Передмова (стр. 29 )

Impulse turbines change the direction of flow of a high velocity fluid jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. There is no pressure change of the fluid in the turbine rotor blades. Before reaching the turbine, the fluid’s pressure head is changed to velocity head by accelerating the fluid with a nozzle. Impulse turbines do not require a pressure casement around the runner since the fluid jet is prepared by a nozzle prior to reaching turbine. Newton’s laws describe the transfer of energy for impulse and reaction turbines.

Reaction turbines develop torque by reacting to the fluid’s pressure or weight. The pressure of the fluid changes as it passes through the turbine rotor blades. A pressure casement is needed to contain the working fluid as it acts on the turbine stage(s) or the turbine must be fully immersed in the fluid flow (wind turbines). The casing contains and directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube. Francis turbines and most steam turbines use this concept. For compressible working fluids multiple turbine stages may be used to harness the expanding gas efficiency.

Wind turbines use an airfoil to generate lift from the moving fluid and impart it to the rotor (this is a form of reaction). Wind turbines also gain some energy from the impulse of the wind by deflecting it at an angle. Turbines with multiple stages may utilize either reaction or impulse blading at high pressure. Steam turbines are usually more impulse while gas turbines are more reaction type designs. At low pressure the operating fluid medium expands in volume for small changes in pressure. Under these conditions (termed Low Pressure Turbines) blading becomes strictly a reaction type design. The reason is due to the effect of the rotation speed for each blade. As the volume increases the blade height increases and the base of the blade spins at a slower speed relative to the tip. This change in speed forces a designer to change from impulse at the base to a high reaction style tip.

Exercise 3. Answer the questions on text 1.

1.  What is the purpose of a turbine?

2.  How do the simplest turbines operate?

3.  What do gas, steam and water turbines have to control the fluid?

4.  What device is similar to a turbine?

5.  What type of turbines (impulse or reaction) requires a pressure casement?

6.  Are wind turbines referred to reaction or impulse turbines?

7.  Are steam turbines or gas turbines more reaction type design?

Exercise 4. Say whether the given statements are true or false. If a statement is wrong, correct. If true, enrich it with details.

1. Gas, steam and water turbines usually have a casing around the blades.

2. A device similar to a turbine but operating in reverse is a compressor or pump.

3. Impulse turbines require a pressure casement.

4. Reaction turbines do not require a pressure casement.

5. Wind turbines may utilize either reaction or impulse blading at high pressure.

6. Steam turbines are usually more reaction while gas turbines are more reaction type designs.

Exercise 5. Memorize the following words and word combinations to text 2.

Guide vane – напрямна лопатка

ratio – коефіцієнт

impinge – наштовхуватися, ударятися

alloy – сплав

melt – плавитися

brittle – крихкий

counterpart – двійник, аналог

shroud – бандаж, кожух

boundary layer – межовий шар, суміжний шар

damping – амортизація, демпфування, гасіння (коливань)

flutter – вібрація; нестійке коливання

nuclear – ядерний

internal combustion machine – двигун внутрішнього згоряння

duct – канал, прохід, трубопровід

heat-exchanger – радіатор, теплообмінник

alternator – генератор

propulsion – рух

exhaust – випускання (газів), вихлоп; випускати, вивільняти, видаляти

with respect to – що стосується, відносно

propellant – паливо (ракетне)

oxygen – кисень

hydrogen – водень

Exercise 6. Read and translate text 2.

Text 2. Turbines operation and purposes

Steam turbines are used for the generation of electricity in thermal power plants such as plants using coal, fuel, oil or nuclear power. They were once used to directly drive mechanical devices such as ship’s propellers, but now most such applications use reduction gears or an intermediate electrical step, where the turbine is used to generate electricity which then powers an electric motor connected to the mechanical load.

Gas turbine engines are sometimes referred to as turbine ch engines usually feature an inlet, fan, compressor, combustor and nozzle (possibly other assemblies) in addition to one or more turbines.

The gasflow in most turbines employed in gas turbine engines remains subsonic throughout the expansion process. In a transonic turbine the gasflow becomes supersonic as it exists the nozzle guide vanes. Transonic turbines operate at a higher pressure ratio than normal but are usually less efficient and uncommon. This turbine works well in creating power from water.

Multi-stage turbines have a set of static (meaning stationary) inlet guide vanes that direct the gasflow onto the rotating rotor blades. In a statorless turbine the gasflow existing in an upstream rotor impinges onto a downstream rotor without an intermediate set of stator vanes that rearrange the pressure / velocity energy levels of the flow.

Conventional high-pressure turbine blades (and vanes) are made of nickel-steel alloys and often utilize internal aircooling passages to prevent the metal from melting. In recent years experimental ceramic blades have been manufactured and tested in gas turbines with a view of increasing rotor inlet temperatures and, possibly, eliminating aircooling. Ceramic blades are more brittle than their metallic counterparts and carry a greater risk of catastrophic blade failure. Many turbine rotor blades have a shroud at the top to increase damping and thereby reduce blade flutter. This turbines are called shrouded turbines. Modern practice is, where possible, to eliminate the rotor shroud reducing the centrifugal load on the blade and the cooling ch turbines are called shroudless turbines. Bladeless turbine uses the boundary layer effect, and not a fluid impinging upon the blades as in a conventional turbine.

Turbines are often a part of a larger machine. A gas turbine, for example, may refer to an internal combustion machine that contains a turbine, ducts, compressor, combustor, heat-exchanger, fan and (in the case of one designed to produce electricity) an alternator. However, it must be noted that the collective machine referred to as the turbine is designed to transfer energy from a fuel to the fluid passing through the internal combustion device as a means of propulsion. Reciprocating piston engines such as aircraft engines can use a turbine powered by their exhaust to drive an intake-air compressor.

Turbines can have incredible power density with respect to volume and weight. This is because of their ability to operate at very high speeds. The Space Shuttle’s main engines use turbopumps (machines consisting of a pump driven by a turbine engine) to feed the propellants (liquid oxygen and liquid hydrogen) into the engine combustion chamber. The liquid hydrogen turbopump is slightly larger than an automobile engine (weighing approximately 700 lb) and produces nearly 70,000 hp (52,2 MW).

Turboexpanders are widely used as sources of refrigeration in industrial processes.

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Exercise 7. Translate the following international words. Mind the difference in their pronunciation and meanings in English and Ukrainian.

Reverse, compressor, gas, energy, turbine, potential, kinetic, physical, rotor, concept, form, type, effect, designer, base, style, electricity, thermal, mechanical, propeller, motor, normal, static, stator, metal, experimental, ceramic, test, risk, effect, thermodynamic, control.

Exercise 8. Determine the parts of speech of the following words, define their prefixes and suffixes, where possible, and translate them.

Windmill, incompressible, compressor, pressure, casement, runner, reaction, slower, generation, directly, propellant, electrical, subsonic, transonic, gasflow, supersonic, higher, less, multi-stage, fluid-flow, upstream, downstream, intermediate, stator, statorless, high-pressure, nickel-steel, greater, counterpart, failure, bladeless, normally, efficiency, larger, heat-exchanger, alternator, collective, provision, incredible, density, turbopump, propellant, combustor, combustion, rearrange, uncommon, propeller, slightly, larger, simplest, assembly, rotor, layer, rotation.

Exercise bine the words of two groups to make all possible «noun+noun» word combinations. Translate them.

Group I: fluid, rotor, water, gas, steam, impulse, reaction, stator, pressure, velocity, wind, rotation, power, inlet.

Group II: assembly, turbine, flow, energy, blade, head, casement, medium, duct, speed, plant, engine, ratio, vane, temperature.

Exercise 10. Translate and comment upon the following grammar forms.

Moving, operating, working, employed, diminished, attached, changed, accelerating, prepared, reaching, needed, immersed, casing, used, expanding, deflecting, blading, operating, using, connected, referred, employed, existing, cooling, being, encountered, melting, manufactured, tested, damping, reducing, impinging, produced, reducing, passing, powered, driven, made, weighing, needed.

Exercise 11. Match the synonymous words and word combinations.

1)  velocity 2)  use 3)  power 4)  thrust 5)  rotor 6)  impulse 7)  propulsion 8)  vane 9)  produce 10)  diminish 11)  work 12)  combustion chamber 13)  supply 14)  fuel

a)  runner b)  draft c)  forward movement d)  feed e)  speed f)  energy g)  propellant h)  manufacture i)  employ j)  blade k)  combustor l)  operation m)  stimulus n)  reduce

Exercise 12. Translate the words used both as verbs and nouns.