A comprehensive review on controlled supersonic jets in improving their mixing characteristics

This article thoroughly reviews the studies on enhancing the mixing and controlling of supersonic jets through passive and active control techniques. At first, the behavior of jets and their interactions with the environment, such as entrainment of surrounding fluid and vortex formation, are explored. Subsequently, the control mechanisms for supersonic jets are described. The impacts of the jet-jet interactions are explicitly demonstrated. The jet behaviors for different nozzle geometries and nozzle lip modification are reviewed, emphasizing the introduction of asymmetry by generating the vortices promoting jet mixing. The asymmetric jets perform better mixing performance than the axisymmetric jets due to the axis-switching behavior and azimuthal asymmetry. The tab-like vortex generators at the nozzle exit and their impact on jet spreading and mixing characteristics are particularly emphasized; different tab shapes, locations, and aspect ratios are reviewed, highlighting their effects on jet mixing and core length reduction. The paper focuses on understanding the behavior of vortices generated by tabs of varying designs and their effect on mixing enhancement. The findings underscore the effectiveness of both passive and active control techniques in promoting jet mixing and reducing core length. Subsequently, the active controls such as fluidic actuators, air tabs, and plasma jets are explored. The main objective of the controlled jet is to introduce additional controlled vortices and to alter the jet instabilities to enhance the interaction between the jet and its surroundings. These strategies lead to enhanced mixing, reduced core length, and are beneficial for jet noise mitigation, combustion augmentation, and the improvement of stealth capabilities.