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8. The torque or turning power applied to the turbine is governed by the rate of gas flow and the energy change of the gas between the inlet and the outlet of the turbine blades, The design of the turbine is such that the whirl will be removed from the gas
stream so that the flow at exit from the turbine will be per cent.
substantially 'straightened out' to give an axial flow into the exhaust system (Part 6). Excessive residual whirl reduces the efficiency of the exhaust system and also tends to produce jet pipe vibration which has a detrimental effect on the exhaust cone supports and struts.
9.
It will be seen that the nozzle guide vanes and blades of the turbine are 'twisted', the blades having a stagger angle that is greater at the tip than at the root (fig. 5-6). The reason for the twist is to make the gas flow from the combustion system do equal work at all positions along the length of the blade and to ensure that the flow enters the exhaust system with a uniform axial velocity. This results in certain changes in velocity, pressure and temperature occurring through the turbine, as shown diagram-matically in fig. 5-7.

10.
The 'degree of reaction' varies from root to tip, being least at the root and highest at the tip, with the mean section having the chosen value of about 50
10．“反力度”從葉根到葉尖是變化的，葉根處最小，葉尖處最大，在平均截面處為選定值，約50％。

結構
 
12.渦輪的基本部件有燃燒室燃氣導管、導向器葉
片、渦輪盤和渦輪工作葉片。轉動組件由裝在渦輪
機匣中的軸承支承，渦輪軸可以和壓氣機軸共用一
軸，或者由自動定心的聯軸器與壓氣機軸相接。
11．由于許多原因，損失總要發生，使渦輪不能獲得100％效率。由于渦輪工作葉片的氣動力損失，典型的非冷卻式三級渦輪會遭受3.5％的損失。另外，由導向器葉片中的氣動損失，燃氣漏過渦輪工作葉片葉尖的損失以及排氣系統的損失總共將產生4.5％的損失。這些損失大致上占相等的比例。計及各種損失之后，總的效率約為92％。

Fig. 5-6 A typical turbine blade showing靜壓
速度
導向器葉片

13．導向器葉片具有翼型截面，相鄰葉片之間的通道構成了收斂的涵道。導向葉片位于(圖5-8)渦輪機匣中其安裝方式應能使它們發生膨脹。
twisted contour.
圖5-6一種典型的渦輪工作葉片，圖中示出了扭曲的外形
安裝角
旋轉方向
氣流方向
安裝角
11. The losses which prevent the turbine from being 100 per cent efficient are due to a number of reasons. A typical uncooled three-stage turbine would suffer a 3.5 per cent loss because of aerodynamic losses in the turbine blades. A further
4.5 per cent loss would be incurred by aerodynamic losses in the nozzle guide vanes, gas leakage over the turbine blade tips and exhaust system losses; these losses are of approximately equal proportions. The total losses result in an overall efficiency of approximately 92 per cent.
CONSTRUCTION
12. The basic components of the turbine are the combustion discharge nozzles, the nozzle guide vanes, the turbine discs and the turbine blades. The rotating assembly is carried on bearings mounted in the turbine casing and the turbine shaft may be common to the compressor shaft or connected to it by a self-aligning coupling.
Nozzle guide vanes
13. The nozzle guide vanes are of an aerofoil shape with the passage between adjacent vanes forming a convergent duct. The vanes are located (fig. 5-8) in the turbine casing in a manner that allows for expansion. 渦輪葉片
進入排氣系統時壓力和速度均勻
壓力增加
(從導向葉片葉根到葉尖)
速度降低

 

圖5-7 流過導向器葉片和渦輪工作葉片的燃氣流的流型
Fig. 5-7 Gas flow pattern through nozzle and blade.

渦輪盤
 
15．渦輪盤通常由機械加工的鍛件制成。它可以與軸制成一個整體，也可以帶安裝邊由螺栓連接渦輪軸，而且，輪盤的外圓處還有渦輪工作葉片安裝用的榫槽。
14．導向器葉片通常是空心結構，可以由壓氣機的
出口空氣在其內部流過進行冷卻，以減輕熱應力和
氣動負荷的影響。對于渦輪冷卻的詳細情況可參看
第9章。

19．工作葉片安裝在渦輪盤上的方法極為重要，因為在固定部位或葉片根部周圍渦輪盤的應力對于限制輪緣速度具有很重要的意義。早期的“惠特爾”(whittle)發動機的葉片曾用拉瓦爾(Laval)的球形葉根固定，但這種設計很快便由樅樹形榫頭所取代，這就是目前大多數燃氣渦輪發動機所使用的榫頭。為保證載荷能由所有齒分擔，這種榫頭要作非常精密的機械加工。當渦輪處于靜止狀態時，葉片在齒上是活動的，當渦輪旋轉時，在離心載荷的作用下根部才變成剛性結合。在圖5-9中示出了葉片的各種連接方法，但是德國BMW公司的空心葉片及拉瓦爾球形葉根式連接方法目前在燃氣渦輪發動機上一般都不使用。
渦輪工作葉片
 
17．渦輪工作葉片設計成翼型截面，每個相鄰葉片之間的通遭使氣流穩定地加速到“喉部”。喉部的面積最小。速度達到了所需的出口速度來產生要求的反力度(第5章)。
16.為了限制從渦輪工作葉片向輪盤的熱傳導的影響，每一級輪盤的兩面都通一股冷卻空氣(第9章)。

18.根據所用材料的許用應力及扣除為冷卻(第9章)目的要求用的孔的尺寸之后，每個工作葉片橫截面的實際面積是固定的。高效率要求截面的后緣薄，但是為了防止在發動機工作中由于溫度的改變使葉片產生裂紋，不得已進行折衷處理。
　
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