Comparison of the flow-field characteristics of a slot synthetic jet with and without sidewalls

Abstract

In this paper, experimental investigation of the flow-field of a slot synthetic jet (SJ) with and without sidewalls, issuing into a quiescent environment is systematically reported. Two parallel sidewalls were mounted along the shorter side of the slot extending in the streamwise direction to constrain the flow along the slot span. Hot-wire anemometry was used to explore the flow-field characteristics of both configurations at a Reynolds number of 4000 based on the slot-width and slot average exit velocity during the ejection phase. The present work is a first step towards the investigation of the SJ flow-field characteristics in a bounded region. In a number of generic situations, this work is of high importance as the SJ is deployed in constrained environments (e.g., in cooling applications) where sidewalls may be present. The relative difference in the magnitude of the distinct peaks in the near-field spanwise velocity profiles for both configurations reveals that the vortex does not get curled up towards the centerline in the case of the synthetic jet with sidewalls due to the presence of the no-slip walls. Spectral analysis in the near-wall region further confirms the absence of the phenomenon of axis-switching in the case of the synthetic jet with sidewalls. This behavior is also demonstrated with the help of the relative spreading rate in both configurations, where the unbounded synthetic jet spreads rapidly compared to the bounded one, due to greater entrainment of the surrounding fluid. The statistically two-dimensional region for a synthetic jet with sidewalls is found to extend over a longer axial distance in the downstream. The other jet properties such as turbulence intensity, skewness, and flatness factors further reveal the differences in the flow-field of the two configurations. The results show that the presence of the sidewalls strongly influences the SJ flow-field and hence, it would significantly impact the heat transfer capacity of the SJ.