# finding drag coefficient in laminar flow

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 June 11, 2009, 00:22 finding drag coefficient in laminar flow #1 New Member   kamal Join Date: Jun 2009 Posts: 2 Rep Power: 0 Sponsored Links hi all, i am doing the flow analysis across a cylinder (2d laminar flow).i am facing the problem in calculating the drag coefficient.it is not matching (whatever the value comes from the erd file in star-cd)with the analytical result. i have few doubts. 1.whether the erd file is valid only for turbulent case 2.what is the definition of tx,tyforce in the erd file in star-cd an how to get cd and cl from tx and ty force. 3.whether any other method is there in calclation of drag coeff. regards. Last edited by ksatpathy; June 11, 2009 at 00:28. Reason: to get more accurate idea

 October 19, 2009, 11:46 #2 Senior Member   Join Date: Oct 2009 Location: Germany Posts: 637 Rep Power: 14 hi ksatpathy, a little bit late, but maybe it will help anyway. maybe there's some other user searching the forum... 1) erd-file should be valid for laminar and turbulent flow 2) the erd-file looks like sx, sy, sz, nx, ny, nz, tx, ty, tz with sx = shear force in x-direction nx = normal force in x-direction tx = total force in x-direction other directions accordingly directions according to coordinate sys 1 in pro-star calculate the lift and drag coefficients like you would do it in the analytical calculation. i think, you have used the formula to get the analytical solution. 3) i don's know any other methods maybe your solution differs from the analytical solution, because it is a unsteady problem. there will be a karman vortex street behind the cylinder. the seperating vortices will cause a oscillation of the forces, while you're looking on just one value (printed in the erd-file). try a transient simulation and repeate the calculation with the time averaged values. regards

 October 22, 2009, 04:05 reply #3 New Member   kamal Join Date: Jun 2009 Posts: 2 Rep Power: 0 thanks a lot mr.abdul for your kind information. regards, satpathy.

 January 14, 2010, 11:43 Question #4 New Member   Alexander Molero Join Date: Jan 2010 Posts: 1 Rep Power: 0 Can you help me to find drag coefficients in laminar flow to irregular shape (Underwater Vehicle)? Any book or Paper (in this mean, teorically)? And if i can use the model 3D-CAD (generated in Wildfire Pro-Engineering) in CFX-Post (in this mean, estimated)? Regards, Alex

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