fvc::ddt(alphac) equals zero

sharonyue · August 3, 2017, 03:10

Hello guys,

Below is the pressure equation In MPPICInterFoam:

Code:

fvScalarMatrix p_rghEqn
        (
            fvm::laplacian(Dp, p_rgh)
         ==
            fvc::ddt(alphac) + fvc::div(alphacf*phiHbyA)
        );

//Info << fvc::ddt(alphac);

The problem is that fvc::ddt(alphac) is zero all the time. After commenting out this term, the solver gives the same result.

Below is from Jasak:

HTML Code:

Thus, if you try to evaluate the ddt the way it is written, it will recognise that the field does not have the oldTime() level stored and will use the current value to initialise it. Basically, fvc::ddt(magSqr(U)) will always give you zero, which is wrong.

One reason is that the alphac is so small, but it should not be zero. I am not sure ifs a bug.

RahulSubbu · July 19, 2019, 07:21

Dear Sharonyue,
I am also trying to use the MPPICinterFoam. I have a few queries:
1. In the lines of UEqn.H, there is no alphaRhoPhic term. How did they include this term?
2. rhoPhi in alphaEqn.H seems to be similar to alphaRhoPhic.
Thanks in advance.

ArminAlavi · June 21, 2021, 10:16

Hello Dongyue
I am facing the very same problem you had, and I wonder if you have managed to solve it. I am using OpenFoam6 by the way. I would really appreciate it if you could share your idea on this problem.

RahulSubbu · October 4, 2021, 04:49

Quote:

Originally Posted by ArminAlavi

Hello Dongyue
I am facing the very same problem you had, and I wonder if you have managed to solve it. I am using OpenFoam6 by the way. I would really appreciate it if you could share your idea on this problem.

Dear Armin,
I found a way to fix this issue. Change the nAlphaSubCycles in fvSolution to 1. Apparently having more than 1 subcycles defaults the ddtalphac to zero. Hope this helps!

Best regards,
Rahul Subburaj

August 3, 2017, 03:10	fvc::ddt(alphac) equals zero	#1
sharonyue Senior Member Dongyue Li Join Date: Jun 2012 Location: Beijing, China Posts: 838 Rep Power: 17	Hello guys, Below is the pressure equation In MPPICInterFoam: Code: fvScalarMatrix p_rghEqn ( fvm::laplacian(Dp, p_rgh) == fvc::ddt(alphac) + fvc::div(alphacf*phiHbyA) ); //Info << fvc::ddt(alphac); The problem is that fvc::ddt(alphac) is zero all the time. After commenting out this term, the solver gives the same result. Below is from Jasak: HTML Code: Thus, if you try to evaluate the ddt the way it is written, it will recognise that the field does not have the oldTime() level stored and will use the current value to initialise it. Basically, fvc::ddt(magSqr(U)) will always give you zero, which is wrong. One reason is that the alphac is so small, but it should not be zero. I am not sure ifs a bug. __________________ My OpenFOAM algorithm website: http://dyfluid.com By far the largest Chinese CFD-based forum: http://www.cfd-china.com/category/6/openfoam We provide lots of clusters to Chinese customers, and we are considering to do business overseas: http://dyfluid.com/DMCmodel.html

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July 19, 2019, 07:21		#2
RahulSubbu New Member Rahul Subburaj Join Date: Apr 2019 Posts: 2 Rep Power: 0	Dear Sharonyue, I am also trying to use the MPPICinterFoam. I have a few queries: 1. In the lines of UEqn.H, there is no alphaRhoPhic term. How did they include this term? 2. rhoPhi in alphaEqn.H seems to be similar to alphaRhoPhic. Thanks in advance.

June 21, 2021, 10:16		#3
ArminAlavi New Member Armin Alavi Join Date: May 2019 Location: Tehran Posts: 22 Rep Power: 6	Hello Dongyue I am facing the very same problem you had, and I wonder if you have managed to solve it. I am using OpenFoam6 by the way. I would really appreciate it if you could share your idea on this problem.