Additive Manufacturing in the Design of an Engine Air Particle Separator

Engine air particle separators are an important technology for aircraft operating in dusty environments. Using either vorticity or inertia to separate particles from the airstream entering the engine staves off premature filter failure that can compromise mission performance. While a body of literature exists on engine air particle separators, it is widely recognized that their design is significantly constrained by traditional manufacturing methods, and that this limits the generation of experimental data available to develop further insight into their design. Computational fluid dynamics can provide a starting point, but such simulations of complex, turbulent, particle-laden flow require considerable time and extensive computing resources while carrying no guarantee of accuracy. Additive manufacturing offers an attractive solution. It is capable of producing complex geometries quickly and economically, facilitating rapid design iteration and generation of experimental data. This work, sponsored by the Air Force Research Laboratory, focuses on the design of an engine air particle separator for use on an unmanned aerial vehicle. The sponsor’s dual intent was to advance engine air particle separator design and, more importantly, showcase the capabilities of additive manufacturing in the design development process for aerospace components.Free from manufacturing constraints, novel particle separator designs were considered. Using computational fluid dynamics to evaluate non-laden flow characteristics such as pressure drop, these designs were evaluated and compared to more conventional inertial and vortex designs. From this analysis a hybrid design that combines features of both the inertial and vortex separators was chosen for testing. Using the fan from a wind tunnel as a source of flow, a custom test section was created and instrumented that included an upstream particle injection system and separate flow paths for clean and dirty air (which in and of itself is geometrically complex and was fabricated using additive manufacturing). Although experiments are ongoing, one interesting result has already emerged. One particular design parameter from the literature for inertial particle separators is the ratio of the axial to radial distance between the splitter and the hump (or, the peak of the inner body) as measured from the central axis. This ratio is essentially a measure of the severity of the flow deflection for which other authors have suggested a “rule of thumb” for its proportions. Our results show that this rule may also be extended to some hybrid particle separators (such as the one examined in this work), where vorticity is introduced upstream of the hump.This project has demonstrated the power of additive manufacturing in product design and development. Its near limitless geometric possibilities allowed the team to examine areas of the design space that were previously unexplored. Further, after developing the test bed, the team demonstrated the ability to complete a full design iteration in one day — testing in the morning, analyzing results and designing the next prototype in the afternoon, and printing the next prototype overnight.Copyright © 2015 by ASME