Question

what is Reynolds number??

Answer 1

Hey mate! Here's your answer!
The Reynolds number is the ratio of a fluid's inertial force to its viscous force. Inertial force involves force due to the momentum of the mass of flowing fluid. 
Hope it helps :)

Answer 2

Hey !!

It is a unitless and dimensionless number given by

            Nr = ρvr / η

A smaller value of Reynold's number (generally Nr ≤ 1000) indicates a streamline flow but a higher value (Nr ≥ 1500) indicates that the flow is turbulent and between 1000 to 1500, the flow is unstable.

Good luck !!