Corrugation geometry effect on jet mixing

An experimental investigation was carried out to assess the mixing promoting efficiency of rectangular, semicircular, and triangular corrugations at the edges of rectangular tabs. Mixing promoting capability of two rectangular tabs with aspect ratio of 1.0, 1.5, and 2.0, with rectangular, semicircular, and triangular corrugations over their edges, located diametrically opposite at the exit of a convergent-divergent Mach 1.73 nozzle was studied. Pressure measurements and optical flow visualization were carried out. The nozzle pressure ratios (NPRs) studied were 4, 5, 6, 7 and 8, in order to cover different levels of expansion at the nozzle exit. At NPR 4, Mach 1.73 nozzle is overexpanded, with about 23% adverse pressure gradient. At NPR 5, the adverse pressure gradient is just 3%. At NPR 6, 7, and 8, the jet is underexpanded with favorable pressure gradients of 16%, 36%, and 55%, respectively. The corrugated tabs were found to be efficient mixing promoters, leading to shorter core and weaker shocks in the core than the uncontrolled jet. The mixing effectiveness of the corrugated tab is found to increase with increase in NPR. The core length reduction associated with all the corrugations is found to increase with increase in tab aspect ratio. At the almost correctly expanded state, for aspect ratio 1, rectangular corrugation is found to be the most efficient mixing promoter, causing a core length reduction of almost 100%, followed by the triangular and semicircular corrugations, leading to a 77% and 73% reduction, respectively. For aspect ratios 1.5 and 2.0, triangular corrugation is found to be the most efficient mixing promoter, causing a core length reduction of almost 100%, followed by the rectangular and semicircular corrugations. The shadowgraph images of the controlled and uncontrolled jets demonstrate the effectiveness of the corrugated tabs in weakening the waves in the jet core.