Schemes to improve pressure drag?

CapSizer · December 2, 2009, 03:55

I'm analysing a series of 3D streamlined shapes with simpleFoam, using meshes created with snappyHexmesh. As far as I can make out, the meshes are OK, as they produce drag figures in Fluent that quite closely match what I was able to achieve with a very high quality block-structured hexahedral mesh. The Fluent results make sense, with pressure drag making up about 10% of the total drag. Re-number based on length is about 10 million, and the finess ratio is around 7. In Fluent I know that least squares interpolation combined with second order momentum differencing is required to get the accuracy. However, in simpleFoam I'm getting pressure drag that is about 4 times too high. FWIW, I'm using the SST turbulence model with wall functions, but changing the turbulence model does not make much difference here. I suspect that although I'm using higher order schemes, there is something important that I am missing. Any suggestions, please?

rcastilla · December 10, 2009, 04:39

Maybe it is a problem with wall function. Have you checked the value of yPlus?

December 2, 2009, 03:55	Schemes to improve pressure drag?	#1
CapSizer Senior Member Charles Join Date: Apr 2009 Posts: 185 Rep Power: 18	I'm analysing a series of 3D streamlined shapes with simpleFoam, using meshes created with snappyHexmesh. As far as I can make out, the meshes are OK, as they produce drag figures in Fluent that quite closely match what I was able to achieve with a very high quality block-structured hexahedral mesh. The Fluent results make sense, with pressure drag making up about 10% of the total drag. Re-number based on length is about 10 million, and the finess ratio is around 7. In Fluent I know that least squares interpolation combined with second order momentum differencing is required to get the accuracy. However, in simpleFoam I'm getting pressure drag that is about 4 times too high. FWIW, I'm using the SST turbulence model with wall functions, but changing the turbulence model does not make much difference here. I suspect that although I'm using higher order schemes, there is something important that I am missing. Any suggestions, please?

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December 10, 2009, 04:39		#2
rcastilla Senior Member Robert Castilla Join Date: Apr 2009 Location: Spain Posts: 109 Rep Power: 17	Maybe it is a problem with wall function. Have you checked the value of yPlus?