Flow visualization using a Sanderson prism

Abstract

The use of a Sanderson prism for the visualization of density gradients in a compressible flow is shown to be an inexpensive and versatile substitute for Wollaston prisms in the application of shearing interferometry. Experimentation using the Sanderson prism in a schlieren optical setup was performed to examine the effectiveness of the prism’s use for flow visualization. A range of polycarbonate prisms were tested for a range of prism heights and different physical deflections to produce a range of divergence angles. For each prism height and deflection, tests were done using a hair dryer, helium jet, a soldering iron and a moving shock wave interaction to generate flow density gradients. The light which passes through the prism was also focused at different distances to determine the effects that different fringe arrangements have on the visibility of the flow. Tests were also done comparing horizontal and vertical fringe arrangements. It was found that the colour of the infinite fringe selected had an influence on the results because the larger the difference in colour between that of the adjacent fringes, the better the contrast in the final result. It was also found that infinite fringe use showed better results due to flow features such as shocks and vortices being more easily identified against a uniform background. It is shown that the technique produces good visualization of the density gradients that form in the flow.