around the perihelion passage is most likely due to a dust jet from a large extended active region on the surface. Coma morphology due to a wide jet is different from that due to a narrow jet. The latter shows foreshortening effects due to observing geometry, wider jet produces more circular features. This circularization effect provides a self-consistent explanation for the evolution of near-perihelion coma morphology. No changes in the direction of the rotational angular momentum vector are required during this period in contrast to the models of Schleicher et al. This circularization effect also enables us to produce near-circular coma features in the S-E quadrant during 1997 late February and therefore questions the basic premise on which Sekanina bases his morphological arguments for a gravitationally bound satellite nucleus.

Samarasinha, Nalin H.↗
NASA NTRS1983

Experimental wing and canard jet-flap aerodynamics

The effects of upper surface blowing on the aerodynamics of a 1/2-span wing/body/canard configuration are shown. The results expand a data base that is limited at high subsonic Mach numbers (M = 0.6-0.9), data that are needed if computational techniques are to be developed for the complex flowfields generated by jet blowing. At lift coefficients greater than about 1.0, the thrust removed drag coefficient was lower with jet blowing than without jet blowing. This favorable effect increased with increasing jet blowing coefficient, and, for a fixed coefficient, simultaneous wing/canard jet blowing was slightly more effective than blowing either surface alone.

Smeltzer, D. B.↗
NASA NTRS2010

Development of a Catalytic Coating for a Shuttle Flight Experiment

A spray-on coating was developed for use on the shuttle wing tiles to obtain data that could be correlated with computational fluid dynamics (CFD) solutions to better understand the effect of chemical heating on a fore-body heat shield having a turbulent boundary layer during planetary entry at hypersonic speed. The selection of a spray-on coating was conducted in two Phases 1) screening tests to select the catalytic coating formulation and 2) surface property determination using both arc-jet and side-arm facilities at NASA Ames Research Center. Comparison of the predicted surface temperature profile over a flat-plate with measured values obtained during arc-jet exposure (Phase I study) was used to validate the surface properties obtained during Phase II.

Stewart, David A.↗
NASA NTRS1989

Effects of swirl and high turbulence on a jet in a crossflow

An experimental study has been conducted on the effects of initial swirl and high turbulence in the exhaust of a circular jet injected from a flat plate at a 90-deg angle into a crossflow. The different jet types studied were low-exit turbulence (3 percent), high-exit turbulence (over 10 percent), and 40 and 58 percent swirl. Surface pressure distributions and mean velocity vector plots were obtained for all of these cases. For the surface pressure distribution tests, the jet to crossflow velocity ratios R were 2.2, 4, and 8 for most of the jet types. For the mean velocity vector plots, R = 4 was chosen. Turbulence information in the jet plume was also obtained for the low-exit turbulence case at R = 4. The results showed that the higher-exit turbulence reduced the penetration height, and it also reduced the surface area influenced by negative pressures. The swirl-caused asymmetric pressure distributions and the swirl effects were more pronounced for lower-velocity ratios.

Kavsaoglu, M. S.↗
NASA NTRS1985

Effect of variable surface catalysis on heating near the stagnation point of a blunt body

This paper describes arc-jet data obtained on the performance of glass coated thermal protection systems in a convectively heated environment. These data confirm earlier flight and arc-jet data that show an increased surface catalysis with salt contamination and a decreased surface catalysis near the softening point temperature of the glass. In addition, surface temperature distributions along sphere-cones with abruptly changing surface catalysis were measured near the stagnation point and compared well with computations using a reacting boundary layer code.

Stewart, D. A.↗
NASA NTRS1971

Oceanographic Interpretation of Apollo Photographs. Coastal Oceanographic and Sedimentologic Interpretation of Apollo 9 Space Photographs; Carolina's Continental Shelf, USA

Apollo 9 photographs, color band separations, and oceanographic and meteorological data are used in the study of the origin, movement, and dissipation of masses of discolored water near the shores of North and South Carolina. A model has been developed incorporating jet theory, climatology, currents, surface temperatures, color separations, and other oceanographic data to explain the processes involved in the life cycle of the discolored water masses. Special treatment is afforded the Gulf Stream boundary definition and the Cape Hatteras oceanographic barrier.

Mairs, R. L.↗
NASA NTRS1973

Impingement heat transfer from turbulent air jets to flat plates: A literature survey

Heat transfer characteristics of single and multiple turbulent air jets impinging on flat surfaces have been studied by many investigators. Results of many of these studies are summarized. Suggested correlations for use in the design of cooled turbine blades are noted, and areas where further research would be advisable are identified.

Livingood, J. N. B.↗
NASA NTRS1975

Perturbation solution of the Navier-Stokes equations and its relation to the Lighthill-Curle solution of aerodynamic sound

The aerodynamic sound described by the Lighthill-Curle solution is reexamined using a method of matched asymptotic expansions. The governing Navier-Stokes equations written in nondimensional form are expanded for a small Mach number. First- and second-order solutions for the pressure field are obtained, and the singular nature of the expansion at large distances is indicated. The nearfield pressure is governed by the Poisson equation, whereas the farfield equations describe a linear wave system in a dissipative medium. The pseudosound is related to the incompressible Reynolds stresses associated with a solenoidal velocity field, the velocity, the pressure perturbation, and their derivatives on the boundaries. A uniformly valid first-order solution for the pressure is obtained. It is shown that viscosity, thermal conductivity, and entropy in the flow do not contribute to the first-order noise generation, while the viscous stress contributes to noise only from some boundaries. The application of the proposed perturbation method to a subsonically moving surface and a hot jet is discussed.

Pan, Y. S.↗
NASA NTRS1977

An experimental investigation of a three dimensional wall jet

One and two point statistical properties are measured in the flow fields of a coflowing turbulent jet. Two different confining surfaces (one flat, one with large curvature) are placed adjacent to the lip of the circular nozzle; and the resultant effects on the flow field are determined. The one point quantities measured include mean velocities, turbulent intensities, velocity and concentration autocorrelations and power spectral densities, and intermittencies. From the autocorrelation curves, the Taylor microscale and the integral length scale are calculated. Two point quantities measured include velocity and concentration space-time correlations and pressure velocity correlations. From the velocity space-time correlations, iso-correlation contours are constructed along with the lines of maximum maximorum. These lines allow a picture of the flow pattern to be determined. The pressures monitored in the pressure velocity correlations are measured both in the flow field and at the surface of the confining wall(s).

Catalano, G. D.↗
NASA NTRS1978

Unsteady loads due to propulsive lift configurations. Part C: Development of experimental techniques for investigation of unsteady pressures behind a cold model jet

As part of an overall study of the scaling laws for the fluctuating pressures induced on the wings and flaps of STOL aircraft by jet engine impingement, an experimental investigation was made of the near field fluctuating pressures behind a cold circular jet, both when it was free and when it was impinging on a flat plate. Miniature static pressure probes were developed for measurements in the free jet and on the flat plate which were connected by plastic tubing to 1/8 inch microphones and acted as pressure transducers. Using a digital correlator together with an FFT program on the CDC 6400 computer, spectral densities, relative amplitudes, phase lags, and coherences were also obtained for the signals from pairs of these probes, and were used to calibrate these probes directly against microphones. This system of instrumentation was employed to obtain single point rms and third octave surveys of the static pressures in the free jet and on the surface of the plate.

Haviland, J. K.↗
NASA NTRS1976

Acoustic-loads research for powered-lift configurations

Data presented from large-scale model tests with jet engines having thrusts of 9 kN (2000 lb) and 36 kN (8000 lb) include acoustic loads for an externally blown wing and flap induced by a TF34 jet engine, an upper surface blown (USB) aircraft model in a wind tunnel, and two USB models in static tests. Comparisons of these results with results from acoustic loads studies on configurations of other sizes are made and the implications of these results on interior noise and acoustic fatigue are discussed.

Schoenster, J. A.↗
NASA NTRS1979

Experimental Study of Low Temperature Behavior of Aviation Turbine Fuels in a Wing Tank Model

An experimental investigation was performed to study aircraft fuels at low temperatures near the freezing point. The objective was an improved understanding of the flowability and pumpability of the fuels under conditions encoutered during cold weather flight of a long range commercial aircraft. The test tank simulated a section of an outer wing tank and was chilled on the upper and lower surfaces. Fuels included commercial Jet A and Diesel D-2; JP-5 from oil shale; and Jet A, intermediate freeze point, and D-2 fuels derived from selected paraffinic and naphthenic crudes. A pour point depressant was tested.

Stockemer, Francis J.↗
NASA NTRS1979

On the global distribution of aerosols

Aerosol concentrations were measured during a 54-hour circumnavigation of the earth at altitudes between 238 and 162 millibars and concurrently by a separate flight at lower altitudes over the Pacific Ocean. The aerosol concentrations were found to be symmetrically distributed about the earth. Concurrent meteorological measurements indicate that tropospheric aerosols enter the stratosphere in the vicinity of jet streams and that surface aerosols are carried aloft over the intertropical convergence and Antarctic polar front.

Hogan, A. W.↗
NASA NTRS1978

A correlation method to predict the surface pressure distribution on an infinite plate from which a jet is issuing

A correlation method to predict pressures induced on an infinite plate by a jet issuing from the plate into a subsonic free stream was developed. The complete method consists of an analytical method which models the blockage and entrainment properties of the jet and a correlation which accounts for the effects of separation. The method was developed for jet velocity ratios up to ten and for radial distances up to five diameters from the jet. Correlation curves and data comparisons are presented for jets issuing normally from a flat plate with velocity ratios one to twelve. Also, a list of references which deal with jets in a crossflow is presented.

Perkins, S. C., Jr.↗
NASA NTRS1984

Aeroacoustics of turbulent shear flows

Recent analytical, numerical-simulation and experimental studies of sound generation by high-Reynolds-number turbulent shear flows are reviewed, with a focus on the application of linear rapid-distortion theory to the calculation of the unsteady flow field producing the sound. This approach is considered the most important alternative to acoustic-analogy methods. Topics surveyed include the linear theory of solid-surface interactions, the jet-noise problem, extensions to more complex turbulent flows, and supersonic flows. Graphs comparing theoretical and experimental results are shown.

Goldstein, M. E.↗
NASA NTRS1987

Effects of thrust reversing in ground proximity

The changes in stability and control characteristics encountered by a thrust reversing aircraft during its final approach, landing, and ground roll are described. These changes include a strong pitch-up accompanied by the loss of horizontal tail and aileron control effectiveness. The magnitude of reverser induced changes in ground effect are much larger than corresponding changes in free air. Some unexpected unsteady motions exhibited in wind tunnel by an aircraft model with reversers operating in ground proximity are also described. The cause of this oscillatory behavior was determined to be an unsteady interaction between the wall jets formed by impingement of reverser jets on the ground and the on-coming free stream. Time histories of rolling moments measured by the wind tunnel balance or support system were removed and frequencies were scaled by Strouhal number to full scale. Corrected time series were used to simulate the motion of a fighter aircraft with thrust reversers in ground effect. The simulation predicted large roll angles and nose down attitude at touchdown. Some phenomena of jet attachment to solid surfaces are discussed and areas for future research are recommended.

Joshi, P. B.↗