The effect of the geometric features of the turbulent/non-turbulent interface on the entrainment of a passive scalar into a jet

Kohan, Khashayar F.; Gaskin, Susan

doi:10.1063/5.0019860

Cited by 26 publications

(17 citation statements)

References 61 publications

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“…The p.d.f. of for the jet in the quiescent ambient follows a Gaussian distribution, similar to previous studies (Mistry, Philip & Dawson 2019; Kohan & Gaskin 2020), while the distribution of for the jet in the turbulent ambient increasingly deviates from a Gaussian one due to a large skewness. The wide spans of the TNTI and TTI outline radial positions indicate the large-scale spatial fluctuations of , which are increasing with .…”

Section: Resultssupporting

confidence: 87%

“…. As noted in Kohan & Gaskin (2020), intense corrugation of the interface is characterised by , since these interface points radially fold back on themselves (see figure 7 of Kohan & Gaskin 2020). Figure 7( c ) shows the effect of ambient turbulence on the interface angle.…”

Section: Resultsmentioning

confidence: 73%

“…2015). Additional support is provided by Kohan & Gaskin (2020), who by coarse graining their PLIF resolution, show that a resolution of approximately 6 properly captures the conditionally averaged mean and r.m.s. scalar profiles.…”

Section: Methodsmentioning

confidence: 87%

“…The jet and the ambient regions are represented by and , respectively. Following Kohan & Gaskin (2020), we only consider points along with one flow status change (turbulent or ambient), i.e. we ignore points inside the islands and holes and after an intersection with them.…”

Section: Resultsmentioning

confidence: 99%

“…Using this definition, concave (bulges) and convex (valley) surface elements are identified as κ I < 0 and κ I > 0, respectively, when looking from the jet region. In Kohan & Gaskin (2020), it was suggested that the TNTI outline of the orthogonal cross-sections of the jet is dominated by flat concave surface elements (smooth bulges; see figure 1a), while its skewness is towards highly curved concave areas. Figure 7(b) reveals that the most probable curvature for all the background cases is at κ I d ≈ −3.…”

Section: The Tti Geometrymentioning

confidence: 99%

See 4 more Smart Citations

On the scalar turbulent/turbulent interface of axisymmetric jets

Kohan

Gaskin

2022

J. Fluid Mech.

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The effect of a zero-mean-flow turbulent ambient on the geometry of the turbulent/turbulent interface (TTI) of an axisymmetric jet is investigated and compared with the traditional turbulent/non-turbulent interface (TNTI). The ambient turbulence is generated using a random jet array. Orthogonal cross-sections of the jet subjected to different levels of ambient turbulence intensities and length scales are captured using planar laser-induced fluorescence. The enhanced radial transport of concentration from the jet core towards the interface and the increased scalar fluctuations within the jet caused by the ambient turbulence result in steeper mean and root-mean-square scalar conditional jumps across the TTI layer compared with those of the TNTI, respectively. When compared with the quiescent ambient, the mean effect of background turbulence is to stretch and corrugate the interface surface area as evident from the wider probability density of the interface radial position, the lowered occurrence of zero-curvature surface elements, the greater misalignment between the radial and normal unit vectors of the interface, the increased tortuosity and the increased magnitude of the fractal exponent.

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Section: Resultssupporting

confidence: 87%

Section: Resultsmentioning

confidence: 73%

Section: Methodsmentioning

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Section: The Tti Geometrymentioning

confidence: 99%

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On the scalar turbulent/turbulent interface of axisymmetric jets

Kohan

Gaskin

2022

J. Fluid Mech.

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On Low-Scalar Patches in Turbulent Wakes with and Without Free-Stream Turbulence

Kohan,

Buxton,

Gaskin

2024

IUTAM Bookseries

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High-resolution, time-resolved, simultaneous particle image velocimetry and planar laser-induced fluorescence are performed to study the characteristics of the low-scalar ‘holes’ in a planar wake exposed to various cases of background turbulence as parameterized by the turbulence intensity and length scale. Several metrics are employed to distinguish the engulfed holes from those generated internally. It is found that beyond a transition distance of 18 Kolmogorov microscales from the wake boundary, holes exhibit comparable behaviour to the wake core, suggesting their generation by local turbulence. It is further revealed that engulfment constitutes less than 1% of the total mass flux in the far-field, regardless of the strength of incoming turbulence intensity.

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Turbulent/Non-turbulent Interface in Water Jet with Polymer Additives

Xi,

Peng,

Zhang

2024

IUTAM Bookseries

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The effect of polymer additives on the global entrainment of a turbulent round jet was found to show two distinct regimes: the reduction and enhancement regimes in the near and far fields, respectively. Using time-resolved simultaneous particle image velocimetry and laser-induced fluorescence measurements, we hereby present an experimental study on the local entrainment and engulfment process along the turbulent/non-turbulent interface (TNTI). We find that the local entrainment velocity is augmented in both regimes, due to the contribution from polymer elastic stress and a higher probability for TNTI to visit jet centreline region where the entrainment velocity is larger. In the entrainment reduction regime, the fractal dimension and length of TNTI are smaller compared to the Newtonian case; while those in the enhancement regime are nearly not changed. The difference between the two regimes results from the fact the jet flow decays in the streamwise direction. In the near field, the flow is intense enough to substantially stretch polymers, which results in a redistribution of energy among different scales and a steeper decay of energy in the inertial range. However, in the far field, the stretching of the polymer and in turn the feedback of polymers is not strong enough to alter the inertial range scaling of the energy spectrum. Moreover, our study reveals although more ambient fluid is engulfed into the turbulent region due to the augmented large scale motion by polymers, engulfment is still not the major contribution to the entrainment in polymer-laden jet, which is similar to the case in Newtonian jet.

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The effect of the geometric features of the turbulent/non-turbulent interface on the entrainment of a passive scalar into a jet

Abstract: The effect of the geometric features of the turbulent/non-turbulent interface on the entrainment of a passive scalar into a jet

Cited by 26 publications

References 61 publications

On the scalar turbulent/turbulent interface of axisymmetric jets

On the scalar turbulent/turbulent interface of axisymmetric jets

On Low-Scalar Patches in Turbulent Wakes with and Without Free-Stream Turbulence

Turbulent/Non-turbulent Interface in Water Jet with Polymer Additives

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