Using non-premixed model on compressible flow

Libing

hi, I am using non-premixed model to model a reacting flow ejecting from a combustion chamber through a small nozzle.

I have a problem with the setting of operating pressure. When I generate the PDF file in prePDF, I have to specify the operating pressure. Once the Fluent read the PDF file, the operating pressure in Fluent is automaticlly set at the same value as the pressure in prePDF.

My questions: 1. since I am modeling a compressible flow (transonic condition), the pressure gradient in my calculation domain is big, what pressure shold I specify in prePDF?

2. The usual practice for modeling a compressible flow is to set the operating pressure at ZERO. but I can no longer change the operating pressure after PDF file is read into FLUENT.

any idea of solving the problem?

many thanks