Penetration and Mixing of Radial Jets in Neck-Down Cylindrical Crossflow

Abstract

A parametric study of the penetration and mixing of radial jets in a neck-down cylindrical crossflow, which is characteristic of the quick-mix section in a generic tubular rich-burn/quick-mix/lean-burn combustor, is performed numerically. The parameters considered are the jet-to-crossflow momentum-flux ratio, number of injection orifices, neck-down ratio, swirling flow, and aspect ratio and orientation of radial slots. The analysis considers only nonreacting flows in order to concentrate on the fluid mechanics aspect of the processes, using temperature as a passive scalar to characterize the mixing performance. Laser-induced fluorescence experiments were also performed to verify the computational model. The results show that 1) the momentum-flux ratio has the most prominent effects on mixing performance, 2) there is a tradeoff between mixing effectiveness and pressure penalty, 3) the optimal configuration changes with the number of orifices and the slot aspect ratio, 4) an empirical optimal mixing correlation was developed for slotted orifices, 5) swirling flow does not improve mixing or pressure loss, and 6) necked-down sections do not necessarily enhance mixing but produce structural blockage, raising the pressure penalty. The implications of the parametric study on designing optimal mixer geometry are also discussed in terms of temperature and pressure penalty.