Problems with convergence and initial guessed fields in compressible steady flows

Pedro Gil

Hi!

I try to solve a supersonic steady problem neglecting the temporal term, in the compresible N-S ecuations with all terms term (i.e time step =inf). The geomtry is the typical test problem (channel with a circular arc "bump") My boundary conditions are density,pressure,end velocity prescribed at inlet , and extrapolate at outlet.

I start with a uniform guessed velocity field with the same value that the inlet velocity. idem for temperature and idem for pressure.

I solve Momentum and pressure correction (simple) since convergence in velocity is reached. (criterium is mean((unew-uold)/uold)).

I use strong underrelaxation in momentum and pressure correction. (p=p+alpha*p');

The two reflecting shock waves begin to develop in the channel and when iterations converge , I solve energy ecuation and actualize properties. Then begin to iterate again.

When I do this two or three times the fiels diverge and the method shut down.

Why this happens?.Is the grid incapable of support great magnitude gradient values? ,Might I regrid for more acuratte?.

The problem ussually ocurrs in the cross of two shock waves.

If anyone has any Solution or explanation to the Problem please contact me!.

You Can help me a lot with my studies-end proyect!!!!.