Closed-loop controlled vortex-airfoil interactions

Abstract

Closed-loop controlled interactions between an airfoil and impinging vortices were experimentally investigated. This work aims to minimize the fluctuating flow pressure ͑p͒ at the leading edge of the airfoil, which is a major source of the blade-vortex interaction noises commonly seen in rotorcrafts. Piezoceramic actuators were used to create a local surface perturbation near the leading edge of the airfoil in order to alter the airfoil-vortex interaction. Two closed-loop control schemes were investigated, which deployed p and the streamwise fluctuating flow velocity ͑u͒ as the feedback signal, respectively. As the control effect on p was measured using a fast response pressure transducer, the oncoming vortical flow was monitored using a particle image velocimetry and a hot wire. It was found that the control scheme based on the feedback signal u led to a pronounced impairment in the strength of oncoming vortices and meanwhile a maximum reduction in p by 39%, outperforming the control scheme based on the feedback signal p. Physics behind the observations is discussed.

Recent advances in active control of turbulent boundary layers

“…This was confirmed both numerically [8,52] and experimentally [29,30,53,54]. Control action must interact with turbulent fluctuations in a boundary layer, and the random aspects of the fluctuations reduce the effectiveness of an open-loop control.…”

Asynchronous control of vortex-induced acoustic cavity resonance using imbedded piezo-electric actuators

“…The effectiveness of this technique has been demonstrated for the case of active control of vortex shedding and associated structural vibrations for different cases of fluid-structure interactions, including resonant flow-structure coupling on a flexible-supported rigid cylinder, 36,37 resonant flow-structure coupling on a fix-supported flexible cylinder, 38 and nonresonant coupling on a fix-supported flexible cylinder. 39 This technique has recently been successfully applied to the control of noise caused by blade-vortex interaction 40 ͑BVI͒ and the control of airfoil aerodynamics. 41 Piezo-ceramic actuators are lighter and smaller than other actuation devices such as loudspeakers and electromagnetic actuators.…”

Control of Post-stall Airfoil Aerodynamics Based on Surface Perturbation

“…Melton et al [13] placed a piezoceramic actuator at the leading edge of a NASA energy-efficient transport high-lift airfoil to manipulate the flow and successfully postponed the flow separation, achieving a maximum increase in C L by 15% at 15 deg. Cheng et al [14] recently developed a surface perturbation technique, based on piezoceramic actuators, to manipulate a square-cylinder wake, which proved to be very effective in manipulating, either enhancing or suppressing, vortex shedding from the cylinder [15,16]. Both open-loop and closed-loop control were deployed.…”