58535 - 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 optimized design of acoustic liner. Therefore, several models are proposed in the literature for the acoustic impedance of perforated acoustic liners. Most of the available acoustic impedance models are developed based on the assumption of no interaction effect between the orifices. These models are developed for a single orifice on the plate and extended to a pattern of orifices considering the number of orifices (area ratio). In practice, the orifices are generally closely distributed such that the interactions between acoustic radiations from neighboring orifices can affect their acoustical behavior. The hole-to-hole interaction effect may vary the resonance frequency of the resonator due to the nonplanar wave propagation in the cavity and orifices. Considering the hole-to-hole interaction 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 multi-orifice perforated plates and discuss the effect of orifice spacing on the end-correction. Furthermore, the hole-to-hole interaction end-correction from a series of perforated plates with different orifice radii and spacings are obtained via the proposed 3D analytical approach. A regression analysis of the resulting hole-to-hole interaction end-corrections was carried out and validated against the experimental results. Perforated plate specimens with different center-to-center holes distances (spacing) are built and tested using an impedance tube. It is mainly shown that in the presence of the hole-to-hole interaction effect, the resonance frequency is shifted towards the low-frequency ranges where the distance of the holes is shorter. These effects on the surface impedance and reflection coefficient are discussed in detail. 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 are not capable of capturing the hole-to-hole 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 porosity ratio of the perforated plate and will be enhanced by the acoustic radiation effect from the perforation. The proposed model is readily applicable in the design of multi-orifice perforated plates.