# Validation using flow around Cylinder

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 November 12, 2015, 11:17 Validation using flow around Cylinder #1 New Member   Karlis Join Date: Nov 2015 Posts: 1 Rep Power: 0 Dear all, I am a new user to OpenFoam, so please forgive me, should I post something silly. Recently I have been trying to validate my case by using flow around cylinder as reference, however, I cannot seem to get any reasonable values for Cd, neither for low nor high Reynolds numbers. FYI, the way I fix Re is simply by varying velocity (from the formula Re=l*v/nu). For this simulation I use a cylinder with diameter and length of 40mm. The Reynolds number is fixed at ~90, with nu being 0.000015 and calculated velocity of 0.03375 m/s. Naturally, I have also edited forceCoeffs file with the appropriate values. Additionally, I am using simpleFoam with kOmegaSST turbulence model. If someone could look at this case, I would really appreciate it. Also, do I need to change turbulent viscosity (nut) values, to obtain the correct results? Finally, please find the case files below. http://www.filedropper.com/90tar Thank you for your help! EDIT: I managed to increase the precision of my results by applying a different (presumably correct) turbulentKE value, however, I have another question now. How do you calculate the turbulent length scale? Also, are the formulas below correct, when used with simpleFoam? turbulentOmega = k / epsilon k = 1.5 * (UI)^2 I = 0.16 Re ^-1/8. epsilon = cmu*k^1.5/l (where l is turbulent length scale) Last edited by CXI; November 13, 2015 at 07:13.

November 16, 2015, 07:21
#3
Member

Davi Barreira
Join Date: Apr 2014
Location: Fortaleza
Posts: 76
Rep Power: 9
Just complementing the response given by Wouter.

The flow past a circular cylinder may seems as a simple case to validate, but it is actually quite complex. Some papers published the results trying to validate k-wSST for flow past a cylinder at various reynolds, but the results are not very good (I actually tried myself). I'm posting here my results using three different RANS models, so perhaps it saves you some time. The main problem is in the intermediate values of Reynolds, in which the boundary layer is partially laminar and partially turbulent.

Regarding the boundary conditions. For external flow, you usually use turbulence intensity of something around 0.5% ~ 1%, then you calculate your k, epsilon and omega. The length scale is 0.07*L, in which L is the characteristic length (in this case, L is the diameter of your cylinder).

Let me know if you make any progress, cause Im still working on this case.
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 November 17, 2015, 05:30 #4 New Member   Aloha Join Date: Sep 2015 Posts: 6 Rep Power: 7 I think maybe you can try laminar flow first

 Tags cylinder flow, nut, validations