On the scaling of separation bubbles

Abstract

A simple analysis, based on the scaling of the Navier-Stokes equations, is presented for general flow situations involving separation bubbles. Three possible functional relations between the separation bubble length L and Reynolds number Re are derived: (i) L ∝ Re, (ii) L ∝ 1/Re, and (iii) L = constant. These relations are shown to correspond to the experimentally observed behavior of laminar, transitional and turbulent separation bubbles, respectively. The results of the analysis are discussed in the context of several internal and external separated flows in various geometries, and the corresponding empirical constants are evaluated from available experimental and numerical data.