turbine

The picture shows a range of turbines in Umatilla, Oregon, USA. Turbines, whether powered by steam, water, gas, or air, are essential tools in today's world. They drive ships and aircraft, spin electricity generators, and power other machinery.

Turbine in a hydroelectric dam. Hydroelectric dams are very ‘high-tech’ but simple machines. The dam holds back water, creating a reservoir of potential power. Water is released through a gate on the upper side of the dam, and surges through a tunnel leading to turbines. The water turns the turbines that in turn spin generators to produce electricity. The electricity is then carried through cables to wherever it is needed.

Engine in which steam, water, gas, or air (see windmill) is made to spin a rotating shaft by pushing on angled blades, like a fan. There are two sets of blades, the stator (does not rotate) and the rotor (does rotate). The rotating turbine shaft can be connected to an electricity generator. Turbines are among the most powerful machines.

Steam turbines are used to drive generators in power stations and ships' propellers; water turbines spin the generators in hydroelectric power plants; and gas turbines (as jet engines; see jet propulsion) power most aircraft and drive machines in industry.

The high-temperature, high-pressure steam for steam turbines is raised in boilers heated by furnaces burning coal, oil, or gas, or by nuclear energy. A steam turbine consists of a shaft, or rotor, which rotates inside a fixed casing (stator). The rotor carries ‘wheels’ consisting of blades, or vanes. The stator has vanes set between the vanes of the rotor, which direct the steam through the rotor vanes at the optimum angle. When steam expands through the turbine, it spins the rotor by reaction. The steam engine of Hero of Alexandria (130 BC), called the aeolipile, was the prototype of this type of turbine, called a reaction turbine. Modern development of the reaction turbine is largely due to English engineer Charles Parsons. Less widely used is the impulse turbine, patented in 1882 by Carl Gustaf Patrick de Laval (1845–1913). It works by directing a jet of steam at blades on a rotor. Similarly there are reaction and impulse water turbines. Impulse turbines work on the same principle as the water wheel and consist of sets of buckets arranged around the edge of a wheel; reaction turbines look much like propellers and are fully immersed in the water.

In a gas turbine a compressed mixture of air and gas, or vaporized fuel, is ignited, and the hot gases produced expand through the turbine blades, spinning the rotor. In the industrial gas turbine, the rotor shaft drives machines. In the jet engine, the turbine drives the compressor, which supplies the compressed air to the engine, but most of the power developed comes from the jet exhaust in the form of propulsive thrust.