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Old   November 2, 1999, 13:48
Default solid surface boundary condition
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qlr
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Hello, everyone:

I use high Reynold number k-epsilon model to solve a flow past a flat plate. to assign the boundary condition at the wall, I just use those points which are just beyond the viscous sublayer and within the law of wall region. As we know, the u,k,and epsilon at this region are related with friction velocity as u/u*=ln(Eyu*/mu)/kappa, k=u*/sqrt(cmu), epsilon=u*^1.5/(kappa*y), where u* is friction velocity. I want to know how to get u, k, epsilon at this region, since the u* is also unknown. Thanks in advance.

qlr
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Old   November 2, 1999, 17:24
Default Re: solid surface boundary condition
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Valdemir G. Ferreira
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Hi qlr,

You must know u* by solving the non-linear equation u/u* = ln(Eyu*...). Use the Newton method.

Valdemir.
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Old   November 2, 1999, 17:51
Default Re: solid surface boundary condition
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qlr
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Hi,Valdemir

How can use u/u*=ln(Eyu*/mu) to solve u*, since I use this equation to get u at the law of wall region. Another problem is: since I use the law of wall region as the wall boundary, how can I know which y value is good to set as the wall boundary. Thanks.

qlr
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Old   November 2, 1999, 17:58
Default Re: solid surface boundary condition
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Valdemir G. Ferreira
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You must solve this equation for X=u*/u. The boundary condition for k and epsilon depend on u*. See the book of Pletcher, for example. More about it, send me E-mail.

Valdemir.
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Old   November 3, 1999, 00:09
Default Re: solid surface boundary condition
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Jin Wook LEE
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1) Best way : another iteration loop in the given global iteration(ITER=N)

2) General way : use the value of previous iteration(ITER=N-1) to get the value of current step(ITER=N)

Sincerely

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