Dynamic load control of a wind turbine blade using synthetic jets

Abstract

This study demonstrated that, through the introduction of periodic momentum near the leading edge of this model, the average tip deflection could be reduced under dynamic conditions. Furthermore, it was demonstrated that, at certain levels of momentum injection, tip deflections might actually be enhanced. Where load oscillations during dynamic conditions were observed, a similar trend occured. Certain levels of momentum injection resulted in higher oscillations in loading observed during dynamic pitching, where higher momentum injection levels reduced load oscillations during dynamic cycles. This work concludes with the suggestion that, moving to full scale testing of this flow control system, it will be necessary to provide sufficiently high momentum injection such that damage will not occur from the implementation and actuation of a flow control system.

Understanding and implementing engineering techniques that serve the purpose of reducing structural vibrations and load variations in wind turbine blades is of critical importance to the goal of reducing the cost of energy of wind energy systems. The effectiveness in reducing structural vibrations and load oscillations of a finite span S809 airfoil was investigated experimentally in the Rensselaer Polytechnic Institute's low speed wind tunnel at the Center for Flow Physics and Control (CeFPaC). The structural vibrations and load oscillations arose due to prescribed dynamic pitching parameters corresponding to non-dimensional motion parameters typically seen in field conditions. Aerodynamic loading was measured through a six component load cell located at the root of the model. Two-component and three-component velocity fields were measured through the use of a stereoscopic PIV system. Structural vibrations were measured through the use of strain gauges placed at the base of the model, and tip deflection was inferred by calibrating voltage variations in the strain gauges with tip deflections measured by a laser displacement sensor.

This process seems to be the result of changing how the flow field transitions from trailing edge separation to a fully separated flow. In a phase-averaged sense, this is defined by the creation of a phase averaged leading edge recirculation region, which interacts with the trailing edge separation. Through the introduction of momentum near the leading edge, this process can be altered, such that the phase averaged trailing edge separation region is the dominant structure present in the flow.