According to the hypotheses, if the pipe is very large and for z > Le, the only nonzero
component of the velocity is vz. In this domain, there is an easy mathematical
solution to describe the behaviour of the flow. Thus, the current CFD analysis will
be useful to corroborate this anaylitical model and to figure out the behaviour of
the flow for z < Le, which is more complex to describe mathematically.
entrance length