hi fellows,

i am having problem of negative cell volume when try to move an object at speeds more than 0.5 mach. i am using DEFINE_DG_MOTION macro in a UDF ,WHICH I COMPILED & HOOKED INTO FLUENT. i used k-epsilon turbulence model.

please enlighten me.

thanks.

I think before any try on the solution, you should first make sure your meshing procedure in fluent is ok! because there are some parameters to set in the dymanic mesh window, which usually we do not know their exact values, there comes at least a Trial & error procedure to find the right values for the parameters. Having done this, one should check the mesh motion (in solve menu) to make sure the algorithm does its job well. Just after these steps, one can setup the BCs and run the program. one another point is to take Dt as small as possible. Also, as I have tested it myself, if there is not relative motion in the solid walls, e.g. deforming body or boundaries, applying the UDF as inlet BC is preffered.