高超声速化学非平衡流动Navier-Stokes/DSMC耦合算法

基于相同的化学反应模型，在已有计算流体力学（CFD）和直接仿真蒙特卡罗（DSMC）方法及程序的基础上，采用Modular Particle-Continuum（MPC）耦合技术，建立了包含化学非平衡Navier-Stokes/DSMC耦合算法。算法结构中DSMC计算区域在CFD计算结果上根据当地克努森数自动选取。发展了适用于流场分区信息交换的亚松弛技术，抑制DSMC方法对CFD计算的影响。把DSMC方法和CFD的应用范围拓展到过渡流区，为复杂飞行器近连续过渡流区高超声速化学非平衡流动数值模拟研究提供了一种工程适用的预测分析手段。通过对二维圆柱高超声速化学非平衡绕流的算例与其他结果的比较研究，表明耦合算法不论在流场结构、流场非平衡现象，还是飞行器表面参数、整体气动力/热特性方面，都能够得到与全DSMC计算吻合的结果，证实了所建立的Navier-Stokes/DSMC耦合计算模型与方法的有效性和可靠性。仿真了某航天器解体碎片在过渡区的化学非平衡流动，得到碎片在过渡区的气动力/热特性，为碎片的陨落计算提供依据。

Navier-Stokes/DSMC hybrid algorithm for hypersonic flows with chemical non-equilibrium

Based on the same chemical reaction model, an Navier-Stokes/Direct Simulation Monte Carlo (DSMC) hybrid algorithm with chemical non-equilibrium is proposed by using the Modular Particle-Continuum (MPC) technique using current Computational Fluid Dynamics (CFD) and DSMC methods. The DSMC region is selected automatically according to the CFD results in this hybrid scheme based on local Knudson numbers. A sub-relax technique for information exchange between CFD and DSMC is developed to restrain the effect of statistical fluctuation from DSMC to CFD. This extends the application of the DSMC and the CFD method, and provides an approach to predict the chemical non-equilibrium characteristics in the near-continuum transition flow regime. The hypersonic flow with chemical non-equilibrium around a 2D cylinder is simulated by the Navier-Stokes/DSMC hybrid method proposed. A comparison of the simulation result obtained with the method proposed and that with other methods shows that the results obtained with the method proposed are good agreement with the results obtained with full DSMC in terms of flow structure, non-equilibrium phenomenon, surface parameters and aerodynamics characteristics. This verifies the adaptability and reliability of the proposed Navier-Stokes/DSMC hybrid algorithm in simulating hypersonic flows for the transition flow regime. The chemical non-equilibrium flows around a fragment from a disintegrated aerocraft are simulated to obtain the aerodynamic force and thermal characteristics of the fragment in the transition region, thus providing some reference for simulation of fragment fall.