I am struggling to find the format of the .geom file in PROSTAR so that i can write .geom file using my program. Can anyone give me a helping hand?

thanks

I don't think you'll be able to do this - the format is completely undocumented. If you want to use your own program as a pre-processor for STAR (which I assume is why you want to write a .geom file using your own program) then a better idea would be to use your program to write the mesh definintion in a PROSTAR-friendly format (such as the coded save or CGNS formats) and then import the mesh into PROSTAR.

I think the easiest way will be to write vertex and cell files - they are plane tables in text format. In vertex file (.vrt) you have colomns: Number GlobalX GlobalY GlobalZ and in cell file (.cel) you have colomns: Number TypeID Vertex1 ... Vertex8