Aerodynamic Optimization of Compact Engine Intakes for High Subsonic Speed Turbofans
Within the gas turbine industry,
turbofan engines are widely implemented to enhance engine efficiency, specific
thrust, and specific fuel consumption. However, these turbofans have yet to be
widely implemented into microgas turbine engines. As turbofans become
implemented into smaller engines, the need to design engine intakes for
high-speed mission becomes more vital. In this work, a design procedure for
compact, highly diffusive engine intakes for high subsonic speed applications
is set about. The aerodynamic tradeoffs between cruise and takeoff flights are
discussed and methods to enhance takeoff performance without negatively
impacting high-speed cruise performance is discussed. Intake performance is
integrated into overall engine analysis to help guide future mission analyses.
Finally, an experimental model for engine intakes is developed for application
to linear wind tunnels; allowing future designers to effectively validate
A multi-objective optimization routine is performed for compact engine intakes at a Mach number of 0.9. This optimization routine yielded a family of related curves that maximize intake diffusive capability and minimize intake pressure losses. Design recommendations to create such optimal intakes are discussed in this work so that future designers do not need to perform an optimization. Due to high diffusion rate of the intake, the intake performance at takeoff suffers greatly (as measured by massflow ingestion). Methods to enhance takeoff performance, from designing a variable geometry intake, to creating slots, to sliding intake components are evaluated and ranked for future designers to get an order of magnitude understanding of the types of massflow enhancements possible. Then, off-design performance of the intake is considered: with different Mach number flights, non-axial flow conditions, various altitudes, and unsteady engine operation considered. These off-design effects are evaluated to generate an intake map across a wide engine operational envelope. This map is then inputted into an engine model to generate a performance map of an engine; which allows for mission planning analysis. Finally, various methods to replicate intake flow physics in a linear wind tunnel are considered. It is shown that replicating diffuser curvature in a linear wind tunnel allows for best replication of flow physics. Additionally, a method to non-dimesnsionalize intake performance for application to a wind tunnel is developed.
This work can be utilized by future engine intake designers in a variety of ways. The results shown here can help guide future designers create highly compact diffuser technology, capable of operating across a wide breadth of conditions. Methods to assess intake performance effects on overall engine performance are demonstrated; and an experimental approach to intake analysis is developed.