Design of Reflective-Type Muffler for Acoustic Noise Control in Space Missions: Numerical and Analytical Approach

One of the most significant challenges in space missions is controlling the noise level within the cabin. Mufflers or silencers are employed to mitigate noise. In the present study, the performance of a basic reflective silencer is first investigated analytically and numerically in its simplest configuration. Based on the analytical evaluation of the base muffler, maximum performance occurs at odd multiples of π/2, while minimum performance is observed at integer multiples of π. Following the analytical analysis, extensions in the form of expanded tubes, designed based on the analytical findings, are added to the muffler. The performance of the reflective muffler is calculated using the sound transmission loss parameter and transfer matrix method, and the results are compared with numerical simulations. The findings reveal that while the numerical results generally align with the analytical predictions, discrepancies exist. Specifically, at frequencies above 1370 Hz, non-ideal effects are observed in the numerical results. As frequency increases, the acoustic wavefront inside the chamber deviates from a planar state, leading to reduced muffler efficiency at higher frequencies. Non-planar waves between the two extended tubes (with lengths L/2 and L/4) form at resonant frequencies of 1026 Hz and 1371 Hz. Although the emergence of non-planar waves disrupts muffler performance, the muffler with a single L/2 extension still outperforms the base muffler. Moreover, the configuration with two extended tubes (L/2 and L/4) exhibits the best performance among all tested mufflers.