On the chaotic motion and acoustic characteristics of confined jet flows

Abstract

An experimental study was conducted to investigate the chaotic motion, and flow‐induced noise and vibration of confined jet flows in a cylindrical duct. Results from flow and acoustic measurements showed that the motion in pipe flow is random or chaotic, whereas the motion in confined jets is deterministic or orderly. Correlations of wall pressure fluctuations and pipe wall acceleration showed that jet flows generate more deterministic features than pipe flow. The coherence functions of the wall pressure and pipe wall acceleration are relatively high near the exit of the jet. The high coherence is due to the large‐scale coherent structures. Further downstream, the activity of jet mixing decreases, the large‐scale turbulence cascades to fine scales, and the flow and acoustic characteristics approach that of pipe flow. Phase portraits of the wall pressure data were generated using the method of delays. The deterministic and coherent structures of jet flows were observed and strange attractors could be identified. However, phase portraits of pipe flow showed that the wall pressure fluctuations were chaotic and that no strange attractors occurred. Similar results were obtained using the Wignet distribution time‐frequency analysis on the acoustic signals.