Proper BCs choice

milene078 · November 9, 2023, 20:51

Hi,
I need to simulate flow in vessel (pipe with one inlet and outlet) based on real-life data. I have time-varying pressure at outlet and time-varying velocity at inlet. What set of boundary conditions for pressure and velocity should I use? As i'm simulating incompressible flow using pimpleFoam I'm aware that i could just prescribe inlet velocity and set outlet pressure to 0. But it's really important to obtain values of presure at inlet which correspond to real values of pressure at outlet. And currently setting any value of pressure that is higher than 0 at outlet results in blowing of simulation after few time steps. I would appreciate any help.

Tobermory · November 10, 2023, 04:45

Since you are running an incompressible solver, i.e. pimpleFoam, then the simulated pressure values are all gauge pressures. So set p = 0 at outflow, which will give you stable behaviour, and then when comparing the results to your experimental data, just add on the reference pressure, ie the expt outlet pressure.

milene078 · November 10, 2023, 10:03

Than you for your answer. My problem is that i need specific pressure at outlet, which changes in time. Does this mean that I need to use different solver?

November 9, 2023, 20:51	Proper BCs choice	#1
milene078 New Member Join Date: Nov 2022 Posts: 4 Rep Power: 4	Hi, I need to simulate flow in vessel (pipe with one inlet and outlet) based on real-life data. I have time-varying pressure at outlet and time-varying velocity at inlet. What set of boundary conditions for pressure and velocity should I use? As i'm simulating incompressible flow using pimpleFoam I'm aware that i could just prescribe inlet velocity and set outlet pressure to 0. But it's really important to obtain values of presure at inlet which correspond to real values of pressure at outlet. And currently setting any value of pressure that is higher than 0 at outlet results in blowing of simulation after few time steps. I would appreciate any help.

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November 10, 2023, 04:45		#2
Tobermory Senior Member Join Date: Apr 2020 Location: UK Posts: 747 Rep Power: 14	Since you are running an incompressible solver, i.e. pimpleFoam, then the simulated pressure values are all gauge pressures. So set p = 0 at outflow, which will give you stable behaviour, and then when comparing the results to your experimental data, just add on the reference pressure, ie the expt outlet pressure.

November 10, 2023, 10:03		#3
milene078 New Member Join Date: Nov 2022 Posts: 4 Rep Power: 4	Than you for your answer. My problem is that i need specific pressure at outlet, which changes in time. Does this mean that I need to use different solver?