| Popis: |
This paper presents the experimental results of a gaseous jet injected into an oscillating-air crossflow. The jet to crossflow momentum flux ratios are chosen as 19, 30 and 58, and the mean air crossflow velocities are chosen as 10m/s, 25 m/s, and 60 m/s. The crossflow is modulated at frequencies up to 280 Hz with a maximum crossflow velocity fluctuation of 30% of its mean velocity. Acetone planar laser-induced fluorescence is used to record the instantaneous jet concentration field. Three distinct regions are observed near the injection location (x/d < 18); the jet core, the fast bending zone, and the fully developed plume zone. The location of the end of potential core can be determined primarily by the momentum flux ratio. Based on observations of these three regions, a set of correlations for the trajectory of maximum jet concentration is proposed for the potential core region and for the fully developed plume zone. The potential core responds quasi-steadily to the crossflow oscillation and the fluctuation of penetration of the potential core zone linearly increases with respect to the crossflow velocity fluctuation level. The jet penetration under oscillating crossflow is slightly lower than that under steady crossflow, especially when the mean crossflow velocity is low (10–25 m/s). However, the differences of trajectories between the oscillating and the steady crossflow cases become almost negligible as the mean crossflow velocity increases further. The axial decay of jet concentration under oscillating crossflow occurs at faster rate than that under steady crossflow, indicating that the oscillating air crossflow enhances the mixing between the jet and the crossflow. The vertical jet concentration profile at different axial location confirms that the main effect of crossflow modulation is enhanced mixing of jet with crossflow. However, no noticeable effect of modulation frequency of crossflow on the jet penetration is found. |
