Innovative design method and experimental investigation of a small-scale and very low tip-speed ratio wind turbine

Abstract

Small horizontal axis wind turbines operating at low wind speeds face the issue of low performance compared to large wind turbines. A high amount of torque is required to start producing power at low wind speed to overtake friction of mechanical parts. A low design tip-speed ratio (λ) is suitable for low power applications. The relevance of the classical blade-element/ momentum theory, traditionally used for the design of large wind turbines operating at high tip-speed ratio, is controversial at low tip-speed ratio. This paper presents a new design methodology for a 300 mm horizontal axis wind turbine operating at very low tip-speed ratio. Chord and blade angle distributions were computed by applying the Euler's turbomachinery theorem. The new wind turbine has multiple fan-type blades and a high solidity. The rotor was tested in wind tunnel. The power and torque coefficients have been measured, and the velocities in the wake have been explored by stereoscopic particle image velocimetry. The results are compared to a conventional 3-bladed horizontal axis wind turbine operating at higher tip-speed ratio λ = 3. The new wind turbine achieves a maximum power coefficient of 0.31 for λ = 1. The conventional wind turbine achieves similar performance. At low tip-speed ratio, the torque coefficient (C τ ) is higher for the new wind turbine than for the conventional one and decreases linearly with the tip-speed ratio. The high magnitude of torque at low tip-speed ratio allows it to have lower instantaneous cut-in wind speed (2.4 m.s −1 ) than the conventional wind turbine (7.9 m.s −1 ). The order of magnitude of the axial and tangential velocities in the near wake are closed to the design requirements. The current method could still be improved in order to better predict the profiles. The analysis of the wake shows that the new wind turbine induces a highly stable and rotating wake, with lower wake expansion and deceleration than the conventional one. This could be usefull to drive a contra-rotating rotor.

Experimental investigation of the effect of blade solidity on micro-scale and low tip-speed ratio wind turbines

“…The latter does not have steady operating point in a wide range of tip-speed ratio 0.7 ≤ λ ≤ 0.9. A similar pattern of results was found in preliminary experiments carried out with a low solidity 3-bladed fast wind turbine [11]. In both cases, no steady experimental C p and C τ points are displayed for a wide range of tip-speed ratio.…”

“…Six micro-scale wind turbines were designed according to the method of Bourhis et al presented in Ref. [11] with a different vortex law. With the exception of the blade solidity σ, all runners are designed with the same parameters.…”

“…Some studies have focused on wind tunnel experiments with scaled-down wind turbines in order to get scaling laws and laws of similarity rather than designing efficient micro-scale runners. Consequently, the vast majority of prototypes found in the open literature achieves lower performance than large-scale runners [11,12].…”

“…Bourhis et al in Ref [11] proposed an alternative method to design high-solidity wind turbines without using the airfoil data. The goal of the method is to design a highsolidity blade cascade arrangement which is able to deflect the airflow as desired.…”

An efficient hybrid reconfigurable wind gas turbine power management system using MPPT algorithm

“…The MPPT regulator supplies a voltage which is paralleled to the 𝑉 𝑑𝑐 actual value. The outcome is supplied to a PI regulator, the output of which is paralleled to a triangular waveform in order to find at what time to make the dc dc boost converter switch OFF or ON [20]. The PWM inverter voltage source interacts with the scheme of wind turbine along with the power grid.…”