Effect of Swirl Recovery Vanes on Propeller Whirl Flutter

Kurzfassung

Future commercial aircraft may incorporate open-fan propulsion systems featuring downstream stator blades designed to recover propeller-induced swirl and improve propulsive efficiency, commonly referred to as swirl recovery vanes (SRVs). When mounted on elastic supports, such propeller configurations are susceptible to whirl flutter, an aeroelastic instability arising from the coupling between the structural pitch and yaw modes of the engine system and the gyroscopic moments of the rotating propeller. While SRVs have demonstrated potential gains in aerodynamic performance, their influence on the aeroelastic stability of the propeller system remains an open question. The present work employs a frequency-domain whirl flutter prediction method based on the Transfer-Matrix (TM) approach to investigate the impact of SRVs on the stability margin of this configuration. This is achieved by analyzing the additional unsteady, motion-induced aerodynamics introduced by the SRVs and the associated hub loads, represented through transfer matrices, under varying operating conditions and using low- to mid-fidelity aerodynamic modeling. The results indicate that, depending on the trim condition considered, the presence of SRVs can significantly alter the stability behavior of the system. Considering the SRVs can lead to lower flutter velocities in a powered condition compared to windmilling, a reverse of the known trend for single-row propellers. Results between low- and mid-fidelity models match very well both in terms of hub loads and whirl flutter stability.