Acoustic Excitation by Flow in T-Junctions

The flow-acoustic nature of sharp-edged T-junctions is investigated experimentally. In this paper, the pipes forming the T-crossbar are referred to as the branches and the pipe forming the central stem of the T-shape is referred to as the main pipe. Four test cases are studied corresponding to: (a) T-junction with flow from each branch into the main pipe; (b) T-junction with flow from one branch into the main pipe, the other branch being closed; (c) T-junction with flow from the main pipe into the two branches, which is the reverse flow situation of the first case; and (d) T-junction with flow from the main pipe into one branch and the other branch is closed, which is the second case with reverse flow. It is found that the flow at the T-junction can excite the pipe acoustic modes to varying degrees, depending on the flow direction and piping configuration. For cases (c) and (d), the dimensionless pressure amplitude of the acoustic mode reaches a maximum at a Strouhal number similar to that of the turbulence broadband peak measured in the separation bubble downstream of the T-junction corner. Cases (a) and (b) exhibit a different type of flow-acoustic coupling. In both cases, the maximum acoustic pressure occurs at a Strouhal number which is different from that observed in the separation bubble. In addition, the pulsation amplitude is substantially stronger than that observed in cases (c) and (d). Detuning the branches weakens the resonance intensity, especially in case (c), which exhibits the strongest acoustic resonance.