PIV Visualization of Dynamic Stall VAWT and Blade Load Determination

Abstract

The increasing awareness of the need for environmentally sustainable housing and cities has driven the promotion of wind energy conversion systems for the built environment. One of the results of the development of solutions for the built environment is the reappearance of Vertical Axis Wind Turbines (VAWTs). In the built environment, the VAWT presents several advantages over the more common Horizontal Axis Wind Turbines (HAWTs), namely: its low sound emission (consequence of its operation at lower tip speed ratios), better esthetics due to its three-dimensionality, its insensitivity to yaw wind direction and its increased power output in skewed ∞ow (see Mertens et al 1 and Sim~ao Ferreira et al 2 ). The phenomenon of dynamic stall is an inherent efiect of the operation of a VAWT at low tip speed ratios (‚). The presence of dynamic stall has signiflcant impact on both load and power. The paper focuses on evaluating the feasibility of estimating loads on Vertical Axis Wind Turbine (VAWT) blades in dynamic stall by velocity data acquired with Particle Image Velocimetry (PIV). The work uses both numerical and experimental data. Simulated velocity data from a Detached Eddy Simulation (DES) at space and time reflnement equivalent to that obtained with PIV is used to estimate the error associated with the method. The method is then applied to experimental data to verify the in∞uence of the complexity of the ∞ow and determination of space and time derivatives. The acquired data over the entire rotation is used to calculate the blade forces from the velocity data and its derivatives (solving the momentum equation), following the methodology presented by Noca et al 3 and Scarano et al. 4 The integration of the forces from the velocity fleld should overcome the di‐culties and limitations presented by pressure sensors for local section loads, but involves the referred di‐culties in determining the correct time-derivatives.