Wind farms extract momentum from the atmospheric flow, generating wind-speed deficits both within the plant, and extending downstream. When located offshore, these deficits modulate air–sea coupling, potentially impacting coastal upwelling in sensitive regions. We investigate impacts of wind farms on coastal upwelling using kilometre-scale, three-way-coupled simulations with the coupled ocean–atmosphere–wave–sediment transport system for the US West Coast. Wind-farm effects are represented by a generalised turbine drag formulation, an idealised, height-dependent body force whose magnitude is systematically varied. This approach isolates the leading-order fluid-dynamical response in a realistic coastal configuration. The atmospheric adjustment exhibits an approximately linear relation between drag force and wind-speed deficit, with wakes that expand downstream and increase in magnitude as drag increases. An empirical orthogonal function analysis of sea-surface-temperature anomalies reveals the emergence of a canonical dipole pattern under strong drag forcing. Subsurface diagnostics show consistent shoaling of the mixed layer and suppressed upward velocities in areas near wind-farm region, accompanied by compensating enhancements of shoaling closer to the coast. These results identify turbine drag as a control parameter in assessing interactions between wind-farm wake and coastal upwelling and provide scaling relationships for understanding offshore wind-farm effects on the coastal circulation dynamics.

Needling of arteriovenous fistulas is a critical aspect of vascular access in haemodialysis, where a particular concern is the venous return needle strongly perturbing local haemodynamics. To isolate and characterise these effects, controlled experiments are performed in an idealised geometry representing venous return, using clinically relevant vessel and needle dimensions with Reynolds-number similarity. Scalar transport and mixing are quantified using planar laser-induced fluorescence, while velocity field and shear stress are obtained from particle image velocimetry. The results demonstrate that needle angle and the vein-to-needle flow-rate ratio jointly govern the development of primary and secondary flow structures. Lower needle angles and higher flow-rate ratios delay mixing, whereas higher angles and lower ratios promote rapid mixing and sustain localised stagnation regions. Complete mixing, when achieved, occurs within approximately 15 needle diameters downstream, although the velocity field remains undeveloped and influenced by the needle jet up to 25 diameters downstream. Viscous shear stresses are found to be highly unsteady (root-mean-square of fluctuation/mean value varying between 0.21 and 0.48 at the location of maximum shear stress), with instantaneous values frequently exceeding physiologically relevant levels. These findings provide fundamental fluid-mechanical insight for clinically informed optimisation of cannulation strategies.

This study presents the first systematic experimental investigation of the streamwise evolution of multi-orifice synthetic jets (MOSJs) driven by a single actuator. A centred hexagonal arrangement of seven circular orifices is examined using particle image velocimetry. Four cases are studied in which Reynolds number and Strouhal number are held constant while the orifice diameter is varied, thereby isolating the effect of the internal orifice geometry through changes in throat aspect ratio. The flow development is shown to consist of four distinct regimes: (i) a near-orifice region dominated by the balance of blowing and suction; (ii) development of individual jets; (iii) a jet-merging regime; and (iv) a merged-jet region that evolves towards self-similar scaling. Despite matched non-dimensional actuation parameters, differences in momentum flux, Reynolds number and turbulence statistics are observed. These differences scale monotonically with orifice diameter and are traced to changes in the exit velocity profile imposed by the orifice throat length. In particular, more diffuse shear layers – resulting from a longer orifice throat – lead to more efficient jet merging, higher downstream momentum and reduced dissipation. The results demonstrate that actuator-internal geometry plays a critical role in MOSJ performance and cannot be neglected in predictive or design-oriented models.

Winds in the atmospheric boundary layer (ABL) display a wide range of velocity profiles and turbulence properties that affect wind turbine wake dynamics. However, standard concurrent-precursor large-eddy simulations (LES) often neglect phenomena such as mesoscale patterns, limiting the range and controllability of inflow parameters that can be studied. Here, we propose a synthetic inflow LES method with high inflow controllability to allow parameters such as shear, turbulence and Coriolis effects to be varied independently, facilitating the efficient exploration of wake dynamics across the full range of conditions observed in the field. The synthetic inflow method faithfully reconstructs wake dynamics when compared with standard concurrent-precursor LES. We then run a suite of over 600 LES cases to investigate the ABL processes that most affect wake dynamics. We find that wake recovery strongly depends on inflow wind veer, especially at low turbulence intensities, due to the elongation of the skewed wake. Furthermore, we identify a novel scaling relation that collapses wake deflections and dynamics onto the combination of shear and veer. The suite of LES cases elucidates ABL regimes and wake dynamics where current and future wind turbines may operate, building towards improved wake modelling for wind farm design and control.

We experimentally investigated the turbulent flow in a water channel developing past a two-dimensional array of photovoltaic panels, with varying incidence angle and spacing. Particle image velocimetry revealed two distinct regimes, depending on the incidence angle, while the dependence on inter-panel spacing was weaker. Positive incidence angles produce high turbulence and intense transport above the panels, with strong mixing between the canopy and the external flow. Conversely, negative incidence angles yield a skimming flow with large recirculation vortices that dominate the canopy layer. Vertical profiles, ventilation rates and turbulent statistics indicate that even a modest positive incidence significantly enhances ventilation and scalar transport, whereas they are substantially lower in the case of negative incidence. A Lagrangian analysis using synthetic passive particles allowed the estimation of the residence times and turbulent dispersion coefficients. The latter were more than an order of magnitude larger for positive than for negative incidence. The results demonstrate how panel configuration changes mixing and dispersion processes, providing a fluid mechanics basis for refined microclimate models useful for guiding the design of advanced photovoltaic farms.

The dynamics of carboxyl-modified polystyrene colloidal particles of varying size and zeta potential were investigated in a microfluidic junction device where merging electrolyte streams generated a steady-state salt concentration gradient. The device featured a long microchannel downstream of the junction, enabling the particle dynamics to be analysed over a time scale comparable to the relaxation time of the salt gradient. In the bulk of the channel, particles migrate outwards through a diffusive-like process arising from the additive contributions of particle diffusiophoresis and wall diffusioosmosis. An analytical expression is derived for the effective diffusion coefficient, and a microfluidic approach is proposed to estimate particle diffusiophoretic mobility. Particles accumulated at the walls also displace sideways but the direction of their motion depends on the counter-acting effects of particle diffusiophoresis and wall diffusioosmosis. This motion is sub-diffusive at short distances from the junction, but either ceases or reverses further downstream. The intensity of the accumulation peaks exhibits a non-monotonic dependence on the distance from the junction and, after calibration, can serve for the microfluidic measurement of particle size or zeta potential, when one property is known a priori. The influence of electric double layer polarisation on diffusiophoretic mobility is also examined.

Subsea gas releases can produce visible surface patches whose size is much larger than the stochastic lateral wandering of individual bubbles during ascent. This distinction is important when laboratory measurements of bubble-swarm dispersion are extrapolated to environmental releases. Here we formulate a scale comparison between three lateral length scales: the Taylor dispersion scale for random bubble motion within a swarm, the entrainment scale for coherent widening of a rising gas–water plume and the surface-spreading scale produced after a plume reaches the free surface and forms a fountain. Applying this framework to the Nord Stream pipeline leaks shows that the observed surface expression was controlled by plume entrainment and surface spreading, rather than by bubble-swarm Taylor dispersion. The resulting regime classification clarifies when bubble-swarm Taylor dispersion can control the observed lateral spread and when plume entrainment and surface transport dominate.

Laminar jet apparatuses (LJAs) are employed to study gas–liquid mass transfer and thereby provide insights into the design of technical separation and reaction equipment. The hydrodynamics of the laminar jet determines the operating window of such apparatuses and must therefore be understood for the proper evaluation of experimental results. Although substantial literature exists on free liquid jets, quantitative analyses directly tailored to LJAs and their operating conditions remain scarce. The present work addresses this gap. We investigate all hydrodynamic aspects relevant to the operation of LJAs using computational fluid dynamics (CFD) simulations: the shape of the jet surface (i.e. the gas–liquid interface), the velocity profile within the jet (including the transition from the nozzle to the free jet) and jet breakup. The study is conducted for a square-edged orifice plate nozzle under various flow conditions and analysed using dimensionless numbers. The CFD simulations account for gravity and surface tension and comprise the entire relevant domain (feed line, nozzle, liquid jet and surrounding gas phase). Complementary experiments using a LJA, in which the jet shape was measured, validate the simulation results. The findings provide quantitative guidance for rational design of LJAs and offer a foundation for replacing ad hoc assumptions in the evaluation of the experiments.

Clustering techniques provide a powerful framework for analysing complex flow dynamics while reducing computational costs in large-scale simulations. In this work, we propose a clustering-based approach using vector quantisation principal component analysis (VQPCA) to identify structural sensitivity zones, i.e. regions where the flow is most receptive to perturbations. To the authors’ knowledge, this is the first application of VQPCA to a fluid dynamics problem for identifying flow patterns and dynamically relevant regions. As a fully data-driven technique, it does not rely on adjoint methods and depends exclusively on direct simulation data. This method extracts dominant flow features by partitioning the flow field into regions characterised by their intrinsic dynamics. Its validity is assessed by analysing the wake behind a circular cylinder, where the identified regions show strong similarity with previously established structural sensitivity zones. Robustness is further evaluated under different operating conditions for this configuration. The approach is then applied to the interaction of two planar synthetic jets to investigate more complex flow dynamics and illustrate how the identified regions can guide flow control strategies. These results highlight the potential of clustering-based methods as practical tools for analysing complex flows and identifying regions where small perturbations can strongly influence global dynamics.

The three-dimensional unsteady flow structures around an aerofoil with leading-edge tubercles at angles of attack up to the post-stall regime are experimentally characterised by high-speed three-dimensional particle tracking, physics-informed neural network data assimilation and proper orthogonal decomposition. At mild incidence (${\lesssim}5^{\circ }$), tubercles generate a spanwise-periodic system of counter-rotating vortices, strongly altering the boundary layer from its inception. The vortices adhere to the aerofoil profile, modulating the shear layer by alternating downwash and upwash motions. In the stall regime, the flow features large-scale separation cells spanning several tubercles with no apparent periodicity. Proper orthogonal decomposition reveals a dominant vertical flapping motion of the shear layer with a Strouhal number of $St \approx 0.1$ (based on chord length and free-stream velocity). The second most energetic mode ($St \approx 0.3$) captures part of a streamwise travelling wave, indicating a shedding behaviour. In the deep-stall regime of ${\gtrsim}25^{\circ }$, the unsteadiness is ascribed to the interaction among neighbouring separated patches. The kinematic description of the flow is further utilised to infer the aerodynamic loads through pressure estimation. These observations help understand the gradual attenuation of lift, ascribed to an extended envelope of cellular separation, which contrasts with the abrupt stall observed for straight-edge aerofoils.

A symmetric two-panel turbulence facility based on loudspeaker-driven synthetic jets is developed to generate negligible-mean-flow homogeneous turbulence in air. The system consists of an array of independently controlled actuators operated using an extended sunbathing algorithm that enables three independent actuation strategies: random frequency switching, random power modulation and spatiotemporal on/off switching. These modes, used individually or in combination, allow systematic generation and fine-tuning of a broad range of turbulence states. Time-resolved velocity fields are measured using particle image velocimetry (PIV) to characterise the resulting flow in terms of turbulent kinetic energy, mean flow, homogeneity and isotropy. Beyond conventional turbulence statistics, facility-induced coherent structures and their energetic contributions are quantified using proper orthogonal decomposition (POD). The results demonstrate that increasing forcing randomness progressively suppresses coherent organisation and reduces coherent energy content while maintaining high turbulence intensity and low mean flow. In addition to negligible-mean-flow operation, the facility can generate controlled mean-flow rotation in laboratory turbulence by imposing a power gradient across the actuator array, without a rotating platform. Overall, the facility offers a flexible and highly configurable experimental platform for generating homogeneous turbulence, tailored turbulence states and turbulence with controlled mean-flow rotation within a confined environment.

Open-channel bifurcations exhibit complex three-dimensional flow structures, such as separation zones and recirculating motions. While traditional representations of the recirculation flow in bifurcation are two-dimensional and closed, recent studies suggest the presence of open three-dimensional (3-D) helical recirculation flows. The present work addresses this question by employing particle tracking velocimetry to measure the time-averaged 3-D velocity field in a simplified bifurcation geometry. The measurements reveal that all examined flow configurations exhibit an open separation zone along the lateral branch’s inner wall, with no evidence of closed, two-dimensional recirculation. Instead, two distinct helical recirculation patterns emerge, governed by the width-to-depth aspect ratio $B/h$. In shallow flows ($B/h \gt $ 4), a vertical-axis helix conveys the recirculating flow from the bed to the free surface. In deeper flows ($B/h \lt $ 4), the recirculation axis transitions from vertical upstream to streamwise downstream, generating a more complex motion. A key finding is the presence of an ‘entrance gate’ in both patterns: a spatially confined near-bed region through which flow enters the separation zone near the intersection, before escaping further downstream near the surface or at mid-depth. This study challenges conventional closed-zone representations, instead revealing two types of open, three-dimensional helical recirculation patterns with finite but prolonged residence times.

Dust storms are high-Reynolds-number particle-laden turbulent flows in which the turbulent airflow, suspended dust particles and electric fields are strongly coupled. Their multiscale dynamics remains difficult to resolve from field observations alone, which are typically limited to time series at a few wall-normal locations and obtained under uncontrolled environmental conditions. Numerical simulation provides a route to overcome these limitations, but existing models of wind–dust–electric coupling in the atmospheric surface layer (ASL) have rarely been tested systematically against measurements. Here we develop and assess a wall-modelled large-eddy simulation framework for electrified dust storm turbulence. The model represents suspended PM10 dust particles using an advection–diffusion–settling transport equation and includes electric-force-induced drift of charged dust particles. The framework is validated using simultaneous measurements of wind velocity, PM10 dust concentration and vertical electric field at 11 heights from the Qingtu Lake Observation Array. The simulations closely reproduce the observed distributions of wind velocity, dust concentration and electric field, demonstrating the ability of the model to capture coupled wind–dust–electric processes in the ASL. This framework provides a validated numerical tool for investigating multiscale interactions among turbulent structures, dust transport and the electric field in natural high-Reynolds-number dust storms.