Phase-locking particle image velocimetry measurements of acoustic-driven flow interactions between tandem deep cavities

Abstract

Acoustic-driven flow interactions between tandem deep cavities, which manifest as resonances between the natural acoustic standing-wave mode and the intrinsic shear-layer vortex structures, were experimentally investigated by using a pressure transducer array, the planar particle image velocimetry (PIV) technique, and phase-locking PIV measurements. Specifically, in the phase-locking PIV measurements, a field-programmable gate array-based phase-determination strategy was used to improve the phase-locking accuracy. The pressure measurement results demonstrated that under certain Reynolds numbers, significantly intensified acoustic pressure pulsations were excited once the magnitude of the acoustic resonance occurring inside the tandem deep cavities reached almost three times the magnitude of the dynamic pressure head at the channel inlet. Beyond that, the planar-PIV results illustrated the elevated turbulent flow quantities, such as the expanded velocity gradients, amplified shear-layer momentum thickness, intensified velocity fluctuations, and statistical Reynolds shear stresses. Subsequently, a proper orthogonal decomposition (POD) analysis was conducted to successfully extract the dominant flow modes underlying the acoustic-driven flow interactions, namely, the cavity-to-cavity flow mode and the counterrotating shedding vortex mode. The first POD mode gave rise to essential flow streaks that shuttled synchronously between the tandem deep cavities, while the second POD mode contributed to the streamwise vortex-shedding motions. Finally, the phase-locking PIV results comprehensively revealed the spatiotemporal evolutions of the coherent flow structures (the upper shedding vortices and the recirculation zones beneath) and their centroid trajectories. The findings of this study could be useful for revealing the flow–acoustic coupling mechanisms in related industrial facilities.

Flow–acoustic resonance mechanism in tandem deep cavities coupled with acoustic eigenmodes in turbulent shear layers

“…Regarding the separation bubble, it originated when the downstream shear layer vortex structures impinged upon the downstream corner and subsequently amplified, convecting along the main duct wall surface. Similar flow structures, characterized by recirculation zones and separation bubbles, can also be observed in Wang et al (2020) and Ho & Kim (2021). This separation bubble was also attributed to the divergence of Reynolds stress, which can lead to an increase in the thickness of the shear layer (Mantič-Lugo & Gallaire 2016).…”

“…Due to the special azimuthal characteristics of the diametral acoustic mode, the interactive shear layers demonstrate an intensified three-dimensionality and even a spinning rotation behaviour (Faure-Beaulieu, Pedergnana & Noiray 2023a;Faure-Beaulieu et al 2023b). These observations were corroborated through phase-locked particle image velocimetry (PIV) measurements (Ziada, Bolduc & Lafon 2017) and high-fidelity LES simulations (Abdelmwgoud, Shaaban & Mohany 2020;Wang et al 2020). As for the depth-oriented acoustic mode, the direction of its acoustic particle velocity is generally perpendicular to that the streamwise-transported shear layer.…”

“…This result shows a good agreement with the PIV measurement by Wang et al . (2020), in which the shear layers were affected by a depth-oriented acoustic standing-wave mode inside a channel with symmetric deep cavities. In figure 7( b ), corresponding to tandem deep cavities with a half-wavelength arrangement, the most distinct finding is that the upstream shear layer is more intensified than the downstream shear layer.…”

“…Similar flow structures, characterized by recirculation zones and separation bubbles, can also be observed in Wang et al . (2020) and Ho & Kim (2021). This separation bubble was also attributed to the divergence of Reynolds stress, which can lead to an increase in the thickness of the shear layer (Mantič-Lugo & Gallaire 2016).…”

“…These observations were corroborated through phase-locked particle image velocimetry (PIV) measurements (Ziada, Bolduc & Lafon 2017) and high-fidelity LES simulations (Abdelmwgoud, Shaaban & Mohany 2020; Wang et al . 2020). As for the depth-oriented acoustic mode, the direction of its acoustic particle velocity is generally perpendicular to that the streamwise-transported shear layer.…”