Sorry if this is to basic of a question. I'm trying to find a formula that will describe a viscous, but compressible fluid. This would just be a generic formula as a starting point. I'm trying to describe the variability of densities through this fluid. The closest thing I can find is a non newtonian fluid, that decribes how stress in an area dissipates through the fluid. But this doesn't really fit what I'm trying to do since i need a "pressure" factor.