S. It serves for accelerating and directing hot gases onto the buckets of the turbine wheel.
T. What does the nozzle diaphragm consist of?
S. It consists of hollow vanes welded between two concentric rings.
T. What are nozzle vanes usually made of?
S. They are made of high-temperature alloys.
T. What does the turbine rotor assembly consist of?
S. It consists of a shaft, a turbine wheel or rotor and a set of stationary vanes.
T. What are turbine discs made of?
S. They are made of corrosion-resistant high-temperature nickel alloys.
T. And turbine buckets?
S. They are usually forged from heat resistant nickel-chrome alloy.
T. What attachment is often used to fasten turbine buckets to the wheel rims?
S. The “fir-tree attachment” is most widely used for that purpose.
T. That’s correct. Thank you.
Exercise 17. Read, translate and give the gist of text 2.
Text 2. Turbine Section
A turbine section of the engine is located after the combustion chamber and comprises two parts: the turbine nozzle diaphragm and the turbine rotor assembly. The function of the nozzle diaphragm is two-fold: it increases the velocity of the heated gases and it directs the flow of gases to strike the turbine buckets at the desired angle. The blades or vanes in the nozzle diaphragm are of airfoil design.
A typical nozzle diaphragm consists of a group of nozzle vanes welded between two concentric rings. The inner and outer bands of a typical nozzle diaphragm contain punched holes to receive the ends of the nozzle vanes. The nozzle vanes are usually constructed of high-temperature alloy, and they must be highly heat-resistant.
In many engines the nozzle vanes are hollow and are formed from stainless-steel sheet.
The usual turbine-rotor assembly consists of a shaft, a wheel or disk, and the buckets fastened to the rim of the disk. The turbine shaft, also called a compressor-drive turbine shaft, is usually made of alloy steel. The method of fastening the wheel to the shaft varies with different manufacturers. And turbine buckets can be attached to turbine-wheel rims by a variety of methods but the most widely used is the “fir-tree” attachment.
Among the most seriously stressed components in a gas-turbine engine is the turbine wheel. The buckets of the wheel are subjected to high centrifugal stresses and to a fluctuating stream of hot gases which raise their temperature and may, at the same time, introduce vibratory stresses. The disk of the wheel is subjected to heat from the buckets and may, in some cases, be directly heated by the combustion gases. Where there is more than one turbine disk in an engine, the second- and third-stage disks do not encounter such high temperatures. Turbine disks are often cooled by means of air bled from the compressor section and directed to flow around the turbine disk.
Exercise 18. Give Ukrainian/Russian equivalents of the following word combinations.
Turbine nozzle diaphragm, turbine rotor assembly, flow of gases, at a desired angle, airfoil design, nozzle vanes, concentric rings, inner and outer bands, punched holes, heat-resistant, stainless-steel sheet, fastened to the rim, compressor-drive turbine shaft, enginemanufacturer, “fir-tree” attachment, centrifugal stresses, fluctuating stream, in some cases, encounter high temperatures.
Exercise 19. Find English equivalents in text 2.
Сопловий апарат турбіни / cопловой аппарат турбины; робоче колесо турбіни / рабочее колесо турбины; лопатки турбіни/лопатки турбины; прикріплювати до обода / прикреплять к ободу; пробивати отвори / пробивать отверстия; порожнисті лопатки / пустотелые лопатки; теплостійкий / жаропрочный; хвостовик типу “ялинка” / хвостовик типа “елочка”; нержавіюча сталь / нержавеющая сталь; відцентрові навантаження / центробежные нагрузки; диск турбіни / диск турбины; диск другої ступені / диск второй ступени; відведене від компресора повітря / отведенный от компресcора воздух.
Exercise 20. Put questions to the italicized words.
1. The hot gas also loses some of its pressure going through the turbine. 2. Nearly three fourths of all the energy available from the products of combustion is necessary to drive the compressor. 3. A turboprop engine combines the advantages of a turbojet engine with the propulsive efficiency of a propeller. 4. The third-stage turbine nozzle serves the same purpose as the other nozzles. 5. The second-stage turbine disc has about 90 blades on the outer periphery of the disc. 6. The turbine shaft is made of alloy steel. 7. The mixed gases are introduced into the turbine inlet nozzle guide vanes.
Exercise 21. Choose the correct answer.
1. What does the turbine section include?
a. the outer casing and the inner casing;
b. the turbine nozzle diaphragm and the compressor;
c. the turbine-nozzle diaphragm and the turbine rotor assembly.
2. What is the function of the nozzle daiphragm?
a. to cool mixed gases and direct them into the exhaust case;
b. to accelerate and direct hot gases onto the buckets of the turbine wheel;
c. to expand hot gases and direct them onto the buckets of the turbine wheel.
3. What stresses are turbine discs subjected to?
a. to a fluctuating stream of hot gases;
b. to a fluctuating stream of cold water;
c. to a continuous stream of hot gas-fuel mixture.
4. What types of gas turbines do you know?
a. impulse, reaction and reaction-impulse types;
b. single-or multiple-stage type;
c. centrifugal and axial-flow type.
Exercise. 22. Put the verbs in brackets into the Present Perfect Tense.
Model: I never (speak) to him.
I have never spoken to him.
I (not finish) my report yet. 2. Someone (take) my cell phone. 3. I (work) here for ten years. 4. Why you (not repair) the door lock? – I (not have) time. 5. You ever (fly) a plane? 6. I (drive) this car once or twice. 7. He (not speak) English all his life. 8. I (see) George recently.
9. The manager already (sign) the letters. 10. I (know) that for a long time. 11. The engineer already (check) the compressor blades for cracks. 12. I (read) many books on gas-turbine design. 13. They (devote) much time to studying the process of combustion. 14. The mechanic already (repair) the damaged inlet duct. 15. The flight engineer (fail) to find the cause of trouble.
Exercise. 23. Change the sentences to the Present Perfect Tense supplying proper adverbial modifiers of time.
Model: The train went five minutes ago.
The train has already gone.
1. I heard about the incident yesterday. 2. You left your report in the reading hall yesterday morning. 3. John studied very hard last term. 4. I flew the plane when I was at the university. 5. He didn’t speak German much. 6. She gave us the tickets two days ago. 7. They went to the theatre together yesterday evening. 8. They told me about your decision not long ago. 9. He started the engine before flight. 10. The mechanic didn’t check the brakes during maintenance.
Exercise. 24. Give answers, positive or negative.
Model: Has Nick passed his exam?
- Yes, he has. - No, he hasn’t. He has failed.
1. Has the aeroplane already landed? 2. Have the mechanics repaired the air intake? 3. Has he checked the tank for leaks? 4. Have they calculated the pressure loss? 5. Has he failed to carry out this experiment? 6. Have you often used this method?
Exercise 25. Read, translate and give the gist of text 3.
Text 3. Types of Turbine
A turbojet engine may have a single-stage turbine or a multi-stage arrangement. Typical turbines are illustrated in figures II.4.3, and II.4.4.
Fig.II.4.3. Single-stage turbine
Fig.II.4.4. Three-stage turbine
Each turbine stage consists of one row of stationary vanes (stator vanes) and one row of moving blades (rotor blades). The turbine may consist of several stages and its number may vary depending on required power, rotational speed and the diameter of a turbine. The number of shafts and therefore turbines, varies with the type of an engine.
The function of the turbine in the turbojet engine is to extract kinetic energy from the high-velocity gases leaving the combustion section of the engine. The energy is converted into useful rotational energy for driving the compressor and accessories. Approximately three-fourths of the energy available from the burning fuel is required for the compressor. If the engine is used for driving a propeller or a power shaft, up to 90 percent of the energy of the gases will be extracted by the turbine section.
Turbines are of three types: the impulse turbine, the reaction turbine, and a combination of the two called a reaction-impulse turbine. Turbojet engines normally employ the reaction-impulse type.
The difference between an impulse turbine and a reaction turbine is illustrated in figures II.4.5, II.4.6. The pressure and speed of the gases passing through the impulse turbine remain essentially the same, the only change being in the direction of a flow. The turbine absorbs the energy required to change the direction of the high-speed gases. A reaction turbine changes the speed and pressure of the gases. As the gases pass between the turbine blades, the cross sectional area of the passage decreases and causes an increase in the gas velocity. This increase in velocity is accompanied by a decrease in pressure according to Bernoulli’s law. In this case the turbine absorbs the energy required to change the velocity of the gases.