# symmetry boundary conditon problem

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 May 13, 2013, 12:35 symmetry boundary conditon problem #1 Senior Member     hamed Join Date: Apr 2009 Posts: 148 Rep Power: 9 Hi dear friendsI am modeling flow through a butterfly valve in a pipe .i have used a symmetry boundary condition splitting the pipe into half and also a velocity inlet and a pressure outlet .i was wondering what happens to the results like torque acting on butterflye valve's disk? Does cfx calculates torque for whole disk or just reports the torque for just half of disk? What about the pressure loss across the valve? I actually want to calculate the hydrodynamic torque coefficient according to following formula Ct=T/(delta P*D^3) Should I multiply the torque which gained in CFX-post bye 2?what about pressure?

 May 13, 2013, 17:51 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 CFX returns the torque for half the disk in this case. It just integrates over the surface and the surface is half as big so you get half the force/torque. Pressure loss is unaffected (providing the assumption of symmetry is valid). The best way of working these things out - if you are unsure is to run a little test case and find out. The best way of learning is always to figure it out for yourself.

 May 14, 2013, 00:36 #3 Senior Member     hamed Join Date: Apr 2009 Posts: 148 Rep Power: 9 if u are right , my problem turns to a disaster !the torque coefficient calculated from experimental data is much closer to torque coefficient calculated for half disk from CFX!!!i am really far away from the target !what should I do !(:O my hands are shaking!)

 May 14, 2013, 00:56 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 You had better start reading the FAQ then: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F hmasenger likes this.

 May 14, 2013, 02:48 #5 Senior Member     hamed Join Date: Apr 2009 Posts: 148 Rep Power: 9 tnx a lot grrocks. your guids always helped me .I hope I will pass this problam again

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