Reynolds Experiment

For a particular fluid flow, depending on the velocity, the flow shows the laminar, transition and turbulent patterns. In laminar flow, the fluid flows in a layer without disturbing the other layer, whereas in turbulent flow the fluid does not follow any regular layer and the flow is highly chaotic. The flow shows the randomness of turbulent flow due to elevated dissipation. The flow exhibits intermittent behaviour in the transition regime, sometimes laminar and sometimes turbulent. You can compare the essence of the flow with a non-dimensional number called the Reynolds number.

Reynolds number is defined as the ratio of inertia to viscous force in a flow. For a particular fluid i.e. for constant viscosity, the flow transits from laminar to turbulent as the velocity of the flow is increased. The Reynolds number at which the flow starts to transit from laminar is called the critical Reynolds number.

The Reynolds number for a flow in a pipe is obtained using following equation:
\[R_e = {\rho V D \over \mu}\] here, ρ is the density, V is the average flow velocity in the pipe, D is the pipe diameter and μ is the dynamic viscosity.

The flow transits from laminar to turbulent for a specific fluid, i.e. for continuous viscosity, as the flow velocity is increased. The critical number of Reynolds is the Reynolds number at which the flow begins to transition from laminar to turbulent. The essential Reynolds number for a flow through a pipe is generally calculated to be 2300. On the basis of the experimental data, Reynolds classified the flow regimes as follows:

Laminar < 2300

2300 < Transition < 4000

Turbulent > 4000