Application of Focusing Schlieren Deflectometry to an Isolator Shock Train

Abstract

The Focusing Schlieren Deflectometer Velocimetry (FSDV) technique, employing a pair of small-diameter fiber optics and avalanche photodetectors in a completely non-intrusive velocimetry arrangement, is applied to study shock-train propagation dynamics in a Mach 2.5 rectangular scramjet isolator model of Aspect Ratio 3.0 and 6.0. Prior to implementation in the isolator flow field, a series of calibration techniques evaluating the resolution, depth of sharp focus, and velocimetry capabilities of the technique were performed to evaluate the performance of the FSDV system. A conditional sampling and cross-correlation algorithm is implemented to highlight the physical signal and increase overall signal-to-noise of the relative shock train velocity calculation. Quadrant oscillation velocity analysis of the propagating shock train suggests a randomized distribution within the temporal regime analyzed. Two components of propagation velocity, vibration and translation, are distinguished. The former suggesting a characteristic shock train oscillation frequency contained below 100Hz, and the latter showing the majority of the translating component to occur in the upstream direction, along with the motion of the bulk flow. The technique is employed to compare relative shock train oscillation dynamics of (a) oblique and normal shock train structure, (b) center-axis and side-wall motion, and (c) aspect ratio of 3.0 and 6.0 flow.