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-   -   K - Epsilon values (http://www.cfd-online.com/Forums/fluent/28267-k-epsilon-values.html)

 David March 4, 2001 18:59

K - Epsilon values

how do i pick the k and epsilon values to use for an aerofoil - transonic turbulent.

all i know is the reynold number and the mach number and the aerofoil dimensions.

thanks

 John C. Chien March 4, 2001 21:15

Re: K - Epsilon values

(1). You don't just pick k and epsilon, you have to define the free stream condition before you can solve your problem. (2). The turbulence kinetic energy can be measured, so, you must set it to the measured condition you are trying to simulate. Otherwise, you just define it for your problem. (say a few percent of the free stream velocity. since what you don't know can hurt you, I suggest that you review the turbulence modeling with two-equation models first.) (3). The epsilon part is more complicated to understand, so, you need to read the user's guide first, there must be a formula you can use. Sometimes, it is related to the length scale you select. Since everyone is doing his own thing these days, I am not sure what is used in the code. (4). Talk to the support engineer, or define your own numbers and check the results. Part of it, like k is real, part of it ,like epsilon is not. So, you have to be careful in defining these numbers. In other words, sometimes the results are sensitive to these values.

 Flav March 5, 2001 10:31

Re: K - Epsilon values

It depends on the experimental data you have. If you don't have values for k and epsilon, remember that you can specify the turbulence data by means of "intensity and length scale" instead of "k and epsilon".

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