# k-w turbulence model

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 January 6, 2003, 13:59 k-w turbulence model #1 Aaron Guest   Posts: n/a Sponsored Links Recently I have been investigating the Wilcox k-w turbulence model, and I have a question that hopefully someone(s) can help me with. Wilcox cites the A.A. Townsend approximation for k as k~t^(-n). I am unclear about what time span the "t" is referring to. Looks like the units don't match, though I'm not sure if they have to in this case. An explanation of the equation and the "t" would be greatly appreciated. Thanks in advance.

 January 7, 2003, 15:21 k-w turbulence model: update #2 Aaron Guest   Posts: n/a After reviewing the equation, my colleagues and I can only conclude that the "t" is actually a "Tau" or a stress tensor without subscripts, and not a time scale or time span. So at a minimum, its a confusing simplification, and possibly a typo. Any comments?

 January 8, 2003, 06:33 Re: k-w turbulence model: update #3 Alec Browne Guest   Posts: n/a I'm assuming you're referring to Wilcox's turbulence and CFD book published by DCW industries. They have a web page devoted to known typos, and reporting newly-discovered ones: http://www.dcwindustries.com/typos.htm I suggest you check it out! Good luck

 January 8, 2003, 21:59 Re: k-w turbulence model: final word #4 Aaron Guest   Posts: n/a After sharing e-mails with the author, I've learned that the equation is correct as written k~t^(-n) and t is indeed time. The time scale for this t is infinity and leads to the asymptotic solution for k.

 January 20, 2003, 10:58 Re: k-w turbulence model: final word #5 Bredberg Guest   Posts: n/a Townsend gives the relation k~t^-n for the (initial) decaying (grid) turbulence and give n the value = 1.25+-0.06. Note that n rises to 2.5 in the final decay. This physical behaviour is one (good) reason for introducing turbulence govern (NOT y+) damping functions. Wilcox and others uses this relation to set the value of the coefficient for the destruction term (C_eps2, beta) in the epsilon/omega-equation. /Jonas

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