Boundary Layer Ingestion Fan Stage Internal Flow Analysis and Characterization of Secondary Flow Topography in the Blade Channel /

Abstract

The robust performance of transonic fans in the presence of inlet distortions for boundary layer ingesting aircraft poses significant design challenges. This paper presents a numerical optimization strategy for distortion tolerant transonic fan design featuring an improved interaction between the transonic fan tips and the upstream flow distortions. The NASA Rotor 67 has been used as a baseline case in this study, while the boundary layer ingestion has been numerically simulated using an S-duct inlet. As a result, the combined modeling of the NASA Rotor 67 and the s-duct are capturing the flow fields typically experienced by the propulsion systems of future blended wing body aircraft concepts. Full annulus, steady-state, three-dimensional modeling has been used for the combined analysis of the rotor and s-duct. The NASA Rotor 67 computational fluid dynamics model is validated by the experimental data available in the open literature. Results indicated that the isentropic efficiency and pressure ratio have reduced by 7.08% and 7.19%, respectively due to the inlet distortions. The flow redistribution upstream of the fan causes a non-uniform work distribution across the complete fan face. A localized multi-objective design optimization featuring a surrogate model-based genetic algorithm setup was then applied to the transonic rotor tips. The optimized rotor design resulted in improved overall performance and relatively stable operation under the influence of inlet distortions compared to the baseline. The findings indicate an overall stable operation under the influence of the upstream distortions across the blade span rather than just an improved tip performance.