dynamic pressure in pimpleFoam

ashkan · April 13, 2018, 02:52

Hi
I was wondering if it is possible to pass dynamic pressure in "forces" function in pimpleFoam rather than total pressure. The case I am interested is single phase with no gravity (so p_rgh is meaningless) and I am interested in calculating forces on a body. To be more precise, I want the "forces" function to calculate forces from pressure estimated "1/2*rho*U^2", where U would be the relative velocity of fluid and boundary patch.

The reason is that I am using this with oscillating flow in the domain and if I use total pressure, I get very wrong lift forces. I have already made the following thread but no comments yet

forces on body in oscillatory flow

I tried to calculate the dynamic pressure form the turbulence kinetic energy (pdyn = (2k/3)/(2I^2)*rho) and then F = sum( Pdyn*Area*n ) but that's also not correct.

I believe there should be much simpler way. So any comments are much appreciated.

Thanks
Ashkan

ashkan · April 13, 2018, 07:14

I have managed to solve my problem. I am not so sure if it was the best approach but I thought someone may find it useful. I basically, put a pressure probe along the line of the body but far away from it. Then I recorded that pressure during the simulation time. Finally, I extracted the surface mesh of the body and the pressure over it, for each element and at each time subtracted the probe pressure from its total pressure and integrated that over the body surface.

The final results matched the experimental data very well.

April 13, 2018, 02:52	dynamic pressure in pimpleFoam	#1
ashkan Member Join Date: Jul 2010 Posts: 55 Rep Power: 15	Hi I was wondering if it is possible to pass dynamic pressure in "forces" function in pimpleFoam rather than total pressure. The case I am interested is single phase with no gravity (so p_rgh is meaningless) and I am interested in calculating forces on a body. To be more precise, I want the "forces" function to calculate forces from pressure estimated "1/2rhoU^2", where U would be the relative velocity of fluid and boundary patch. The reason is that I am using this with oscillating flow in the domain and if I use total pressure, I get very wrong lift forces. I have already made the following thread but no comments yet forces on body in oscillatory flow I tried to calculate the dynamic pressure form the turbulence kinetic energy (pdyn = (2k/3)/(2I^2)rho) and then F = sum( PdynArea*n ) but that's also not correct. I believe there should be much simpler way. So any comments are much appreciated. Thanks Ashkan

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April 13, 2018, 07:14		#2
ashkan Member Join Date: Jul 2010 Posts: 55 Rep Power: 15	I have managed to solve my problem. I am not so sure if it was the best approach but I thought someone may find it useful. I basically, put a pressure probe along the line of the body but far away from it. Then I recorded that pressure during the simulation time. Finally, I extracted the surface mesh of the body and the pressure over it, for each element and at each time subtracted the probe pressure from its total pressure and integrated that over the body surface. The final results matched the experimental data very well.