Fan Flutter at Mild Wind Conditions at Sea-Level-Static

Abstract This paper investigates the impact of ground vortex on the flutter stability of a fan blade during Sea-Level-Static (SLS) operation under mild and zero crosswind conditions. Flutter rig tests or CFD simulations are typically performed assuming clean intakes without considering the ground plane. However, when an aircraft engine operates close to the ground in static or near-static conditions, a strong vortex forms at the ground plane and is ingested into the intake. With the rise of Ultra-High Bypass Ratio (UHBR) engines, with shorter intakes and reduced ground clearances, it is crucial to determine whether and how distortions such as ground vortex influence the flutter stability of the fan blade. A three-dimensional unsteady Computational Fluid Dynamics (CFD) model is used to analyse the phenomenon. The findings in this work indicate that at sea-level-static conditions with a mild crosswind, the ground vortex modifies the intake acoustics slightly, which in turn influences the flutter stability of the fan blade, leading to a small reduction in the flutter margin. To the best of the authors’ knowledge, this is the first time the effects of ground vortex on fan blade flutter stability have been presented, offering valuable insights for aero-engine manufacturers and researchers in the field of aeroelasticity.