A computational fluid dynamics (CFD) investigation of the wake closure phenomenon

Using a computational fluid dynamics (CFD) software, the gas dynamics of the open-wake and closed-wake conditions of an annular-slit high-pressure gas atomization (AS-HPGA) nozzle were investigated to validate the predictions of a pulsatile atomization model that was recently proposed. The location of the recirculation zones, the oblique shocks and the Mach disks were analyzed for this type of closed-coupled gas atomization nozzle. The stagnation pressures located downstream of the Mach disk, in closed-wake condition, were found to be approximately twice as high as the stagnation pressure in an open-wake condition at a slightly lower atomization gas pressure. The turbulence model utilized within the CFD calculation scheme appeared to be inadequate for calculating aspiration pressure just below wake-closure pressure when the recirculation zone is extremely long and narrow. However, overall, the CFD calculation correlated well with the experimental results, showing that the aspiration pressure progressively lowers as operation pressure increases in open-wake condition, and rises as operation pressure increases in closed-wake condition.