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

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 April 8, 2009, 14:27 Urgent: Modeling the drag on a stationary sphere in a parabolic Pres driven pipe flow #1 New Member   Farhan Join Date: Mar 2009 Posts: 6 Rep Power: 17 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.

 April 8, 2009, 20:29 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,727 Rep Power: 143 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? Glenn Horrocks

 April 8, 2009, 21:20 #3 New Member   Farhan Join Date: Mar 2009 Posts: 6 Rep Power: 17 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.

 April 8, 2009, 23:02 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,727 Rep Power: 143 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? Glenn Horrocks

 April 9, 2009, 00:36 #5 New Member   Farhan Join Date: Mar 2009 Posts: 6 Rep Power: 17 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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