Abstract
A vertical axis drag-based turbine is proposed that allows for an improved performance by feathering its blades during recovery strokes to eliminate adverse blade forces. The turbine blades resemble flat plates and pitch by 90 ∘ between the two turbine strokes using a novel dual-cam mechanism. This passive mechanism orients the blades vertically during the drive stroke for maximum effective area and horizontally for minimum effective area during the recovery stroke. This allows maximizing the positive drive stroke force and minimizing the recovery stroke losses, in turn maximizing the net energy capture and the turbine performance. It is called the cyclic pitch turbine, and a mathematical model is developed that predicts the turbine performance. It shows that the turbine is self-starting for all orientations and has a higher and more uniform static torque coefficient than the popular Savonius turbine. The dynamic analysis also indicates a higher performance, and the predicted values for torque and power coefficients match very closely with those from water channel and wind tunnel experiments on a prototype. Results of testing several blade shapes indicate that airfoil section blades with long and narrow continuous shapes that have less area towards the blade’s tip result in higher performance.
Highlights
Power generation using renewable energy sources has been a topic of utmost interest in recent years because of factors like global warming [1], pollution [2], and depletion of fossil fuel [3] among many others
Static torque coefficient values were calculated for both Cyclic Pitch Turbine (CPT)
The cyclic pitch turbine had an average CTS that was 7% higher than that of the Savonius turbine for all three configurations
Summary
Power generation using renewable energy sources has been a topic of utmost interest in recent years because of factors like global warming [1], pollution [2], and depletion of fossil fuel [3] among many others. Present-day wind turbines are classified as horizontal axis or vertical axis, based on the orientation of their rotation axes They are further classified as lift-based or drag-based wind turbines depending on the type of forces utilized by their blades. Lift-based wind turbines include all the horizontal axis wind turbines (HAWT) and some vertical axis wind turbines (VAWT) like Darrieus. These turbines use lift forces acting on their blades with airfoil cross-sections to generate torque [8]. The Savonius turbine [10], developed by S.J.Savonius in 1922, is the most popular drag-based turbine and rotates about a vertical turbine axis These turbines experience a higher positive drive stroke drag force Fd in the downwind direction than the adverse recovery
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