What is reynold number?

In this post, i am going to explain the importance of  Reynolds number.
Reynolds number plays an important role in the study of fluid mechanics and as well in aerodynamics.

REYNOLDS NUMBER
The concept of mathematically predicting the flow of fluid was first introduced by Gorge Gabriel Stokes, however later it was developed by Osbourne Reynolds in 1883. Thus, it came to be called the Reynolds Number. 

LET US UNDERSTAND REYNOLDS NUMBER WITH A SIMPLE EXPERIMENT.
SETUP: From the below setup it is seen that a water tank has glass pipe (transparent) through which flow of liquid takes place, at its output an adjustable tap is fitted to it.and an ink injector is placed at the inlet of the glass pipe.such that flow of ink takes place.

Procedure: Once the above setup is arranged, perform the following steps and note down the observations.

Step 1: Open the tap partially so that the water flows slowly through the see-through pipe. Make sure that there is a constant rate of flow. Fill the ink injector with ink, and observe as a steady stream of ink starts flowing through the pipe. You should observe something similar to the following diagram.

 Step 2: Now, fully open the output tap and observe the flow of ink through it. You should see something which looks like the following.

OBSERVATION: From the above two cases it very clear that when the tap is open partially, the flow is seen linear, when the tap is fully open, disorder of fluid is seen.and ink particles gets displace randomly throughout the water within the pipe.


so now mathematically Reynolds number is given by:

Typically, the following values apply:

If Re < 2100, flow is laminar.
For Re > 4000, flow is turbulent.
For 2100 < Re < 4000, flow is in transition from laminar to turbulent.

THANK YOU FOR READING.