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
刷式封嚴件
22．刷式封嚴件(圖9-7中左側第4圖)有一個由很多細鋼絲制成的刷組成的靜止環。它們不斷地與旋轉軸相接觸，與硬的陶瓷涂層相摩擦。這種封嚴件的優點是可以承受徑向摩擦而不增加滲漏。
熱燃氣吸入
23.防止高溫主燃氣流吸人渦輪盤的空腔是非常重要的，因為這會導致過熱和引起有害的熱膨脹和疲勞。渦輪環腔內的壓力迫使旋轉的輪盤和相鄰的靜止零件之間的高溫燃氣進入渦輪盤輪緣的空間。而且，靠近旋轉輪盤表面的空氣由于摩擦而加速，使它被向外抽走。這就會誘發一股向里填補的高溫燃氣流。
Internal air system
圖9-7 幾種典型的封嚴件
渦輪向后的載荷
壓氣機向前的載荷
圖9-8 軸承軸向載荷的控制
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 飛機服務
26．為了提供座艙增壓、飛機機體防冰和座艙供熱，從壓氣機中引出了大量的空氣。最好是盡可能從壓氣機前幾級引氣，以減小對發動機性能的影響。但是，在飛行循環的某些階段，可能需要將引氣部位變換到壓氣機的后面級，以維持足夠的壓力和溫度。
軸承載荷控制
25．發動機軸承受交變的軸向燃氣載荷(第20章)，在壓氣機中是向前的，在渦輪上是向后的。壓氣機與渦輪之間的軸便經常處于拉伸應力之下，載荷之間的差額則由裝在靜止機匣上的定位軸承(又稱止推軸承)承受(圖9-8)。內部空氣的壓力作用在一個固定直徑的壓力平衡封嚴件上，以保證在整個發動機推力范圍內，定位軸承承受的載荷是適當的。
增大面積導致
增大向前的載荷
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.
羅爾斯-羅伊斯公司
“寶石”(Gem)60發動機
Rolls-Royce Gem 60
設計推力為6500磅的軸流式渦輪噴氣發動機AJ65的設計工作于1945年初開始進行，指標于1951年在100系RA3發動機達到。1953年，基本重新設計的200系RA14進行了定型試驗，推力為9500磅。最終制成300系RB146，帶加力的推力為17,110磅。
羅爾斯-羅伊斯公司
AJ65“埃汶”(Avon))發動機
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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