Abstract

Non-synchronous vibrations (NSV) arising near the stall boundary of compressors are a recurring and potentially safety-critical problem in modern axial compressors and fans. Recent research has improved predictive capabilities and physical understanding of NSV but prevention measures are still lacking. This paper addresses this by systematically studying the influence of aerodynamic and structural mistuning on NSV. This is achieved by incorporating mistuning effects in a validated linear model, in which individual blade modes are modelled as single-degree of freedom mass oscillators coupled by a convected aerodynamic disturbance term. The results demonstrate that both structural and aerodynamic mistuning are effective. While structural mistuning improves stability by preventing aero-structure lock-in, aerodynamic mistuning, which locally reduces the tip blockage, attenuates the aerodynamic disturbance causing NSV. In the latter case, the circumferentially-averaged conditions are shown to be most influential, while the pattern plays a minor role. A combination of moderate aerodynamic and structural mistuning (1%) was also found to be effective. These findings are relevant for design decisions, demonstrating that small blade-to-blade variations can suppress NSV.

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