When the inertial forces dominate over the viscous forces (when the fluid flows faster and Re is larger), the flow is turbulent. Even very low Re indicates viscous creeping motion, where inertia effects are negligible.
If they are sufficient enough to keep all the fluid particles in line, then the flow is laminar. The Reynolds number can be interpreted when the viscous forces are dominant (slow flow, low Re). The Reynolds number can be used to compare a real situation (e.g., airflow around an airfoil and water flow in a pipe) with a small-scale model. In the above equation, V represents the mean flow velocity, D is a characteristic linear dimension, ρ fluid density, μ dynamic viscosity, and ν kinematic viscosity. When the inertial forces dominate over the viscous forces (when the fluid flows faster and Re is larger), the flow is determined as turbulent.When the viscous forces are dominant (slow flow, low Re), they are sufficient to keep all the fluid particles in line.Osborn Reynolds discovered that the flow regime depends mainly on the ratio of the inertia forces to viscous forces in the fluid.It is defined as the product of the characteristic length and the characteristic velocity, divided by the kinematic viscosity. The Reynolds number represents the ratio of inertial forces to viscous forces and is a convenient parameter for predicting if a flow condition will be laminar or turbulent.
