Effect of orifice shape on impinging synthetic jet

Abstract

The present experimental study investigated the synthetic jet flow characteristics issued from four different orifice shapes (Re = 4739–5588). The flow dynamics of the jet is examined using the particle image velocimetry technique for circular, rectangular, square, and elliptical orifice shapes and two different surface spacings (z/d = 3 and 8). The results are presented in terms of streamwise distribution of velocity, normal stress, and shear stress. Furthermore, the most dominant modes of higher energy containing structures are obtained using proper orthogonal decomposition and compared for different orifice shapes. The results show that for a lower nozzle to surface spacing, vortices formed in the wall jet from the elliptical orifice contain higher energy than the other orifice shapes. The higher energy-containing vortices cause a delay in attaining self-similarity. Therefore, the self-similarity in the wall jet for the elliptical orifice is delayed than that of the other orifice shapes. Also, the elliptical orifice shape has relatively higher normal and shear stresses than that of other orifice shapes. The elliptical orifice shows 30% and 17% higher crosswise normal and shear stress than that of the circular orifice, respectively. However, for the larger nozzle to surface spacing, the least dominant mode of the structure is observed for the rectangular orifice shape, which results in a shifting of the self-similarity location toward the stagnation point. The findings from the present work are used to explain the variation of the heat transfer rate from a synthetic jet having different orifice shapes and impinging at different surface spacings.