# Energy Engineering Questions and Answers – Vertical Axis Wind Mill

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This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Vertical Axis Wind Mill”.

1. In which wind measuring device a tubular piece of thin flexible fabric hanged vertically to determine direction?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers

Explanation: Wind sock is a very basic device that measure wind direction and provide a rough idea of the wind’s intensity. A wind sock is a tubular piece of fabric or thin, flexible fabric attached to a pole. When there is no wind, the fabric hangs vertically from the attached pole.

2. A device which is used as device for showing direction wind as well used as a decorative purpose?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers

Explanation: A weather vane works similarly to wind sock. Instead of a tubular sock, the weather vane is made by placing a horizontal pole at the top of vertical pole. The poles are joined together so that the horizontal pole has a flattened, vertical end that reacts to wind.

3. Which is the wind direction showing device that spins perpendicularly?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers

Explanation: A pinwheel is a windmill-style turbine that spins perpendicularly to the wind affecting it. Like wind socks and weather vanes, a pinwheel can be attached to a rotating base. This allows the pinwheel to change direction with the wind, and it will spin facing into the oncoming wind.
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4. Which is the device that measures wind direction and its intensity?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers

Explanation: An anemometer is any device that measures wind direction and intensity. It may be simple, such as the devices described above, or it may be a complex, computer-aided machine that measures and records wind patterns over time. More advanced anemometer machines are used to aid in professional weather reporting and air traffic control.

5. What units does the anemometer measure in?
a) Feet per minute
b) Liters per minute
c) Centimeters per minute
d) Meter per seconds

Explanation: The anemometer measures in feet per minute, or FPM. The rotation is sensed by a magnetic or optical sensor that converts the signal to FPM measurement. An arrow on the vane head identifies the direction the airflow must travel through the vane to obtain proper measurements.

6. Which of the following type of turbine or the rotor requires relatively low velocity winds for operation?
a) Cup anemometer
b) Savonius rotor
c) Darrieus type rotor
d) Magnus effect rotor

Explanation: Savonius rotor is a simple WEC system which woks like a cup anemometer. This type was invented by S.J. Savonius in the year 1920. It requires relatively low velocity winds for operation. It consists of two half cylinders facing opposite directions forming as S-shaped cross section.

7. Which type of axis does a Savonius Rotor has?
a) Horizontal axis
b) Mediolateral axis
c) Vertical axis
d) Lateral Axis

Explanation: A Savonius wind energy conversion system has a vertical axis and hence eliminates the expensive power transmission system from the rotor to the axis. Since it is a vertical axis machine it does not matter much about the wind direction.

8. Why is Savonius rotor not suitable for installation?
a) Because of long drive shaft
b) Because of its low capacity motor
c) Because of its typical blade design
d) Due to the light material it is made of

Explanation: Savonius rotor is not useful for very high installation because of long drive shaft problems. Bracing of the topmost bearing above the rotor of a very tall vertical axis machine is difficult requiring very long guy wires.

9. When was the Darrieus type machine invented?
a) 1925
b) 1932
c) 1929
d) 1948

Explanation: Darrieus type machine was invented originally and patented in 1925 by G.J.M > Darrieus, a French engineer. The Darrieus wind mill is a vertical axis machine that has the same advantage of a modern rapidly rotating propeller type windmill, by use of an efficient airfoil, effectively intercepts large area of wind with a small blade area.

10. What form of force acts on the blades of Darrieus machine?
a) Pure tension
b) Compression
c) Shear force
d) Air resistance force

Explanation: Darrieus wind mill has two or three thin, curved blades with airfoil cross section and constant chord length. Both ends of blades are attached to a vertical shaft. Thus the force in the blade due to rotation is pure tension.

11. Which type of vertical wind machine has relatively low solidity and low starting torques?
a) Cup anemometer
b) Savonius rotor
c) Darrieus type rotor
d) Magnus effect rotor

Explanation: Darrieus type rotors are lift devices characterized by curved blades with air foil cross sections. They have relatively low solidity and low starting torques, but high tip to wind speeds and therefore relatively high power outputs per given rotor weight and cost.

12. Which type of vertical wind machine consists of spinning cylinders?
a) Cup anemometer
b) Savonius rotor
c) Darrieus type rotor
d) Magnus effect rotor

Explanation: Magnus effect rotor concept was first demonstrated by Magnus in 1912. It consists of spinning cylinders. When cylinders spun in wind stream, translational forces are produced perpendicular to the wind stream by the Magnus effect. Such a device can be used to propel ships or land vehicles.

13. Aero turbine is the fraction of power in the wind through the swept area which is converted into useful mechanical shaft power is called _____________
a) Coefficient of performance
b) Coefficient of variation
c) Coefficient of lift
d) Coefficient of spin

Explanation: The coefficient of performance of an aero turbine is the fraction of power in the wind through the swept area which is converted into useful mechanical shaft power. Cp for horizontal axis wind machine has theoretical maximum value = 0.593.

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