Showing papers by "Japan Aerospace Exploration Agency published in 1991"

Variable soft sphere molecular model for inverse-power-law or Lennard-Jones potential

Abstract: The variable soft sphere (VSS) molecular model is introduced for both the viscosity and diffusion cross sections (coefficients) to be consistent with those of the inverse‐power‐law (IPL) or Lennard‐Jones (LJ) potential. The VSS model has almost the same analytical and computational simplicity (computation time) as the variable hard sphere (VHS) model in the Monte Carlo simulation of rarefied gas flows. The null‐collision Monte Carlo method is used to make comparative calculations for the molecular diffusion in a heat‐bath gas and the normal shock wave structure in a simple gas. For the most severe test of the VSS model for the IPL potential, the softest practical model corresponding to the Maxwell molecule is chosen. The agreement in the molecular diffusion and shock wave structure between the VSS model and the IPL or LJ potential is remarkably good.

Comparison of velocity distribution functions in an argon shock wave between experiments and Monte Carlo calculations for Lennard-Jones potential

Abstract: The velocity distribution functions (VDF’s) in an argon normal shock wave at an upstream high Mach number 7.183 and low temperature 16 K are calculated using the null‐collision direct‐simulation Monte Carlo method for the Lennard‐Jones (LJ) potential to compare with the experimental results of Holtz and Muntz [Phys. Fluids 26, 2425 (1983)]. The convolved VDF’s for the LJ potential are in reasonable agreement with the measured data in early and late regions of the shock wave but significantly different in the middle region. This discrepancy cannot be explained by a possible uncertainty in the potential well depth. Moreover, the difference in the convolved VDF’s between the LJ potential and the softest and hardest unrealistic molecular models with no attractive force, i.e., the Maxwell molecule and hard sphere, is much smaller than the discrepancy between the experiments and Monte Carlo calculations.

A test of equivalence of the variable-hard-sphere and inverse-power-law models in the direct-simulation Monte Carlo method

Abstract: A test of the equivalence of the variable‐hard‐sphere (VHS) and inverse‐power‐law (IPL) models in rarefied gas flows is made for the molecular diffusion in a heat‐bath gas and the two‐dimensional rarefied gas flow around a circular cylinder using the null‐collision Monte Carlo method. For the most severe test, the softest practical model corresponding to the Maxwell molecule is chosen. It is shown that the VHS diffusion is slower than the IPL one in the viscosity mean‐free‐path (mean‐collision‐time) scale but agrees with the IPL one in the diffusion scale. The VHS and IPL flow fields around a circular cylinder reveal a small but appreciable discrepancy in the usual viscosity scale. These facts should call attention to the equivalence of the VHS and IPL models especially when the molecular diffusion may play an important role in a (gas mixture) flow, where the diffusion scale may be preferable to the viscosity scale.

ACT wind-tunnel experiments of a transport-type wing

Abstract: This paper summarizes the wind-tunnel experiments on the active control technology that have been conducted in the large low-speed wind tunnel of the National Aerospace Laboratory. The experiments include a gust load alleviation (GLA) and two active flutter suppression (AFS) tests. A wind-tunnel model of the cantilevered elastic wing is designed to simulate an energy efficient transport

Euler flow analysis of turbine powered simulator and fanjet engine

Abstract: An Euler flow analysis of turbine powered simulator (TPS) and fanjet engine was made utilizing MacCormack's finite volume scheme. TPS simulation computations for an axisymmetric geometry were compared with experimental data obtained in the National Aerospace Laboratory transonic wind tunnel. The pressure distributions on the inlet cowl and corejet cowl surfaces showed excellent agreement. The effect of differences in engine conditions of corejet temperature and mass flux between the TPS flow and a real fanjet engine was analyzed with the computations. The results showed no significant differences in the external flowfield surrounding the exhaust jet plume. A three-dimensional analysis showed the effects of angle of attack on the inlet flowfield and exhaust jet plume.

Experimental Examination of Theory of CTE (Coefficient of Thermal Expansion) Control Technology

Abstract: A previously proposed lamination tailoring technique for precise control of a coefficient of thermal expansion (CTE) under a wide range of temperature is examined by detailed measurements of a CTE of two types of specimens: rectangular plates and tubes of carbon/epoxy composite