# How to calculate velocity at cell face?

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 November 6, 2012, 23:55 How to calculate velocity at cell face? #1 New Member   Trent Join Date: Nov 2012 Posts: 3 Rep Power: 4 Currently I am looping over all the cells in my 2-D geometry to find u and v at each cell; however, at the corners and boundaries where I am getting recirculation, the math isn't coming out correctly using the u and v values taken from Fluent. I would assume that the velocity at the centroid is just interpolated from the face velocities so I am trying to find a way to use the velocities at the faces instead; is there a way to do this? I tried writing this quick code to test this but I am getting a Fluent access error when I try to run it: #include"udf.h" #include"metric.h" #include"stdio.h" #include"math.h" #include"stdlib.h" #include"mem.h" DEFINE_ADJUST(velocity_profile_face,d) { Thread *t; face_t f; real cent[2]; double centr_x, centr_y; double vel_x, vel_y; thread_loop_f(t,d) { begin_f_loop(f,t) { F_CENTROID(cent,f,t); centr_x = cent[0]; centr_y = cent[1]; vel_x = F_U(f,t); vel_y = F_U(f,t); printf("%f, %f\n", vel_x, vel_y); } end_f_loop(f,t) } } After reading some other threads I saw that this only works for boundaries so I may not be able to do it this way. Is there a way I can get this to work? If not are there any other macros that will help me do what I want? If not I may need to play around with the math and see if I can get it to work better instead. Thanks for your help.

November 7, 2012, 02:42
#2
Senior Member

Ji Junjie
Join Date: Feb 2010
Location: Shanghai, China
Posts: 106
Rep Power: 7
F_U, F_V are only valid for boundary.

For those face in the domain, you can use the averaged value of F_C0 and F_C1.

Quote:
 Originally Posted by tjmartian Currently I am looping over all the cells in my 2-D geometry to find u and v at each cell; however, at the corners and boundaries where I am getting recirculation, the math isn't coming out correctly using the u and v values taken from Fluent. I would assume that the velocity at the centroid is just interpolated from the face velocities so I am trying to find a way to use the velocities at the faces instead; is there a way to do this? I tried writing this quick code to test this but I am getting a Fluent access error when I try to run it: #include"udf.h" #include"metric.h" #include"stdio.h" #include"math.h" #include"stdlib.h" #include"mem.h" DEFINE_ADJUST(velocity_profile_face,d) { Thread *t; face_t f; real cent[2]; double centr_x, centr_y; double vel_x, vel_y; thread_loop_f(t,d) { begin_f_loop(f,t) { F_CENTROID(cent,f,t); centr_x = cent[0]; centr_y = cent[1]; vel_x = F_U(f,t); vel_y = F_U(f,t); printf("%f, %f\n", vel_x, vel_y); } end_f_loop(f,t) } } After reading some other threads I saw that this only works for boundaries so I may not be able to do it this way. Is there a way I can get this to work? If not are there any other macros that will help me do what I want? If not I may need to play around with the math and see if I can get it to work better instead. Thanks for your help.

 November 8, 2012, 01:45 #3 New Member   Trent Join Date: Nov 2012 Posts: 3 Rep Power: 4 Thank you, I hadn't seen those macros before. I think I can get what I need from there.

 Tags face cells, velocity components

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