arXiv subjects

P. J. Cobelli

Publications and source records attributed to P. J. Cobelli.

6 recordsLinked to original sources

arXiv2024

Effect of local flow geometry on particle pair dispersion angle

We combine experiments in a von Kármán flow with numerical simulations of Taylor-Green and homogeneous and isotropic turbulence to study the effect of the local flow geometry on particle pair dispersion. To characterize particle dispersion we use the pair dispersion angle, defined as the angle between the relative position and relative velocity of particle pairs. This angle was recently introduced as a means to more effectively identify the different dispersion regimes in finite-Reynolds-number flows. Our results show that, at a global scale, all flows considered show similar dispersion properties in terms of this metric, characterized by ballistic, super-diffusive, and diffusive regimes. Locally, however, these systems exhibit distinct behaviors, with anisotropies and local geometric features significantly influencing dispersion in both the von Kármán and Taylor-Green flows.

physics.flu-dyn↗

arXiv2024

Conformal invariance in out-of-equilibrium Bose-Einstein condensates governed by the Gross-Pitaevskii Equation

We study density isolines in quantum turbulence under the Schramm-Loewner framework using direct numerical simulations of the truncated Gross-Pitaevskii equation, in both spherical and cylindrical traps with three-dimensional dynamics. Density isolines develop increasing complexity as turbulence matures. As the systems evolves towards a thermalized regime, it spontaneously develops conformal invariance. In contrast to other systems exhibiting conformal invariance, this system manifests it during the transition towards disorder rather than to self-organization. We discuss a link between this behavior in quantum turbulence and other 4-wave interacting systems.

cond-mat.quant-gas↗

arXiv2024

Conformal invariance in water-wave turbulence

We experimentally investigate the statistics of zero-height isolines in gravity wave turbulence as physical candidates for conformal invariant curves. We present direct evidence that they can be described by the family of conformal invariant curves called stochastic Schramm-Löwner evolution (or SLE$_κ$), with diffusivity $κ= 2.88(8)$. A higher nonlinearity in the height fields is shown to destroy this symmetry, though scale invariance is retained.

physics.flu-dyn↗

arXiv2015

The spatio-temporal spectrum of turbulent flows

Identification and extraction of vortical structures and of waves in a disorganised flow is a mayor challenge in the study of turbulence. We present a study of the spatio-temporal behavior of turbulent flows in the presence of different restitutive forces. We show how to compute and analyse the spatio-temporal spectrum from data stemming from numerical simulations and from laboratory experiments. Four cases are considered: homogeneous and isotropic turbulence, rotating turbulence, stratified turbulence, and water wave turbulence. For homogeneous and isotropic turbulence, the spectrum allows identification of sweeping by the large scale flow. For rotating and for stratified turbulence, the spectrum allows identification of the waves, precise quantification of the energy in the waves and in the turbulent eddies, and identification of physical mechanisms such as Doppler shift and wave absorption in critical layers. Finally, in water wave turbulence the spectrum shows a transition from gravity-capillary waves to bound waves as the amplitude of the forcing is increased.

physics.flu-dyn↗

arXiv2014

Wave turbulence in shallow water models

We study wave turbulence in shallow water flows in numerical simulations using two different approximations: the shallow water model, and the Boussinesq model with weak dispersion. The equations for both models were solved using periodic grids with up to $2048^2$ points. In all simulations, the Froude number varies between $0.015$ and $0.05$, while the Reynolds number and level of dispersion are varied in a broader range to span different regimes. In all cases, most of the energy in the system remains in the waves, even after integrating the system for very long times. For shallow flows, non-linear waves are non-dispersive and the spectrum of potential energy is compatible with $\sim k^{-2}$ scaling. For deeper (Boussinesq) flows, the non-linear dispersion relation as directly measured from the wave and frequency spectrum (calculated independently) shows signatures of dispersion, and the spectrum of potential energy is compatible with predictions of weak turbulence theory, $\sim k^{-4/3}$. In this latter case, the non-linear dispersion relation differs from the linear one and has two branches, which we explain with a simple qualitative argument. Finally, we study probability density functions of the surface height and find that in all cases the distributions are asymmetric. The probability density function can be approximated by a skewed normal distribution as well as by a Tayfun distribution.

physics.flu-dyn↗

arXiv2014

Quantification of the strength of inertial waves in a rotating turbulent flow

We quantify the strength of the waves and their impact on the energy cascade in rotating turbulence by studying the wave number and frequency energy spectrum, and the time correlation functions of individual Fourier modes in numerical simulations in three dimensions in periodic boxes. From the spectrum, we find that a significant fraction of the energy is concentrated in modes with wave frequency $ω\approx 0$, even when the external forcing injects no energy directly into these modes. However, for modes for which the period of the inertial waves $τ_ω$ is faster than the turnover time $τ_\textrm{NL}$, a significant fraction of the remaining energy is concentrated in the modes that satisfy the dispersion relation of the waves. No evidence of accumulation of energy in the modes with $τ_ω= τ_\textrm{NL}$ is observed, unlike what critical balance arguments predict. From the time correlation functions, we find that for modes with $τ_ω< τ_\textrm{sw}$ (with $τ_\textrm{sw}$ the sweeping time) the dominant decorrelation time is the wave period, and that these modes also show a slower modulation on the timescale $τ_\textrm{NL}$ as assumed in wave turbulence theories. The rest of the modes are decorrelated with the sweeping time, including the very energetic modes modes with $ω\approx 0$.

physics.flu-dyn↗