CFD Online Discussion Forums - RAS setup for oscillating flow

Hello everybody,

i am currently trying run an transient RANS simulation of an oscillating flow in a simple environment with a structured grid. Unfortunately i am confronted with problems while running the simulation.

The Problem:
The simulation is crashing at around 280-290 seconds. (flow reversing starts at 219.3; oscillating sin period is 438.6). The results until this point are fine, usable and uncompromised.

The Mesh:
The Mesh is a small cylindrical inlet tube into a cylindrical open room with an o-grid setup. The surface of the room, where the inlet tube enters, is treated as a closed wall. All other room surfaces are open. (see attachments)

The Simulation:
I am running an incompressible RAS Simulation with pimpleFoam in PISO mode with 2 correctors, no underrelaxation and the standard kepsilon turbulence model. The maximum Re.-Num. is approx. ~ 2000.

My BC
patch outlet = outlet form the inlet tube into the cylindrical room
patch outletRoom = open surfaces of the room

k

Code:

internalField   uniform 0.015;



boundaryField

{

    inlet

    {

       type                 turbulentIntensityKineticEnergyInlet;

       intensity         0.1;

       value                 $internalField;

    }

    inletWall

    {

        type                 kqRWallFunction;

        value           $internalField;

    }

    outlet

    {

        type            zeroGradient;

    }

    roomOutlet

    {

        type            zeroGradient;

    }

    roomWall

    {

        type                 kqRWallFunction;

        value           $internalField;

    }

}

epsilon

Code:

internalField   uniform 4.312e-3;



boundaryField

{

    inlet

    {

        type                turbulentMixingLengthDissipationRateInlet;

        mixingLength        0.07;

        value                 $internalField;

    }

    inletWall

    {

        type            epsilonWallFunction;

        value           $internalField;

    }

    outlet

    {

        type            zeroGradient;

    }

    roomOutlet

    {

        type            zeroGradient;

    }

    roomWall

    {

        type            epsilonWallFunction;

        value           $internalField;

    }

}

nut

Code:

internalField   uniform 0;



boundaryField

{

    inlet

    {

        type            calculated;

        value           uniform 0;

    }

    inletWall

    {

            type            nutkWallFunction;

            value           $internalField;

    }

    outlet

    {

        type            zeroGradient;

    }

    roomOutlet

    {

        type            zeroGradient;    

    }

    roomWall

    {

        type            nutkWallFunction;

        value           $internalField;

    }

Inlet with FlowRateInletVelocity with a Sine profile
noSlip on Walls
zeroGrad at outlets

totPressure = 0 at outletRoom
zeroGrad. everywhere else

-------
Add. Inf.
I've run some laminar sim. with this setup without any Problems. I have as well tried k- and nutLowRe, which did not show any significant differences. I would still be guessing that this is a BC Problem?

I am hoping anybody cloud help me with some advise. Please let me know if add. Information is needed. Thanks in advance.:)
Noah