Development of High Speed Aeropropulsion Engine Simulator With Foil Bearings

Small turbo jets with engine thrust below ∼2000N are designed with fuel-lubricated rolling element bearings with very short lifespan requirement, i.e., just a few hrs. Some expandable engines above 2000N of thrust are designed as turbofan. These expandable turbo fan engines are also designed with rolling element bearings, and they require frequent maintenance, replenishing oil to prevent oil degradation over long period of stocking. Replacing the rolling element bearings with foil bearings on these expandable turbofan engines, especially, on high-speed spools, greatly simplifies maintenance issues, and allows higher operating temperature of the turbine core. The range of engine thrust of expandable turbo fan engines, where foil bearings are applicable, is 2000N∼22,250N, considering the shaft size, speed, and rotor weight. Foil bearings were developed for 4450N and 22250N class turbo fan engines, focusing on high-speed spools, where maintenance is difficult and the working environment is also very harsh in temperature. The development of foil bearings for such demanding applications requires not only improving the foil bearing design/analysis tool, but also a comprehensive experimental program. This paper presents design features of the high-speed rotor of 4450N class turbofan engines and engine simulator rig, and the current status of developmental tests. The test rig is designed with environmental temperature control on the bearing compartment mimicking actual engine operating temperature, and axial force to the thrust bearing is applied through balance piston seals.