Ian Eames

The energy partition and impact force of viscoelastic Phan–Thien–Tanner (PTT) droplets on solid surfaces are investigated numerically across two decades of Weissenberg and Weber numbers and dynamic contact angles spanning hydrophilic to hydrophobic wetting. Simulations use xanthan-gum solutions at three polymer concentrations and the Kistler dynamic contact-angle model. Viscous dissipation overwhelmingly dominates the energy budget, with elastic energy storage well below 1 % (instantaneous maximum ≈0.06%), extending the Newtonian half-rule for kinetic-energy partitioning to the viscoelastic regime. The inertia-driven first peak force is essentially independent of surface wettability, whereas the retraction-driven second peak force appears only on neutral or hydrophobic surfaces and below a critical elasticity number of approximately 50. We introduce an effective Reynolds number built on the rate-dependent PTT shear viscosity evaluated at the impact shear rate. Plotted against this effective Reynolds number, the first peak forces from all three fluids and three wettabilities collapse onto a single master curve with an inertial plateau, a shear-thinning viscous correction, and a capillary correction in the Weber number. Replacing the Ohnesorge number by its effective counterpart recovers one-to-one agreement with the recent Newtonian energy-budget theory. The second peak force follows an empirical power law in the effective Reynolds number that approaches the Newtonian asymptote at high values but is not universal across fluids (per-fluid R2 ≈ 0.2 for the weakest solution near the existence boundary), reflecting the sensitivity of the retraction-driven Worthington jet to interface topology. Together these results provide a physics-informed prediction framework for the peak impact forces of viscoelastic drops.

This paper presents a theoretical and computational investigation into how a propagating three-dimensional vortex modifies ambient turbulence. Using rapid distortion theory and numerical simulations, the study explores both local and non-local changes in the external vorticity field resulting from fluid displacement and stretching. Cases involving structured and unstructured turbulence reveal that the vortex introduces permanent distortions along its path, and alters the far field turbulence through reflux effects. The findings extend classical models by quantifying the impact of vortex-induced strain and displacement on turbulence, offering new insights into turbulent–turbulent interfaces and the role of coherent structures in modulating external turbulent fields.

Hospital operating theatre suites are a particularly resource- and energy-intensive component of the health sector. Reducing their carbon footprint presents a significant challenge due to the necessity of maintaining patient safety. In this paper, we apply a multidisciplinary methodology to investigate and assess various strategies aimed at reducing the carbon footprint in hospital theatres. The strategies evaluated include (i) the duration of theatre ventilation operation, (ii) the efficiency of the ventilation strategy, and (iii) heat recovery systems and technologies. These approaches are assessed using a combination of theatre space monitoring (via building management systems), computational air-flow modelling and mathematical models. We develop a robust methodology that applies these modelling techniques to general hospital suites, enabling the estimation of reductions in CO ₂ equivalent.

Despite numerous studies of droplet impact onto substrates, the splashing dynamics of droplets on biological material surfaces and its implications for infection transmission have rarely been studied. It is hypothesized that the splashing mechanism is influenced by the droplet size, the impact velocity, and the substrate wettability and morphology. The transmission of contamination from initial droplets or liquid films to biofilms upon impact is experimentally investigated. Splashing mechanisms involving biological droplets (e.g., water, urine, blood, and saliva) on a range of biological substrates (e.g., bone, meat, eye, skin, hair, nail, and tooth) and medical surfaces across a range of droplet velocities are comparatively analyzed. The study demonstrates that contaminants located in either an initial droplet or a liquid biofilm can be transmitted by splashing when the droplet impacts onto the biofilm. The Weber number, a descriptor of secondary droplet splashing, expressed as a function of the surface roughness (R_a) is considered. For a droplet of radius R, the prominence of the surface curvature (R_a/R) is highlighted through comprehensive experimentation, underscoring the importance of using tailored surface materials within clinical environments.Developing advanced biomaterials and designs can thus help reduce droplet splashing and promote safer medical procedures.

Ophthalmology outpatient treatment in the NHS reached 5.5 million visits in 2020–21 and has accumulated a significant backlog due to the COVID-19 pandemic. A case study is described which brings together various disciplines to create a smart building environment. This chapter details what was done in order to aggregate digital and physical information in the iterative delivery of an Ophthalmology outpatient clinic. IoT people tracking, CO₂ Sensors and Discrete Event Simulation were applied alongside virtual, augmented and physical mock-ups and modular prototyping. There are complexities in assimilating large volumes of data (e.g. IoT) and challenges caused by various data formats and visual representations (e.g. hand-drawn, 2D drawings, AR and VR), however we show how an iteration approach can support advanced digital twin development for high technology healthcare building types. This work has informed rapid diagnostics, and shown how an empty commercial real estate space can be repurposed for healthcare.

Vision relies on the continuous exchange of material between the photoreceptors, retinal pigment epithelium and choriocapillaris, a dense microvascular bed located underneath the outer retina. The anatomy and physiology of the choriocapillaris and their association with retinal homeostasis have proven difficult to characterize, mainly because of the unusual geometry of this vascular bed. By analysing tissue dissected from 81 human eyes, we show that the thickness of the choriocapillaris does not vary significantly over large portions of the macula or with age. Assessments of spatial variations in the anatomy of the choriocapillaris in three additional human eyes indicate that the location of arteriolar and venular vessels connected to the plane of the choriocapillaris is non-random, and that venular insertions cluster around arteriolar ones. Mathematical models built upon these anatomical analyses reveal that the choriocapillaris contains regions where the transport of passive elements is dominated by diffusion, and that these diffusion-limited regions represent areas of reduced exchange with the outer retina. The width of diffusion-limited regions is determined by arterial flow rate and the relative arrangement of arteriolar and venular insertions. These analyses demonstrate that the apparent complexity of the choriocapillaris conceals a fine balance between several anatomical and functional parameters to effectively support homeostasis of the outer retina. imageKey points The choriocapillaris is the capillary bed supporting the metabolism of photoreceptors and retinal pigment epithelium, two critical components of the visual system located in the outer part of the retina. The choriocapillaris has evolved a planar multipolar vascular geometry that differs markedly from the branched topology of most vasculatures in the human body. Here, we report that this planar multipolar vascular geometry is associated with spatially heterogenous molecular exchange between choriocapillaris and outer retina. Our data and analyses highlight a necessary balance between choriocapillaris anatomical and functional parameters to effectively support homeostasis of the outer retina.

The free-surface channel flow around a square cylinder is analysed, over a wide range of blocking ratios, using three-dimensional simulations. The state of the flow is characterised in terms of the Froude number upstream and downstream of the square cylinder. The simulations confirm the presence of the subcritical and choked states, and provide new insight into the supercritical state and band-gap through an analysis of how the momentum flux varies with Froude number along the channel. The influence of the blocking ratio on the flow state and drag force is analysed and shows the significant rise of drag in the choked regime.