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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Sheaths: A Comparison of Magnetospheric, ICME, and Heliospheric Sheaths

When a supersonic flow encounters an obstacles, shocks form to divert the flow around the obstacle. The region between the shock and the obstacle is the sheath, where the supersonic flow is compressed, heated, decelerated, and deflected. Supersonic flows, obstacles, and thus sheaths are observed on many scales throughout the Universe. We compare three examples seen in the heliosphere, illustrating the interaction of the solar wind with obstacles of three very different scales lengths. Magnetosheaths form behind planetary bow shocks on scales ranging from tens to 100 planetary radii. ICME sheath form behind shocks driven by solar disturbances on scale lengths of a few to tens of AU. The heliosheath forms behind the termination shock due to the obstacle presented by the interstellar medium on scale lengths of tens to a hundred AU. Despite this range in scales some common features have been observed. Magnetic holes, possibly due to mirror mode waves, have been observed in all three of these sheaths. Plasma depletion layers are observed in planetary and ICME sheaths. Other features observed in some sheaths are wave activity (ion cyclotron, plasma), energetic particles, transmission of Alfven waves/shocks, tangential discontinuities turbulence behind quasi-parallel shocks, standing slow mode waves, and reconnection on the obstacle boundary. We compare these sheath regions, discussing similarities and differences and how these may relate to the scale lengths of these regions.

Sibeck, D. G.↗
NASA NTRS2002

Parametric Time-Dependent Navier-Stokes Computations for a YAV-8B Harrier in Ground Effect

The Harrier Jump Jet has the distinction of being the only powered-lift aircraft in the free world to achieve operational status and to have flown in combat. This V/STOL aircraft can take-off and land vertically or utilize very short runways by directing its four exhaust nozzles towards the ground. Transition to forward flight is achieved by rotating these nozzles into a horizontal position. Powered-lift vehicles have certain advantages over conventional strike fighters. Their V/STOL capabilities allow for safer carrier operations, smaller carrier size, and quick reaction time for troop support. Moreover, they are not dependent on vulnerable land-based runways. The AV-8A Harrier first entered service in the British Royal Air Force (RAF) during 1969, and the U.S. Marine Corps (USMC) in 1971. The AV-8B was a redesign to achieve improved payload capacity, range, and accuracy. This modified design first entered service with the USMC and RAF in 1985. The success and unique capabilities of the Harrier has prompted the design of a powered-lift version of the Joint Strike Fighter (JSF). The flowfield for the Harrier near the ground during low-speed or hover flight operations is very complex and time-dependent. A sketch of this flowfield is shown. Warm air from the fan is exhausted from the front nozzles, while a hot air/fuel mixture from the engine is exhausted from the rear nozzles. These jets strike the ground and move out radially forming a ground jet-flow. The ambient freestream, due to low-speed forward flight or - headwind during hover, opposes the jet-flow. This interaction causes the flow to separate and form a ground vortex. The multiple jets also interact with each other near the ground and form an upwash or jet fountain, which strikes the underside of the fuselage. If the aircraft is sufficiently close to the ground, the inlet can ingest ground debris and hot gases from the fountain and ground vortex. This Hot Gas Ingestion (HGI) can cause a sudden loss of thrust (powered lift), and the vehicle may crash. The high-speed jet flow along the ground can also entrain the ambient flow, resulting in a low pressure region underneath the vehicle. The accompanied loss of lift is referred to as the suckdown effect. The ground vortex may also be highly unsteady, dramatically changing its size and position with time at low frequencies, e.g., 1 Hz.

Chaderjian, Neal M.↗
NASA NTRS1972

Non-isothermal laminar flow of gases through cooled tubes.

Numerical solutions of the laminar-flow equations in differential form are presented for gas flows through cooled tubes. For nearly isothermal flow there is good agreement with available experimental data, as is also found for the case of a large amount of wall cooling. This correspondence along with a check on the satisfaction of the global momentum and energy constraints allowed an appraisal of the effect of wall cooling on flow through tubes. In general, the effect of wall cooling was to decrease the wall friction and the change in pressure along tubes, but the average heat-transfer coefficient did not vary much.

Back, L. H.↗
NASA NTRS2005

Near-Field Acoustical Characterization of Clustered Rocket Engines

This paper presents an approach for the prediction and characterization of the near-field acoustic levels from closely-spaced clustered rocket engines. The calculations are based on the method proposed by Eldred, wherein the flowfield from the clustered rockets is divided into two zones. Zone 1 contains the isolated nozzles which produce noise independently, and extends up to a distance where the individual flows completely mix to form an equivalent single nozzle flow. Zone 2 is occupied by the single mixed stream starting from the station where the jets merge. The acoustic fields from the two zones are computed separately on the basis of the NASA-SP method of Eldred developed for a single equivalent nozzle. A summation of the spectra for the two zones yields the total effective sound pressure level for the clustered engines. Under certain conditions of nozzle spacing and flow parameters, the combined sound pressure level spectrum for the clustered nozzles displays a double peak. Test cases are presented here to demonstrate the importance of hydrodynamic interactions responsible for the double peak in the sound spectrum in the case of clustered rocket nozzles, and the role of ground reflections in the case of non-interfering jets. A graphics interface (Rocket Acoustic Prediction Tool) has been developed to take into account the effects of clustered nozzles and ground reflections.

Kandula, Max↗
NASA NTRS1986

The Lakshmi Plateau structure as an indicator of asthenosphere horizontal flows on Venus

The structure of Lakshmi Planum in the western part of Ishtar Terra in a fold-fault setting which conforms to the basic massif of the plateau with eruptive centers is constructed concentrically and is interpreted from the point of view of the subsurface flow of materials in the form of horizontally diverging asthenospheric flows and gravitational creep. The surrounding structures are formed by the deformation of the more rigid lithosphere as it breaks away from the asthenospheric flow.

Pronin, A. A.↗
NASA NTRS1970

Laminar wave train structure of collisionless magnetic slow shocks

The laminar wave train structure of collisionless magnetic slow shocks is investigated using two fluid hydromagnetics with ion cyclotron radius dispersion. For shock strengths less than the maximally strong switch-off shock, in the shock leading edge dispersive steepening forms a magnetic field gradient, while in the downstream flow dispersive propagation forms a trailing wave train; dispersion scale lengths are the ion inertial length if beta is smaller than 1 and the ion cyclotron radius if beta is greater than 1. In the switch-off slow shock leading edge, dispersion only produced rotations of the magnetic field direction; the gradient of the magnetic field magnitude, and hence the shock steepening length, is determined solely by resistive diffusion. The switch-off shock structure consists of a long trailing of magnetic rotations which are gradually damped by resistivity.

Coroniti, F. V.↗
NASA NTRS1983

Photoionization models for the winds from cataclysmic variables

Photoionization models are presented for the relative abundances of Si IV, C IV, and N V as a function of the ionization parameter and shape of the ionizing continuum spectrum in the EUV and X-ray energy range. These models are applied to the interpretation of the UV resonance lines observed from the cataclysmic variable TW Virginis by Cordova and Mason. The observed lines are assumed to be formed in gas flowing supersonically out from the continuum source in the form of a stellar wind. It is shown that the shape of the ionizing spectrum can be determined without assuming that the outflow is spherical by fitting to ratios of the line strengths. Models which fit the observed ratios include an X-ray continuum with a low-energy cutoff and may also include a lower luminosity component in the EUV spectral region. Under the added assumption of spherical outflow the derived ionization parameter for the X-ray component can be used to constrain the total mass flux in the wind.

Kallman, T. R.↗
NASA NTRS1976

An experimental study of a self-confined flow with ring-vorticity distribution

A new form of self-confined flow was investigated in which a recirculation zone forms away from any solid boundary. An inviscid flow analysis indicated that in a purely meridional axisymmetric flow a stationary, spherical, self-confined region should occur in the center of a streamlined divergent-convergent enlargement zone. The spherical confinement region would be at rest and at constant pressure. Experimental investigations were carried out in a specially built test apparatus to establish the desired confined flow. The streamlined divergent-convergent interior shape of the test section was fabricated according to the theoretical calculation for a particular streamline. The required inlet vorticity distribution was generated by producing a velocity profile with a shaped gauze screen in the straight pipe upstream of the test section. Fluid speed and turbulence intensity were measured with a constant-temperature hot-wire anemometer system. The measured results indicated a very orderly and stable flow field.

Lin, K. M.↗
NASA NTRS1988

Computation of steady and unsteady vortex-dominated flows with shock waves

The unsteady Euler equations have been derived in the conservation form for the flow relative motion with respect to a rotating frame of reference. The resulting equations are solved by using a central-difference finite-volume scheme with four-state Runge-Kutta time stepping. For steady flow applications local time stepping is used, and for unsteady applications the minimum global time stepping is used. A three-dimensional fully vectorized computer program has been developed and applied to steady and unsteady maneuvering delta wings. The capability of the three-dimensional program has been demonstrated for a rigid sharp-edged delta wing undergoing uniform rolling in a conical flow and rolling oscillations in a locally conical flow.

Kandil, Osama A.↗
NASA NTRS1982

Mare basin filling on the moon - Laboratory simulations

Laboratory simulations of lavas filling a stylized lunar multi-ringed basin demonstrate several relationships between the morphology of the emplaced lavas and various eruption conditions. The rate of effusion is the primary control on the gross shape of the accumulated lavas, with relatively low rates (e.g., Hawaiian style) leading to shield volcanoes and high rates (e.g., flood eruptions) producing flat, ponded lavas. Pre-flow topography can have a significant effect on the general form of individual flows and the position of flow features such as lava channels. Rootless vents develop in many parts of the flow, including areas apparently related to the position of basin rings, giving the false appearance of aligned true vent systems.

Greeley, R.↗
NASA NTRS1985

Unsteady flow in a supersonic cascade with two in-passage shocks

A model for a supersonic blade row with two in-passage shock waves is developed. It accounts for three-dimensional effects in real flows by using an altered blade shape in a two-dimensional cascade. There is enough flexibility in the choice of blade shape to accommodate a desired entrance angle, exit angle, boundary-layer thickness and stage pressure ratio at a given entrance Mach number. The model divides the mean flow into regions of uniform or one-dimensional flow in which the solutions for the unsteady flow may be formed successively. The analysis makes use of previous solutions for unsteady flow in cascades and over an oscillation wedge. Six flow conditions are chosen in the range of parameters for which the two-shock model is valid for studies of flutter in torsion and bending. It is found, in keeping with previous results from a single-shock model, that in each case there is increasing instability with decreasing frequency.

Braun, W. H.↗
NASA NTRS1992

Interferometry and computational studies of an oscillating airfoil compressible dynamic stall flow field

A unique comparison has been made between real time interferograms and full Navier-Stokes computations of the density field over an oscillating airfoil undergoing dynamic stall for compressible flow conditions. Good agreement was found until a dynamic stall vortex formed in the flow. Subsequent evolution of the flow field was found to be very different in the computations. The reasons for this difference have been explained in terms of the leading edge region flow physics and the refined flow modeling that needs to be used for the post-stall flow field.

Chandrasekhara, M. S.↗
NASA NTRS1996

Experimental Investigation of Crossing Shock Wave-Turbulent Boundary Layer-Bleed Interaction

Results of an experimental investigation of a symmetric crossing shock wave/turbulent boundary layer/bleed interaction are presented for a freestream unit Reynolds number of 1.68 x 10(exp 7)/m, a Mach number of 2.81, and deflection angles of 8 degrees. The data obtained in this study are bleed mass flow rate using a trace gas technique, qualitative information in the form of oil flow visualization, flow field Pitot pressures, and static pressure measurements using pressure sensitive paint. The main objective of this test is two-fold. First, this study is conducted to explore boundary layer control through mass flow removal near a large region of separated flow caused by the interaction of a double fin-induced shock wave and an incoming turbulent boundary layer. Also, a comprehensive data set is needed for computational fluid dynamics code validation.

Kim, Hyun↗
NASA NTRS2009

2D and 3D Numerical Simulations of Flux Cancellation

Cancellation of magnetic flux in the solar photosphere and chromosphere has been linked observationally and theoretically to a broad range of solar activity, from filament channel formation to CME initiation. Because this phenomenon is typically measured at only a single layer in the atmosphere, in the radial (line of sight) component of the magnetic field, the actual processes behind this observational signature are ambiguous. It is clear that reconnection is involved in some way, but the location of the reconnection sites and associated connectivity changes remain uncertain in most cases. We are using numerical modeling to demystify flux cancellation, beginning with the simplest possible configuration: a subphotospheric Lundquist flux tube surrounded by a potential field, immersed in a gravitationally stratified atmosphere, spanning many orders of magnitude in plasma beta. In this system, cancellation is driven slowly by a 2-cell circulation pattern imposed in the convection zone, such that the tops of the cells are located around the beta=1 level (i.e., the photosphere) and the flows converge and form a downdraft at the polarity inversion line; note however that no flow is imposed along the neutral line. We will present the results of 2D and 3D MHD-AMR simulations of flux cancellation, in which the flux at the photosphere begins in either an unsheared or sheared state. In all cases, a low-lying flux rope is formed by reconnection at the polarity inversion line within a few thousand seconds. The flux rope remains stable and does not rise, however, in contrast to models which do not include the presence of significant mass loading.

Karpen, Judith T.↗
NASA NTRS2009

20 and 3D Numerical Simulations of Flux Cancellation

Cancellation of magnetic flux in the solar photosphere and chromosphere has been linked observationally and theoretically to a broad range of solar activity, from filament channel formation to CME initiation. Because this phenomenon is typically measured at only a single layer in the atmosphere, in the radial (line of sight) component of the magnetic field, the actual processes behind this observational signature are ambiguous. It is clear that reconnection is involved in some way, but the location of the reconnection sites and associated connectivity changes remain uncertain in most cases. We are using numerical modeling to demystify flux cancellation, beginning with the simplest possible configuration: a subphotospheric Lundquist flux tube surrounded by a potential field, immersed in a gravitationally stratified atmosphere, spanning many orders of magnitude in plasma beta. In this system, cancellation is driven slowly by a 2-cell circulation pattern imposed in the convection zone, such that the tops of the cells are located around the beta= 1 level (Le., the photosphere) and the flows converge and form a downdraft at the polarity inversion line; note however that no flow is imposed along the neutral line. We will present the results of 2D and 3D MHD-AMR simulations of flux cancellation, in which the flux at the photosphere begins in either an unsheared or sheared state. In all cases, a lOW-lying flux rope is formed by reconnection at the polarity inversion line within a few thousand seconds. The flux rope remains stable and does not rise, however, in contrast to models which do not include the presence of significant mass loading.

Karpen, Judith T.↗
NASA NTRS1986

Geological-morphological description of the Ishtar Terra (photomap of the Venusian surface sheet B-5)

The main part of the Ishtar Terra east of the Maxwell Montes is covered with systems of areal dislocations of several directions, which are called Parquet. According to the structural patterns these may be divided into: (1) the central stable block; (2) the lesser peripheral blocks separated from the central one by gaps and grabens; (3) the zones of mobilized parquet, whose substance flowed downward at an incline in the directions away from the central block in the form of plastic flows; and (4) the partially parqueted lava sheets. The Maxwell Montes were formed as a result of the collision between the central parquet block and the Lakshmi Planum.

Sukhanov, A. L.↗