You can see in the attached for what I am talking about. I have a counter flow between two fluids which are separated by a wall (solid domain). I'm trying to write a UDF , in which I am coping the velocity of the outlet face to inlet. But I got more problem in that code.nSo, I am looking for better way to solve this problem. or how I can copy the velocity at outlet face to inlet to make as periodic. Another issue is with Temerature.nnBest regards.nAbbasnn