Large-eddy simulation of sonic coaxial jets with different total pressure ratios of the inner to outer nozzle

Large-eddy simulation of sonic coaxial jets issuing into a quiescent environment was carried for two total pressure ratios of the inner to outer nozzle, i.e. 5/3 and 3/5. The effects of the total pressure ratio on the flow characteristics were mainly investigated. Various fundamental mechanisms dictating the complex flow characteristics, including jet shear layer evolution, shock system formation, shock/shear-layer interaction, turbulence behavior, and mixing property, have been studied. It is found that the total pressure ratio has an important influence on the flow evolution of coaxial jets as well as turbulence behavior and jet mixing property. The fluid-dynamic shearing and compressing processes are analyzed based on the Lamb vector curl and divergence. The multi-layer structures of the shear layers and shock waves are reasonably captured and the relevant fluid-dynamic processes are clearly clarified. It is also identified that the turbulence behavior and mixing property of the coaxial jets are mainly associated with the shearing effect in the outer shear layer region and the shearing and compressing coupled effect in the jet core region.