Simultaneous 3-D Flow Visualization with 2-D PIV to Observe a Turbulent Boundary Layer

Abstract

A high speed 3-D flow visualization system is synchronized with a 2-D particle image velocimetry (PIV) system to simultaneously capture instantaneous 3-D images with a 2-D PIV slice through the center of the measurement volume. Trials were performed on a zero pressure gradient (ZPG) turbulent boundary layer (Reθ ~ 4900) on the wall of a 2 ft x 2 ft open circuit wind tunnel. The experimental setup, including the two lasers, two cameras, wind tunnel, and seeding technique is described. Comparison of the velocity and vorticity fields with the 3-D flow visualization images show agreement in locating the edge of the boundary layer as marked by smoke injected into the boundary layer well upstream of the measurement location. Proper orthogonal decomposition (POD) is used to elucidate the most common structures in the flow from both a flow visualization and velocity field perspective. The coefficients used to construct velocity POD modes are used on flow visualization images to create a conditionally averaged image that corresponds to the velocity mode. The similarities in these constructed images and the modes indicate a connection between the velocity and flow visualization for this experiment. Additional trials with a larger set of images will be run to further investigate the connections between the flow visualization and PIV.