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Hi,

I am working on simulating swirling flow through a nozzle. I have been able to run steady-state incompressible flow using simpleFoam, but when I attempt to run the same geometry compressibly using rhoSimpleFoam the pressure goes negative.

I am using:
- Atmosphere BCs at inlet and outlet (totalPressure and pressureInletOutletVelocity)
- Default discretization except div(phi,U) which is limitedLinearV 1.0
- Cyclic boundary conditions
- Relatively low under-relaxation factors (0.2 p, 0.4 U, 0.1 k, eps, h, and rho)

Varying these parameters changes when the pressure goes negative, but it always does at some time or another. The blowup appears in a straight channel portion of the domain where a region of low pressure will move upstream, followed by high pressure, then low, etc. There seems to be no effect on velocity that I can see as a result of these pressure oscillations.

I am just about out of ideas as to what could be causing this. Does anyone know what might be wrong and what I can do to fix it? I'd appreciate any advice you can give.

Thanks.

Greg Z.