Classification of Hydraulic Turbines :

Classification of Hydraulic turbines is based on the type of available energy at the inlet of the turbine, head at the inlet of the turbine, the direction of flow through the runner, and the specific speed of the turbine. 

  1. According to available energy at the inlet of the turbine. 
    (a) Impulse Turbine, and (b) Reaction Turbine.
  2. According to the head at the inlet of the turbine.
    (a) High head turbine (b) Medium head turbine, and (c) Low head turbine
  3. According to the direction of flow through the runner.
    (a) Tangential flow turbine (b) Radial flow turbine 
    (c) Axial flow turbine         (d) Mixed flow turbine. 
Impulse Turbine and Reaction Turbine
Impulse Turbine
Pelton Wheel

If at the turbine is driven by the available kinetic energy of fluid at the inlet, the turbine is known as impulse turbine. In impulse turbines, high kinetic energy is obtained using a nozzle at the inlet which directs the water flow to the vanes of the turbine.  If the turbine is driven by the fluid’s kinetic energy as well as pressure energy, the turbine is known as a reaction turbine. Mostly turbines are based on both impulse and reaction turbine principles. But, Pelton turbine is purely based on the principle of impulse turbines.

Tangential and Radial Flow Turbine

If the water flows in a tangent direction to the runner, this type of turbine known as a tangential flow turbine. If water flows in the radial direction to the runner, the turbine is a Radial flow turbine. While, the water flows from outwards to inward or center of the radii of the runner, this type of turbines are inward radial flow turbines. And in outward radial flow turbine, this water flows radially from inwards to the outward side.

Axial Flow Turbine

In the axial flow turbine, the water flows through the runner, along the parallel direction of the rotational axis of the runner. But, when water enters the runner radially but leaves in the parallel direction of the rotational axis, that turbine is a mixed flow turbine.

Axial Flow Turbine
Kaplan Turbine

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