Structural-borne sound mitigation in small wind turbines using constrained viscoelastic layer

Abstract

As the growing acceptance of small wind turbines operating in suburban and rural communities coincides with increasingly stringent regulations on the sound emitted by these turbines, the need for sound mitigation solutions becomes urgent. Small turbines need to be affordable for small business use, and thus, proposed solutions must be cost-effective and low maintenance. Easy retrofit to existing turbines is also desirable. Wind turbines generate sound via two main mechanisms: structural borne sound generated by the gearbox and generator and transmitted through the nacelle structure and aeroacoustic sound generated by the interaction of the airstream with the rotating blades and other turbine components. Current study focused on the mitigation of structural-borne sound in a 50 kW wind turbine using a constrained viscoelastic layer. The viscoelastic layer comprised of multiple tiles with normal force to the nacelle structure provided by ratcheting bands. Optimal value for the normal force was empirically determined, and the resulting reductions in generated sound were documented both in the laboratory and on a working turbine under a number of operating conditions. The result is a cost-effective solution with zero cost of ownership and easy installation on a wide range of small to medium-size wind turbines.