Unsteady Flow Characteristics of an Oscillating Piezoelectric Fan Blade at High Reynolds Numbers

Piezoelectric fans have started to play an essential role in small-scale heat removal applications in recent years due to their high reliability and efficiency. In this study, an experimental study on the flow field characteristics produced by an oscillating piezoelectric fan at various Reynolds numbers (140 < Re < 550) in a quiescent air environment is investigated. Time resolved particle image velocimetry (PIV) measurements are performed for the flow field visualization. The flow pattern generated by the oscillating fan blade in the longitudinal plane changes as the Reynolds number increases. The ratio between the trailing edge velocity and side edge velocity increases as the Reynolds number increases. As a result, the trailing edge plays a more important role in driving fluid at a higher Reynolds number. Multiple vortexes are shed from the trailing edge during one oscillation cycle and is observed only at a high Reynolds number. This vortex shedding increases the unsteadiness of velocity field significantly, resulting in a turbulence intensity level beyond 100%. This result implies that turbulence models used in numerical studies need to be carefully validated as some might struggle at this highly turbulent flow regime.