Circular or “ring manifolds” are used to solve a variety of problems, from feeding fuel and/or oxidizer into an axially symmetric combustion chamber where there is one inlet and multiple outlets, to water fountains with multiple inlets.
Assuming that you have read about modeling “normal” manifolds, and that you are familiar with FloCAD pipes, you might be wondering why it would present any challenge to model a closed circuit such as those shown above. The answer is that it isn’t difficult to address, but it isn’t automatic either.
This sample problem demonstrations methods for "closing the loop:" making both ends of a single Pipe connect like an ouroboros: a self-eating snake. It also discusses challenges associated with modeling the priming of such a loop using flat-front methods.