Effects of ground vortex on flutter stability of a fan blade under quiescent conditions

This paper examines the impact of ground vortex on the flutter stability of a fan blade under quiescent conditions. With the development of Ultra-High Bypass Ratio (UHBR) engines, with resulting shorter intakes and lower ground clearances, it is paramount to establish if (and how) distortions such as ground vortex will influence the flutter stability of a fan blade during ground operation. This work is carried out by using a three-dimensional unsteady Computational Fluid Dynamics (CFD) model. The results from this preliminary study indicate that the ground vortex (at static engine operating condition without crosswind) can slightly reduce the flutter stability of the blade. To the best knowledge of the authors this is the first time that the work-per-cycle and critical damping ratio is computed for the cases with inlet distortion. Classical post-processing techniques fail to extract damping because of the multiple frequencies present in the system. A novel post-processing technique that performs fitting on the modal force signals using standard square root regression has been used in this paper to overcome this issue.