# Question about Low Re turbulence modelling.

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 May 28, 1999, 11:49 Question about Low Re turbulence modelling. #1 ghlee Guest   Posts: n/a Hi! Friends. I had implemented the Chien's low Re Number Turbulence Modelling . But I had a problme to calculate the dimensionless distance, y+. y+ is generally expressed in the following form. y+ = u* y/nu In above expression, friction velocity, u* ,is equal to sqrt(tau_w / rho ). What is the concrete definition of tau_w ? Would you like to inform me the implementation method of tau_w? For example, as laminar flow, does tau_w have only the form, mu (partial U /partial y)? Is it right? Thank you.

 May 28, 1999, 19:29 Re: Question about Low Re turbulence modelling. #2 David Creech Guest   Posts: n/a y+ is the same for the Low K-e model as it is for the standard K-e model: y+ = (((density^2 * Cmu^(1/2) * K)^(1/2))/viscosity) * (distance from wall) where Cmu is the constant 0.09 and K is the kinetic energy. Remember that you need a very fine mesh at the wall for the low K-e model, usually with y+ < 1. David Creech CFD Literature CFX User Subroutine Archive

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