Appearance and alignment with strain rate of coherent fine scale eddies in turbulent mixing layer

Tanahashi, Mamoru; Iwase, Shiki; Miyauchi, Toshio

doi:10.1088/1468-5248/2/1/006

Cited by 63 publications

(50 citation statements)

References 26 publications

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“…The inner dimension of vortex clusters in figure 6(d) is r 1 ≈ 6η, independently of the cluster volume, which approximately agrees with the diameter of individual filamentary vortices in turbulence (Jiménez & Wray 1998;Tanahashi, Iwase & Miyauchi 2001;del Álamo et al 2006;Pirozzoli, Bernardini & Grasso 2008;Stanislas, Perret & Foucaut 2008). It is also consistent with the description of vortex clusters as 'sponges of strings' (LFJ12).…”

Section: Flow Anisotropysupporting

confidence: 82%

Coherent structures in statistically stationary homogeneous shear turbulence

et al. 2017

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The three-dimensional vortex clusters, and the structures based on the quadrant classification of the intense tangential Reynolds stress (Qs), are studied in direct numerical simulations of statistically stationary homogeneous shear turbulence (HST) at Taylor microscale Reynolds number Re λ ≈ 50-250, with emphasis on comparisons with turbulent channels (CHs). The Qs and vortex clusters in HST are found to be versions of the corresponding detached (in the sense of del Álamo et al. (J. Fluid Mech., vol. 561 (2006), pp. 329-358)) structures in CHs, although statistically symmetrised with respect to the substitution of sweeps by ejections and vice versa. In turn, these are more symmetric versions of the corresponding attached Qs and clusters. In both flows, only co-gradient sweeps and ejections larger than the local Corrsin scale are found to couple with the shear. They are oriented anisotropically, and are responsible for carrying most of the total Reynolds stress. Most large eddies in CHs are attached to the wall, but it is shown that this is probably a geometric consequence of their size, rather than the reason for their dynamical significance. Most small Q structures associated with different quadrants are far from each other in comparison to their size, but those that are close to each other tend to form quasi-streamwise trains of groups of a sweep and an ejection paired side by side in the spanwise direction, with a vortex cluster in between, generalising to three dimensions the corresponding arrangement of attached eddies in CHs. These pairs are organised around an inclined large-scale conditional vortex 'roller', and it is shown that the composite structure tends to be located at the interface between high-and low-velocity streaks, as well as in strong 'co-gradient' shear layers that separate streaks of either sign in which velocity is more uniform. It is further found that the conditional rollers are terminated by 'hooks' reminiscent of hairpins, both upright and inverted. The inverted hook weakens as the structures approach the wall, while the upright one changes little. At the same time, the inclination of the roller with respect to the mean velocity decreases from 45 • in HST to quasi-streamwise for † Email address for correspondence: jimenez@torroja.

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Section: Flow Anisotropysupporting

confidence: 82%

Coherent structures in statistically stationary homogeneous shear turbulence

et al. 2017

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“…The preponderance of the vorticity vector to be aligned with the intermediate strainrate eigenvector was first observed by Ashurst et al (1987) and subsequently confirmed by several other studies (e.g. Tsinober et al 1992;Tanahashi, Iwase & Miyauchi 2001;Mullin & Dahm 2006). Jiménez (1992) offers an explanation for this by using a twodimensional argument.…”

Section: Introductionsupporting

confidence: 58%

Amplification of enstrophy in the far field of an axisymmetric turbulent jet

Buxton

Ganapathisubramani

2010

J. Fluid Mech.

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The amplification of enstrophy is explored using cinematographic stereoscopic particle image velocimetry data. The enstrophy production rate is investigated by observation of the statistical tendency of the vorticity vector (ω) to align with the eigenvectors of the rate of strain tensor (e i ). Previous studies have shown that ω preferentially aligns with the intermediate strain-rate eigenvector (e 2 ) and is arbitrarily aligned with the extensive strain-rate eigenvector (e 1 ). This study shows, however, that the nature of enstrophy amplification, whether it is positive (enstrophy production) or negative (enstrophy destruction), is dictated by the alignment between ω and e 1 . Parallel alignment leads to enstrophy production (ω i S ij ω j > 0), whereas perpendicular alignment leads to enstrophy destruction (ω i S ij ω j < 0). In this way, the arbitrary alignment between ω and e 1 is the summation of the effects of enstrophy producing and enstrophy destroying regions. The structure of enstrophy production is also examined with regards to the intermediate strain-rate eigenvalue, s 2 . Enstrophy producing regions are found to be topologically 'sheet-forming', due to an extensive (positive) value of s 2 in these regions, whereas enstrophy destroying regions are found to be 'spotty'. Strong enstrophy producing regions are observed to occur in areas of strong local swirling as well as in highly dissipative regions. Instantaneous visualizations, produced from the volume of data created by Taylor's hypothesis, reveal that these 'sheet-like' strong enstrophy producing regions encompass the high enstrophy, strongly swirling 'worms'. These 'worms' induce high local strain fields leading to the formation of dissipation 'sheets', thereby revealing enstrophy production to be a complex interaction between rotation and strain -the skew-symmetric and symmetric components of the velocity gradient tensor, respectively.

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“…The distribution of entropy term is determined by the energy dissipation rate in the area where the heat release rate is very small. Fine scale eddies are closely related to the entropy term, because turbulent energy dissipation rate is very high around fine scale eddies (12), (13) . The fine scale eddies are also closely related with the Reynolds stress term (10) .…”

Section: Journal Of Thermal Science and Technologymentioning

confidence: 99%

Large-Scale Vortical Motion and Pressure Fluctuation in Noise-Controlled, Swirl-Stabilized Combustor

Shimura

Tanahashi

Choi

et al. 2009

JTST

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To clarify the mechanisms of combustion oscillation, combustion noise and their suppression by secondary fuel injection, simultaneous measurements of stereoscopic particle image velocimetry (SPIV) and pressure fluctuation in combustion chamber were conducted on several planes of a swirl-stabilized turbulent premixed flame for no control case and noise-controlled case by continuous secondary fuel injection. Velocities measured by SPIV were averaged in 8 phases of the pressure fluctuation and streamlines were obtained from the phase-averaged velocities. For no control case, large-scale vortical structures are generated in regions around the axial centerline of the combustor and outer edge of the swirl nozzle in the phase of low pressure. With increasing pressure, they move near the contour surface of mean progress variablec = 0.5 which have been obtained in the previous study. These large-scale vortical motions induce fluctuation of flame front and enhance entropy term in the acoustic sound source. The secondary fuel injection suppresses the velocity fluctuation in the inner recirculation zone, resulting in reduction of combustion noise. These results show that control of the large-scale vortical motion is important for reduction of combustion noise.

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Appearance and alignment with strain rate of coherent fine scale eddies in turbulent mixing layer

Cited by 63 publications

References 26 publications

Coherent structures in statistically stationary homogeneous shear turbulence

Coherent structures in statistically stationary homogeneous shear turbulence

Amplification of enstrophy in the far field of an axisymmetric turbulent jet

Large-Scale Vortical Motion and Pressure Fluctuation in Noise-Controlled, Swirl-Stabilized Combustor

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