[Gary51075607]

Hi, all

I want to solve the energy conservation equations as attached in the OpenFoam.

The problem lies in the second and third terms in the right. For example, i can not use the keyword grap(p) in the OpenFoam. if i shoud add them as a source term?

Thanks

Gary

[cutter]

Hi,

could you please repost the formula as image file. Unfortunately LibreOffice is not able to open the file properly. This excludes many potential readers of your post.

Please also post the code you've already written. This allows to understand your problems more easily.

Have a look at http://www.openfoam.org/docs/user/pr...#x9-670003.1.3, section 'Equation representation'.

Cutter

[dkxls]

Originally Posted by Gary51075607

i can not use the keyword grap(p) in the OpenFoam.

fvc::grad(p)

You might want to have a look at exciting OpenFOAM solvers, e.g. the code in UEqn.H or EEqn.H is pretty self explanatory.

Also, can you please write the equation you want to solve properly in the forum using the [math] tags, e.g. to denote the gradient of p?
Have a look at this http://www.cfd-online.com/Forums/sit...ne-forums.html

[Gary51075607]

The energy conservation is as follows:

The thermophysical properties, including the density, heat capacity and thermal conductivity, are the functions of pressure and temperature.

The code i have written is listed below:

fvScalarMatrix TEqn
(
    fvm::div(phi, T)
  - fvm::laplacian(lamdaEff, T)
 ==
   -T/rho*drho/dT*U*grad(p)

);

The problem lies in the second and third terms in the right of the equation. I don't know how can l add the second term and the form i write the third term is wrong.

Thanks

Gary

[hajott]

You should calculate from your equation of state. For example, for an ideal gas
.

[dkxls]

Originally Posted by Gary51075607

The thermophysical properties, including the density, heat capacity and thermal conductivity, are the functions of pressure and temperature.
...
The problem lies in the second and third terms in the right of the equation. I don't know how can l add the second term and the form i write the third term is wrong.

Without checking your actual equation, I see there several possible problems:

1. You are using several fields OpenFOAM does not provide per default, i.e. you need to make sure that all fields like lamdaEff, drho and dT are correctly initialized.
2. OpenFOAM denotes the thermal diffusivity for temperature typically with kappa and not lambda, hence make sure you are really using the right fields there. (see src/thermophysicalModels/basic/heThermo/heThermo.H)
3. You are still missing fvc for the pressure gradient!
4. You are multiplying several scalar (T,rho) fields with two vector fields (U,), I'm not quite sure, but that code should give you a tensor fields if I'm not mistaken now.

Altogether I see very little to no benefit in writing the thermal energy in this way. I admit that the energy equation in OF versions 2.1 and later is a bit more involved, but they work just fine.

If you are really just interested in the thermal energy, why not solve for sensible enthalpy as it was done up to OF version 2.0, see here for example:
https://github.com/OpenFOAM/OpenFOAM...pleFoam/hEqn.H

[Gary51075607]

Thanks, dkxls.
Sorry to forget fvc.
In my case, the thermophysical properties, including the density, heat capacity, enthalpy, viscosity and thermal conductivities, are strongly depended on the temperature and pressure. So i want the obtain the temperature directly from the energy equation.

The fields, such as lamdaEff, drho and dT has been correctly defined and initialized.

Could i group the terms of and as the source terms? And then how to write the source term?

[dkxls]

Originally Posted by Gary51075607

In my case, the thermophysical properties, including the density, heat capacity, enthalpy, viscosity and thermal conductivities, are strongly depended on the temperature and pressure. So i want the obtain the temperature directly from the energy equation.

For me it always was more natural to solve a transport equation for a conserved quantity, i.e. here enthalpy h, and compute the derived quantities, i.e. temperature T, from .
This is the way it's done in pretty much all OpenFOAM solvers. Also, this is a widely used approach in combustion simulation, where you have very strong dependencies on temperature.
Note that a formulation in terms of internal energy is equivalent to the above, it's merely a matter of taste!

Originally Posted by Gary51075607

Could i group the terms of and as the source terms? And then how to write the source term?

Well it doesn't matter how you call it, it boils down to the same thing anyway. Effectively it's an explicit term on the right hand side of the equation (i.e. computed from old time values).