Influence of freestream turbulence on the near-field growth of a turbulent cylinder wake: Turbulent entrainment and wake meandering

Kankanwadi, Krishna S.; Buxton, O. R. H.

doi:10.1103/physrevfluids.8.034603

Cited by 12 publications

(21 citation statements)

References 37 publications

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“…First, in the near wake (say ), the large-scale vortices are more distinct in the case of the non-turbulent background, whilst the locus of the vortices’ positions in the turbulent background extends to a further lateral distance from the wake centreline (). This confirms the observation of Kankanwadi & Buxton (2023) that the large-scale vortices of the near wake (identified via the velocity field, not the scalar field) in a turbulent background generally drift to further positions in the lateral () direction than those in a non-turbulent background at the same location. Second, the TTI is also characterised by a ‘rougher’ boundary with the ambient fluid, at both large and small scales.…”

Section: Visualisation and Determination Of The Interfacesupporting

confidence: 89%

“…However, at (marked by the right-hand dashed line), the position of the modal location of the TTI is larger than that of the TNTI, especially when the background turbulence intensity is high (figure 6 e ). Kankanwadi & Buxton (2023) showed that in the near-wake region (), the wakes exposed to background turbulence were always wider on average than the wake embedded in a non-turbulent background. Our results show that in the near wake, the modal position of the TTI is similar to the TNTI, and the reason why the mean wakes are wider for the TTI cases is because of the diminished contribution from the left tails of the PDFs (e.g.…”

Section: Resultsmentioning

confidence: 99%

“…By conducting a control experiment in which the large-scale coherent vortices in the wake (the von Kármán vortex street) were suppressed via the addition of a splitter plate, they deduced that the presence of freestream turbulence effectively enhances entrainment via engulfment but suppresses the small-scale ‘nibbling’. Kankanwadi & Buxton (2023) also reported that the presence of freestream turbulence increases the locus of the wake's large-scale coherent vortices (i.e. wake ‘meandering’ with a larger amplitude), with the integral length scale of the background turbulence playing the most important role in determining this.…”

Section: Introductionmentioning

confidence: 99%

“…Yule 1978; Bisset, Hunt & Rogers 2002; Cimarelli & Boga 2021; Long, Wang & Pan 2022). For TTIs, Kankanwadi & Buxton (2023) observed that both the turbulence intensity and the integral length scale in the ambient flow correlate to enhanced entrainment in the presence of the large-scale coherent vortices in the near wake of a cylinder – a contrasting result to the far-field study in which background turbulence was observed to suppress entrainment rate (Kankanwadi & Buxton 2020). By conducting a control experiment in which the large-scale coherent vortices in the wake (the von Kármán vortex street) were suppressed via the addition of a splitter plate, they deduced that the presence of freestream turbulence effectively enhances entrainment via engulfment but suppresses the small-scale ‘nibbling’.…”

Section: Introductionmentioning

confidence: 99%

“…Will the dominant parameter change before and after the transition region? All these intriguing questions emerging from the findings of Kankanwadi & Buxton (2020, 2023) are imperative for understanding the dynamics of TTIs as the wake develops downstream. We aim to answer all these questions in the present study, so as to contribute to an in-depth and complete comprehension of the behaviours of the TTI/TNTI in planar wakes.…”

Section: Introductionmentioning

confidence: 99%

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Spatial evolution of the turbulent/turbulent interface geometry in a cylinder wake

Chen

Buxton

2023

J. Fluid Mech.

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This study aims to examine the spatial evolution of the geometrical features of the turbulent/turbulent interface (TTI) in a cylinder wake. The wake is exposed to various turbulent backgrounds in which the turbulence intensity and the integral length scale are varied independently, and comparisons to a turbulent/non-turbulent interface (TNTI) are drawn. The turbulent wake was marked with a high Schmidt number ( $Sc$ ) scalar, and a planar laser induced fluorescence experiment was carried out to capture the interface between the wake and the ambient flow from $x/d = 5$ to 40, where $x$ is the streamwise coordinate from the centre of the cylinder, and $d$ is the cylinder's diameter. It is found that the TTI generally spreads faster towards the ambient flow than the TNTI. A transition region of the interfaces’ spreading is found at $x/d \approx 15$ , after which the interfaces propagate at a slower rate than previously (upstream), and the mean interface positions of both the TNTI and TTI scale with the local wake half-width. The locations of both the TNTI and TTI have non-Gaussian probability density functions (PDFs) in the near wake because of the influence of the large-scale coherent motions present within the flow. Further downstream, after the large-scale coherent motions have dissipated, the TNTI position PDF does become Gaussian. For the first time, we explore the spatial variation of the ‘roughness’ of the TTI, quantified via the fractal dimension, from near field to far field. The length scale in the background flow has a profound effect on the TTI fractal dimension in the near wake, whilst the turbulence intensity becomes important only for the fractal dimension farther downstream.

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