Wind turbines come in various designs, but they are generally divided into two main categories: horizontal-axis wind turbines (HAWTs) and vertical-axis wind turbines (VAWTs). In HAWTs, the rotor shaft is parallel to the direction of the wind, while in VAWTs, the rotor shaft is perpendicular to the wind flow or the ground.
This article focuses on vertical-axis wind turbines. VAWTs can be further classified into two types: resistance-type and lift-type. Resistance-type turbines rely on the drag force created by air flowing over the blades, whereas lift-type turbines use the lift generated by the airflow. As the blade speed increases, the resistance decreases, but the lift increases, making lift-type turbines more efficient than their resistance-based counterparts.
There are several types of resistance-based VAWTs, such as flat-plate and cup-shaped turbines, which are purely drag devices. Some S-shaped windmills also have a mix of lift and drag characteristics, but they are primarily resistance-based. These systems offer high starting torque but suffer from low tip-speed ratios and limited power output for their size, weight, and cost.
The Darrieus turbine, invented by French engineer G.J.M. Darrieus in the 1930s, is a classic example of a lift-type VAWT. It was later studied extensively by the Canadian National Research Council in the 1970s and became a strong competitor to HAWTs. The Darrieus design features curved, airfoil-shaped blades that generate lift. Although it has a lower starting torque compared to resistance-type turbines, it can achieve higher tip-speed ratios, resulting in greater power output per unit weight and cost. Various configurations exist, including Φ, Δ, Y, and H shapes, with single, double, triple, or multiple blades.
Despite being over 180 years old, the Darrieus turbine has not been widely adopted due to several limitations. One major issue is its inability to self-start, and another is its narrow operational range—both in terms of wind speed and load variations. This makes it difficult to adapt to fluctuating conditions.
Fixed-blade lift-type VAWTs, like the traditional Darrieus design, feature blades with a fixed chord angle that cannot be adjusted. Figure 1 shows the layout of the blades on a typical lift-type VAWT. Most airfoil blades operate efficiently within an angle of attack of 0 to 15 degrees, with maximum lift occurring between 8 to 13 degrees. At this range, lift is high and drag is minimal.
Figure 2 illustrates the airflow and forces acting on the blades at different positions. When the blade is facing the wind (0 degrees), the relative wind speed combines with the blade’s motion, creating a lift force that drives the turbine. However, when the tip-speed ratio drops below 4, the blade enters a stall condition, reducing lift and increasing drag, which can lead to negative torque and unstable operation.
As shown in Figure 3, the power coefficient (Cp) of a fixed-blade VAWT peaks when the tip-speed ratio is between 4 and 6. Beyond this range, efficiency drops significantly. Wind conditions are often unpredictable, and sudden changes in wind speed or load can cause the turbine to operate outside its optimal range, leading to instability or reduced performance.
Because of these limitations, fixed-blade lift-type VAWTs require a very narrow operating window, making them less suitable for real-world applications where wind conditions vary frequently. Their inability to self-start also adds to the challenges of deployment and maintenance. Despite their potential for high efficiency, these issues continue to hinder their widespread adoption.
industrial electronic PCBA,PCBA components assembly,Robots Motherboard,Electronic Custom Pcb
Dongguan Jinglin Communication Technology Co., Ltd. , https://www.jlpcba.com