Sea Technology

JUL 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Hydrodynamic Analysis of a Drag-Type Water Turbine Confguration With Retractable Blades Increases Power Effciency By Wenlong Tian • Baowei Song I n recent years, an interest in hydropower has been growing in the wake of environmental pollution, rising energy demand and depleting fossil fuel resources. Water turbines, which have been widely used for hydropower generation, can be classifed as lift type or drag type, depending on the driving force that rotates the rotor. Drag-type water turbines, like the Savonius, have the advantages of low-noise operation, good self-start performance and are more suitable for small-scale, distributed power generation. However, they are less effcient compared with their lift-type counterparts, despite the considerable effort made to enhance the performance. Existing drag-type water turbines are equipped with fxed blades. During a whole revolution, blades generate positive torque in the advancing half cycle and negative torque in the returning cycle. Because torque generated in the advancing half cycle is larger than that in the returning half cycle, the rotor rotates in the direction of the positive torque. A limitation of a drag-type water turbine's effciency is the negative torque that acts on the blade in the returning half cycle. The SNAIL is a drag-type water turbine that uses retractable blades to generate hydrokinetic power. The axial position of each blade is positioned by a control mechanism to produce high energy output. Returning blades can be entirely hidden in the drum, and negative torques can then be considerably deduced as the drum shields the blades. Two-dimensional computational fuid dynamic (CFD) simulations were performed to determine the output of the turbine. The simulation results show that blades generate high positive torque in the advancing half cycle, while in the returning half cycle, the blades generate nearly zero torque. 24 st / July 2013 Turbine Design In order to reduce the negative torque in the returning half cycle and eventually increase the net driving torque, the SNAIL water turbine was designed with retractable blades in a drag-type confguration. The turbine is made up of a power shaft, an eccentric shaft, a drum and several rectangular fat blades. The power shaft is fxed coaxially with the drum-rotating axis. The eccentric shaft is axially parallel to the power shaft with an eccentricity. The rotating motion of the power shaft is transmitted to the eccentric shaft through a synchronous belt, which The SNAIL turbine.

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