Abstract
The concept of a vertical-axis spiral wind rotor is proposed and implemented in the interest of adapting it to air flows from all directions and improving the rotor’s performance. A comparative study is performed between the proposed rotor and conventional Savonius rotor. Turbulent flow features near the rotor blades are simulated with Spalart-Allmaras turbulence model. The torque coefficient of the proposed rotor is satisfactory in terms of its magnitude and variation through the rotational cycle. Along the height of the rotor, distinct spatial turbulent flow patterns vary with the upstream air velocity. Subsequent experiments involving a disk generator gives an in-depth understanding of the dynamic response of the proposed rotor under different operation conditions. The optimal tip-speed ratio of the spiral rotor is 0.4–0.5, as is shown in both simulation and experiment. Under normal and relative-motion flow conditions, and within the range of upstream air velocity from 1 to 12 m/s, the output voltage of the generator was monitored and statistically analyzed. It was found that normal air velocity fluctuations lead to a non-synchronous correspondence between upstream air velocity and output voltage. In contrast, the spiral rotor’s performance when operating from the back of a moving truck was significantly different to its performance under the natural conditions.
Highlights
The wind turbine is one of the most economically viable renewable energy conversion systems with the turbine’s aerodynamic and structural performance having a direct impact on the performance of the whole system [1]
Two torque coefficient curves corresponding to the blade rotation angle ranging from 0° to 360° are extracted from the simulation results after the residual errors converge to the limiting values
In particular a negative torque coefficient was found within two narrow ranges of blade rotation angle, which exactly reflects the intermittent disturbance to the flow field by the rotating blades with a uniform vertical profile
Summary
The wind turbine is one of the most economically viable renewable energy conversion systems with the turbine’s aerodynamic and structural performance having a direct impact on the performance of the whole system [1]. The well-known Betz limit caps the maximum ratio of transformable wind energy by wind rotor, significant effort is still being devoted to wind turbine innovation, especially for vertical-axis wind turbines. In spite of the low energy transformation efficiency of conventional Savonius rotor, its high start-up torque and simple mechanical structure are two significant advantageous factors that suggest a promising future for this kind of rotor. A recent review of Savonius wind turbine by Fan et al [2] summarizes its advantages and applications
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