CFD Online Discussion Forums - Defining a polynomial viscosity depending on temperature

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)

- OpenFOAM Running, Solving & CFD (https://www.cfd-online.com/Forums/openfoam-solving/)

- - Defining a polynomial viscosity depending on temperature (https://www.cfd-online.com/Forums/openfoam-solving/230540-defining-polynomial-viscosity-depending-temperature.html)

Defining a polynomial viscosity depending on temperature

Hello all,

I'm currently trying to run an analysis using temperature integrated simpleFoam. As of my observations, temperature range for the fluid is between 20-50 C and due to this large range, viscosity changes in a wide range which leads my computation into a big error, at about 50%.

So here is my question. I would like to apply a curve-fitting to viscosity of my fluid flowing through and integrate it in the OpenFOAM by NOT using a non-Newtonian approach. Because fluid is definetely Newtonian.

How can I achieve it?

There are more options. Either you switch to, e.g., rhoSimpleFoam and use a polynomial approach or you derive your current solver (simpleFoam) and implement new volScalarField´s which relates to temperature and viscosity. Then you have to solve an appropriate temperature/energy equation and calculate the viscosity based on your temperature field.

Probably, the rhoSimpleFoam solver fits better as you don´t have to program anything yourself. An example:

Code:

thermoType

{

    type            heRhoThermo;

    mixture         pureMixture;

    transport       polynomial;

    thermo          hPolynomialt;

    equationOfState polynomial;

    specie          specie;

    energy          sensibleEnthalpy;

}

The thermo and equation of state polynomials might be just set-up with the first coefficient (its the constant). The transport polynomial is related to the viscosity.

Thank you for your reply Tobi,

The thing is I would like to compute the viscosity for each cell using its temperature and have this value used in governing equations. I don't want any contour for viscosity, to say. Do you have any recommendation for this goal?

Quote:

Originally Posted by Tobi (Post 783996)

Code:

thermoType

{

    type            heRhoThermo;

    mixture         pureMixture;

    transport       polynomial;

    thermo          hPolynomialt;

    equationOfState polynomial;

    specie          specie;

    energy          sensibleEnthalpy;

}

The thermo and equation of state polynomials might be just set-up with the first coefficient (its the constant). The transport polynomial is related to the viscosity.

Well, I am not sure if you read my reply or not because I wrote the stuff you need. Hence, I don't get your statement.

Thank you for your help and kindness.

Just a quick question. Is it clear to you now or not? I don't have the feeling that my statement is sufficient for you or maybe I misunderstood your inquiry!?