Wall Shear force  any suggestions on turbulence modelling
Hallo everybody
In my work i am currently calculating on a valve with a rather complex flow pattern. Highly turbulent. I am specially interested in simulating the wall shear forces as correct as possible. For this I have a couple of questions for the Forum: 1) any suggestions to the choice of turbulence model and not least the choise of wall threatment (should I use a twolayer model or just a regular lowreynolds number ke model)? 2) For the verification of the simulations I have the possibility to make velocity measurements in the main flow of the valve. Now, if the verification of the CFD calculations looks alright for the main flow, then it would not be totally wrong to presume that the CFDsimulations also give a result for the wall shear stress that approximates the once excisting in the valve?? Yours Sincerly Bo 
Re: Wall Shear force  any suggestions on turbulence modelling
(1). Try a twolayer model first. (2). The wall shear stress is very hard to predict accurately. In the complicated flow field, the main flow is more or less controlled by the continuity equation (mass conservation), while the wall shear stress is controlled by the momentum equations. you will have to match both the velocity field and the pressure field everywhere in order to get the correct wall shear stress.

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