# Sphere at Re=1e+7

 Register Blogs Members List Search Today's Posts Mark Forums Read

 June 13, 2018, 07:08 Sphere at Re=1e+7 #1 Member   Danny Join Date: Jun 2018 Location: Rome, Italy Posts: 36 Rep Power: 6 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-

 August 28, 2018, 14:28 #2 Senior Member     mauricio Join Date: Jun 2011 Posts: 171 Rep Power: 17 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

August 29, 2018, 03:03
#3
Member

Danny
Join Date: Jun 2018
Location: Rome, Italy
Posts: 36
Rep Power: 6
Quote:
 Originally Posted by calim_cfd 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
Hey,
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.

 August 29, 2018, 07:34 #4 Senior Member     mauricio Join Date: Jun 2011 Posts: 171 Rep Power: 17 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 __________________ Best Regards /calim "Elune will grant us the strength"

 May 17, 2022, 11:40 #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.

 Tags drag coefficient, mesh 3d, star ccm+