典型标模音爆的数值预测与分析

摘要

精确预测音爆对超声速民机的研制具有重要意义.主流的音爆强度预测方法分为两步,首先通过风洞试验或CFD方法得到近场音爆过压(Over-pressure)分布,再运用修正线化理论或非线性声学理论将近场过压传播至地面,最终获得地面音爆的声压信号.本文运用典型标模对当前音爆数值预测方法的精度进行了验证和确认.在近场音爆过压分布的数值预测方面,分别考察了超声速尖点构型前缘修形尺度、不同空间离散格式和无黏/有黏流动控制方程求解对近场过压计算结果的影响.远场音爆预测方面,以LM1021全机构型近场过压分布为输入,使用基于波形参数法的远场传播工具分别考察了不同离散格式和有/无黏性计算的近场过压分布差异对地面音爆结果的影响.算例结果表明,尖点构型近场音爆预测中进行几何修形是十分必要的,使用相对合理的过渡球半径可以保证近场音爆预测精度,过大的修形尺度会对激波形状、激波和膨胀波的峰值均产生较明显的影响;就近场波形而言,熵相容格式计算得到的结果与试验测量值吻合最好,但不同离散格式导致的近场预测波形差异对传播到远场的波形关键指标(主要是最大过压和上升时间)的影响很小;是否计入黏性对近场波形结果尽管仅有小幅的影响,但将近场信号传播到远场得到地面波形时,这些细微差异会在远场波形的音爆评价关键指标上表现出明显的区别.%Accurate prediction and simulation of sonic boom are of significant importance to the design of supersonic aircraft.The mainstream research approach for sonic boom prediction consists of two steps.First,the distribution of overpressure in near field is calculated with wind tunnels or CFD,then the over-pressure is propagated to the ground by the modified linear wave equations or nonlinear Burger's equations.Using several benchmark cases,the accuracy of typical nearfield sonic boom prediction method is verified.For nearfield over-pressure prediction,the influence of semi-sphere radius,spatial discretization schemes and viscosity are investigated.For far-field sonic boom prediction,based on the nearfield over-pressure of LM1021 configuration,the influence of different discretization and with/without viscosity in nearfield simulation to the far-field signature prediction have been investigated.The results show that it is necessary to use semi-sphere to deal with the sharp tip in supersonic model.Using semi-sphere with reasonable radius will help guarantee the accuracy of nearfield prediction.The scale of modification will influence the shape of shock wave and the peak values of shock wave and expansion waves.For nearfield sonic boom prediction,the entropy consistent scheme performs better than the Roe and Central schemes.However,the discretization scheme has little influence on the key indicators of the far-field propagated signatures (mainly peak value of over-pressure and raise time).The effect of viscosity in the nearfield prediction is small,however,the slight difference caused by the viscosity in the nearfield domain would cause obvious difference in the far-field domain.