# Initial Turbulence Conditions

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 April 4, 2013, 12:15 Initial Turbulence Conditions #1 Member     Anonymous Join Date: Dec 2011 Location: Everywhere Posts: 75 Rep Power: 5 I am doing an automotive analysis using the k-omega SST turbulence model and I have a question on initial conditions. The two values: turbulentKE turbulentOmega So to calculate these first I calculated Reynolds Number: Re = U * L / nu = 45 * 4.16 / 1.5e-5 = 12.5 E6 Then initial turbulence %: I = 0.16 Re ^-1/8 = 0.0208 Now to turbulentKE: k = 1.5 * (UI)^2 = 1.5 * (45 * 0.0208)^2 = 1.309 Now is the real question. I found 2 equations for epsilon with one being an approximation. After calculating both a get a big difference in numbers and wonder which one I should use to calculate omega. epsilon ~ (k^1.5) / L = (1.309^1.5) / 4.16 = 0.360 epsilon = (cmu^.75) * (k^1.5) * (l^-1) cmu = 0.09 (seems to be most commonly used) l = 0.07 * L = 0.07 * 4.16 = 0.2912 epsilon = (0.09^0.75) * (1.309^1.5) * (0.2912^-1) epsilon = 0.845 :::: :::: :::: epsilon = 0.360 epsilon = 0.845 So am I doing this right? If so, which epsilon value should I be using? :::: :::: :::: turbulentOmega = k / epsilon JR22 likes this.

 April 6, 2013, 00:09 #2 Senior Member   Fumiya Nozaki Join Date: Jun 2010 Location: Yokohama, Japan Posts: 170 Rep Power: 7 Hi plucas, For external flows the freestream effective viscosity will be on the order of laminar viscosity so small values of are appropriate, say = 0.1 – 0.2: For k-omega SST turbulence model, the turbulent eddy viscosity is computed from: You can estimate value using the above equations. References: Hope this helps, Fumiya plucas and JR22 like this.

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