Application of Rainbow Schlieren Techniques to Shock-Containing Jets from Cylindrical Nozzles

Abstract

A rainbow schlieren system with a spatial resolution of 20 m is employed to determine the hue and density profiles in shock-containing jet from a cylindrical nozzle with a field of view of 100 mm diameter. Experiments have been conducted with the operating pressure ratio equal to 5.0 which corresponds to the range of underexpanded sonic jet. Underexpanded sonic jet structure can be clearly observed by schlieren pictures with horizontal and vertical rainbow filters. As a result, rainbow schlieren images show jet boundaries, expansion waves, barrel shock waves, Mach disks, and reflected shock waves by continuous color gradation. Also, the rainbow schlieren image reveals that the Mach disk is concave facing downstream in shape. Density profiles at any jet cross-section can be efficiently inferred from the Abel inversion of the schlieren images. The hue and density distributions along the jet centerline and radial density profile elucidate flow properties of shock-containing jet structure quantitatively. Furthermore, an analytical model to predict flow properties at the exit plane of the cylindrical nozzle is proposed and compared with the results from the rainbow schlieren.