What is defined as a rotary mechanical device that extracts energy from fluid flow?

The correct answer is a turbine, which is specifically designed to convert the kinetic energy of fluid flow into rotational mechanical energy. Turbines operate by using the movement of gases or liquids to turn blades attached to a rotor. As the fluid passes over the blades, it imparts energy that causes the rotor to spin, thus extracting energy from the fluid movement effectively.

In the context of engineering and power generation, turbines are crucial for various applications, including hydroelectric plants, where water flow is harnessed to generate electricity, and in gas or steam turbines used for driving generators. This energy conversion is fundamental to many mechanical and electrical systems.

The other options represent different types of devices: pumps move fluids but do not extract energy; compressors increase the pressure of gases and do not convert fluid energy into mechanical energy; and generators convert mechanical energy into electrical energy, but they do not extract energy from fluid flow. Each of these devices serves distinct functions within mechanical and fluid systems, emphasizing the unique role of the turbine in energy extraction from moving fluids.