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-   -   Negative drag at low y+ (http://www.cfd-online.com/Forums/cfx/26143-negative-drag-low-y.html)

rc2v07 July 23, 2008 19:41

Negative drag at low y+
 
Hi,

Im having a problem while doing some mesh independence studies on a foil with a bulb attached on the end. I have completed a mesh independence study with y+ ~ 30 and had goodish drag (at lest positive) now I am looking at Y+ independence of the SST model with the same domain and mesh apart from the boundary layer resolution and the drag values have becom negative. This looks to be down to the viscous drag becoming larger and the pressure drag dropping by nearly hlf compared to the high Y+ results. Any suggestions would be great!

Thanks.

Glenn Horrocks July 23, 2008 22:52

Re: Negative drag at low y+
 
Hi,

Have a look at the results and see if you can find any unusual flow features, such as an unexpected recirculation.

Also consider using the turbulence transition model for your meshes with y+ around 1.

Also don't forget spanwise and radial mesh density in your analysis.

Glenn Horrocks


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