[Aristine]

Hello,

My project is the Design and analysis of a rocket nozzle. I have already done the design using axisymmetric MOC of its diverging part (begging with Mach 1 in the throat). Now, I am trying to analyse this design with CFD. My CFD code is an unstructured-FVM that follows the TVD-MUSCL approach using SUPERBEE limiter and HLLC solver for the intercell fluxes. Besides, I am using local time stepping to advance in time in order to achieve the steady state. (I have followed Toro's book to write the code)

The results are correct and converge for designs with exit Mach numbers: 1.5, 2.0 or 2.5. However, my problem is that my ideal exit Mach number should be 3.5 but I can't solve this problem because my program always blows up for Machs above 3 no matter how much little I put the CFL parameter.

I would be very grateful if anyone could explain me how to fix this problem and/or why this is happening.

Thanks a lot.