Large number of iterations using PCG in pressure equation
I am running a DNS case using buoyantPimpleFoam (OF V2.4). The case is a long pipe with an inlet and outlet. The fluid is air. Inlet Re is about 5400.
For getting better scalability, I use PCG for pressure equation. If I use perfect gas equation of state, the number of iterations will be around 100, which is acceptable. If I use icopolynom or rhoConst to describe the density, the number of iterations will be around 4000! If I use GAMG for p equation, number of iteration will be under 5, but the scalability is poor with above 500 cores. Does anyone has any opinion? How can I improve PCG solver to decrease the number of iterations? Thank you. fvSchemes Code:
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Did you try the obvious things such as trying a different preconditioner?
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Yes, I did. I tried GAMG as preconditioner but this leads to a bad scalability. I found that the PCG solver can decrease the residual to about 1e-5 within about 100 iterations. But from computation of residual from 1e-5 to 1e-7 costs several thound time of iterations. Adding number of correctors does not work.
I also tried different different BC on the wall like simple zeroGradient, but it does not bring anything. I also tried different schemes in fvschemes e.g. backward/Crank Nicolson for time, and so on. Quote:
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I am also interested in this topic, any suggestion is highly appreciated.
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