Optimization and Experimental Validation of a Robust S-Duct Geometry With Boundary-Layer Ingestion

An S-duct intake for a boundary-layer ingesting engine has been designed using a gradient-based aerodynamic shape optimization framework based on the Reynolds-averaged Navier–Stokes equations. The optimization minimizes a composite objective function that combines total pressure loss and circumferential flow distortion at the fan face. To improve robustness across varying operating conditions, a multi-point optimization was conducted over a range of incoming boundary-layer thicknesses between 20 and 40% of the inlet height. The optimized geometry was fabricated and tested experimentally using a custom-built test rig. Experimental measurements of pressure loss, circumferential distortion, and swirl at the fan face are compared to numerical predictions, showing good agreement. Low circumferential flow distortion was observed experimentally with the multi-point-optimized geometry, confirming the effectiveness of the optimization framework.