低温振动非平衡流动数值模拟研究

Numerical study of vibrational non-equilibrium flow at low temperature

在高速低密度风洞喷管流动中,振动温度出现冻结,与平动温度和转动温度产生了严重的非平衡现象。相关数值模拟结果中,振动温度完全冻结,而试验结果明显低于计算结果。为合理解释此现象,对数值模拟方法在低温条件下的应用进行分析,基于直接模拟蒙特卡罗(direct simulation Monte Carlo,DSMC)方法中热力学非平衡模拟技术,对振动松弛碰撞数进行修正,给出了修正系数1×10^(-7),建立了低温振动非平衡流动数值模拟方法。利用该方法对低密度风洞M16喷管流场和10 N姿控发动机羽流流场开展数值模拟,得到了与试验结果相符合的振动温度。研究表明:在低温条件下,由于振动松弛碰撞数很大,气体分子很难发生振动松弛碰撞,振动能不能向平动能转化,振动温度完全冻结;通过修正,降低振动松弛碰撞数,增加振动松弛碰撞的概率,可以降低振动冻结温度,使得数值模拟结果与试验结果吻合。

In hypersonic low density nozzle flow,the vibrational temperature is frozen,causing serious nonequilibrium relative to the translational and rotational temperatures.In related numerical simulations,the vibrational temperature is completely frozen,but the experimental data is obviously lower than the simulation result.To address this issue,analyses have been performed on the numerical method in the applications of low temperature conditions.Based on the simulation method of thermal non-equilibrium used in direct simulation Monte Carlo(DSMC),by modifying the number of vibrational relaxation collision,a numerical method for vibrational non-equilibrium flow at low temperature is proposed,in which the modified coefficient is set to be 1×10^(-7).The flow in a M16 nozzle of the low density wind tunnel and the plume of 10 N attitude control thruster is simulated,and the vibrational temperature agrees with the experimental result.It is shown that,due to the large value of the number of vibrational relaxation collision in the low temperature condition,gas molecules can rarely have vibrational relaxation collisions,and the vibrational energy cannot transform to the translational energy,thus the vibrational temperature is completely frozen.With the present introduced modification,the number of vibrational relaxation collision is reduced,the probability of vibrational relaxation collision is increased,and the vibrational temperature can be reduced to match the experimental results.