求教BULB的问题

jimmy

请教各位前辈,小弟是新手,在用NUMECA算一离心风机叶轮.因为进口有一整流锥,希望连同此处一起计算,看说明书选用了BULB那个块,但计算时总是突然间的发散,并告诉我说进口BULB的这个块出现负的压力和负的密度,请教一下这个问题是怎么回事.好多天了一直没解决.
问题二,对于网格的正交性,最小可以为多少角度,小弟做出的网格最小的为3点几度,是否还需要将这个值提高.

qazxsw

>10度较好

redboy

将bulb块的网格重新划分一下，保证这块的正交性好一些
有几个参数是专门调整bulb块的参数，你可以看一下

jimmy

谢谢前辈的指教，我再试着改一下网格。

belkang

With the bulb configuration, the Singular Suface boundary condition will be involved. This kind of condition is not so stable, such as the computation could be well converged in most of cases but not sometimes. So, if possible and you do have difficulty in convergence, you should try to avoid using the bulb. Another option is to creat the mesh in bulb range separately so that you can make the first cell near the machine axis (R=0) being larger. When this cell is too small in the radial direction, its dummy cell might be have negative volume which may cause convergence problem.
As I known, NUMECA is working at making this boundary condition more robust.

jimmy

Thank you.