rapidly moving fluid against the blades and turnthe rotor (fig. 10-17).REACTION TURBINEThe reaction turbine, as the name implies, isturned by reactive force rather than by a directpush or impulse. In reaction turbines, there areno nozzles as such. Instead, the blades that projectradially from the periphery of the rotor areformed and mounted so that the spaces betweenthe blades have, in cross section, the shape ofnozzles. Since these blades are mounted on therevolving rotor, they are called moving blades.Fixed or stationary blades of the same shapeas the moving blades (fig. 10-18) are fastened tothe stator (casing) in which the rotor revolves. Thefixed blades guide the gas into the moving bladesystem and, since they are also shaped andmounted to provide nozzle-shaped spaces betweenthe blades, the freed blades also act as nozzles.A reaction turbine is moved by three mainforces: (1) the reactive force produced on themoving blades as the gas increases in velocity asit expands through the nozzle-shaped spacesbetween the blades; (2) the reactive force producedon the moving blades when the gas changesdirection; and (3) the push or impulse of the gasimpinging upon the blades. Thus, as previouslynoted, a reaction turbine is moved primarily byreactive force but also to some extent by directimpulse.Impulse and reaction blades can be combinedto form an impulse-reaction turbine. This turbinecombines the rotational forces of the previouslydescribed turbines; that is, it derives its rotationfrom both the impulse of the gas striking theturbine blades and the reactive force of the gaschanging direction.Figure 10-17 .—Impulse turbine.Figure 10-18.—Reaction turbine blading.10-12
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