Advective BC with Zero Gradient for Pressure

D.B · January 21, 2016, 01:17

Hi All,
I am trying to simulate laminar flow over a flat plate using Icofoam. The problem I am facing is that I need to apply advective BC at the outlet to avoid any reflections. When I use a zero Gradient condition for pressure it doesn't work and gives the error as below

Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux : 0.0223463493786885
Specified mass inflow : 5e-05
Specified mass outflow : 4.99988894160287e-05
Adjustable mass outflow : 0

My initial condition is uniform (1 0 0) and inlet BC is the same.

Strangely when I use fixed Value uniform 0; for pressure it works just fine. On the contrary it even runs fine when I give advective BC for pressure ( even though it is an absolutely horrendous and incorrect BC).

Can someone help me understand the reason behind it and if its possible some way to run a simulation with advective BC for U and zeroGradient for p.

Cheers,

nimasam · January 22, 2016, 05:46

maybe fixedFluxPressure work for you

, the problem usually happens when the solver can not preserve global continuity for your simulation

D.B · February 4, 2016, 00:43

Hi,
But doesn't the data shown mean that the continuity is already satisfied and the solver is not able to proceed further ?

January 21, 2016, 01:17	Advective BC with Zero Gradient for Pressure	#1
D.B Member DB Join Date: Apr 2011 Posts: 87 Rep Power: 15	Hi All, I am trying to simulate laminar flow over a flat plate using Icofoam. The problem I am facing is that I need to apply advective BC at the outlet to avoid any reflections. When I use a zero Gradient condition for pressure it doesn't work and gives the error as below Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow. Total flux : 0.0223463493786885 Specified mass inflow : 5e-05 Specified mass outflow : 4.99988894160287e-05 Adjustable mass outflow : 0 My initial condition is uniform (1 0 0) and inlet BC is the same. Strangely when I use fixed Value uniform 0; for pressure it works just fine. On the contrary it even runs fine when I give advective BC for pressure ( even though it is an absolutely horrendous and incorrect BC). Can someone help me understand the reason behind it and if its possible some way to run a simulation with advective BC for U and zeroGradient for p. Cheers, __________________ -D.B

January 22, 2016, 05:46		#2
nimasam Senior Member Nima Samkhaniani Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,267 Blog Entries: 1 Rep Power: 25	maybe fixedFluxPressure work for you , the problem usually happens when the solver can not preserve global continuity for your simulation __________________ My Personal Website (http://nimasamkhaniani.ir/) Telegram channel (https://t.me/cfd_foam)

February 4, 2016, 00:43		#3
D.B Member DB Join Date: Apr 2011 Posts: 87 Rep Power: 15	Hi, But doesn't the data shown mean that the continuity is already satisfied and the solver is not able to proceed further ? __________________ -D.B

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