Let V = Velocity of the jet
u = Velocity of the vane (cups) at the impact point
u = DN/ 60
where D = Diameter of the wheel corresponding to the impact point
= Pitch circle diameter.
At inlet the shape of the vane is such that the direction of motion of the jet and the
vane is the same. i.e., Ȑ = 0, ș = 0
Relative velocity at inlet Vr = V —u
This is the ratio of the work done per second per
head at inlet to the turbine. Energy head at inlet = V2/2g
The speed of any water turbine is represented by N rpm. A turbine has speed, known as specific speed and is represented by N
‘Specific speed of a water turbine in the speed at which a geometrically similar turbine would run if producing unit power (1 kW) and working under a net head of
1 m. Such a turbine would be an imaginary one and is called specific turbine.