After a brief review of the status and relevance of jet noise, we discuss wavepacket structures that are observed in the near pressure field of turbulent jets, and their relation with the radiated acoustic field. These wavepackets have been observed for many years, but their importance to the far-field noise is still debated, particularly in subsonic jets. We use the linear Parabolized Stability Equations (PSE) to model the wavepacket structures; the results provide excellent quantitative agreement with the spatial distribution of wavepacket amplitude and phase from microphone measurements and real-time particle image velocimetry, especially when the data are processed to filter out contributions associated with uncorrelated fluctuations. We extend the theory to jets from serrated nozzles, and conclude by describing current research efforts to use wave packet models to devise jet noise control strategies.
About the Speaker
Tim Colonius is Professor of Mechanical Engineering at the California Institute of Technology. He received his B.S. from the University of Michigan in 1987 and M.S and Ph.D. in Mechanical Engineering from Stanford University in 1988 and 1994, respectively. He joined the Caltech faculty in 1994, where he and his group develop and use numerical simulations to study a range of problems in fluid mechanics, including aeroacoustics, flow control, instabilities, and bubble dynamics. He is a Fellow of the American Physical Society and has held visiting positions at Cambridge University and the University of Poitiers.