有相对运动多体动力学系统流动计算方法若干问题讨论

对应用非结构动网格技术数值模拟有相对运动多体动力学系统的流动现象时发现的若干问题进行了讨论.应用动网格技术求解均匀流场,验证了几何守恒律方程离散形式对流场计算精度的重要性,还发现格式时间精度越高、网格运动速度越接近声速,几何守恒律的作用越明显;采用类似于可控轨迹实验的准定常计算方法和非结构动网格技术,分别对超声速气流中物体运动的动力学过程进行了数值模拟,通过流场和运动特性比较和理论分析,指出准定常计算方法本质上无法反映非定常流动特征,即使时间步长趋向零也不会趋向于真解;还讨论了数值模拟非定常流动的双时间法,分析时间推进步长对解的影响,随着时间步长减小解的误差降低,但是这一方法与动网格技术结合解决多体分离问题有难度.

Analysis of simulation method for flows past multi-body in relative motion

Several problems discovered in simulating unsteady flows past multi-body in relative motion with Dynamic Unstructured-grid Method(DUM) are discussed here.By computing uniform flows with DUM,the significance of the Geometric Conservation Law(GCL) on computation precision is validated,and it's also found that the more accurate is a given scheme on time discrete,the more close is the grid velocity to sound and the more important it is to satisfy GCL.Computing the motion of an object in supersonic flow using quasi-steady methods(just as the Captive Trajectory Support(CTS)) and DUM separately,via comparison and analysis of flow field and object's motion,it's indicated that quasi-steady method can't reflect unsteady flow character,and it couldn't reach accuracy solution even if the time step converge to zero.Finally,the dual time-stepping method in simulating unsteady flows is discussed,analyzing the influence of time step,it's proved that calculation error decreases along with the time step,but it's still difficult for dual time-stepping to couple with dynamic grid in solving multi-body separation problems.