Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System—Part I: Measurements

Abstract

Implementation of gas foil bearings (GFBs) into micro gas turbines requires careful thermal management with accurate measurements verifying model predictions. This two-part paper presents test data and analytical results for a test rotor and GFB system operating hot (157°C maximum rotor outer diameter (OD) temperature). Part I details the test rig and measurements of bearing temperatures and rotor dynamic motions obtained in a hollow rotor supported on a pair of second generation GFBs, each consisting of a single top foil (38.14 mm inner diameter) uncoated for high temperature operation and five bump strip support layers. An electric cartridge (maximum of 360°C) loosely installed inside the rotor (1.065 kg, 38.07 mm OD, and 4.8 mm thick) is a heat source warming the rotor-bearing system. While coasting down from 30 krpm to rest, large elapsed times (50–70 s) demonstrate rotor airborne operation, near friction free, and while traversing the system critical speed at ∼13 krpm, the rotor peak motion amplitude decreases as the system temperature increases. In tests conducted at a fixed rotor speed of 30 krpm, while the shaft heats, a cooling gas stream of increasing strength is set to manage the temperatures in the bearings and rotor. The effect of the cooling flow, if turbulent in character, is most distinctive at the highest heater temperature. For operation at a lower heater temperature condition, however, the cooling flow stream demonstrates a very limited effectiveness. The measurements demonstrate the reliable performance of the rotor-GFB system when operating hot. The test results, along with full disclosure on the materials and geometry of the test bearings and rotor, serve to benchmark a predictive tool. A companion paper (Part II) compares the measured bearing temperatures and the rotor response amplitudes to predictions.