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-   -   Application of a pressure gradient/forcing term in a compressible pipe flow (http://www.cfd-online.com/Forums/openfoam/120191-application-pressure-gradient-forcing-term-compressible-pipe-flow.html)

mrs206 July 2, 2013 08:30

Application of a pressure gradient/forcing term in a compressible pipe flow
 
Dear All,

Im a little bit stuck as to the best way to go about adding a forcing term to a low Mach number compressible pipe flow case. So far, i have played around with the channelFoam method of ensuring a bulk mean velocity, which has worked very well for all of the incompressible cases i have run on the same geometry. Ive also tried specifying a pressure gradient using the fvOptions source term in rhoPimpleFoam which has pretty much the same effect as the channelFoam method, the only difference being that the forcing is applied more times during each time step.

As far as i can tell, the problem with the compressible cases is related to the varying density at the inlet. This causes a change in the velocity at the inlet and also seems to cause a divergence of the pressure gradient to gradually to infinite negative values. I have thought that it may be possible to validate the mass flow rate for this case using a target mass flow value, but im unsure of how to add a source term to phi over the whole internal field. Does this even seem feasible?

Details of my case setup are as follows: 100mm diameter circular tube of 2m in length. Clean pipe with no obstructions. Solved using rhoPimpleFoam with a k-eps model. Mach number of 0.072 with velocity and temperature fixed at the inlet and fixed pressure at outlet. Any comments on the boundary conditions used are welcomed.

Id be very grateful for any help, ive been thinking about this for days without any luck!

Michael


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