Small knowledge, big questions! Why do common fans only have 3 blades?

One leaf fan is invisible

Two-blade fans are rare

Three-blade fans are everywhere

......

Why do common fans only have three blades?

Huaneng Puyang County 500MW Wind Farm Project

The fans with 2, 4, or 6 blades

Is there any? ?

Of course the answer is yes.

"Yang County uses several sails to turn the wheels when the wind blows, and stops when the wind dies down." - Song Yingxing, "The Exploitation of the Works of Nature" "Use six sails to turn the wheels to irrigate the fields, and Huaiyang Sea is used for this." - Fang Yizhi, "A Brief Knowledge of Physics"

Humans have been using wind energy as an energy source for thousands of years. Before the invention of the steam engine, wind energy was an important source of power. Through sails and windmills, ships were able to navigate, draw water for drinking and irrigation, drain water for land reclamation, grind flour, saw wood, etc. Zheng He and his huge fleet of sailboats sailed to the West seven times. After the Ming Dynasty, windmills were widely used in farmland irrigation and drainage, which shows that China had mastered the manufacturing and application of sail and windmill technology.

Simulation of ancient Chinese windmills used to irrigate farmland

But the windmills we are most familiar with are the large windmills from the developed country of the Netherlands. These large windmills use wind energy to convert into power to drain water, crush crops, process various raw materials, etc., and have also become a cultural symbol unique to the Netherlands.

Dutch windmill

But whether it is our impression of Dutch windmills or according to Chinese historical records, windmills that use wind energy can have 4 blades, 6 blades or even more. Why do modern wind turbines that use wind power generation basically have only 3 blades?

Guangdong Yueping Pingyuan Sishui 40MW Wind Farm Project

Come, come, let's explore the mystery together

We know that the purpose of designing, manufacturing and operating wind turbines is to obtain the maximum benefit with the minimum investment under the same wind resource conditions. To put it bluntly, it is to reduce the cost of wind turbines as much as possible and maximize power generation.

Youyou wind turbines dot the agricultural photovoltaic integrated photovoltaic project of Guangdong Power Zhanjiang Harvest Company

So is it better for us to choose high torque or low torque?

Fan structure diagram

Therefore, we need to reduce the torque as much as possible, increase the tip speed ratio, achieve a higher wind energy utilization coefficient, and obtain greater power generation.

The torque increases with the number of blades. In practical applications, the torque of three blades is the lowest compared to four blades or more. The fewer blades, the higher the speed and the higher the tip speed ratio.

The 2-blade fan

Isn't it true that the higher the speed, the higher the tip speed ratio?

2-blade fan

Of course. But we need to consider that although using two blades can obtain the maximum tip speed ratio, the power generation efficiency is reduced, because the torque of using two blades is lower, and at low wind speeds, the lower torque cannot reach the power generation speed, and there is no power output. Secondly, the fewer blades, the higher the rated speed. When the speed reaches a certain level, the circumferential speed of the blade tip is very large, causing great wind resistance, and the resistance torque limits the further increase of power generation and speed.

Vietnam Ninh Thuan Cheng Thanh 50MW Wind Power Project

In addition, the fan with two blades has a larger gap between the blades, so the wind collection efficiency is not as good as that of the fan with three blades. In order to improve the wind collection efficiency, the rotor speed of the fan with two blades is usually higher than that of the fan with three blades, which will also increase the fan noise and visual impact.

AVIC Xiangzhou Baizhang 50MW wind power project

So, too few blades is not good. What about fans with 4 blades or even more?

Three blades make it easier for the wind turbine to maintain balance. When there are too many blades, it is difficult to balance the wind turbine and the cost is high. Multi-blade wind turbines have greater resistance, which will interfere with the rotation of the blades and reduce the energy conversion rate. State Power Investment Jieyang Shenquan II Offshore Wind Power Project

Therefore, using a three-blade fan can obtain the best tip speed ratio, thereby achieving maximum energy capture and maximum power generation efficiency, while also having the advantages of good balance and low cost . After a long period of verification, the three-blade fan has become the most common form of fan today.

At the China Energy Construction Shaoguan Nanxiong Liniuping Phase III Wind Farm Project, under the blue sky and white clouds, on the top of the green peaks, arrays of wind turbines slowly rotate, and neat and standardized green electricity is gathered here and continuously sent to the land of southern Guangdong. At the Huadian Yangjiang Qingzhou III 500MW Offshore Wind Power Project, the first offshore wind farm in the deep water area of ​​the country undertaken by China Energy Construction Guangdong Thermal Power, rows of large windmills stand tall above the vast sea, rotating with the wind...Huaneng Mengcheng County Xutuan Phase II 50MW Wind Farm Project

Editor: Zhang Shuo

Proofreader: Chu Xinyan Source: China Energy Construction Guangdong Thermal Power