Session: 31-09 Fan Inlet Distortion II

Paper Number: 152053

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

Advanced air vehicle propulsion concepts propose using boundary layer ingestion (BLI) to leverage integration between engines and airframe to improve propulsive efficiency, reducing fuel burn and emissions. The presence of non-uniform engine inlet flow (inlet distortion), however, can negatively affect engine performance, reducing fan efficiency, and causing unsteady loads on rotating blades. Non-axisymmetric inlet and exit guide vane designs may be used to mitigate these effects by modifying the upstream and downstream flow fields to "shield" the rotor from the influence of the non-uniformity.

In this paper, a linearized, two-dimensional, inviscid flow model is used to explore the design of fan stages with non-axisymmetric inlet flow and vane geometries. Blade rows are modeled as actuator disks that cause changes in velocity, pressure, and enthalpy. Entropy rise across each blade row is described using a blade stagnation pressure loss model based on compressor cascade test data. The model describes circumferential variations in flow conditions at each blade row and the effects on stage efficiency and unsteady forces on the rotor blade row. Two different designs are investigated. The first is a single-stage design consisting of a rotor and exit guide vane (EGV). The second is a 1.5-stage design consisting of an inlet guide vane (IGV) followed by a rotor and EGV.

Using a non-axisymmetric EGV in the single-stage design, there is a trade-off between reducing unsteady force perturbations and stage losses, allowing for one design that eliminates unsteady rotor force, another design that minimizes losses, and leading to a multi-objective optimization for designs in between. Addition of a non-axisymmetric IGV enables designs that have zero unsteady forces and lower losses than an equivalent axisymmetric fan designs with uniform inlet conditions. The results suggest that a non-axisymmetric design approach may be effective at simultaneously improving efficiency and aeromechanics of fan stages with known inlet distortion.

Presenting Author: Michael Kramer The Pennsylvania State University

Presenting Author Biography: Michael Kramer is a graduate research assistant in the Department of Aerospace Engineering at The Pennsylvania State University.

Authors:

Michael Kramer The Pennsylvania State University
David Hall The Pennsylvania State University