Diffusion performance of lobed jet in the developed states consistent across temporally and spatially developing flows

Abstract

This study demonstrates that temporally developing lobed jets can qualitatively reproduce the diffusion performance in the fully developed states of spatially developing lobed jets in laboratory experiments. The jet exit geometries, Reynolds number $(=70,000)$ , and turbulence intensity (3% of mean velocity) were set to be the same across the temporally and spatially developing jets. Four types of jet flows were tested, one being a round jet and three being lobed jets with different numbers or curvatures of lobes, referred to as 6L, 6S, and 3L, respectively. The half-width of the mean streamwise velocity distributions and centerline mean streamwise velocity of the four jets in the developed states were consistent between the numerical simulations and experiments. The round jet displayed the highest diffusion performance, followed by 3L, while 6L and 6S were the smallest and were comparable with each other. Despite such consistency in the developed states, the diffusion performance and formation of the streamwise swirling flows did not agree between the numerical and experimental results. These results suggest that unique large-scale structures corresponding to the initial conditions are reproduced in temporally developing jets, which is in good agreement with the spatially developing lobed jets. Therefore, the current study demonstrated that the temporally developing simulations can reproduce similar diffusion processes to those of the spatially developing ones.