Fig.1 R.J Mitchell Wind Tunnel

Fig.1 R.J Mitchell Wind Tunnel

​​Abstract


This project focuses on the experimental characterization of wall bounded flows, particularly turbulent boundary layers and its control.  

In order to develop physical understanding of Reynolds shear stress activity associated with very large scale motion in the outer-layer and its relationship with the skin-friction fluctuations at the wall, simultaneous wide field particle image velocimetry (PIV) and hot-film shear stress sensor measurements were performed to study the large-scale structures associated with shear stress events in a flat plate turbulent boundary layer at a high Reynolds number (Reτ≈4000). This experiment was performed in the .J. Mitchell wind tunnel of the University of Southampton (Figure 1). PIV measurement was performed in a streamwise-wall normal plane using an array of six high resolution cameras (4*16MP and 2*29MP). The resulting field of view covers 8δ (where δ is the boundary layer thickness) in the streamwise direction and captures the entire boundary layer in the wall-normal direction (Figure 2). In association with the PIV setup, a spanwise array of 10 skin-friction sensors (spanning one δ) was used to capture the footprint of the large-scale structures. This combination of measurements allowed the analysis of the 3D organization of the flow related to shear stress events from velocity field measurements..























The large coherent structures in the boundary layer play an important role in the self-sustaining mechanisms in wall-bounded flows. With the purpose to manipulate these structures, an experimental investigation of the interaction of a turbulent boundary layer and synthetics jets was performed. An array of 2 synthetic jets are oriented in the spanwise direction and located approximately 2.7 meters downstream from the leading edge of a flat plate. Actuation is applied perpendicular to the surface of the flat plate with varying blowing ratios and reduced frequencies (open-loop). Two-component large window particle image velocimetry (PIV) was performed in the streamwise-wall-normal plane. Complementary stereo PIV measurements were performed at the University of Toronto Institute for Aerospace Studies (UTIAS), in the spanwise-wall-normal plane. The skin friction Reynolds number is 1,200 based on the skin friction velocity. The experiments at Southampton allow for the observation of the control effects as the flow propagates downstream. The experiments at UTIAS allow for the observation of the streamwise vortices induced from the actuation. Overall the two experiments provide a 3D representation of the flow field with respect to actuation effects.  The video below presents the phase average velocity of the wall normal component of velocity for different frequency and blowing ratio



















Current researcher: Tim Berk

Previous researcher: Dr Guillaume Gomit

Supervisor: Prof. Ganapathisubramani

​Physics and control of wall turbulence using synthetic jet actuators