Kaplan Turbine

Kaplan Turbine• 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.• 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.

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.

Major Parts of A Kaplan Turbine

Design of Guide WheelD0

N

gHkD ug

260

0

kug 1.3 to 2.25 : Higher values for high specific speeds

Number of guide vanes : 8 to 24 : Higher number of vanes for large diameter of guide wheel.

Outlines of Kaplan Runner

Whirl ChamberGuide Vanes

a

b

The space between guide wheel outlet and kaplan runner is known as Whirl Chamber.

a=0.13 Drunner & b=0.16 to 0.2 Drunner.

Design of Kaplan Runner

Drunner

Dhub

Wicket Gates for Kaplan Turbine

Blades of Kaplan Turbine

Cavitation Stages in Kaplan Turbine

Runner Case

Regulating Blade Angles in Kaplan Turbines

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

53.2282

HN s

45

H

PNN s

P in kilo watts.

Example of Rotational Speed

Suppose we have a head of 36m. Flow of 300 m^3/sP =0.90* 9.81 *36*300 kW =95353.2 kWNs = 2282.53/ 36^.486 =400.0

N = Ns* H^1.25/ P^0.5 = 6.887*36^1.25/(95352.2^0.5)

N = 280 rpm

Selection of Speed

Runner diameter section

The runner diameter De can be calculated by the following equation:

N

HND qsrunner

60

602.179.05.84

Nqs =(N/60) Q^0.5/(gH)^0.75

Hub diameter

• The hub diameter Di can be calculated with the following equation:

runnerqs

hub DN

D

0951.025.0

Dimensions of Kaplan Systems

Dimensions of Kaplan Systems I

Dimensions of Kaplan Systems II

DRAFT TUBE

DESIGN OF THE BLADE

Two different views of a blade

Hydrodynamics of Kaplan Blade

Design of Blade

• Many factors play significant roles in design of blade. • The leading edge is thicker than the trailing edge for a

streamlined flow. • Furthermore, the blade should to be as thin as possible to

improve the cavitation characteristics; • It is thicker near the flange becoming thinner and thinner

towards the tip. • In addition, the blade has to be distorted on the basis of

the tangential velocity. • The “Tragflügel theorie” is also an important factor in

defining the shape of the profile and the distortion of the blade.

Uwheel

V ri

Vai

Vfi

Uwheel

V re

Vae

Vfe

Speed Specific toalProportion

24 to8 :blades ofNumber :

1.05 9.0

ZZ

Dt

tot

l

runner

Details of Blade Arrangement

Blade Design

Vri

CAVITATION

• Cavitation occurs especially at spots where the pressure is low. • In the case of a Kaplan turbine, the inlet of the runner is quite

susceptible to it. • At parts with a high water flow velocity cavitation might also

arise.• The major design criteria for blades is : Avoid Cavitation.• First it decreases the efficiency and causes crackling noises. • The main problem is the wear or rather the damage of the

turbine’s parts such as the blades.• Cavitation does not just destroy the parts, chemical properties are

also lost.

The suction head

• The suction head Hs is the head where the turbine is installed; • if the suction head is positive, the turbine is located above the trail

water; • if it is negative, the turbine is located under the trail water. • To avoid cavitation, the range of the suction head is limited. • The maximum allowed suction head can be calculated using the

following equation:

netdesvapatm

s Hg

V

g

ppH

2

2

net

des gH

VN

25241.1

246.1

Characteristics of Blades

• Blade lift coefficient:

2

22min

22 2

rl

deaedraftsatmrireblade KV

VVpHpgVV

draft: Efficiency of draft tube: 0.88 to 0.91K : Profile characteristic number: 2.6 to 3.0

ibladeblade

flow

ri

turbine

U

V

V

Hg

t

l

180sin

cos12

When the lifting coefficient is known, the sufficiency of ratio l/t can be established as follows:

Methodology of Testing the Design

• The following are steps, which must be undertaken in order to successfully complete design testing: – 1) Numerical model – full geometry of the turbine including – - Intake – - Spiral casing – - Distributor (all stay vanes and wicket gates) – - Runner – - Draft tube – 2) Tuning-up the numerical model – - Grid quality: verification and refinement. Based on couple

of runs of the flow analysis, the nodes distribution is adjusted according to the velocity/pressure field.

– - Operating parameters. In the non-dimensional factors, the CFD results must be within a certain range from the field measurements.

– 3) CFD analysis – flow solver – 4) Analysis of results – - Energy dissipation field (losses). – - Pressure gradients – estimate possibilities for cavitation – - Determination of the flow areas, where the velocity field has

highest non-uniformity – 5) Strategy for upgrade based on expected cost/benefit ratio – - Intake shape – - Distributor (wicket gates profile, stay vanes set-up) – - Runner design – - Draft tube shape

CFD Model

Verification of Velocity Distribution

Verification of Pressure Distribution