Principles of naval engineering - Historic Naval Ships Association

Chapter 23. -GAS TURBINE147.145Figure 23-11.— Rotor element of turbineassembly.147.144Figure 23-10.— Stator element of turbineassembly.or multiple-rotor turbines may be used witheither centrifugal or axial-flow compressors.In the single-rotor type of turbine, the poweris developed by one rotor and all engine-drivenparts are driven by this single wheel. In themultiple-rotor type, the power is developed bytwo or more rotors. It is possible for one ormore rotors to drive the compressor and theaccessories, while one or more other rotorsare used for the power output.Main BearingsThe main bearings in a gas turbine engineserve the critical function of supporting thecompressor, the turbine, and the engine shaft.The number and position of main bearings requiredfor proper support vary according tothe length and stiffness of the shaft, with bothlength and stiffness being affected by the typeof compressor used in the engine. In general,a gas turbine engine requires at least threemain bearings and may require six or evenmore.Several types of main bearings are usedin gas turbine engines. Ball and roller bearingshave been quite commonly used in the past, andthey are still used in many aircraft gas turbineengines. Sleeve bearings, split-sleeve bearings,floating-sleeve bearings, and slipper bearingsare commonly used in gas turbine engines designedfor marine propulsion.The slipper or pivoted-shoe type of bearinghas recently attracted considerable attention andis being used increasingly for main bearings ongas turbine engines and other high speed engines.This type of bearing is designed withrelatively large radial clearances. Since arotating object tends to rotate about its truebalance center when it is not restrained bybearings or supports, the large radial clearancesin the slipper bearings allow a kind ofself-balancing action or automatic compensation603