Adverse-Pressure-Gradient effects on Turbulent Boundary Layers

Abstract

Wall-bounded turbulence is present in many relevant fluid-flow problems such as the flow around wings, land and sea vehicles, or in turbines, compressors, etc. Simplified scenarios, such as the zero-pressure-gradient (ZPG) turbulent boundary layers (TBL) developing over a flat plate, have been deeply investigated in the past. Unfortunately, TBL seldom develop under ZPG conditions, with pressure gradients having significant impact on their features. In particular, adverse pressure gradients (APG) might produce flow separation with the consequent losses in performances. In this talk a unique experimental database of APG TBL covering a wide range of Reynolds numbers and with different pressure-gradient histories is presented. The measurements were performed by means of hot-wire anemometry (HWA) and oil-film interferometry (OFI) in the Reynolds-number range , and for pressure-gradient intensities resulting in values of the Clauser pressure-gradient parameter in the range . The primary objective is to study and compare near-equilibrium and non-equilibrium APG TBLs developing on a flat plate, discerning Reynolds-number effects from those due to the pressure-gradient.