Velocity output at face centers (instead of cell centers)

myuse2 · April 2, 2018, 02:50

If I understand correctly with FVM CFD the velocities (fluxes) are computed at face centers while pressures are defined in the cell centers (so as to avoid checkerboard effects).

The output from OpenFOAM however is only cell centered, I wonder if it somehow possible to extract the un-interpolated (raw) face centered velocity vector instead of an interpolated cell centered one?

LuckyTran · April 4, 2018, 17:54

The face fluxes are interpolated.

The fluxes are the phi field. In many solvers, if you include a phi file at the start it will write it thereafter (just like rho). If you have an incompressible solver then the phi is the velocity. If compressible you have to calculate the velocity from phi/rho but the rho must be interpolated.

Here is an function object that writes the rho and phi fields. Alternatively you can also go to createFields.H in the solver, change the autoWrite and recompile.

Do you want the fluxes or the face velocities? Because it differs by the face area.

sourav0921 · February 17, 2020, 09:00

Hello guys,

I able to print the phi value for eaxh writing time step in pisoFoam. But can you please tell me whether is there any direct way to calculate phi per unit cell area ?

April 2, 2018, 02:50	Velocity output at face centers (instead of cell centers)	#1
myuse2 New Member Join Date: Apr 2018 Posts: 2 Rep Power: 0	If I understand correctly with FVM CFD the velocities (fluxes) are computed at face centers while pressures are defined in the cell centers (so as to avoid checkerboard effects). The output from OpenFOAM however is only cell centered, I wonder if it somehow possible to extract the un-interpolated (raw) face centered velocity vector instead of an interpolated cell centered one?

April 4, 2018, 17:54		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,668 Rep Power: 65	The face fluxes are interpolated. The fluxes are the phi field. In many solvers, if you include a phi file at the start it will write it thereafter (just like rho). If you have an incompressible solver then the phi is the velocity. If compressible you have to calculate the velocity from phi/rho but the rho must be interpolated. Here is an function object that writes the rho and phi fields. Alternatively you can also go to createFields.H in the solver, change the autoWrite and recompile. Do you want the fluxes or the face velocities? Because it differs by the face area. LeeRuns, Marpole and skyoon like this. Last edited by LuckyTran; April 6, 2018 at 13:46.

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February 17, 2020, 09:00		#3
sourav0921 New Member SOURAV GANGULI Join Date: Dec 2018 Posts: 11 Rep Power: 7	Hello guys, I able to print the phi value for eaxh writing time step in pisoFoam. But can you please tell me whether is there any direct way to calculate phi per unit cell area ?