Viscosity and pressure - Newtonian

yambanshee · January 18, 2019, 05:32

Good day all,

I am using the simpleFoam solver with a Newtonian transport model, where only kinematic viscosity is needed (nu).
After solving, my main point of consideration is pressures, which is by default given as P/rho. I am working with air at 15C so

nu = 1.47e-5
mu = 1.802e-5
rho = 1.225

Would there be any negative consequence to changing the properties such that I set rho = 1, and therefore use a nu = 1.802e-5? This would mean that my pressures don't need to be multiplied by density, but I am unsure if this would cause differences in regards to the turbulence models when computing turbulent viscosity.

HenrikJohansson · January 18, 2019, 07:16

Hi Zander,

Density is not solved with simpleFoam. The effect of density is as you said pressure(in OpenFoam) = P/rho.
Thus your indata for pressure shall be P divided by density of your fluid. Changing density to 1 would be unphysical if you are trying to solve air at 15C.

January 18, 2019, 05:32	Viscosity and pressure - Newtonian	#1
yambanshee Senior Member Zander Meiring Join Date: Jul 2018 Posts: 125 Rep Power: 9	Good day all, I am using the simpleFoam solver with a Newtonian transport model, where only kinematic viscosity is needed (nu). After solving, my main point of consideration is pressures, which is by default given as P/rho. I am working with air at 15C so nu = 1.47e-5 mu = 1.802e-5 rho = 1.225 Would there be any negative consequence to changing the properties such that I set rho = 1, and therefore use a nu = 1.802e-5? This would mean that my pressures don't need to be multiplied by density, but I am unsure if this would cause differences in regards to the turbulence models when computing turbulent viscosity.

January 18, 2019, 07:16		#2
HenrikJohansson Member Henrik Johansson Join Date: Oct 2017 Location: Gothenburg Posts: 38 Rep Power: 10	Hi Zander, Density is not solved with simpleFoam. The effect of density is as you said pressure(in OpenFoam) = P/rho. Thus your indata for pressure shall be P divided by density of your fluid. Changing density to 1 would be unphysical if you are trying to solve air at 15C. __________________ / Henrik Johansson

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