Numerical Investigation of Single and Multiphase Supersonic Swirl Flow in Convergent-Divergent Nozzle

For decades, abrasive fow blasting, has been used for surface cleaning. As with all surface cleaning methods, of course the challenge is to achieve effective cleaning without damaging the surface. In abrasive fow process, the supersonic air fow is made to accelerate the suspended solid media particles transferring the momentum of the particles to a surface force creating the cutting/cleaning action. Therefore, the crucial performance parameters are those associated with the jet. However, the exhaustive literature search was unable to fnd much relevant reported work on improving the effciency and energy consumption of sand blasting process. It is believed that the inherent problems associated with analysis of multiphase fow may be one reason for this. Accordingly, this study has focused on single and multiphase jet fow with swirl in supersonic convergent-divergent nozzle using different range of inlet pressures (150kPa-400kPa). The Swirl was achieved by patented helical insert at the inlet of the nozzle, where the swirl effect provides a better mixing feature inside the nozzle and hence reduces the cleaning process time and energy consumption above 35%. Numerical modelling was used to simulate both single and multiphase supersonic swirling fow inside and outside the nozzle. Eulerian and Lagrangian multiphase simulations were performed and it has been shown that for abrasive particles, the Lagrangian model (DPM) provides more accurate results. FLUENT and OpenFOAM, CFD software were used to solve governing equations of the fow with RANS turbulence modelling. This research has found that the swirl effect reduces the shock cells strength inside the nozzle and increases the damping ratio on shock waves. The shock structure and separation zone for the non-swirl nozzle simulations was symmetrical; however, the nozzle with helical insert showed a very complex unsteady and asymmetric fow pattern. Additionally, it was observed that the swirl fow inside the nozzle creates larger separation zones at the exit of the nozzle which helps to improve the mixing feature. Furthermore, in this type of fow it was shown that, even if the nozzle was choked, increasing the inlet pressure increases the mass fow rate.