Stall flutter is suppressed on a NACA0012 airfoil at a low Reynolds number (Re $=$ 1000–5000) through a counter-intuitive strategy: targeted enhancement of the second leading-edge vortex (sLEV) via phase-optimised surface morphing, in contrast to the conventional paradigm of suppressing vortices. Two distinct flow topologies are identified: (I) boundary-layer-eruption-induced leading-edge vortex (LEV) shedding at large amplitudes ($A_\alpha$ ≥ 10°), accompanied by sLEV formation, and (II) bluff-body-type shedding at small amplitudes ($A_\alpha$ ≤ 5°) without sLEV. A new circulation scaling is introduced to identify topology I, which drives severe structural oscillations. Flow-structure analysis reveals a novel sLEV–trailing-edge vortex (TEV) interaction mechanism that mitigates stall flutter: strengthening sLEV triggers a chain effect that weakens the TEV, elevates the aerodynamic moment trough and disrupts the feedback loop sustaining the oscillation. An energy-based map is constructed to characterise the boundary of stall flutter across control parameters and to enable rapid prediction of control performance. By combining the clustering-based vortex-induced load partitioning method with this energy framework, an optimal phase indicator is established: actuation synchronised with the peak sLEV-induced moment consistently yields near-optimal control performance, providing a direct quantitative link between pre-control flow features and optimal control parameters. A phase-locked-loop strategy further demonstrates that surface morphing with an amplitude an order of magnitude smaller than the characteristic LEV scale can nonetheless achieve complete suppression of stall flutter within the topology I regime. These findings not only demonstrate the efficacy of surface morphing control but also offer new physical insight into stall flutter dynamics and their precision control via targeted vortex interactions.

Highly stretched capillary jets produced by gravity are central to drop generation, micro-thread formation and extensional-rheometry concepts. For Newtonian fluids, the transition from steady jetting to self-excited oscillations in a gravitationally stretched jet is predicted accurately by one-dimensional slender-jet equations that retain the exact interfacial curvature and admit a global eigenvalue analysis (Rubio-Rubio et al. 2013, J. Fluid Mech., vol. 729, pp. 471–483). Separately, weakly viscoelastic jets governed by Oldroyd-B/Giesekus constitutive laws exhibit elastocapillary regimes and beads-on-a-string dynamics that are well captured by one-dimensional free-surface models (Ardekani et al. 2010 J. Fluid Mech., vol. 665, pp. 46–56). Here, we study the global linear stability of a one-dimensional full-curvature model for gravitationally stretched viscoelastic jets in the Oldroyd-B limit. We first benchmark the Newtonian limit, reproducing marginal spectra and base-flow profiles, and then quantify how elasticity shifts the critical jetting–dripping boundary by tracking the leading global Hopf eigenpair across the rheological parametric space. For experimentally relevant moderate elasticity, characterised by order-unity Deborah numbers, polymeric tension modifies both the critical Weber number and the selected oscillation frequency, and endogeneity, i.e. the local contribution of the unperturbed flow dynamics to the selected global eigenvalue, reveals that marginality results from a balance between capillary/kinematic contributions and an additional elastic-stress feedback pathway. To interpret and predict the onset mechanism, we compute wavemakers and receptivity/structural-sensitivity fields from direct–adjoint eigenfunctions, showing that viscoelasticity broadens the sensitivity region downstream while the adjoint remains strongly localised near the inlet, thereby identifying the near-nozzle region as the dominant receptive location.

Nonlinear interactions between free-surface gravity waves and acoustic–gravity motions provide a mechanism for energy exchange in weakly compressible fluids and have long been discussed in connection with microseisms and low-frequency underwater sound. While elastic solid-Earth response has been incorporated in microseism modelling, existing formulations of acoustic–gravity wave resonant triads are almost exclusively developed for a rigid seabed, which introduces a shallow-water cutoff where the acoustic–gravity member becomes evanescent and resonance cannot occur. Here, we extend the resonant-triad framework to a compressible fluid over an elastic half-space. Seabed elasticity modifies the acoustic–gravity eigenstructure and dispersion relation, admitting propagating or interface-guided acoustic–gravity modes in regimes inaccessible under rigid-bottom assumptions and thereby removing the rigid cutoff in frequency (or depth). Using a multiple-scale expansion in the small compressibility parameter, we derive modulation equations for two counter-propagating gravity waves coupled to a single elastic acoustic–gravity mode. A key feature is an interfacial term in the solvability condition arising from the parameter dependence of the elastic boundary operator, which alters the modal normalisation and the resulting coupling and detuning coefficients. The enlarged admissible parameter space also makes laboratory-scale realisations of acoustic–gravity triad resonance substantially more feasible, enabling controlled investigation of the triad mechanism.

There is a lack of comprehensive reviews examining workplace health promotion (WHP) interventions targeting nutrition; most of the reviews focus on productivity-related outcomes. This narrative review, based on articles extracted from PubMed between January 2015 and July 2024, aims at providing a critical analysis of the current evidence regarding WHP interventions, and proposes practical principles for companies and human resource management to develop more effective WHP initiatives. The review includes 54 eligible randomized controlled trials conducted in various workplace settings across high-income countries, involving a general adult working population of both sexes, with or without metabolic chronic diseases. Among the 54 eligible articles analysed, 8 different strategies were identified for environmental, 6 for educational, and 5 for behavioural interventions. A combined educational and behavioural intervention was the solution most frequently applied (24 studies). Less than half of the studies were effective. Outcomes that improved most frequently in WHP interventions were waist circumference (11/20 studies evaluating this outcome), consumption of unhealthy food/nutrients (10/17), vending machines or worksite cafeteria purchases (4/5), and metabolic syndrome (2/4). 46% of the WHP interventions tackled ≥ 2 healthy lifestyle domains promoted by the World Health Organization, and 71% used technology. WHP programmes often fail due to poor design, but with evidence-based, tailored strategies and international guidelines, they could drive lasting, widespread benefits. Effective frameworks should balance scientific rigor with practical tools to ensure engagement and impact, providing concrete benefits for the employees, their families and the entire society.

We report on the shape taken by the interface of a liquid bath when hit by a smooth oblique steady jet. When the angle between the jet and the bath decreases below $50^\circ$, a cavity is formed in front of the jet. In the inertial regime that we explore, the jet boundary layer detaches in the impact region, thereby delimiting a core jet region outside of which the liquid is mainly in hydrostatic equilibrium. The shape of the outer meniscus is shown to be related to that outside a tilted fibre piercing the fluid interface. In order to unravel the flow features and separation, we perform direct numerical simulations and show that the flow detachment displays an asymmetry, which results in the acceleration of the liquid below the surface, thereby creating a depression. With this observation, we propose a model balancing the suction force of this depression with the weight of the displaced water and the surface tension force to obtain a prediction for the typical width of the cavity.

Mortuary traditions offer a wealth of insights into the social landscapes of human communities. Here, the author examines anthropomorphic representations in the decorated tombs of Kyushu Island, Japan, dating from the Late Kofun period (sixth–seventh centuries AD). The consistently subordinate scale, strategic architectural placement and systematic anonymity of these figures suggest that they did not function as portraits of the dead but were likely symbolic agents embodying a collective rather than individual identity. By demonstrating that the human figure is not consistently the protagonist in these funerary contexts, this study reframes our understandings of Late Kofun deathways.

So-called engineering or analytical wind farm flow solvers typically build upon two submodels: one for the velocity deficit and one for the wake-added turbulence intensity. While velocity-deficit modelling has received considerable attention, wake-added turbulence models are less prevalent in comparison. Yet, accurate estimates of local turbulence intensity are essential for predicting flow interactions and energy yield, as turbine wakes are both sensitive to, and sources of, turbulence. Existing wake-added turbulence models are typically empirical or assume axial symmetry despite the inherently three-dimensional nature of turbulent wake fields. In this work, we present a new model for wake-added turbulence intensity. Our approach is based on the analysis of the turbulent kinetic energy and the streamwise Reynolds stress budget, incorporating classical Reynolds-averaged Navier–Stokes modelling assumptions and far-wake approximations. The resulting model maintains a simple and practical form, demonstrating strong agreement with large eddy simulation and wind-tunnel measurements. Our model provides a more physically consistent and predictive tool for wind farm flow modelling and performance estimation.

The two-layer coating plug propagation and rupture are studied computationally as a model for airway reopening for the eighth-to-tenth generations of a typical adult lung. The computational model incorporates the bi-layer structure of the serous–mucus liquid film lining the rigid tube, where the outer serous layer is treated as a Newtonian fluid, while the inner mucus layer is modelled as an elastoviscoplastic fluid governed by the Saramito–Herschel–Bulkley model. Compared with the one-layer plugs: (i) the two-layer plugs necessitate a higher driving pressure for rupture and exhibit a longer propagation distance, both of which increase the risk of failed airway reopening; (ii) both the wall shear stress and the wall shear stress derivative exhibit a significant reduction of approximately $75\,\%$ in the two-layer plugs; (iii) the two-layer liquid film cannot be modelled using a one-layer plug model by simply applying the Navier boundary conditions. The critical mechanism due to dynamic elastic stretching (Hao et al. J. Fluid Mech. 1023, 2025, A14) persists for the two-layer plug. The serous layer appears to limit the transmission of elastic resonance to the airway wall, which underscores the protective role of the serous layer. The shear stress and shear stress derivative increase with increasing Weissenberg number. At low Weissenberg numbers, rupture time increases as a result of an increase in the Bingham number and a decrease in the power-law index; at high Weissenberg numbers, viscoelastic effects dominate the elastoviscoplastic airway reopening. These distinct two-layer phenomena offer crucial insights for developing more physiologically accurate models of airway fluid mechanics.