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turbulent & laminar result comparison

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Old   November 24, 2006, 10:29
Default turbulent & laminar result comparison
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may i know if it makes sense to compare laminar and turbulent flow results? i've got a published result which is simulated assuming turbulent flow at Re~2x10^4. I tried to follow its parameters but using laminar flow. The results are different (my cd is twice of his).

so, is there something wrong with my solver (assuming his is correct) or the results can't be compared directly.

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Old   November 25, 2006, 06:25
Default Re: turbulent & laminar result comparison
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Dear Quarkz,

To use a laminar code for a turbulent flow, does not capture the true flow physics. It is evident that for a separated turbulent flow the drag would be much more than for the laminar flow, and viceversa if the flow is attcahed. This is evident becase laminar flows are more prone to flow separation, and a larger drag result, while the turbulent flow is less prone to separation resulting in comparitively lesser drag. If the turbulent flow also separates, it would result in much larger drag when compared to a separated laminar flow. If the simulation is a turbulent unseparated flow, then it is quite possible that both your solver and his results are correct; it is just not fair from the flow physics point of view to compare a laminar simulation with a turbulent one. However, if you still want to make some rough comaprison, run an Euler code and get the prssure distribution, and it must match quite well with the published turbulent result(if he has provided it in tha paper). That would help you to have a quick check- both on the sokver and the published result you are attempting to have a comparison with. A direct comparison of Cd with the published result would necessarily requiare simulating turbulence via RANS using a 1-eqn Spalart-Allmaras or a 2eqn k-w SST model.

Hope this helps

Regards, Ganesh
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