| Quantifying turbulent mixing in a post detonation environment has remained a challenge for modern fluid tracking techniques. In recent years, schlieren and shadowgraph imaging have been used to quantify velocity field characteristics of a detonation in two dimensions, but no thorough study of the turbulence or three-dimensional motion has been completed. The present work explores the capabilities of tracking turbulent flow in three dimensions by combining the information from schlieren and shadowgraph imaging with multi-camera systems. 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. The cameras were calibrated using a target checkerboard with known dimensions and the MATLAB Stereo Camera Calibrator App, plus additional MATLAB functions to ultimately build three-dimensional reconstructions of the flow. A two-dimensional helium jet study using particle image velocimetry and schlieren image velocimetry was performed to validate the three-dimensional reconsturcted velocities. The three-dimensional 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. Following the validation experiments, a series of explosive tests were conducted with each system. The stereo schlieren test identified even with small camera angles, the parallel light in each schlieren system may not refract the same due to local changes in temperature and density along the two different optical paths. The projective shadowgraph explosively-driven field-scale test successfully reprojected the shock wave, fireball and gas cloud expansion into three-dimensional space. Velocity measurements were taken by manually identifying locations that could be matched over a series of frames. The work here shows promise for this technique to be used for tracking the shock, fireball and gas cloud propagation, but additional development of image processing routines must be made to allow automation of the process. |
