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Milos, Frank S.

Publications and source records attributed to Milos, Frank S..

44 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Thermal analysis of an arc heater electrode with a rotating arc foot

A smoothly rotating arc foot and an arc foot that jumps between multiple sticking points were analyzed using analytic formulations and numerical solution procedures. For each case the temperature distribution for a copper electrode was obtained for the plausible range of operating conditions. It is shown that the smoothly rotating arc foot is an extremely safe mode of operation, whereas the jumping arc foot produces excessively high electrode surface temperatures which are not greatly alleviated by increasing the average rotational frequency of the arc foot. It is suggested to eliminate arc-foot rotation and rely on the distribution of fixed electrodes with stationary arc attachment to avoid electrode failure at high current.

Milos, Frank S.↗
NASA NTRS1993

A sonic flow equation for electric arc jets

The relationship between total enthalpy and the flow parameters of two types of electric arc jets is discussed. A simple equation for the supersonic arc jet, based on ARCFLO code calculations for mass-average total enthalpy, is presented in terms of a sonic flow parameter. At enthalpies greater than about 25 MJ/kg, this equation shows better agreement with experimental arc jet data than a previous equation.

Shepard, Charles E.↗
NASA NTRS1993

Simulated rarefied entry of the Galileo probe into the atmosphere of Jupiter

Flow properties and aerodynamics are computed with a direct simulation Monte Carlo (DSMC) method for rarefied entry of the Galileo Probe into the atmosphere of Jupiter. Accurate predictions of vehicle drag coefficients are needed in order to assess atmospheric properties from the onboard Atmosphere Structure Experiment where highly-sensitive accelerometers will measure the drag force to within 10-6 barr during the initial entry phase at high altitudes. The corresponding flow rarefraction extends from the free molecule limit to the near continuum transition regime (Re less than 1000). Simulation results indicate that C(sub D) varies from 2.1 at the free molecule limit down to 1.6 at Re(infinity) = 1,000. Temperatures, densities, and internal energies throughout the flow field were also computed at each altitude ranging from 735 km to 353 km above the 1 barr level in the Jovian atmosphere. Surface heating and temperatures of the probe were computed directly in the DSMC code by assuming radiative equilibrium. Material response was re-asssessed accurately during entry by accounting for conductivity, heat capacity, and pyrolysis which led to surface material mass efflux several times that of the freestream mass influx. The simulation also accounted for the quantum nature of the rotational energy mode of the dominant atmospheric species H2 through partial internal excitation in the freestream gas.

Hass, Brian L.↗
NASA NTRS1992

Numerical procedures for three-dimensional computational surface thermochemistry

Models and equations for surface thermochemistry and near-surface thermophysics of aerodynamically-heated thermal protection materials are reviewed, with particular emphasis on computational boundary conditions for surface mass and energy transfer. The surface energy and mass balances, coupled with an appropriate ablation or surface catalysis model, provide complete thermochemical boundary conditions for a true multidisciplinary solution of the fully coupled fluid-dynamics/solid mechanics problem. Practical approximate solutions can be obtained by using a detailed model with full thermophysics for either the solid or fluid phase amd a semianalytic method for the other half of the problem. A significant increase in the state-of-the-art in aerothermal computational fluid dynamics is possible by uniting CFD methodology with surface thermochemistry boundary conditions and the heat-balance-integral method.

Milos, Frank S.↗
NASA NTRS1991

ARCFLO analysis for high-enthalpy arc heaters

Feasibility, physical constraints, and preliminary design and operating envelope are calculated for a next-generation segmented arc heater with enthalpies of 70-90 MJ/kg, for simulation of fast lunar or Martian return trajectories. The ARCFLO computer program is modified for improved accuracy in high-enthalpy radiation-dominated flows. The ARCFLO band-radiation model is compared with the state-of-the-art spectral-radiation code NEQAIR. The band-radiation model is corrected, and band-absorption coefficients are reduced by up to 40 percent at high temperatures. Parametric studies show that, with conventional wall-heating limitations, high mass flow and high enthalpy are contradictory design goals owing to the increase of radiation losses with pressure, current density, and constrictor diameter. With existing hardware limitations, an enthalpy of 70 MJ/kg with a flow rate of 0.1 kg/s can be achieved in a constrictor with 5-6 cm diameter operating near 3-atm stagnation pressure. The total power is under 100 MW, but the current is very high: 14,000-18,000 amperes.

Milos, Frank S.↗
NASA NTRS1990

Computational equations for radiating and ablating shock layers

The computational equations governing the shock-layer flowfield over a blunt body dominated by radiation and ablation are derived. The flowfield considered is that expected around the vehicles entering the atmosphere of the planet Mars or the earth on return from Mars on a sprint-type manned mission. To determine the appropriate method of approach, the radiative transfer calculations are made first using the existing computer code RASLE (Nicolet et al., 1978), which uses the assumption of equilibrium and a coarse spectral band model for radiative transfer, and the code NONEQ which accounts for thermochemical nonequilibrium and carries out line-by-line calculation of radiation. By comparing the results, it is concluded that a thermochemical nonequilibrium model and a line-by-line spectral model must be used.

Park, Chul↗
NASA NTRS1987

Steady flow past sudden expansions at large Reynolds number. II - Navier-Stokes solutions for the cascade expansion

The equations of motion in the steady laminar flow past a sudden expansion at large Reynolds number, R, reduce to the boundary layer equations as R tends to the freestream valve, when the longitudinal length scale of the separated eddy increases linearly and indefinitely with R. A global Newton method is presently used to obtain finite difference solutions to the steady Navier-Stokes equations up to R of 1000 for a uniform inflow past a cascade of sudden expansions. For large expansion ratio values, the eddy length increases linearly with R; for smaller values, however, where boundary layer equation solutions could not be found, the steady solutions to the Navier-Stokes equations approach the limit of an inviscid eddy in length with increasing R.

Milos, Frank S.↗