Effectiveness of Central Swirlers in the Thermal Uniformity of Jet-in-Crossflow Mixing

Abstract

The present paper introduces the analysis-led-design concept in attaining the thermal homogeneity at the exit section of a mixing chamber. Staggered holes (SH) chamber type is representing jet-in-crossflow (JICF) where cold air is injected radially into an axially flowing hot air with a different velocity. Streamlined body of prolate-spheroid shape is fitted in the center of the chamber, and equipped with swirl generating fins (Swirlers). Numerical simulations were first run to predict the flow and energy fields and assess the performance of seven cases representing distinct swirlers setting (shape, dimension, and number). An unsteady turbulent condition was adopted considering high Reynolds number (Re) at the boundaries and large eddy simulation (LES) model for solving the eddy motion in the domain. Afterward, experimental measurements worked on validating the numerical results through proving the effectiveness of the recommended swirler design. Graphical and tabulated results showed the difference between the mixing patterns in thermal dimensionless numbers (normalized mixture fraction and uniformity factor), and consideration of total pressure drop was taken. All swirling designs enhanced the mixing process by generating substantial central swirl besides the small eddies formed from the jet interaction. Numerically, average uniformity improvement achieved in all cases studied was 46%, while the recommended geometry (football with four short rectangular swirlers, F4SR) is 16% better than plain football (FB), but loses pressure by 17%. Upon experimentation, F4SR had almost the same positive outcomes against plain football and SH by 24% and 47%, respectively. Finally, F4SR acts well at lower Re.