Mitigation of Circumferential Inlet Distortion Effects Using Non-axisymmetric Fan Inlet and Exit Guide Vanes

This paper explores the use of non-axisymmetric inlet and exit guide vanes (IGVs and EGVs) to mitigate losses and unsteady rotor force due to inlet distortion. A linearized two-dimensional flow description combined with an empirical blade performance model is used to capture relevant fan-distortion interaction and to assess the impact of non-axisymmetric leading and trailing edge metal angles on the flow field, stage losses, and unsteady rotor forces. The results show that single-stage designs, consisting of a rotor and non-axisymmetric EGV, have a trade-off between minimizing stage losses and unsteady rotor forces, while an optimal 1.5-stage design, including a non-axisymmetric IGV, can eliminate unsteady loading with lower losses than an equivalent axisymmetric single-stage design with the same inlet distortion. The IGV and EGV blade angle variations needed for such a design are on the order of ±10^◦ for inlet stagnation pressure non-uniformities equal to one-third the inlet dynamic pressure. Variations in distortion response of non-axisymmetric stage designs to changes in inlet distortion magnitude and phase are also considered; the results show the losses and unsteady rotor force induced by non-axisymmetric guide vanes with uniform inlet flow are comparable to the losses and unsteady rotor force in axisymmetric designs with the inlet distortion for which the non-axisymmetric geometries were designed. These previously unreported results suggest fan stages with non-axisymmetric inlet and outlet guide vanes may offer a practical means to mitigate distortion effects in advanced propulsion concepts such as boundary layer ingesting fans.