On Instability Waves and the Noise Generated by Turbulent Jets

Tim Colonius Mechanical Engineering Department California Institute of TechnologyPasadena, CA Reduction of jet noise remains an important goal for commercial and military aircraft, as well as a challenging problem for experimental and computational fluid dynamics. We present analysis and results from recent experiments that suggest that the pressure fluctuations associated with large-scale structures in turbulent jets are well modeled by linear instability waves of the mean velocity profile. An 80 microphone phased-array was used to measure pressure fluctuations just outside the jet shear layers of turbulent jets over a range of subsonic Mach numbers and temperature ratios. Measured pressures are decomposed into azimuthal modes and compared to predictions of linear instability theory based using measured and/or predicted mean flow profiles. Agreement in terms of streamwise evolution, phase speed, and radial decay are demonstrated. The near-field pressure measurements are also projected to the far-field using a Kirchhoff surface approach and compared with the directly measured far-field. We also analyze serrated (chevron) nozzles in an attempt to understand how they reduce low frequency noise. Work supported by the Aeroacoustics Research Consortium and the Naval Air Systems Comma

Location: Stauffer Science Lecture Hall, Rm 102

Audiences: Everyone Is Invited

Contact: April Mundy