Constant pressure drop condition
 

Hello, I will be working on a model where I will make a simple tapered pipe, run it on a SuperFlow flow bench to obtain flow and pressure data. Then do a CFD simulation of the problem in Fluent.

I have used the flow bench a lot in the past so I know what I am trying to achieve with it and how it works. So I have tried to set-up a hypothetical case now in Fluent to see how it will work.

The problem I have is the flow bench will maintain a constant pressure drop accross an orifice, say we have an atmospheric pressure of 101350pa and the pressure on the other side is 99850pa. So I set these up as boundary conditions in Fluent as "pressure inlet" and "pressure outlet" with a K Epsilon viscous model. The problem I have is the pressure at the outlet does not stay constant once the solution have converged. It has risen from 99850 to slightly over 100000, even though I set the condition to be constant.

Does anyone have any ideas or have done similar cases previously?
It is not for any Uni work but for me, to look at correlation of models.

Thanks a lot.