Two-dimensional lattice Boltzmann investigation of sound absorption of perforated orifices with different geometric shapes

To gain insight into sound absorption mechanism and to evaluate its acoustic damping performance, two-dimensional numerical simulation of acoustically excited flow through perforated orifices with different geometric shapes is conducted by using lattice Boltzmann method. It is shown that vortex rings are formed when incident sound waves interact with and destabilize the shear layers formed at the orifice rims, and the sound energy is converted into kinetic energy being dissipated by the surrounding air. To quantify the orifice damping performance, sound absorption coefficient is used, which describes the fraction of incident acoustical energy being absorbed. Unlike frequency-domain simulations, the present study is conducted in time domain and the damping behavior of different shaped orifices is quantified over a broad frequency range at a time by forcing an oscillating flow with multiple tones. Comparing the numerical results with those obtained from the theoretical models and experimental measurements, good agreement is observed. And the square-shaped orifice is associated with larger damping effect than that of a rounded one. Finally, parametric study is conducted. It is found that the maximum sound absorption and the effective frequency bandwidth depend strongly on the combination of the bias flow Mach number and the orifice thickness. The successful demonstration reveals that the lattice Boltzmann method has great potential to be applied in aeroacoustics research field.