A water turbine has a velocity of 6 m/s at the entrance of the draft tube and a velocity of 1.2 m/s at the exit. The tailrace is 5 m below the entrance of the draft tube.

Calculate the pressure head at the entrance of the draft tube, if the friction losses in the draft tube are 0.1 m.

Given:

Velocity at inlet, V1= 6m/s

Velocity at outlet,V2=1.2 m/s

Friction loss $h_f$ =0.1m

Vertical height between tail race and inlet of draft tube = 5m

Let y= vertical height between tailrace and outlet of draft tube.

Applying Bernoulli's equation at the inlet and outlet of draft-tube and taking reference …