Experimental Investigation of the Log-Law for an Adverse Pressure Gradient Turbulent Boundary Layer Flow at Re θ = 10000

Abstract

We present an experimental investigation of a turbulent boundary layer flow at a significant adverse pressure gradient at Reynolds number Re θ = 10000 using large field PIV. The testcase is designed to start from a zero pressure gradient flow at Re θ = 8000 with a distinct log-law region following a slowly rising adverse pressure gradient. This allows to reveal a breakdown of the log-law under the effect of the adverse pressure gradient. The region described by the log-law is progressively reduced in terms of y + and then joins into a modified log-law which gives a good fit to the data up to at least y/δ 99 ≈ 0.2. The scaling in the overlap region is demonstrated using the mean velocity slope diagnostic function, enabled due to the high quality of the PIV data. Locally, the velocity profile is measured down to the wall using long-range microscopic PIV with particle tracking velocimetry to determine the wall shear stress directly in the adverse pressure gradient region.