Monthly Archives: January 2022

Paper published on J. Fluid Mech.

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“INFLUENCE OF REYNOLDS NUMBER ON THE DYNAMICS OF RIGID, SLENDER AND NON-AXISYMMETRIC FIBRES IN CHANNEL FLOW TURBULENCE”
Experiments are performed in the TU Wien Turbulent Water Channel for three values of shear Reynolds number, namely 180, 360 and 720. The paper is open access and available here. This article follows our previous work on the reconstruction and tracking on anisotropic particles in channel flow turbulence.

In this work, we investigate experimentally the dynamics of non-axisymmetric fibres in channel flow turbulence, focusing specifically on the importance of the fibres size relative to the flow scales. To this aim, we maintain the same physical size of the fibres and we increase the shear Reynolds number. Experiments are performed in the TU Wien Turbulent Water Channel for three values of shear Reynolds number, namely 180, 360 and 720. 

Fibres are slender – length to diameter ratio of 120 -, rigid, curved and neutrally buoyant particles and their shape ranges from low curvature – almost straight fibres – to moderate curvature. In all cases, fibres size remains small compared to the channel height (1.5%). Three-dimensional and time-resolved recordings of the laser-illuminated measurement region are obtained from four high-speed cameras and used to infer fibres dynamics. With the aid of multiplicative algebraic reconstruction techniques, fibres position, orientation, velocity and rotation rates are determined. Our measurements span over half channel height, from wall to center, and allow a complete characterization of the fibres dynamics in all the regions of the flow. Specifically, we measure fibre preferential distribution and orientation. We observe that the fibres dynamics is always influenced by their curvature. Through a comparison between measurements of near-wall dynamics of fibres and near-wall dynamics of flow, we identify a causal relationship between fibre velocity and orientation, and the near-wall turbulence dynamics. Finally, we have been able to provide original measurements of the tumbling rate of the fibres, for which we report the influence of fibres curvature. We underline that our measurements confirm previous findings obtained in numerical and experimental works.

Summer School on Porous Media

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Udine, JULY 11, 2022 to JULY 15, 2022

26TH CISM-IUTAM INTERNATIONAL SUMMER SCHOOL ON “CONVECTION AND DEFORMATION IN POROUS MEDIA: GEOPHYSICAL AND BIOLOGICAL FLOWS”

This course is organised at CISM (Udine, Italy) and coordinated by Prof. Chris. MacMinn (University of Oxford) and me. All the details about the course are available here. You can download the flyer here.

Flow and transport in porous media are relevant for many geophysical, industrial, and biological applications, including carbon sequestration, glacial drainage, papermaking, transport across vascular walls, and bacteria motility. Predicting the evolution of these systems is difficult because of the interplay between different physical features, such as complex flow patterns, convection and reaction, and transformation of the porous matrix through deformation and phase change. In addition, flow and transport in porous media are governed by physical processes that span a wide range of length and time scales. Rapidly increasing computational power has recently enabled threedimensional, high-resolution and time-dependent simulations of these flows at both the pore-scale and the Darcy-scale, producing an entire branch of flourishing research into multiphase flow in porous media. Experimental progress has also been substantial, thanks to improved measurement techniques inboth 2D and 3D. Therefore, it is now useful to review the many studies on the subject to provide an overview of the current state of the art, and to put future research paths in perspective.
This course will provide an overview of the most up-to-date modelling approaches, numerical simulations, and experimental methods used to study the dynamics and properties of porous media flows characterized by convection and deformation.

Schematic representation of CO2 dissolution in saline aquifers

Fundamentals of transport in porous media will be presented, including upscaling techniques, thermodynamics of two-phase mixtures, Lagrangian interpretations, fractional diffusion, non-locality and memory.

Time-dependent evolution of convection-driven flows in different configurations will be analyzed, with reference to geophysical and industrial applications and with particular attention to the dynamics and structures of convection, effect of porous media properties on convection and transition from 2D to 3D convection. An overview of experimental and numerical techniques for convective flows in porous media will be presented and reviewed.

Principles of the coupling between flow, transport, and deformation in porous media will be presented. The small-deformation limit and classical linear poroelasticity will be discussed in the context of subsurface flows. Large-deformation poromechanics will be discussed in the context of polymeric hydrogels (including swelling and drying phenomena), paper-pulp suspensions (including viscoelasticity and plasticity), and granular media (including friction and rearrangement).
The implications of deformation for the dispersion and mixing of solutes will be considered. Two-phase flows will be considered, including capillary and wettability effects. Phase-field approaches will be introduced in the context of multiphase solidification problems (including ice, methane clathrates, and lava) and applied to the growth and migration of gas bubbles in soft porous media.

The course is addressed to graduate students and researchers in applied mathematics, physics and chemical/mechanical engineering.
The advanced topics and the presentation of current progress in this very active field will also be of considerable interest to senior researchers and industrial practitioners having a strong interest in understanding the multiscale complex behavior of such multiphase flows.

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