Influence of tab corner geometry on supersonic jets

Abstract

Purpose The purpose of this study is to evaluate the effect of tabs having different corner geometries on the flow characteristics of a supersonic convergent–divergent (C-D) nozzle. Design/methodology/approach A circular C-D nozzle of Mach 2.0 was used, and the tabs were positioned at the exit of the nozzle in diametrically opposite directions. Three tabs having different corner geometry implemented in the experiments were rectangular tab with triangular top edge, triangular tab with a bell-shaped edge and tapered tab. The pressure profiles across the tabs and the centerline pressure decay along the jets were measured. The shadowgraph technique illustrated the waves present in the center of an oncoming jet. The nozzle pressure ratios (NPR) were varied from 4 to 8, in the steps of one, covering various overexpansion and under expansion levels at the exit of the nozzle. Findings The results showed tapered tabs act as a better mixing promoter than the other tabs used in the study. A reduction of 91.25% in core length for NPR 8 was observed for the tapered tabs. Subsequently, core length reductions generated by triangular tabs with a bell-shaped top edge were 87.5%, and those caused by rectangular tabs with a triangular top edge were 7.5%. Practical implications The research results could be used for designing combustion chambers and chemical reactors that require jets to enhance mixing levels. Originality/value The tabs having three different corners geometries, i.e. sharp or pointed, bell-shaped and straight edge has never been investigated before. The idea of only modifying corners is the innovative step of this research.