湍流结构方向边界条件对平面后台阶突扩通道粘性分离区的影响

EFFECT OF BOUNDARY CONDITIONS OF TURBULENCE STRUCTURE DIRECTION ON REATTACHMENT DOWNSTREAM OF A BACKWARD FACING STEP

标准的Ｋ－ＥＥＶＭ或ＡＳＭ算出的平面后台阶突扩通道粘性分离区长度比实验值低３０％，原因在于该模型违反了边界条件的独立性原则。为此本文提出一能独立加入有关湍流结构的边界条件的Ｋ－ＥＬＡＡＳＭ，问题得到圆满解决。与此相反，层流粘性分离流动的分离区的预测值常常过大，一个重要原因在于进口速度型与实际不符，但同样是由于边界条件原故。

The turbulent reattachment length downstream of a backward-facing step has been underpredicted about 30% by standard turbulence model K-E EVM or ASM, it is because the modelling principle of independence of the boundary conditions has been violated by these models. As a cure of this shortcoming, it is suggested that the traditional ASM could be corrected to be a K-E LAASM, in which the boundary conditions of turbulence structure can be specified independent of the mean velocity profile and turbulence intensity. In contrast to this, the laminar reattachment length is often overpredicted, since the practical upstream velocity profile is actually not as symmetric as usually assumed in computation, however, this is another kind of violation to the above principle of independence of boundary conditions.