Experimental investigation of stator stagger angle effect on fan tonal noise

Classical analytical models for rotor–stator interaction noise are developed under a zero-incidence assumption, which simplifies the complex interaction to a wake–cascade problem. However, the validity of this assumption across different stator vane stagger angles has not been systematically examined experimentally. In this study, the influence of stator vane stagger angle ranging from 0^∘-35^∘ on fan tonal noise were investigated using the Fan-200 with replaceable rotor and stator. Flow-field measurements were first conducted to verify that the inlet flow conditions remained nearly constant throughout the tests. In acoustic measurements, to match the reflection-free boundary condition used in analytical models, a microphone array was installed upstream of the rotor, and modal decomposition was employed to separate the upstream- and downstream-propagating components, enabling accurate extraction of tonal sound pressure levels at blade-passing frequencies. Measurements were performed at multiple rotational speeds to verify the repeatability and reliability of the observed trends. The results indicate that varying the stator vane stagger angle from 0^∘ to 35^∘ induces a tonal noise amplitude change of approximately 5–6 dB at both the 1BPF and 2BPF frequencies. The variation trends differ notably between the two frequencies: at 1BPF, the noise level remains nearly constant at small stagger angles and increases significantly as the stagger angle increases, whereas at 2BPF, the noise decreases initially and then stabilizes. These findings provide experimental evidence for assessing the validity of the zero-incidence assumption under the conditions considered and offer reliable data on the role of stator stagger angle in fan tonal noise.