VAWT Stochastic Loads Produced by Atmospheric Turbulence

Abstract

Blade fatigue life is an important element in determining the economic viability of the Vertical-Axis Wind Turbine (VAWT). A principal source of blade fatigue is thought to be the stochastic (i.e., random) aerodynamic loads created by atmospheric turbulence. This paper discusses the development of a model for the simulation of these stochastic loads, given the rotor geometry, operating conditions, and assumed turbulence properties. A Double-Multiple-Streamtube analysis is employed, which includes the effects of wind shear, Reynolds number variations, different airfoil sections and chord lengths along the blade span, and an empirical model for dynamic stall effects. Calculations are presented for the VAWT 34-m Test Bed recently erected at Bushland, Texas. Time histories of the loads, as well as their Fourier spectra, are presented and discussed. An unexpected finding is that the average output power is predicted to be more sensitive to turbulence level than had previously been thought.