When fluid flows over a surface, the Reynolds number will output whether the flow is laminar (smooth), transitional, or turbulent. Verify that the Reynolds number is dimensionless using the SI. The Reynolds number is expressed as

where ρ is the density of the fluid, V is the free stream fluid velocity, D is the characteristic length of the surface, and µ is the fluid viscosity. The units of fluid viscosity are kg/(m · s).

pVD R =