Recovery of reattached turbulent shear layers

Abstract

Abstract Turbulence structure of the recovering flow downstream of a backward facing step is investigated for five different flow conditions. Reynolds number Re h = U 0 h / v and δ / h (representing a measure of a perturbation strength) appear to be the chief governing parameters of turbulence characteristics. Present measurements reveal that the skin-friction coefficient magnitude decreases every-where in the flow (including the recirculating region) as the Reynolds number increases. The pressure coefficient distribution Ĉ p collapses on a single curve for x x r in the examined parameter range. All Ĉ p distributions appear to reach approximately constant values by x ≈ 1.5 x r ( x r is a mean reattachment length). The turbulence structure near the wall recovers to that of an equilibrium boundary layer by x =15 h , while the outer region takes much longer distance (order of 100 h ). The slope of the Prandtl mixing length near the wall does not approach the equilibrium value of 0.41 until x ≈ 40 h . The normalized maximum eddy viscosity in the outer layer appears to take more than 100 h to approach the equilibrium value of 0.0168.