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-   -   BC for pressure driven compressor cascade (http://www.cfd-online.com/Forums/openfoam/106719-bc-pressure-driven-compressor-cascade.html)

MattWright September 6, 2012 06:38

BC for pressure driven compressor cascade
 
Hi. I am currently doing a thesis where I am running a simulation on a cascade of compressor blades in OpenFOAM. The simulation is 2D and consists of 1 blade with cyclic boundaries on the top and bottom of the domain for the cascade effect. I am running a compressible, laminar case. I ran rhoSimplecFoam and adapted my case from the tutorial, and this runs fine with the BCs the same as the tutorial. However, when I try my own BCs it crashes. I want total pressure specified at the inlet and static pressure at the outlet. The velocity is driven by the pressure at and angle of 55deg at the inlet. Total temperature is also specified at the inlet. Here are my p, U and T files. Can someone tell me what I am doing wrong. Thanks.

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [1 -1 -2 0 0 0 0];

internalField uniform 101300;

boundaryField
{
BC1_on_INLET
{
type totalPressure;
p0 uniform 101300;
value uniform 101300;
gamma 1.4;
}
BC1_on_LOWER_PERIODIC
{
type cyclic;
}
BC1_on_OUTLET
{
type fixedValue;
value uniform 88131;
}
BC1_on_PROFILE
{
type zeroGradient;
}
BC1_on_SYM1
{
type empty;
}
BC1_on_SYM2
{
type empty;
}
BC1_on_UPPER_PERIODIC
{
type cyclic;
}
}


// ************************************************** *********************** //

FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
BC1_on_INLET
{
type pressureDirectedInletVelocity;
inletDirection uniform (1.428 1 0);
value uniform (0 0 0);
}
BC1_on_LOWER_PERIODIC
{
type cyclic;
}
BC1_on_OUTLET
{
type zeroGradient;
}
BC1_on_PROFILE
{
type slip;
}
BC1_on_SYM1
{
type empty;
}
BC1_on_SYM2
{
type empty;
}
BC1_on_UPPER_PERIODIC
{
type cyclic;
}
}


// ************************************************** *********************** //

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object T;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 0 0 1 0 0 0];

internalField uniform 300;

boundaryField
{
BC1_on_INLET
{
type totalTemperature;
T0 uniform 300;
value uniform 300;
gamma 1.4;
}
BC1_on_LOWER_PERIODIC
{
type cyclic;
}
BC1_on_OUTLET
{
type zeroGradient;
}
BC1_on_PROFILE
{
type zeroGradient;
}
BC1_on_SYM1
{
type empty;
}
BC1_on_SYM2
{
type empty;
}
BC1_on_UPPER_PERIODIC
{
type cyclic;
}
}


// ************************************************** *********************** //

Sunxing April 26, 2013 21:18

Hi Matthew,

I also want to simulate a cascade with same inlet and outlet BC as your. Do you have solved this problem? Please let me know any progress that you have made.
http://www.cfd-online.com/Forums/ope...-pressure.html

Regards
Sunxing

akashjangid August 27, 2013 03:02

floating point exception
 
Hey, I am also doing the same case. I have the same boundary condition.
After some iteration there is an error coming floating point exception. Does anyone has solved this kind of error

Thanks !!

bscphil August 29, 2013 04:16

Quote:

Originally Posted by akashjangid (Post 448246)
Hey, I am also doing the same case. I have the same boundary condition.
After some iteration there is an error coming floating point exception. Does anyone has solved this kind of error

Thanks !!

Hey Foamer's,

by a pressure driven flow simulated with rhoSimpleFoam:
  1. check your initial conditions (e.g. don't set the initial value for U to (0 0 0), but to a small value like (0.1 0.1 0); just trying to set the initial value for p to your static pressure at the outlet)
  2. check your discretization schemes
  3. check your under relaxation factors
  4. check your solver settings
That's it ;) for more information, please post your case as *.zip with the files: fvSchemes, fvSolution, thermophysicalProperties, RASProperties, BC's.

For your next post/problem, please, just characterize your case: solver, discretization schemes, turbulence model, mesh (y+values), fluid properties, physical properties (Mach-range) etc.

akashjangid August 29, 2013 15:13

1 Attachment(s)
I changes the initial condition for velocity but still same error is coming. I have attached my case here.

Thanks!!

bscphil August 31, 2013 18:32

Quote:

Originally Posted by akashjangid (Post 448783)
I changes the initial condition for velocity but still same error is coming. I have attached my case here.

Thanks!!

Your boundary conditions seem's to be right. Please post the terminal output of the last time steps. In which equation is the error ??

For your next try change your relaxation factors to:
Code:

relaxationFactors
{   
    fields
    {
        p    0.3;
        rho    0.05;   
    }
    equations
    {
        U    0.7;
        k    0.7;
        epsilon    0.7;
        h    0.5;
    }
}

and set
Code:

    transonic      false;
For better results, you've change the schemes from upwind scheme to a more non-diffusive scheme, e.g. linearUpwind or QUICK for the convective terms and decrease the relTol values for p and U,k,epsilon

Good luck;)

akashjangid September 8, 2013 18:01

Difference in results
 
2 Attachment(s)
Hello bscphil

My simulation results are coming good now, but there is still one problem.
I have the results in fluent for same case(which are correct), but the openfoam results differ by a lot.
I have attached 2 screen-shot of Mach contour at 50 % span length for fluent and openfoam.

I have the same BC, but the velocity is coming much much higher in openfoam :(
Any suggestions for this ?

Thanks

akashjangid September 13, 2013 10:55

Temperature Problem
 
Hello,

I gave total temp boundary condition at my inlet

outlet
{
type totalTemperature;
T0 uniform 517.5; ( 517.5 is the total temperature)
value uniform 517.5;
gamma 1.4;
}

But in the result my static temp is going as high as 580 k.
Why is the happening ? plz help me with this ..

Thanks


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