Flow‐induced noise and vibration of confined jets

Abstract

An experimental program was conducted in the acoustical water tunnel to determine the flow‐induced noise and vibration on pipes due to various flow restrictors. Several flow restrictor configurations were tested for a range of flow velocities (up to 15 m/s). The flow configurations tested include: pipe flow, and flow restrictors with circular, coannular, rectangular cross‐sectional areas, as well as multiple circular and slot jets. Wall pressure fluctuation and acceleration measurements were made using miniature hydrophones, flush‐mounted on the inside wall of the pipe, and accelerometers mounted on the outside wall. Spectral and cross‐spectral densities of the wall pressure and acceleration signals were determined. Experimental results showed that the flow‐induced noise levels vary with the pipe axial location. The peak noise is located at the vicinity of the end of the jet potential core (six jet diameters downstream of the jet). Correlation of noise versus velocity showed a velocity to the 4.8th power relationship. Normalized noise spectra were obtained for the various flow configurations. The spectral shapes of the various flow configurations are quite similar, except that the coannular and slots jets show more high‐frequency noise. The pipe‐wall structural resonances were identified by correlating the various hydrophone signals. These resonance frequencies were consistent with the results obtained by impact testing. Furthermore, results from the correlation of hydrophone signals showed the existence of coherent structures, which probably control the generation of turbulence generated noise, near the exit of the jet.