Focusing of jet from synthetic jet array using non-linear phase delay

Abstract

In the present investigation, a novel focusing technique is proposed and demonstrated to enhance the strength of a synthetic jet array (SJ array). Here, for the same geometric and operating parameters, focusing of the SJ array is achieved by providing a non-linear phase delay (∅) between the actuators. An open-source software, OpenFOAM, is used to study the influence of the Strouhal number (St=0.028, 0.086, and 0.13) and ∅ s (range: 0°−180°) on the focusing behavior of the SJ array for fixed Reynolds number Re=300. Irrespective of ∅s, due to strong suction effect, focusing is not achieved for the SJ array operated at low St=0.028. However, maximum focusing is achieved for intermediate St=0.086 and ∅=90°, which shows an increment of ∼52% in the time-averaged streamwise velocity (Vavg) measured at y=20d compared to ∅=0°. Similarly, the Vavg is enhanced by ∼37% for high St=0.13 with ∅=120°. Also, the variation of Vavg along the jet centerline shows a decrease in the slope of the decay profiles due to focusing. Most importantly, the temporal evolution of the pumping power shows that no additional energy is required for enhancing the strength of SJ array. The proper orthogonal decomposition analysis illustrates that maximum focusing (St=0.086 and ∅=90°) conserves ∼ 43% of total kinetic energy, which was lost due to destructive interaction between the vortices in the case of ∅=0°. Hence, for effective implementation in flow control, electronic cooling, and other applications, it is recommended to focus the SJ array by operating it at intermediate St with a moderate non-linear phase delay (∅=60° and 90°).