Ml. Munjal et Pt. Thawani, EFFECT OF PROTECTIVE LAYER ON THE PERFORMANCE OF ABSORPTIVE DUCTS, Noise control engineering journal, 45(1), 1997, pp. 14-18
Acoustically absorptive lining in ducts and parallel-baffle mufflers i
s invariably protected from the abrasive effect of grazing flow and du
st by means of a protective layer in the form of highly porous thin me
tallic plate or cloth, or a very thin impervious layer of synthetic ma
terial like Mylar. An investigation of effects of protective layers on
the acoustic performance of lined circular ducts and parallel-baffle
mufflers (modeled as two-dimensional rectangular ducts) is the subject
of this paper. Analytical models are presented for both cases with bu
lk reacting as well as locally reacting absorptive linings protected b
y a perforated or un-perforated layer, These simple models based upon
a stationary inviscid medium are then used in a parametric study to pr
ovide noise control engineers with necessary design information, The e
ffect of grazing flow on the impedance of a perforated protective plat
e is duly accounted for in the model. (C) 1997 Institute of Noise Cont
rol Engineering.