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June 13, 2018, 07:08 |
Sphere at Re=1e+7
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#1 |
Member
Danny
Join Date: Jun 2018
Location: Rome, Italy
Posts: 36
Rep Power: 8 |
Hi,
i'm trying to simulate a 3D-Sphere in water at Reynolds Number 1e+7 (i.e. 10'000'000) in Star-CCM+, but at the moment i'm not achieving the correct CD result of about 0.19. My physics options are: Velocity Inlet V = 10.014 m/s Density rho= 998.6 kg/m3 Sphere Diameter D = 1m Turbulence Model = K-w Time = Steady Fluid Type = Liquid. The Mesh options on the body are: Number of Prism Layer = 10 Stretching Factor = 1.5 Can someone please help me? I really appreciate much. -Danny- |
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August 28, 2018, 14:28 |
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#2 |
Senior Member
mauricio
Join Date: Jun 2011
Posts: 172
Rep Power: 18 |
Hey.
Might be a bit 2 late, but anyway, here it goes: To correctly derive any force coefficients in CFD you need to solve the boundary layer, which means that you need to use low Reynolds models and have y+< 5 (maybe 1) around the surface of the sphere, which is really computational expansive for high Reynolds. Say you have 10m/s of reference speed but the maximum speed near the surface is 3x that, so, for 30m/s you'd need the first cell to be approx. 1e-5<h<1e-6m tall. Considering the 1m diameter, we are talking about some really fine mesh. A way around would be to try your best to have 30 <y+<100 for the first layer of elements around the sphere and use the Hi Re kw SST turbulence model and hope for the best. You could also try a transient solver and average the results of the last 20-50 values, after convergence. Also, check for boundary interference in the results (narrow domains). The stretch value might be a bit high for hydrodynamics, try the default 1.2. gl l8r
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Best Regards /calim "Elune will grant us the strength" |
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August 29, 2018, 03:03 |
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#3 | |
Member
Danny
Join Date: Jun 2018
Location: Rome, Italy
Posts: 36
Rep Power: 8 |
Quote:
it's not late at all. Thanks for your suggestions, much appreciated. I'm trying to do the mesh with your advices. Can i send you my results? Really thanks again. |
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August 29, 2018, 07:34 |
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#4 |
Senior Member
mauricio
Join Date: Jun 2011
Posts: 172
Rep Power: 18 |
Hi.
I could try to have a look! Send as much info as you can. You could send the model file too without mesh and/or results so we can get a small file. If you could also send your reference with the problem description and the target CD value that's good too. l8r
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Best Regards /calim "Elune will grant us the strength" |
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May 17, 2022, 11:40 |
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#5 |
New Member
Join Date: May 2022
Posts: 1
Rep Power: 0 |
Hi ,
Im running into the same issue of underpredicting the Cd of a sphere at High Re cases (1e6). Were you able to figure out a set-up that gets close to correlating to literature. |
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drag coefficient, mesh 3d, star ccm+ |
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