Solving the density equation

shock77 · August 5, 2020, 05:28

Hi,

in rhoCentralFoam the density equation raises me questions:

Code:

        solve(fvm::ddt(rho) + fvc::div(phi));

There is no need to specify a scheme for div(phi) in rhoCentralFoam, only for tauMC. For discretization the Kurganov or Tadmor scheme should be used. I suppose thats why I dont have to specify it?

Phi is defined in createField.H as:

Code:

surfaceScalarField phi("phi", fvc::flux(rhoU));

and in rhoCentralFoam.C as:

Code:

phi = aphiv_pos*rho_pos + aphiv_neg*rho_neg;

How can it be both?

I would be very glad, if someone could explain me how phi is actually calculated.

Kind regards,
shock77

clapointe · August 5, 2020, 10:35

You are correct that Kurganov/Tadmor flux reconstruction is used in rhoCentralFoam. The line in createFields is just used to initialize phi; it is computed (and updated) in the solver, ultimately with that line you referenced. I suggest taking a look at the publication associated with the solver : "Implementation of semi‐discrete, non‐staggered central schemes in a colocated, polyhedral, finite volume framework, for high‐speed viscous flows."

Caelan

shock77 · August 7, 2020, 08:03

Thank you very much for your reply, it already helped me.

I have read the paper and understand how its done mathematically, I am struggling with the implementation in OpenFOAM.

Kind regards

shock77

August 5, 2020, 05:28	Solving the density equation	#1
shock77 Senior Member Join Date: Dec 2019 Posts: 215 Rep Power: 7	Hi, in rhoCentralFoam the density equation raises me questions: Code: solve(fvm::ddt(rho) + fvc::div(phi)); There is no need to specify a scheme for div(phi) in rhoCentralFoam, only for tauMC. For discretization the Kurganov or Tadmor scheme should be used. I suppose thats why I dont have to specify it? Phi is defined in createField.H as: Code: surfaceScalarField phi("phi", fvc::flux(rhoU)); and in rhoCentralFoam.C as: Code: phi = aphiv_posrho_pos + aphiv_negrho_neg; How can it be both? I would be very glad, if someone could explain me how phi is actually calculated. Kind regards, shock77

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August 5, 2020, 10:35		#2
clapointe Senior Member Join Date: Aug 2015 Posts: 494 Rep Power: 14	You are correct that Kurganov/Tadmor flux reconstruction is used in rhoCentralFoam. The line in createFields is just used to initialize phi; it is computed (and updated) in the solver, ultimately with that line you referenced. I suggest taking a look at the publication associated with the solver : "Implementation of semi‐discrete, non‐staggered central schemes in a colocated, polyhedral, finite volume framework, for high‐speed viscous flows." Caelan

August 7, 2020, 08:03		#3
shock77 Senior Member Join Date: Dec 2019 Posts: 215 Rep Power: 7	Thank you very much for your reply, it already helped me. I have read the paper and understand how its done mathematically, I am struggling with the implementation in OpenFOAM. Kind regards shock77