The Effect of Stagger Variability in Gas Turbine Fan Assemblies

Fan blades of high bypass ratio gas turbine engines are subject to substantial aerodynamic and centrifugal loads, producing the well-known phenomenon of fan blade untwist. The accurate prediction of the running geometry, as opposed to the cold geometry at rest, is crucial in the assessment of aerodynamic performance, vibratory response, and noise production of the fan. The situation is further complicated by the fact that some geometric variation is inevitable even for the state-of-the-art manufacturing processes used. The aim of this paper is to investigate the effect of static stagger variability on the dynamic untwist behavior of fan assemblies. An aeroelastic model was used to show that under certain conditions the stagger pattern changes significantly, both in form and amplitude, relative to the static configuration. At other conditions, a strong correlation between the running and static patterns is demonstrated.