Development of stereo schlieren image velocimetry

Schlieren and shadowgraph imaging have been used to quantify velocity field characteristics of jets in two dimensions, but no thorough study of the turbulence or three-dimensional motion using these techniques has been completed. This work explores the capabilities of tracking turbulent flow in three dimensions by combining the information from schlieren and shadowgraph imaging with a multi-camera stereo-imaging system. Schlieren and projective shadowgraph setups were used with two high-speed cameras at small stereo angles to develop three-dimensional reconstructions of refractive index fields. A two-dimensional helium jet study was performed with schlieren image velocimetry (SIV) to track turbulent structure motions. Particle image velocity was conducted with the helium jet to validate the three-dimensional SIV measurements. The study showed that stereo schlieren imaging with parallel-light lens systems did not yield a depth effect. However, the projective shadowgraphy experiment was able to reconstruct the helium jet into three-dimensional space because of the inherent diverging light rays.