Foil Bearing Dust Filtration

Auxiliary power units, or APUs, ingest more dust in high-growth regions such as Asia and the Middle East. Dust ingestion causes premature wear to foil bearing surfaces and reduces bearing life. Three different filters were designed that use inertial separation to isolate clean air from dust: a reverse pitot tube, reverse pitot tube with vanes, and a straight tube. Trade-offs in weight, size, cost and performance were made to determine optimal configurations. The filters draw in air by a pressure differential, require no additional parts, and are virtually maintenance free. A flow chamber was designed to simulate the Mach 0.1 flow experienced in APUs. The flow chamber can accommodate the three filter geometries and features the same integration piece used in APUs. The design features a dust release system that disperses dust at a constant rate into the flow chamber. Airflow, efficiency and particle size were tested using this system. Overall, the prototypes either met or exceeded the project requirements.