Influence of hole-to-hole interaction on the acoustic behavior of multi-orifice perforated plates

A key factor for developing low-emission combustion systems in modern gas turbines and aero-engines is the acoustic liner's optimized design. Several models are available in the literature for the acoustic impedance of perforated acoustic liners. Most of these impedance models neglect the interaction effect between the orifices. In practice, the orifices are generally closely distributed such that the interactions between acoustic radiation from neighboring orifices can affect their acoustical behavior. The hole-to-hole interaction effect may change the resonance frequency of the resonator due to the nonplanar wave propagation in the cavity, the orifices in the perforated plate, and the near-wall region in the combustor. Considering this effect may help to predict the resonance frequency of the resonator accurately. In this work, a three-dimensional (3D) analytical approach is developed to account for the nonplanar wave propagation in the cavity and orifices on the perforated plate. The present study employs the proposed 3D analytical method to determine the hole-to-hole interaction end-correction of multiorifice perforated plates. Additionally, the hole-to-hole interaction end-correction from a series of perforated plates with different orifice radii and spacings is obtained via the Finite Element Method (FEM). Perforated plate specimens with different center-to-center hole spacing are tested using an impedance tube. Experimental results show that the resonance frequency is shifted towards a lower frequency with decreasing holes' spacing. The resulting model is compared with the experiments and the end-correction models available in the literature. The comparison shows that the available end-correction models cannot capture the hole-tohole interaction effect, which is observed in experiments. In contrast, the proposed model can reproduce measurements with high quality. The resulting model demonstrates that the acoustic end-correction length for orifices is closely related to the perforated plate's porosity ratio and orifice radius. The proposed model is readily applicable in the design of multi-orifice perforated plates.