Effect of cross-section on flow three-dimensionality for prismatic bodies and the associated noise emission

Pinto, Wagner J.; Margnat, Florent; Gervais, Yves

doi:10.2514/6.2019-2531

Cited by 5 publications

(5 citation statements)

References 44 publications

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“…As compared to the 𝑅𝑒 = 150 global mode, the structures are more and more pulled in the downstream direction as we move closer to the 𝑦 = 0 axis. The eigenvalue for this mode, 𝜆 = 1.3575 − 0.1251𝑖 which corresponds to 𝑆𝑡 = 0.216, is close to the dominant fluctuation frequency in the flow field and also to the tonal far-field noise frequency (Pinto et al [19]).…”

Section: Global Stability Analysismentioning

confidence: 62%

Modeling Aeolian Tones by Global Instability Modes

Prinja

Jordan

Margnat

2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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A noise prediction approach is proposed for bluff body wakes such as flow over a cylinder, where the primary noise source comprises of large scale coherent structures such as the vortex shedding flow feature. With the aim of developing low-order noise models, the strategy of this work is to extract and model such coherent structures. The modeling is based on a linear global stability analysis on the time-averaged mean flow to extract the dominant structures, whose amplitudes are then calibrated via two-point statistics. Curle's analogy is then implemented for far-field noise predictions. The overall approach is validated for flow over a circular cylinder for two cases of Reynolds numbers, 𝑅𝑒 =150 and 13000, and the noise predictions are found to be < 2dB off from the actual measurements.

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Section: Global Stability Analysismentioning

confidence: 62%

Modeling Aeolian Tones by Global Instability Modes

Prinja

Jordan

Margnat

2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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“…In the present work [1], the acoustic radiation of bluff body flows was also measured with microphones [38] while the 2D, laminar case was deeply investigated for numerous geometries [43]. The results show that, among the four geometries considered in the spanwise coherence study, the rectangular section of AR = 3 is the most silent in the 2D configuration and the loudest in the wind tunnel.…”

Section: Coherence Length As An Ingredient Of Acoustic Efficiencymentioning

confidence: 95%

“…Firstly, for the rectangular shape of AR = 2, the peak at St % 0.145 has a coherence length twice that of circular or square cylinder flow at lift peak while it is not visible in the acoustic spectrum. This may be considered as an exception, however, because for the three other geometries, all of the coherent peaks emerge from the noise radiated in the transverse direction [38]. Next, some porous covers of a circular cylinder have been able to reduce the tone intensity while (drastically) increase the spanwise coherence of the flow with respect to the hardwall cylinder of same outer diameter [17].…”

Section: Coherence Length As An Ingredient Of Acoustic Efficiencymentioning

confidence: 98%

“…The above described approximations notwithstanding, Figure 7 provides direct visualizations of the influence of cross-section shape on the spanwise coherence length spectrum in cylinder flows, that is, in Curle's formulation framework, of their aeroacoustic efficiency. To estimate the far-field noise spectrum, this should be multiplied by the source amplitude, as given by the sectional force spectrum, whose estimation [12,38] is outside the scope of the present contribution. The geometry influences not only the coherence length value at peak frequencies, but also the shape of the full spectrum, in terms of peak width and harmonics.…”

Section: Influence Of Shape and Velocitymentioning

confidence: 99%

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Cylinder aeroacoustics: experimental study of the influence of cross-section shape on spanwise coherence length

Margnat

Pinto

Noûs³

2023

Acta Acust.

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New data and review of the spanwise coherence length is provided for flows over cylinders of different cross-sections: circular of diameter d, and rectangular of sectional aspect ratios (breadth (b) to height (d) ratio AR = b/d) of 1, 2 and 3. In the present measurements, the body has both d and spanwise length of 70d fixed, and the Reynolds number (based on d) range 6000–27,000 is covered. Two-point data are obtained from two hot-wire probes, one fixed in the symmetry plane and the other moving on the corresponding spanwise axis. Their position in a cross plane are deduced from preliminary measurement of the mean flow with a single probe, allowing fair comparisons between the different geometries and the introduction of uncertainty bars on coherence length values. At all tested regimes, a very good agreement is noticed between velocity-based and pressure-based coherence experimental data. Coherence length definitions are revisited, and the aeroacoustically consistent, integral length definition is selected, allowing fair synthesis of literature data into a single chart and empirical functions. Definitions for coherence decay models (e.g. Gaussian or Laplacian) are also adapted so that coherence length and coherence integral shall be equivalent. This preliminary work on coherence data and its spanwise integration enables transparent regressions and model selection. Generally, the Gaussian model is relevant for the lift peak, while the coherence exhibits a Laplacian decay at harmonics. On average, at peak Strouhal number, the coherence length for the circular and square cylinders is of 5d while it is of the order of 15d for the rectangular sections. It is concluded that the flow over those latter geometries is still a two-dimensional dynamics at the tone frequency. These values are almost preserved over the tested Reynolds number range. Coherence length value at harmonics is extensively documented. Spanwise coherence length is also discussed as an ingredient of acoustic efficiency.

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“…With this approach in mind, several investigations has been combined including numerical [8][9][10][11], theoretical [12,13] and experimental [14,15] approaches. The analysis of the microphone signals for different diameters of a circular cylinder lead us to notice a specific influence of span to diameter ratio on the noise level, which is the subject of the present paper.…”

Section: Introductionmentioning

confidence: 99%

Influence of the Length of a Cylinder on its Aeolian Tone Level: Measurement and Modelling

Pinto¹,

Margnat²,

Noûs³

2021

14th WCCM-ECCOMAS Congress

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The tonal noise generated by the flow over elongated cylinders is measured using microphones in the anechoic wind tunnel BETI of Institut Pprime. The effect of the length to diameter ratio of the cylinder is assessed by varying the diameter from 6 mm to 20 mm within the constant width (750mm), open jet, test section. The velocity is varied from 10 to 40 m/s, leading to a Reynolds number range of about 4,000 -53,000. A proper normalization is needed to obtain a good collapse of experimental data from nearly 10 studies on the same evolution in 3 steps: for very short cylinders, the tone level does not depend on the length; for semi-long cylinders, it follows the fourth power of the length to diameter ratio; for very long cylinder, the length's influence vanishes in the form of a sound level asymptote. This sigmoidal evolution is noticed for both the circular section and the square section cylinders, and questions the classical modelling of the aeroacoustic process using compact, coherent segments of cylinder associated with a coherence length to account for spanwise phase loss. Literature data from numerical simulation or experiment using end-plates are included in the analysis too.

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Effect of cross-section on flow three-dimensionality for prismatic bodies and the associated noise emission

Cited by 5 publications

References 44 publications

Modeling Aeolian Tones by Global Instability Modes

Modeling Aeolian Tones by Global Instability Modes

Cylinder aeroacoustics: experimental study of the influence of cross-section shape on spanwise coherence length

Influence of the Length of a Cylinder on its Aeolian Tone Level: Measurement and Modelling

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