# Stokes Drag

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 December 3, 2003, 14:18 Stokes Drag #1 Ajay Rao Guest   Posts: n/a Hello everyone , I am trying to calculate the stokes drag on a sphere held stationary in a flow at reynolds number = 0.1 particle size is 2mm dia and the outer domain I have is 12 dia ( R2/R1 = 24 ). Stokes drag claculated using the formula Drag=6*pi*Meu*radius*U0 U0 = 5.024e-5 based on Re Stokes Drag= 9.48e-10 N FLUENT gives me the Drag ( I use Report -> x dir force ) as a) 6.29 e-9 N when I do a steady case, initializing the velocity as 0 . Applying BC ( Setting X dir velcoity ) on the outer domain with U0=5.024e-5. b) 1.81e-10 N when I do a steady case but initialize the velocity as 5.024e-5 and use the same BC as above. c) 1.06e-9 when i do an Unsteady case and I run the simulation for 50 seconds. But in any case its not close enough to 9.48e-10 the stokes drag . Any ideas as to why i am off ??and what to do to get the exact stokes drag ? Thanks -A

 December 4, 2003, 11:04 Re: Stokes Drag #2 ccc Guest   Posts: n/a hi Ajay, have you raised the convergence criterion to see if results change? good luck

 December 4, 2003, 16:41 Re: Stokes Drag #3 Ajay Rao Guest   Posts: n/a yes i tried this , now my error is around 8 % ie FLUENT drag is 8 % higher than the actual stokes drag. I dont know if that is exceptable. I thought the stokes drag could be predicted quiet accurately. Thanks for the advice, Ajay

 December 5, 2003, 03:18 Re: Stokes Drag #4 ccc Guest   Posts: n/a hi Ajay, have you checked the indepence of grid and the size of domain? good luck.