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Reynolds Number

This is a non-dimensional number (consistent units) which describes whether fluid flow is laminar, turbulent, or transitional between the two. It is significant in the design of a model of any system in which the effect of viscosity is important in controlling the velocities or the flow pattern of a fluid.

where: R_e = Reynolds Number; ρ = density [kgm^-3]; U = characteristic velocity [ms^-1]; L = characteristic length scale [m]; η = dynamic viscosity [Nsm^-2]

Note:

R_e < 2000 – laminar flow.

2000 < R_e < 3000 – unstable flow.

R_e > 3000 – turbulent flow.

See also: Froude Number, Poise, Scale Effect, Strouhal Number.

Subjects: Mechanical Engineering Physics