Find Re = ρ v L / μ, the ratio of inertial to viscous forces in a flow.
| Re | – |
Use this calculator for the Reynolds number: Re = ρ v L / μ. L is a characteristic length (pipe inside diameter for internal flow, chord for a wing).
Water μ ≈ 0.001 Pa·s. Pipe flow is often laminar below Re ≈ 2300 and turbulent well above. Air needs a much smaller μ (~1.8×10⁻⁵ Pa·s). Re is dimensionless; it is a guide, not a full CFD result.
Density (kg/m³): Fluid density. Fresh water ≈ 1000, air ≈ 1.2.
Speed (m/s): Typical flow speed, in metres per second.
Length (m): Diameter for a pipe, chord for a wing, in metres.
μ (Pa·s): Dynamic viscosity. Water ≈ 0.001.
Re: Reynolds number, ρ v L / μ.
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