Experimental investigation of adverse pressure gradient turbulent boundary layers by means of large-scale PIV

With an ever increasing need for drag and in turn emission reduction, flow control concepts aiming the manipulation of turbulent boundary layers are focused more strongly. Over the last decades, attempts in finding active and passive flow control methods were examined in detail. However, investigations show that efficient turbulent boundary layer flow control concepts require a deep understanding of the dynamics within a turbulent boundary layer. Thus, this paper presents an experimental study using multiple large-scale PIV systems combined with long range micro PIV, with the purpose of shedding more light into the field of turbulent boundary layers. Therefore, a new experiment was designed to investigate turbulent boundary layers over a run length of almost 2.3 m for a wide range of Reynolds numbers and pressure gradients. Statistical averaged quantities of flows subjected to zero, favorable and adverse pressure gradient are presented. In terms of mean velocity profiles, experimental results show that the law of the wall still holds even in low Reynolds number flows subjected to adverse pressure gradients and moreover support Perry and Schofield’s hypothesis of an u ~ sqrt(y) region. A second outer layer peak was observed in streamwise turbulent intensity profiles when subjecting the flow to an adverse pressure gradient similar to the one reported for high Reynolds number ZPG turbulent boundary layers. This peak might be associated with the superstructures which are additionally characterized in this paper by means of two-point correlations