Experimental Analysis of a Cyclic Pitch Turbine

Cyclic pitch turbine is a drag based vertical axis fluid turbine which aims to optimize the drag forces that act on its blades. During operation, the turbine blades remain perpendicular to the flow in the drive stroke for maximum positive drag force and remain parallel to the flow in the recovery stroke for minimal negative drag. The blades pitch by 90 degrees between the two strokes using a dual cam mechanism. The blade pitching principle is inspired by bird’s wing motion and oar blade motion in rowing. Multiple turbine prototypes have been built and have been tested in air and water for functionality as well as for quantifying the performance. Water tunnel tests are conducted to measure power output at different turbine loads and flow velocities. Experimental setup included turbine speed, position senor and also a torque sensor. Experiments were aimed at understanding the performance of the turbine at different conditions and also finding the best blade configuration for maximum efficiency. The results show the cyclic variation of speed, torque and power output and coefficient of performance (C_P) at different tip speed ratios (TSR). They show that the coefficient of performance is maximum which is 0.17 at around 0.55 tip speed ratio which is typical of drag based turbines and the value reduces with both increase and decrease in the value of TSR similar to conventional turbines.