An airfoil with a hole can be applied to many devices. Below are the 3 most practical applications.
On an airplane, a hole in its wing could be a feature which will slow down the aircraft. The opening will also create loss of lift. Such a feature would be useful during landing, and could act as an air brake in flight. The area of the opening could be controlled via flaps which will adjust the amount of airflow through the opening.
On a helicopter the device could be adapted by placing a small airfoil on its tail section, with a small propeller inside the hole. The pilot could control the steering, lift and tilt of the helicopter by adjusting the speed of the propeller. To turn in different directions, the propeller would spin clockwise and counterclockwise and at varying speeds to change the magnitude. The propeller could control the amount of lift the airfoil produces, because it will control the amount of airflow passing through the hole.
The most original of the three applications is the wind generator / turbine.
Today’s most common wind generators are the horizontal axis wind turbines. These have a tower holding a four, three, two or even one bladed rotor which is connected to a generator. There are several disadvantages to this design. Because it is on a horizontal axis, there are more moving parts which have to be maintained. The blades only spin when there’s a lot of wind, and because the blades are usually large, they cut through more air which resonates a lot of noise. Finally, these wind turbines take up a lot of space because of their dimensions, which means that they are only suitable in open areas.
My new proposed design for a wind generator will be based on the hole in a wing concept, and it will resolve most of today’s wind turbines flaws.
Instead of having multiple blades for the rotor, a Savonius Rotor will be used. A Savonius Rotor has the shape of a drum, with multiple plates inside. These capture air and rotate the drum. This type of rotor spins at slow wind speeds, and since it sits on a vertical axis, it doesn't need extra mechanisms to rotate in the direction of the wind.
The rotor will be adapted to the airfoil and act as a wind turbine. The rotor will be connected to a multi-pole generator, and placed inside the hole in an airfoil. Because of the pressure differences, air will be sucked from the bottom, and exit from the top, spinning the rotor. The rotor will also stick out from the top (curved) side of the airfoil, where airflow velocity is increased. Airflow will grab the blades of the rotor, and spin it even faster, therefore harnessing more energy. To make generation even more efficient, an identical airfoil will be placed beside the first one, which will increase the velocity of air flowing through the narrow gap between the two airfoils (Bernoulli's principle). Adding endplates will connect the two airfoils together, and will also eliminate the wing tip vertices effect. To increase the power output, several levels of this structure could be secured one on top of each other (though they will rotate seperatly depending on the direction of the wind at different altitudes).
This new type of airfoil turbine will have advantages over today's windmill design; such as that it could be used in smaller areas, and generate electricity more effectively compared to today’s turbines.
Typical wind turbine Source: www.skf.com
To test this application, several experiments were done. First, several types of Savonius rotors were built to find the ideal design. 2, 3, and 4 bladed rotors were tested, and the 4 bladed rotor was observed to spin the fastest, as it's blades had the greatest surface area, meaning they captured the most airflow.
In the next experiment, the four bladed Savonius rotor was placed in a rectangular box (which was observed to create the greatest velocity through the hole HPC 32 30 39 – 33 32 38), and inserted into the airfoil. The airflow was turned on, and the rotor was observed to be spinning. The ideal position for the rotor was being experimented. First it was positioned inside the box, where it spun at a low velocity. Next it was taken out, until the edges of the rotor's blades stuck outside the hole. In this position, the rotor spun faster, because the airflow over the surface of the airfoil also captured the blades, increasing the number of rotations.
The final experiment dealt with finding the ideal distance between the two airfoils. This was accomplished by placing two identical airfoils side by side, and measuring the airflow velocity in the space between them. It was observed that the ideal distance between the airfoils is 45 mm. Any less, and air will flow around the airfoils. Any more and there will be more pressure, and therefore a lower airflow velocity.
In conclusion, this type of wind generator has a lot of potential for generating more electricity, in a smaller space, and more efficiently. In the future, this design will be explored further, and one day it may replace today's wind mill design.
Watch an animation of the wind generator... (Size:11.4 MB, allow time to load)