Small wind turbines are key devices for micro generation in particular, with a notable contribution to the global wind energy sector. Darrieus turbines, despite being highly efficient among various types of vertical axis turbines, received much less attention due to their starting characteristics and poor performance in low wind speeds. Radically different concepts are proposed as a potential solution to enhance the performance of Darrieus turbine in the weak wind flows, all along the course of Darrieus turbine development. This paper presents a comprehensive review of proposed concepts with the focus set on the low wind speed performance and critically assessing their applicability based on economics, reliability, complexity, and commercialization aspects. The study is first of its kind to consolidate and compare various approaches studied on the Darrieus turbine with the objective of increasing performance at low wind. Most of the evaluated solutions demonstrate better performance only in the limited tip speed ratio, though they improve the low wind speed performance. Several recommendations have been developed based on the evaluated concepts, and we concluded that further critical research is required for a viable solution in making the Darrieus turbine a low speed device.

Strategies for Enhancing the Low Wind Speed Performance of H-Darrieus Wind Turbine—Part 1

The invention discloses a novel auto-launching-type Darrieus-Savonius combined type vertical shaft wind machine which comprises an S-shaped wind machine, an overrun clutch, a generator, D-shaped wind machines and a plurality of stand rods. A rotating shaft of the generator is connected with a shaft of the S-shaped wind machine in a transmission mode, and the plurality of stand rods are evenly distributed on the generator. The S-shaped wind machine is connected with the D-shaped wind machines through the overrun clutch, and the S-shaped wind machine is placed above the D-shaped wind machines. The D-shaped wind machines form an H-shaped wind machine with three blades, and the blades of the D-shaped wind machines are in an arc shape. The S-shaped wind machine is a double-blade spiral wind machine with 90-degree blade twist angle. After the S-shaped wind machine drives the D-shaped wind machines to be launched, the action of the S-shaped wind machine on the D-shaped wind machines is interrupted, so that the D-shaped wind machines are launched, the aerodynamic performance of the D-shaped wind machines is not affected by the S-shaped wind machine, and the property of the combined type vertical shaft wind machine is greatly improved.

Novel auto-launching-type Darrieus-Savonius combined type vertical shaft wind machine

The purpose of the work described in this paper was to determine the aerodynamic loads and performance of a Darrieus wind turbine by including the expansion effects of the streamtubes through the rotor. The double-multiplestreamtube model with variable interference factors was used to estimate the induced velocities with a modified CARDAAV computer code. Comparison with measured data and predictions shows that the streamtube expansion effects are relatively significant at high tip-speed ratios, allowing a more realistic modeling of the upwind/downwind flow field asymmetries inherent in the Darrieus rotor.

Streamtube expansion effects on the Darrieus wind turbine

The invention discloses an inner and outer sleeved type stirring damping wind power heating device which comprises a double-S-shaped vertical axis wind turbine, a phi-shaped vertical axis wind turbine, a non-contact type overrun clutch, a stirring damping heater and a large base The double-S-shaped vertical axis wind turbine is connected with a center shaft of the phi-shaped vertical axis wind turbine and the stirring damping heater through the non-contact type overrun clutch The double-S-shaped vertical axis wind turbine is arranged above the phi-shaped vertical axis wind turbine and the stirring damping heater The phi-shaped vertical axis wind turbine is connected with the stirring damping heater through the non-contact type overrun clutch and an annular guide rail sliding block mechanism The middle portion inside the phi-shaped vertical axis wind turbine is sleeved with the stirring damping heater which is fixed to the large base The inner and outer sleeved type stirring damping wind power heating device has the beneficial effects that wind power is captured through the advantages of two types of wind turbines, the wind power use range is wide, and the wind power use rate is increased

Inner and outer sleeved type stirring damping wind power heating device

The invention discloses a vertical axis wind turbine which comprises a spindle and wind wheels The main wind wheels and an auxiliary wind wheel are adopted Due to the fact that the diameter of the auxiliary wind wheel is smaller than that of each main wind wheel, when wind force is small, the wind force can drive the auxiliary wind wheel to achieve small-power electricity generation, and when wind force is large, the main wind wheels and the auxiliary wind wheel generate electricity at the same time, so that electricity generation efficiency is improved Sub wind wheels are arranged on first blades, sub wind wheel blades are in an S shape, and the sub wind wheels can rotate in weak wind so as to drive outer shafts to rotate; the sub wind wheels can be used for starting the main wind wheels and also generating electricity in a weak wind state; meanwhile, due to the fact that the main wind wheels are slowly started, equipment is prevented from being damaged when the main wind wheels are suddenly started, and the service life is prolonged

Vertical axis wind turbine

A combined vertical axis wind turbine comprises a Savonius wind turbine, a Darrieus wind turbine, a vertical rod and a non-contact overrun clutch. The non-contact overrun clutch comprises an outer ring, an inner ring, a wedge block device, a fixing retaining ring, a retaining collar, two end caps, two bearings, a retaining ring and a torsion spring, wherein the inner ring is mounted on a shaft extension of the Savonius wind turbine, the outer ring is supported by the two bearings mounted on the inner ring and is connected with the Darrieus wind turbine prior to being fastened together with the two end caps through screws, and the Savonius wind turbine is connected with the Darrieus wind turbine through the overrun clutch and is arranged above the Darrieus wind turbine. The combined vertical axis wind turbine has the advantages that self-starting of the Darrieus wind turbine is achieved, and hindering influences of the Savonius wind turbine on the Darrieus wind turbine after starting of the Darrieus wind turbine are avoided, so that the performance of the combined vertical axis wind turbine is optimal.

Combined vertical axis wind turbine

Based on Spalart-Allmaras turbulence model, numerical simulation on NACA0015 airfoil with Gurney flap is carried out in this paper. Then the double Disks multiple stream-tube model is introduced to predict aerodynamic performance of VAWT of NACA0015 airfoil with Gurney flap. Results show that the Gurney flap can improve the lift coefficient of the airfoil and the height of the flap plays an important role. At the same time, output power of the wind turbine with Gurney flap increases compared with wind turbine without flap, and range of tip speed ratio to increase the wind power efficient broaden, which is useful for control and adjustment of wind turbine.

Zhang Xu

Papers

Combined vertical axis wind turbine

Study on improvement in aerodynamic performance of Vertical Axis Wind Turbine using Gurney flap