Corrugated Truncated Triangular Tabs for Supersonic Jet Control

Abstract

An experimental investigation has been carried out to assess the effectiveness of truncated triangular tabs, provided with corrugations (semicircular, triangle, and square shapes) all along their edges, capable of shedding smallscale vortices of continuously varying size, in enhancing the mixing of axisymmetric Mach 2 jet, at different levels of expansion. The performance of all the tabs were found to be effective only in the nearfield of the jet at all levels of expansion of the present investigation. Both the semicircular and square corrugated tabs were found to bifurcate the jet, in two parts (lobes), at x/D ≤ 1, than the triangular corrugated tab, at all the nozzle pressure ratios (NPRs) of the present study. Among the controlled jets, the semicircular corrugated tab is found to be the best mixing promoter at NPRs 6 and 7, for the Mach 2 jet. However at NPRs 4, 5 and 8, the mixing promoting performance of uncorrugated tabs is the best; as high as 91% reduction in jet core length is achieved with semicircular corrugations. Therefore, the mixing promoting capability of truncated triangular tabs with semicircular corrugated tab assumes a maximum, around the overexpansion level with adverse pressure gradient of around 10% (corresponding to NPR7). Shadowgraph images reveal, that the waves prevailing in the nearfield for the controlled jets are rendered weaker than those of uncontrolled jet.