constant effective viscosity

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jean marais
Posts: 175

constant effective viscosity

Postby jean marais » Fri May 16, 2014 6:21 am

"Alternatively, you may consider using the constant effective viscosity turbulence model with a relatively high turbulent viscosity or turbulent viscosity multiplier but bear in mind that this will introduce an artificially high level of diffusion into the flow and also, the constant effective viscosity model is incapable of modelling the transport of turbulence."

Is the diffusion referenced refering to velocity diffusion or temperature diffusion?
Steve Potter
Posts: 646
Location: newcastle

Postby Steve Potter » Tue May 27, 2014 8:48 am

Hi Jean,

The turbulent or eddy viscosity is applied to both the energy and momentum equations and so use of the constant effective viscosity model will increase the diffusion of both heat and momentum throughout the domain.

The main difference between the constant effective viscosity model and the k-e turbulence model is that the latter calculates a turbulent viscosity for each cell throughout the domain using an additional couple of equations (one for turbulent kinetic energy and the second for the dissipation rate) whereas the constant effective viscosity model just employs a multiplier (applied to the molecular viscosity) to calculate the same value of turbulent viscosity for every cell in the domain.

Steve
designbuilderbig
Posts: 44

Postby designbuilderbig » Tue May 03, 2016 1:37 pm

I hope this has been asked before...how does one guess a good value for the constant effective viscosity. Can the model output me the results of this variable using the effective aggrigate average using the k-e turbulence model and then if the values don't "range" widely (due to only a few cells with high turbulance) somehow calculate a good guess.

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