MEASUREMENTS OF ENTRAINMENT CHARACTERISTICS OF SWIRLING JETS

Entrainment characteristics of free swirling jets were investigated by the schlieren flow visualization and the newly contrived technique fo r measuring the entrainment velocity, which is demonstrated to be reas onably accurate and reliable. The visualization studies reveal that th e entrainment rate increases with the swirl intensity. Schlieren photo graphs, which were synchronized with the fluctuation velocity signal, display that the precessing vortex core (PVC) induces large scale peri odic motion in the jet boundary regions near the nozzle exit. The PVC effect on entrainment is scrutinized by employing two swirling jets, o ne with a PVC and the other with a substantially suppressed PVC. The r esults clearly indicate that the entrainment is enhanced considerably due to the PVC. For swirl number S < 0.6, the entrainment rate is fair ly independent of the Reynolds number (Re) and increases more or less nonlinearly with the downstream region, while, for S > 0.6, it becomes higher with Re; this is due to the fact that the high-frequency PVC i s induced at higher Reynolds number.