Truncated Triangular Tabs for Supersonic-Jet Control

Abstract

An experimental investigation has been carried out to study the mixing-promoting efficiency of triangular tabs with sharp and truncated vertices. The mixing promotion caused by two identical triangular tabs, with sharp and truncated vertices, offering a geometrical blockage of 2.5% each, placed at the exit of a Mach 2 circular nozzle, was studied in the presence of adverse and marginally favorable pressure gradients. The pressure decay along the jet centerline and the pressure profiles along and normal to the tabs were measured. The waves present in the core of the uncontrolled and controlled jets were visualized with the shadowgraph technique. The nozzle-pressure ratio was varied from 4 to 8, in the step of one, covering overexpansion and marginally underexpansion levels at the nozzle exit. The results of the present study demonstrate the validity of the hypothesis that the triangular tabs shedding vortices of continuously varying sizes is a better mixing promoter than the rectangular tabs, of identical blockage, shedding vortices of uniform size. Furthermore, the truncated triangular tab is found to be a better mixing promoter than the triangular tab of sharp vertex. As high as 87% reduction in core length was achieved with truncated triangular tabs at nozzle-pressure ratio 8. The corresponding core-length reduction caused by triangular tabs with a sharp vertex and rectangular tabs are 83 and 25%, respectively.