Unit-1Hydraulic machinesJet Propulsion

& Pelton Turbines

FromAnkit Saxena

Jet PropulsionJet propulsion means the propulsion or movement of the bodies such as ships, aircrafts, rocket etc. with the help of jet.There are following cases which are used

(a) Jet propulsion of a tank to which orifice is fitted, and

(b) Jet propulsion of ships.

(a)Jet propulsion of a tank with an Orifice

Condition for maximum efficiency and expression for maximum efficiency

(b) Jet propulsion of ShipsA ship is driven through water, A jet of water is discharged at the

back also called stern of the ship, exerts a propulsive force on the ship.

The water from the surrounding media is taken by following two ways:

1) Through inlet orifice which are at right angles to the direction of the motion of the ship, and

2) Through the inlet orifices, which are facing the direction of motion of the ship.

(1) Through inlet orifice which are at right angles to the direction of the motion of the ship

(2) Through the inlet orifices, which are facing the direction of motion of the ship

Turbines• 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.

• 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 Hydroelectric energy. Hydraulic turbines belong to the category of roto- dynamic machinery.

• The main components of a hydroelectric system may be classified into two groups:

• The hydraulic system components that include the turbine, the associated conduits-like penstocks, tunnel and surge tank-and its control system, and

• The electric system components formed by the synchronous generator and its control system.

Layout of a Hydro-Electric Power Plant

History of Hydraulic Turbines• Water wheels – China and Egypt – thousands of years ago.• Reaction runner – J A Segnar – 1950.• Euler turbine theory – Leonard Euler – valid till today• Turbine is a designation that was introduced in 1824 in a dissertation of the French

engineer Burdin.• Fourneyron designed a radial turbine and put to operation the first real turbine• in 1827 – power 20-30 kW and runner diameter of 500 mm.• Henschel and Jonval in 1840 independently developed turbine with axial water flow

through it. They were the first ones to apply draft tube and in that way to utilize the water head between runner outlet and tail water level.

• Francis in 1849 developed the radial turbine, named Francis turbine.• In 1870 professor Fink introduced an important improvement in Francis turbine by

making the guide vanes turning on a pivot in order to regulate the flow discharge.• In 1890 American engineer Pelton developed impulse turbine, named Pelton Turbine• In 1913 Kaplan designed a propeller turbine, named Kaplan turbine, Subsequent

developments were made on Francis, Pelton and Kaplan turbines.

Turbine

Tangential flow (Pelton

wheel)

Axial flow (Kaplan turbine)

Mixed: Radial and axial (Modern

francis turbine)

Outward radial flow (Fourneyron

turbine)

Inward radial flow (Old

francis turbine)

Classification of Hydraulic Turbines

Hydraulic turbines are generally classified asA) According to hydraulic action/ Type of energy available at inlet (a) Impulse turbine (b) Reaction turbine• The flow energy to the impulse turbines is

completely converted to kinetic energy before transformation in the runner.

• The impulse forces being transferred by the direction changes of the flow velocity vectors when passing the buckets create the energy converted to mechanical energy on the turbine shaft.

• The flow enters the runner from jets spaced around the rim of the runners. The jet hits momentarily only a part of the circumference of the runner.

• In the reaction turbines two effects cause the energy transfer from the flow to the mechanical energy on the turbine shaft:

• Firstly, it follows from a drop in pressure from inlet to outlet of the runner. This is denoted as the reaction part of the energy conversion.

• Secondly, the changes in the directions of the flow velocity vectors through the runner blade channels transfer impulse forces. This is denoted as the impulse part of the energy conversion.

• The pressure from inlet to outlet of the runners is obtained because the drop runners are completely filled with water.

B) According to the direction of flow through runner:• Tangential flow turbines: In this type of turbines, the water

strikes the runner in the direction of tangent to the wheel. Example: Pelton wheel turbine.

• Radial flow turbines: In this type of turbines, the water strikes in the radial direction. Accordingly, it is further classified as,

a. Inward flow turbine: The flow is inward from periphery to the centre (centripetal type). Example: old Francis turbine.

b. Outward flow turbine: The flow is outward from the centre to periphery (centrifugal type). Example: Fourneyron turbine

• Axial flow turbine: The flow of water is in the direction parallel to the axis of the shaft. Example: Kaplan turbine and propeller turbine.

• Mixed flow turbine: The water enters the runner in the radial direction and leaves in axial direction. Example: Modern Francis turbine.

C) According to the head at inlet of turbine:• 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.

D) According to the specific speed of the turbine• Low specific speed turbine: The specific speed is less than 50.

(varying from 10 to 35 for single jet and up to 50 for double jet ) Example: Pelton wheel turbine.

• Medium specific turbine: The specific speed is varies from 50 to 250. Example: Francis turbine.

• High specific turbine: the specific speed is more than 250. Example: Kaplan turbine.

Difference between Impulse and Reaction turbine

Basic definitions

Gross head (Hg): Difference b/w the head race level and tail race level when no water is flowing. Therefore it is also called static head or total head.

Net head or effective head (H): Head available at the inlet of the turbine. It is also called effective head. When water is flowing from reservoir to turbine, considering the loss due to friction alone, the net head is given by

H= Hg− hfFor reaction turbine, the net head is given as H= (Total energy at exit from penstock)-(Total energy at exit from

the draft tube) = 2 2

2 2penstock drafttube

p pv vZ Zg g g g

Tangential flow impulse turbine/ Pelton Turbine

Constructional details of Pelton turbine1) Nozzle with Flow regulating mechanism

2) Casing: casing has no hydraulic function to perform its only function is to prevent splash of water, guide the water to the tail race, and provide safety against accidents.

3) Runner and Buckets

Thank you