Acoustic transmission loss and noise from Kevlar wind tunnel walls

Abstract

In this paper we will develop a model for the acoustic transmission loss and self-noise generated by a Kevlar wind tunnel wall. It is shown that the porosity of the fabric is the most important controlling factor of the transmission loss, and the effect of wind tunnel flow speed is to increase the losses, as observed in experiments. In addition, a model is developed for the weave noise generated by a Kevlar wind tunnel wall, which is found to be caused by the pumping of the fluid through the pores in the Kevlar and depends on their open area ratio. The mechanism for this sound generation is similar to the roughness noise mechanism for a turbulent boundary layer in that the pore spacing couples with the small wavelength disturbances in the boundary layer to cause acoustic radiation at the sum and difference frequencies.