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-   -   Why the drag coefficient has negative value? (http://www.cfd-online.com/Forums/star-ccm/84361-why-drag-coefficient-has-negative-value.html)

suiede January 27, 2011 03:55

Why the drag coefficient has negative value?
 
Hi, all. I'm trying 2D simulation of NACA0012 in re=2.88e6. I'm using k-w sst gamma re theta in steady, stationary condition.

I had have a good result in using k-e solver, but in this case, it shows me negative value of drag coefficient.

I have no idea about it, please help me to solve this problem.

Thank you.

naimishharpal January 28, 2011 21:19

Make sure that you are defining the Drag force in Positive-X axis (downstream) direction.

BASU HM December 4, 2013 01:39

hello every one,i'm also using same turbulence model k-omega sst,im trying to simulate 3D ship in viscous flow under open channel wave BC,multiphase,inlet velocity,outlet pressure,but im getting negative Drag, Lift and moment coefficient.net mass flow rate is not zero.......suggestion please

ggulgulia December 4, 2013 07:36

Hey Suide

The drag value has nothing to do with the turbulence model as far as you have selected the right turbulence model ( I know this sounds a little ambiguous)

In star CCM+ there are two directions. Make sure the direction of the report is along the downstream direction of flow.

SST K-w models should be used for low RE flow to capture the near wall phenomena. If your boundary layer is not that important, then I suggest you go with realizable K-e turbulence model.


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