Need help for boundary condition
 

Hi everyone,

I am doing my numerical simulation of cavitating flow in rectangular Nozzle. I am having trouble with boundary condition.

Firstly, I use mixed Neumman and Drichlet boundary condition at inlet and outlet section. Inlet is subsonic flow so that I fixed total pressure, flow direction and void fraction. Outlet also assume that subsonic flow, so just static pressure fixed. But the solution divergent due to very strong pressure wave propagation.

I read in book that, for this situation, I need use non-reflective BC or Convective BC.

example, convective BC at oulet: d(phi)/dt + U d(phi)/dx = 0 with phi: velocity, pressure, density, mass fraction,...

But my question, if use CBC, how to fix the outlet pressure?
And which boundary is suitable for my case?

Check this paper

Poinsot T. et Lele S. (1992). Boundary conditions for direct simulations of compressible reacting flows. Journal of Computational Physics. 101, 1, 104-129.

CBC will perform a decent job in absorbing the waves but may not be sufficient depending on the problem. An easy option is to have a sponger layer/PML to absorb the outgoing waves.

Depending on your numerical scheme(if it is high-order), you can also use the energy transfer and annihilation method of Visbal.