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-   -   Compressible Convergence problem (http://www.cfd-online.com/Forums/fluent/34387-compressible-convergence-problem.html)

Graeme Young August 12, 2004 03:26

Compressible Convergence problem
 
Hi, I'm trying to model transonic/supersonic flow through a nozzle/diffuser using Ideal-gas compressible flow with Spalart-Allmaras viscous model. My solutions are fine when I use incompressible however I'm having trouble getting my solution to converge when I try Ideal-gas. I'm getting temperature limit warnings as well as divergent solution warnings. I tried reducing the Courant number which allowed the solver to keep iterating however the residuals all remained between 1 and 0.1 after about 600 iterations. Any suggestions on what I can do to get a good solution?

shang August 12, 2004 04:41

Re: Compressible Convergence problem
 
You can begin the calculation using a explicit formulation and observe the residuals. When the residuals become relatively steady you could switch to the implicit formulation.

Graeme August 12, 2004 12:46

Re: Compressible Convergence problem
 
thanks for the suggestion but i still have the same problem

N Menon August 13, 2004 03:57

Re: Compressible Convergence problem
 
Try running the simulation as a transient case with explicit flrmulation for the time step calculation. set the courant number to about 0.6.

You can either run this through until a steady state, or use its soultion as an intial point for the steady state simulation.

Nandu


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