高壓空氣
高壓中間空氣
低壓空氣
圖9-1 內(nèi)部空氣流的簡(jiǎn)圖
Fig. 9-1 General internal airflow pattern.
6．圖9-2示出了氣冷式高壓導(dǎo)向葉片和渦輪葉片的布置，圖中示出了冷卻空氣流向。渦輪導(dǎo)向葉片和渦輪葉片的壽命不僅取決于它們的結(jié)構(gòu)形式，而且還與冷卻方法有關(guān)，因此內(nèi)部流道的氣流設(shè)計(jì)很重要。在整個(gè)燃?xì)鉁u輪發(fā)展歷程中，曾經(jīng)對(duì)渦輪導(dǎo)向葉片和渦輪葉片使用過許多的冷卻方法。在一般的情況下，單通道內(nèi)部(對(duì)流)冷卻具有很大的實(shí)用效果。但是，在研究發(fā)展中又實(shí)現(xiàn)了多通道的內(nèi)部冷卻渦輪葉片，帶外部氣膜冷卻沖擊式冷卻導(dǎo)向葉片，這種外部氣膜冷卻在導(dǎo)向葉片和轉(zhuǎn)子葉片均用，如圖9-3和圖9-4所示。
Internal air system
圖9-2 導(dǎo)向葉片和渦輪葉片的冷卻布置圖
7．“預(yù)旋噴嘴”(圖9-2)降低了供往輪盤用于葉片冷卻的空氣的壓力和溫度。這些噴嘴還使空氣得到很大的周向速度，以幫助空氣有效地進(jìn)入旋轉(zhuǎn)的冷卻通道。
8．冷卻渦輪盤的冷卻空氣進(jìn)入輪盤之間的空腔。并往外流過輪盤的表面。氣流由級(jí)間封嚴(yán)件控制，在完成冷卻功能之后，排入主燃?xì)饬?圖9-5)，參見第23段熱燃?xì)馕氩糠帧?br />
6.
An air cooled high pressure nozzle guide vane and turbine blade arrangement illustrating the cooling airflow is shown in fig. 9-2. Turbine vane and turbine blade life depends not only on their form but also on the method of cooling, therefore the flow design of the internal passages is important. There have been numerous methods of turbine vane and turbine blade cooling which have been used throughout the history of gas turbines. Generally, single pass internal (convection) cooling was of great practical benefit but development has lead to multi-pass internal cooling of blades, impingement cooling of vanes with external air film cooling of both vanes and blades, these are shown in fig. 9-3. and fig. 9-4.
7.
The 'pre-swirl nozzles' (fig. 9-2) reduce the temperature and pressure of the cooling air fed to the disc for blade cooling. The nozzles also impart a
Internal air system
substantial whirl velocity to assist efficient entry of the air into the rotating cooling passages.
8. Cooling air for the turbine discs enters the annular spaces between the discs and flows outwards over the disc faces. Flow is controlled by interstage seals and, on completion of the cooling function, the air is expelled into the main gas stream (fig. 9-5); see para. 23., Hot gas ingestion.
Bearing chamber cooling
9. Air cooling of the engine bearing chambers is not normally necessary since the lubrication system (Part 8) is adequate for cooling purposes. Additionally, bearing chambers are located, where possible, in the cooler regions of the engine. In instances where additional cooling is required, it is good practice to have a double skinned bearing housing with cooling air fed into the intermediate space.
圖9-3 高壓渦輪葉片冷卻的發(fā)展
附件冷卻
10．發(fā)動(dòng)機(jī)的一些附件會(huì)產(chǎn)生大量的熱，其中發(fā)電機(jī)即是一例。這些附件常常需要有它們自己的冷卻通路。當(dāng)用空氣進(jìn)行冷卻時(shí)，氣源可以是壓氣機(jī)，或者是從發(fā)動(dòng)機(jī)整流罩中進(jìn)氣道的引氣口處引入的外界空氣。
Internal air system
11．當(dāng)一個(gè)附件裝置在飛行中由外界空氣冷卻的時(shí)候，通常需要配備一條誘導(dǎo)通路，以便在地面靜態(tài)運(yùn)轉(zhuǎn)沒有外部空氣流的時(shí)候使用。這是將壓氣機(jī)輸出的空氣流經(jīng)位于附件冷卻空氣出口導(dǎo)管處的幾個(gè)噴口而實(shí)現(xiàn)的。流經(jīng)這些噴口的空氣速度造成一個(gè)低壓區(qū)，這個(gè)低壓區(qū)形成了一個(gè)引射器，由此來引射一股大氣空氣流流經(jīng)進(jìn)氣道中的引氣口。為了保證該引射器系統(tǒng)僅僅在地面工作，來自壓氣機(jī)的空氣流由一個(gè)活門控制。帶引射器的發(fā)電機(jī)冷卻系統(tǒng)示于圖9-6。
封嚴(yán)
12．封嚴(yán)件用于防止滑油從發(fā)動(dòng)機(jī)軸承腔漏出，控制冷卻空氣流和防止主氣流的燃?xì)膺M(jìn)入渦輪盤空腔。
沖擊冷卻管
圖9-4 高壓渦輪導(dǎo)向葉片的結(jié)構(gòu)和冷卻
Fig. 9-4 High pressure nozzle guide vane construction and cooling.
13．在燃?xì)鉁u輪發(fā)動(dòng)機(jī)上使用了多種封嚴(yán)方法。選擇何種方法取決于周圍的溫度和壓力、可磨蝕性、發(fā)熱量、重量、可用的空間，易于制造及易于安裝和拆卸。下列各段敘述了某些封嚴(yán)方法。圖9-5所示為一臺(tái)假想的渦輪，用來表明這些封嚴(yán)的使用方法。
Accessory cooling
10.
A considerable amount of heat is produced by some of the engine accessories, of which the electrical generator is an example, and these may often require their own cooling circuit. When air is used for cooling, the source may be the compressor or atmospheric air ducted from intake louvres in the engine cowlings.
11.
When an accessory unit is cooled during flight by atmospheric air it is usually necessary to provide an induced circuit for use during static ground running when there would be no external airflow. This is achieved by allowing compressor delivery air to pass through nozzles situated in the cooling air outlet duct of the accessory. The air velocity through the nozzles create a low pressure area which forms an ejector, so inducing a flow of atmospheric air through the intake louvres. To ensure that the ejector system only operates during ground running, the flow of air from the compressor is controlled by a valve. A generator cooling system with an ejector is shown in fig. 9-6.
SEALING
12. Seals are used to prevent oil leakage from the engine bearing chambers, to control cooling airflows and to prevent ingress of the mainstream gas into the turbine disc cavities.
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