Qualitative and quantitative characterization of a synthetic jet mounted on a convex torpedo-like surface under cross-flow

Abstract

Understanding the fundamental flow physics of a synthetic jet in cross flow is important for a variety of engineering and scientific applications. In Particular, a synthetic jet mounted on a convex torpedo surface at high velocity ratios is of great importance for naval applications. However, despite exhaustive research done in this area, most of the studies have been conducted for synthetic jets on a flat surface and at low velocity ratios (ratio of average jet velocity and the cross-flow velocity). Studies at high velocity ratios particularly on a curved surface has largely not received much attention. Thus, the present study employs flow visualization and the laser doppler velocimetry (LDV) to qualitatively and quantitatively characterize such a synthetic jet under cross-flow conditions. Experiments have been conducted for quiescent flow conditions (i.e. 0 Hz) and at jet actuation frequencies of 1, 2, 4 and 6 Hz, at cross-flow velocities of 7.2, 20 and 32 cm/s. Our study indicates that the behaviour of synthetic jet changes significantly in the presence of cross-flow since it affects the formation, convection, and interaction among vortices, particularly at higher velocity ratios. Flow visualization provides interesting insights into the two major types of vortex rings and the interplay between the vortex structures and the boundary layer. Further, a comparison of the time-averaged velocity variation in the vertical direction reveals the formation of two local peaks at high velocity ratios and high actuation frequency of the jet. While the cross-flow is also found to be significantly affected by the high velocity ratio jet, the low velocity ratio jet in cross flow does not show substantial influence on the cross-flow except in regions close near the wall. The high velocity ratio jet shows the formation of a wake behind the jet region which is believed to be generated because of the blockage of the cross-flow created by the jet. Trailing jet and leading rings follow two different projectiles. Finally, a test-bed of LDV data has been reported in the study, which can prove useful in the validation of computational results of synthetic jets on a curved torpedo surface.