UNIVERSITY OF ENGINEERIGN AND TECHNOLOGY LHR, NWL CAMPUS

DEARTMENT OF CIVIL ENGINEERING

Reaction Turbine

Subject Instructor Mr. Shafqat

Subject Fluid Mechanics II

Student Name M. Adnan

Student I.D. 2013-CIV-317

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Reaction Turbine

1.Objective The objective of this job is to study the various parts of a Reaction Turbine and also to study performance

of Francis turbine.

2. Introduction A type of turbine that develops torque by reacting to the pressure or weight of a fluid; the operation

of reaction turbines is described by Newton's third law of motion (action and reaction are equal

and opposite). In a reaction turbine, unlike in an impulse turbine, the nozzles that discharge the

working fluid are attached to the rotor.

The acceleration of the fluid leaving the nozzles produces a reaction force on the pipes, causing

the rotor to move in the opposite direction to that of the fluid. The pressure of the fluid changes as

it passes through the rotor blades. In most cases, a pressure casement is needed to contain the

working fluid as it acts on the turbine; in the case of water turbines, the casing also maintains the

suction imparted by the draft tube. Alternatively, where a casing is absent, the turbine must be

fully immersed in the fluid flow as in the case of wind turbines. Francis turbines and most steam

turbines use the reaction turbine concept.

3. History

A really efficient water turbine was now within reach it appeared, and a prize was offered in

France by the Societe d'Encouragement pour l'Industrie Nationale. The prize was won by the

French mining engineer Claude Burdin (1778-1873), who published his results in 1828. It was in

this publication that Burdin coined the word "turbine" which he took from the Latin "turbo"

meaning a whirling or spinning top. It was Burdin's student, Benoit Fourneyron (1801-1867), who

improved and developed his master's work and who is considered to be the inventor of the modern

hydraulic turbine. Four-neyron built a six-horsepower turbine and later went on to build larger

machines that worked under higher pressures and delivered more horsepower.

His main contribution was his addition of a distributor which guided the water flow so that it acted

with the greatest efficiency on the blades of the wheel. His was a reaction type turbine, since water

entering through the vanes of the distributor (that was fitted inside the blades) then acted on the

blades of the wheel. Following Fourneyron's first turbine, which happened to be a hydraulic or

water turbine, other turbines were developed that used the energy of a different material like gas

or steam.

Although these different types of turbines have different means of operation and certainly different

histories, they still embody the basic characteristics of a turbine. They all spin, or receive their

energy from some form of a moving fluid, and they all convert it into mechanical energy.

4. Working Principle In a reaction turbine, forces driving the rotor are achieved by the reaction of an accelerating water

flow in the runner while the pressure drops. The reaction principle can be observed in a rotary

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lawn sprinkler where the emerging jet drives the rotor in the opposite direction. Due to the great

variety of possible runner designs, reaction turbines can be used over a much larger range of heads

and flow rates than impulse turbines. Reaction turbines typically have a spiral inlet casing that

includes control gates to regulate the water flow. In the inlet a fraction of the potential energy of

the water may be converted to kinetic energy as the flow accelerates. The water energy is

subsequently extracted in the rotor.

There are four major kinds of reaction turbines in wide use: the Kaplan, Francis, Deriaz, and

propeller type. In fixed-blade propeller and adjustable-blade Kaplan turbines (named after the

Austrian inventor Victor Kaplan), there is essentially an axial flow through the machine. The

Francis- and Deriaz-type turbines (after the British-born American inventor James B. Francis and

the Swiss engineer Paul Deriaz, respectively) use a “mixed flow,” where the water enters radially

inward and discharges axially. Runner blades on Francis and propeller turbines consist of

fixed blading, while in Kaplan and Deriaz turbines the blades can be rotated about their axis, which

is at right angles to the main shaft.

5. Types Following are the main types of reaction turbine.

Propeller

Francis

Kinetic

5.1 Propeller Turbine

A propeller turbine applies conventional propeller theory in reverse to harness the latent kinetic

energy in gas and fluid flows. Propellers consist of a central shaft with a minimum of two

opposed, airfoil shaped blades or vanes attached to it. These are generally turned by an external

energy source to produce thrust by pushing or displacing air or liquid over the blades. In a propeller

Fig. 1 Propeller Turbine

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turbine, this principle is flipped; a flow or air or liquid displaces the blades causing them to turn

the shaft. A typical image of propeller turbine is shown in figure 1.

5.2 Francis Turbine

The most commonly used turbine in Hydro-Québec's power system. Water strikes the edge of the

runner, pushes the blades and then flows toward the axis of the turbine. It escapes through the draft

tube located under the turbine. It was named after James Bicheno Francis (1815-1892), the

American engineer who invented the apparatus in 1849.Francis turbine is shown in figure 2.

5.3 Kinetic Turbine

Kinetic energy turbines, also called free-flow turbines, generate electricity from the kinetic energy

present in flowing water rather than the potential energy from the head. The systems may operate

in rivers, man-made channels, tidal waters, or ocean currents. Kinetic systems utilize the water

stream's natural pathway. They do not require the diversion of water through man-made channels,

riverbeds, or pipes, although they might have applications in such conduits. Kinetic systems do

not require large civil works; however, they can use existing structures such as bridges, tailraces

and channels. Wind turbine is example of kinetic turbine. Wind turbine is shown in figure 3.

Fig. 2 Francis Turbine

Fig 3 Kinetic Turbine ( Wind Turbine)

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6. Main Parts of Francis Turbine Main Parts of reaction turbine are following.

Spiral Casing

Guide Mechanism

Turbine Runner

Draft Tube

6.1 Spiral Casing.

The water, from pipeline, is distributed around the guide ring in a casing. This casing is designed

in such a way that its cross sectional area goes on reducing uniformly around the circumference.

The cross sectional area is maximum at the entrance, and minimum at the zip. As a result of this,

the casing will be of spiral shape, that is why it is called a spiral casing or scroll casing. The spiral

casing is provided with inspection holes and pressure gauges. The material of casing depends upon

the head of water, under which the turbine is working, as below,

Concrete – up to 30m head

Welded rolled steel plate- up to 100m head

Cast steel –more then 100m head.

6.2 Guide Mechanism.

The guide vanes are fixed between two rings in the form of a wheel. This wheel is fixed in the

spiral casing. The guide vanes are properly designed in order to

I. Allow the water to enter the runner without shock (This is done by keeping the relative

velocity at inlet of the runner tangential to the vane angle)

II. Allow the water to flow over them, without forming eddies.

III. Allow the required quantity of water to enter the turbine (This is done by adjusting the

opening of vanes)

Fig. 4 Spiral Casing , Draft Tube, Stay Vanes

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All the guide vanes can rotate about their respective pivots, which are connected to the regulating

ring by some mechanical means. The regulating ring is connected to the regulating shaft by means

of two regulating rods. The guide vanes may be closed to flow according to the need. The

regulating shaft is operated by means of governor, whose function is to govern the turbine. The

guide vanes are generally made of cast steel.

6.3 Turbine Runner.

The runner of reaction turbine consists of runner, blades fixed either to a shaft or ring, depending

upon the type of turbine. The blades are properly designed, in order to allow the water to enter and

leave the runner without shock. The runner is keyed to a shaft. The surface of the runner is made

very smooth. The runner may be cast in one piece or may be made of separate steel plates welded

together. For low heads, the runner may be made of cast iron. But for high head, runner is made

of steel or alloys. When the water is chemically impure, the runner is made of the special alloy.

6.4 Draft Tube.

The water, after passing through the runner, flow down through a tube called draft tube. It is,

generally, drowned approximately 1m below the tail race level so that atmospheric pressure can’t

effect its follow. A draft tube has the following function.

Fig. 5 Cross Section

Fig. 6 Runner

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Its increases the head of water by an amount equal to height of the runner outlet above the tail race.

It increase efficiency of the turbine.

7. Velocity Profile o V : Absolute velocity of the fluid.

o U : Tangential velocity of the fluid.

o 𝑉𝑟: Relative velocity of the fluid after contact with rotor.

o 𝑉𝑤: Tangential component of V (absolute velocity), called Whirl velocity.

o 𝑉𝑓: Flow velocity (axial component in case of axial machines, radial component in case of

radial machines).

o α: Angle made by V with the plane of the machine (usually the nozzle angle or the guide

blade angle).

o β: Angle of the rotor blade or angle made by relative velocity with the tangential direction.

Velocity profile of francis turbine is shown in figure 8.

8. Difference between Impulse and reaction turbine The functioning of reaction turbines differs from impulse turbines in two aspects.

1. In the impulse turbine the potential energy available is completely converted to kinetic energy

by the nozzles before the water enters the runner. The pressure in the runner is constant at

atmospheric level. In the case of reaction turbine the potential energy is partly converted to kinetic

energy in the starter guide blades. The remaining potential energy is gradually converted to kinetic

energy and absorbed by the runner. The pressure inside the runner varies along the flow.

2. In the impulse turbine only a few buckets are engaged by the jet at a time In the reaction turbine

as it is fully flowing all blades or vanes are engaged by water at all the time. The other differences

Fig. 7 Velocity Profile

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are that reaction turbines are well suited for low and medium heads (300 m to below) while impulse

turbines are well suited for high heads above this values.

9. Governing of Reaction Turbine Demand for power may vary over time. The guide vane mechanism is used to control water flow

rate and makes sure that power production is synchronized with power demand. Governing

mechanism is batter explained in figure 9.

Fig. 8 Governing Mechanism

Apart from controlling flow rate guide vanes also control flow angle to inlet portion of runner

blade. Thus guide vanes make sure that inlet flow angle is at optimum angle of attack for maximum

power extraction from fluid.

10. Cavitation Most often local pressure at exit side of runner goes below vapor pressure of water. This will result

in formation water bubbles and eventually damage to turbine blade material. This phenomenon is

known as cavitation. It is impossible to prevent cavitation completely. So a carefully designed

draft tube is fitted at exit side to discharge the fluid out. Draft tube will transform velocity head to

static head due to its increasing area and will reduce effect of cavitation.