Flow-Acoustics of T-Junctions: Effect of T-Junction Geometry

Abstract

This study focuses on the mechanism of flow-acoustic coupling in a T-junction, which has a transitional section entailing an expansion of pipe diameter. Six cases with varying length of the transitional section have been tested. It is shown that T-junctions with transitional sections can be a strong source of acoustic excitation and therefore can cause powerful acoustic resonance in the associated piping systems. Elimination of the transitional section reduces the excitation level drastically. The length of the transitional section with enlarged diameter is found to be the fundamental length scale determining the Strouhal number of flow excitation in the T-junction. To investigate the mechanism further, a series of experiments were conducted in a rectangular pipe system, which was considered as the 2D case of the T-junction. The results showed that the vortices formed in the outer and inner sides of the T-junction are both acoustic sources. They appear to form independently without interaction with each other, but are synchronized by the acoustic field. Flow visualization was carried out to gain images of the flow pattern when the resonance occurs. The images from flow visualization provided support to the measurements of the rectangular pipe system. Numerical simulations of the mean flow and acoustic field in the rectangular T-junction were performed. A simplied analysis of acoustic energy generation was also carried out.