The reynolds number is the major parameter that relates fluid flow momentum to friction forces. how is the reynolds number defined? how does the boundary layer thickness vary with reynolds number?

Reynolds number determines whether a flow is laminar or turbulent flow.

Explanation:

Reynolds number is defined as ratio of inertia force to the viscous force. it is a dimension less  number. Reynolds number is used to describe the type of flow in a fluid whether it is laminar flow or turbulent flow. Reynolds number is denoted by Re.

When Reynolds number is in the range of 0 to 2000, the flow is considered to be laminar.

When Reynolds number is in the range of 2000 to 4000, the flow is considered to be transition.

And when Reynolds number is more than 4000, the flow is turbulent flow.

                     The boundary layer thickness for a fluid is given by

                                      δ =

where δ is boundary layer thickness

           x is distance from the leading edge

           Re is Reynolds number

Thus from the above boundary layer thickness equation, we can see that the boundary layer thickness varies inversely to square root of reynolds number.