Flywheel is an internal energy storage device. It absorbs mechanical energy during the period when the supply of energy is more than the requirement and releases it during the period when the requirement of energy is more than the supply. The main function of a fly wheel is to smoothen out variations in the speed of a shaft caused by torque fluctuations. If the source of the driving torque or load torque is fluctuating in nature, then a flywheel is used. Many machines have load patterns that cause the torque time function to vary over the cycle as shown in Figure 14.1. Internal combustion engines with one or two cylinders are a typical example. Piston compressors, punch presses, rock crushers, etc., are the other systems that have fly wheel.
Figure 14.1 (a) T − q Diagram and (b) ω − q Diagram
The change in the shaft speed during a cycle is called the speed fluctuation and is equal to ωmax − ωmin. We can normalize this to a dimensionless ratio by dividing it by the average or nominal shaft speed.
where Kf is coefficient of speed fluctuation, ωmax and ωmin are maximum and minimum angular velocities, respectively, and ω is mean angular velocity.
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