How is the Reynolds number defined What is its physical inte

How is the Reynolds number defined? What is its physical interpretation? What role is played by the critical Reynolds number?

Solution

Reynolds number is defined as Re = rho * V * D / mu

where rho is the density of the fluid

         V is the velocity of flow

         D is the characteristic length of flow

         mu is the dynamic viscosity of fluid

The Reynolds number is defined as the ratio of inertial forces to viscous forces and consequently quantifies the relative importance of these two types of forces for given flow conditions. It is used to characterize different flow regimes within a similar fluid, such as laminar or turbulent flow:

Critical reynolds number is the reynolds number at which laminar flow transistions into turbulent flow. For flow in a pipe of diameter D, experimental observations show that for \"fully developed\" flow laminar flow occurs when Re_D < 2300 and turbulent flow occurs when Re_D > 4000. The critical Reynolds number is different for every geometry^.