Many people are surprised the first time they look at wind turbine blades and rotors close up. The flat sides of the blades face the wind, and they have a distinctive twist to them, from a steep pitch at the root to a very shallow pitch at the tip. Why is this, and why do some wind turbines have more blades than others?
Darrieus, Giromill, and H-rotor designs are big improvements over drag-based machines, since the blades have airfoils and utilize lift to move faster than the wind.
The ancient Persian design shown before, the Panemone, is one example. Other designs include the Savonious Rotor which can be easily built using coffee cans, plastic buckets, or metal barrels.A simple anemometer is another drag-based vertical axis wind turbine design.While fun for experimenters and students to build and test, these designs are extremely inefficient, and give only low torque since the blades or cups can never travel faster than the wind. Yes, I know ...
HORIZONTAL AXIS WIND TURBINES are what most people first think of when someone says? windmill-blades moving perpendicular to the ground.
In a vertical axis wind turbine, the blades move parallel to the ground. Both HAWTs and VAWTs can be either drag or lift based, though only lift designs are commonly used as they are reasonably efficient for electricity generation. Below are some commonly seen wind power designs, and explanations of the principles on which they work.
Wind turbines are divided into two types, drag wind turbine and lift wind turbine, based on the aerodynamic principles they utilize, and two more types - Horizontal Axis wind turbine and Vertical Axis wind turbines - depending on their physical configuration.
If you are considering buying or building a wind turbine for making electricity, you?ll almost certainly be comparison shopping for a modern, electricity producing, lift-based horizontal axis machine. But by taking a look at some historical wind turbine designs, it gets easier to explain the physics concepts involved.
All wind turbines should have some mechanical or electrical way to shut them down (stop the blades from spinning) during severe weather events. These can including shorting the alternator phases, a crank that turns the tail into fully-furled position, or a mechanical brake.
These regulation techniques are no longer used in commercial wind turbines because they are very noisy and prone to mechanical failure from fatigue, rust, and ice. Nevertheless, I have to admit it?s exciting watching and hearing a 1930s vintage Wincharger deploy its air brakes during a gale!
Some very small wind turbines use flexible plastic blades that bend, twist and flutter when power input gets too high for the wind generator to handle. This technique is effective, but also noisy.Some of the extra power in the wind is being turned directly into noise, and the sound of blades fluttering at high speed is very distinctive. It?s only used on very small turbines, and is effective only using modern plastic blades that are highly resistant to fatigue.
This is the most common high wind regulation technique in small wind turbines. The turbine frame is designed with a built-in offset, and the tail or the generator head is hinged both upwards and inwards. When windspeed starts to approach the generator?s maximum power output capacity, the tail or head folds up, yawing the machine at an angle to the wind.This reduces the effective swept area and thus the available power to the maximum power output level of the generator, so it continues to make peak power while furled.