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In this paper, the problem of near continuum gas flows over a sphere is investigated numerically. Three types of boundary conditions for the sphere surface are adopted: (1) non-slip and constant temperature surface; (2) velocity slip with considerations of velocity gradient, and temperature jump at the surface; and (3) velocity slip with considerations of both velocity and temperature gradients, as well as temperature jump at the surface. Navier–Stokes equations in a cylindrical coordinate system for compressible flows are adopted with the Roe numerical scheme. The numerical simulation results include coefficient distributions for surface pressure, friction, heat flux, velocity slip, temperature jump and total drag. The results are obtained with different free stream Knudsen and Mach numbers. Several conclusions include: (i) the third surface boundary condition does not create significant differences from the second type, (ii) however, an adoption of non-slip or a slip surface boundary condition can create significant differences in C f , C q and C D . [ABSTRACT FROM AUTHOR]

Abstract: The direct simulation Monte Carlo (DSMC) method is a widely used approach for flow simulations having rarefied or nonequilibrium effects. It involves heavily to sample instantaneous values from prescribed distributions using random numbers. In this note, we briefly review the sampling techniques typically employed in the DSMC method and present two techniques to speedup related sampling processes. One technique is very efficient for sampling geometric locations of new particles and the other is useful for the Larsen–Borgnakke energy distribution. [Copyright &y& Elsevier]

Abstract: An improved space–time Conservation Element and Solution Element (CE/SE) scheme is constructed by proposing a new structure of solution elements and conservation elements based on the rectangular mesh. Furthermore, the improved CE/SE scheme was applied to dilute gas–particle two-phase flows. A two-fluid model and two corresponding chemical reaction models, i.e., two-step reaction model and detailed chemical reaction model, were used to describe the physical and chemical characteristics in the two-phase flows. Shock wave reflection in gas, shock wave diffraction in air–sand mixture, explosive synthesis of TiO2 nanoparticle and air–fuel two-phase detonation were simulated by the improved CE/SE scheme and appropriate physical and chemical models. All the numerical results were compared and discussed carefully. The results show that the improved CE/SE scheme is clear in physical concept, easy to be implemented and high accurate for the above-mentioned problems. Thus, the improved CE/SE scheme can be applied to gas–particle flows widely. [Copyright &y& Elsevier]