Saving pipes from damaging vibrations

Pipe-cavities and their surrounding structures can be damaged by noise emitted by out-flow and internal sources. Reducing such noise is crucial to oil, gas and aerospace industries, in which pipe systems play a vital role.

Kabilan Baskaran and K. Srinivasan quantified the acoustic radiation of pipe cavity jet noise to understand the flow and acoustic characteristics of the jet and mitigate the damaging effects of noise and vibration.

They discovered that by increasing the upstream pipe length, the initial shear layer at the leading edge of the cavity would become thicker, resulting in reduction of far-field noise. Since thicker shear layers are more resistant to amplification, future engineers may use this to improve pipe designs to curb certain negative effects related to acoustics.

The authors compare different pipe-cavity configurations and pipe lengths and document how they affect a pipe’s acoustic properties such as the waves’ frequency, pressure levels, directions, and power.

“This study cleverly utilizes an upstream cavity as a tool for mitigating jet noise. By simply increasing the upstream pipe length, the propensity of the pipe-cavity system for unstable oscillations is weakened. In this respect, this work is one of the first of its kind,” Srinivasan said.

Based on their conclusions, the authors suggest that careful placement of cavities in flow systems could help mitigate instability problems. They believe that solutions to pipe cavity instabilities will need to be tailored to specific situations, as other factors such as cavity shapes and wall effects may also play a role.

Source: “Effects of upstream pipe length on pipe-cavity jet noise,” by Kabilan Baskaran and K. Srinivasan, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5120460 .