The influence of turbulent flow on the sound attenuation in a narrow rectangular duct is calculated by a finite difference approximation of the differential equation for inviscid flow. The absorptive lining at one duct wall is characterized by a flow‐independent wall impedance. Results are found in good agreement with experimental data from a duct with 1‐in.2open area lined on one side with a resistive layer of very fine metal fibers in front of a partitioned air backing. For resistive layers of fibers with larger diameter or of perforated plate used in the same configuration, the wall impedance depends greatly upon the flow velocity. A correlation is found between the nonlinearity of resistive layers due to turbulent flow and due to high sound‐pressure levels in a duct. The influence of the nonlinearity due to high sound‐pressure levels up to 160 dB is studied in the absence of flow. Measured attenuation data agree with those from a theoretical model, which correlates the varying attenuation along the duct with the varying sound‐pressure difference across the resistive lining. By comparison of theoretical and experimental results, the influence of nonlinearity due to turbulent flow can be described by an equivalent level of sound‐pressure difference across the resistive lining. A biasing effect of flow on nonlinear duct lining material linearizes the attenuation along the duct, if that equivalent level due to flow exceeds the actual sound level.