Effects of Jet-to-Jet Spacing on Wake Dynamics and Interactions for Multiple Jets in a Crossflow

Abstract

Abstract. This work extends our previous study to investigate the variations in wake vortex formation and jet-to-jet interactions with changes in jet spacing for a single jet and multiple jets in crossflow with jet spacings of 3.2D, 2.5D, and 1.6D (D = jet nozzle diameter). In this study, large eddy simulations (LESs) were performed employing a jet-to-crossflow velocity ratio of 3.3 and a Reynolds number of 2100 based on the crossflow mean velocity and jet nozzle diameter. Dynamic mode decomposition (DMD) and statistical analysis revealed that wake vortices are formed at a jet-to-jet spacing of ≥3.2D but not at jet spacings of 2.5D and 1.6D. A strong pulsating jet flow, as an important characteristic of jet-to-jet interactions, occurs in the space between adjacent jets for jet spacings of 2.5D and 1.6D but nearly disappears at a jet spacing of 3.2D. For multiple jets with a jet spacing of 1.6D, our previous study demonstrated that a pulsating jet flow is generated at a frequency of 32 Hz between adjacent jets. In addition, the variable-interval time-averaging technique in this study revealed that strong intermittent bursts of velocity fluctuations occur at lower frequencies of 7–12 Hz. These intermittent bursts persist over a long distance along the jet trajectory until the shear layer vortex rings collapse owing to the damping effect of counter-rotating vortex pairs, substantially enhancing the generation of turbulence and mixing of the temperature field at the rear of jets. The findings in this paper offer new insight into the fluid dynamics of multiple-jet configurations.