In fluid mechanics, the Reynolds number Re is a dimensionless number that gives a measure of the ratio of inertial forces to viscous forces and consequently quantifies the relative importance of these two types of forces for given flow conditions:
where ν is the kinematic viscosity, V is the mean velocity of the fluid, and Lc is the characteristic length of the geometry. The higher the Reynolds number is, the more turbulent the flow will be. The following simulation compares four different Reynolds numbers. The fluid is the same in the four separate flow channels, but the driving velocities are different. The viscosity of the fluid can be altered using a slider.