10:30
Intermittency and scaling 3
Chair: Carlos da Silva
10:30
15 mins
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Influence of internal intermittency on drop breakage and coalescence in turbulent liquid-liquid dispersion
Wioletta Podgorska
Abstract: Break-up and coalescence of droplets in stirred dispersion is considered and the influence of highly intermittent nature of turbulence on scale-up is discussed. Drop breakup occurs when disruptive stresses overcome the stabilizing ones. Three different situations are taken into account: (a) pure liquid-liquid system with dispersed phase of low viscosity in which the only disruptive stress is due to pressure fluctuations and stabilizing stress is due to interfacial tension, (b) pure system with dispersed phase of high viscosity in which viscous stress generated within the drop increases stabilizing effect, (c) system with surfactant and additional disruptive stress. In all cases internal intermittency causes faster breakage in larger scale when average energy dissipation rate in the tank is maintained. Additionally, for system (a) coalescence was taken into account. In this system drop interfaces are partially mobile and coalescence is faster in larger scale due to intermittency.
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10:45
15 mins
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INTERMITTENCY IN ELASTIC WAVE TURBULENCE
Sergio Chibbaro, Christophe Josserand
Abstract: We study numerically the long-time evolution of waves of a thin elastic plate for different energy input. In particular, we focus on the possible existence of intermittency, intended mainly as highly non-gaussian features. We show that deviations from the Kolmogorov- Zakharov scenario are present in high-order structure functions of the deplacement. This is more pronounced for higher- energy input even though the limit of small deformation so that modes of oscillations interact weakly is globally kept valid.
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11:00
15 mins
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Stochastic simulation of non-stationary continuous multifractal time series
Francois G Schmitt, Yongxiang Huang
Abstract: Intermittency is an ubiquitous property of fully developed turbulence, for Eulerian and Lagrangian fields, and for velocity, passive and
active scalars. Intermittency corresponds to multi-scale high fluctuations, with some underlying long-range correlations. Such property
is usually characterized using scaling approaches, verified using experimental or numerical data. However there are only
few studies devoted to the generation of continuous stochastic processes having non-stationary multifractal properties,
able to mimic Eulerian or Lagrangian velocity or passive scalar time series. Here we review recent works on this topic, and
we provide stochastic simulations in order to verify the theoretical predictions. In the lognormal framework we provide a $h-\mu$ plane
expressing the scale invariant properties of these simulations.
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11:15
15 mins
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MARKOV CLOSURE FOR THE LUNDGREN-MONIN-NOVIKOV HIERARCHY OF VELOCITY INCREMENTS IN BURGERS TURBULENCE
Jan Friedrich, Rainer Grauer
Abstract: A central, yet unsolved issue in the longstanding problem of hydrodynamic turbulence is the closure problem of turbulence,
which is due to the nonlinear character of the Navier-Stokes equation. We formulate the closure problem for the many-increment
probability distributions (PDF’s) in Burgers turbulence and introduce a new method for closing the hierarchy. To this end, we rely
on the experimentally and numerically verified assumption in [1] that the turbulent cascade possesses a Markov property in scale
down to the so-called Einstein-Markov length. The hierarchy is closed at the stage of the two-increment PDF corresponding to a
three-point closure that allows for a description of intermittency effects, not captured by other closure approximations, i.e. Gaussian
closures etc. The proposed closure also opens up a possible way to a perturbative treatment of the Navier-Stokes equation beyond the
Einstein-Markov length in successively taking into account a larger and larger scale “history” of the system.
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11:30
15 mins
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Real-space Manifestations of Bottlenecks in Turbulence Spectra,
Uriel Frisch, Samriddhi Sankar Ray, Ganapati Sahoo, Debarghya Banerjee, Rahul Pandit
Abstract: An energy-spectrum bottleneck, a bump in the turbulence spectrum
between the inertial and dissipation ranges, is shown to occur in
the non-turbulent, one-dimensional, hyperviscous
Burgers equation and found to be the Fourier-space signature of
oscillations in the real-space velocity, which are explained by
boundary-layer-expansion techniques. Pseudospectral simulations are
used to show that such oscillations occur in velocity correlation
functions in one- and three-dimensional hyperviscous hydrodynamical
equations that display genuine turbulence.
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11:45
15 mins
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Dissipative Range Scaling of Higher Order Structure Functions for Velocity and Passive Scalars
Michael Gauding, Jonas Boschung, Christian Hasse, Norbert Peters
Abstract: Differently to Kolmogorov's second similarity hypothesis, we find
that the 2n-th order velocity and scalar structure functions scale
with n-th order moment of the energy dissipation and the scalar dissipation, respectively. The
origins of this scaling are analyzed by the transport equations of
the fourth order velocity and scalar increment moments and by direct
numerical simulations.
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