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

Victor Maldonado,Soham Gupta

doi:10.4236/ojfd.2017.72012

Abstract

A low Reynolds number wind turbine blade model based on the S809 airfoil was tested in a subsonic wind tunnel to study the structural vibration of the blade under dynamic pitching maneuvers. Piezoelectric-based synthetic jet actuators were embedded inside the blade and activated with a synthetic jet momentum coefficient, Cμ of 2.30 × 10-3. Structural vibration was quantified for a range of unsteady angles undergoing “pitch up and down” and “sinusoidal pitch” maneuvers at a Reynolds number of 5.28 × 104. The blade tip deflection amplitude and frequency were acquired utilizing a pair of strain gauges mounted at the root of the model. Using active flow control vibration reduction was more effective during the pitch up portion of the blade motion cycle compared to the pitch down portion. This effect is due to dynamic stall, where a leading edge vortex is shed during the pitch up motion and contributes to higher lift compared to static angles of attack and lower lift when the blade is pitched down. Dynamic stall was measured with phase-locked stereoscopic particle image velocimetry (SPIV), where global mean flow measurements reveal a shift in location and reduction in the size of a recirculating flow structure near the suction surface of the blade during the pitch up motion compared to the pitch down.

Highlights

IntroductionIn addition to regulating blade loads, individual blade control is principally used to limit output power and torque in above-rated wind speeds in order to keep turbine operation within its design limits
The objective of the present paper is to reduce a wind turbine blade model’s structural vibration in a wind tunnel by efficiently controlling the blade’s aerodynamic characteristics along its span for dynamic blade pitch maneuvers under the influence of dynamic stall conditions
The implementation of a synthetic jet based flow control system for a low Reynolds number high aspect ratio wind turbine blade model was presented, and the reduction of structural vibration reduction was measured for dynamic blade pitch maneuvers representative of dynamic stall conditions

Summary

Introduction

In addition to regulating blade loads, individual blade control is principally used to limit output power and torque in above-rated wind speeds in order to keep turbine operation within its design limits. While this type of control method has the ability to respond sufficiently to changing wind speeds (due to blade rotation) and asymmetric aerodynamic loading at each blade at a relatively slow once-per-revolution manner, it cannot respond to higher frequency atmospheric phenomena such as turbulence, wind gusts, and wind shear. These loads are often unavoidable due to the slow response of conventional pitch control actuators in decreasing the angle of attack; the development of locally distributed high bandwidth flow control actuators with built in intelligence embedded on the blades is needed

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