10.1 INTRODUCTION

The differences between an aircraft power plant and a power generation turbine are probably best highlighted by the type of bearings used to support the rotor. In the former, the overall weight of the rotating system, speed range, and length of the bearing make rolling element type of bearings most suitable, while the load carrying capacity and durability considerations in the latter make it imperative to use hydrodynamic journal bearings. Power generation steam and gas turbines operate at two most typical speeds, 3000 rpm for 50 Hz units and 3600 rpm for 60 Hz units. However, gas turbines not tied directly to the generator can have a higher operating speed. Siemens V84.3 gas turbine, for example, runs at 5400 rpm, with a speed reducer placed between the turbine and the generator. The turbine speed for naval and merchant marine ships must be reduced to low propeller revolutions per minute. Since the rotor weight may run into several thousand pounds for larger power generation units, rolling element bearings cannot provide the required capacity to carry the load. The journal bearing diameter may reach 27.5 in and length of 25 in.

Rolling element bearings are designed to operate at high speeds, and provide a large power density to reduce the overall size of the package and to control the weight of the engine. Aircraft engines rely exclusively on ball and roller element bearings to provide a rotating support for the shaft. Limiting static and dynamic axial and radial excursions of...