# udf boundary condition (vorticity)

 Register Blogs Members List Search Today's Posts Mark Forums Read

 May 18, 2020, 08:37 udf boundary condition (vorticity) #1 New Member   yassine Join Date: Apr 2020 Posts: 7 Rep Power: 2 Hi I don't know how to write udf boundary condition for vorticity .I bring to your attention that my work has been done on the nanofluid and more precisely I am working on the configuration of Rayleigh Bénard (natural convection). Fig. 1 shows a schematic diagram of the Rayleigh-Bénard (RB) problem. For the RB problem, the distance between the upper cold and lower hot plates is defined by H and the width of the top and bottom plates is defined by W. The plates’ width W is considered infinite and treated by a periodicity boundary condition. The bottom plate is maintained at a hot temperature TH=50 C whereas the top plate is maintained at a cold temperature TC=22 C. The fluid enclosed between the plates is water based nanofluid containing CuO nanoparticles. The nanofluid is assumed incompressible and the flow is assumed as laminar and twodimensional. thanks Inkedgh_LI.jpg

 May 18, 2020, 09:08 boundary using UDF -vorticity- #2 New Member   yassine Join Date: Apr 2020 Posts: 7 Rep Power: 2 Can anyone tell me how to apply dv/dx=0 and omega=du/dy at a boundary using UDF. [v=delta(psi)/delta(x) u=-delta(psi)/delta(y)] Inkedgh_LI.jpg

 May 18, 2020, 09:15 Wall boundary #3 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,554 Blog Entries: 1 Rep Power: 28 Fluent uses momentum conservation and not vorticity or Poisson's equation. The equation you have is written in terms of streamfunction and implies no-slip condition. That is the default condition in Fluent and you don't need to do anything yassine.bt likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared on the Forum

May 18, 2020, 09:52
#4
New Member

yassine
Join Date: Apr 2020
Posts: 7
Rep Power: 2
Quote:
 Originally Posted by vinerm Fluent uses momentum conservation and not vorticity or Poisson's equation. The equation you have is written in terms of streamfunction and implies no-slip condition. That is the default condition in Fluent and you don't need to do anything
But I fond in the results that dv/dx is not equal 0

 May 18, 2020, 09:55 Gradient #5 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,554 Blog Entries: 1 Rep Power: 28 That won't be 0 and should not be. Look at the document you shared. The condition is NOT but , implying velocity is 0. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared on the Forum

May 18, 2020, 10:05
#6
New Member

yassine
Join Date: Apr 2020
Posts: 7
Rep Power: 2
Quote:
 Originally Posted by vinerm That won't be 0 and should not be. Look at the document you shared. The condition is NOT but , implying velocity is 0.
I think psi=0 that mean (noslip) and omega(rotational flow)??

 May 18, 2020, 10:15 Noslip #7 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,554 Blog Entries: 1 Rep Power: 28 That's correct and no-slip implies velocity is 0 at the wall, i.e., the default condition in Fluent. As far as rotation is concerned, in a 2D case, rotation is possible only around z-axis, so, where is a function of velocity gradient. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared on the Forum

May 18, 2020, 10:21
#8
New Member

yassine
Join Date: Apr 2020
Posts: 7
Rep Power: 2
Quote:
 Originally Posted by vinerm That's correct and no-slip implies velocity is 0 at the wall, i.e., the default condition in Fluent. As far as rotation is concerned, in a 2D case, rotation is possible only around z-axis, so, where is a function of velocity gradient.
so I don't need to do anything
okay thank you so much