Analysis of Fan Stage Design Attributes for Boundary Layer Ingestion

Abstract

This paper describes a new conceptual framework for threedimensional turbomachinery flow analysis and its use to assess fan stage attributes for mitigating adverse effects of inlet distortion due to boundary layer ingestion (BLI). A non-axisymmetric throughflow method has been developed to describe the fan flow field with inlet distortion. In this the turbomachinery is modeled using momentum and energy source distributions that are determined as a function of local flow conditions and a specified blade camber surface geometry. Comparison with higher-fidelity computational and experimental results shows that the method captures the principal flow redistribution and distortion transfer effects associated with BLI. Distortion response is assessed for a range of (i) rotor spanwise work profiles, (ii) rotor-stator spacings, and (iii) non-axisymmetric stator geometries. For the parameters examined, changes in axisymmetric design result in trades between rotor and stator distortions, or between different radial sections of a given blade row with marginal overall gain. Of the approaches examined, non-axisymmetric stator exit flow angle distributions were found to provide the greatest reduction in rotor flow distortion and thus may offer the most potential for mitigating decreases in performance due to BLI inlet distortion.