Adding a scalar transport equation to buoyantPimpleFoam

Pavithra · July 4, 2019, 22:44

Hello Everyone,

I am trying to add a scalar transport equation to buoyantPimpleFoam, which is a compressible solver.

Code:

     fvScalarMatrix rhoEEqn
     (
         fvm::ddt(rhoE)              
       + fvm::div(phi, rhoE)       
       - fvm::laplacian(a, rhoE)   
     );
     rhoEEqn.solve();

I get the following dimension mismatch error.

Code:

  --> FOAM FATAL ERROR: 
incompatible dimensions for operation 
    [rhoE[0 -3 0 0 0 1 0] ] + [rhoE[1 -6 0 0 0 1 0] ]

    From function void Foam::checkMethod(const  Foam::fvMatrix<Type>&, const Foam::fvMatrix<Type>&,  const char*) [with Type = double]
     in file /home/user/OpenFOAM/OpenFOAM-6/src/finiteVolume/lnInclude/fvMatrix.C at line 1283.

In order find out the source of error, I ran the simulation by neglecting the terms in scalar transport equation, one by one.

The error pops up when the divergence term is included.

I was able to successfully add this scalar equation to buoyantBoussinesqPimpleFoam (incompressible solver).

The dimension of rhoE is [0 -3 1 0 0 1 0]

Does adding a scalar transport equation to a compressible solver, need any special modification?

Is the dimension of phi different in a compressible sovler?

Unfortunately, I could not find any tutorial on adding a scalar transport equation to a compressible solver.

Kindly, please give me a direction in solving this.

Thank You.

With Thanks,
Pavithra.

Tobi · July 5, 2019, 03:15

Hi,

if you have a passive scalar transport equation the general equation is:

$\frac{\partial \rho \phi}{\partial t} + \nabla \bullet (\rho \textbf{U} \phi) = S_\phi$

Thus, the time derivative in FOAM should have the following:

Code:

fvm::ddt(rho, rhoE)

The unit mismatch is based on the missing density.

Pavithra · July 5, 2019, 03:43

Quote:

Originally Posted by Tobi

Hi,

if you have a passive scalar transport equation the general equation is:

$\frac{\partial \rho \phi}{\partial t} + \nabla \bullet (\rho \textbf{U} \phi) = S_\phi$

Thus, the time derivative in FOAM should have the following:

Code:

fvm::ddt(rho, rhoE)

The unit mismatch is based on the missing density.

Respected Sir,

Thank you so much for your kind help. I followed your advice and defined the scalar transport equation as below

Code:

     fvScalarMatrix rhoEEqn
     (
         fvm::ddt(rho, rhoE)                 //Time derivative
       + fvm::div(phi, rhoE)        //Convective term
       - fvm::laplacian(a*rho, rhoE)    //Diffusive Term
     );
      rhoEEqn.solve();

Now, I am able to successfully run the simulation and validate the solver.

Thank You.

With Thanks,
Pavithra.

olesen · July 16, 2019, 05:52

Quote:

Originally Posted by Pavithra

Hello Everyone,

I am trying to add a scalar transport equation to buoyantPimpleFoam, which is a compressible solver.

What about using the scalarTransport functionObject instead?

Tobi · July 16, 2019, 05:57

Hi Mark,

the function object is a possible and very easy option, I agree. Also the fields should be available during run-time while you can lookup the quantity and re-use it whereever you want.

Crazy how powerful the function objects are.

Pavithra · July 18, 2019, 03:25

Respected Prof. Mark Olesen,

Thank you so much for your suggestion. I am very new to OpenFoam. Could you please give me some direction for me to learn about functionObjects. I am interested in learning about that and solve a scalar transport equation using fucntionObject.

Thank You.

With Thanks,
Pavithra.

Pavithra · July 22, 2019, 22:20

Hello Everyone,

I tried to use functionObject to solve a scalar transport equation as suggested by Dr. Mark Olesen. I was able to do it successfully.

Now I have a transport equation, which has two convective fluxes. I am puzzled, if I can solve this using functionObject. My base solver is buoyantPimpleFoam and I use OF v6.

My transport equation is

$\frac{\partial \phi}{\partial t} + \nabla \bullet (\textbf{U} \phi) + \nabla \bullet (\textbf{A} \phi) - \alpha \nabla^2 \phi = 0$

Here,

$\phi$ - Electric charge density
$\textbf{U}$ - velocity
$\textbf{A}$ - flux field defined by user
$\alpha$ - Diffusion coefficient

Kindly, please give me a direction to solve this.

I want to define a source term which is dependent on this scalar ( $\phi$ ).

Thank You.

July 4, 2019, 22:44	Adding a scalar transport equation to buoyantPimpleFoam	#1
Pavithra Member Join Date: Apr 2019 Location: India Posts: 81 Rep Power: 7	Hello Everyone, I am trying to add a scalar transport equation to buoyantPimpleFoam, which is a compressible solver. Code: fvScalarMatrix rhoEEqn ( fvm::ddt(rhoE) + fvm::div(phi, rhoE) - fvm::laplacian(a, rhoE) ); rhoEEqn.solve(); I get the following dimension mismatch error. Code: --> FOAM FATAL ERROR: incompatible dimensions for operation [rhoE[0 -3 0 0 0 1 0] ] + [rhoE[1 -6 0 0 0 1 0] ] From function void Foam::checkMethod(const Foam::fvMatrix<Type>&, const Foam::fvMatrix<Type>&, const char*) [with Type = double] in file /home/user/OpenFOAM/OpenFOAM-6/src/finiteVolume/lnInclude/fvMatrix.C at line 1283. In order find out the source of error, I ran the simulation by neglecting the terms in scalar transport equation, one by one. The error pops up when the divergence term is included. I was able to successfully add this scalar equation to buoyantBoussinesqPimpleFoam (incompressible solver). The dimension of rhoE is [0 -3 1 0 0 1 0] Does adding a scalar transport equation to a compressible solver, need any special modification? Is the dimension of phi different in a compressible sovler? Unfortunately, I could not find any tutorial on adding a scalar transport equation to a compressible solver. Kindly, please give me a direction in solving this. Thank You. With Thanks, Pavithra.

July 5, 2019, 03:15		#2
Tobi Super Moderator Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,708 Blog Entries: 6 Rep Power: 51	Hi, if you have a passive scalar transport equation the general equation is: $\frac{\partial \rho \phi}{\partial t} + \nabla \bullet (\rho \textbf{U} \phi) = S_\phi$ Thus, the time derivative in FOAM should have the following: Code: fvm::ddt(rho, rhoE) The unit mismatch is based on the missing density. cryabroad, Pavithra and adnre_ronconi like this. __________________ Keep foaming, Tobias Holzmann

July 16, 2019, 05:57		#5
Tobi Super Moderator Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,708 Blog Entries: 6 Rep Power: 51	Hi Mark, the function object is a possible and very easy option, I agree. Also the fields should be available during run-time while you can lookup the quantity and re-use it whereever you want. Crazy how powerful the function objects are. __________________ Keep foaming, Tobias Holzmann

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Pavithra Member Join Date: Apr 2019 Location: India Posts: 81 Rep Power: 7	Respected Prof. Mark Olesen, Thank you so much for your suggestion. I am very new to OpenFoam. Could you please give me some direction for me to learn about functionObjects. I am interested in learning about that and solve a scalar transport equation using fucntionObject. Thank You. With Thanks, Pavithra.

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Pavithra Member Join Date: Apr 2019 Location: India Posts: 81 Rep Power: 7	Hello Everyone, I tried to use functionObject to solve a scalar transport equation as suggested by Dr. Mark Olesen. I was able to do it successfully. Now I have a transport equation, which has two convective fluxes. I am puzzled, if I can solve this using functionObject. My base solver is buoyantPimpleFoam and I use OF v6. My transport equation is $\frac{\partial \phi}{\partial t} + \nabla \bullet (\textbf{U} \phi) + \nabla \bullet (\textbf{A} \phi) - \alpha \nabla^2 \phi = 0$ Here, $\phi$ - Electric charge density $\textbf{U}$ - velocity $\textbf{A}$ - flux field defined by user $\alpha$ - Diffusion coefficient Kindly, please give me a direction to solve this. I want to define a source term which is dependent on this scalar ( $\phi$ ). Thank You.