Three Dimensional Flow Visualization of the Adverse Pressure Gradient Turbulent Boundary Layer

Abstract

An adverse pressure gradient (APG) turbulent boundary layer is investigated using a three dimensional scanning flow visualization technique. This dissertation includes an introduction to the structures and past research of the zero pressure gradient (ZPG) and APG turbulent boundary layer, as well as a description of three experiments to investigate the turbulent boundary layer. The first experiment of this work uses simultaneous 2-D particle image velocimetry (PIV) to complement 3-D flow visualization measurements in a turbulent boundary layer to compare the boundary layer edge. Building off of the first experiment, a separate experiment was performed to compare 2-D velocity with 2-D flow visualization. The edge of the boundary layer identified from flow visualization generally matches the edge determined from velocity and vorticity. The correlation between velocity deficit and smoke intensity indicated a moderate to strong relationship between the two. In many cases, velocity fields estimated from smoke intensity were similar to the actual velocity fields. While not suitable for estimating the velocity given an intensity field, the correlations validate the use of flow visualization techniques for determining the edge and large-scale shape of a turbulent boundary layer, specifically when quantitative velocity measurements are not possible. The third experiment described in this dissertation consists of using a scanning 3-D flow visualization technique to compare the large scale features in a ZPG and APG boundary layer. In general, structures in a ZPG boundary layer are larger and spaced farther apart compared to the APG cases. Flow features identified through conditional averaging extend higher into the freestream flow for the APG cases and are more distinct and separated from the wall than in the ZPG case. The difference in the three cases is more pronounced with increasing wall-normal height.