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Published November 11, 2012 | Submitted
Conference Paper Open

Low-speed jet dynamics and sound radiation

Abstract

Experimental velocity measurements of a low-speed jet, performed using time-resolved tomographic PIV, are used to study the dynamics of large-scale structures and their sound radiation. The experimental results show the roll-up of axisymmetric vortices that pair downstream, and subsequently lose their azimuthal coherence. Models of linear instability waves using both steady laminar and mean-field base flows flow are applied. While good agreement can be obtained for the vortex roll-up frequency in the near-nozzle region using the laminar base flow, non-linear effects must be included, via the mean field, in order to capture the downstream evolution of both the fundamental and subharmonic (vortex pairing). The velocity fluctuations for both frequencies have a wave-packet structure with some jitter in the form of modulations of the spatial extent and amplitude of the envelope. The sound radiation is modelled using a jittering wave-packet model, an shows agreement with the exponential directivity shape of Laufer and Yen (J. Fluid Mech. 134, 1983).

Additional Information

© 2012 by Peter Jordan. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Published Online: 11 Nov 2012. The authors kindly acknowledge LaVision GmbH and Piero Colonna for providing the CMOS cameras used in the TOMO-PIV experiments. This work was conducted as part of the FLOVIST project (Flow Visualization Inspired Aeroacoustics with Time Resolved Tomographic Particle Image Velocimetry), funded by the European Research Council (ERC), grant no 202887. This present work was partially supported by CNPq, National Council of Scientific and Technological Development – Brazil, and through the EU-Russian program ORINOCO (FP7-AAT-2010-RTD-Russia; project number 266103).

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August 19, 2023
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