Effect of tab parameters on the near-field mixing characteristics of a Mach 1.5 elliptic jet

Abstract

The effect of delta-tabs with its apex leaning downstream on the jet mixing characteristics of a Mach 1.5 elliptic jet of aspect ratio (AR) 3.37 is reported in this paper. The delta-tabs were placed along the minor and major axes of the elliptic nozzle, referred to as tab configuration C1 and C2, respectively. For each tab configuration, four different orientation angles varying from θ= 90∘ to 150∘ were studied, where θ= 90∘ is the tab positioned normal to the nozzle exit and θ= 150∘ is the tab oriented in the downstream direction at the nozzle exit. The tab effects on jet manipulation were investigated via shadowgraph visualization, and the mean Pitot pressure was measured along the jet centerline and along the orthogonal planes of the jet. The non-dimensonalized supersonic core length Lc*, average shock-cell spacing Ls¯*, and the axis-switching location xas* were examined in detail to understand the jet characteristics of the natural and manipulated jets. The mixing capability of the manipulated jets quantified based on the reduction in supersonic core length ΔLc* depends strongly on the ideally expanded jet Mach number Mj, tab configuration (C1 and C2), and θ. As such, the ΔLc* for the manipulated jet at θ= 135∘ is the largest, revealing the optimal tab orientation for jet mixing enhancement, as also observed for the circular jet [Zaman et al., “Control of an axisymmetric jet using vortex generators,” Phys. Fluids 6(2), 778–793 (1994)]. The relationship between ΔLc* and ΔLs* is presented to understand the correlation between the jet mixing and noise characteristics of the manipulated jet. Discussion is conducted based on the dependence of ΔLc* and ΔLs* with θ, which provides useful insight into the jet flow physics. With suitable placement of tabs C1 and C2, the axis switching could be either stopped or augmented. The superior mixing characteristics of an elliptic jet relative to a circular jet, which were found in previous works on the supersonic over-expanded jet [Kumar and Rathakrishnan, “Characteristics of a supersonic elliptic jet,” Aeronaut. J. 120(1225), 495 (2016)] prevail in the supersonic jet under-expanded jet as well.