supersonic flow
 

Hi everyone

I am about to simulate a supersonic flow in a safety valve.Actually in the flow near the smallest diameter is expexted to appear normal shocks, oblique shocks and also expansion fans.The problem right now is that a supersonic flow is appearing all across the smallest diameter but I don't see any shocks when teh flow decelerates afterwards.Perhaps you could help me somehow especially with the settings I have to adjust.Moreover I am not sure which solver to use.I started with the segerated one although it is a high-compressible flow.But if I use the coupled one the program always shows me a divergence.Maybe you could give me some hints about that because I am quite sure that the problem has nothing to do with the grid because I only have quadrates in there.

Thanx

Re: supersonic flow
 

Did you turn on ideal gas law? (it's under the material properties)

Even with a quad mesh, you need enough refinement to capture shocks and expansion.

You can try turning of the turbulence model when solving with the coupled solver. Also, the coupled solver has problems dealing with large separation regions. I talked to a tech support today who won't use the coupled solver until you get above Mach 1.5. He swears by the segregated solver, and he has good results to back it up. It might be the way to go for your situation. Just remember your mesh has to be a little finer if you use the segregated solver than the coupled solver.

Hope this helps.

Goodluck, Jason

Re: supersonic flow
 

hi, if you use segregated solver than start simulation with reduced underrelaxtion factor of momentum nabeel

what are the boudary
 

I am solving the supersonic flow through a rectangular duct. I am giving stagnation pressure and temparature at inlet. I know static pressure at outlet. what are the conditons that are to be given at outlet for supersonic flow

ravi

Re: what are the boudary
 

If you know the pressure at the exit, then use a pressure outlet boundary condition.

Jason

supersonic flow with multiple shocks
 

Hello..!

I'm trying to simulate in FLUENT, a very complex flow through a supersonic inlet, involving multiple oblique shocks and one normal shock near outlet. I had given mass-flow inlet conditions and pressure-outlet conditions. I'm able to get the required Pressure temperature results at the outlet, but after a few iterations, the inlet became subsonic, with a feeble velocity when compared to a high inlet mach number that i had assigned.
I have tried segregated solving, zero shear-stress etc.still the inlet flow is subsonic. please advice me.

Thank you..!

Make sure that you also specified the correct total temperature at the inlet as this determines the inlet Mach number.

Also make sure (as others have noted in upstream discussion) that your system can actually support a shockwave in the domain.

If so, then try switching to a pressure inlet boundary condition and specify the inlet stagnation pressure and temperature explicitly. This will help ensure that your flow is definitely supersonic and then you can switch to a mass-flow inlet after you have a reasonable initial flow field.