气动热数值模拟中的网格相关性及收敛

针对气动热数值模拟中的网格相关性和收敛问题,采用计算流体力学(CFD)计算方法,以典型的钝头为算例,进行了数值模拟研究。研究结果表明:网格是气动热数值模拟中的关键因素,壁面附近法向网格间距最为敏感,热流结果随网格间距不同会出现数倍乃至数量级的差异,在得出正确的壁面压力结果的网格上不能保证得到正确的热流结果。分析认为壁面附近客观存在的巨大温度梯度是网格要求敏感的原因。计算表明:气动热计算的收敛过程比压力和流场收敛慢得多;在压力和流场完全收敛时,热流与最终的迭代收敛值偏差达20%以上;以方程残值的下降量级和压力收敛作为热流收敛的判别标准是不合适的。在气动热计算中,应直接观察热流数据的收敛,确保得到真正的收敛解。

Grid Dependency and Convergence of Hypersonic Aerothermal Simulation

Hypersonic aerothermal simulation is conducted in a blunt flow, and its grid dependency and iteration convergence are investigated by means of a computational fluid dynamic (CFD) method. The grid effect is crucial to aerothermal simulation. The study demonstrates that heat transfer prediction is very sensitive to grid spacing in the normal direction near the wall. The value of heat transfer exhibits dramatic differences of several times, or even an order of magnitude depending on grid spacing. It is shown that a computational mesh which results in accurate surface pressure does not guarantee accurate heattransfer values. The authors hold the view that the great temperature gradient near the wall results in grid sensitivity for heat transfer simulation. Aeroheating computation is converged significantly slower than the convergence of pressure and flow field. The difference of the value of heat transfer with the last convergence value is as high as 20% when the pressure and flow field is fully converged. Therefore, in aerothermal numerical simulation it is not appropriate to take the falling orders of equation residual and pressure convergence as heat transfer convergence criteria. In order to get the convergence solution it is necessary to monitor the convergence of heat transfer data directly.