Schlieren imaging investigation on azimuthally varying shock net from four-lobed corrugated nozzle

Abstract

Purpose The purpose of this paper is to conduct an experimental investigation on the shock cell structure of jets emanating from a four-lobed corrugated nozzle using Schlieren imaging technique. Design/methodology/approach The Schlieren images were captured for seven different nozzle pressure ratios (NPR = 2, 3, 4, 5, 6, 7 and 8) and compared with the shock cell structure of a round nozzle with an identical exit area. The variation in the length of the shock cell, width of boundary interaction between adjacent shock cells, maximum width of first shock cell, Mach disk position and diameter for different NPR was measured from the Schlieren images and analysed. Findings A three-layer shock net observed in the jet emanating from the four-lobed corrugated nozzle is a novel concept in the field of under-expanded jet flows. A shock net represents interconnected layers of shock cells developed because of the interaction between the core and peripheral shock waves in a jet emanating from a corrugated lobed nozzle. Also, the pattern of shock net is different while taking Schlieren images across the groove and lobe sections. Thus, the shock net emerging from a corrugated lobed nozzle varies azimuthally and primarily depends on the nozzle exit cross section. The length of the shock cell, width of boundary interaction between adjacent shock cells, maximum width of first cell, Mach disk position and diameter were found to exhibit increasing trend with NPR. Originality/value A novel concept of interconnected layers of shock waves defined as “shock net” developed from a single jet emanating from a four-lobed corrugated nozzle was observed.