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renyun0511 May 11, 2013 11:02

problem for centrifugal pump transient simulation
 
5 Attachment(s)
Hi, all,

Recently, I try to simulate the transient inner flow of centrifugal pump by PimpleDyMFoam on OpenFOAM-2.1.0. But it always ended with the floating point exception error after some steps. I looked into the internal Field of my case by Ensight software and I found that there was a wrong pressure distribution in this centrifugal pump, although the directions of both velocity at inlet and velocity at outlet are right and the direction of impeller rotation is also right. I don't know why it was this? Can someone give me some hints? I will be very appreciated it!

In order to explain my questions better, I give the pressure distributions of this pump with steadystate and transient simulation at the first output time step, respectively. Here are:

Attachment 21641,Attachment 21642

The boundary file:
Attachment 21648
The fvSchemes file:
Attachment 21649
The fvSolution file:
Attachment 21650
The controlDict file:
Attachment 21651

The initial BCs:
Code:

FoamFile
{
    version    2.0;
    format      ascii;
    class      volVectorField;
    location    "3500";
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions      [0 1 -1 0 0 0 0];
internalField  nonuniform List<vector>
1196068
(
(0.716798 0.840057 -7.4744)
(0.638485 0.861783 -7.48279)
(0.681562 0.835391 -7.58056)
...  ...
    wall
    {
        type            fixedValue;
        value          nonuniform List<vector>
88020
(
(0 0 0)
(0 0 0)
(0 0 0)
...  ...
    wallimp4
    {
        type            movingWallVelocity;
        value          uniform (0 0 0);
    }
    wallimp3
    {
        type            movingWallVelocity;
        value          uniform (0 0 0);
    }
    wallimp2
    {
        type            movingWallVelocity;
        value          uniform (0 0 0);
    }
    wallimp1
    {
        type            movingWallVelocity;
        value          uniform (0 0 0);
    }
    outlet
    {
        type            zeroGradient;
    }
    inlet
    {
        type            fixedValue;
        value          uniform (0 -2.708 0);
    }
}

Code:

FoamFile
{
    version    2.0;
    format      ascii;
    class      volScalarField;
    location    "3500";
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions      [0 2 -2 0 0 0 0];
internalField  nonuniform List<scalar>
1196068
(
0.38443
0.248261
0.21847
...  ...
    wall
    {
        type            zeroGradient;
    }
    wallhgb
    {
        type            zeroGradient;
    }
    wallqgb
    {
        type            zeroGradient;
    }
    interafcevol1
    {
        type            cyclicAMI;
        value          nonuniform List<scalar>
1446
(
5.50122
5.60699
5.11278
...  ...
    interfacevol
    {
        type            cyclicAMI;
        value          nonuniform List<scalar>
22196
(
-92.0152
-109.644
-123.262
...  ...
    interfacesuc
    {
        type            cyclicAMI;
        value          nonuniform List<scalar>
2368
(
-675.839
-676.411
-675.763
...  ...
    interfaceimp1
    {
        type            cyclicAMI;
        value          nonuniform List<scalar>
1120
(
-676.74
-675.488
-676.987
...  ...
    interfaceimp
    {
        type            cyclicAMI;
        value          nonuniform List<scalar>
8680
(
-105.911
-104.788
-102.254
...  ...
    interfaceckyc
    {
        type            cyclicAMI;
        value          nonuniform List<scalar>
748
(
-6.02945
-7.33232
-6.99204
...  ...
    outlet
    {
        type            fixedValue;
        value          uniform 0;
    }
    inlet
    {
        type            zeroGradient;
    }
}

Thank you very much!


Yun Ren

renyun0511 May 11, 2013 11:15

2 Attachment(s)
Some description for the above attached pictures:
the pressure distribution by steady-state simulation, that is, Time=0s:
Attachment 21641
the pressure distribution by transient simulation, that is, Time=0.00005s:
Attachment 21642

linnemann May 11, 2013 13:40

2 Attachment(s)
Try with these

renyun0511 May 11, 2013 22:50

Hi, Linnemann,

Thank you very much for your reply, but I'm afraid I can only open the fvSolution.txt file. There is something wrong with fvSchemes.txt. Can you uploaded it again?

Regards,

Yun Ren

linnemann May 12, 2013 03:02

1 Attachment(s)
Here we go again

renyun0511 May 12, 2013 07:11

Hi, Linnemann,

I'm afraid that " Gauss faceMDLimited 1" is not a valid scheme in Version-2.1.0. When I added it in my original fvSchemes file, there is an error occured:

Code:

[0] --> FOAM FATAL IO ERROR:
[0] Unknown discretisation scheme faceMDLimited
Valid schemes are :
59
(
Gamma
GammaV
LUST
MUSCL
MUSCLV
Minmod
MinmodV
OSPRE
OSPREV
Phi
QUICK
QUICKV
SFCD
SFCDV
SuperBee
SuperBeeV
UMIST
UMISTV
biLinearFit
blended
clippedLinear
cubic
cubicUpwindFit
downwind
filteredLinear
filteredLinear2
filteredLinear2V
filteredLinear3
filteredLinear3V
fixedBlended
limitWith
limitedCubic
limitedCubicV
limitedLinear
limitedLinearV
limiterBlended
linear
linearFit
linearPureUpwindFit
linearUpwind
linearUpwindV
localBlended
localMax
localMin
midPoint
outletStabilised
pointLinear
quadraticFit
quadraticLinearFit
quadraticLinearUpwindFit
quadraticUpwindFit
reverseLinear
skewCorrected
upwind
vanAlbada
vanAlbadaV
vanLeer
vanLeerV
weighted
)


Regards,

Yun Ren

linnemann May 13, 2013 01:37

Hi

Im sorry was writing based on memory and the memory was wrong :-)

here is the correct syntax

Code:

faceMDLimited Gauss linear 1;

renyun0511 May 13, 2013 10:13

Hi, Linnemann,

I changed the fvSchemes and fvSolution as you uploaded, but there is error about "mpi". So, I changed little by little, and finally, I found that it is wrong with the relaxationFactors:
Here is yours:
Code:

relaxationFactors
{
    fields
    {
 "p.*"  0.3;
    }
    equations
    {
        "U.*"          0.7;
 "k.*"  0.5;
 "omega.*" 0.5;
    }
}

and when I return to my original setup, the case can going. The difference between your fvSolution and mine is only the relaxationFactors, and here is mine:
Code:

relaxationFactors
{
    fields
    {
    }
    equations
    {
        "U.*"          1;
    }
}

I think in the transient simulation, there is not a relationship with the relaxation factors any more.

At last, when I use your fvSchemes instead of mine and my fvSolution, the result didn't changed a little.


Regards,

Yun Ren

ARohit January 15, 2014 05:55

Why only few timesteps in transient simulation
 
Dear all,

I am having fundamental question regarding steady and transient simulation.

In steady sim, it takes around 100 to 150 iterations to solve a perticular problem. any problm for instance.

But while doing transient sim, we give maximum coefficient loops i.e max iterns per timestep as 5 or 6..

How it is possible for computer to get soln at that timestep in such small no of iterns.?

thanks in advance.


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