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-   -   drag predicitions (http://www.cfd-online.com/Forums/fluent/28493-drag-predicitions.html)

hakeem April 30, 2001 06:18

drag predicitions
 
Hi everybody ...

As most of you are aware, for creeping (slow) flow of Newtonian fluid moving over a sphere the ratio of pressure

coefficient to viscous coefficient should be ~ 0.5. Unfortunately, when I use Fluent 5.3, it is not the case. The

total coefficient is right, namely, for Re = 0.01, the total drag coefficient should be ~ 2400. I got it 2400.8.

However the ratio of pressure coefficient to viscous coefficient is 640.66629/1760.1434 = 0.36. Could anyone

think of possible reason.


Xiao Hu May 2, 2001 12:33

Re: drag predicitions
 
I would do a mesh adaption based on pressure gradient. And then do a second mesh adaption based on velocity gradient. After those adaptions, run it again and see if you observe any changes.

gangxia May 7, 2001 21:12

Re: drag predicitions
 
I have the same experience. In most cases, mesh adaption is the key point,because the accuracy of viscous coefficient rely on the mesh quality. I would inspect into the velocity profile and see if the velocity gradient in boundary layer is smooth. That's important, I think.


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