- In these turbines, a part of pressure energy is first converted into kinetic energy before supplied to runner.
- Turbine to run in closed passages which one completely fills with water supplied to runner.
- Therefore, the water enters the runner having partly the pressure energy and partly the kinetic energy. Both these energies are reduced simultaneously while passing over the runner and produce mechanical energy.
- Hence, Reaction turbine works on the principle of impulse-reaction.
- The runner of these turbines being under pressure above atmospheric, it requires the blades of turbine to run in closed passages which one completely fills with water in all conditions.
- Examples of reaction turbine are Francis, Kaplan and Propeller turbines.
Classification of Reaction Turbines:
- The reaction turbines may be classified as:
- Radial flow turbines
- Axial flow turbines
- Mixed flow turbines
1.Radial flow turbines:
- Firstly in a radial flow turbine, the water flows along the radial direction in the runner.
- It may be an inward flow type or outward flow type.
- In an inward flow turbine, the water enters at the outer periphery of the runner and flows radially inwards towards the centre of runner e.g. old Francis, turbine, Girard radial flow turbine etc.
- In an outward flow turbine the water enters at the centre of runner and flows radially outwards towards the outer periphery of the runner. e.g. the Fourneyron turbine.
2.Axial flow turbines:
- One also calls it as parallel flow turbines.
- In these turbines the water enters and leaves the runner along the direction parallel to the axis of the shaft.
- Same examples of axial flow turbine are Kaplan and propeller turbines, Girard axial flow turbine, Jonal turbine etc.
3.Mixed flow turbines:
- In mixed flow turbines, the water enters at the other periphery of runner in radial direction and leaves at the centre in the direction parallel to the axis of rotation of runner.
- Modern Francis turbine is the example of mixed flow turbine.