Active control of vortex shedding from a blunt trailing edge using oscillating piezoelectric flaps

Piezoelectric bending actuators have been used to drive flaps to manipulate vortex shedding from a nominally two-dimensional blunt trailing edge (BTE) using three different actuation methods. The experiments were conducted in a wind tunnel at a Reynolds number of Re(h) = 2600 where h is the height of the BTE. A combination of base-pressure measurements at the BTE and high-speed particle image velocimetry was used to characterize actuator performance over their operating range. Proper orthogonal decomposition was also applied to study the energy content of the primary vortex shedding structures in the wake during actuation. Cases of significant vortex shedding amplification and suppression were investigated. Vortex shedding amplification occurred when the frequency of actuation matched that of the natural wake process, resulting in the turbulent kinetic energy associated with two-dimensional vortex shedding increasing from 70% to 90%. This led to higher turbulence intensities, a shortened recirculation region, and more organized vortex shedding in general. Vortex shedding suppression was caused by the generation of small spanwise vortices at the tips of the actuators, which disrupted the interaction between the separating shear layers. The energy associated with vortex shedding was reduced from 70% to 20% in this case, resulting in a significant attenuation of the shedding pattern for at least six BTE thicknesses downstream. Vortex shedding suppression was accompanied by greatly reduced turbulence intensities, a narrowed wake, and a lengthened recirculation region. The actuators were also capable of forcing symmetry in the near-wake using a symmetric actuation method, but the vortex shedding resumed downstream, although with a reduced frequency. Finally, an adaptive slope-seeking controller was designed using the base-pressure measurements at the BTE in real time. The closed-loop controller was capable of seeking and maintaining an optimal input for vortex shedding suppression, even during slow variations in freestream velocity.