Eligibility of further modularization of narrow sidebranch array for duct noise control

Narrow sidebranch array is a kind of wall-mounted duct silencer system to attenuate wideband noise. Further modularization of the system can strengthen the performance along the frequency range of interest. It can also reduce the bulkiness of the design. The details of the arrays of full duct width are presented in previous studies. In the present study, more arrangements of the sidebranch array coupling are investigated through 3-dimensional finite-element method. Arrays of half of the duct width are installed in an infinitely long duct under no flow condition. The sound transmission loss and the isobaric contours in different trials are investigated. The first part of this study involves sidebranch arrays only. They are installed either symmetrically or asymmetrically alone the centre line of the duct. The result shows that coupling the half-width arrays in opposite side walls in normal condition is able to escalate the transmission loss nadirs across the frequency range of interest compared to the results of single traditional full-width array in one side. The reversed installations of one of the coupling arrays are also attempted, the corresponding performances are much poor that they are not comparable to the normal arrangement. An expansion chamber is introduced in the second part of this study. It is placed either alongside or in the opposite sidewall of the array. It is found that such arrangement can shift the effective span to lower frequency, while sacrificing the attenuation performance in higher frequencies. This shows the potential of enhanced duct noise attenuation by coupling various kinds of silencers with sidebranch array.