Dust Filtration System for Air Bearings

Project goal: To identify, prototype and test a filtration system that can reduce dust intake by filtering out large particulates. The sponsor is developing air bearing technology for 131-9 auxiliary power units, or APUs, used in narrow-body commercial airliners, which use pressurized air generated by the APU to operate. In areas such as the Middle East and American Southwest, dust particulates from the environment can enter the air bearing housing and cause premature wear to the air foil. After conducting trade studies, the team selected a lightweight reverse-pitot tube design, which uses inertial separation to isolate clean air from dust without any moving parts. The filtered air is drawn through a tube by a pressure differential, so no additional transport systems are necessary. The design is virtually maintenance-free and can operate for the life of the APU. Testing of various pitot tube prototypes involved a design of experiments and construction of an airtight fabricated flow chamber that could simulate key APU conditions (Mach 0.1 velocity) and accommodate different pitot tube geometries. A measurable amount of dust was passed through the flow chamber, and filters were fitted to catch dust entering a simulated bearing housing and dust continuing through the main flow. Filter efficiency and particulate size could be verified by this method, and the prototype design that met or exceeded all requirements was deemed to have met the project goal.