Bluff Bodies Flow Control using Innovative Piezoelectric Actuators

An active flow control technique based on “smart-tabs” is proposed to delay flow separation on a circular cylinder and on a simplified bi-dimensional automotive geometry body. The actuators are retractable and orientable multilayer piezoelectric tabs which protrude perpendicularly from the model surface. They are mounted along the spanwise direction with constant spacing. The effectiveness of the control was tested in pre-critical and in post-critical regime by evaluating the effects of several control parameters of the tabs like frequency, amplitude, height, angular position and plate incidence with respect to the local flow. Measurements of the mean static pressure distribution around the cylinder were used to estimate the pressure drag and lift coefficient. To take into account friction and the parasite drag of the actuators wake analysis was performed. The maximum drag reduction achieved in the pre-critical regime was of the order of 30%, whereas in the post-critical regime was about 15%, both for the highest forcing available. In pre-critical condition the active forcing plays an important role on drag and pressure fluctuations reduction. Spectral analysis of the signals from instantaneous pressure transducers (electret microphones) indicated an almost complete suppression of the vortex shedding in active forcing conditions. In post-critical regime, instead, most of the effects are due to passive forcing limiting the active contribution to a maximum of 3%. The results related to the automotive geometry confirm the ones obtained on the circular cylinder, with a maximum attained drag reduction of 13.4% with only small contributions due to active forcing. To evaluate the potentialities of the smart-tabs in real applications power absorption measurements are reported together with energy budget considerations. Finally, the identification of the key non-dimensional control parameters, was performed.