Problem in collocated grid
 

I am solving unsteady shock tube problem with pressure correction approach. I am solving 2 momentum equation, updated pressure correction equation for compressible case, Energy equation and Equation of state. I used Rhie & Chow formulation for dealing pressure checker boarding problem. I am using SIMPLE.
I have some issues in my code which are following:

My code is working for high relaxation parameter like from 0.5-0.9. But it is not working at low relaxation parameter like less than 0.5??????

Thanks in advance

I recommend you to apply modified Rhie and choe method introduced by Majumdar.
"Role of underrelaxation in momentum interpolation for calculation of flow with nonstaggered grids".

In this method numerical solving is independent of under-relaxation parameter. for me, It worked very well.