Direct Aeroacoustic Simulation of Sound Generation and Absorption in a Cross-Flow Fan with Helmholtz Resonators

Abstract

This study examined the feasibility of simultaneously simulating aerodynamic sound generation by low-speed fans and sound absorption by Helmholtz resonators using the lattice Boltzmann method with an overset grid. A resonator tuned to the blade-passing frequency (BPF) was mounted near the lower side of the tongue. Simulations and experiments showed that the resonator minimally affected aerodynamic performance but significantly reduced sound at the BPF while increasing low-frequency sound. Visualizations revealed that BPF sound originated from dipole sources near the tongue. Anti-phase pressure fluctuations around the lower tongue contributed to sound cancellation, whereas in-phase fluctuations on the upper side amplified sound. At lower frequencies, synchronized fluctuations between the duct and resonator raised sound levels.