Abstract
This paper studies the relationship between unsteady flow features and instantaneous torque and power performance of straight bladed vertical axis wind turbine at variable tip speed ratios. The rotor unsteady flow field simulation was carried out by using computational fluid dynamics method. The flow physics and the principle of changing flow field acting on torque performance and power performance have been analyzed where the rotating rotor was the major concern. The results show that the flow feature alters from periodical blade dynamic stall vortexes generation, development and shedding at low tip speed ratio to cyclical formation, evolution and diffusion of blade wake flow with the rising tip speed ratio. Both vortex shedding around the blade and interaction of blade wakes degrade the rotor aerodynamic performance. It is suggested that, to absorb maximum wind energy, delay the blade vortex shedding and reduce the range of blade wake, evolution and diffusion should be included in the rotor aerodynamic design.
Highlights
Modern wind turbines are classified into horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs) based on their axis of rotation
Straight bladed VAWTs have no need for yawing system which simplifies the structure, are easy to manufacture because blades can be of constant profile along the span, and have relatively small noise emission level due to lower operating blade tip speeds
In order to illustrate the influence of the changing unsteady flow field on power and torque performance, instantaneous torque coefficient and power coefficient in conjunction with flow field at three tip speed ratios (λ=0.5, λ=2.5 and λ=3.5) will be analyzed in the following part
Summary
Modern wind turbines are classified into horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs) based on their axis of rotation. VAWTs, especially straight bladed VAWTs have begun to play a major role in wind power in recent years, because there is a growing interest in harvesting wind energy within the environment built in urban sites [1,2,3]. Straight bladed VAWTs have no need for yawing system which simplifies the structure, are easy to manufacture because blades can be of constant profile along the span, and have relatively small noise emission level due to lower operating blade tip speeds. All these merits are important in building the environment and in this connection straight bladed VAWTs are good candidate for urban wind energy utilization
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