- On the basis of the type of energy at the turbine inlet
- total head of the incoming fluid is converted in to a large velocity head at the exit of the supply nozzle ( entire available energy of the water is converted in to kinetic energy.)
- water entering the runner of a reaction turbine has only kinetic energy
- the rotation of runner or rotor (rotating part of the turbine) is due to impulse action
- Flow regulation is possible without loss
- Unit is installed above the tailrace
- Casing has no hydraulic function to perform, because the jet is unconfined and is at atmospheric pressure. Thus, casing serves only to prevent splashing of water.
- It is not essential that the wheel should run full and air has free access to the buckets.
eg - Pelton wheel turbine ( efficient with a large head and lower flow rate.)
- the penstock pipe feeds water to a row of fixed blades through casing that convert a part of the pressure energy into kinetic energy before water enters the runner
- water entering the runner of a reaction turbine has both pressure energy and kinetic energy
- the rotation of runner or rotor (rotating part of the turbine) is partly due to impulse action and partly due to change in pressure over the runner blades
- Water leaving the turbine is still left with some energy (pressure energy and kinetic energy)
- It is not possible to regulate the flow without loss
- Unit is entirely submerged in water below the tailrace
- Casing is absolutely necessary, because the pressure at inlet to the turbine is much higher than the pressure at outlet. Unit has to be sealed from atmospheric pressure.
- Water completely fills the vane passage.
eg - Francis and Kaplan turbines ( efficient with medium to low heads and high flow rates )
- On the basis of the direction of flow through the runner
Direction of flow is along the tangent of the runner
eg - Pelton wheel turbine.
Direction of flow is in radial direction
- radially inwards or centripetal type, eg- old Francis turbine
- radially outwards or centrifugal type, eg -Fourneyron turbine
- Direction of flow is parallel to that of the axis of rotation of the runner
- the shaft of the turbine is vertical, lower end of the shaft is made larger which is known as hub (acts as runner)
eg - Propeller turbine ( vanes are fixed to the hub and they are not adjustable )
Kaplan turbine (vanes on hub are adjustable )
- Water flows through the runner in the radial direction but leaves in a direction parallel to the axis of rotation of the runner
eg- Modern Francis turbine.
- On the basis of the head at the turbine inlet
High head turbine
- net head varies from 150m to 2000m or even more
- small quantity of water required
eg -: Pelton wheel turbine.
Medium head turbine
- net head varies from 30m to 150m
- moderate quantity of water required
eg -: Francis turbine.
Low head turbine
- net head less than 30m
- large quantity of water required
eg -: Kaplan turbine.
- On the basis of the specific speed of the turbine
Before getting into this type, one should know what the specific speed of a turbine is. It defined as, the speed of a geometrically similar turbine that would develop unit power when working under a unit head (1m head).
Low specific speed turbine
- specific speed is less than 50. (varying from 10 to 35 for single jet and up to 50 for double jet )
eg -: Pelton wheel turbine.
Medium specific speed turbine
- specific speed varies from 50 to 250
eg -: Francis turbine
High specific speed turbine
- specific speed more than 250
eg -: Kaplan turbine
1. Course contents on NPTEL website
2. A textbook of Fluid Mechanics and HydraulicMachines - R.K. Bansal
3. Fluid Mechanics: Including Hydraulic Machines - A.K. Jain