An improved characteristics length in strouhal number for internal flow induced acoustics in corrugated pipe

Corrugated pipes often experience self-sustained oscillations which leads to high intensity noise, known as "whistling" during critical flow conditions. In order to determine the peak whistling Strouhal number (Sr_p−w) and whistling amplitude, a two dimensional (2D) numerical simulation method using Fluent software is proposed in this paper. The flow pattern of the fluid passing through the corrugated pipe and the effect of pipe geometries on the Sr_p−w and whistling amplitude are investigated. A ratio of $\frac{1}{w+r_{up}}$ is found to be a good indicator of the consistency of Sr_p−w where the l is the plateau length, w is the width of the corrugation, and r_up is the upstream radius of the corrugation. Furthermore, optimal characteristic length is also assessed among three different characteristic lengths including w + r_up, w and $\frac{l^2}{w+r_{up}}$. The $\frac{l^2}{w+r_{up}}$ is found to be the optimal as the characteristic length. This finding is significant as it can allow us to avoid critical flow condition to minimize and prevent the whistling phenomenon more accurately and effectively by using the proposed equations. (paper)