Pelton Turbine Design and its Suitability for Aircraft Application

1) In general, the Pelton turbine designs are used only to convert the kinetic energy possessed by a jet of
water stream into mechanical energy which is further converted into electrical energy with the help of
generator or alternator. In this case, the engineer suggests to utilize the Pelton turbine design in the
aircraft application, an aircraft engine utilizes a gas turbine which runs on a gas cycle also known as
Brayton cycle which is named after the George Brayton who invented it. There are 4 processes in any gas
turbine which follows the Brayton cycle they are intake, compression, Combustion and Exhaust to the
atmosphere. In gas turbine, The gas is sucked in from the atmosphere compressed with the help of
compressor and then it is burnt with the fuel which finally escapes via Nozzle. The nozzle is a critical part
of any engine that runs on the Brayton cycle. The nozzle generates the thrust that is required to propel the
engine forward. So as per the engineer says if we place a Pelton blade at the rear end of the gas turbine
then the back pressure will be reduced which in turn reduces the efficiency of the cycle. The back
pressure generated at the rear end of the nozzle is directly associated with the amount of thrust produced
so if a negative pressure is developed at the end of nozzle it will directly affect the efficiency of the
engine. The peloton turbine is an impulse turbine which is dependent upon the density of the fluid as the
water is denser than the air the striking force is higher. The impulse force of a fluid with higher density is
very much greater than that of the impulse force of a fluid with lower density, as a density of any fluid is
directly related with the impinging mass and velocity. Thus the Pelton turbine is suited well only for the
applications involving water or denser fluid mediums. The efficiency, dependability, cost of operation
and the service life are directly affected thus the idea proposed by the engineer is not a viable one.

2) Forces on the turbine blades:
Fig1. Jetstream impinging on the Pelton bucket.
Now let us solve the forces that are acting on the buckets of the Pelton wheels.
Considering the System as a control volume and applying the moment of energy principle the moment
force imparted by the jet stream is equal to the moment imparted on the blades of the turbine wheel.
Let, H be the net head of fluid acting upon the Pelton wheel
H = Hg-hf
hf is given by
hf = 4 fL V 2
Dp X 2 g
here,
Dp is the dia of the penstock
D is the dia of the Pelton wheel
N is the rpm of wheel