说New words

•        Task 任务

•        Extract提取

•        Torque扭矩

•        Permit允许、准许

•        Interpose介入

•        Mean 平均

•        Deflection偏转

•        Thickness厚度

•        Compromise妥协、折中

•        Broadly概括的

•        Compatible兼容的

•        Aerofoil翼型

•        Impulse脉冲

•        Reaction反应、反作用

•        Fixed 固定的

•        Spin 旋转

•        Detrimental有害的

•        Strut 支柱

•        Incurred发生的

•        Disc 轮盘

•        Mount 安装

•        Self-aligning自动定心

•        Coupling联轴器

•        Hollow空心的

•        Forge 锻造

•        Integral完整的

•        Flange安装边

•        Perimeter外缘、周长

•        Conduction传导

•        Actual实际的

•        Trailingedge 尾缘

•        Crack 裂纹、裂缝、破裂

•        Rimspeed 轮缘速度

•        Bulbroot fixing 球形榫头

•        Fir-treefixing 枞树形榫头

•        Serration锯齿状

•        Stiffened绷紧、变强硬

•        Shroud叶冠

•        Segment段、片

•        Peripheral次要的、附带的

•        Abradable耐磨的

•        Backpressure 背压

•        Surge 喘振

•        Choke 阻塞

•        Obstacle阻碍

•        Tensile拉伸

•        Cast 锻造

•        Diffusionbond 扩散粘接

•        Powder粉末

•        Endure忍耐、承受、持续

•        Nickelalloy 镍合金

•        Melt 融化

•        Ceramic陶瓷

•        Fatigue疲劳

•        Equi-axedcrystal structure 等轴晶结构

•        Longitudinalaxis 纵轴

•        Columnar柱状

•        Directionallysolidified 定向结晶

•        Singlecrystal 单晶

•        Ferriticsteel 铁素体钢

•        Austeniticsteel 奥氏体钢

•        Metallurgydisc 冶金轮盘

•        Ounce 盎司

•        Fluctuation波动

•        Corrosion腐蚀

•        Oxidization氧化

•        Foregoing前述的

•        Metallurgist冶金学家

•        Creep 蠕变

•        Myriad无数的

•        Column列

•        Substantially基本上

•        Reinforced加固、加强

•        Balancing平衡

读Sentence

•        1. Theturbine has the task of providing the power to drive the compressor andaccessories and, in the case of engines which do not make use solely of a jetfor propulsion, of providing shaft power for a propeller or rotor. It does thisby extracting energy from the hot gases released from the combustion system andexpanding them to a lower pressure and temperature. High stresses are involvedin this process, and for efficient operation, the turbine blade tips may rotateat speeds over 1,500 feet per second, The continuous flow of gas to which theturbine is exposed may have an entry temperature between 850 and 1,700 deg. C.and may reach a velocity of over 2,500 feet per second in parts of the turbine.

•        4. Themean blade speed of a turbine has considerable effect on the maximum efficiencypossible for a given stage output. For a given output the gas velocities,deflections, and hence losses, are reduced in proportion to the square ofhigher mean blade speeds. Stress in the turbine disc increases as the square ofthe speed, therefore to maintain the same stress level at higher speed thesectional thickness, hence the weight, must be increased dis- proportionately.For this reason, the final design is a compromise between efficiency and weight.Engines operating at higher turbine inlet temperatures are thermally moreefficient and have an improved power to weight ratio. By-pass engines have abetter propulsive efficiency and thus can have a smaller turbine for a giventhrust.

•        7.whenthe gas is expanded by the combustion process (Part 4), it forces its way intothe discharge nozzles of the turbine where, because of their convergent shape,it is accelerated to about the speed of sound which, at the gas temperature, isabout 2,500 feet per second. At the same time the gas flow is given a 'spin' or'whirl' in the direction of rotation of the turbine blades by the nozzle guidevanes. On impact with the blades and during the subsequent reaction through theblades, energy is absorbed, causing the turbine to rotate at high speed and soprovide the power for driving the turbine shaft and compressor.

•        9. Itwill be seen that the nozzle guide vanes and blades of the turbine are'twisted', the blades having a stagger angle that is greater at the tip than atthe root (fig. 5-6). The reason for the twist is to make the gas flow from thecombustion system do equal work at all positions along the length of the bladeand to ensure that the flow enters the exhaust system with a uniform axialvelocity. This results in certain changes in velocity, pressure and temperatureoccurring through the turbine, as shown diagrammatically in fig. 5-7.

•        12.The basic components of the turbine are the combustion discharge nozzles, thenozzle guide vanes, the turbine discs and the turbine blades. The rotatingassembly is carried on bearings mounted in the turbine casing and the turbineshaft may be common to the compressor shaft or connected to it by aself-aligning coupling.

•        14.The nozzle guide vanes are usually of hollow form and may be cooled by passingcompressor delivery air through them to reduce the effects of high thermalstresses and gas loads. For details of turbine cooling, reference should bemade to Part 9.

•        17.The turbine blades are of an aerofoil shape, designed to provide passagesbetween adjacent blades that give a steady acceleration of the flow up to the'throat', where the area is smallest and the velocity reaches that required atexit to produce the required degree of reaction (para. 5).

•        20. Agap exists between the blade tips and casing, which varies in size due to thedifferent rates of expansion and contraction. To reduce the loss of efficiencythrough gas leakage across the blade tips, a shroud is often fitted as shown infig. 5-1. This is made up by a small segment at the tip of each blade whichforms a peripheral ring around the blade tips. An abradable lining in thecasing may also be used to reduce gas leakage as discussed in Part 9. ActiveClearance Control (A.C.C.) is a more effective method of maintaining minimumtip clearance throughout the flight cycle. Air from the compressor is used tocool the turbine casing and when used with shroudless turbine blades, enableshigher temperatures and speeds to be used.

•        22.Very high stresses are imposed on the blade root fixing of high work rateturbines, which make conventional methods of blade attachment impractical. Adual alloy disc, or 'blisk' as shown in fig. 5-11, has a ring of cast turbineblades bonded to the disc. This type of turbine is suitable for small highpower helicopter engines.

•        28. Abrief mention of some of the points to be considered in connection with turbineblade design will give an idea of the importance of the correct choice of bladematerial. The blades, while glowing red-hot, must be strong enough to carry thecentrifugal loads due to rotation at high speed. A small turbine blade weighingonly two ounces may exert a load of over two tons at top speed and it mustwithstand the high bending loads applied by the gas to produce the many thousandsof turbine horse-power necessary to drive the compressor. Turbine blades mustalso be resistant to fatigue and thermal shock, so that they will not failunder the influence of high frequency fluctuations in the gas conditions, andthey must also be resistant to corrosion and oxidization. In spite of all thesedemands, the blades must be made in a material that can be accurately formedand machined by current manufacturing methods.

•        30. Over a period of operational time the turbine blades slowly grow inlength. This phenomenon is known as 'creep' and there is a finite useful lifelimit before failure occurs.

读全文并回答以下问题：

•       Whatdetermines the number of turbine stages?

•       Describethe classification and application of the turbine.

•       Whatare the hazards of excessive residual swirl?

•       How tolimit the effect of heat conduction from the turbine blades to the disc?

•       What’sthe advantage for contra-rotating turbines?

•       What will happen if the turbine and compressor’s flow don’t match?