Reynolds' spark-lit experiment and the number Re = UL/ν behind turbulence
jo_brandstetter · x · 2026-10-26
A historical detail: Reynolds observed his dye cloud by the light of an electric spark, and what looked like a blob of color resolved into distinct curls and eddies (original experiment sketch attached). The companion post gives the Reynolds number Re = UL/ν — with U a typical speed, L a length scale, ν the kinematic viscosity — where inertia outweighs viscosity at high values and turbulence occurs.
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