Microscale flows of viscoelastic fluids through complex geometries exhibit rich spatiotemporal dynamics, with significant implications for microfluidic applications and porous media transport. However, current understanding of such complex flow behaviors remains limited. In this study, we investigate the unsteady flow of polymer solutions, ranging from dilute to entangled regimes, in microcavity arrays by employing streak imaging and micro-particle image velocimetry. We report a robust “multistable flow” phenomenon characterized by spontaneous, stochastic switching between a “full-vortex” and a “partial-vortex” state. By mapping the global spatiotemporal dynamics, we reveal a mechanism of “topological decoupling,” where the contraction channels effectively decorrelate the local flow dynamics, rendering the switching dynamics of neighboring cavities statistically independent. Furthermore, a quantitative phase diagram allows us to delineate two distinct instability mechanisms governed by fluid rheology. Specifically, we identify an inertio-elastic instability that follows a cooperative empirical scaling law between the Reynolds (Re) and Weissenberg numbers (Wi), Wi∝Re−0.5. Rooted in boundary-layer dynamics, this scaling reveals that inertia facilitates symmetry breaking by amplifying the local shear rate and elasticity at the channel constrictions. Conversely, when elasticity becomes highly dominant, the system transitions to a purely elastic instability, governed by a dynamic competition between elastic destabilization and shear-thinning stabilization. This competition explains the threshold paradox, where pronounced shear-thinning raises the critical energy barrier for instability. These findings provide a comprehensive physical framework linking molecular dynamics to macroscopic flow topology, offering new theoretical insights into porous media transport and microfluidic control.

Enhanced geothermal systems (EGS) are a promising technology for exploiting deep hot dry rock resources. In this study, a numerical model of a dual-horizontal-well EGS incorporating full-wellbore heat transfer was developed to investigate thermal evolution, wellbore heat loss, and the effects of key parameters on heat extraction performance. Orthogonal experimental design combined with a normalized weighted scoring method was further applied for multiparameter optimization. The results show that during a 50-year operation period, the reservoir cooling rate decreases from 0.47 to 0.39 °C/year, indicating a transition from rapid thermal depletion to a slower heat decay stage. Parameter analysis reveals clear trade-offs among thermal power, outlet temperature, and long-term thermal sustainability. Increasing the flow rate to 0.035 m3/s improves thermal power by 56.7% but accelerates reservoir cooling, whereas reducing the injection temperature to 20 °C increases thermal power by 26.5%. Increasing well spacing effectively delays thermal breakthrough, while a higher geothermal gradient further enhances heat extraction performance. Range analysis indicates that flow rate is the most sensitive factor affecting cumulative heat production, whereas well spacing plays the dominant role in outlet temperature stability. The optimal balanced parameter combination is a flow rate of 0.030 m3/s, an injection temperature of 20 °C, a well spacing of 300 m, and three fractures. Under this scheme, the cumulative heat production reaches 22.57 PJ and the final outlet temperature is 113.42 °C after 50 years of operation.

Under terrestrial gravity, alloy solidification is significantly influenced by temperature gradients, intense natural convection, and non-uniform solute redistribution, often leading to preferential dendritic growth and reduced structural symmetry. This article investigates dendritic growth in levitated Ti47.5Ni47.5V5 alloy droplets under microgravity, where buoyancy-driven convection is strongly suppressed, and Marangoni convection becomes the dominant flow mechanism. With the Marangoni number of Ma ≈ 4, the velocity ratio between dendritic growth and liquid flow of vd/vL ∼ 104 indicates that the solidification front propagates much faster than the interfacial flow. Therefore, dendritic growth is primarily governed by diffusion, resulting in nearly isotropic branching and highly symmetrical microstructures. Increased undercooling further enhances the fractal dimension and spatial filling efficiency through its effect on dendritic growth kinetics. The findings provide quantitative implications of weak Marangoni transport and rapid interfacial instability during phase change and establish a benchmark for understanding how Marangoni convection perturbs interfacial dynamics in rapid solidification systems under microgravity.

This study carries out a boundary element analysis to numerically investigate the hydrodynamic performance of a pile-supported oscillating water column breakwater wave energy converter subjected to obliquely incident waves, within the framework of linear potential flow theory. A bottom undulation effect, created by varying water depths on the lee and seaward sides, is adopted as an effective strategy to enhance wave power extraction under obliquely incident waves. Key hydrodynamic parameters, including optimal efficiency, wave reflection, transmission, wave loads, damping characteristics, diffraction flux, and optimal power exerted, are systematically investigated. Besides, the key hydrodynamic parameters are formulated and validated against the newly derived Haskind relation for obliquely incident waves. The findings reveal that an optimal chamber width ratio (b/h1=0.15) and front wall submergence (a1/h1=0.15), combined with a rear wall draft of a2/h1=0.40 maximize the energy capture while maintaining structural balance. Additionally, moderate oblique wave angles (30° and 45°) significantly enhance resonance and power output. Furthermore, a lower water depth ratio (h2/h1=0.55) effectively broadens resonance bandwidth and minimizes wave transmission, improving both efficiency and resilience. The study also demonstrates that seabed non-uniformity and concave bottom profiles can significantly enhance energy extraction compared to a conventional stepped seabed by amplifying the wave propulsion of the incident wave within the water column.

Rotating detonation engines (RDEs), with their inherent capabilities of local self-pressurization and continuous thrust output, represent a promising propulsion technology for aerospace applications. The nozzle plays a crucial role in RDE performance. This study examines the effect of different nozzles on the internal flow field and explores how the inlet equivalence ratio (ER) influences optimal injector selection. Three-dimensional non-reactive flow fields were simulated using large eddy simulation to analyze cold-flow characteristics under various equivalence ratio conditions. Research findings indicate that the axial fuel inlet (AFI) configuration yields superior performance in non-premixed combustion chambers. Specifically, when the equivalence ratio reaches 1.0, the AFI nozzle not only achieves a more uniform equivalence ratio distribution but also attains a volumetric fraction of the near-stoichiometric mixing zone reaching 74%, thereby promoting the formation and stable propagation of detonation waves. Research indicates that altering the slit structure alone can reduce head turbulence energy while maintaining a mixing efficiency greater than 0.6, which facilitates ignition and the formation of rotating detonation waves.

Ultra-fine atomization (droplet diameter 0.1–10 μm) is critically important in precision manufacturing and biopharmaceuticals. However, conventional atomization techniques still face challenges when handling high-viscosity liquids or pursuing high-output stability. This work studied a novel thin-film jet atomization mechanism based on “forced bubble breakup at interfaces.” By establishing an experimental platform combined with high-speed photography and laser diffraction techniques, this paper quantitatively investigates the effects of operating pressure, micro-orifice geometric parameters (angle, diameter), and tube material properties on atomization performance (Sauter mean diameter D32 and gas-to-liquid mass ratio GLR). Experimental results indicate that increasing gas pressure significantly reduces D32, but the fine droplet size stabilizes after exceeding a critical threshold of 0.35 MPa. Regarding geometry, a micro-orifice angle of 45° exhibits optimal atomization fineness, while the influence of micro-orifice diameter on D32 is relatively limited. Furthermore, to address the high energy consumption of rigid PFA (Perfluoroalkoxy Alkane) tubes, this paper proposes an innovative dual-silicone tube parallel design, successfully reducing the GLR by 51% while maintaining excellent atomization performance. This study reveals the non-linear regulation laws of bubble–jet interactions, providing important theoretical basis and a guiding framework for the structural optimization and energy-saving design of industrial ultra-fine atomization equipment.

This study presents water-tunnel experiments on the interaction between two staggered ventilated supercavities, focusing on asymmetric cavity morphology, critical ventilation demand, and closure-mode transitions induced by a streamwise offset. The transverse spacing ratio is fixed at LH/DC = 5.3, while the streamwise spacing ratio LV/DC = 0, 1.67, and 4 over a range of Fr and CQ. A robust asymmetric mode is found: the gap-side interface of the upstream cavity is compressed and flattened, whereas that of the downstream cavity expands toward the gap passage and is likewise flattened. This asymmetry is attributed to the streamwise offset breaking the symmetry of pressure recovery near the closure region, driving the closure region to a new equilibrium location. Critical formation and collapse coefficients (CQf and CQc) are quantified using two ventilation protocols. In case 1, CQf and CQc exceed the single-cavity thresholds at low Fr owing to the downstream stagnation high-pressure region, but become lower as Fr increases; both increase with LV/DC. In case 2, the critical thresholds are reduced because the upstream stagnation high-pressure region does not directly elevate Pout near the closure region. These trends are interpreted using the dimensionless pressure difference across the gas–liquid interface. Three closure modes are observed: foam cavity, hybrid foam cavity and re-entrant jet (FCRJ), and twin vortex (TV). Relative to the single-cavity condition, the TV regime expands, while the FCRJ regime contracts slightly, and the TV regime shrinks with increasing LV/DC.

This study investigated wave scattering by a slotted, arc-shaped breakwater (SAB) consisting of an array of closely spaced piles, considering energy dissipation arising from the formation of vortices between adjacent piles. The far-field solution, valid in the region away from the SAB, is derived using a matched eigenfunction expansion method based on potential theory, where the boundary-value problem includes a porous boundary condition that incorporates energy dissipation determined by the near-field solution. The near-field solution is obtained by resolving two-dimensional viscous channel flow with varying pile cross sections (circle, rectangle, and diamond) using the computational fluid dynamics (CFD) software StarCCM+. Through systematic simulations, the empirical formula of the drag coefficient is established as a function of pile geometry and porosity. Numerical results reveal that the diamond shape among them causes more energy dissipation due to the formation of stronger vortices. By incorporating the near-field CFD-derived dissipation, including turbulent eddies, into the far-field solution, the present model effectively predicts wave deformation around the slotted, arc-shaped breakwater and identifies an optimal porosity of 0.05, achieving both effective wave attenuation and reduction of wave force. This approach of integrating potential and viscous theories by leveraging the inherent strengths of both provides an efficient design tool for assessing the hydrodynamic performance of slotted, arc-shaped breakwater configurations with varied pile geometries and porosities, enabling optimized wave-attenuation performance.

In this paper, we investigate the sliding dynamics of droplets on an inclined surface using two-fluid flow simulations. Droplet motion is resolved using a front-tracking method, with wettability at the contact line modeled by the generalized Navier boundary condition. The effects of droplet coalescence on sliding dynamics are examined by varying the volume difference between two droplets, their lateral offset, and the substrate wettability. The migration behavior is characterized in terms of sliding velocity, interface evolution, and energy conversion. During droplet coalescence, both surface energy and gravitational potential energy decrease, and the released energy is converted into kinetic energy and viscous dissipation. For a single droplet with the same total volume, the motion is driven solely by gravitational potential energy. The additional release of surface energy during coalescence leads to a higher migration velocity of the coalesced droplet. Smaller volume differences promote more symmetric interface reconstruction and more efficient surface energy release, resulting in higher post-coalescence velocities. Lateral offsets induce complex interfacial interactions, reduce energy transfer efficiency, and lead to curved migration trajectories. On hydrophobic substrates, reduced contact-line resistance enables more efficient energy conversion and higher post-coalescence migration velocities than on hydrophilic substrates.

We discussed a variant of a new theory of local similarity (NTLS) that uses, as basic parameters, the “spectral” Prandtl mixing length and the second moment of the vertical velocity. This approach allows turbulent exchange coefficients, the dissipation of turbulent kinetic energy, and mixed moments of buoyancy and vertical velocity to be expressed solely through two independent basic parameters of local similarity. Comparison of the local similarity approximations with experimental data supports the proposed relations and demonstrates the high effectiveness of NTLS. The results of the new theory of local similarity are compared with well known semi-empirical turbulence theories. It is shown that, throughout the atmospheric convective boundary layer, the local similarity approximations for the turbulent exchange coefficient and the dissipation of kinetic energy are fully consistent with the relations of the semi-empirical theories of Prandtl, Richardson–Onsager, and Hanna. Under weak wind conditions, partial consistency with Taylor's semi-empirical theory is demonstrated. For the semi-empirical theories of von Kármán and Prandtl–Kolmogorov, partial consistency with local similarity is established. Above the surface convective layer, the relations of these theories differ from the NTLS approximations, while within the convective surface layer their relations are identical to the local similarity approximations. In the surface layer, the NTLS approximations are also compared with the classical Monin–Obukhov similarity theory (MOST). It is established that, in windless conditions, the surface asymptotics of NTLS are identical to the free convection limits of MOST.