Reynolds number and time-dependent velocity
 

Dear friends,

Could anyone please explain to me how I should calculate Reynolds number for a time-dependent entrance velocity in a pipe or a time-dependent rotational velocity in a tank and subsequently how I am able to determine the flow regime?

Thank you so much for your time!

Use a statistically time-averaged velocity

Dear Filippo,
Thank you for your reply. Do you have any reference for what you said?

There is not a specific reference, the definition of non-dimensional number is a standard topic of fluid dynamics textbooks and the choice of the reference variables depends on the problem. You are both right if you use the max velocity or the averaged velocity.