DSMC 및 IP 방법을 이용한 2차원 아음속 희박기체 유동 해석

Abstract

In the present study, to investigate the characteristics of subsonic rarefied gas flows efficiently, the information preservation(IP) method was applied to the direct simulation Monte-Carlo(DSMC) method to reduce statistical scatters from the DSMC method for low speed rarefied gas flows. To find the effects of the IP method, the results of the IP method were compared to the results of the DSMC method for the same numbers of sampling. Before the comparison, it was necessary to verify the DSMC solver. The verification of the solver was conducted by simulations of the micro-channel flows by comparing to the other researchers’ DSMC results. The velocity profiles at the 2/3 section of the channel agreed well with the other researchers’ results. In addition, the normalized slip velocity distributions on the wall and the pressure distributions along the centerline also agreed well with the other researchers’ results. After the DSMC solvers were verified, two types of Couette flows were considered. One is the flows that have temperature differences between two plates, and the other is the flows that have moving plates. For the first Couette flows, the temperature of 373K was used for the upper plate, and of 173K for lower plate. For the second Couette flows, the upper plate is moving at 300m/s, and the temperature of 273K was used for both two plates. All simulations of Couette flows were conducted from near-continuum to free-molecular regimes. From both Couette flow simulations, it was found that the temperature jump and the velocity slip occurred on the plate surface. In addition, it was also shown that the temperature and the velocity differences between the plate and the gas became larger as the flow fields became more rarefied. Lastly, flow simulations around a NACA0012 airfoil were conducted to identify the effects of the IP method. The freestream Mach number of 0.8 was used, and the Knudsen number of 0.014 was considered. It was observed that more clear contours were obtained from the IP method than the DSMC method, since the statistical scatter error was reduced by the IP method. In addition, it was found that the velocity slip on the airfoil surface occurred due to the effects of the rarefied atmospheric environment.