EXPERIMENTAL CHARACTERIZATION AND SCALE MODELING OF A VERTICAL AXIS WIND TURBINE

A novel method of harnessing wind energy utilizes fixed surrounding stators which converge on a vertical axis turbine. Destructive fluid interactions cause inconsistent starting and diminished efficiency of such a design. In this research, experimental performance analysis of scaled turbine geometries is used to evaluate design parameters and predict turbine behavior, in order to minimize these effects. Purely vertical turbine blades paired with parallel stators create a passing interference along with points of force balance during low wind conditions. The varying low-wind torque outputs of such states decreases the predictable starting of the proposed design. This adds further complication to anticipating the turbine size needed to start a preselected generator with known breaking torque. One method of reducing symmetrical loading is to add a helical form to the turbine. Another is to increase the distance between stator and turbine tips within the windward cavities. The latter being achievable by allowing a portion of the stator to pivot away from the turbine in the direction of rotation. To analyze the performance of varied geometries, scale turbine replicas, with a height of 2.5 and 5-inches, were constructed. Each was designed to fit within the Aerolab wind tunnel of the University of Rhode Island Mechanical Engineering Laboratory. The 5-inch model was built with interchangeable stators and turbines allowing for various combinations of open or closed stators with a range of turbine helices. The output shafts were equipped with a load cell or optical encoder paired with custom data acquisition hardware and software. The static performance of different stator and turbine combinations was measured by fixed turbine torque readings at various starting angles. Rotational performance was quantified by measuring angular change of the turbine released from rest and free moving in constant and ramped wind conditions. Dimensional analysis was applied to the gathered data in order to develop torque scaling equations. The replica testing indicated that the combination of open stators with a 45° top-to-bottom offset helix provided the least propensity for stalling, along with the greatest acceleration, top speed and static torque generation. These results were scaled to predict that a 5 kW generator could be started by a 7-foot-tall turbine exposed to a 2 m/s wind velocity. The prediction was then validated by testing a full 7-foot prototype