Numerical Investigation of Supercritical Mixing dynamics of the Coaxial Swirl Injectors

A numerical study has been conducted to identify the cryogenic injection and mixing characteristics of a coaxial swirl injector under supercritical pressure. An improved formulation of the Reynolds-averaged Navier-Stokes turbulence models (to close the governing equations), Soave-Redlich-Kwong equation of state (to estimate thermodynamic properties), NIST database (to estimate transport properties) and PISO algorithm (for velocity-pressure coupling) are employed in the flow solver. The present study –distinguished from many other studies by considering real injectors’ geometrical complexities and propellants’ thermodynamic nonlinearities–characterizes supercritical mixing dynamics of the coaxial swirl jets through vorticity budget analysis. Results highlight the tilting/stretching term as the only mechanism of vorticity generation within the injector vortex chamber. At the injector nozzle, the baroclinic torque and volume dilatation terms control the mixing dynamics, too. Numerical observations indicate that the effects of recirculating bubbles (in front of the injector exit plane) are significant and improve the contribution of vortex stretching/tilting in terms of vorticity generation. In addition, the Kelvin-Helmholtz hydrodynamic instabilities also play an important role in the mixing process in the injector nearfield.