Development and Evaluation of a Performance Estimation Methodology for Fans Operating Within Non-Homogeneous Inflow

Abstract

The design process of modern aircraft engines extensively makes use of computational fluid dynamics (CFD). During the design process fan, compressor and turbine stages are typically evaluated using single passage CFD-simulations. For the design of an inlet distortion tolerant fan, the inhomogeneity of the inflow in circumferential direction does not allow the application of periodic boundary conditions and hence single passage simulations. Accordingly transient full annulus simulations have to be applied to correctly resolve the underlying physical interactions. The associated computation time for such a high fidelity simulation prohibit its application in today’s design procedures. This paper compares the simulation results of the ingestion of a mild and generic fuselage boundary layer of a blended wing body aircraft into an UHBR engine on the basis of four different simulation methods. The four different simulations include: transient full annulus CFD, Harmonic Balance frequency domain based CFD, steady full annulus CFD (Frozen Rotor) and steady single passage CFD for each blade passage. The results of the simulations are assessed using a newly developed stream tube based post-processing procedure. For the ingestion of the fuselage boundary layer the four numerical setups result in different aerodynamic conditions in the fan stage. For different aerodynamic measures different discrepancies are encountered for the different simulation methods. While the Harmonic Balance method can reproduce most features well, the simpler models overestimate the variations in the different flow features.