20.
Hydraulic seals (fig. 9-7) are formed by a seal fin immersed in an annulus of oil which has been created by centrifugal forces. Any difference in air pressure inside and outside of the bearing chamber is compensated by a difference in oil level either side of the fin.
Carbon seals
21. Carbon seals (fig. 9-7) consist of a static ring of carbon which constantly rubs against a collar on a rotating shaft. Several springs are used to maintain contact between the carbon and the collar. This type of seal relies upon a high degree of contact and does not allow oil or air leakage across it. The heat caused by friction is dissipated by the oil system.
Brush seals
22. Brush seals (fig. 9-7) comprise a static ring of fine wire bristles. They are in continuous contact with a rotating shaft, rubbing against a hard ceramic coating. This type of seal has the advantage of with-standing radial rubs without increasing leakage.
Hot gas ingestion
23.
It is important to prevent the ingestion of hot mainstream gas into the turbine disc cavities as this would cause overheating and result in unwanted thermal expansion and fatigue. The pressure in the turbine annulus forces the hot gas, between the rotating discs and the adjacent static parts, into the turbine disc rim spaces. In addition, air near the face of the rotating discs is accelerated by friction causing it to be pumped outwards. This induces a comple-mentary inward flow of hot gas.
24.
Prevention of hot gas ingestion is achieved by continuously supplying the required quantity of cooling and sealing air into the disc cavities to oppose the inward flow of hot gas. The flow and pressure of the cooling and sealing air is controlled by interstage seals (fig. 9-5),
CONTROL OF BEARING LOADS
25. Engine shafts experience varying axial gas loads (Part 20) which act in a forward direction on the compressor and in a rearward direction on the turbine. The shaft between them is therefore always under tension and the difference between the loads is carried by the location bearing which is fixed in a static casing (fig. 9-8). The internal air pressure acts
刷式封严件
22．刷式封严件(图9-7中左侧第4图)有一个由很多细钢丝制成的刷组成的静止环。它们不断地与旋转轴相接触，与硬的陶瓷涂层相摩擦。这种封严件的优点是可以承受径向摩擦而不增加渗漏。
热燃气吸入
23.防止高温主燃气流吸人涡轮盘的空腔是非常重要的，因为这会导致过热和引起有害的热膨胀和疲劳。涡轮环腔内的压力迫使旋转的轮盘和相邻的静止零件之间的高温燃气进入涡轮盘轮缘的空间。而且，靠近旋转轮盘表面的空气由于摩擦而加速，使它被向外抽走。这就会诱发一股向里填补的高温燃气流。
Internal air system
图9-7 几种典型的封严件
涡轮向后的载荷
压气机向前的载荷
图9-8 轴承轴向载荷的控制
Fig. 9-8 Control of axial bearing load.
upon a fixed diameter pressure balance seal to ensure the location bearing is adequately loaded throughout the engine thrust range.
AIRCRAFT SERVICES
26. To provide cabin pressurization, airframe anti-icing and cabin heat, substantial quantities of air are 飞机服务
26．为了提供座舱增压、飞机机体防冰和座舱供热，从压气机中引出了大量的空气。最好是尽可能从压气机前几级引气，以减小对发动机性能的影响。但是，在飞行循环的某些阶段，可能需要将引气部位变换到压气机的后面级，以维持足够的压力和温度。
轴承载荷控制
25．发动机轴承受交变的轴向燃气载荷(第20章)，在压气机中是向前的，在涡轮上是向后的。压气机与涡轮之间的轴便经常处于拉伸应力之下，载荷之间的差额则由装在静止机匣上的定位轴承(又称止推轴承)承受(图9-8)。内部空气的压力作用在一个固定直径的压力平衡封严件上，以保证在整个发动机推力范围内，定位轴承承受的载荷是适当的。
增大面积导致
增大向前的载荷
Internal air system
bled from the compressor. It is desirable to bleed the air as early as possible from the compressor to minimize the effect on engine performance. However, during some phases of the flight cycle it may be necessary to switch the bleed source to a later compressor stage to maintain adequate pressure and temperature.
罗尔斯-罗伊斯公司
“宝石”(Gem)60发动机
Rolls-Royce Gem 60
设计推力为6500磅的轴流式涡轮喷气发动机AJ65的设计工作于1945年初开始进行，指标于1951年在100系RA3发动机达到。1953年，基本重新设计的200系RA14进行了定型试验，推力为9500磅。最终制成300系RB146，带加力的推力为17,110磅。
罗尔斯-罗伊斯公司
AJ65“埃汶”(Avon))发动机
Rolls-Royce AJ65 Avon
Work commenced early in 1945 on the AJ65 axial flow turbo-jet with a design thrust of 6500 lb. This figure was reached in 1951 with the 100 series RA3. In 1953 the considerably redesigned 200 series RA14 was type tested at 9500 lb thrust. Development culminated in the 300 series RB146 which produced 17.110 lb thrust with afterburning.
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