Parametric Analysis and Design for Embedded Engine Inlets

Abstract

The present paper demonstrates the aerodynamic feasibility of boundary-layer ingesting embedded-engine inlet designs with low total pressure losses and distortion harmonic content. The inlet was designed using a hierarchical multi-objective computational fluid dynamics optimization that combined global and local shaping. Global parameters including duct offset and length, wall curvature and shape, inlet aspect ratio, lip contour and thickness, and upstream airframe contour were used to identify optimal design space regions. Local inlet shaping optimization further reduced total pressure losses and harmonic distortion upstream of the fan. Coupled inlet/fan design iterations were carried out for selected inlet designs to assess the fan/engine stability and operability benefits. The resulting inlet design has the potential of achieving a 3–5% boundary-layer ingesting fuel burn benefit for NASA’s Generation-After-Next aircraft relative to a baseline high-performance pylon-mounted propulsion system. It shows significantly improved performance when compared with NASA’s “inlet A” reference geometry with a length-to-diameter ratio of 3. The new inlet was shortened to a length-to-diameter ratio of 0.6, total pressure losses were reduced by three times, dominant distortion harmonic amplitudes were reduced by 30–50%, and fan efficiency losses were reduced from 6 to 0.5–1.5%. No flow control was required.