Quantitative visualization of boundary layers by developing quasi-common-path phase-shifting interferometer

The objective of this study is to achieve accurate and quantitative visualization of the boundary layer using a novel optical system that offers a large visualization area, fewer disturbance effects, integration with a wind tunnel and high phase, spatial and temporal resolution. A novel optical configuration was proposed to realize these features. In addition, high phase and spatial resolution could be realized by introducing a phase-shifting image processing technique. Finally, a novel prism was specially designed to implement the phase-shifting technique. In this study, the proposed system was evaluated by using it to quantitatively visualize boundary layers around a circular cylinder and over a flat plate. The effect of a tripwire on the flow was visualized by an interferogram. In the experiments on flow over a flat plate, the temperature distributions in the thermal boundary layer were measured accurately, and the velocity distributions were estimated from the measured temperature distributions. The experimental data were compared with a semi-analytical solution. Good agreement was obtained, and the relative error was within 5.0% in the temperature measurement.