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lenght and number of nodes for an orifice meter flow problem - k-eps model

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Old   November 15, 2009, 04:49
Default lenght and number of nodes for an orifice meter flow problem - k-eps model
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I have to state fully the mathematical problem of turbulence in a pipe including an orifice plate meter. I know inlet pressure, and Temp, diameters, turbulence lenght and turbulence intensity. My Re est 300000. I have decided to use the stanstard k-eps model, and a near wall model (even I don't know if I have to use near-wall model or wall functions, what is the difference? and do I have to replace all my equations or it's a new model just for the zone near of the wall??)
Secondly I have some difficulties with the boundary conditions? Do I have to five the velocity at inlet (U1, P1, k and eps)? Moreover how to find k and eps at the inlet, is it computed automatically??

Finally, I have to find the adapted lenghts before and after the orifice to have a fully developed flow, knowing my number of nodes should not exceed 10000, what does it mean? Apparently I have to reduce my first lenght L1 found thanks to the empirical equations L = 4.4 x Re^(1/6) x D and adapt my lenght to have a fully developed flow before and after the orifice but also a adapted grid.

Please, I need help.
Thanks so much
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