Kaplan Turbine

Pure Axial Flow with Aerofoil Theory….

Kaplan Turbine• The kaplan turbine is a great development of early 20th century. • Invented by Prof. Viktor Kaplan of Austria during 1913 – 1922.• The Kaplan is of the propeller type, similar to an airplane propeller.• The difference between the Propeller and Kaplan turbines is that the

Propeller turbine has fixed runner blades while the Kaplan turbine has adjustable runner blades.

• It is a pure axial flow turbine uses basic aerofoil theory.• The kaplan's blades are adjustable for pitch and will handle a great

variation of flow very efficiently. • They are 90% or better in efficiency and are used in place of the old

(but great) Francis types in a good many of installations. • They are very expensive and are used principally in large

installations. • The kaplan turbine, unlike all other propeller turbines, the runner's

blades were movable.

AEROFOIL THEORY

• An aerofoil-shaped body moved through a fluid produces an aerodynamic force. The component of this force perpendicular to the direction of motion is called lift. The component parallel to the direction of motion is called drag. Foils designed with water as the working fluid are called hydrofoils.

Pressure distribution and torque

LiftLift

DragDrag

Torque

Arm

LL

DD

c

Specific Speed of Kaplan Turbine

• Using statistical studies of schemes, F. Schweiger and J. Gregory established the following correlation between the specific speed and the net head for Kaplan turbines:

486.0

827.39

HN s

45

H

PNN s

P in watts.

Selection of Speed

The Schematic of Kaplan Turbine

Major Parts of A Kaplan Turbine

Superior Hydrodynamic Features

Section of Guide Wheel Runner

Essential for High Efficiency at low Heads

Classification of Kaplan Turbines

• The Kaplan turbine can be divided in double and single regulated turbines.

• A Kaplan turbine with adjustable runner blades and adjustable guide vanes is double regulated while one with only adjustable runner blades is single regulated.

• The application of Kaplan turbines are from a head of 2m to 40m.

• The advantage of the double regulated turbines is that they can be used in a wider field.

• The double regulated Kaplan turbines can work between 15% and 100% of the maximum design discharge;

• the single regulated turbines can only work between 30% and 100% of the maximum design discharge.

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 design combines features of radial and axial turbines.

• The inlet is a scroll-shaped tube that wraps around the turbine's wicket gate. Water is directed tangentially through the wicket gate and spirals on to a propeller shaped runner, causing it to spin.

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

• The turbine does not need to be at the lowest point of water flow as long as the draft tube remains full of water. A higher turbine location, however, increases the suction that is imparted on the turbine blades by the draft tube. The resulting pressure drop may lead to cavitation.

• Variable geometry of the wicket gate and turbine blades allow efficient operation for a range of flow conditions. Kaplan turbine efficiencies are typically over 90%, but may be lower in very low head applications.

• Current areas of research include CFD driven efficiency improvements and new designs that raise survival rates of fish passing through.

• Because the propeller blades are rotated by high-pressure hydraulic oil, a critical element of Kaplan design is to maintain a positive seal to prevent emission of oil into the waterway. Discharge of oil into rivers is not permitted

• Kaplan Turbine Working

Absolute Velocity

Relative velocity

Flow velocity

Runner speed

umean

V2v2 Vf2

u2

α2β2

V3v3

u3

α3β3

Draft Tube

Runner

Wicket Gates

V1

Approach Velocity

V4

Salient Features of Kaplan Turbine

• Very high efficiency

• Optimise efficiency with guide vanes

• No gearbox – save up to 3% efficiency

• Reduced pollution risk

• Control at heart of turbine (maximises head even at low flows)

• Gate control at weir allows full isolation for maintenance and repair

• Electro Screen in tailrace – deters fish from area

Applications• Kaplan turbines are widely used throughout the world for

electrical power production. They cover the lowest head hydro sites and are especially suited for high flow conditions.

• Inexpensive micro turbines on the Kaplan turbine model are manufactured for individual power production with as little as two feet of head.

• Large Kaplan turbines are individually designed for each site to operate at the highest possible efficiency, typically over 90%. They are very expensive to design, manufacture and install, but operate for decades.

A Bonneville Dam Kaplan turbine after 61 years of service

On this Kaplan runner the pivots at the base of the blade are visible; these allow the angle of the blades to be changed while running. The hub contains hydraulic cylinders for adjusting the angle.

• Variations of Kaplan Turbine• Propeller Turbines

– Have non-adjustable propeller vanes.

– They are normally used for producing a few hundred Watts of power at low heads (H < 0.6 m).

– Large propeller turbines can produce power in excess of 100 MW.

• Bulb or Tubular Turbines– Bulb or tubular turbines are built into the water delivery tubes.

– A large bulb is centered in the water pipe which holds the wicket gates and runner.

– In contrast to Kaplan turbines, tubular turbines are fully axial.

• VLH Turbines– VLH turbines are open flow, very low head

Kaplan turbines slanted at an angle to the water jet.

– They are larger diameter runners, and operate at low speeds.