Long-range μPIV to resolve the small scales in a jet at high Reynolds number

Fiscaletti, Daniele; Westerweel, J.; Elsinga, Gerrit E.

doi:10.1007/s00348-014-1812-7

Cited by 24 publications

(14 citation statements)

References 71 publications

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“…Regions of intense swirling within a turbulent flow have been shown to be structured in worms [27,41,42] with a typical diameter on the order of 5η-10η and possibly an axial length of up to several Taylor microscales in length [43]. These observations over the scaling of the diameter of the coherent structures of vorticity were confirmed at much larger Reynolds numbers in a recent experimental study [44] and in DNS simulations of homogeneous isotropic turbulence [29].…”

Section: Resultsmentioning

confidence: 63%

Scale dependence of the alignment between strain rate and rotation in turbulent shear flow

et al. 2016

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The scale dependence of the statistical alignment tendencies of the eigenvectors of the strain-rate tensor e i , with the vorticity vector ω, is examined in the self-preserving region of a planar turbulent mixing layer. Data from a direct numerical simulation are filtered at various length scales and the probability density functions of the magnitude of the alignment cosines between the two unit vectors |e i ·ω| are examined. It is observed that the alignment tendencies are insensitive to the concurrent large-scale velocity fluctuations, but are quantitatively affected by the nature of the concurrent large-scale velocity-gradient fluctuations. It is confirmed that the small-scale (local) vorticity vector is preferentially aligned in parallel with the large-scale (background) extensive strain-rate eigenvector e 1 , in contrast to the global tendency for ω to be aligned in parallel with the intermediate strain-rate eigenvector [Hamlington et al., Phys. Fluids 20, 111703 (2008)]. When only data from regions of the flow that exhibit strong swirling are included, the so-called high-enstrophy worms, the alignment tendencies are exaggerated with respect to the global picture. These findings support the notion that the production of enstrophy, responsible for a net cascade of turbulent kinetic energy from large scales to small scales, is driven by vorticity stretching due to the preferential parallel alignment between ω and nonlocal e 1 and that the strongly swirling worms are kinematically significant to this process.

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Section: Resultsmentioning

confidence: 63%

Scale dependence of the alignment between strain rate and rotation in turbulent shear flow

et al. 2016

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“…These structures are strongly correlated with each other in space (e.g. Yeung et al (2012); Fiscaletti et al (2014)) and have strongly non-Gaussian probability density functions (PDFs) (Wilczek & Friedrich 2009;Yeung et al 2012). Their properties are a subject of interest in relation to flame extinction (Sreenivasan & Antonia 1997;Sreenivasan 2004), clustering of particles (Chun et al 2005), cloud formation (Bodenschatz et al 2010) and mixing (Pumir 1994b).…”

Section: Introductionmentioning

confidence: 99%

On the small-scale structure of turbulence and its impact on the pressure field

Vlaykov

Wilczek

2018

J. Fluid Mech.

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Understanding the small-scale structure of incompressible turbulence and its implications for the non-local pressure field is one of the fundamental challenges in fluid mechanics. Intense velocity gradient structures tend to cluster on a range of scales which affects the pressure through a Poisson equation. Here we present a quantitative investigation of the spatial distribution of these structures conditional on their intensity for Taylorbased Reynolds numbers in the range [160, 380]. We find that the correlation length, the second invariant of the velocity gradient, is proportional to the Kolmogorov scale. It also is a good indicator for the spatial localization of intense enstrophy and strain-dominated regions, as well as the separation between them. We describe and quantify the differences in the two-point statistics of these regions and the impact they have on the non-locality of the pressure field as a function of the intensity of the regions. Specifically, across the examined range of Reynolds numbers, the pressure in strong rotation-dominated regions is governed by a dissipation-scale neighbourhood. In strong strain-dominated regions, on the other hand, it is determined primarily by a larger neighbourhood reaching inertial scales.

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“…The reason for the disparity is the azimuthal averaging, which was used when determining the vortex core sizes (e.g. Jimenez et al 1993), the vorticity 44 G. E. Elsinga, T. Ishihara, M. V. Goudar, C. B. da Silva and J. C. R. Hunt auto-correlation map (Fiscaletti, Westerweel & Elsinga 2014) or the conditionally averaged vorticity field (Mui, Dommermuth & Novikov 1996). The vorticity vector defines only a single direction and a perpendicular plane.…”

Section: Dissipationmentioning

confidence: 99%

The scaling of straining motions in homogeneous isotropic turbulence

et al. 2017

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The scaling of turbulent motions is investigated by considering the flow in the eigenframe of the local strain-rate tensor. The flow patterns in this frame of reference are evaluated using existing direct numerical simulations of homogeneous isotropic turbulence over a Reynolds number range from Re λ = 34.6 up to 1131, and also with reference to data for inhomogeneous, anisotropic wall turbulence. The average flow in the eigenframe reveals a shear layer structure containing tube-like vortices and a dissipation sheet, whose dimensions scale with the Kolmogorov length scale, η. The vorticity stretching motions scale with the Taylor length scale, λ T , while the flow outside the shear layer scales with the integral length scale, L. Furthermore, the spatial organization of the vortices and the dissipation sheet defines a characteristic small-scale structure. The overall size of this characteristic small-scale structure is 120η in all directions based on the coherence length of the vorticity. This is considerably larger than the typical size of individual vortices, and reflects the importance of spatial organization at the small scales. Comparing the overall size of the characteristic small-scale structure with the largest flow scales and the vorticity stretching motions on the scale of 4λ T shows that transitions in flow structure occur where Re λ ≈ 45 and 250. Below these respective transitional Reynolds numbers, the small-scale motions and the vorticity stretching motions are progressively less well developed. Scale interactions are examined by decomposing the average shear layer into a local flow, which is induced by the shear layer vorticity, and a non-local flow, which represents the environment of the characteristic small-scale structure. The non-local strain is 4λ T in width and height, which is consistent with observations in high Reynolds number flow of a 4λ T wide instantaneous shear layer with many η-scale vortical structures inside (Ishihara et al., Flow Turbul. Combust., vol. 91, 2013, pp. 895-929). In the average shear layer, vorticity aligns with the intermediate principal strain at small scales, while it aligns with the most stretching principal strain † Email address for correspondence: g.e.elsinga@tudelft.nl ‡ Present address: Graduate School of Environmental and Life Science, Okayama University, Okayama 700-8530, Japan. 32 G. E. Elsinga, T. Ishihara, M. V. Goudar, C. B. da Silva and J. C. R. Hunt at larger scales, consistent with instantaneous turbulence. The length scale at which the alignment changes depends on the Reynolds number. When conditioning the flow in the eigenframe on extreme dissipation, the velocity is strongly affected over large distances. Moreover, the associated peak velocity remains Reynolds number dependent when normalized by the Kolmogorov velocity scale. It signifies that extreme dissipation is not simply a small-scale property, but is associated with large scales at the same time.

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Long-range μPIV to resolve the small scales in a jet at high Reynolds number

Cited by 24 publications

References 71 publications

Scale dependence of the alignment between strain rate and rotation in turbulent shear flow

Scale dependence of the alignment between strain rate and rotation in turbulent shear flow

On the small-scale structure of turbulence and its impact on the pressure field

The scaling of straining motions in homogeneous isotropic turbulence

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