非定常喷流有限差分方法数值试验

以欠膨胀自由喷流初期流动为例,采用Euler方程和Beam Warming TVD有限差分格式,对比分析了Beam WarmingAF方法,隐式亚迭代方法和简化Runge Kutta五步格式的非定常流场描述能力,结果表明:(1)隐式近似因式分解方法基本上可以描述非定常流动现象;(2)隐式亚迭代一阶时间精度格式会导致流场结构的变化,其精度可能是不足的;(3)隐式亚迭代二阶时间精度与简化Runge Kutta五步格式的计算结果一致,可以认为是计算非定常问题的适当方法.

COMPARATIVE STUDY OF FINITE DIFFERENCE METHODS FOR UNSTEADY FREE JET

Under the frame of Euler equations and Beam Warming TVD scheme,three time derivative discretion methods,i.e.Beam Warming implicit approximative factorization algorithm,implicit subiteration algorithm and simplified Runge Kutta five stage scheme,are numerically tested for the early evolution of underexpanded free jet flow.The results show that (i)Beam Warming implicit approximative factorization algorithm can give reasonable patterns of flowfield in whole.Some detailed features should be further studied;(ii)Implicit subiteration scheme with first-order accuracy in time would result in some abnormal phenomena so that the accuracy may not be enough for the unsteady flow;(iii)The results computed by implicit subiteration scheme with second order accuracy in time are well in agreement with that by simplified Runge Kutta five stage scheme, so we can regard these two difference methods as feasible algorithms for unsteady flow computation.