When I simulate the flow in a channel and after solution is converged .When I calculate the mean velocity by surface integrals the mean velocity is found 1-differ from the inputed value at the velocity inlet B.C and 2-differ from the mean velocity at the outlet of the channel which have pressure outlet B.C In fact as I know must be the mean velocity is equal from inelt to outlet .So why this happened ?please how know the answer to help me

Thanks alot

if you solve with non-fully developed flow it usually differ but if your case was fully developed it must become the same.

My case is developing flow.But why it differ since according to the continouty equation must be the mean velocity inlet is the same at outlet to conserve the momentum .But in my results it differ I need the physical meaning of this change

Thank you for your replay and answer