Characteristics of cold-flow modes and gas concentration distributions behind a novel unconfined nozzle

This study utilized a novel Tai-Chi swirl generator (TCSG) to modulate the cold-flow behaviour behind a conventional/pure-jet nozzle. This TCSG significantly increased the air-CO2 mixing efficiency. The TCSG was installed at the exit of the pure-jet nozzle so as to transform the axial momentum into tangential momentum. The turbulence intensity increased when the flow passed through the TCSG. Laser-light sheet and smoke-wire flow visualization schemes were utilized to explore the modulated flow characteristics behind the TCSG. The flow patterns were categorized into five modes: jet flow, recirculation bubble, deflected flow, unstable flow, and turbulent flow modes. The vortex-shedding frequency behind the pure-jet nozzle increased as the Reynolds number of the annular jet (Rea) increased. However, the vortex-shedding frequency behind the bluff disc controller and TCSG decreased as Rea increased. The mixing efficiency of air and CO2 in each characteristic mode was determined by measuring the concentration o...