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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Effects of reaction control system jet simulation on the stability and control characteristics of a 0.015 scale space shuttle orbiter model tested in the Langley Research Center unitary plan wind tunnel

An experimental investigation was performed in the Langley Research Center Unitary Plan Wind Tunnel (Test 0A70) to obtain the detailed effects that RCS jet flow interactions with local orbiter flow field have on supersonic stability and control characteristics of the space shuttle orbiter. Six-component force data were obtained through an angle-of-attack range from 15 to 35 degrees at angles of sideslip of 0, +5, and -5 degrees. The test was conducted with yaw jet simulation at free-stream Mach numbers of 2.5 and 4.6, simulating SSV re-entry flight conditions at these Mach numbers. In addition to the basic force measurements, fuselage base pressures and pressures on the non-metric RCS pods were obtained.

Daileda, J. J.↗
NASA NTRS1975

Analysis of liquid-metal-jet impingement cooling in a corner region and for a row of jets

A conformal mapping method was used to analyze liquid-metal-jet impingement heat transfer. The jet flow region and energy equation are transformed to correspond to uniform flow in a parallel plate channel with nonuniform heat addition along a portion of one wall. The exact solution for the wall-temperature distribution was obtained in the transformed channel, and the results are mapped back into the physical plane. Two geometries are analyzed. One is for a single slot jet directed either into an interior corner formed by two flat plates, or over the external sides of the corner; the flat plates are uniformly heated, and the corner can have various included angles. The heat-transfer coefficient at the stagnation point at the apex of the plates is obtained as a function of the corner angle, and temperature distributions are calculated along the heated walls. The second geometry is an infinite row of uniformly spaced parallel slot jets impinging normally against a uniformly heated plate. The heat-transfer behavior is obtained as a function of the spacing between the jets. Results are given for several jet Peclet numbers from 5 to 50.

Siegel, R.↗
NASA NTRS1984

Effects of very high turbulence on convective heat transfer

The effects of high-intensity, large-scale turbulence on turbulent boundary-layer heat transfer are studied. Flow fields were produced with turbulence intensities up to 40% and length scales up to several times the boundary layer thickness. In addition, three different types of turbulence will be compared to see whether they have the same effect on the boundary layer. The three are: the far field of a free jet, flow downstream of a grid, and flow downstream of a simulated gas turbine combustor. Each turbulence field will be characterized by several measures: intensity (by component), scale, and spectrum. Heat transfer will be measured on a 2.5 m long, 0.5 m wide flat plate using the energy-balance technique. The same plate will be used in each of the four flow fields; a low-turbulence tunnel for baseline data, and the three flow situations mentioned.

Moffat, R. J.↗
NASA NTRSDate not supplied

Initial Characterization of the 30 kW Miniature Arc Jet (mARC II) at NASA Ames Research Center

The second-generation Miniature Arc jet Research Chamber (mARC II) at NASA Ames is undergoing integrated systems testing. Once fully operational, this facility will be added to the range of available test facilities operated by the NASA Ames Thermophysics Facilities Branch, with primary focus on applications such as new arc jet flow diagnostics and new arc column diagnostics. Initial characterization of the mARC II is reported here, specifically, measured arc current, arc voltage, column and chamber pressures, mass flow rates, and initial emission measurements carried out at a range of conditions.

arc jet↗
NASA NTRS1986

Experiments on annular liquid jet instability and on the formation of liquid shells

An annular jet flow of liquid surrounding a flow of gas at its core is extremely unstable. Experiments are described in which such a flow is generated by an annular nozzle operated at fairly specific conditions. It is shown that periodic, axisymmetric oscillations arise spontaneously within the cylindrical sheet emerging from the nozzle and grow with such rapidity along the axial dimension that a sealing-off and encapsulation of the core gas occurs within a few jet diameters. This is closely followed by a pinchoff of the liquid between adjacent bubbles. The liquid shells set free thereby assume spherically symmetric form under capillary forces, and each contains a precisely uniform measure of gas and of liquid on account of the extremely high frequency-stability of the process. Description is given of the fluid dynamic processes by which the shells are formed, and mention is made of exploiting the instability for the production of rigid shells for technological applications.

Kendall, J. M.↗
NASA NTRS2015

Jet-Surface Interaction: High Aspect Ratio Nozzle Test, Nozzle Design and Preliminary Data

The Jet-Surface Interaction High Aspect Ratio (JSI-HAR) nozzle test is part of an ongoing effort to measure and predict the noise created when an aircraft engine exhausts close to an airframe surface. The JSI-HAR test is focused on parameters derived from the Turbo-electric Distributed Propulsion (TeDP) concept aircraft which include a high-aspect ratio mailslot exhaust nozzle, internal septa, and an aft deck. The size and mass flow rate limits of the test rig also limited the test nozzle to a 16:1 aspect ratio, half the approximately 32:1 on the TeDP concept. Also, unlike the aircraft, the test nozzle must transition from a single round duct on the High Flow Jet Exit Rig, located in the AeroAcoustic Propulsion Laboratory at the NASA Glenn Research Center, to the rectangular shape at the nozzle exit. A parametric nozzle design method was developed to design three low noise round-to-rectangular transitions, with 8:1, 12:1, and 16: aspect ratios, that minimizes flow separations and shocks while providing a flat flow profile at the nozzle exit. These designs validated using the WIND-US CFD code. A preliminary analysis of the test data shows that the actual flow profile is close to that predicted and that the noise results appear consistent with data from previous, smaller scale, tests. The JSI-HAR test is ongoing through October 2015. The results shown in the presentation are intended to provide an overview of the test and a first look at the preliminary results.

Aeroacoustics↗
NASA NTRS1994

A new technique for the measurement of surface shear stress vectors using liquid crystal coatings

Research has recently shown that liquid crystal coating (LCC) color-change response to shear depends on both shear stress magnitude and direction. Additional research was thus conducted to extend the LCC method from a flow-visualization tool to a surface shear stress vector measurement technique. A shear-sensitive LCC was applied to a planar test surface and illuminated by white light from the normal direction. A fiber optic probe was used to capture light scattered by the LCC from a point on the centerline of a turbulent, tangential-jet flow. Both the relative shear stress magnitude and the relative in-plane view angle between the sensor and the centerline shear vector were systematically varied. A spectrophotometer was used to obtain scattered-light spectra which were used to quantify the LCC color (dominant wavelength) as a function of shear stress magnitude and direction. At any fixed shear stress magnitude, the minimum dominant wavelength was measured when the shear vector was aligned with and directed away from the observer; changes in the relative in-plane view angle to either side of this vector/observer aligned position resulted in symmetric Gaussian increases in measured dominant wavelength. Based on these results, a vector measurement methodology, involving multiple oblique-view observations of the test surface, was formulated. Under present test conditions, the measurement resolution of this technique was found to be +/- 1 deg for vector orientations and +/- 5% for vector magnitudes. An approach t o extend the present methodology to full-surface applications is proposed.

Reda, Daniel C.↗
NASA NTRS1988

Three-dimensional viscous flow computations of a circular jet in subsonic and supersonic cross flow

Three-dimensional viscous flow computations are presented for 90 deg injection angle jets in subsonic and supersonic cross flow. Comparisons with experimental data include jet centerline and vortex trajectories for the subsonic cross flow, and surface pressure measurement for the supersonic crossflow case. The vortices induced in the jet/freestream interaction are computed and illustrated. The vortices persist in subsonic flow and die out quickly in supersonic flow. The structure of the shocks in the unconfined supersonic flow is illustrated.

Harloff, G. J.↗
NASA NTRS1995

Nonlinear Waves in Magnetized Accretion Disks

Time-dependent accretion for a magnetized disk can exhibit short timescale outbursts of high-power jets associated with bursts of disk radiation. The burst of energy in jets can produce outward propagating disturbances in preexisting (+/- z) jet flows. the disturbances are strong and can be expected to steepen and form strong shock waves. The strong linear polarization (up to approximately 30%) and large polarization position angle changes (90 deg and more) seen in the optical outbursts of some quasars clearly indicate synchrotron radiation, and this component of the radiation is probably associated with the burst in jet energy in the present model.

Lovelace, R. V. E.↗
NASA NTRS1986

Simulating AOTV heating environment in an arc jet

The application of arc-jet facilities to the simulation of the combined radiative and convective heating environments calculated for AOTV return missions is presented. The AOTV mission requirement and design configuration determine the magnitude of the radiative and convective heating rates. This paper considers methods for obtaining radiation from the high temperature plasma in arc-jet flows. A computer code that predicts arc-heater performance was used to determine the effect of gas mixtures on arc-heater performance, with the intent of increasing the gas temperature and resultant radiative emission. Numerical radiation solutions were compared with direct measurements of the radiative intensity from the gas cap. Convective heating measurements were made as well. The arc-jet was operated at AOTV enthalpy and pressure levels for these measurements to assess the simulation capabilities for AOTV material development/testing. A parametric study is presented that defines the capability of the Interaction Heating Facility arc jet at Ames to simulate both the radiative and the convective heating for current AOTV configurations.

Balboni, J.↗
NASA NTRS1993

Mixing noise reduction for rectangular supersonic jets by nozzle shaping and induced screech mixing

Two methods of mixing noise modification were studied for supersonic jets flowing from rectangular nozzles with an aspect ratio of about five and a small dimension of about 1.4 cm. The first involves nozzle geometry variation using either single (unsymmetrical) or double bevelled (symmetrical) thirty degree cutbacks of the nozzle exit. Both converging (C) and converging-diverging (C-D) versions were tested. The double bevelled C-D nozzle produced a jet mixing noise reduction of about 4 dB compared to a standard rectangular C-D nozzle. In addition all bevelled nozzles produced an upstream shift in peak mixing noise which is conducive to improved attenuation when the nozzle is used in an acoustically treated duct. A large increase in high frequency noise also occurred near the plane of the nozzle exit. Because of near normal incidence, this noise can be easily attenuated with wall treatment. The second approach uses paddles inserted on the edge of the two sides of the jet to induce screech and greatly enhance the jet mixing. Although screech and mixing noise levels are increased, the enhanced mixing moves the source locations upstream and may make an enclosed system more amenable to noise reduction using wall acoustic treatment.

Rice, Edward J.↗
NASA NTRS1982

The modeling and prediction of multiple jet VTOL aircraft flow fields in ground effect

An engineering methodology based on an empirical data base and analytical fluid dynamic models was developed for the prediction of propulsive lift system induced aerodynamic effects for multiple lift jet VTOL aircraft operating in the hover mode in and out of ground effect. The effects of aircraft geometry, aircraft orientation (pitch, roll) as well as height above ground are considered. Lift jet vector and splay directions fit the airframe, lift jet exit flow conditions, and both axisymmetric and rectangular nozzle exit geometry are also accommodated. The induced suckdown flows are computed from the potential flowfield induced by the turbulent entrainment of both the free jets and wall jets in ground effect and from the free jets alone out of ground effect. The methodology emphasized geometric considerations, computation of stagnation lines and fountain upwash inclination, fountain upwash formation and development, and fountain impingement on the airframe.

Kotansky, D. R.↗
NASA NTRS1981

Jet noise suppression by porous plug nozzles

Jet noise suppression data presented earlier by Maestrello for porous plug nozzles have been supplemented by the testing of a family of nozzles having an equivalent throat diameter of 11.77 cm. Two circular reference nozzles and eight plug nozzles having radius ratios of either 0.53 or 0.80 were tested at total pressure ratios of 1.60 to 4.00. Data were taken both with and without a forward motion of coannular flow jet, and some tests were made with a heated jet. Jet thrust was measured. The data were analyzed to show the effects of suppressor geometry on nozzle propulsive efficiency and jet noise. Jet noise reductions in overall sound pressure level of up to 15 dB were obtained with a 3.5 percent reduction in thrust, but reductions of 10 dB were obtained at thrust reductions on the order of 0.3 percent. The noise reductions for subsonic pressure ratios were much less than those for supersonic pressure ratios.

Bauer, A. B.↗
NASA NTRS2001

Gravitational Effects on Near Field Flow Structure of Low Density Gas Jets

Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of site measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and helium mole percentage obtained from color schlieren images taken at 60 Hz. Results show that the jet flow was significantly influenced by the gravity. The jet in microgravity was up to 70 percent wider than that in Earth gravity. The jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low density jet was buoyancy induced. The paper provides quantitative details of temporal flow evolution as the experiment undergoes a change in gravity in the drop tower.

Yep, Tze-Wing↗
NASA NTRS1986

The preferred spatial mode of instability for a Mach 2 jet

Phase-averaged schlieren video and an array of azimuthally oriented microphones were used in the experiments performed to determine the preferred spatial structure associated with supersonic nozzle design for an exhaust Mach number of 2. The jet flow was unheated, chemically inert, and submerged in a static environment, conditions that are satisfactory for the quasi-linear wave-analytical model of Tam and Morris (1980) and Tam and Burton (1984). For general conditions of undeterminate phase-averaged optical records, a conditional sampling method was devised, based on fundamental multimode components. This method uncovers the preferred spatial structure, and shows that in addition to the dominant jet flapping mode, there is also a significant contribution from the axisymmetric mode. Near-field correlations with a moving microphone indicate that the flapping plane is nearly stationary, and not spinning as in the Westley and Wolley (1975) experiment.

Seiner, J. M.↗