# simpleFoam - Change physical properties of liquid

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 March 5, 2014, 06:06 simpleFoam - Change physical properties of liquid #1 Member   Join Date: Feb 2014 Posts: 57 Rep Power: 4 Hi, I am new user of OpenFoam. I would like to ask for help in modifying the physical properties of liquid which are: - mass density - viscosity Thanks in advance. T

 March 5, 2014, 06:44 #2 Senior Member   Alexey Matveichev Join Date: Aug 2011 Location: Nancy, France Posts: 1,371 Rep Power: 23 Hi, kinematic viscosity of the fluid is kept in constant/transportProperties file. Density is not actually used in simpleFoam as fluid is incompressible.

March 5, 2014, 09:34
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I am not sure but in the system of equations for RANS, we have rho (mass density of fluid) and nut (kinematic turulent viscosity), right?

May we change them somewhere in OpenFOAM?

T

Quote:
 Originally Posted by alexeym Hi, kinematic viscosity of the fluid is kept in constant/transportProperties file. Density is not actually used in simpleFoam as fluid is incompressible.

March 5, 2014, 10:28
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Alexey Matveichev
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Quote:
 Originally Posted by vut Thank you, Alexey, for your answer. I am not sure but in the system of equations for RANS, we have rho (mass density of fluid) and nut (kinematic turulent viscosity), right? May we change them somewhere in OpenFOAM? T
For incompressible fluid we can divide equations by density, so there will be no density and just kinematic viscosity.

OpenFOAM uses nuEff = nu + nut, where nu is kinematic viscosity of a fluid and you change it in constant/transportProperties, nut is calculated by turbulence model and again AFAIK there is no density in equations (well, you can pass density field to the model, but there's no density field in simpleFoam) as it is non-zero constant so we again can divide equations by it.

March 6, 2014, 05:32
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OK, I understand what you mean.

T

Quote:
 Originally Posted by alexeym For incompressible fluid we can divide equations by density, so there will be no density and just kinematic viscosity. OpenFOAM uses nuEff = nu + nut, where nu is kinematic viscosity of a fluid and you change it in constant/transportProperties, nut is calculated by turbulence model and again AFAIK there is no density in equations (well, you can pass density field to the model, but there's no density field in simpleFoam) as it is non-zero constant so we again can divide equations by it.

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