Lattice Boltzmann simulation of low-speed fans with sound absorbers using impedance boundary condition

• Impedance-based modeling used for aeroacoustic simulations of low-speed fans. • Impedance boundary condition validated using NASA Langley impedance tube. • Overfitting low-frequency impedance causes unphysical vortices at boundaries. • Proper fitting replicates sound absorption effects of resonators and glass wool. This study investigated the feasibility of using impedance-based modeling in the lattice Boltzmann method (LBM) to simulate the flow and acoustic fields around low-speed fans equipped with sound absorbers. A boundary condition based on the bounce-back method was employed to integrate the impedance model into the LBM simulations, enabling easy application to complex geometries. Initially, the impedance boundary condition based on the bounce-back method was validated using the NASA Langley impedance tube. The simulation results demonstrated good agreement with both the experimental data and conventional LBM simulations, confirming the effectiveness of the bounce-back method for implementing the impedance boundary condition. Subsequently, this method was applied to aeroacoustic simulations of a cross-flow fan equipped with resonators and glass wool. The resonance frequencies of the resonators were tuned to match the blade-passing frequency of the fan, and the impedance characteristics of the sound absorbers were measured using an acoustic impedance tube. The results revealed that overfitting the impedance model to the low-frequency characteristics generated unphysical vortices at the boundaries. In contrast, proper fitting successfully simulated the sound absorption effects of the resonators and glass wool in the aeroacoustic simulations of the cross-flow fan.