Since the temperature of the burning gases in a gas-turbine engine decreases substantially as the gases pass though each turbine stage, it is usually necessary to provide special cooling for the first stage only. In some engines, the second-stage nozzle vanes and turbine blades are also air-cooled. Turbine blades are made in shrouded and unshrouded configurations.
Exercise 26. Look at Figures II.4.5., II.4.6. and answer the questions.
1. What is the difference between changing magnitudes of inlet and discharge velocity in impulse and reaction turbines?
2. How does inter-blade cross sectional area of the passage change in an impulse and reaction turbine?
Exercise 27. The following questions on text 3 have been jumbled. Arrange them correctly and answer them.
the, function, What, is, the, of, turbine?
What is the function of the turbine?
1) drive, in, Does, engines, as well, the turbine, the propeller. turboprop?
2) much, required, for, is, compressor, the, energy, driving, How?
Корисна енергія / полезная энергия; кінетична енергія / кине-тическая энергия; високотемпературні сплави / високотемпера-турные сплавы; концентричні кільця / концентрические кольца; реактивна турбіна / реактивная турбина; активна турбіна / активная турбина; пульсуючий потік / пульсирующий поток; стаціонарні лопатки / стационарные лопатки; хвостовик типу “ялинка”/ хвостовик типа “елочка”; багатоступенева турбіна / многоступенчатая турбина; потужність на валу / мощность на валу; площа поперечного перерізу / площадь поперечного сечения.
Exercise 32. Say whether the following statements are true or false. Correct the false ones.
1. The function of the turbine is to extract kinetic energy from the gases leaving the compressor section. 2. Approximately 75% of the energy available from the burning fuel is required for the compressor. 3. The speed and pressure of the gases in a reaction turbine remain essentially the same. 4. The increase in velocity is accompanied by an increase in pressure according to Bernoulli’s law. 5. The nozzle vanes and turbine buckets in gas-turbine engines should be constructed of high-temperature alloys.
Exercise 33. Memorize the rules of working with figures.
1. We say 10 thousand (NOT*10 thousands).
We say 10 thousand students (NOT*10 thousand of…)
But we say thousands of students, hundreds of hours, etc.
2. For figures over 100, British English (B.E.) uses “and” between the hundreds and the tens. E.g.: 345 (B.E.) - three hundred and forty-five. American English (A.E.) - three hundred forty-five. 1,000 - a thousand or one thousand.
We use “and” when there are no hundreds: 1,070 one/a thousand and seventy, but we do not use “and” before a number of hundreds: 1,634 one thousand six hundred and forty three (NOT*one thousand and six hundred…)
3. If we use a decimal we say point. Each figure is said separately.
UK/USA (zero) point five
UK (nought) point five
(zero) point four eight
(nought) point four eight
4. Fractions are expressed using ordinal numbers:
1/3 – a third, 1/4 – a quarter, 1/2 – a half, 2/3 – two thirds, 3/4 – three quarters.
7. To indicate changes in figures prepositions from, to, and by are used.
The pressure ratio has risen by 50% from 10:1 to 15:1.
8. When speaking about money we say the currency unit after the figure:
F 65 sixty five francs
C $ 200 two hundred Canadian dollars.
Exercise 34. Choose the correct way of pronouncing the numbers in these sentences.
1. The government have announced a 1.5% reduction in interest rates.
a) “one point five”;
b) “one comma five”
2. Have you seen the film ’2001 – a space Odyssey’?
a) “twenty thousand and one”;
b) “two thousand and one”
3. Give me a ring. My number is Oxford 932811
a) “nine-three two eight double one”;
b) “ninety-three, twenty-eight, eleven”
4. The reception area in the new building will be 10m x 15m.
a) “ten metres times fifteen”;
b) “ten metres multiplied by fifteen metres”
5. He joined the company in 1947.
a) “nineteen hundred and forty-seven”;
b) “nineteen forty-seven”
6. In some countries higher earners pay out 2/3 of their salaries in tax.
a) “ two thirds”;
7. Our tax year ends on March 31.
a) March the thirty-first;
b) March thirty-first
8. Nicaragua’s GNP (Gross National Profit) is approximately $ 2.000 000 000.
a) “two billion dollars”;
b) “ two billions dollars”
9. The optimum operating temperature for this equipment is - 8°C.
a) “below eight degrees Centigrade”;
b) “ minus eight degrees Centigrade”
10. The world cup final ended in a O-O-draw.
a) “nil – nil”;
b) “zero – zero”.
Exercise 35. Read these sentences out loud paying attention to pronunciation of figures.
1. The flight BA 325 has been delayed till 2.30 p.m. 2. I stay at the Kyiv hotel in room 732. 3. Could you ask him to call me? My telephone number is 5287632. 4. About 1/3 of foreign investments in the USA is in manufacturing. 5. The International Monetary Fund (IMF) was created with a fund of $ 8.8 billion. 6. The starting price of the package is Hr 1.4 million.
.Exercise 36. Match the English-Ukrainian / Russian terms.
Еxercise 37. Read and translate text 4. Make a list of key words.
Text 4. Turbine and Exhaust Section
The turbine section includes the turbine front case, the turbine rear case, an inner case and seal, four stages of turbine-nozzle vanes, two turbine rotors with four stages, and the coaxial drive shafts.
The turbine front case is a comparatively short section attached to the rear of the combustion-chamber outer case. It is of decreasing diameter and extends to the first-stage turbine. The first-stage turbine vanes are mounted in the rear of the turbine front case and immediately to the rear of the nozzle vanes is the first-stage turbine. The case is constructed of corrosion- and heat-resistant steel.
The turbine nozzle vanes are mounted in the inside diameter of the turbine front case and turbine rear case. It will be remembered that the turbine blade tips form a complete ring or shroud to reduce gas losses. The outer rim of the shroud forms a knife-edge seal.
The first-stage turbine-nozzle vanes are coated and air-cooled. In later models of the JT8D engine, the cooling air is passed inside the vanes and out through air-exit holes in the airfoil trailing edge on the concave side.
In later engines, the first-stage turbine is a separate unit bolted to the shaft flange. The turbine blades are attached to the turbine disk by means of fir-tree slots in the rim of the disk. They are held in the slots by means of rivets.
The front-compressor-drive turbine rotor includes the front-compressor-drive turbine shaft, three turbine stages, and the spacers and airseals between the disks.
The turbine-exhaust case, constructed of welded steel, is the most rearward section of the basic inner engine. It is bolted to the rear flange of the turbine case and decreases from front to rear in order to increase the velocity of the exhaust gases.
Exercise 38. Say whether the following statements are true or false. Correct the false ones.
1. The function of the combustion chamber is to extract kinetic energy from the expanding gases. 2. The expanded gases flow from the combustion chamber into the turbine inlet nozzle guide vanes. 3. The purpose of the turbine section is to accelerate and direct hot gases into the combustion chamber. 4. The second-stage turbine nozzle is mounted between the first stage and second-stage turbines. 5. The third-stage turbine nozzle serves the same purpose as the other nozzles. 6. The blades are secured by rivets. 7. Turbine buckets are usually forged from high-quality steel alloys. 8. In the case of multiple-stage turbines the wheels may operate independently of one another.
Exercise 39. Translate the text in writing and entitle it.
Turbine blades are made in two principal configurations: shrouded and unshrouded. The shrouded blade is provided with a shroud section at the outer end, so that when the buckets are installed, they form a continuous rim or shroud around the outer ends of the blades. With the unshrouded blades, it is necessary to provide a closely fitting shroud ring to prevent the escape of the hot gases which drive the turbine.
Some consideration has been given to the possibility of using hollow steel or nickel-alloy blades for the turbine wheels, and some experimentation has been accomplished along this line.
Since the nozzle vanes and turbine blades in gas-turbine engines are subjected to extremely high temperatures, it is essential that they be constructed of high-temperature alloys and that some type of special cooling be provided. It must be remembered that the efficiency of an engine becomes greater as the temperature of the gases at the burner outlet becomes greater. The development of high-temperature alloys has made it possible to increase the operating temperature of gas-turbine engines, thus increasing the power available from the engines. A further development is the application of coatings to the vanes and blades to withstand heat and prevent high-temperature corrosion.
Exercise 40. Describe the design of the turbine section shown in Figure II.4.7., using the vocabulary notes below.
Fig. II.4.7. Design of the turbine section
1. Вал ротора НТ (низького тиску)
1. Вал ротора НД (низкого давления)
1. LP rotor shaft
2. Вал ротора ВТ (високого тиску)
2. Вал ротора ВД (высокого давления)
2. HP rotor shaft
3. Внутрішній кожух камери згорання
3. Внутренний кожух камеры сгорания
3. Combustion section inner casing
4. Сопловий апарат першого ступеня
4. Сопловой аппарат первой ступени
4. First stage nozzle vanes
5. Турбіна (ротора високого тиску)
5. Турбина (ротора высокого давления)
5. HP turbine
6. Сопловий апарат другого ступеня
6. Сопловой аппарат второй ступени
6. Second stage nozzle vanes
7. Турбіна ротора низького тиску (з сопловим апаратом 3-го ступеня)
7. Турбина ротора низкого давления (с сопловым аппаратом 3-й ступени)