Experimental Investigation of a Turbulent Boundary Layer Using Simultaneous 3-D Flow Visualization and 2-D PIV

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, seeding technique, and synchronization is described. In this experiment the turbulent boundary layer is investigated using complementary proper orthogonal decomposition (POD) and linear stochastic estimation (LSE) on a set of 440 flow visualization and PIV images. The correlation between flow visualization POD modes and velocity POD modes is used with LSE to give a rough estimate of the velocity field given only a flow visualization image. Limited success has been achieved in this regard, though a larger data set and a higher resolution flow visualization camera could yield more accurate results. Future experiments will be enhanced by the use of a higher resolution flow visualization camera and will explore adverse pressure gradient turbulent flows.