Critical Velocity and Reynolds number

Critical velocity:

The flow of a fluid, whether streamline or turbulent, is differentiated on the basis of velocity of the flow. The velocity beyond which a streamline flow becomes turbulent is called critical velocity. According to Osborne Reynolds, critical velocity is given by 

Reynold's number:

Reynolds number is a pure number. It has no unit and dimensions. It is found that for Rn < 1000, the flow of a fluid is streamline while for Rn > 2000, the flow of fluid is turbulent. When Rn is between 1000 and 2000, the flow of fluid becomes unsteady, i.e., it changes from a streamline flow to a turbulent flow.