We report numerical evidence of elastic turbulence phenomenology in a two-dimensional periodic Kolmogorov flow. By direct simulations the Oldroyd-B viscoelastic model at very small Reynolds numbers, we find that above instability threshold flow develops an turbulent regime. observe both drag and Lyapunov exponent increase with Weissenberg number, indicating presence disordered, turbulentlike mixing The energy spectrum power-law scaling range close to experimental theoretical expectations.

We investigate the dynamics of two-dimensional periodic Kolmogorov flow a viscoelastic fluid, described by Oldroyd-B model, means direct numerical simulations. Above critical Weissenberg number displays transition from stationary to randomly fluctuating states, via ones. The increasing complexity in both time and space at progressively higher values elasticity accompanies establishment mixing features. peculiar dynamical behavior observed simulations is found be related appearance filamental...

Abstract In the framework of Monitoring by Ocean Drifters (MONDO) project, a set Lagrangian drifters were released in proximity Brazil Current, western branch subtropical gyre South Atlantic Ocean. The experimental strategy deploying part buoys clusters offers opportunity to examine relative dispersion on wide range scales. Adopting dynamical systems approach, authors focus their attention scale-dependent indicators, like finite-scale Lyapunov exponent (FSLE) and (mean square) velocity...

Swimming at a micrometer scale demands particular strategies. When inertia is negligible compared to viscous forces, hydrodynamics equations are reversible in time. To achieve propulsion, microswimmers must therefore deform way that not invariant under time reversal. Here, we investigate dispersal properties of the microalga Chlamydomonas reinhardtii by means microscopy and cell tracking. We show tracked trajectories well modeled correlated random walk. This process based on short...

The evolution of heat flux through an initially solid pure substance that is heated from below and undergoes both phase-change natural convection studied numerically contrasted with the dynamics Rayleigh-B\'enard system in laminar turbulent regimes.

Ocean flows at scales smaller than few hundreds of kilometers display rich dynamics, mainly associated with quasi- geostrophic motions and internal gravity waves. Although both these processes act on comparable lengthscales, the former, which include meso submesoscale turbulent flows, are considerably slower latter, take part in ocean fast variability. Understanding how their effects overlap is crucial for several fundamental applied questions, including interpretation exploitation new,...

Phase separation between two fluids in two-dimensions is investigated by means of Direct Numerical Simulations coupled Navier-Stokes and Cahn-Hilliard equations. We study the phase ordering process presence an external stirring acting on velocity field. For both active passive mixtures we find that, for a sufficiently strong stirring, coarsening arrested stationary dynamical state characterized continuous rupture formation finite domains. Coarsening arrest shown to be independent chaotic or...

The statistical properties of turbulent fluids depend on how local the energy transfers among scales are, i.e. whether transfer at some given scale is due to eddies that particular scale, or larger (non-local) scale. This locality in may have consequences for relative dispersion passive particles. In this paper, we consider a class generalized two-dimensional flows (produced by so-called $\unicode[STIX]{x1D6FC}$ -turbulence models), theoretically possessing different terms transfers. It...

The small scale statistics of homogeneous isotropic turbulence dilute polymer solutions is investigated by means direct numerical simulations a simplified viscoelastic fluid model. It found that polymers only partially suppress the turbulent cascade below Lumley scale, leaving remnant energy flux even for large elasticity. As consequence, acceleration in flows reduced with respect to Newtonian turbulence, whereas its rescaled probability density left unchanged. At scales velocity field be...

Theoretical and numerical turbulent flow studies either consider turbulence as generated by fluid-solid interactions or focus on intrinsic, bulk properties. There is another group of flows for which homogeneity isotropy are broken the body force that sustains flow, not physical boundaries. In this class we cellular produced a two-dimensional spatially periodic forcing whose laminar state corresponds to regular array counter-rotating vortices. We find that, despite developed recovering...

We report evidence of irregular unsteady flow two-dimensional polymer solutions in the absence inertia cross-slot geometry using numerical simulations Oldroyd-B model. By exploring transition to time-dependent versus both fluid elasticity and concentration, we find periodic behaviour close instability threshold more complex flows at larger elasticity, agreement with experimental findings. For high enough obtain dynamics pointing elastic turbulence, temporal spectra velocity fluctuations...

Upper-ocean turbulent flows at horizontal length scales smaller than the deformation radius depart from geostrophic equilibrium and develop important vertical velocities, which are key to marine ecology climatic processes. Due their small size fast temporal evolution, these fine difficult measure during oceanographic campaigns. Instruments such as Lagrangian drifters have provided another way characterize through analysis of pair-dispersion pointed out striking particle convergence events....

Understanding the conditions ensuring persistence of a population is an issue primary importance in biology. The first theoretical approach to problem dates back 1950s with Kierstead, Slobodkin, and Skellam (KiSS) model, namely continuous reaction-diffusion equation for growing on patch finite size L surrounded by deadly environment infinite mortality, i.e., oasis desert. main outcome model that only patches above critical allow persistence. Here we introduce individual-based analog KiSS...

Turbulence in the upper ocean submesoscale range (scales smaller than deformation radius) plays an important role for heat exchanges with atmosphere and oceanic biogeochemistry. Its dynamics should strongly depend on seasonal cycle associated mixed-layer instabilities. The latter are particularly relevant winter responsible formation of energetic small scales that extend over whole depth mixed layer. knowledge transport properties flows at depth, which is essential to understand coupling...

We numerically investigate the spatial and temporal statistical properties of a dilute polymer solution in elastic turbulence regime, i.e., chaotic flow state occurring at vanishing Reynolds high Weissenberg numbers. aim elucidating relations between measurements performed domain with ones taken domain, which is key point for interpretation experimental results on to discuss validity Taylor's hypothesis. To this end, we carry out extensive direct numerical simulations two-dimensional...

Turbulence has been recognized as a factor of paramount importance for the survival or extinction sinking phytoplankton species. However, dealing with its multiscale nature in models coupled fluid and biological dynamics is formidable challenge. Advection by coherent structures, such those related to winter convection Langmuir circulation, also play role localization phytoplankton. In this work we revisit theoretically appealing model vertical dynamics, numerically investigate how...

An autocatalytic reacting system with particles interacting at a finite distance is studied. We investigate the effects of discrete-particle character model on properties like reaction rate, quenching phenomenon, and front propagation, focusing differences respect to continuous case. introduce renormalized rate depending both interaction radius particle density, we relate it macroscopic observables (e.g., speed thickness) system.

Standard Reaction-Diffusion (RD) systems are characterized by infinite velocities and no persistence in the movement of individuals, two conditions that violated when considering living organisms. Here we consider a discrete particle model which individuals move following persistent random walk with finite speed grow logistic dynamics. We show number is very large, individual-based well described continuous Reactive Cattaneo Equation (RCE), but for smaller values carrying capacity important...

We study the evolution of a reactive field advected by one-dimensional compressible velocity and subject to an ignition-type nonlinearity. In limit small molecular diffusivity problem can be described spatially discretized system, this allows for efficient numerical simulation. If initial profile is supported in region size l < lc one has quenching, i.e., flame extinction, where characteristic length-scale depending on system parameters (reacting time, field). derive expression terms...