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 V. G. Ferreira August 13, 2000 11:55

Mean Wall Stress

Hi Dear Friends,

By using the wall-function approach, how can I obtain the mean wall stress in a turbulent bondary layer? In reality, I need of the value of the friction velocity in order to use the classic k-epsilon model.

 John C. Chien August 13, 2000 13:48

Re: Mean Wall Stress

(1). There have been many discussions related to the wall functions before. You can simply use the search command at the top right of the page to read the previous messages. In the edit box of the search , just type in wall function, and it will list all the messages which contain the key word. (2). It used to be limited to those PhD candidates' research subject,in using cfd and wall functions. But this "black art" is begining to have larger impact because of the use of commercial codes by non-phD candidates. (3). In turbulent flows, the handling of the turbulent boundary is one of the most difficult part of cfd. In the Euler equation, you don't need to know anything about the turbulence modeling at all. The same is true for those doing the structure analysis. (4). Unfortunately, our knowledge about the turbulent flow is very limited. I would say that the use of wall function by non-professional for general flow problem will always lead to wrong solutions, not to mention about the mesh independent solution problem related to the implementation of the wall function through the black art approach. (5). The use of the low Reynolds number model will eliminate the need to use the wall function, but the right model for the right problem is hard to come by. (6). The field of turbulence modeling is still wide open. In other words, we don't know what we are doing. (7). Please read all of the previously posted messages first. If you still have questions, feel free to ask .

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