Types of windmills and working of Horizontal Axis Wind Machine.

5.a) List the types of windmills. Explain the working of a Horizontal Axis Wind Machine.

Answer:

Types of Windmills:

Windmills are broadly classified into two types based on the orientation of their axis of rotation:

1. Horizontal Axis Wind Machines (HAWTs)
   • (a) Horizontal axis with two aerodynamic blades
   • (b) Horizontal axis propeller type using single blade
   • (c) Horizontal axis multibladed type
   • (d) Dutch type windmill
   • (e) Sail type windmill
2. Vertical Axis Wind Machines (VAWTs)
   • (a) Savonius type rotor
   • (b) Darrieus type rotor

Working of a Horizontal Axis Wind Machine:

In a Horizontal Axis Wind Machine, the rotor shaft is positioned horizontally, and the blades rotate in a vertical plane facing the wind. These machines are the most common type used for wind energy generation.

• The rotor blades are designed aerodynamically to capture kinetic energy from the wind.
• When wind flows over the blades, it creates a lift force, causing the rotor to spin.
• The rotor is connected to a generator through a step-up gearbox, which increases the rotational speed to generate electricity efficiently.
• The entire rotor assembly is mounted on a bedplate that is fixed to a pintle at the top of the tower, allowing it to turn and face the wind.
• These blades are typically placed downwind of the tower, meaning the wind hits the tower before reaching the blades.
• While in operation, the rotor blades undergo unsteady aerodynamic forces, gravitational effects, and inertia, causing them to flex continuously.
• If not properly designed, this flexing can lead to fatigue in metal blades and resonance issues if the frequency of blade vibrations matches the tower’s natural frequency, which can potentially destroy the machine.
• Two-blade systems are preferred as they offer a balance between performance and cost. Adding more blades increases power output slightly but significantly raises manufacturing and maintenance costs.

These turbines require yaw mechanisms to constantly adjust the rotor’s direction to face the wind and may also include braking systems and pitch control to regulate power output in varying wind speeds.