10:30
Vortex Dynamics 3
Chair: Jean-Marc Foucaut
10:30
15 mins
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FINE SCALE EDDIES IN TURBULENT TAYLOR-COUETTE FLOW UP TO RE = 25 000
Kosuke Osawa, Yoshitsugu Naka, Naoya Fukushima, Masayasu Shimura, Mamoru Tanahashi
Abstract: Reynolds number effects on fine scale eddies in the turbulent Taylor-Couette flow have been investigated by high accuracy direct numerical simulations from Re = 8000 to 25 000. The Reynolds number dependency of the mean torque changes near Re = 10 000, and the transition is closely linked to the turbulence characteristics. As the Reynolds number increases, the fine scale eddies are more densely populated and take more various tilting angles. The joint probability density function of the tilting angle and the radial position exhibits a preferential pattern corresponding to the large scale motion of Taylor vortices. The present results suggest that in this Reynolds number range, the fine scale eddies progressively prevail a large part of the domain, and their contribution to the fundamental statistics such as the Reynolds shear stress becomes more evident.
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10:45
15 mins
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A numerical analysis of detailed energy transfers in elastic-wave turbulence
Naoto Yokoyama, Masanori Takaoka
Abstract: Triad interaction functions in elastic-wave turbulence are numerically investigated to show detailed energy transfers due to nonlinear interactions among wavenumbers. The energy exchange is active between the small-wavenumber stretching energy and the large-wavenumber kinetic energy. It is indicated that these nonlocal interactions carry the energy from the small-wavenumber forcing range to the large-wavenumber dissipation range.
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11:00
15 mins
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Spatial structures of energy transfers in elastic wave turbulence
Masanori TAKAOKA, Naoto YOKOYAMA
Abstract: Spatial structures of energy transfers in both the real and Fourier spaces
are investigated by simulating the F\"{o}ppl-von K\'{a}rm\'{a}n (FvK) equation.
Distinctive structures of the stretching-energy field,
which is the bundle of ridges in the real space
and the line segment at small wavenumbers in the Fourier space,
appear in the active phases of turbulent state.
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11:15
15 mins
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Effect of confinement on the decay of vortex ring
Sooraj R, Sameen A
Abstract: The effect of confinement on the decay of vortex ring is studied computationally using Lattice Boltzmann Method. An Initial vortex ring, introduced inside a wall bounded cubical domain, is let to evolve and its decay is noted in terms of maximum vorticity at the core and the total kinetic energy inside the domain. The study shows distinct regimes of decay in all cases of confinement ratios(ratio of vortex ring diameter to length of the cubical domain).
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11:30
15 mins
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SCALE INTERACTION IN A MIXING LAYER. THE ROLE OF THE LARGE-SCALE GRADIENTS.
Daniele Fiscaletti, Antonio Attili, Fabrizio Bisetti, Gerrit Elsinga
Abstract: The interaction between scales is investigated in a turbulent mixing layer. The large-scale amplitude modulation of the small scales already observed in other works depends on the crosswise location. Large-scale positive fluctuations correlate with a stronger activity of the small scales on the low speed-side of the mixing layer, and a reduced activity on the high speed-side. However, from physical considerations we would expect the scales to interact in a qualitatively similar way within the flow and across different turbulent flows. Therefore, instead of the large-scale fluctuations, the large-scale gradients modulation of the small scales has been additionally investigated.
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11:45
15 mins
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Measurements of small radius ratio turbulent Taylor-Couette flow
Roeland van der Veen, Sander Huisman, Sebastian Merbold, Chao Sun, Uwe Harlander, Chirstoph Egbers, Detlef Lohse
Abstract: In Taylor-Couette flow, the radius ratio ($\eta = r_i/r_o$) is one of the key parameters of the system. For small $\eta$, the asymmetry of the inner and outer boundary layer becomes more important, affecting the general flow structure and boundary layer characteristics. Using high-resolution particle image velocimetry we measure flow profiles for a radius ratio of 0.5 and Taylor number of up to $6.2\cdot10^9$. By measuring at varying heights, roll structures are characterized for two different rotation ratios of the inner and outer cylinder. In addition, we investigate how the turbulent bursts coming from the inner and outer cylinder affect the flow profiles. These results exemplify how curvature affects flow in strongly turbulent Taylor-Couette Flow.
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12:00
15 mins
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Predicting growth rates of interfaces and internal layers in a turbulent boundary layer using a first order jump model
Jerke Eisma, Jerry Westerweel, Gerrit E. Elsinga
Abstract: Experimental research is presented on the characteristics of interfaces and internal layers that are present in a turbulent boundary layer (TBL). Both the turbulent non-turbulent interface (T/NT) and internal shear layers are detected in snapshots of the stereo-PIV data. It turns out that the internal layers exhibit similar characteristics compared to the T/NT interface. A theoretical approximation of the large scale boundary layer growth indicates that the correct boundary layer growth can be obtained by employing a modified first order jump model on the conditional statistics. Employing the same framework to the internal shear layers indicates that shear layers tend to move slower in close proximity to the wall, whereas they accelerate when moving away from the wall. Based on previous research it is believed that these internal layers separate large regions of approximately uniform momentum. Hence, boundary entrainment velocities may be interpreted as growth rates of large scale motions in a TBL.
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