I'm studying a fixed circular cylinder in Fluent. I'd like to impose an instantaneous constant velocity on this fixed object, as if the movement of the cylinder were quasistatic. The trouble is that for Fluent, the boundary condition on a wall corresponds a zero normal velocity. I've tried to use an udf but it doesn't work. Has anyone an idea to solve this problem ?

Hi, I had your same problem. I was not able to use transpiration because Fluent does not allow to set a normal velocity. So I used dynamic mesh. If anybody has suggestions about this topic, please let me know. Luca

Sometimes, depending on the situation, it is possible to eliminate the difficulty by reformulating the problem in a moving coordinate system. If the cylinder is moving parallel to the system's solid boundaries, then you can fix the cylinder in place and move the boundaries with the opposite velocity. If there are two solid boundaries that are moving toward one another, however, then it is true that Fluent doesn't seem to provide a capability to find the "quasi-steady" velocity in a straightforward manner.