On the temporal analysis of acoustic waves using schlieren imaging

Jagadeesh, Chetan; Gowree, Erwin Ricky; Jadidbonab, Hesamaldin; Atkin, Chris

doi:10.1016/j.measurement.2017.11.018

Cited by 7 publications

(7 citation statements)

References 15 publications

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“…A second important problem, as already anticipated, is the coexistence of hydrodynamic and acoustic flow fluctuations of very different scales in the same medium. A clear visualization of the coexistence of flow-based and acoustic pressure (or density) fluctuations in a medium can be found in figure 3, including the flow field from a jet, together with other interesting examples from daily life [13,14]. The work of Chu and Kovásznay [15] further clarifies the problem, by carrying out a disturbance analysis on Lighthill's aeroacoustic analogy.…”

Section: The Physics Behind the Measurement Problemmentioning

confidence: 94%

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Measurement techniques for aeroacoustics: from aerodynamic comparisons to aeroacoustic assimilations

Ragni¹,

Avallone²,

Casalino³

2022

Meas. Sci. Technol.

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Sustainability has encouraged studies focusing on lowering the aeroacoustic impact of new aerodynamically optimized mechanical systems for several applications in wind energy, aviation, automotive and urban air mobility. The deployment of effective noise reduction strategies start with a deep understanding of the underlying mechanisms of noise generation. To elucidate the physics behind the formation of aerodynamic sources of sound, experimental techniques used for aerodynamic purposes have been combined with acoustic measurements. In the last decades, new experimental post processing techniques have additionally been developed, by leveraging aeroacoustic analogies in a new multi disciplinary framework. New approaches have been developed with the intent of translating near field velocity and pressure information into sound. The current review describes how such breakthroughs have been achieved, briefly starting from an historical overview, to quickly bridge to the measurement techniques and the facilities employed by the scientific community. Being the measurement principles already reported in literature, this review only focuses on the most relevant studies trying to relate near field information to the perceived sound in the far field. Aspects related to the uncertainty of the measurement techniques will be thus very briefly discussed, together with their relation to the background noise of the testing facilities, including acoustic reflections/refractions, and issues due to installation of the instrumentation.

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Section: The Physics Behind the Measurement Problemmentioning

confidence: 94%

“…Reproduced with permission from Dr Tuinstra (www.nlr.org/research-infrastructure/aeroacoustic-wind-tunnel/). (11) Reproduced with permission from[50] (13). Reproduced from[65].…”

mentioning

confidence: 99%

Measurement techniques for aeroacoustics: from aerodynamic comparisons to aeroacoustic assimilations

Ragni¹,

Avallone²,

Casalino³

2022

Meas. Sci. Technol.

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“…Because this is the fundamental topic of interest in the field of aeroacoustics, further study on the mechanism of screech-tone generation [8] [9], selection mechanism of oscillation modes [10] [11] [12] [13], and the shock-cell structure in the jet [14] [15] are investigated experimentally. Furthermore, the flow characterizations of screeching jet were performed by introducing the particle image velocimetry [14] and frequency analysis by high-speed schlieren imaging [15]. Note that these characteristics of screech tone were well reproduced in the numerical simulations [16] [17].…”

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Visualization of Shock Cell Structure and Screech Tone Emission in Underexpanded Circular Jet

Ozawa¹,

Yamagata²,

Fujisawa³

2022

JFCMV

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The three-dimensional visualization of flow and screech-tone emission from an underexpanded circular jet is first investigated experimentally using high-speed cross-schlieren imaging and microphone measurements in the cross-sectional planes along the jet axis. This experimental technique allows the visualization of the shock-cell structure, directivity of sound intensity, and frequency spectrum in the cross-sectional planes of the screeching jet. The high-speed cross-schlieren observation of the screeching jet shows the occurrence of an asymmetrical shock-cell structure that is generated by the flapping mode in the screeching jet. This contributes to the generation of a screech tone propagating upstream along the jet axis and non-uniform sound intensities around the jet in circumferential direction. These observations by high-speed cross-schlieren imaging were validated by the microphone measurements.

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“…For example, hypersonic boundary layer receptivity under free-stream disturbance refers to the process that occurs when disturbances in the free-stream enter the boundary layer and result in the generation of perturbations in the boundary layer. Many scholars have researched hypersonic boundary layer receptivity [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ], but it is not yet fully understood because the hypersonic boundary layer receptivity is affected by many factors. These factors interact with each other, which increases the complexity of the hypersonic boundary layer receptivity.…”

Section: Introductionmentioning

confidence: 99%

“…They found that the dominant mode of the acoustic waves in free-stream occurs in a lower frequency region, a larger spatial extent, and a smaller bulk propagation speed. Jagadeesh et al [ 9 ] used the Schlieren imaging technique to measure the unstable motion of acoustic waves in the boundary layer and reported that this method could be used to study laminar-turbulent transition and the flow in a large gradient region. Compared with acoustic waves, the influence of other types of free-stream disturbance on hypersonic boundary layer is less studied.…”

Section: Introductionmentioning

confidence: 99%

Effect of a Roughness Element on the Hypersonic Boundary Layer Receptivity Due to Different Types of Free-Stream Disturbance with a Single Frequency

Shi

Wang

et al. 2019

Entropy

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The hypersonic flow field around a blunt cone was simulated using a high-order finite difference method. Fast acoustic waves, slow acoustic waves, entropy waves, and vortical waves were introduced into the free-stream to determine the influence of a free-stream with disturbances on the hypersonic flow field and boundary layer. The effect of disturbance type on the evolution of perturbations in the hypersonic boundary layer was analyzed. Fast Fourier Transform was adopted to analyze the effect of the disturbance type on the evolution of different modes in the boundary layer. A roughness element was introduced into the flow field to reveal the impact of the roughness element on hypersonic boundary layer receptivity. The results showed that a free-stream with disturbances affected the hypersonic flow field and boundary layer; acoustic waves had the greatest influence. The impact of slow acoustic waves on the flow field was mainly concentrated in the region between the shock and the boundary layer, whereas the influence of fast acoustic waves was mainly concentrated in the boundary layer. Multi-mode perturbations formed in the boundary layer were caused by the free-stream with disturbances, wherein the fundamental mode was the dominant mode of the perturbations in the boundary layer caused by fast acoustic waves, entropy waves, and vortical waves. The dominant modes of the perturbations in the boundary layer caused by slow acoustic waves were both the fundamental mode and the second harmonic mode. The roughness element changed the propagation process of different modes of perturbations in the boundary layer. In the downstream region of the roughness element, perturbations in the boundary layer caused by the slow acoustic waves had the greatest influence. The second harmonic mode in the boundary layer was significantly suppressed, and the fundamental mode became the dominant mode. The effects of fast acoustic waves and entropy waves on the boundary layer receptivity were similar, except the amplitude of the perturbations in the boundary layer caused by the fast acoustic waves was larger.

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On the temporal analysis of acoustic waves using schlieren imaging

Cited by 7 publications

References 15 publications

Measurement techniques for aeroacoustics: from aerodynamic comparisons to aeroacoustic assimilations

Measurement techniques for aeroacoustics: from aerodynamic comparisons to aeroacoustic assimilations

Three-Dimensional Visualization of Shock Cell Structure and Screech Tone Emission in Underexpanded Circular Jet

Effect of a Roughness Element on the Hypersonic Boundary Layer Receptivity Due to Different Types of Free-Stream Disturbance with a Single Frequency

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