Simulation of a Lifting Surface with a Flexible Piezoelectric Actuator in a Rotating Environment

Abstract

In the past years, the consumption of energy produced by wind turbines had an exponential growth. This requirement gave momentum to the development of larger turbines with the goal of producing more energy at the same site, reducing the initial investment, and the operation and maintenance costs. In order to achieve this objective, longer, lighter, maintenance-free blades are required so that smaller loads are transferred to the other, more expensive, wind turbine components.
The resulting larger flexibility, imposes new challenges to the blade and controller designs; henceforth, new concepts are being developed to add more intelligence into these systems. During the last few years, the electronics industry had invested resources into the research and development of practical applications for piezoelectric ceramic materials. The result of this effort was the development of high precision piezoelectric actuators and sensors, which achieve forces and deformations that are compatible with the ones needed for the control of aerodynamic surfaces.
In a former study made by the authors, the aeroservoelastic behavior of a lifting surface with a fixed end and a flexible piezoelectric actuator was analyzed. In that work it was shown that the flexible piezoelectric actuator is an effective tool for vibration control. In the present paper, the analysis of the aeroservoelastic behavior of a lifting surface with a flexible piezoelectric actuator is extended to a non-inertial coordinate system that spins around an inertial one. The actuator is composed of a flexible trailing edge with embedded piezoelectric layers that enables the active control of the local aerodynamic forces. Structurally, both the flexible surface and flap are modeled as continuous beams with fixed-free end conditions. The displacements are described by a series expansion of assumed modes. The system aerodynamics are modeled with an unsteady version of the vortex lattice method (UVLM). High Reynolds number flow is assumed, therefore viscous effects are confined at the boundary layers and the wake shed by the surface. Both surface and wake are idealized as vortex sheets which in turn are discretized with vortex rings. In order to capture the physical aspects from the fluid-structure-control interaction, the aerodynamic and structural numerical models are combined by means of a strong coupling technique. The system equations of motion are integrated iteratively in the time domain. Numerical experiments are performed on a 100m test blade. The results show the feasibility of utilizing this type of actuators in the control of large horizontal axis wind turbines.