arXiv subjects

Ianto Cannon

Publications and source records attributed to Ianto Cannon.

7 recordsLinked to original sources

arXiv2026

Stretching by outer eddies sets the turbulent breakup rate of drops and bubbles

Fragmentation of drops and bubbles in turbulence controls interfacial area generation, mixing, and transport in environmental and engineering flows. The nonlinear coupling between interfacial and hydrodynamic stresses has long prevented predictive modeling, a challenge we here overcome by decomposing the flow into outer and inner regions. We show that breakup is driven by isolated events of extreme interfacial stretching caused by the non-local action of the outer field. For breakup to occur, extreme events must inject energy faster than the interface can dissipate it through the formation of inner eddies. Leveraging the separation between inner and outer processes, we derive an analytical model that quantitatively predicts breakup statistics. Our results establish a direct, causal link between turbulent intermittency and the memoryless nature of breakup, providing a first-principles framework for turbulent fragmentation that can be generalized to complex fluids.

physics.flu-dyn↗

arXiv2024

Spheres and fibres in turbulent flows at various Reynolds numbers

We perform fully coupled numerical simulations using immersed boundary methods of finite-size spheres and fibres suspended in a turbulent flow for a range of Taylor Reynolds numbers $12.8<Re_λ<442$ and solid mass fractions $0\leq M\leq1$. Both spheres and fibres reduce the turbulence intensity with respect to the single-phase flow at all Reynolds numbers, with fibres causing a more significant reduction than the spheres. The particles' effect on the anomalous dissipation tends to vanish as $Re \to \infty$. A scale-by-scale analysis shows that both particle shapes provide a "spectral shortcut" to the flow, but the shortcut extends further into the dissipative range in the case of fibres. Multifractal spectra of the near-particle dissipation show that spheres enhance dissipation in two-dimensional sheets, and fibres enhance the dissipation in structures with a dimension greater than one and less than two. In addition, we show that spheres suppress vortical flow structures, whereas fibres produce structures which completely overcome the turbulent vortex stretching behaviour in their vicinity.

physics.flu-dyn↗

arXiv2024

Morphology of clean and surfactant-laden droplets in homogeneous isotropic turbulence

We perform direct numerical simulations of surfactant-laden droplets in homogeneous isotropic turbulence with Taylor Reynolds number of 180. The droplets are modelled using the volume of fluid method, and the soluble surfactant is transported using an advection-diffusion equation. Effects of surfactant on the droplet and local flow statistics are well approximated using a lower, averaged value of surface tension, allowing us to extend the framework developed by Hinze (1955) and Kolmogorov (1949) for surfactant-free bubbles. The Kolmogorov-Hinze scale $d_H$ is indeed found to be a pivotal length scale in the droplets' dynamics, separating the coalescence-dominated (droplets smaller than $d_H$) and the breakage-dominated (droplets larger than $d_H$) regimes in the droplet size distribution. We find that droplets smaller than $d_H$ have compact, regular, spheroid-like shapes, whereas droplets larger than $d_H$ have long, convoluted, filamentous shapes with a diameter equal to $d_H$. This results in two different scaling laws for the interfacial area of the droplet. The normalised area, $A/d_H^2$, of droplets smaller than $d_H$ is proportional to $d^2$, while the area of droplets larger than $d_H$ is proportional to $d^3$, where $d$ is the droplet size. We further characterise the large filamentous droplets by computing the number of handles (loops of the dispersed phase extending into the carrier phase) and voids (regions of the carrier fluid entirely enclosed by the dispersed phase) on each droplet. The number of handles per unit length of filament scales inversely with surface tension. The number of voids is proportional to the droplet size and independent of surface tension. Handles are indeed an unstable feature of the interface and are destroyed by the restoring effect of surface tension, whereas voids can move freely in the interior of the droplets, unaffected by surface tension.

physics.flu-dyn↗

arXiv2023

Anisotropic mean flow enhancement and anomalous transport of finite-size spherical particles in turbulent flows

We investigate the influence of dispersed solid spherical particles on the largest scales of the turbulent Arnold-Beltrami-Childress (ABC) flow. The ABC flow is an ideal instance of a complex flow: it does not have solid boundaries, but possesses an inhomogeneous and three-dimensional mean shear. By tuning the parameters of the suspension, we show that particles deviate towards quasi-straight trajectories and exhibit anomalous transport. In doing this, they enhance the mean-flow energy and modulate the largest scales of the flow towards an anisotropic and quasi two-dimensional state.

physics.flu-dyn↗

arXiv2023

Scaling and intermittency in turbulent flows of elastoviscoplastic fluids

Non-Newtonian fluids have a viscosity that varies with applied stress. Elastoviscoplastic fluids, the elastic, viscous and plastic properties of which are interconnected in a non-trivial way, belong to this category. We have performed numerical simulations to investigate turbulence in elastoviscoplastic fluids at very high Reynolds-number values, as found in landslides and lava flows, focusing on the effect of plasticity. We find that the range of active scales in the energy spectrum reduces when increasing the fluid plasticity; when plastic effects dominate, a new scaling range emerges between the inertial range and the dissipative scales. An extended self-similarity analysis of the structure functions reveals that intermittency is present and grows with the fluid plasticity. The enhanced intermittency is caused by the non-Newtonian dissipation rate, which also exhibits an intermittent behaviour. These findings have relevance to catastrophic events in natural flows, such as landslides and lava flows, where the enhanced intermittency results in stronger extreme events, which are thus more destructive and difficult to predict.

physics.flu-dyn↗

arXiv2022

The effect of particle anisotropy on the modulation of turbulent flows

We investigate the modulation of turbulence caused by the presence of finite-size dispersed particles. Bluff (isotropic) spheres vs slender (anisotropic) fibers are considered to understand the influence of the object shape on altering the carrier flow. While at a fixed mass fraction - but different Stokes number - both objects provide a similar bulk effect characterized by a large-scale energy depletion, a scale-by-scale analysis of the energy transfer reveals that the alteration of the whole spectrum is intrinsically different. For bluff objects, the classical energy cascade is shrinked in its extension but unaltered in the energy content and its typical features, while for slender ones we find an alternative energy flux which is essentially mediated by the fluid-solid coupling.

physics.flu-dyn↗

arXiv2021

The effect of droplet coalescence on drag in turbulent channel flows

We study the effect of droplet coalescence on turbulent wall-bounded flows, by means of direct numerical simulations. In particular, the volume-of-fluid and front-tracking methods are used to simulate turbulent channel flows containing coalescing and non-coalescing droplets, respectively. We find that coalescing droplets have a negligible effect on the drag, whereas the non-coalescing ones steadily increase drag as the volume fraction of the dispersed phase increases: indeed, at 10\% volume fraction, the non-coalescing droplets show a 30\% increase in drag, whereas the coalescing droplets show less than 4\% increase. We explain this by looking at the wall-normal location of droplets in the channel and show that non-coalescing droplets enter the viscous sublayer, generating an interfacial shear stress which reduces the budget for viscous stress in the channel. On the other hand, coalescing droplets migrate towards the bulk of the channel forming large aggregates, which hardly affect the viscous shear stress while damping the Reynolds shear stress. We prove this by relating the mean viscous shear stress integrated in the wall-normal direction to the centreline velocity.

physics.flu-dyn↗