Understanding supersonic jet mixing has been critical in high-speed aerospace combustion and jet mixing. The last three decades have seen many noteworthy findings in achieving faster decay of supersonic non-circular jets. Many researchers have proposed asymmetric nozzle shapes as practical means of passive control of supersonic jets. From non-circular nozzles, the mixing characteristics of the jet proved superior to those from circular nozzles. The morphology and complexity of the jet structure of non-circular jet structures are investigated in this study.
When the jet expanded or compressed symmetrically in the flow direction, the shock wave or expansion fans of equal strength were instigated at the nozzle exit to turn the flow inward or outward symmetrically. For example, the supersonic flow from a circular nozzle would create symmetrical flow, so the shock wave or expansion fans were always equal in strength, making the symmetrical flow about the nozzle axis.
In the non-circular nozzle, the behavior of the flow could not be generalized. Therefore, the flow characteristics were considered on a case-to-case basis. In the current case study, the geometry of nozzles has straight sides, sharp corners, and stiff curvature. Unequal strength of compression and expansion were instigated at different locations of nozzle exit; as a result, the flow pattern changed about the centerline of shape geometry.
The symmetrical pressure expansion is shown in Fig. 1. For a given location, the flow characteristics remained equal on either side of the centerline, and the slip line maintained its position along the jet axis.
The instigated shock wave strength from points A and B was different for axisymmetric geometry. The flow characteristics of the upper and lower side of the centerline were determined by instigated shock waves and turning angles \(a \text{a}\text{n}\text{d} b.\) The flow turns through reflected shock so that change in pressures and flow directions in regions 4 and 5 should be the same. Due to axisymmetric expansion, the flow characteristics differed in these two regions. There would be no slip line if a = b, as shown in Fig. 1. The instigated shock waves were of the same strength as the reflected wave. But in axisymmetric flow, the turning angle \(a \ne b\). The strength of shock waves or expansion fans changed in each instigate point. As a result, the turning angles were different, as shown in Fig. 2.
The flow characteristics would change when \(a \ne b\) and the slip lines flow structure are formed, as shown in Fig. 3. Due to the deformation and misalignment of slip lines, the shock cell structures, shapes, and spread characteristics differed in non-circular exit-shaped nozzles.
Srinivasan and Tide (2010)[1] studied the impact of the number of chevrons on noise reduction. The mixing of jets with air or gas was investigated by William (2013) [2] for the dissipation rate (\(\epsilon\)) and turbulent kinetic energy ( TKE). They studied jet half-width by using velocity reference. The researchers found that the non-circular jet has a faster spread and higher decay rate than the circular jet for a shorter potential core in case of incompressible flow. The axis switching phenomenon was observed during the current study, which earlier researchers identified. The finding of Zaman (1995)[3] on-axis switching phenomenon was comparable with the current investigation results. The effect of aspect ratio and exit shape have produced similar on-axis switching phenomena. The multiple axes switching phenomena were observed (Kanamori et al. 2011)[4]. Gutmark and Grinstein (1999)[5] studied the effect of exit shape, articulating with current findings. Zare-Behtash H. et al. (2008)[6] studied different non-circular shapes and stated that the formations of vertices were found near corners. Similar vortexes were found during the current numerical investigation. Mohanta and Sridhar(2016)[7][8][9] studied the square and hexagonal jet decay characteristics. During their investigation, the corner vortices were noticed. The researchers extended their investigation on spread characteristics further.
When the jet expanded or compressed symmetrically in the flow direction, the shock wave or expansion fans of equal strength were instigated at the nozzle exit to turn the flow inward or outward symmetrically. For example, the supersonic flow from a circular nozzle would create symmetrical flow, so the shock wave or expansion fans were always equal in strength, making the symmetrical flow about the nozzle axis. In the non-circular nozzle, the behavior of the flow could not be generalized. Therefore, the flow characteristics were considered on a case-to-case basis. In the current case study, the geometry of nozzles has straight sides, sharp corners, and stiff curvature. Unequal strength of compression and expansion were instigated at different locations of nozzle exit; as a result, the flow pattern changed about the centerline of shape geometry. The symmetrical pressure expansion is shown in Fig. 1. For a given location, the flow characteristics remained equal on either side of the centerline, and the slip line maintained its position along the jet axis[10].