[Deli]

Hi

I am a student in mechanical engineering and for my homework, I'm willing to solve 1D steady flow in a convergent-divergent nozzle with MATLAB, I have total pressure and total temperature at inlet and static pressure at the outlet as boundary condition. It should be a normal shock in the divergent part and I have to capture it.
for solving this flow I utilize the MacCormack method and when I check my answers in the first iteration there is no problem or any unnormal number but after 915 iterations I face negative temperature and also complex numbers.
I would be grateful if anyone could help me.

[duri]

Divergence could be due to stability or boundary condition. A quick look in the code raised some doubts on time step calculation. It is not clear how those numbers are calculated, it should be simple (fabs(v)+a) the viscous term can be ignored for this case as it is less restrictive.

On the inlet boundary condition it is not clear (I haven't checked it thoroughly) how the mach number is calculated. It should be straight forward. Use energy equation to estimate static temperature from velocity and total temperature. With this any other variable can be estimated easily unless specific heat capacities are functions of temperature and pressure.