14．壓氣機從前往后，即從低壓端向高壓端，轉子與靜止機匣之間的氣流的環形通道面積逐漸減小。這是隨著空氣密度沿壓氣機長度增加而要保持一個接近恒定的軸向氣流速度所必須的。氣流環形通道的收斂是通過機匣或者轉子作成斜的來實現的。二者綜合使用也是可能的，因為這里的安排要受制造問
題及其它機械設計因素的影響。
Fig. 3-5 Typical impellers for centrifugal 圖3-5 典型的離心壓氣機的葉輪
compressors.
radial vanes are usually employed. To ease the air from axial flow in the entry duct on to the rotating impeller, the vanes in the centre of the impeller are curved in the direction of rotation. The curved sections may be integral with the radial vanes or formed separately for easier and more accurate manufacture.
Diffusers
12. The diffuser assembly may be an integral part of the compressor casing or a separately attached assembly. In each instance it consists of a number of vanes formed tangential to the impeller. The vane passages are divergent to convert the kinetic energy into pressure energy and the inner edges of the 擴壓器
Compressors
vanes are in line with the direction of the resultant airflow from the impeller (fig. 3-6). The clearance between the impeller and the diffuser is an important factor, as too small a clearance will set up aerodynamic buffeting impulses that could be transferred to the impeller and create an unsteady 圖3-6 擴壓器進口處的氣流
葉輪
葉尖間隙
擴壓器葉片
airflow and vibration.
軸流式壓氣機
Fig. 3-6 Airflow at entry to diffuser.
THE AXIAL FLOW COMPRESSOR
13.
An axial flow compressor (fig. 3-7 and fig. 3-8) consists of one or more rotor assemblies that carry blades of airfoil section. These assemblies are mounted between bearings in the casings which incorporate the stator vanes. The compressor is a multi-stage unit as the amount of pressure increase by each stage is small; a stage consists of a row of rotating blades followed by a row of stator vanes. Where several stages of compression operate in series on one shaft it becomes necessary to vary the stator vane angle to enable the compressor to operate effectively at speeds below the design condition. As the pressure ratio is increased the incorporation of variable stator vanes ensures that the airflow is directed onto the succeeding stage of rotor blades at an acceptable angle, ref. para. 30, Airflow Control.
14.
From the front to the rear of the compressor, i.e. from the low to the high pressure end, there is a gradual reduction of the air annulus area between
來自渦輪的主軸傳動
燃燒系統
安裝邊
附近傳動
來自渦輪的低壓軸傳動
雙轉子壓氣機
來自渦輪的高壓軸傳動
高壓壓氣機
低壓壓氣機
單轉子壓氣機
附件傳動
燃燒系統
安裝邊
進氣機匣 靜子葉片 轉子葉片
Compressors
圖3-7 兩種典型的軸流壓氣機
Fig. 3-7 Typical axial flow compressors.
15．單轉子壓氣機(圖3-7)由一轉子組件和一些靜子組成，其級數的多寡必須滿足所要求的增壓比，所有進氣道來的氣流都將通過壓氣機。
16．多轉子壓氣機由二個或多個轉于組件組成，每一轉子由各自的渦輪以最佳轉速驅動，以達到更高的增壓比和提供更大的工作靈活性。
Compressors
來自渦輪的高壓傳動
來自渦輪的低壓軸傳動
低壓壓氣機
17.雖然雙轉于壓氣機(圖3-7)可以用于純噴氣發動機，但是，它最適合內外涵式發動機。在內外涵發動機中，前壓氣機或低壓壓氣機是設計來處理比高壓壓氣機更多的空氣流量。只有一定百分比的低壓壓氣機氣流流入高壓壓氣機；其余的空氣是外涵氣流，被引入高壓壓氣機周圍的涵道。這兩股氣流在排氣系統中混合，然后流入推進噴管(第6章)。這種安排將噴氣速度匹配得更加接近飛機要求的最佳速度，并導致更高的推進效率，因而得到更低的燃油
消耗。為此，所有氣流流過整個壓縮過程的純噴氣發動機目前已為除最高速飛機以外的所有飛機廢棄不用了。
圖3-8 典型的三轉子壓氣機
Fig. 3-8 Typical triple spool compressor.
來自渦輪的中壓軸傳動
燃燒機匣安裝邊
高壓壓氣機
中壓壓氣機
the rotor shaft and the stator casing. This is necessary to maintain a near constant air axial velocity as the density increases through the length of the compressor. The convergence of the air annulus is achieved by the tapering of the casing or rotor. A combination of both is also possible, with the arrangement being influenced by manufacturing problems and other mechanical design factors.
15.
A single-spool compressor (fig. 3-7) consists of one rotor assembly and stators with as many stages as necessary to achieve the desired pressure ratio and all the airflow from the intake passes through the compressor.
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