# Re: Outlet Boundary condition CFX

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 February 4, 2011, 02:47 Re: Outlet Boundary condition CFX #1 New Member   creddy Join Date: Aug 2010 Location: Kanpur/UP/India Posts: 25 Rep Power: 8 Hi, (1).Can any one tell me, how I can specify zero gradient boundary condition at OUTLET for Velocity, Pressure and Temperature in CFX. (2). How to specify shear-stress free boundary condition in CFX. Here I am trying to simulate single phase buoyant flow. Thanks in advance

 February 4, 2011, 06:30 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,726 Rep Power: 99 You cannot specify zero gradient for both velocity and pressure. Either specify velocity and the solver works out the pressure or specify pressure and the solver works out the velocity. You can set zero gradient on velocity, pressure and temperature using a symmetry plane. By stress free do you mean fully developed?

February 4, 2011, 07:43
#3
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creddy
Join Date: Aug 2010
Location: Kanpur/UP/India
Posts: 25
Rep Power: 8
Quote:
 Originally Posted by ghorrocks You cannot specify zero gradient for both velocity and pressure. Either specify velocity and the solver works out the pressure or specify pressure and the solver works out the velocity. You can set zero gradient on velocity, pressure and temperature using a symmetry plane. By stress free do you mean fully developed?
Glenn thnx for u r reply

Stress free refers to the shear stress at the surface is zero.

Can you please tell me in CFX how can I specify zero-Gradient Temperature using outlet boundary condition...because there is no option to specify BC for temperature in outlet.......

 February 5, 2011, 05:58 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,726 Rep Power: 99 CFX uses the convected temperature at the outlet. Nothing else makes any physical sense. That is why you do not have any options.

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