KAPLAN AND PROPELLER TURBINE

The Kaplan turbine is a propeller-type  water turbine, which has adjustable blades.

Is also an axial flow reaction turbine in which water flows in the direction parallel to the axis of rotation of the runner.

Developed in 1913 by the Austrian professor Viktor Kaplan.

Evolution of the Francis turbine.

Allowed efficient electrical power production in low-head applications that was not possible with Francis turbines.

Both the turbines(kaplan and propeller) are the important types of axial flow reaction turbine.

Kaplan turbine :- 

When the vanes are fixed to the hub and they are adjustable , the turbine is known as kaplan turbine.

Propeller turbine :- 

When the vanes are fixed to the hub and are not adjustable , the turbine is known as propeller turbine

 PRINCIPLE

      Water from penstock enters the scroll casing and then moves to the guide vanes , which are fixed on the hub acting as runner for axial flow reaction turbine. From the guide vanes , the water turns through 90 degrees and flows axially through the runner as shown in figure . Also the draft tubes is of circular  inlet and rectangular outlet.

Construction of Kaplan turbine

Kaplan turbine is the only type of water turbine with adjustable blades , which allow work with low performance. Ex. In small hydropower plants.

The main parts of the kaplan turbine are :
1)Scroll casing
2)Guide vanes mechanism
3)Hub with vanes or runner of the turbine , and
4)Draft tubes

Functions:

    Scroll casing : Water from the penstocks enters the scroll casing and then moves to the guide vanes.
Guide vanes : Directs fluid flow and control its rotation and hence used as flow control valve. 
Hub : Shaft of turbine is vertical and its lower end is made larger called ‘Hub’ or ‘Boss’ . Vanes are fixed on the hub acting as runner.
Draft tubes : Water at exit cannot directly be discharged to the tail race. A tube of gradually increasing area is used for discharging water from exit of turbine to the tail race , known as draft tubes.

Theory of operation

The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid changes pressure as it moves through the turbine and gives up its energy. Power is recovered from both the hydrostatic head and from the kinetic energy of the flowing water. 

The inlet is a scroll-shaped tube that wraps around the turbine's wicket gates through which water is directed tangentially and spirals on to the hub, causing it to spin.

The  outlet is a specially shaped draft tube that helps decelerate the water and recover kinetic energy.

The  one end of the tube is connected to the exit of the runner  while another is submerged into the water below the tail race. 

Important points for Kaplan and Propeller Turbine

The discharge from runner is obtained as

Applications

Widely used throughout the world for electrical power

Are very expensive to design, manufacture and install, but operate for decades.

Cover the lowest head hydro sites and are especially suited for high flow conditions.

Manufactured for individual power production with as little as two feet of head.