STRUCTURAL DESIGN CONSIDERATIONS OF A CIRCULATION CONTROLLED VERTICAL AXIS WIND TURBINE

In the latter half of the twentieth century extensive research had been performed to improve the efficiency and operational life of Vertical axis wind turbines (VAWTs) in order to make them competitive with the more common horizontal axis wind turbines (HAWTs). Due to the completely random wind conditions and a continuously changing angle of attack of the rotating airfoil, fatigue of the system components was a major contributor to the short operational life of these traditional VAWTs. The fluctuating aerodynamic forces generated by the airfoil during rotation subject the support shaft to a substantial amount of torque ripple. In addition to the varying torque produced by the turbine, the centripetal forces generated by the airfoil's rotation proved to be extremely large and create problems with deflection and fatigue in the airfoil's internal support structure and especially at the attachment point of the airfoil to the support arm. One method for improving the efficiency of an aerodynamic system is to reduce the weight of the system. However, because of the forces generated during turbine operation, this proved to be a nontrivial task. West Virginia University's (WVU) Center for Industrial Research Applications (CIRA) is exploring the implementation of circulation control on a vertical axis wind turbine to increase the lift to drag ratio of the turbine's airfoils in order to produce a greater turning force and improve the efficiency of the system. While the common structural challenges of vertical axis wind turbines still apply, those implementing circulation control introduce additional design hurdles which must be overcome. These additional design problems concern mainly with the airfoil construction and support shaft in that they must be capable of accommodating the circulation control system components. This paper introduces the geometrical design constraints imposed on a vertical axis wind turbine through the operational requirements and serviceability of the circulation control system in addition to the traditional aerodynamic and centripetal forces generated and how they are resolved onto the individual turbine components.