Low frequency interactions between coupled narrow sidebranch arrays and the resulted sound transmission losses

The low frequency sound interactions between coupled narrow sidebranch arrays installed in an infinitely long rectangular duct are investigated numerically using the finite-element method in the present study. The corresponding transmission losses achieved these coupled sidebranch arrays are also examined. The interactions between the coupled sidebranch arrays result in both dipole-like and quadrupole-like radiations into the main duct. Results show that the coupling of two sidebranch arrays of different sidebranch length series side-by-side on one side of the duct wall can improve the performance in term of spectral uniformity of sound transmission loss compared with the cases where only one array covers the whole spanwise width of the duct. The installation of two coupled arrays on opposite sides of the duct cross-section improves the magnitudes of the sound transmission loss in general. The performance of the coupled array system can be further enhanced by removing the separating wall between sub-arrays of one of the coupled sidebranch arrays. It is also found that reversing the sidebranch arrangement of one of the coupled arrays is detrimental to the low frequency performance of the array system.