Active control of flow separation and structural vibrations of wind turbine blades

Abstract

The feasibility of using synthetic jet actuators to enhance the performance of wind turbine blades was explored in wind tunnel experiments on a small scale model blade. Using this technique, the global fl ow fi eld over the blade was altered such that fl ow separation was mitigated. Consequently, this resulted in a signifi cant decrease in the vibration of the blade. Global fl ow measurements were conducted, where the moments and forces on the blade were measured using a six component wall-mounted load cell. The effect of the actuation was also examined on the surface static pressure at two spanwise locations; near the blade's root and near its tip. In addition, Particle Image Velocimetry (PIV) technique was used to quantify the fl ow fi eld over the blade. Using synthetic jets, the fl ow over the blade was either fully or partially reattached, depending on the angle of attack, and the Reynolds number. Furthermore, the changes induced on the moments and forces, as well as on the blade vibrations were found to be proportionally controllable by either changing the momentum coeffi cient, the number of synthetic jets used, or by the driving waveform. Finally, a proof-of-concept closed-loop control system was developed to test the ability of using synthetic jet actuators to restore and maintain fl ow attachment and reduce the vibrations in the blade during dynamic pitching maneuvers. The control system demonstrated the ability of synthetic jet actuators to reduce blade vibrations during dynamic motion depending upon their control concept, which might be either pitch or active stall control. 222Active control of fl ow separation and structural vibrations V. Maldonado et al.

Active Flow Control of a Low Reynolds Number S809 Wind Turbine Blade Model under Dynamic Pitching Maneuvers

“…According to Maldonado et al [14], the strength of the synthetic jets (relative to the momentum of the external flow) is quantified using the momentum coefficient, C µ , defined as the following:…”

“…Separation control using synthetic jets has recently been demonstrated as a viable means to reduce wind turbine blade structural vibration, Maldonado et al [14] by exploiting the narrow-band receptivity of the separating shear layer and the upstream boundary layer to external actuation. Previously, Oster and Wygnanski [15] and Roberts [16] showed that V. Maldonado, S. Gupta the actuation can affect the global flow field by modifying the evolution and interactions of the large-scale vortical structures.…”

“…As discussed by Maldonado et al [14], this approach was implemented to improve the aerodynamic performance of stalled airfoils and flaps [17] [18] [19].…”

“…Seifert et al [17] and Wygnanski [20] As reported by Maldonado et al [14], another approach to control the flow is based on fluidic modification of aerodynamic lifting surfaces using embedded synthetic jets that are activated at high frequencies typically about an order of magnitude higher than the characteristic frequencies of the flow. [25] demonstrated that flow separation at high angles of attack can be mitigated by using synthetic jets that tailor the apparent surface curvature thereby modifying the distribution of the streamwise pressure gradient in advance of separation.…”

Emerging trends in vibration control of wind turbines: a focus on a dual control strategy

“…Use of active strut elements based on resonant controllers [15] inspired by the concept of TMDs has been proposed for active control of vibrations in wind turbines. Investigations on the use of synthetic jet actuators [16], microtabs and trailing edge flaps [17,18] have also been considered by researchers. Active control strategies have been proposed by Staino et al [19] and Fitzgerald et al [14].…”