DESIGN of large and fast jet-propelled aircraft and large booster rocket engines have focused on noise problems. Difficulties in devising satisfactory solutions stem from the inherent complexities of the phenomena of jet noise generation. Consequently, over the past two decades, extensive theoretical and experimental studies have been conducted in an attempt to understand the basic mechanism of jet noise generation and its abatement. Supersonic jets normally possess complex shock patterns. Therefore, the role of shock waves in noise generation becomes significant. The main sources of highspeed jet noise are the turbulent nature of the flow, shock–turbulence interaction, flow-induced oscillations of shocks, and resonance effects. Noise from such jets is complex and may even be nonlinearly interdependent. Noise prediction for such flows for a wide range of operating conditions is not possible as yet. An intense discrete acoustic emission termed “screech” or “whistle,” as a consequence of oscillating shock waves within a supersonic jet, usually dominates the noise emitted by a cold model converging jet operated at slightly above choked flow condition. From literature, it is evident that supersonic jet noise reduction can be achieved by enhancing mixing and eliminating or weakening and/or reducing the effective axial extent of the shock structure. To achieve these goals, many jet controls have been devised and studied. In general, jet control techniques can broadly be divided into passive or active. Passive control techniques may be permanent or deployable, but have no moving parts during operation. They range from alterations of the jet nozzle exit shape to the implementation of toothlike tabs and vortex generators at the nozzle exit. In contrast, active flow controls use energized actuators to dynamically manipulate flow phenomena based on open-or closed-loop algorithms. For example, pulsed jets [1] use piezoelectric actuators for active mixing enhancement. As a simple passive means to enhance jet mixing and reduce jet noise, many studies have focused on the placement of small tabs and vortex generators at the exit of axisymmetric and rectangular nozzles [2]. They introduce streamwise vortices to transport the low-speed fluid entrained at the jet periphery toward the centerline while forcing out higher speed core fluid. The main difference between the two methods is the type of vortex generated. Tabs (which are placed normal to the flow) generate a pair of counter-rotating vortices, but a half-delta-wing vortex generator produces only a simple vortex. A tab is a small protrusion into the flow which produces a counterrotating streamwise vortex pair that can affect the jet flow development significantly. The streamwise vortices usually have a long life and, once introduced in the flow, tend to persist over tens of jet diameters downstream. This is in contrast to azimuthal, vertical structures that are more energetic but have a shorter life span. The generation mechanism of the streamwise vortex pairs by the tabs and their effect on the entrainment and spreading of free jets have been discussed in literature [3–7]. In the studies carried out so far, various factors have been found to influence the jet decay. Also, the nozzle boundary-layer thickness, turbulence level, and convergence were found to have insignificant influence on the jet development. In contrast, the insertion of small rectangular tabs at the exit was found to have a profound effect on the jet development. In a continuing effort to increase the mixing in free shear flows, vortex generators in the form of tabs have been investigated by several researchers [3–9]. Bradbury and Khadem [10] were the first to …