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Solution not converging, but oscillating residuals around a constant value

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Old   February 7, 2012, 07:29
Default Solution not converging, but oscillating residuals around a constant value
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Hi Fluent users,

I am a new fluent user and I am analysing an impingement system for a vane internal cooling passage, using a realizable k-eps model.
I started using a incompressible ideal gas, the solution converged without any problems but the calculated density was completely wrong, so I changed the material as an ideal gas. Now my solution doesn't converge anymore: all the residuals oscillate around a constant value, and in particular the continuity residuals oscillate around a value which is far from the convergence criteria one.
I tried to change the under relaxation factors (it dumps the oscillatins but it doesn't improve the convergence), to use a finer mesh and to use the fluent mesh adaptation tool but without any results.

Can anbody help me?


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Old   February 7, 2012, 12:21
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It is difficult to judge from the few information you gave
What is the pressure and velocity value at the injection system (or maximum pressure in the system) ? Do you have good values of y+ ? Did you check the quality of your mesh ?

Below are a few things you could try :
- Using the density based solver
- start with a lower mass flow (or velocity or pressure) inlet and increase it gradually
- Start by an inviscid flow then add turbulence

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Old   February 7, 2012, 12:55
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I think your case is transient! not steady-state.
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convergence issues, oscillating residuals

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