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Setting up boundary conditions for chtMultiRegionSimpleFoam

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Old   July 31, 2016, 20:34
Default Setting up boundary conditions for chtMultiRegionSimpleFoam
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Sebastian
Join Date: Jun 2016
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Hello, I want to simulate a egr cooler and i have trouble with the region of the water. I get unrealistic results for the temperature and the simulation crashes. I think i made a mistake with the boundary conditions.

For U:
Code:
water_inlet
   	  {
       		type            flowRateInletVelocity;
       		massFlowRate    constant 0.967222; //=3480kg/h
       		rho             rho;
       		rhoInlet        1000;   
   	  }
water_outlet
   	  {
       		type            inletOutlet;
       		value           uniform ( -0.01 0 0 );  //unsure of the value. Had only the mass flow
        	inletValue      uniform ( 0 0 0 );
   	  }
"water_wall.*"
   	  {
      	 	type            fixedValue;
      	 	value           uniform (0 0 0);
   	  }
For T:
Code:
    water_inlet
    {
        type            fixedValue;
        value           uniform 358.65;
    }
    water_outlet
    {
        type            inletOutlet;
        value           uniform 360.55;
        inletValue      uniform 360.55;
    }
water_wall_to_solid
    {
        type            compressible::turbulentTemperatureCoupledBaffleMixed;
        value           uniform 360;
        Tnbr            T;
        kappa           fluidThermo;
        kappaName       none;
    }
water_wall_adiabat
    {
        type            zeroGradient;
        value           uniform 360;
    }
For p and p_rgh:
Code:
	  
"water_wall.*"
    {
        type            zeroGradient;
        value           uniform 1000;
    }
    	  water_inlet			
    {
        type            zeroGradient;
        value           uniform 1000;
    }
	  water_outlet				
   {
        type            fixedValue;
        value           uniform 1000;
    }
For k (same with epsilon but with type compressible::epsilonWallFunction):
Code:
    water_inlet
    {
        type            fixedValue;
        value           uniform 0.01;
    }
    water_outlet
    {
        type            inletOutlet;
        inletValue      uniform 0.01;
        value           uniform 0.01;
    }
    "water_wall.*"
    {
        type            compressible::kqRWallFunction;
        value           uniform 0.1;
    }
Following the error message:
Code:
--> FOAM FATAL ERROR: 
Maximum number of iterations exceeded

Last edited by astronauti; August 2, 2016 at 05:57.
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Old   August 1, 2016, 09:45
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For p your boundary should be calculated on all patches. For p_rgh you could switch to fixedFluxPressure on walls. But boundary conditions are often not the problem. cht simulations are easy to crash or get wrong. In most cases your mesh is just not good enough. Even if checkMesh does not yet complain. If your mesh is of good quality you can check your schemes. Start with upwind if possible. Another way to get better results is to initialize the velocities without solving the temperature. All of this depends on your flow conditions/turbulence model etc. For industrial cases kOmega might be more stable....You might want to try turning turbulence modeling of to see if this is the problem....there are to many options for this kind of error message.

The easiest way to test your boundaries is a test case. Check your boundary conditions on a simple duct or something like it. This way the mesh won't be an issue and you can easily see if the results are reasonable
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