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Arnab January 24, 2005 12:04

lots of warnings
 
Hello

I am running a compressible supersonic-subsonic flow with stagnation inlet conditions and pressure outlet conditions.

If I switch OFF the Thermal Models option for Material 1 (Air)-the only material I have , the simulation is running with lots of warnings of these 2 types:

*** WARNING #060 *** DENSITY OUT OF BOUND DUE TO PRESSURE CORRECTION AT CELL 509895 DENSITY= 1.2515E-03 LIMITER APPLIED GIVING UP AFTER PRINTING 50 #060 WARNINGS Total number of #060 warnings: 5820

AND

*** WARNING #057 *** EQUATION OF STATE IMBALANCE AT CELL 509774 IS 1.710664E+00 EQUATION OF STATE IMBALANCE FOUND AT MORE THAN 100 CELLS - PRINTOUT OF WARNING MESSAGE STOPPED

And when i run the model with the Thermal Models option switched ON , I get these same errors and after 6 time steps, the simulation stops due to divergence.

Will be waiting for help,


Brian January 26, 2005 14:47

Re: lots of warnings
 
You really can't run transonic cases without solving for temperature. It just won't work.

Often, the problem with transonic cases is that the initialization sets up huge and unrealistic pressure gradients. As the solver tries to resolve these, they get worse and you get divergence, or more often, the dreaded "negative density".

Make sure your setup is for compressible flow - i.e. density is ideal gas.

The first thing to try is to switch off the default initialization.

If that doesn't help, try running the case as transient. This allows a gradual and realistic initialization. I find this solves most transonic flow problem cases.

Arnab January 27, 2005 16:36

Re: lots of warnings
 
Hello,

Thanks Brian for responding. I will solve for temperature for transonic cases. But if I switch off default initialization, then how would I initialize? Also my case is transient case. But I want to give you more details of my simulation for you and others to better understand the problem and give me suggestions.

My CASE:

1.Transient, Moving mesh (Rotor moving at 10300 rpm and stators stationary).

2 stagnation inlets and 2 pressure outlets as it is a 4 port configuration.

3. Molecular properties: Ideal f (T,P) , Constant default properties for Air in terms of Molecular viscocity, Cp, Conductivity and Molecular weight.

4. Turbulence Model - K-epsilon High Re

Thermal Models - (conservation- static enthalpy, enthalpy- thermal)

Initialization - Default Initialization flow with 0 max vel and atmosphere pressure and temp.

5 Monitoring and Reference cells at outlet with atmospheric pressure assigned.

6. Max number of corrector stages : 50

Reduction in Residual for corrector stages = 0.25

under relaxation for pressure correction = 0.01

scalar solver - method - CG

Implicit Temporal Discretization

Solving for U, V,W, Pres, Turb KE, Turb Diss, T .

Differencing schemes - UD and MARS

7. Time step : 1.21 e -10 sec.

run for 0.005825 secs

Still I am getting these warnings at all time steps for almost all the cells i guess:

*** WARNING #060 *** DENSITY OUT OF BOUND DUE TO PRESSURE CORRECTION AT CELL 509895 DENSITY= 1.2515E-03 LIMITER APPLIED GIVING UP AFTER PRINTING 50 #060 WARNINGS Total number of #060 warnings: 5820

AND

*** WARNING #057 *** EQUATION OF STATE IMBALANCE AT CELL 509774 IS 1.710664E+00 EQUATION OF STATE IMBALANCE FOUND AT MORE THAN 100 CELLS - PRINTOUT OF WARNING MESSAGE STOPPED


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