Aeroacoustic source analysis using time-resolved PIV in a free jet

• Published in: Experiments in fluids 2013-05, Vol.54 (5), p.1-16, Article 1531
• Main Authors: Breakey, David E. S., Fitzpatrick, John A., Meskell, Craig
• Format: Article
• Language: English
• Subjects: Acoustics; Aeroacoustics; Aeroacoustics, atmospheric sound; Application of Laser Techniques to Fluid Mechanics 2012; Coherence; Correlation analysis; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Error analysis; Estimates; Exact sciences and technology; Fluctuation; Fluid dynamics; Fluid flow; Fluid- and Aerodynamics; Fundamental areas of phenomenology (including applications); Heat and Mass Transfer; Instrumentation for fluid dynamics; Noise (turbulence generated); Physics; Research Article; Turbulent flows, convection, and heat transfer
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-013-1531-5

Time-resolved particle image velocimetry (TR-PIV) has become a valuable tool for spatio-temporally resolved flow measurements. Current camera and laser technology has advanced such that time-domain events leading to sound generation can now be resolved over a reasonable spatial extent. This paper reports on the application of TR-PIV for the analysis of aeroacoustic sources in a free jet using the direct correlation between in-flow velocity fluctuations on the jet center-line and near-field pressure fluctuations. This correlation is considered both in the time domain and in the frequency domain (coherence), and the effect of TR-PIV errors on these estimates is considered by comparison to hot-wire anemometer measurements. In addition, a recently developed wavelet filtering technique is used to separate the acoustic and hydrodynamic components of recorded near-field pressure signals, enabling a gain in the signal-to-noise ratio. The results show that TR-PIV can recover the same time-domain correlation available from hot-wire and traditional PIV measurements, but that the frequency-domain estimates are corrupted by error, particularly at high frequencies. This result negates the principal benefit of using TR-PIV over PIV (the availability of coherence estimates). Despite this result, an analysis of the correlation signature gives evidence that large-scale, convecting, wave-like structures are associated with sound production, a result consistent with observations by many recent investigators. The analysis shows that in the presence of such large-scale structures, noise source localization based on the traditional correlation technique is ambiguous.