What is a flywheel and what is its purpose?

Short Answer:

A flywheel is a heavy rotating mechanical device used to store rotational energy and maintain uniform speed in machines. It resists sudden changes in angular velocity by its large moment of inertia, which helps smooth out fluctuations in energy or speed.

The purpose of a flywheel is to regulate the speed of a machine by absorbing excess energy when the supply is greater than demand and releasing it when the supply is less. It is commonly used in engines, machines, and turbines to ensure smooth and steady operation.

Detailed Explanation :

Flywheel and Its Purpose

A flywheel is a rotating mechanical device designed to store and release energy in the form of rotational kinetic energy. It plays an essential role in maintaining a steady speed of rotation in machines where torque or power output varies throughout the operation. The energy stored in a flywheel depends on its moment of inertia and angular velocity.

In simple terms, when a machine runs faster than required, the flywheel stores extra energy by increasing its speed. When the machine slows down, it releases the stored energy to keep the operation smooth. Thus, a flywheel acts as a mechanical energy buffer, helping in speed control and energy stabilization.

Definition

A flywheel can be defined as:

“A flywheel is a heavy rotating body that stores rotational energy by virtue of its moment of inertia and helps to regulate the speed of a machine.”

The energy stored in a flywheel is given by:

where,
= Energy stored (Joules)
= Moment of inertia (kg·m²)
= Angular velocity (rad/s)

This equation shows that the energy stored in a flywheel increases with both its mass moment of inertia and its angular speed.

Construction of a Flywheel

A flywheel consists of the following main parts:

  1. Rim:
    The outer circular part that provides most of the mass and hence the moment of inertia.
  2. Hub:
    The central portion that is mounted on the shaft of the machine.
  3. Arms or Web:
    The arms or web connect the rim and hub together. In high-speed flywheels, solid web designs are preferred.

Flywheels are usually made of cast iron, steel, or composite materials depending on their application and speed requirements. Their design ensures that maximum mass is located away from the axis to increase the moment of inertia.

Working of a Flywheel

A flywheel works based on the principle of conservation of energy. It stores energy during periods of excess power and releases it when power supply drops.

  • During the power stroke (in engines), when the torque is higher than average, the flywheel absorbs extra energy and speeds up.
  • During the idle or weaker stroke, when the torque is lower than average, it releases the stored energy to maintain constant speed.

This continuous exchange of energy smooths out fluctuations and keeps the machine running at a nearly uniform speed.

Energy Stored in a Flywheel

The energy stored in a flywheel is the difference between its maximum and minimum kinetic energy during operation.

If  and  are the maximum and minimum angular velocities, then:

The change in angular velocity () depends on how much speed variation is allowed in the machine. For smoother operation, this variation is kept small.

Factors Affecting Energy Storage

The amount of energy a flywheel can store depends on:

  1. Moment of Inertia (I):
    The larger the mass and the farther it is distributed from the axis, the greater the energy storage.
  2. Angular Speed (ω):
    Energy increases with the square of angular velocity.
  3. Material Strength:
    The material must be strong enough to withstand centrifugal stresses at high speeds.
  4. Speed Fluctuation:
    The smaller the speed variation allowed, the more effective the flywheel will be in maintaining constant motion.

Purpose of a Flywheel

The main purpose of a flywheel in a mechanical system is to maintain uniform rotational speed despite variations in torque or power. The key purposes include:

  1. Regulating Speed:
    A flywheel absorbs excess energy when torque is high and releases it when torque is low, maintaining steady motion.
  2. Energy Storage:
    It acts as an energy reservoir by storing energy in the form of rotational kinetic energy.
  3. Balancing Power Supply and Demand:
    In engines, it balances energy between power strokes and non-power strokes.
  4. Reducing Vibrations:
    Flywheels help in damping out fluctuations and vibrations in rotating machinery.
  5. Providing Continuous Motion:
    In mechanical presses, punching machines, and textile looms, the flywheel ensures smooth and continuous operation even with intermittent power input.
  6. Improving Efficiency:
    By smoothing power output, it prevents mechanical shocks and increases machine life.

Applications of Flywheel

  1. Internal Combustion Engines:
    To maintain constant engine speed between power strokes.
  2. Steam Engines:
    To balance the irregular torque output during piston movement.
  3. Punching and Shearing Machines:
    To provide energy during the punching operation when torque demand is high.
  4. Textile Machines and Rolling Mills:
    To maintain uniform operation and avoid jerks.
  5. Energy Storage Systems:
    Used in modern hybrid vehicles and power systems to store and reuse kinetic energy efficiently.
  6. Gyroscopic Devices:
    Flywheels are used in gyroscopes to stabilize ships, spacecraft, and aircraft.

Advantages of Flywheel

  • Maintains constant machine speed.
  • Reduces power fluctuations.
  • Stores and releases energy effectively.
  • Increases efficiency and smoothness of operation.
  • Extends machine life by reducing load variations.

Limitations

  • Adds extra weight to the system.
  • Requires space and strong materials for high-speed operation.
  • Needs balancing to avoid vibrations.
  • Not suitable for systems requiring instant response to load changes.
Conclusion

A flywheel is a heavy rotating device that stores rotational energy to regulate machine speed and balance energy supply and demand. It plays a vital role in ensuring smooth operation by absorbing excess energy and releasing it during load variations. The performance of a flywheel depends on its moment of inertia, material strength, and rotational speed. Flywheels are widely used in engines, turbines, power plants, and mechanical presses, making them an essential component in maintaining steady mechanical motion and improving overall efficiency.