Interscale energy transfer in the merger of wakes of a multiscale array of rectangular cylinders

Baj, Paweł; Buxton, O. R. H.

doi:10.1103/physrevfluids.2.114607

Cited by 17 publications

(70 citation statements)

References 57 publications

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“…Besides these, two other clear frequency signatures appeared, at , with a well-defined spatial arrangement, as the highest frequency () resides between the wakes of the main cylinder and the control rod and the other () resides closer to the control rod's wake. Baj & Buxton (2017) investigated the interactions between wakes produced by a multi-scale array of bluff bodies and identified the same spectral signature with the same spatial arrangement at the intersection of different-sized wakes. Although the geometries and were different, the similarity between the spectra and their spatial configuration is remarkable, which suggests that the physical phenomena behind the interaction are also similar.…”

Section: Resultsmentioning

confidence: 99%

“…The facility has a 0.6 m square test section and the length is 8.2 m. For all experiments the flow velocity was set at and at this speed the turbulence intensity is approximately 1.5 % at the position of the test cylinder. A thorough characterisation of the free-stream turbulence in this facility, including its two-point correlation, can be found in Baj & Buxton (2017). The Froude number in these experiments was .…”

Section: Experimental Arrangement and Methodologymentioning

confidence: 99%

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The role of separation on the forces acting on a circular cylinder with a control rod

et al. 2021

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Section: Resultsmentioning

confidence: 99%

Section: Experimental Arrangement and Methodologymentioning

confidence: 99%

The role of separation on the forces acting on a circular cylinder with a control rod

et al. 2021

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“…Verification of the SSU mechanism will thus depend on observing "bursts" of scalar being exchanged at, or close to, the wake intersection points of the various intersecting wakes downstream of the multi-scale array. However, as shown in Baj & Buxton (2017) largescale coherent motions are dominant in the near-field of both the single-scale and multiscale arrays, with the most energetic motion being that corresponding to the shedding of the largest obstacle present. By deploying the multi-scale triple decomposition technique of Baj et al (2015) we can track all of the coherent motions present in the flow and hence assess the relative importance of the largest bar versus the combination of different bars, and hence the multi-scale nature of the geometry, in stirring the scalar.…”

Section: Introductionmentioning

confidence: 84%

“…The velocity fields in the flows past the same arrays have been investigated recently by Baj & Buxton (2017). The main reported finding is that multi-scale generated turbulence is rich in a number of distinctive coherent fluctuations on top of the quasi-stochastic turbulent fluctuations.…”

Section: Introductionmentioning

confidence: 99%

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Passive scalar dispersion in the near wake of a multi-scale array of rectangular cylinders

Baj

Buxton

2019

J. Fluid Mech.

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The near wakes of flows past single- and multi-scale arrays of bars are studied by means of planar laser induced fluorescence (PLIF) and particle image velocimetry (PIV). The aim of this research is to better understand dispersion of passive scalar downstream of the multi-scale turbulence generator. In particular, the focus is on plausible manifestations of the space-scale unfolding (SSU) mechanism, which is often considered in the literature as the reason for the enhancement of the turbulent scalar flux in flows past fractal grids (i.e. specific multi-scale turbulence generators). The analysis of qualitative and quantitative PLIF results, as well as the simultaneously acquired PIV results, confirms the appearance of a physical scenario resembling the SSU mechanism. Unlike the anticipation of the literature, however, this scenario applies to some extent also to the flow past the single-scale obstacle. Application of a triple decomposition technique (which splits the acquired fields into their means, a number of coherent fluctuations and their stochastic parts) and a conditional-averaging technique reveals that the SSU mechanism is active in the vicinity of an intersection point between two adjacent wakes and is driven almost exclusively by coherent fluctuations associated with the larger of the intersecting wakes. This suggests that the SSU mechanism is related to the coherent fluctuations embedded in the flow rather than to the fine-scale turbulence and its underlying integral length scale, as proposed in previous works.

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Inter-scale Energy Transfer in a Multi-scale Flow

Buxton

Baj

2019

Springer Proceedings in Physics

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Multi-scale generated turbulent flows are observed to possess some remarkable features, such as the rapid spreading of forest fires. Here, for simplicity, we consider the flow past a two-dimensional multi-scale arrangement of bars of various thicknesses in which wakes of different characteristic sizes and frequencies interact. We apply a novel multi-scale triple decomposition on the velocity field in order to distinguish between the mean flow, coherent fluctuations of various characteristic frequencies (associated with the various length scales present in the multi-scale array) and the residual/stochastic fluctuations. In this chapter we report on the observation of secondary coherent modes at the various wake intersection points, appearing at frequencies f l ± f m , where f l and f m are the fundamental shedding frequencies associated with the bars producing the intersecting wakes. We subsequently derive the multi-scale triple-decomposed energy budgets to reveal the source term for these secondary coherent modes. Consideration of these energy budgets reveals an inverse cascade mechanism by which energy is transferred from the higher frequency of the two interacting fundamental coherent motions to the lower frequency secondary coherent mode under the catalytic action of the lower frequency fundamental mode.

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Interscale energy transfer in the merger of wakes of a multiscale array of rectangular cylinders

Abstract: The near wake of a flow past a multiscale array of bars is studied by means

Cited by 17 publications

References 57 publications

The role of separation on the forces acting on a circular cylinder with a control rod

The role of separation on the forces acting on a circular cylinder with a control rod

Passive scalar dispersion in the near wake of a multi-scale array of rectangular cylinders

Inter-scale Energy Transfer in a Multi-scale Flow

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