Abstract
The effects of scattering at the beginning of a finite length, cylindrical duct wall treatment was studied. Single frequency attenuation and optimal impedance of a locally reacting lining was considered. The effect of backward scattering was found to be small, but that of forward scattering substantial. Optimal wall impedance is presented as a function of the ratio of treatment length to duct radius and the mode cutoff ratio, which has been introduced as a design criterion (E. J. Rice, NASA TMX‐73411). Although the optimal impedance can be reasonably well described by the cutoff ratio, the attending attenuation cannot, but must be presented as a function of both azimuthal and radial mode indices.
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