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-   -   finding drag coefficient in laminar flow (http://www.cfd-online.com/Forums/star-cd/65301-finding-drag-coefficient-laminar-flow.html)

ksatpathy June 11, 2009 00:22

finding drag coefficient in laminar flow
 
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.

abdul099 October 19, 2009 11:46

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

ksatpathy October 22, 2009 04:05

reply
 
thanks a lot mr.abdul for your kind information.

regards,
satpathy.

moleroaj January 14, 2010 11:43

Question
 
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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