Compressible flow
 

Hi guys,

I am modeling a converging diverging geometry, like all oyu know the nozzle-diffuser.

it is a compressible flow of air. my BC is :

pressure inlet: 3.18 atm (gauge total pressure), 1 atm (supersonic/gauge) and total temprature 417. (actually i set inlet mach number1.4 and i computed these condition by putting the ration of outlet to throat equal 2).

pressure outlet : 1 atm and total temrature 300.

my solver is pressure based, energy eq., vis : spalart. material air, density ideal gas. operating pre. eq. zero.

under relaxation deafault, adapt gradient/ pressure with coarsen threshold 0 and refine 0.3.

why it is diverging?

thanks a lot.

Hi,

Converging the solution with pressure inlet and pressure outlet is difficult especially for compressible flow simulations. I don't know your geometry size and solver set up. Just try these suggestion.
If possible try with mass flow inlet boundary condition or gradually increase the inlet pressure to your desired value.

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Hi,

Thanks for your reply.
Goemetry: 6 cm length and 8 mm height. I am trying these methods, it is better now, but not perfect.

Try extending your outlet boundary past the end of the diffuser. When you do this, stretch the grid. Also, is your y+ in the correct range for the S-A model?