# Reynolds Number

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Reynolds number ( $$Re$$ ) (dimensionless number) is the ratio of inertial forces (forces that remain at rest or in uniform motion) to viscosity forces (the resistance to flow).

### Reynolds Number formula

$$\large{ Re = \frac{ \rho v l }{ \eta } }$$

Where:

$$\large{ Re }$$ = Reynolds number

$$\large{ l_c }$$ = Characteristic Length (diameter of the fluid flow)

$$\large{ \rho }$$  (Greek symbol rho) = density of the fluid

$$\large{ v }$$ = velocity of the fluid

$$\large{ \eta }$$  (Greek symbol eta)  = viscosity of the fluid

Tags: Equations for Flow