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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Interfacial Stability of Converging Plasma Jets for Magnetized Target Fusion

The merging of a spherical distribution of plasma jets to dynamically form a gaseous liner has been proposed for use in magnetized target fusion propulsion. In this paper, a study is made of the interfacial stability of the interaction of these jets. Specifically, the Orr-Sommerfeld equation is integrated to obtain the growth rate of a perturbation to the primary flow at the interface between the colliding jets. The analysis lead to an estimate on the tolerances on the relative flow velocities of the merging plasma jets to form a stable, imploding liner. The results show that during the merging of the jets to form a liner and before contact with the target plasma the growth of the perturbed flow at the jet interface is not likely to destabilize the liner. These data suggest that, as far as the stability of the interface between the merging jets is concerned, the formation of liner can withstand velocity variation up to 50% between the neighboring jets over the density and temperature ranges investigated.

Cassibry, J. T.↗
NASA NTRS1966

Perforations in jet engine supersonic inlet increase shock stability

Modification of a conventional jet engine internal compression supersonic inlet results in increased shock stability and thus, engine instantaneous response to changes in inlet air properties. This technique provides a large amount of bleed near the maximum pressure recovery at the expense of minor bleed flow during critical operation.

Keppler, C. R.↗
NASA NTRS1983

Effect of deoxygenation and prestressing on hydrocarbon fuel thermal stability

A jet fuel thermal oxidation tester was used to study the effect of deoxygenation and deoxygenated prestressing on deposit formation when hydrocarbon fuels are thermally stressed. Four pure hydrocarbons (n-decane, cyclohexane, benzene and 1-hexene) and two mixtures (10 percent tetralin in n-dodecane and commercial Jet A) were used at temperatures of 250 C to 400 C. Deoxygenation decreased deposit formation for cycloheaxane but increased it for benzene. Deoxygenation decreased deposit formation for the two fuel mixtures at 250 C but had no effect at 350 C. Deoxygenated prestressing either increased or decreased deposit formation depending on the fuel used and the temperature.

Bittker, D. A.↗
NASA NTRS1974

Free-flight investigation of the stability and control characteristics of a STOL model with an externally blown jet flap

The stability and control characteristics of a four-engine turbofan STOL transport model having an externally blown jet flap have been investigated by means of the flying-model technique in the Langley full-scale tunnel. The flight characteristics of the model were investigated under conditions of symmetric and asymmetric (one engine inoperative) thrust at lift coefficients up to 9.5 and 5.5, respectively. Static characteristics were studied by conventional power-on force tests over the flight-test angle-of-attack range including the stall. In addition to these tests, dynamic longitudinal and lateral stability calculations were performed for comparison with the flight-test results and for use in correlating the model results with STOL handling-qualities criteria.

Parlett, L. P.↗
NASA NTRS1979

Some aspects of aircraft jet engine fuels

Technologies are reviewed for improving the thermal stability of jet fuels, with reference to the overheating of fuel tanks in supersonic aircraft. Consideration is given to the development of a jet fuel with high thermal stability by the Polish petroleum industry.

Bekiesinski, R.↗
NASA NTRS1975

Flame stability in combusting turbulent jets

A simplified theoretical model for turbulent methane/air flames from a subscale power plant burner is developed and applied to predict the stability of flames as a function of (1) ambient atmosphere temperature and composition, (2) initial preheat temperature, and (3) percentage of external product gas recirculation. The flame model equates the rate at which mass is supplied per unit volume to the rate it is chemically reacted per unit volume using a one-step reaction and a perfectly stirred reactor (PSR). The model contains a free parameter which is evaluated by comparing the theoretical results to experimental results available in the literature. The stability results show that premixed, turbulent flames are stable over a wide equivalence ratio range if the ambient gas is air; however, if combustion products are entrained, the stability is sharply reduced.

Nelson, H. F.↗
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 NTRS1978

Effect of winglets on a first-generation jet transport wing. 4: Stability characteristics for a full-span model at Mach 0.30

The static longitudinal and lateral directional characteristics of a 0.035 scale model of a first generation jet transport were obtained with and without upper winglets. The data were obtained for take off and landing configurations at a free stream Mach number of 0.30. The results generally indicated that upper winglets had favorable effects on the stability characteristics of the aircraft.

Meyer, R. R., Jr.↗
NASA NTRS1973

Effects of reaction control system jet simulation on the stability and control characteristics of a 0.015-scale space shuttle orbiter model in the Ames Research Center 3.5-foot hypersonic wind tunnel

An experimental investigation was performed in the Ames Research Center 3.5-Foot Hypersonic Wind Tunnel to obtain detailed effects which interactions between the RCS jet flow field and the local orbiter flow field have on orbiter hypersonic stability and control characteristics. Six-component force data were obtained through an angle-of-attack range of 15 to 35 deg with 0 deg angle of sideslip. The test was conducted with yaw, pitch and roll jet simulation at a free-stream Mach number of 10.3. These data simulate two SSV reentry flight conditions at Mach numbers of 28.3 and 10.3. Fuselage base pressures and pressures on the nonmetric RCS pods were obtained in addition to the basic force measurements. Model 42-0 was used for these tests.

Dziubala, T. J.↗
NASA NTRS1989

Effects of heat release on the structure and stability of a coflowing, chemically reacting jet

It is shown how linear stability analysis and full simulations can be used to study the stability and structure of reacting flows. The small effect of gravity on steady laminar flame heights can be modeled if allowance is made for the density variations due to heat release. It is found that cold transitional jet simulations yield perturbation growth rates which are consistent with the predictions of the inviscid stability theory.

Mahalingam, S.↗
NASA NTRS1989

Instability of jets of arbitrary geometry

This paper describes a calculation technique for determining the stability of jets of arbitrary cross section. In particular, elliptic and rectangular jets are considered. The numerical procedure involves both a conformal transformation between the computational domain and the physical plane and a solution of the transformed stability equation in the computational domain. Modern, efficient, conformal mappings are used for both simply and doubly connected domains. The numerical solution is based on a finite difference/pseudospectral discretization of the stability equation. The technique is verified by comparison with previous calculations for circular and elliptic jets. Calculations are performed for the stability of elliptic and rectangular jets of aspect ratio 2. Growth rates, phase velocities, and pressure eigenfunctions are calculated.

Baty, Roy S.↗
NASA NTRS1986

Coupled ice-ocean dynamics in the marginal ice zones Upwelling/downwelling and eddy generation

This study is aimed at modeling mesoscale processes such as upwelling/downwelling and ice edge eddies in the marginal ice zones. A two-dimensional coupled ice-ocean model is used for the study. The ice model is coupled to the reduced gravity ocean model through interfacial stresses. The parameters of the ocean model were chosen so that the dynamics would be nonlinear. The model was tested by studying the dynamics of upwelling. Wings parallel to the ice edge with the ice on the right produce upwelling because the air-ice momentum flux is much greater than air-ocean momentum flux; thus the Ekman transport is greater than the ice than in the open water. The stability of the upwelling and downwelling jets is discussed. The downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence. The constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling/downwelling regions, i.e., wind-forced vortices. Steepening and strengthening of vortices are provided by the nonlinear terms. When forcing is time-varying, the advection terms will also redistribute the vorticity. The wind reversals will separate the vortices from the ice edge, so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underneath the ice.

Hakkinen, S.↗
NASA NTRS1989

Linear properties of eddies in a Jovian troposphere forced by deep jets

A linear quasi-geostrophic beta-plane model is used to study large-scale instabilities of the Jovian upper troposphere forced from below by zonal jets. The jets are presumed to be barotropically stable in the isentropic deep interior, but barotropically unstable in the statically stable upper troposphere. The effect on this barotropic instability of weak vertical shear causing the jets to decay with height is examined. It is found that eastward jets are stabilized by weaker shear than westward jets, the most unstable eddies are strongly confined by the shear, and eddy fluxes contribute to vertical decay of the jets. The lower residual mean meridional circulation cells exhibit rising motion in regions of anticyclonic shear, but these are overlain by reverse cells.

Orsolini, Y.↗
NASA NTRS1997

The Stability of Radiatively Cooling Jets. 2: Nonlinear Evolution

We use two-dimensional time-dependent hydrodynamical simulations to follow the growth of the Kelvin-Helmholtz (K-H) instability in cooling jets into the nonlinear regime. We focus primarily on asymmetric modes that give rise to transverse displacements of the jet beam. A variety of Mach numbers and two different cooling curves are studied. The growth rates of waves in the linear regime measured from the numerical simulations are in excellent agreement with the predictions of the linear stability analysis presented in the first paper in this series. In the nonlinear regime, the simulations show that asymmetric modes of the K-H instability can affect the structure and evolution of cooling jets in a number of ways. We find that jets in which the growth rate of the sinusoidal surface wave has a maximum at a so-called resonant frequency can be dominated by large-amplitude sinusoidal oscillations near this frequency. Eventually, growth of this wave can disrupt the jet. On the other hand, nonlinear body waves tend to produce low-amplitude wiggles in the shape of the jet but can result in strong shocks in the jet beam. In cooling jets, these shocks can produce dense knots and filaments of cooling gas within the jet. Ripples in the surface of the jet beam caused by both surface and body waves generate oblique shock "spurs" driven into the ambient gas. Our simulations show these shock "spurs" can accelerate ambient gas at large distances from the jet beam to low velocities, which represents a new mechanism by which low-velocity bipolar outflows may be driven by high-velocity jets. Rapid entrainment and acceleration of ambient gas may also occur if the jet is disrupted. For parameters typical of protostellar jets, the frequency at which K-H growth is a maximum (or highest frequency to which the entire jet can respond dynamically) will be associated with perturbations with a period of - 200 yr. Higher frequency (shorter period) perturbations excite waves associated with body modes that produce internal shocks and only small-amplitude wiggles within the jet. The fact that most observed systems show no evidence for large-amplitude sinusoidal oscillation leading to disruption is indicative that the perturbation frequencies are generally large, consistent with the suggestion that pro- tostellar jets arise from the inner regions (r less than 1 AU) of accretion disks.

Stone, James M.↗