14．压气机从前往后，即从低压端向高压端，转子与静止机匣之间的气流的环形通道面积逐渐减小。这是随着空气密度沿压气机长度增加而要保持一个接近恒定的轴向气流速度所必须的。气流环形通道的收敛是通过机匣或者转子作成斜的来实现的。二者综合使用也是可能的，因为这里的安排要受制造问
题及其它机械设计因素的影响。
Fig. 3-5 Typical impellers for centrifugal 图3-5 典型的离心压气机的叶轮
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 扩压器
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 图3-6 扩压器进口处的气流
叶轮
叶尖间隙
扩压器叶片
airflow and vibration.
轴流式压气机
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
来自涡轮的主轴传动
燃烧系统
安装边
附近传动
来自涡轮的低压轴传动
双转子压气机
来自涡轮的高压轴传动
高压压气机
低压压气机
单转子压气机
附件传动
燃烧系统
安装边
进气机匣 静子叶片 转子叶片
Compressors
图3-7 两种典型的轴流压气机
Fig. 3-7 Typical axial flow compressors.
15．单转子压气机(图3-7)由一转子组件和一些静子组成，其级数的多寡必须满足所要求的增压比，所有进气道来的气流都将通过压气机。
16．多转子压气机由二个或多个转于组件组成，每一转子由各自的涡轮以最佳转速驱动，以达到更高的增压比和提供更大的工作灵活性。
Compressors
来自涡轮的高压传动
来自涡轮的低压轴传动
低压压气机
17.虽然双转于压气机(图3-7)可以用于纯喷气发动机，但是，它最适合内外涵式发动机。在内外涵发动机中，前压气机或低压压气机是设计来处理比高压压气机更多的空气流量。只有一定百分比的低压压气机气流流入高压压气机；其余的空气是外涵气流，被引入高压压气机周围的涵道。这两股气流在排气系统中混合，然后流入推进喷管(第6章)。这种安排将喷气速度匹配得更加接近飞机要求的最佳速度，并导致更高的推进效率，因而得到更低的燃油
消耗。为此，所有气流流过整个压缩过程的纯喷气发动机目前已为除最高速飞机以外的所有飞机废弃不用了。
图3-8 典型的三转子压气机
Fig. 3-8 Typical triple spool compressor.
来自涡轮的中压轴传动
燃烧机匣安装边
高压压气机
中压压气机
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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