First of All, I appreciate you for taking the time to read my question.
I need some help finding the right path to start modeling the transition from undeveloped flow to fully developed flow on a pipe (in laminar flow region). For example, I want to model the flow from the beginning when the tube is empty until it is filled with the liquid. I presume this model has to be a time-dependent model, but I do not know which modules I have to implement other than laminar flow module. Also, I do not know if I had to use a "moving" mesh, with which I have zero experience. What should I try first on COMSOL?