Seeing the Pressure Behind the Noise: Ruthenium-Based Pressure-Sensitive Paint (PSP) Enables Noise Diagnostics of Axial Fans for Server Cooling

This study presents the use of pressure-sensitive paint (PSP) measurements to diagnose potential noise sources on the blades of axial fans used for server cooling applications. Because the fan operates at high rotational speeds (3745-4392 rpm), time-resolved capture of surface-pressure fluctuations is achieved using a ruthenium-based PSP with enhanced sensitivity. The PSP measurements provide both mean pressure distributions and pressure fluctuations, revealing complex aerodynamics features associated with blade rotation and flow-structure interaction. To investigate the coupling between surface-pressure dynamics and acoustic emissions, proper orthogonal decomposition (POD) is applied to the pressure-fluctuation data. The resulting temporal coefficients exhibit spectral characteristics that closely match the measured fan noise spectra, indicating a strong correlation between blade-surface pressure fluctuations and noise generation. This correspondence enables qualitative identification of dominant pressure-driven noise sources and their spatial locations. Overall, the results demonstrate that PSP-based pressure visualization is a powerful diagnostic tool for linking aerodynamic pressure phenomena to noise generation mechanisms in axial fans. By revealing pressure features associated with acoustic signatures, the proposed approach offers valuable insights for identifying noise-critical regions and guiding targeted design modifications toward quieter and more efficient server cooling systems.