Statistics and scaling of adverse pressure gradient turbulent boundary layers

Turbulent boundary layers in regions of strong adverse pressure gradient (APG) acting over a flat plates are investigated using a series of particle image velocimetry measurements. Experiments are performed in a large horizontal water tunnel with a flexible roof whose height can be adjusted in order to tailor the pressure distribution on the flat plate at the floor of the tunnel. In the present case an self-similar APG TBL is formed over a domain of 7 boundary layer thickness at a momentum thickness based Reynolds number ranging from Re_δ2 = 2000 to 3000. Profiles of mean velocity and Reynolds stress are presented normalised by a variety of velocity and length scales, all of which should provide the same collapse for a truly self-similar flow. Each scaling was found to provide a better collapse of some quantities with respect to the others but no single scaling is able to account for the variation in all quantities due to slight departures from self-similarity.