[Yaroslav]

Hello, I'm new to Star CCM+. Please help me. Imagine a pipe and water flows in it. I only know the value of the differential pressure, such as inlet pressure(P1) and outlet pressure (P2). Given: P1-P2=15 atmospheres (atm). How do I do that? I think it is necessary to create a field function, but how?

P.S. forgive me for my English. I don't speak it well.

[cwl]

Inlet: Stagnation Inlet with Pressure set to 15 atm
Outlet: Pressure Outlet with Pressure set to 0 atm
All those pressure values are given with respect to Reference Pressure (in Continua -> Physics -> Reference Values -> Reference Pressure) which is 1 atm by default, so absolute pressure would be 16 atm and 1 atm.
No difference for incompressible flow, but keep that in mind for compressible flows.

But if you just set 15 atm at Inlet - you'll get high velocity in first iterations, so it is better to increase the pressure at inlet as iterations go, for example via a Field Function:

($Iteration <= 100)
?
$Iteration/100 * 15E5 // keep in mind that default units (m, s, g, K, Pa) are used
:
15E5

this will make pressure on the inlet grow from 0 (+Reference Pressure) to 15 atm in 100 iterations.

PS Если с английским тяжко - найди группу по стар вконтакте.