2.2.2.   Reaction-type turbine

 

Strictly speaking such turbines should be termed 'impulse/50% reaction' turbines. The term 50% reaction was used because only half the stage heat drop occurs in the fixed blades, the remaining half occurring in the moving blades. This results in a rise in steam velocity at the moving blades, creating a thrust or reaction in the opposite direction to the flow leaving the blades. Some impulse also occurs in the moving blades due to the change of direction of the flow but it is not sufficient to cause a net drop in velocity. The fixed blades behave in the same way as the impulse turbine fixed blades by converting heat drop into velocity.

Figure 1.10 shows a typical reaction-type stage velocity diagram. The relative velocity of the steam leaving the moving blades (W2) is greater than the relative velocity of the steam entering the moving blades (W,): this is because of the increase in velocity through the moving blades due to the presence of the heat drop there.

reaction-type stage velocity diagram

 

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