CD coefficient for a Sphere at Re=1e+7

danny9019 · July 9, 2018, 03:41

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 = Spalart-Allmaras
Time = Steady
Fluid Type = Liquid.

The Mesh options on the body are:
Number of Prism Layer = 20
Thickness of the first element = 1e-7m
Prism Layer thickness = 1cm

Can someone please help me? Some advices are appreciated.
I really appreciate much.

P.S
K-w and K-epsilon have not shown any convergence

-Danny-

fluid23 · July 9, 2018, 09:47

Is this steady or unsteady?

danny9019 · July 9, 2018, 09:48

Quote:

Originally Posted by fluid23

Is this steady or unsteady?

The simulation is steady

fluid23 · July 9, 2018, 09:56

At that Re your flow is going to have an unsteady wake. Change your simulation over to unsteady and give it an appropriate time step, you should see at least some improvement. You will want to make sure that you setup a plot or data file of cd vs time so you can extract the oscillating drag value over a few periods after it has 'converged'.

danny9019 · July 9, 2018, 10:20

Quote:

Originally Posted by fluid23

At that Re your flow is going to have an unsteady wake. Change your simulation over to unsteady and give it an appropriate time step, you should see at least some improvement. You will want to make sure that you setup a plot or data file of cd vs time so you can extract the oscillating drag value over a few periods after it has 'converged'.

For my purpose i have to run the analysis in steady mode

fluid23 · July 9, 2018, 10:21

Then you should expect to get the wrong drag value.

July 9, 2018, 03:41	CD coefficient for a Sphere at Re=1e+7	#1
danny9019 Member Danny Join Date: Jun 2018 Location: Rome, Italy Posts: 36 Rep Power: 7	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 = Spalart-Allmaras Time = Steady Fluid Type = Liquid. The Mesh options on the body are: Number of Prism Layer = 20 Thickness of the first element = 1e-7m Prism Layer thickness = 1cm Can someone please help me? Some advices are appreciated. I really appreciate much. P.S K-w and K-epsilon have not shown any convergence -Danny-

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July 9, 2018, 09:47		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	Is this steady or unsteady?

July 9, 2018, 09:56		#4
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	At that Re your flow is going to have an unsteady wake. Change your simulation over to unsteady and give it an appropriate time step, you should see at least some improvement. You will want to make sure that you setup a plot or data file of cd vs time so you can extract the oscillating drag value over a few periods after it has 'converged'.

July 9, 2018, 10:21		#6
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	Then you should expect to get the wrong drag value.