Nce403 mod unit5

Open channel surge, celerity of the gravity wave, deep and shallow water waves

Rectangular free overfall. Rotodynamic Machines, Pelton Turbine, equations for jet and

rotor size, efficiency. spear valve, reaction turbines, Francis and Kaplan type, Head

on reaction turbine, unit quantities, similarity laws and specific speed, cavitation,

characteristic curves.

05/02/23 1MODASSAR ANSARI

BY MODASSAR ANSARI 2nd Year Department of civil Engineering SUBJECT- HYDRAULICS & HYDRAULIC

MACHINES SUBJECT CODE-NCE 403


Hydraulic machinery

• Turbine is a device that extracts energy from a fluid (converts the energy held by the fluid to mechanical energy)

• Pumps are devices that add energy to the fluid (e.g. pumps, fans, blowers and compressors).


It is well known from Newton’s Law that to change momentum of fluid, a force is required. Similarly, when momentum of fluid is changed, a force is generated. This principle is made use in hydraulic turbine.

In a turbine, blades or buckets are provided on a wheel and directed against water to alter the momentum of water. As the momentum is changed with the water passing through the wheel, the resulting force turns the shaft of the wheel performing work and generating power.


A hydraulic machine is a device in which mechanical energy is transferred from the liquid flowing through the machine to its operating member (runner, piston and others) or from the operating member of the machine to the liquid flowing through it.

Hydraulic machines in which, the operating member receives energy from the liquid flowing through it and the inlet energy of the liquid is greater than the outlet energy of the liquid are referred as hydraulic turbines.

Hydraulic machines in which energy is transmitted from the working member to the flowing liquid and the energy of the liquid at the outlet of the hydraulic machine is less than the outlet energy are referred to as pumps.


Turbines• Hydro electric power is the most remarkable

development pertaining to the exploitation of water resources throughout the world

• Hydroelectric power is developed by hydraulic turbines which are hydraulic machines.

• Turbines convert hydraulic energy or hydro-potential into mechanical energy.

• Mechanical energy developed by turbines is used to run electric generators coupled to the shaft of turbines

• Hydro electric power is the most cheapest source of power generation.


A hydraulic turbine uses potential energy and kinetic energy of water and converts it into usable mechanical energy. The mechanical energy made available at the turbine shaft is used to run an electric power generator which is directly coupled to the turbine shaft

The electric power which is obtained from the hydraulic energy is known as Hydro- electric energy. Hydraulic turbines belong to the category of rotodynamic machinery.

The hydraulic turbines are classified according to type of energy available at the inlet of turbine, direction of flow through vanes, head at the inlet of the turbines and specific speed of the turbines.


Turbines• J.V. Poncelet first introduced the idea of the

development of mechanical energy through hydraulic energy

• Modern hydraulic turbines have been developed by L.A. Pelton (impulse), G. Coriolis and J.B. Francis (reaction) and V Kaplan (propeller)


Types of turbines

Turbines can be classified on the basis of:• Head and quantity of water available• Hydraulic action of water• Direction of flow of water in the runner• Specific speed of turbines• Disposition of the shaft of the runner


• Based on hydraulic action of waterAccording to hydraulic action of water, turbines can be classified intoa) impulse turbinesb) Reaction turbines

Classification of turbines


Impulse turbine: - In the impulse turbine, the total head of the incoming fluid is converted in to a large velocity head at the exit of the supply nozzle. That is the entire available energy of the water is converted in to kinetic energy. Although there are various types of impulse turbine designs, perhaps the easiest to understand is the Pelton wheel turbine. It is most efficient when operated with a large head and lower flow rate.


Reaction turbine: Reaction turbines on the other hand, are best suited -for higher flow rate and lower head situations.

In this type of turbines, 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; therefore, it is called as reaction turbine.

For, a reaction turbine, the penstock pipe feeds water to a row of fixed blades through casing. These fixed blades convert a part of the pressure energy into kinetic energy before water enters the runner. The water entering the runner of a reaction turbine has both pressure energy and kinetic energy.


Impulse turbine Reaction turbineThe entire available energy of the water is converted into kinetic energy

Only a portion of the fluid energy is converted into kinetic energy before the fluid enters the turbine runner.

The work is done only by the change in the kinetic energy of the jet.

The work is done partly by the change in the velocity head, but almost entirely by the change in pressure head.

Flow regulation is possible without loss. It is not possible to regulate the flow without loss

Unit is installed above the tailrace. Unit is entirely submerged in water below 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

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.

It is not essential that the wheel should run full and air has free access to the buckets.

Water completely fills the vane passage.


• Based on head and quantity of waterAccording to head and quantity of water available, the turbines can be classified intoa) High head turbinesb) Medium head turbinesc) Low head turbines



High head turbine: In this type of turbines, the net head varies from 150m to 2000m or even more, and these turbines require a small quantity of water. Example: Pelton wheel turbine.

Medium head turbine: The net head varies from 30m to 150m, and also these turbines require moderate quantity of water. Example: Francis turbine.

Low head turbine: The net head is less than 30m and also these turbines require large quantity of water. Example: Kaplan turbine


• Based on head and quantity of waterb) Medium head turbines The turbines that work under a head of 45m to 250m are

called medium head turbines. it requires medium flow of water. Francis turbines are used for medium heads.

c) Low head turbines Turbines which work under a head of less than 45m are

called low head turbines. Owing to low head, large quantity of water is required. Kaplan turbines are used for low heads.



• Based on direction of flow of water in the runnerDepending upon the direction of flow through the runner, following types of turbines are there.a) Tangential flow turbinesb) Radial flow turbinesc) Axial flow turbinesd) Mixed flow turbines



Radical flow turbines are those turbines in which the water flows in radial direction. The water may flow radically from outwards to inwards or from inwards to outwards.

If the water flows from outwards to inwards through the runner, the turbine is known as inward radial flow turbine. If the water flows from inwards to outwards, the turbine is known as outward radial flow turbine.

Reaction turbine means that the water at inlet of turbine possesses kinetic energy as well as pressure energy.


The main parts of a radial flow reaction turbine are: Casing: - The water from penstocks enters the casing which

is of spiral shape in which area of cross section of casing goes on decreasing gradually. The casing completely surrounds the runner of the turbine.

Guide mechanism: - It consists of stationary circular wheel all round the runner of the turbine. The stationary guide vanes are fixed on guide mechanism. The guide vanes allow the water to strike the vanes fixed on the runner without shock at inlet.


Runner: - It is a circular wheel on which a series of radial curved vanes are fixed. The surfaces of the vanes are made very smooth. The radial curved are so shaped that the water enters and leaves without shock.

Draft tube: - The pressure at the exit of the runner of reaction turbine is generally less than atmospheric pressure. The water exit cannot be directly discharged to the tail race. A tube or pipe of gradually increasing area is used for discharging water from the exit of turbine to the tailrace. This tube of increasing area is called draft tube.


If the water flows parallel to the axis of the rotation of the shaft, the turbine is known as axial flow turbine. If the head at the inlet of the turbine is the sum of pressure energy and kinetic energy and during the flow of water through runner a part of pressure energy is converted into kinetic energy, the turbine is known as reaction turbine.

Axial flow turbines


For the axial flow reaction turbines, the shaft of the turbine is vertical. The lower end of the shaft is made larger which is known as hub. The vanes are fixed on the hub and hence hub acts as runner for axial flow reaction turbine.

The following are the important type of axial flow turbines: 1. Propeller turbine 2. Kaplan turbine When the vanes are fixed to the hub and they are not adjustable,

the turbine is known as propeller turbine. If vanes on hub are adjustable the turbine is known as a Kaplan

turbine. This turbine is suitable where a large quantity of water at low heads is available.


• Based on direction of flow of water in the runnera) Tangential flow turbines When the flow is tangential to the wheel circle, it is a tangential flow turbine. A Pelton turbine is a Tangential flow turbine.b) Radial flow turbines in a radial flow, the path of the flow of water remains in the radial direction and in a plane normal to the runner shaft. No pure radial flow turbine is in use these days.



• Based on direction of flow of water in the runnerc) Axial flow turbines When the path of flow water remains parallel to the axis of

the shaft, it is an axial flow turbine. The Kaplan turbine is axial flow turbine

d) Mixed flow turbines When there is gradual change of flow from radial to axial

in the runner, the flow is called mixed flow. The Francis turbine is a mixed flow turbine.



• Based on specific speed of turbinesSpecific speed of a turbine is defined as the speed of a geometrically similar turbine which produces a unit power when working under a unit head.The specific speed of Pelton turbine ranges between 8-30, Francis turbines have specific speed between 50-250, Specific speed of Kaplan lies between 250-850.

• Based on disposition of shaft of runnerUsually, Pelton turbines are setup with horizontal shafts, where as other types have vertical shafts.



Heads, Losses and Efficiencies of Hydraulic Turbines

• Heads These are defined as below: (a) Gross Head: Gross or total head is the difference between

the headrace level and the tail race level when there is no flow. (b) Net Head: Net head or the effective head is the head

available at the turbine inlet. This is less than the gross head, by an amount, equal to the friction losses occurring in the flow passage, from the reservoir to the turbine inlet.



• Losses Various types of losses that occur in a power plant are given

below: (a) Head loss in the penstock: This is the friction loss in the

pipe of a penstock. (b) Head loss in the nozzle: in case of impulse turbines, there

is head loss due to nozzle friction. (c) Hydraulic losses: in case of impulse turbines, these losses

occur due to blade friction, eddy formation and kinetic energy of the leaving water. in a reaction turbine, apart from above losses, losses due to friction in the draft tube and disc friction also occur.



(d) Leakage losses: in case of impulse turbines, whole of the water may not be striking the buckets and therefore some of the water power may go waste. in a reaction turbine, some of the water may be passing through the clearance between the casing and the runner without striking the blades and thus not doing any work. These losses are called leakage losses.

(e) Mechanical losses: The power produced by the runner is not available as useful work of the shaft because some power may be lost in bearing friction as mechanical losses.

f) Generator losses: Due to generator loss, power produced by the generator is still lesser than the power obtained at the shaft output.



• Efficiencies Various types of efficiencies are defined as under: (a) Hydraulic efficiency: it is the ratio of the power developed

by the runner to the actual power supplied by water to the runner. it takes into account the hydraulic losses occurring in the turbine

ηh = Runner output / Actual power supplied to runner

= Runner output / (ρQgH) Where, Q = Quantity of water actually striking the runner

blades H = Net head available at the turbine inlet



(b) Volumetric efficiency: it is the ratio of the actual quantity of water striking the runner blades to the quantity supplied to the turbine. it takes into account the volumetric losses.

Let ∆Q = Quantity of water leaking or not striking the runner blades

ηv = Q / (Q+ ∆Q)

(c) Mechanical efficiency: The ratio of the shaft output to the runner output is called the mechanical efficiency and it accounts for the mechanical losses.

ηm = Shaft output / Runner output



• Efficiencies (d) Overall efficiency: Ratio of shaft output to the net power

available at the turbine inlet gives overall efficiency of the turbine

ηm = Shaft output / Net power available

Thus all the three types of losses, mechanical, hydraulic and volumetric have been taken into account.

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