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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

The magnetic field of Mars - Implications from gas dynamic modeling

On January 21, 1972, the Mars 3 spacecraft observed a variation in the magnetic field during its periapsis passage over the dayside of Mars that was suggestive of entry into a Martian magnetosphere. Original data and trajectory of the spacecraft have been obtained (Dolginov, 1983) and an attempt is made to simulate the observed variation of the magnetic field by using a gas dynamic simulation. In the gas dynamic model a flow field is generated and this flow field is used to carry the interplanetary magnetic field through the Martian magnetosheath. The independence of the flow field and magnetic field calculation makes it possible to converge rapidly on an IMF orientation that would result in a magnetic variation similar to that observed by Mars 3. There appears to be no need to invoke an entry into a Martian magnetosphere to explain these observations.

Russell, C. T.↗
NASA NTRS1985

Current Concepts and Future Directions of CELSS

Bioregenerative life support systems for use in space were studied. Concepts of such systems include the use of higher plants and/or microalgae as sources of food, potable water and oxygen, and as sinks for carbon dioxide and metabolic wastes. Recycling of materials within the system will require processing of food organism and crew wastes using microbiological and/or physical chemical techniques. The dynamics of material flow within the system will require monitoring, control, stabilization and maintenance imposed by computers. Studies included higher plant and algal physiology, environmental responses, and control; flight experiments for testing responses of organisms to weightlessness and increased radiation levels; and development of ground based facilities for the study of recycling within a bioregenerative life support system.

Macelroy, R. D.↗
NASA NTRS1985

Feasibility study for convertible engine torque converter

The feasibility study has shown that a dump/fill type torque converter has excellent potential for the convertible fan/shaft engine. The torque converter space requirement permits internal housing within the normal flow path of a turbofan engine at acceptable engine weight. The unit permits operating the engine in the turboshaft mode by decoupling the fan. To convert to turbofan mode, the torque converter overdrive capability bring the fan speed up to the power turbine speed to permit engagement of a mechanical lockup device when the shaft speed are synchronized. The conversion to turbofan mode can be made without drop of power turbine speed in less than 10 sec. Total thrust delivered to the aircraft by the proprotor, fan, and engine during tansient can be controlled to prevent loss of air speed or altitude. Heat rejection to the oil is low, and additional oil cooling capacity is not required. The turbofan engine aerodynamic design is basically uncompromised by convertibility and allows proper fan design for quiet and efficient cruise operation. Although the results of the feasibility study are exceedingly encouraging, it must be noted that they are based on extrapolation of limited existing data on torque converters. A component test program with three trial torque converter designs and concurrent computer modeling for fluid flow, stress, and dynamics, updated with test results from each unit, is recommended.

Source record↗
NASA NTRS1986

Recent developments in rotary-wing aerodynamic theory

Current progress in the computational analysis of rotary-wing flowfields is surveyed, and some typical results are presented in graphs. Topics examined include potential theory, rotating coordinate systems, lifting-surface theory (moving singularity, fixed wing, and rotary wing), panel methods (surface singularity representations, integral equations, and compressible flows), transonic theory (the small-disturbance equation), wake analysis (hovering rotor-wake models and transonic blade-vortex interaction), limitations on computational aerodynamics, and viscous-flow methods (dynamic-stall theories and lifting-line theory). It is suggested that the present algorithms and advanced computers make it possible to begin working toward the ultimate goal of turbulent Navier-Stokes calculations for an entire rotorcraft.

Johnson, W.↗
NASA NTRS1988

Microgravity science at Langley Research Center

Although space research is still in an embryonic state, a combination of Earth based and space flight experiments are being coupled to yield a better understanding of the complex interaction of heat and fluid flow on the dynamics of crystal growth. Continued efforts on the ground as well as additional flight opportunities are needed to continue the drive to fully understand the advantages, both scientifically and economically, of microgravity crystal growth.

Fripp, Archibald L.↗
NASA NTRS1988

Environmental effects of large impacts on the earth; relation to extinction mechanisms

Since Alvarez et al., discovered a worldwide approx. cm-thick layer of fine sediments laden with platinum group elements in approximately chondritic proportions exactly at the Cretaceous-Tertiary (C-T) boundary, and proposed bolide-impact as triggering mass extinctions, many have studied this hypothesis and the layer itself with its associated spherules and shocked quartz. At issue is whether the mass extinctions, and this horizon has an impact versus volcanic origin. A critical feature of the Alvarez hypothesis is the suggestion that the bolide or possibly a shower of objects delivered to the earth approx. 0.6 x 10 to the 18th power g of material which resulted in aerosol-sized ejecta such that global insolation was drastically reduced for significant periods. Such an event would lower temperatures on continents and halt photosynthesis in the upper 200 m of th eocean. The latter would strangle the marine food chain and thus produce the major marine faunal extinctions which mark the C-T boundary. Crucial issues examined include: What are the dynamics of atmospheric flow occurring upon impact of a large bolide with the earth; What is the size distributions of the very fine impact ejecta and how do these compare to the models of ejecta which are used to model the earth's radiative thermal balance. The flow field due to passage of a 10 km diameter bolide through an exponential atmosphere and the interaction of the gas flow and bolide with the solid ear was calculated. The CO2 released upon impact onto shallow marine carbonate sections was modeled and found that the mass of CO2 released exceeds the present 10 to the 18th power g CO2 budget of the earth's atmosphere by several times. Using the calculations of Kasting and Toon it was found that to compute the temperature rise of the earth's surface as a function of CO2 content, it was found that sudden and prolonged global increases are induced from impact of 20 to 50 km radius projectiles and propose that sudden terrestrial greenhouse-induced heating, not cooling, produced the highly variable extinctions seen at the C-T boundary.

Okeefe, John D.↗
NASA NTRS1989

Solution of the hydrodynamic device model using high-order non-oscillatory shock capturing algorithms

A micron n+ - n - n+ silicon diode is simulated via the hydrodynamic model for carrier transport. The numerical algorithms employed are for the non-steady case, and a limiting process is used to reach steady state. The simulation employs shock capturing algorithms, and indeed shocks, or very rapid transition regimes, are observed in the transient case for the coupled system, consisting of the potential equation and the conservation equations describing charge, momentum, and energy transfer for the electron carriers. These algorithms, termed essentially non-oscillatory, were successfully applied in other contexts to model the flow in gas dynamics, magnetohydrodynamics, and other physical situations involving the conservation laws in fluid mechanics. The method here is first order in time, but the use of small time steps allows for good accuracy. Runge-Kutta methods allow one to achieve higher accuracy in time if desired. The spatial accuracy is of high order in regions of smoothness.

Fatemi, Emad↗
NASA NTRS1990

Transatmospheric vehicle research

Research was conducted into the alternatives to the supersonic combustion ramjet (scramjet) engine for hypersonic flight. A new engine concept, the Oblique Detonation Wave Engine (ODWE) was proposed and explored analytically and experimentally. Codes were developed which can couple the fluid dynamics of supersonic flow with strong shock waves, with the finite rate chemistry necessary to model the detonation process. An additional study was conducted which compared the performance of a hypersonic vehicle powered by a scramjet or an ODWE. Engineering models of the overall performances of the two engines are included. This information was fed into a trajectory program which optimized the flight path to orbit. A third code calculated the vehicle size, weight, and aerodynamic characteristics. The experimental work was carried out in the Ames 20MW arc-jet wind tunnel, focusing on mixing and combustion of fuel injected into a supersonic airstream. Several injector designs were evaluated by sampling the stream behind the injectors and analyzing the mixture with an on-line mass spectrometer. In addition, an attempt was made to create a standing oblique detonation wave in the wind tunnel using hydrogen fuel. It appeared that the conditions in the test chamber were marginal for the generation of oblique detonation waves.

Adelman, Henry G.↗
NASA NTRS1989

Direct numerical simulations of transition in a compressible wake

Direct numerical simulations of a compressible wake are performed to determine the sensitivity of large-scale motions to initial phase lags between the most unstable two-dimensional wave and a pair of oblique waves, and to determine the effect of Mach number on the development of three-dimensional motions. The vorticity dynamics of the flow are studied, and it is determined that, depending upon the initial phase lag, the interaction of the streamwise vorticity with the spanwise vortices may result in the formation of closed vortex loops, or in the removal of streamwise vorticity from the saddle region between the spanwise vortices. Due to lower growth rates experienced at high Mach numbers, the roll-up process is delayed, and the resultant nonlinear motions are much more diffuse.

Chen, Jacqueline H.↗
NASA NTRS1991

A time-accurate implicit method for chemically reacting flows at all Mach numbers

The objective of this work is to develop a unified solution algorithm capable of treating time-accurate chemically reacting flows at all Mach numbers, ranging from molecular diffusion velocities to supersonic speeds. A rescaled pressure term is used in the momentum equation to circumvent the singular behavior of pressure at low Mach numbers. A dual time-stepping integration procedure is established. The system eigenvalues become well behaved and have the same order of magnitude, even in the very low Mach number regime. The computational efficiency for moderate and high speed flow is competitive with the conventional density-based scheme. The capabilities of the algorithm are demonstrated by applying it to selected model problems including nozzle flows and flame dynamics.

Withington, J. P.↗
NASA NTRS1991

Solution of the hydrodynamic device model using high-order non-oscillatory shock capturing algorithms

A micron n+ - n - n+ silicon diode is simulated via the hydrodynamic model for carrier transport. The numerical algorithms employed are for the non-steady case, and a limiting process is used to reach steady state. The simulation employs shock capturing algorithms, and indeed shocks, or very rapid transition regimes, are observed in the transient case for the coupled system, consisting of the potential equation and the conservation equations describing charge, momentum, and energy transfer for the electron carriers. These algorithms, termed essentially nonoscillatory, were successfully applied in other contexts to model the flow in gas dynamics, magnetohydrodynamics, and other physical situations involving the conservation laws in fluid mechanics. The method here is first order in time, but the use of small time steps allows for good accuracy. Runge-Kutta methods allow one to achieve higher accuracy in time if desired. The spatial accuracy is of high order in regions of smoothness.

Fatemi, Emad↗
NASA NTRS1989

The topology and vorticity dynamics of a three-dimensional plane compressible wake

The three-dimensional aspects of transition in a low Mach number plane compressible wake are studied numerically. Comparisons are made between the topology of the velocity field and the vorticity dynamics of the flow based on results from direct numerical simulations of the full compressible Navier-Stokes equations. The velocity field is integrated to obtain instantaneous streamlines at different stages in the evolution. A generalized three-dimensional critical point theory is applied to classify the critical points of the velocity field.

Chen, Jacqueline H.↗
NASA NTRS1991

Shear-induced instability and arch filament eruption - A magnetohydrodynamic (MHD) numerical simulation

A situation wherein a bipolar magnetic field embedded in a stratified solar atmosphere undergoes symmetrical shear motion at the footpoints is investigated via a 2D (nonplanar) MHD simulation. It was found that the vertical plasma flow velocities grow exponentially, leading to a new type of global MHD instability. The growth rate increases almost linearly until it reaches the same order of magnitude as the Alfven speed. Then a nonlinear MHD instability occurs beyond this point. It was found that the central loops are pinched by opposing Lorentz forces, and the outer closed loops stretch upward with the vertically-rising mass flow. The nonlinear dynamical shearing instability is illustrated by a numerical example that is given for three different values of the plasma beta that span several orders of magnitude.

Wu, S. T.↗
NASA NTRS1993

Automatic array alignment in data-parallel programs

FORTRAN 90 and other data-parallel languages express parallelism in the form of operations on data aggregates such as arrays. Misalignment of the operands of an array operation can reduce program performance on a distributed-memory parallel machine by requiring nonlocal data accesses. Determining array alignments that reduce communication is therefore a key issue in compiling such languages. We present a framework for the automatic determination of array alignments in array-based, data-parallel languages. Our language model handles array sectioning, reductions, spreads, transpositions, and masked operations. We decompose alignment functions into three constituents: axis, stride, and offset. For each of these subproblems, we show how to solve the alignment problem for a basic block of code, possibly containing common subexpressions. Alignments are generated for all array objects in the code, both named program variables and intermediate results. We assign computation to processors by virtue of explicit alignment of all temporaries; the resulting work assignment is in general better than that provided by the 'owner-computes' rule. Finally, we present some ideas for dealing with control flow, replication, and dynamic alignments that depend on loop induction variables.

Chatterjee, Siddhartha↗
NASA NTRS1992

Generation of magnetic fields by chaotic fluid convection - The fast dynamo problem

In the kinematic fast dynamo problem, the underlying nonlinear dynamics of the flow play a critical role in the behavior of a dynamo field. It is presently noted that the two important facets of the problem are the approximately lognormal distribution of vector lengths, and the presence of partial cancellation. It is suggested that these features may be reflected in the magnetic fields observed on the sun.

Finn, John M.↗
NASA NTRS1993

The effect of gravitational modulation on convection in vertical Bridgman growth

During vertical directional solidification of a binary alloy at constant velocity, buoyancy-driven solutal convection may occur due to the solute gradient associated with the solidification process. This problem is further complicated if time-periodic forcing is considered, which is relevant to materials processing in a microgravity environment or as a means of dynamic control of flow instabilities. The effect of time-periodic modulation is studied by introducing a gravitational acceleration which is a sinusoidal function of time. The onset of solutal convection is treated by a stability analysis of the linearized governing equations and boundary conditions. Solutions are obtained numerically employing two distinct computational implementations of Floquet theory. Results are presented for materials with large Schmidt number, and an analysis for large frequency and large Schmidt number yields a more complete description of the behavior in this relevant limit.

Murray, B. T.↗
NASA NTRS1993

Reconnection of vorticity lines and magnetic lines

Magnetic field and fluid vorticity share many features. First, as divergence-free vector fields they are conveniently visualized in terms of their field lines, curves that are everywhere tangent to the field. The lines indicate direction and their density indicates field strength. The question arises of the extent to which the evolution of the fields can be treated in terms of the evolution of their field lines. Newcomb (1958) derived the general conditions on the evolution of vector fields that permit the identification of field lines from one instant to the next. The equations of evolution of the vorticity field and the magnetic field fall within Newcomb's analysis. The dynamics of the flows differ between these two systems, so that geometrically similar phenomena happen in different ways in the two systems. In this paper the geometrical similarities are emphasized. Reconnection will be defined here as evolution in which it is not possible to preserve the global identification of some field lines. There is a close relation between reconnection and the topology of the vector field lines. Nontrivial topology occurs where the field has null points or there are field lines that are closed loops.

Greene, John M.↗
NASA NTRS1991

Interactions between synoptic-scale eddies and the large-scale flow during the development of blocking over the North Atlantic Ocean

Earlier studies of blocking are extended by examining the interactions that occur between the synoptic-scale eddies and the large-scale flow during the development of wintertime blocking events over the North Atlantic Ocean. In particular, attention is given to the change of synoptic-scale eddy activity during the development of blocking and to the role of anomalous forcing by synoptic-scale eddies in the development of large-scale flow anomalies. The dynamical mechanisms accounting for the observed variations in eddy activity are identified.

Neilley, Peter P.↗