A.D. PATEL INSTITUTE
DESIGN OF FLYWHEEL
Dhiren P. Patel(120013119002)
• A flywheel is an inertial energy-storage device.
• It absorbs mechanical energy and serves as a reservoir, storing 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.
FLYWHEELS-FUNCTION NEED AND
• 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 usually
called for. Many machines have load patterns that cause the torque time
function to vary over the cycle. 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.
• Flywheel absorbs mechanical energy by increasing its angular velocity
and delivers the stored energy by decreasing its velocity.
Traditionally, flywheel are made of cast iron. From design consideration, cast
iron flywheel offer the following advantages:-
• Cast iron flywheels are the cheapest.
• Cast iron flywheel can be given any complex shape without involving
• Cast iron flywheel has excellent ability to damp vibrations.
however, cast iron has poor tensile strength compare to steel. The failure of
cast iron is sudden and total. The machinability of cast iron flywheel is
poor compared to steel flywheel.
There are two stages to the design of a flywheel.
• First, the amount of energy required for the desired degree of smoothening
must be found and the (mass) moment of inertia needed to absorb that
• Then flywheel geometry must be defined that caters the required moment
of inertia in a reasonably sized package and is safe against failure at the
designed speeds of operation.
• It depend upon acceptable changes in the speed.
• The change in the shaft speed during a cycle is called the speed
fluctuation and it is given by
DESIGN OF FLYWHEEL
∗ 𝝎 𝒂𝒗𝒈
where “Cf”is the co-efficient of speed fluctuation
and “Ek”is the kinetic energy and “𝝎avg” is the
average rotational motion.
Torque Variation and Energy:-
The required change in kinetic energy Ek is obtained from the known torque
time relation or curve by integrating it for one cycle and it is given by
(𝑇1 − 𝑇𝑎 𝑣𝑔)d𝜃=Ek
GEOMETRY OF FLYWHEEL
• It can be a solid cylindrical disc.
• It can be like conventional wheel design.
But energy requirements and size of the flywheel increases the
geometry changes to disc of central hub and peripheral rim connected
by webs and to hollow wheels with multiple arms.
GEOMETRY OF FLYWHEEL
• For a solid disc geometry with inside radius ri and out side radius ro, the
mass moment of inertia I is
• The mass of a hollow circular disc of constant thickness t is
• Combing the two equations we can write
• Where is material’s weight density
STRESSES IN FLYWHEEL
• Flywheel being a rotating disc, centrifugal stresses acts upon its distributed
mass and attempts to pull it apart. Its effect is similar to those caused by an
internally pressurized cylinder.
• = material weight density, ω= angular velocity in rad/sec. ν= Poisson’s
ratio, is the radius to a point of interest, ri and ro are inside and outside radii
of the solid disc flywheel.
ADVANCE AND MODERN
• Advanced flywheels are also now used for protecting against interruptions
to the national electricity grid.
– The flywheel provides power during period between the loss of utility
supplied power and either the return of utility power or the start of a
sufficient back-up power system
• Flywheels have also been proposed as a power booster for electric vehicles.
Speeds of 100,000 rpm have been used to achieve very high power
• Modern high energy flywheels use composite rotors made with carbon-
fibre materials. The rotors have a very high strength-to-density ratio, and
rotate at speeds up to 100,000 rpm. in a vacuum chamber to minimize
BENEFITS IN AEROSPACE
Flywheels are preferred over conventional batteries in many aerospace
applications because of the following benefits:
• 5 to 10+ times greater specific energy
• Lower mass / kW output
• Long life. Unaffected by number of charge / discharge cycles
• 85-95% round trip efficiency
• Fewer regulators / controls needed
• Greater peak load capability
• Reduced maintenance / life cycle costs