Which of the following is NOT a type of turbine used in turbine engines?

In turbine engine design, the types of turbines commonly recognized include impulse, reaction, and the combination known as impulse/reaction turbines. Each of these types serves specific operational functions and principles:

• Impulse turbines utilize the kinetic energy of the fluid to turn the turbine. High-pressure fluid is directed through a nozzle, causing it to accelerate and hit the turbine blades, imparting force.

• Reaction turbines operate differently; they extract energy from the fluid in both the nozzle and the turbine blades. The design allows the fluid to expand as it passes through the turbine, combining velocity and pressure changes to generate power.

• Impulse/reaction turbines combine features from both types, leveraging the advantages of impulse turbines in generating initial energy and then converting it with reaction principles in the subsequent stages.

While these types are integral to turbine operations, direct-flow is not classified as a type of turbine engine. The term 'direct-flow' typically refers to a type of flow within a system rather than a standalone turbine system recognized in turbine engine technology. Therefore, identifying direct-flow as not being a recognized turbine type aligns with current aviation knowledge.