RECOVERY OF REATTACHED TURBULENT SHEAR LAYERS

Turbulence structure of the recovering flow downstream of a backward f acing step is investigated for five different flow conditions. Reynold s number Re-h = U(0)h/nu and delta/h (representing a measure of a pert urbation strength) appear to be the chief governing parameters of turb ulence characteristics. Present measurements reveal that the skin-fric tion coefficient magnitude decreases everywhere in the flow (including the recirculating region) as the Reynolds number increases. The press ure coefficient distribution <(C)over cap (p)> collapses on a single c urve for x < x(r) in the examined parameter range. All <(C)over cap (p )> distributions appear to reach approximately constant values by x ap proximate to 1.5x(r) (x(r) is a mean reattachment length). The turbule nce structure near the wall recovers to that of an equilibrium boundar y layer by x = 15h, while the outer region takes much longer distance (order of 100h). The slope of the Prandtl mixing length near the wall does not approach the equilibrium value of 0.41 until x approximate to 40h. The normalized maximum eddy viscosity in the outer layer appears to take more than 100h to approach the equilibrium value of 0.0168. ( C) 1998 Elsevier Science Inc. All rights reserved.