Effect of Gerlach Cross-Section on S-Duct Inlet Performance in High Subsonic Flow

It was hypothesized in literature that Gerlach re-shaping of the cross-section of S-duct inlet bends may reduce the transverse pressure gradient and mitigate or eliminate flow separation. This paper presents an internal performance evaluation of an S-duct diffuser with Gerlach cross-sectional area compared to a baseline S-duct. The generic baseline test article was a rectangular-entrance S-duct transitioning to a circular exit, a configuration typical of single-engine air vehicles. The important geometric parameters were exit-to-entrance area ratio of 1.57 and an offset-to-length ratio of 0.37. The performance of the intake was evaluated at Ma = 0.80 by measuring the axial static pressure distribution, exit total pressure and three-dimensional velocity at the aerodynamic interface plane. The measurements were used to evaluate and compare the aerodynamic performance of the S-duct variants. The geometries and flow conditions were also simulated numerically and validated using experimental performance metrics. The static pressure recovery decreased for the Gerlach S-duct; however, total pressure recovery improved. This work will contribute to the development of improved performance for S-duct inlets and for predicting the performance of aero-engines and air vehicles at high-subsonic flight conditions.