Influence of thickness on the flow field generated by an oscillating cantilever beam

 The aerodynamic performance of oscillating piezoelectric fans has been the focus of many research studies due to their potential as active cooling mechanisms for thermal management applications. These studies have typically focused on commercially available fans with flexible beams that are made to oscillate by tuning the alternating input voltages to the beam’s resonant frequency. Geometric variables such as fan height and length have previously been investigated; however, fan thickness has remained a fixed geometric constraint (\({\mathcal {O}}\sim 0.1\) mm) to allow feasible resonant frequencies to be achieved. This study investigates the influence of beam thickness on the flow field generated by an oscillating beam. The beam in this study is a rigid cantilever that is mechanically oscillated at a fixed amplitude and frequency thereby obviating the requirement to operate at resonance. Thicknesses of 1 and 3.7 mm are considered. A custom-designed particle-image velocity (PIV) facility was used to capture the induced phase-locked and time-averaged flow fields in two planes. The beams were noted to produce markedly different wakes within the oscillation plane. The 1-mm beam induced two distinct diverging jets—consistent with much of the literature on piezoelectric fans. In comparison, the 3.7-mm beam created two strong lateral wake regions with minimal fluid disturbance downstream of the beam tip. Out-of-plane measurements, as well as numerical models, revealed that fluid separation from the 3.7-mm beam is inhibited due to the more dominant influence of viscous friction on the larger, upper and lower surfaces of the rigid structure. The numerical analysis also revealed the significant influence of shed, counter-rotating vortex pairs on the pressure fields around the beam structures during the subsequent half-stroke. The results of this work may inform the design of oscillating fans for use in thermal management applications, as well as contribute to the literature on the complex phenomenon of flapping wing flight.