Double-Multiple Streamtube Analysis of a Flexible Vertical Axis Wind Turbine

Abstract

Vertical-axis wind turbines (VAWTs) have drawn increased attention for off-grid and off-shore power generation due to inherent advantages over the more popular horizontal-axis wind turbines (HAWTs). Among these advantages are generator locale, omni-directionality and simplistic design. However, one major disadvantage is lower efficiency, which can be alleviated through blade pitching. Since each blade must transit both up- and down-stream each revolution, VAWT blade pitching techniques are not yet commonplace due to increased complexity and cost. Utilizing passively-morphing flexible blades can offer similar results as active pitching, requiring no sensors or actuators, and has shown promise in increasing VAWT performance in select cases. In this study, wind tunnel tests have been conducted with flexible and rigid-bladed NACA 0012 airfoils, in order to provide necessary input data for a Double-Multiple Stream-Tube (DMST) model. The results from this study indicate that a passively-morphing VAWT can achieve a maximum power coefficient (Cp) far exceeding that for a rigid-bladed VAWT CP (18.9% vs. 10%) with reduced normal force fluctuations as much as 6.9%. Operational range of tip-speed ratio also is observed to increase by a maximum of 40.3%.

Optimization Methods for Wind Turbines

“…However, one of the main disadvantages is lower efficiency, which can be reduced by angling the blades. The use of passively pitching flexible blades [33] can achieve the same results as active pitching without requiring any sensors or actuators and has shown promising results in improving VAWT performance in some cases. Wind tunnel testing was conducted with flexible and rigid NACA 0012 airfoil blades to provide the necessary input data for the Dual Multiple Stream Tube (DMST) model.…”

An overview of aerodynamic performance analysis of vertical axis wind turbines

“…20%). Roy et al 110 performed experimental testing based on the double multiple streamtube model of VAWT with flexible and rigid-blades configurations. Passively-morphing VAWT resulted in improvement of maximum C .1em p and operating range of TSR by 8.9% and 40.3%, respectively than rigid bladed VAWT.…”

Investigation of vertical axis wind turbine with guiding flat plates

“…Usually, it consists of blades with a symmetrical profile and works on the principle of lifting force. The theoretical efficiency can be calculated accurately with the double multiple stream model [6,7,8], which uses the blade element theory [9] and the actuator disk theory [10]. It's easier to choose a generator for Darrius due to the higher rotational speed and lower torque.…”