[Nedersander]

I am trying to model the Reynolds dye experiment for my project and my supervisor has told me to try to model the change in Reynolds number with a varying body force. I tried to use gravity in the reference values tab to artificially make an acceleration due to a force, but when looking at further documentation, I found that for incompressible flow this is only possible if the Boussinesq model is selected. My supervisor has told me that Boussinesq is not applicable since it is relevant for modeling buoyancy effects and my model has to do with pipe flow. Is there another way to assign a body force to the model? Thanks in advance for your help.