Correct Answer - Option 2 : 12 m/sec
Concept:
Kaplan Turbine:
Kaplan Turbine is an axial reaction flow turbine and has adjustable blades. When the water flows parallel to the axis of the rotation of the shaft, the turbine is known as the axial flow turbine.
Flow ratio (ψ) for a Kaplan Turbine is given by:
\({\rm{ψ }} = \frac{{{{\rm{V}}_{\rm{f}}}}}{{\sqrt {2{\rm{gH}}} }}\)
Where Vf is the flow velocity at the inlet of the runner and 'H' is the head available.
Calculation:
Given:
ψ = 0.6, H = 20 m.
Taking g = 10 m/s2
\({\rm{ψ }} = \frac{{{{\rm{V}}_{\rm{f}}}}}{{\sqrt {2{\rm{gH}}} }}\)
\(0.6 = {\rm{\;}}\frac{{{{\rm{V}}_{\rm{f}}}}}{{\sqrt {2 \times 10 \times 20} }}\)
Vf = 12 m/s
∴ The velocity of flow at the inlet of the runner is 12 m/s.