Abstract
The paper presents a joint experimental and numerical characterization of double-orifice synthetic jet actuators for flow control. Hot-wire measurements of the flow field generated by the device into a quiescent air environment were collected. The actuation frequency was systematically varied to obtain the frequency response of the actuator; its coupled resonance frequencies were detected and the velocity amplitude was measured. Direct numerical simulations (DNS) of the flow field generated by the device were subsequently carried out at the actuation frequency maximizing the jet output. The results of a fine-meshed parametric analysis are outlined to discuss the effect of the distance between the orifices: time-averaged flow fields show that an intense jet interaction occurs for small values of the orifice spacing-to-diameter ratio; phase-averaged velocity and turbulent kinetic energy distributions allow to describe the vortex motion and merging. A novel classification of the main regions of dual synthetic jets is proposed, based on the time- and phase-averaged flow behaviour both in the near field, where two distinct jets converge, and in the far field, where an unique jet is detected. The use of three-dimensional DNS also allows to investigate the vortex merging for low values of the jet spacing. The work is intended to provide guidelines for the design of synthetic jet arrays for separation control and impinging configurations.
Highlights
The use of synthetic jet (SJ) actuators for flow control has become widespread during the last years
Synthetic jets are generated by arrays or multi-orifice devices, in order to maximize their efficiency in impinging configurations or to cover extended regions for separation control purposes [6,7]
The flow field generated by these devices and their heat transfer performance are dramatically influenced by the presence of adjacent jets, which can interact and merge, affecting their control authority
Summary
The use of synthetic jet (SJ) actuators for flow control has become widespread during the last years. The flow field generated by these devices and their heat transfer performance are dramatically influenced by the presence of adjacent jets, which can interact and merge, affecting their control authority For this reason, research activities on multi-orifice actuators in quiescent conditions appeared as a compulsory step before introducing them in more complex environments. Ceglia et al [19] performed an experimental study, using hot-wire anemometry (HWA) and particle image velocimetry (PIV) to investigate the external flow behavior of an array of slotted synthetic jets in quiescent condition Their analysis considered both the time-averaged flow characteristics, including jet spreading, axis switching and streamwise velocity decay, and phase-averaged velocity data to discuss the vortex organization and trajectory.
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