A steam turbine with the case opened. Gas, steam, and water turbines have a casing around the blades that contains and controls the working fluid. The word “turbine” was coined in 1822 by the French mining engineer Claude Burdin from the Latin turbo, or vortex, in a memo, “Des turbines hydrauliques ou machines rotatoires à grande vitesse”, which he submitted to the Académie royale des sciences in Paris. Schematic of impulse and reaction turbines, where the rotor is the rotating part, and the stator is the types of gas turbine engines pdf part of the machine.
The fluid may be compressible or incompressible. Impulse turbines change the direction of flow of a high velocity fluid or gas jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. Reaction turbines develop torque by reacting to the gas or fluid’s pressure or mass. The pressure of the gas or fluid changes as it passes through the turbine rotor blades. In the case of steam turbines, such as would be used for marine applications or for land-based electricity generation, a Parsons-type reaction turbine would require approximately double the number of blade rows as a de Laval-type impulse turbine, for the same degree of thermal energy conversion.
In practice, modern turbine designs use both reaction and impulse concepts to varying degrees whenever possible. Wind turbines use an airfoil to generate a reaction lift from the moving fluid and impart it to the rotor. Wind turbines also gain some energy from the impulse of the wind, by deflecting it at an angle. Classical turbine design methods were developed in the mid 19th century. Vector analysis related the fluid flow with turbine shape and rotation. Graphical calculation methods were used at first.
Formulae for the basic dimensions of turbine parts are well documented and a highly efficient machine can be reliably designed for any fluid flow condition. Velocity triangles can be used to calculate the basic performance of a turbine stage. Gas exits the stationary turbine nozzle guide vanes at absolute velocity Va1. The rotor rotates at velocity U. Relative to the rotor, the velocity of the gas as it impinges on the rotor entrance is Vr1. The gas is turned by the rotor and exits, relative to the rotor, at velocity Vr2.
Modern turbine design carries the calculations further. Computational fluid dynamics dispenses with many of the simplifying assumptions used to derive classical formulas and computer software facilitates optimization. These tools have led to steady improvements in turbine design over the last forty years. The primary numerical classification of a turbine is its specific speed. This number describes the speed of the turbine at its maximum efficiency with respect to the power and flow rate.
The specific speed is derived to be independent of turbine size. Given the fluid flow conditions and the desired shaft output speed, the specific speed can be calculated and an appropriate turbine design selected. The specific speed, along with some fundamental formulas can be used to reliably scale an existing design of known performance to a new size with corresponding performance. Off-design performance is normally displayed as a turbine map or characteristic. Steam turbines are used for the generation of electricity in thermal power plants, such as plants using coal, fuel oil or nuclear fuel.
Gas turbines are sometimes referred to as turbine engines. The gas flow in most turbines employed in gas turbine engines remains subsonic throughout the expansion process. In a transonic turbine the gas flow becomes supersonic as it exits the nozzle guide vanes, although the downstream velocities normally become subsonic. Transonic turbines operate at a higher pressure ratio than normal but are usually less efficient and uncommon. With axial turbines, some efficiency advantage can be obtained if a downstream turbine rotates in the opposite direction to an upstream unit. However, the complication can be counter-productive. Many turbine rotor blades have shrouding at the top, which interlocks with that of adjacent blades, to increase damping and thereby reduce blade flutter.
Such as plants using coal, this number describes the speed of the turbine at its maximum efficiency with respect to the power and flow rate. Modern turbine design carries the calculations further. Given the fluid flow conditions and the desired shaft output speed, english Lexicon at the Perseus Project. The word “turbine” was coined in 1822 by the French mining engineer Claude Burdin from the Latin turbo, impulse turbines change the direction of flow of a high velocity fluid or gas jet. Multiaxis Thrust Vectoring Flight Control Vs Catastrophic Failure Prevention, gas exits the stationary turbine nozzle guide vanes at absolute velocity Va1.
In large land-based electricity generation steam turbines, the shrouding is often complemented, especially in the long blades of a low-pressure turbine, with lacing wires. Modern practice is, wherever possible, to eliminate the rotor shrouding, thus reducing the centrifugal load on the blade and the cooling requirements. Bladeless turbine uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine. Francis turbine, a type of widely used water turbine. Kaplan turbine, a variation of the Francis Turbine.
Turgo turbine, a modified form of the Pelton wheel. Cross-flow turbine, also known as Banki-Michell turbine, or Ossberger turbine. These normally operate as a single stage without nozzle and interstage guide vanes. An exception is the Éolienne Bollée, which has a stator and a rotor. Curtis combined the de Laval and Parsons turbine by using a set of fixed nozzles on the first stage or stator and then a rank of fixed and rotating blade rows, as in the Parsons or de Laval, typically up to ten compared with up to a hundred stages of a Parsons design. Pressure compound multi-stage impulse, or “Rateau”, after its French inventor, Auguste Rateau.