Large eddy simulation for aeroacoustic prediction and characterization of electronics cooling axial fans under various operating conditions

This study provides a comprehensive investigation into the aerodynamic and aeroacoustic characteristics of a small-sized axial fan under various operating conditions, representing different system resistances in electronics cooling applications. A wall-resolved large eddy simulation (LES) approach, combined with the Ffowcs Williams-Hawkings (FW-H) acoustic analogy, is used to analyze the flow and noise characteristics for a realistic fan configuration. The numerical simulations are validated through comparison with experimental measurements, showing excellent agreement. The study reveals distinct flow and noise characteristics between normal and stall conditions of the fan. During normal operating conditions, paired inlet vortex tubes are observed due to the asymmetric inlet-rotor interaction. The flow structures near the blade tip, such as the inlet vortex tubes and tip vortices, exhibit higher coherence. However, during stall conditions, these structures become more disorganized. Additionally, laminar-turbulent separation and high leading-edge turbulence are observed during stall conditions, resulting in increased broadband noise level. Aeroacoustic analysis shows that tonal noise is more prominent during normal operating conditions, while broadband noise becomes more significant during stall conditions. The main tonal noise sources during normal conditions are the asymmetric inlet-rotor interaction and the rotor-stator interaction. On the other hand, the tip-gap noise serves as the primary source of broadband noise. During stall conditions, the leading-edge noise and flow separation noise become the main sources of broadband noise. The shroud noise significantly contributes to the tonal noise across all operating conditions. This study identifies the locations and dominant characteristics of the noise sources and analyzes the contributions of different noise sources to the overall fan noise. • Analyzed aeroacoustic noise of a realistic axial fan using LES and the FW-H method. • Distinguished flow and noise features in normal vs. stall conditions. • Tonal noise from asymmetric inlet-rotor and rotor-stator interaction. • Leading-edge and flow separation noise as main stall broadband sources. • Shroud noise contributes significantly to tonal noise across all conditions.