The reaction turbine blades are different from impulse blading. To be precise, their profiles are different. The exit angle of the reaction blade is smaller, and the trailing edge is made as thin as possible. Older reaction turbine blade section used to have a sharp, hooked inlet edge quite similar to that of impulse blade. However, in modern designs, the hooked inlet has been replaced by a blunt rounded entrance, similar to the leading edge of an airfoil. This blading might be called “airfoil blading”. The efficiency of rounded entrance blading is higher than the earlier types. For this type of blading, it is difficult to determine the inlet angle accurately. However, in general, the inlet relative velocity makes an angle that ranges from 80° to 90° with the tangential velocity.
Axial-flow reaction turbine is the most widely employed turbine. Their nozzles and blades act as expanding nozzles. Thus, the static pressure drops in both the fixed and moving blade. The fixed blades function as nozzles as they direct the flow to the moving blades at a velocity slightly higher than the moving blades velocity. In a reaction turbine, the velocities are generally much lower, and the entering blade relative velocities are nearly axial. In most designs, the reaction of reaction of the turbine varies from hub to shroud. The employment factor for a fixed nozzle angle will rise as the reaction approaches 100%. However, the 100% reaction turbine is not practical because of the high rotor speed necessary for a good utilization factor. On the other hand, the 50% reaction turbine has the highest efficiency of all the various types of turbines.
Below, schematic drawing of a reaction-type turbine. It shows the distribution of the thermodynamic and the fluid mechanic properties.
