Short engine intakes: Design and trade-off aerodynamic recommendations

This work sets forth a design procedure for compact, highly diffusive engine intakes for high subsonic speed applications. The aerodynamic tradeoffs between cruise and take-off flights are discussed, as well as methods to enhance take-off performance without negatively impacting high-speed cruise performance. Intake performance is integrated into overall engine analysis to help guide future mission analyses. A multi-objective optimization routine is performed for compact engine intakes at a Mach number of 0.9 using two dimensional axisymmetric Reynolds Averaged Navier Stokes simulations. This optimization routine yielded a family of related curves that maximize intake diffusive capability and minimize pressure losses. Design recommendations to achieve intakes with minimal pressure losses and maximal diffusion, including intake length and inlet lip design are discussed. Due to the high diffusion rate of the intake, the intake performance at take-off suffers greatly as measured by massflow ingestion. Methods to enhance take-off 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. The slotted design was assessed through three-dimensional computations, and performance was compared to the isentropic limit. Additionally, the 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 comprehensive engine operational envelope. Off-design intake performance is integrated into an engine model for mission planning based on intake performance. Finally, an experimental model of an optimized intake geometry is tested to validate the proposed numerical method.(c) 2023 Elsevier Masson SAS. All rights reserved.