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Urgent: Modeling the drag on a stationary sphere in a parabolic Pres driven pipe flow

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Old   April 8, 2009, 14:27
Default Urgent: Modeling the drag on a stationary sphere in a parabolic Pres driven pipe flow
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Farhan
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Hi,
My question is that how can I simulate to find the drag force on a stationary sphere in a cylinderical pressure driven poiseuille flow.

What I am doing is

I made sphere in a pipe
Inlet condition is parabolic using Umax*(abs(1-(r/Rmax)^2)
Outlet condition is zero average static pressure
No slip at the cylinder and the sphere with zero wall velocity on both.

When I model it I do not get the right answer as availble in literature.

Kindly help me out and tell me where I am wrong.
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Old   April 8, 2009, 20:29
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Glenn Horrocks
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Hi,

If this question is urgent then talk to your CFX support person, that's what they are paid to do. Please don't post urgent questions here.

What is the Re number based on cylinder size and sphere size? Can you describe how you have modelled it? If you post an "urgent" question with no details how are we meant to help you?

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Old   April 8, 2009, 21:20
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Farhan
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Sorry for any inconvinience. No support person is currently available that is why i had to post it on the forum.

Re is very low typical value 0.01 based on the centre line velocity of the cylindrical flow.
sphere radius is constant at 0.5 mm whereas the sphere to cylinder diameter ratio varies from 0.1 to 0.9.
Steady state without any heat transfer and turbulence model
flow inlet velocity profile is parabolic using user defined expression option
sphere and cylinder having no slip BC with zero wall velocity
Outler average static pressure is zero
Mesh is unstructured tetrahedral

anything else you want to know????

It gives a higher value I do not know why.

I once again apologize to everyone for posting an urgent question.
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Old   April 8, 2009, 23:02
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Glenn Horrocks
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Hi,

So the Re number based on the sphere is very low also?

If you can post the output file as an attachment that gives a lot of information which can help.

Have you done various sensitivity checks - mesh resolution, convergence tolerance, inlet/outlet boundary proximity, double precision etc? What is the size of the error you are currently getting? What size error do you want?

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Old   April 9, 2009, 00:36
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Farhan
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the drag force I need should be in the range of
1.2x10^-10 N but I am getting 1.6 x 10^-10 N

I think there is some problem with the application of boundary condition or modelling because with the same mesh I solved another problem which gave quite accurate result.

the file is not uploading.
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