Effect of Geometric Variability on Running Shape and Performance of a Transonic Fan

Abstract

Abstract Due to imperfection in the manufacturing process and in-service wear, fan blades in a turbofan engine do not have the same geometry. This lack of symmetry inevitably leads to difficulties in predicting the fan blades' running geometry in an assembly as blade variability is amplified by the aerodynamic and centrifugal loading. This variability can lead to an aeromechanical phenomenon termed “alternate passage divergence” (APD). As the name suggests, it manifests itself as alternating geometric and aerodynamic patterns in a fan assembly during operation. APD can potentially influence the fan performance, the stability, and the multiple pure tone (MPT)/“Buzz-Saw” noise and is therefore an important area of research. For this study, the APD phenomenon is purposely triggered on a transonic fan blade. A full-assembly computational domain with one mis-staggered blade is used to examine the whole assembly performance and the untwist behavior with APD. In particular, the influence of fan blade stiffness on the APD behavior is examined. The behavior of the current blade is compared with that of a blade used in a precursor study, and it is found that, under certain conditions, the blades show similar behavior even though they have distinctly different geometry features. This illustrates that it is important to understand the phenomenon as the accurate prediction of running geometry is vital at early design stage.