Test: Kaplan Turbines - Civil Engineering (CE) MCQ

The Kaplan turbine is an axial flow reaction turbine. The water inlet is axial and the water outlet is axial too.

In a Kaplan turbine, the guide vanes are adjustable and not fixed to the hub of the turbine. Francis and Pelton turbines are not low head turbines. In a propeller turbine, the guide vanes are fixed to the hub of the turbine.

The flow velocity of turbine at the outlet of the Kaplan turbine will be lesser than that of the inlet due to effects of friction in the blade. Hence, practically a lower value would be obtained. 0.8V is the only option lower than V.

cos (β₁) = (u – V_w1)/ V_r1. Substituting the given values in the above equation and rearranging to find the value of u, we get 36.124 m/s.

The Kaplan turbine is said to be a Low head turbine. The low head ranges from 0 to 60 m. Only 50 m falls in this range and hence, it’s the correct option.

The volume flow rate is given by

Substituting the given values in the above equation, we get Q = 95 m³/s.

As the head for Kaplan turbine is low, the discharge of water through the turbine is high and hence, blade resistance should be low. That’s why Kaplan turbine will have the lowest number of blades.

Considering the velocity diagram of a Kaplan turbine at the inlet for a fast runner, we notice that the whirl velocity is lower the blade velocity along the same direction. They are equal in case of a medium runner.

In the inlet velocity triangle, tan (α₁) = V_f1/ V_{w1o, Vf1 = Vw1 = 10 m/s.}

Hydraulic turbine - 
The main classification depends upon the type of action of the water on the turbine. These are :
(i) Impulse Turbine
(ii) Reaction Turbine. 
(i) Impulse turbine:-

• In the case of an impulse turbine, all the potential energy is converted to kinetic energy in the nozzles. The impulse provided by the jets is used to turn the turbine wheel. 
• This type is found suitable when the available potential energy is high and the flow available is comparatively low.
• The relative velocity over the moving blades either remains constant or slightly decreases so the correct answer is option 1

(ii) Reaction Turbine:-

• In reaction turbines, the available potential energy is progressively converted in the turbine's rotors and the reaction of the accelerating water causes the turning of the wheel.
• The relative velocity over the moving blades increases.
• These are again divided into (a) radial flow, (b) mixed flow, and (c) axial flow machines