# Zero equation turbulence model velocity scale

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 February 19, 2009, 09:36 Zero equation turbulence model velocity scale #1 Kim Guest   Posts: n/a Sponsored Links Hello, I am simulating a ventilated room with inlet, outlet, and heat flux. I have tried the zero equation turbulence model for the simplicity, and the question is how to compute the velocity scale. Here's the zero equation: mu_t = rho * f_mu * U_t * l_t where U_t, the velocity scale, is the defined as the maximum velocity in the domain. Does this mean that CFX takes the maximum inlet/outlet velocity? What if it's a closed room with inlet and outlet replaced with wall BCs. Then is U_t zero? What if pressure boundary conditions are placed at the inlet and outlet? Is there a way to output this variable? I would greatly appreciate your help! Sincerely, Kim

 February 24, 2009, 17:28 Re: Zero equation turbulence model velocity scale #2 Glenn Horrocks Guest   Posts: n/a Hi, If you have problems defining a length/velocity scale then why not use SST or k-e and you don't need to define it? SST and k-e are going to give much better accuracy than a zero eqn model for room ventilation and should not add too much computational overheads. Glenn Horrocks

 February 25, 2009, 10:56 Re: Zero equation turbulence model velocity scale #3 Kim Guest   Posts: n/a Thank you for your response, Glenn. I am aware that the zero equation model is not the best option, but I tried it for the simplicity. My project involves performing Galerkin projection of the Navier-Stokes and the energy equations onto the basis (from SVD anaysis) I create from the CFD data. As a preliminary step towards doing the same to the k-e equation, I ran the model with the zero equation model since I don't have to worry about time varying viscosity just yet.

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