Abstract To improve the understanding and enhance the predictability of nonsynchronous vibration (NSV) and rotating stall, an extensive experimental campaign was conducted with the open-test-case ECL5, which is representative of modern ultra-high-bypass-ratio (UHBR) fan architectures. These experiments indicate an influence of test conditions (absence of turbulence control screen (TCS), shortened intake configuration, and mechanical rotation speed) on the measured aerodynamic and aeroelastic behavior of the fan stage. This influence occurs superimposed on the actual parameter under investigation (for example, structural mistuning) and must be clearly characterized to avoid misleading data interpretation. Based on a detailed investigation of several test conditions, this article provides a characterization of different influential parameters. One main outcome is the impact of mechanical rotation speed on NSV amplitudes at subsonic operating conditions. This influence challenges the comparability of different rotor and facility configurations since experiments are usually conducted at corrected mechanical speed (to account for changing atmospheric conditions) to achieve Mach similarity. The findings of the study clearly emphasize that standard experimental procedures have to be adapted to account for the identified effects.
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