Detailed numerical investigation of the CO[formula omitted] two-phase ejector 3-D CFD model based on the flow visualisation experiments

Abstract

3-D CFD-based simulations of CO2 flow inside two-phase ejectors are commonly used with various turbulence models. However, none of the previously published studies examined the influence of a local turbulence phenomenon on the simulation results. Therefore, in this study, a detailed numerical analysis of CO2 local flow behaviour was compared to experimental flow visualisation data as well as to turbulence approach validation. Furthermore, the kinetic behaviour of mixed streams in the boundary layer was examined under transcritical operating conditions for motive nozzle pressures above 80.0 bar. The mixing process mapped by different turbulence models showed differences in recapturing the angle of suction flow in the mixing chamber. Furthermore, the different flow shapes of the simulated motive expanded flow were observed. The best prediction of the mixed two-phase flows was obtained using the Reynolds stress model with linear pressure-strain approach with the suction mass flow rate discrepancy of 2%. The higher pressure lift caused the suction flow to be more perpendicular towards the motive flow, elongating the suction flow course in the mixing chamber and intensifying the mixing process. A further increase in the pressure lift eventually leads to the possible occurrence of suction reverse flow.