Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERING,. .;-• > * ^'» » T' *'^' f ^* £^*-^i^f^fSBt^^Figure 23-9. — Can-annular combustion chamber.147.143material used, the means provided for coolingthe bearings and highly stressed parts, and thehigher ratio of blade length to wheel diameterwhich is required to accommodate the largegas flow.The turbine section of a gas turbine engineis located directly behind the combustion chamberoutlet. The turbine consists of two basicelements, the stator and the rotor . Part of astator element is shown in figure 23-10; a rotorelement is shown in figure 23-11.The stator element is referred to by variousnames, including turbine nozzle vanes and tur -bine guide vanes . The vanes of the stator elementserve the same purpose as the nozzlesin an impulse steam turbine or the stationaryblading in a reaction steam turbine— that is,they convert thermal energy into mechanicalkinetic energy. The vanes of the stator elementare contoured and set at such an angle thatthey form a number of small nozzles whichdischarge the gas as extremely high speed jets.As in the case of the nozzles (or stationaryblading) of steam turbines, the increase invelocity may be equated with the decrease inthermal energy. The vanes of the stator elementdirect the flow of gas to the rotor blades at therequired angle while the turbine wheel is rotating.The rotor element of the turbine consistsof a shaft and a bladed wheel or disk. The wheelis attached to the main power transmitting shaftof the gas turbine engine. The jets of combustiongas leaving the vanes of the stator elementact upon the turbine blades and cause the turbinewheel to rotate at a very high rate of speed.The high rotational speed imposes severe centrifugalloads on the turbine wheel, and at thesame time the very high temperatures result ina lowering of the strength of the material.Consequently, the engine speed and temperaturemust be controlled to keep turbine operationwithin safe limits. Even so, the operating lifeof the turbine blading is accepted as the governingfactor in determining the life of the gasturbine engine.The turbine may be of the single-rotor typeor of the multiple-rotor type. Either single-rotor602