Impact of tab location relative to the nozzle exit on the shock structure of a supersonic jet

Abstract

This paper presents an experimental study of a Mach 2.0 jet manipulated using rectangular tabs to understand the mixing enhancement at the overexpanded and perfectly expanded state of the jet. This paper also compares the mixing effectiveness of the tabs in comparison with the fluidic injection reported in our previous work [Kumar et al., "Empirical scaling analysis of supersonic jet control using steady fluidic injection," Phys. Fluids 31(5), 056107 (2018)]. Tabs used in this investigation were rectangular strips of aspect ratio, AR, 2 (AR = length of the tab/width of the tab) and are positioned at 0De, 0.25De, 0.5De, and 0.95De (De is the nozzle exit diameter) downstream of the nozzle exit. Pitot pressure measurements were carried out along the jet centerline and in the radial directions to examine the supersonic core length (Lc∗) and jet spread, respectively. The jet stream has been visualized using the shadowgraph technique in the orthogonal planes of the manipulated jet. The mixing capability of the manipulated jet quantified based on the reduction in supersonic core length ΔLc∗ strongly depends on the control technique and its location along the downstream direction. Three types of flow categories are identified, i.e., the "jet bifurcation," "complex and strong shock-cell structure," and "weak shock structure," which depend on the tab location (xt∗) and account for the jet mixing. The present study reveals that the tabs should be positioned downstream of the first shock crossover point which results in shorter core length and, hence, higher jet mixing. A conceptual model of the flow structure under control is proposed. © 2019 Author(s).