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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

A shock-layer theory based on thirteen-moment equations and DSMC calculations of rarefied hypersonic flows

Grad's thirteen-moment equations are applied to the flow behind a bow shock under the formalism of a thin shock layer. Comparison of this version of the theory with Direct Simulation Monte Carlo calculations of flows about a flat plate at finite attack angle has lent support to the approach as a useful extension of the continuum model for studying translational nonequilibrium in the shock layer. This paper reassesses the physical basis and limitations of the development with additional calculations and comparisons. The streamline correlation principle, which allows transformation of the 13-moment based system to one based on the Navier-Stokes equations, is extended to a three-dimensional formulation. The development yields a strip theory for planar lifting surfaces at finite incidences. Examples reveal that the lift-to-drag ratio is little influenced by planform geometry and varies with altitudes according to a 'bridging function' determined by correlated two-dimensional calculations.

Cheng, H. K.↗
NASA NTRS1992

DSMC analysis of species separation in rarefied nozzle flows

The direct-simulation Monte Carlo method has been used to investigate the behavior of a small amount of a harmful species in the plume and the backflow region of nuclear thermal propulsion rockets. Species separation due to pressure diffusion and nonequilibrium effects due to rapid expansion into a surrounding low-density environment are the most important factors in this type of flow. It is shown that a relatively large amount of the lighter species is scattered into the backflow region and the heavier species becomes negligible in this region due to the extreme separation between species. It is also shown that the type of molecular interaction between the species can have a substantial effect on separation of the species.

Chung, Chan-Hong↗
NASA NTRS1991

Application of the DSMC method to hypersonic flow about a delta wing

The direct simulation Monte Carlo method was applied to a hypersonic rarefied flow about a delta wing at angle of incidence. Three-dimensional calculations were performed using a single-species gas model that accounts for energy exchange with the internal modes. Computed results were compared with the available experimental data obtained in a nitrogen wind-tunnel experiment. Discrepancies were shown to exist between the experimental and calculated results. These differences may be caused by the inadequately defined freestream conditions.

Celenligil, M. C.↗
NASA NTRS1993

A systems approach to a DSMC calculation of a control jet interaction experiment

This study deals with the development of a methodology for numerically simulating the interaction of a reaction control system (RCS) jet with a low-density external flow. A European Space Agency (ESA) experiment was chosen as a test case since it provided experimental data that could validate some of the numerical results. The initial approach was to focus on several subproblems having direct relevance to the full interaction problem. This enabled different numerical methods to be separately investigated and validated for each part of the interaction problem. In this manner, the best methodology for solving the full interaction problem was developed. The subproblems considered in this study included typical RCS nozzle and plume flows, a flat plate at zero incidence, and the flow past the experimental test model without the control jet firing. Once these calculations were completed, a simulation was performed with a control jet operating at a relatively low density. The results from this latter simulation provided qualitative insight into the complex interaction process.

Tartabini, Paul V.↗
NASA NTRS1993

DSMC simulation of ionized rarefied flows

Recently a renewed interest has been exhibited in understanding contamination and space environmental effect in the LEO range of 200 to 600 km as well as in low density microelectronics manufacturing technologies. Realistic simulations must model the physics of the highly coupled effects of neutral and charged particle flows, thermodynamic nonequilibrium, surface charging, and electromagnetic field effects. The computational requirements are enormous for this level of modeling and are almost impossible on current single processor supercomputers. An effort was initiated to develop this capability on a massively parallel MIMD supercomputers. The Wake Shield Facility experiment will be used for test case calculations. Preliminary results indicate that parallel supercomputers may be the only computers capable of simulating the required level of physics and spatial resolution. Calculations which contain from 1 to 8 million simulation particles are presented.

Bartel, Timothy J.↗
NASA NTRS1997

DSMC Simulations of Blunt Body Flows for Mars Entries: Mars Pathfinder and Mars Microprobe Capsules

The hypersonic transitional flow aerodynamics of the Mars Pathfinder and Mars Microprobe capsules are simulated with the direct simulation Monte Carlo method. Calculations of axial, normal, and static pitching coefficients were obtained over an angle of attack range comparable to actual flight requirements. Comparisons are made with modified Newtonian and free-molecular-flow calculations. Aerothermal results were also obtained for zero incidence entry conditions.

Moss, James N.↗
NASA NTRS2004

DSMC Simulations in Support of the Columbia Shuttle Orbiter Accident Investigation

Three-dimensional Direct Simulation Monte Carlo simulations of Columbia Shuttle Orbiter flight STS-107 are presented. The aim of this work is to determine the aerodynamic and heating behavior of the Orbiter during aerobraking maneuvers and to provide piecewise integration of key scenario events to assess the plausibility of the candidate failure scenarios. The flight of the Orbiter is examined at two altitudes: 350-kft and 300-kft. The flowfield around the Orbiter and the heat transfer to it are calculated for the undamaged configuration. The flow inside the wing for an assumed damage to the leading edge in the form of a 10- inch hole is studied.

Boyles, Katie↗
NASA NTRS2014

State-to-State Internal Energy Relaxation Following the Quantum-Kinetic Model in DSMC

A new model for chemical reactions, the Quantum-Kinetic (Q-K) model of Bird, has recently been introduced that does not depend on macroscopic rate equations or values of local flow field data. Subsequently, the Q-K model has been extended to include reactions involving charged species and electronic energy level transitions. Although this is a phenomenological model, it has been shown to accurately reproduce both equilibrium and non-equilibrium reaction rates. The usefulness of this model becomes clear as local flow conditions either exceed the conditions used to build previous models or when they depart from an equilibrium distribution. Presently, the applicability of the relaxation technique is investigated for the vibrational internal energy mode. The Forced Harmonic Oscillator (FHO) theory for vibrational energy level transitions is combined with the Q-K energy level transition model to accurately reproduce energy level transitions at a reduced computational cost compared to the older FHO models.

Liechty, Derek S.↗
NASA NTRS2018

Full-Scale MSL Heatshield Material Response Using DSMC and CFD to Compute the Aerothermal Environments

During Mars atmospheric entry, the Mars Science Laboratory (MSL) was protected by a 4.5 meters diameter ablative heatshield assembled in 113 tiles [1]. The heatshield was made of NASA's flagship ablative material, the Phenolic Impregnated Carbon Ablator (PICA) [2]. Prior work [3] compared the traditional one-dimensional and three-dimensional material response models at different locations in the heatshield. It was observed that the flow was basically one-dimensional in the nose and flank regions, but three-dimensional flow effects were observed in the outer flank. Additionally, the effects of tiled versus monolithic heatshield models were also investigated. It was observed that the 3D tiled and 3D monolithic configurations yielded relative differences for in-depth material temperature up to 18% and 28%, respectively, when compared to the a 1D model.

Aerothermal↗