Which turbine classification involves a change in both pressure and velocity?

The classification of turbines that involves a change in both pressure and velocity is the reaction turbine. In a reaction turbine, steam or water enters the turbine blades at high pressure and flows through them, causing a reduction in pressure as it does work on the blades. This dual change is crucial for the turbine’s operation, as both the pressure drop and the change in velocity contribute to the rotation and efficiency of the turbine.

In detail, as fluid passes through the reaction turbine blades, it expands and accelerates, producing thrust that causes the rotor to spin. This makes reaction turbines particularly effective for applications where sustained energy transfer and efficiency are necessary. The operation relies on the pressure differential created across the blades, where both pressure and velocity play integral roles in the overall performance.

In contrast, other classifications like impulse turbines primarily focus on a change in velocity, where the pressure remains constant, and the fluid's kinetic energy is used to produce work. Similarly, compound turbines are configurations combining different turbine types but do not specifically define the change in both pressure and velocity as the primary mechanism. The term "classical" does not correspond to a standard classification in turbine types and is therefore less relevant in this context.