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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Surface Characterization of LMMS Molybdenum Disilicide Coated HTP-8 Using Arc- Jet Hypersonic Flow

Surface properties for an advanced Lockheed Martin Missile and Space (LMMS) molybdenum disilicide coated insulation (HTP-8) were determined using arc-jet flow to simulate Earth entry at hypersonic speeds. The catalytic efficiency (atom recombination coefficients) for this advanced thermal protection system was determined from arc-jet data taken in both oxygen and nitrogen streams at temperatures ranging from 1255 K to roughly 1600 K. In addition, optical and chemical stability data were obtained from these test samples.

Stewart, David A.↗
NASA NTRS1978

Heat transfer from a row of jets impinging on concave semi-cylindrical surface

Heat transfer from impinging jets has been analyzed. Based on similarities of the boundary conditions of the related flow fields, analogies between heat transfer from impinging jets at the stagnation point and in the wall jet region have been shown for several flow geometries. Calculation of heat transfer in the stagnation region and in the wall jet region, based on available theory and the parameters, obtained from direct measurements, have been carried out, for the single, round, impinging jets. It has been shown that heat transfer from a row of round jets impinging on flat and concave surfaces can be comprehensively described through analysis of impinging jets of simpler geometries. Finally, experimental results for the local and average heat transfer effects are presented and discussed. Comparisons are made with theory and results of other investigators, with fairly satisfactory agreement.

Hrycak, P.↗
NASA NTRS1975

Cross-correlation methods for studying near- and farfield noise characteristics of flow-surface interactions

Systematic methods based on cross-correlation techniques are presented for experimental studies of near- and farfield noise characteristics in airflow-surface interaction problems. Analyses show that, in near- and farfields, the noise characteristics due to the surface contribution of fluctuating pressures and velocities and due to the volume contribution of the turbulence in the flow can be determined separately. Both farfield noise intensities and nearfield acoustic energy fluxes can be expressed in terms of appropriate cross correlations. These correlations can be obtained by making microphone measurements in the farfield, in the nearfield, and on the surface. Examples of the applications to the noise field generated by impinging jets, by surface blowing jets, and by turbulent flow over trailing edges are presented. Advantages of the present method over conventional methods are also discussed.

Pan, Y. S.↗
NASA NTRS1983

A lifting surface computer code with jet-in-crossflow interference effects. Volume 1: Theoretical description

A method is proposed to combine a numerical description of a jet in a crossflow with a lifting surface panel code to calculate the jet/aerodynamic-surface interference effects on a V/STOL aircraft. An iterative technique is suggested that starts with a model for the properties of a jet/flat plate configuration and modifies these properties based on the flow field calculated for the configuration of interest. The method would estimate the pressures, forces, and moments on an aircraft out of ground effect. A first-order approximation to the method suggested is developed and applied to two simple configurations. The first-order approximation is a noniterative precedure which does not allow for interactions between multiple jets in a crossflow and also does not account for the influence of lifting surfaces on the jet properties. The jet/flat plate model utilized in the examples presented is restricted to a uniform round jet injected perpendicularly into a uniform crossflow for a range of jet-to-crossflow velocity ratios from three to ten.

Furlong, K. L.↗
NASA NTRS1983

Some observations on the aerodynamics of an airfoil with a jet exhausting from the lower surface

A preliminary investigation was carried out to study the aerodynamics of an 18% symmetrical airfoil with a rectangular jet exhausting from the lower surface. Static pressures on the airfoil surface and total pressures in the near wake were measured at jet momentum coefficients ranging from 0 to 2. Results from these measurements were used to study the effects of a jet-cross flow interaction on the aerodynamics of an airfoil. These results were also compared with those obtained from a two-dimensional inviscid theoretical model. Measurements indicate positive and negative pressure regions in front of and behind the jet respectively. The intensity of the pressure in these regions increases with increasing jet strength. Upper surface pressures also decrease due to an effective angle of attack induced by the jet-cross flow interaction. The pressure variations on the upper and lower surfaces induce a positive sectional lift coefficient on the airfoil. The magnitude of the lift coefficient for a given momentum coefficient decreases with decreasing aspect ratio of the nozzle.

Leopold, D.↗
NASA NTRS1984

A study of flow past an airfoil with a jet issuing from its lower surface

The aerodynamics of a NACA 0018 airfoil with a rectangular jet of finite aspect ratio exiting from its lower surface at 90 deg to the chord were investigated. The jet was located at 50% of the wing chord. Measurements include static pressures on the airfoil surface, total pressures in the near wake, and local velocity vectors in different planes of the wake. The effects of jet cross flow interaction on the aerodynamics of the airfoil are studied. It is indicated that at all values of momentum coefficients, the jet cross flow interaction produces a strong contra-rotating vortex structure in the near wake. The flow behind the jet forms a closed recirculation region which extends up to a chord length down stream of the trailing edge which results in the flow field to become highly three dimensional. The various aerodynamic force coefficients vary significantly along the span of the wing. The results are compared with a jet flap configuration.

Krothapalli, A.↗
DOE OSTI2023

Cast or Additively Manufactured Coils with End Turn Enhanced Heat Transfer Surfaces for Spray or Jet Cooling

Cast or additively manufactured coils present a new opportunity for creativity in thermal management of electric machines. Improvements to the heat transfer of spray or jet cooling of coil end turns through the incorporation of pins or enhanced heat transfer surfaces in the cast end turn surfaces is explored. The thermal response of cast copper half-turns is measured for a range of spray/jet volumetric flow rates and ohmic loss heat fluxes. A significant reduction, ~30%, in the steady state temperature and increased spray cooling heat transfer coefficients was experimentally measured when the pins or enhanced heat transfer surfaces are incorporated.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRS1974

Cross-correlation methods for studying near- and far-field noise characteristics of several flow-surface interaction problems

Systematic methods based on cross-correlation techniques are presented for experimental studies of near- and far-field noise characteristics of airflow-surface interaction problems. By cross-correlating any two of three-kinds of microphone measurements: one flush-mounted on the surface, one located in the near field, and one placed in the far field, far-field noise intensities and near-field acoustic energy fluxes can be determined. In both near and far fields, the noise characteristics due to the flow turbulence and surface fluctuating pressure contributions can be evaluated separately. Specific applications to the noise field generated by impinging jets, by surface blowing jets, and by turbulent flow over trailing edges are discussed.

Pan, Y. S.↗
NASA NTRS1997

Enhancement of Nucleate Boiling Heat Flux on Macro/Micro-Structured Surfaces Cooled by Multiple Impinging Jets

An experimental investigation of nucleate boiling heat transfer from modified surfaces cooled by multiple in-line impinging circular jets is reported and found to agree with single jet results. A copper block is heated from the back by two electrical arcs, and cooled on the opposite side by three identical liquid jets of distilled water at subcoolings of 25 C 50 C and 77 C and Freon 113 at 24 C subcooling. Liquid flow rates are held constant at 5, 10, and 15 GPH for each of the three jets with jet velocities ranging from 1.4 m/s to 1 1.2 m/s and jet diameters from 0.95 mm to 2.2 mm. To increase the maximum heat flux (CHF) and heat removal rate, the boiling surface was modified by both macro and micro enhancements. Macro modification consists of machined radial grooves in the boiling surface arranged in an optimally designed pattern to allow better liquid distribution along the surface. These grooves also reduce splashing of liquid droplets, and provide 'channels' to sweep away bubbles. Micro modification was achieved by flame spraying metal powder on the boiling surface, creating a porous, sintered surface. With the addition of both micro and macro structured enhancements, maximum heat flux and nucleate boiling can be enhanced by more than 200%. Examination of each surface modification separately and together indicates that at lower superheats, the micro structure provides the enhanced heat transfer by providing more nucleation sites, while for higher superheats the macro structure allows better liquid distribution and bubble removal. A correlation is presented to account for liquid subcoolings and surface enhancements, in addition to the geometrical and fluid properties previously reported in the literature.

Kugler, Scott Lee↗
DOE OSTI2026

Distortion of a Relativistic Jet Echoing a Magnetic Flux Eruption

Magnetized accretion onto spinning black holes (BHs) can accumulate a large magnetic flux across the event horizon and launch a pair of relativistic jets via the Blandford–Znajek mechanism. In the magnetically saturated (arrested) state, excess magnetic flux is ejected from the BH in episodic magnetic flux eruptions, which result in a significant yet temporary reduction of jet power. We analyze results of a high-resolution 3D general-relativistic magnetohydrodynamic numerical simulation of geometrically thick magnetically saturated accretion onto a high-spin Kerr BH for a single cycle of magnetic flux eruption and accumulation. We show that following an eruption, a weakened jet develops a strong helical distortion with a distinct structure of magnetic fields—the poloidal field along the jet core is unaffected by the eruption; while toroidal field lines, ejected from the BH during the eruption and later readvected onto it, form poloidal “bypasses” along the inner jet sheath. Such a distortion may appear in sources fed by geometrically thick accretion flows as an asymmetric superluminal knot, strongly interacting with the jet sheath along an oblique working surface. The jet section repowered by magnetic flux reaccumulated on the BH is tilted by a few degrees, implying significant variations in radiation boost towards observers of BL Lac blazars. The intrinsic structure of the jet spine is consistent with axisymmetric semi-analytical models.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1985

Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow

A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configutations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.

Simon, F. F.↗
NASA NTRS1987

Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow

A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configurations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.

Simon, Frederick F.↗
NASA NTRS2001

Frequency Stratification of the Nonthermal Emission in Blazars

Research supported by this grant involved theoretical investigations of the multifrequency nonthermal emission from the relativistic jets in blazars, which are quasars and related objects with highly variable brightness. In the initial stage of the project, one-dimensional, conical (i.e., spherical symmetry between the jet axis and surface is assumed) jet models were used to explain the multi-waveband spectra and variability of blazars. The results were applied to two flares observed in the object PKS 2155-304, leading to the conclusion that the distinct differences in the observed characteristics of the two flares can be explained with the same jet model if two different physical parameters (the magnetic field in the first flare and the efficiency of acceleration of electrons to high energies in the second) varied.

Marscher, Alan P.↗
NASA NTRS1976

Free-jet expansions from laser-vaporized planar surfaces

Characteristics of free-jet vapor expansions created by the pulsed-laser vaporization of some refractory materials are examined. Such expansions were generated from planar surfaces at laser power densities up to 2.5 MW/sq cm. Time-integrated and time-resolved photography were used to show that the structure and pressures of such flows are correlated by the same relationship that is valid for free jets from orifice flows. Data show that the vapor velocity becomes sonic at or very near the vaporizing surface. A method is presented for deriving vaporization pressure from flow-field photos; such pressures from carbon-vaporization data for temperatures to 4500 K are in good agreement with extrapolated equilibrium vapor pressures. It is shown that this technique may be a means to determine vapor pressures of refractory materials at high temperatures.

Covington, M. A.↗
NASA NTRS1988

Axisymmetric confined turbulent jet directed towards the liquid surface from below

A numerical simulation is presented of an axisymmetric turbulent jet discharging axially from below into a cylindrical tank and directed towards the liquid vapor interface. The liquid vapor interface is assumed to be flat and shear free. The k-epsilon turbulence model is used to calculate the eddy viscosity. The turbulence intensity distribution and the length scale associated with the k-epsilon model are calculated as functions of jet flow rates and systems parameters. Numerical results are compared with appropriate experimental data. The problems associated with the free surface boundary conditions for the turbulent quantities are discussed.

Hasan, Mohammad M.↗
NASA NTRS1989

Axisymmetric confined turbulent jet directed towards the liquid surface from below

A numerical simulation is presented of an axisymmetric turbulent jet discharging axially from below into a cylindrical tank and directed towards the liquid vapor interface. The liquid vapor interface is assumed to be flat and shear free. The k-epsilon turbulence model is used to calculate the eddy viscosity. The turbulence intensity distribution and the length scale associated with the k-epsilon model are calculated as functions of jet flow rates and systems parameters. Numerical results are compared with appropriate experimental data. The problems associated with the free surface boundary conditions for the turbulent quantities are discussed.

Hasan, Mohammad M.↗