说New words

•        Distortion扭曲

•        Crack 裂纹、裂缝

•        Heatconduction 热传导

•        Thrustreverser 反推装置

•        Suppressor抑制器

•        Entail牵连、使承担

•        Thorough彻底的

•        Insulating绝缘

•        Residual残余

•        Wastage损耗

•        Throat喉部

•        Flare 闪耀、喇叭型

•        Corresponding对应、相关的

•        Parallel平行

•        Longitudinal纵向的

•        Seldom很少

•        Ventilating通风

•        Lagging滞后、延迟

•        Dimpled凹坑

•        Cone 圆锥形

•        Streamline流线型

•        Fairing整流罩

•        Vent 通风口

•        Chute 斜道、滑槽

读Sentence

•        1.Aero gas turbine engines have an exhaust system which passes the turbinedischarge gases to atmosphere at a velocity, and in the required direction, toprovide the resultant thrust. The velocity and pressure of the exhaust gasescreate the thrust in the turbo-jet engine (para. 5) but in the turbo-propellerengine only a small amount of thrust is contributed by the exhaust gases,because most of the energy has been absorbed by the turbine for driving thepropeller. The design of the exhaust system therefore, exerts a considerableinfluence on the performance of the engine. The areas of the jet pipe andpropelling or outlet nozzle affect the turbine entry temperature, the massairflow and the velocity and pressure of the exhaust jet.

•        4. Gasfrom the engine turbine enters the exhaust system at velocities from 750 to1,200 feet per second, but, because velocities of this order produce highfriction losses, the speed of flow is decreased by diffusion. This isaccomplished by having an increasing passage area between the exhaust cone andthe outer wall as shown in fig. 6-1. The cone also prevents the exhaust gasesfrom flowing across the rear face of the turbine disc. It is usual to hold thevelocity at the exhaust unit outlet to a Mach number of about 0.5, i.e.approximately 950 feet per second. Additional losses occur due to the residualwhirl velocity in the gas stream from the turbine. To reduce these losses, theturbine rear struts in the exhaust unit are designed to straighten out the flowbefore the gases pass into the jet pipe.

•        7.From the illustration (fig. 6-3), it will be seen that the convergent sectionexit now becomes the throat, with the exit proper now being at the end of theflared divergent section. When the gas enters the convergent section of thenozzle, the gas velocity increases with a corresponding fall in staticpressure. The gas velocity at the throat corresponds to the local sonic velocity.As the gas leaves the restriction of the throat and flows into the divergentsection, it progressively increases in velocity towards the exit. The reactionto this further increase in momentum is a pressure force acting on the innerwall of the nozzle. A component of this force acting parallel to thelongitudinal axis of the nozzle produces the further increase in thrust.

•        14.When the gas temperature is very high (for example, when afterburning isemployed), the complete jet pipe is usually of double-wall construction (Part16) with an annular space between the two walls. The hot gases leaving thepropelling nozzle induce, by ejector action, a flow of air through the annularspace of the engine nacelle. This flow of air cools the inner wall of the jetpipe and acts as an insulating blanket by reducing the transfer of heat fromthe inner to the outer wall.

•        17.Due to the wide variations of temperature to which the exhaust system issubjected, it must be mounted and have its sections joined together in such amanner as to allow for expansion and contraction without distortion or damage.

读全文并回答以下问题：

•       Definethe pressure thrust.

•       Why isthe propelling nozzle size important?

•       Howdoes high by-pass engine exhaust the gas?