Search Results (430)

Dense granular materials under low confining stress and low shear velocity—conditions relevant to low-pressure powder handling, near-surface transport, and the upper layers of stored bulk solids—remain insufficiently characterized at the microstructural level. We perform three-dimensional discrete element method (DEM) simulations of annular shear of monodisperse glass spheres at σ = 1 kPa and v = 0.01 m/s, corresponding to an inertial number I ≈ 1.06 × 10⁻³ at the quasi-static limit of the dense flow regime. The steady-state friction coefficient stabilizes at μ_ss ≈ 0.78, consistent with the quasi-static limit of the μ(I) framework. The solid volume fraction decreases monotonically from φ ≈ 0.50 at the base to φ ≈ 0.35 near the top, while the tangential velocity decays exponentially with depth (decay length δ_s ≈ 10 mm). Particle trajectory tracking reveals a sharp kinematic transition near z ≈ 5–6 mm separating a quasi-rigid basal layer (z ≲ 5 mm) from an upper shear-active zone (z ≳ 6 mm). The contact force distribution follows an exponential decay P($f$/$⟨f⟩$) ∝ exp(−β·$f$/$⟨f⟩$) with β ≈ 0.45, with strong force chains selectively concentrated in the upper zone. Together, these four microstructural descriptors co-locate within a single transition band, providing quantitative benchmarks for material characterization and constitutive modelling at the lower boundary of dense flow. Full article

To protect human health and the environment, it is necessary to reduce the number of solid particles and harmful gases in the air or to minimize such pollution. Filtration and separation devices are intended for various industrial operations to capture pollutants from various technological processes. In the introduction, this article points out the use of cyclone filters in individual operations, names the most frequently occurring elements of pollution, and suggests the most suitable method of separation. In paint shops, grinding shops, welding workplaces, machining lines, and when handling powder materials, particles with very different properties are created. An important advantage of using cyclone filters is not only their simple construction but also their usability at high temperatures and pressures. Furthermore, this article highlights that cyclones are easy to maintain, typically contain no moving parts, are simple to manufacture, and are cost-effective, particularly as pre-filtration devices. Their efficiency generally ranges from 50% to 99% and is strongly influenced by design and operating parameters, especially cyclone geometry, which affects pressure drop, flow structure, cut diameter, and fractional collection efficiency. The article also summarizes that various modifications of the inlet, vortex finder, outlet pipe, and cyclone body have been proposed to enhance separation performance, particularly for smaller particles. Nevertheless, due to the centrifugal and inertial nature of cyclone separation, fine and submicrometric particulate matter remains difficult to remove using cyclones alone. Fabric filters are also analyzed as a possible solution, but high loading by coarse particles may cause clogging, increased pressure drop, and higher maintenance costs. In the end, the combination of a cyclone with an electrostatic precipitator is presented as a staged separation approach, enabling efficient removal of both coarse particles and fine particulate matter from the gas stream. Full article

Non-exhaust emissions (NEEs), particularly brake wear particles (BWPs), have become a dominant source of traffic-related particulate matter (PM), accounting for approximately 77% of PM10 and 60% of PM2.5 emissions. Accurate quantification of these emissions is essential under increasingly stringent regulations such as Euro 7. However, measurement reliability is strongly influenced by particle transport and sampling losses. This review provides a state-of-the-art analysis of laboratory-scale methodologies for investigating BWP emissions, focusing on pin-on-disc (PoD) tribometers and inertia dynamometer systems. Particular attention is given to chamber design, airflow management, sampling configurations, and the mechanisms governing particle transport efficiency. The literature indicates that PoD systems are often affected by complex and non-uniform flow fields, leading to incomplete particle capture and reduced representativeness, whereas inertia dynamometers, especially when coupled with constant volume sampling (CVS), provide more controlled and reproducible conditions. Key loss mechanisms, including inertial deposition, diffusion, gravitational settling, and non-isokinetic sampling effects, are major contributors to uncertainty. The reviewed studies highlight that aerodynamic limitations in PoD systems, particularly box-shaped chambers, promote flow recirculation and particle losses. Advanced optimization approaches that combine artificial neural networks (ANNs) with computational fluid dynamics (CFD) simulations show strong potential to improve system design and measurement reliability. Full article

The present work investigates fluid–structure instabilities and flow-induced oscillations of a pitching NACA0012 airfoil through numerical simulations. The flow is modeled using the compressible Navier–Stokes equations in a non-inertial rotating reference frame, while the structural dynamics are represented by a torsional spring–mass–damper system. The analysis focuses on the effects of reduced velocity, equilibrium angle of attack, and elastic axis position on the aeroelastic behavior at low Reynolds number ($Re=1000$). Particular attention is devoted to characterizing the transition from vortex-shedding-dominated oscillations to fully developed limit-cycle oscillations and to assessing its sensitivity to aerodynamic and structural parameters. The results show a transition from steady flow to vortex shedding and, at higher reduced velocities, to limit-cycle oscillations. Increasing the equilibrium angle of attack promotes an earlier onset of instability and stronger aerodynamic forcing, while moving the elastic axis downstream has a similar destabilizing effect due to the larger aerodynamic moment arm (up to approximately 20% reduction of the critical reduced velocity). The nature of the transition is found to depend strongly on the equilibrium angle of attack, with distinct behaviors observed at low and high incidence. Frequency analysis highlights the progressive coupling between fluid and structural dynamics: vortex shedding dominates in the weakly coupled regime, whereas the structural frequency governs the response in the limit-cycle regime. The study provides a consistent description of the mechanisms driving flow-induced oscillations and of the parameters controlling aeroelastic stability. Full article

This study utilizes a large-scale numerical simulation model to investigate the hydrodynamic behavior and particle transport characteristics of gas–liquid–solid three-phase flow in vertical wellbores featuring multi-source confluence and curved geometries. Simulation results indicate that increasing flow velocity shifts the dominant control mechanism from surface tension to inertial forces, transitioning the flow pattern from slug flow to churn flow. In curved pipe sections, centrifugal phase separation and geometric shielding effects cause significant flow asymmetry and maintain large bubble stability at the inner wall. Additionally, the multi-inlet structure induces shear rate gradients that result in the spatial coexistence of two distinct bubble scales. Furthermore, localized gas concentrations exceeding 70% at the upper inlet can trigger severe gas-locking phenomena and intense pressure pulsations. Full article

To improve the operational stability and mass transfer performance of fluidized bed reactors under dynamic conditions, this study examines radial particle velocity distributions at different bed cross-sections using a dual-probe measurement method across a range of rocking frequencies and superficial gas velocities. The analysis identifies the dominant influence of additional inertial forces generated by rocking motion, including the Euler force and Coriolis force, in determining the time-averaged flow structure, leading to the development of a spatiotemporally averaged flow field model and clarification of the interaction mechanisms between these forces. Results indicate that the flow field exhibits two representative macroscopic patterns governed by the interplay between inertial forcing and particle response characteristics: at low frequencies, the slowly varying Euler force combines with gravity to produce a coherent large-scale single-circulation structure, whose stability is sustained under higher gas velocities due to reduced internal energy dissipation associated with stronger drag; at high frequencies, the Coriolis force promotes structural division while the rapidly oscillating Euler force introduces disturbances, resulting in the formation and persistence of double or multi-circulation flow structures under their combined action. Full article

Silicon micromachining serves as the foundational enabling technology for high-precision MEMS inertial sensors. However, the relentless pursuit of enhanced sensitivity and multi-functionality in emerging applications encounters a fundamental bottleneck when confined to two-dimensional scaling. The evolution toward complex three-dimensional (3D) stacking architectures is an inevitable trajectory for devices including MEMS inertial sensors, yet performance is constrained by the limitations of conventional processes in fabricating and integrating intricate 3D hollow structures. Specifically, uniformity in large-area deep silicon etching, structural integrity of convex corners in wet etching, and residual stress induced by multi-layer wafer bonding have emerged as critical, shared challenges. To address these issues, this paper proposes a triple-layer wafer-level stacking scheme that synergistically combines wet/dry hybrid etching with low-temperature adhesive bonding. This stacking scheme incorporates an innovative linear compensation model for wet-etched convex corners, enabling high-precision fabrication of complex corner structures under deep etching conditions. Furthermore, a collaborative strategy involving temporary bonding and plasma flow-field optimization improves the uniformity and integrity of dry etching for large perforated structures. A low-temperature triple-layer wafer-level stacking process is developed, encompassing precise adhesive dispensing, optical alignment, and a stepped low-temperature curing profile, thereby achieving highly symmetric 3D integration with controlled adhesive distribution. The efficacy of this stacking scheme is validated through the fabrication of a symmetrically stacked triple-layer MOEMS accelerometer sensing element. Test results demonstrate a noise floor as low as 0.40 µg/√Hz and a bias instability of 1.81 µg over 10 min. Compared with a double-layer counterpart, improved performance is obtained. The wafer-level stacking scheme established in this work not only provides a viable pathway for pushing the manufacturing limits of high-precision inertial devices but also offers a generic methodology for tackling complex hollow structure formation and low-temperature integration, holding referential value for broader applications in high-precision 3D microsystems. Full article

Accurate prediction of hydrodynamic forces on confined oscillating structures is essential in applications related to nuclear engineering, energy systems, offshore devices, and mechanical components subjected to flow-induced vibrations. In this work, two computational fluid dynamics (CFD) methodologies implemented in ANSYS CFX are compared to determine the added-mass coefficients for a square cross-section cylinder confined within a square container: a deforming-mesh method (DMM) and an immersed-boundary method (IBM). Unlike previous studies restricted either to concentric square cylinders or to eccentric configurations treated with potential flow, the present study addresses eccentric confined configurations by solving the incompressible Navier–Stokes equations and focuses primarily on the prediction of added mass under strong confinement. Horizontal, vertical, and combined eccentric displacements are analyzed in detail. Mesh-independence, domain-size sensitivity, and temporal-convergence analyses are performed. Results show that both methods provide closely matching added-mass predictions over a wide range of eccentricities, with relative differences typically below 1% for moderate eccentricities, although discrepancies increase under extreme confinement. Relative to the concentric configuration, the added-mass coefficient increases by about 44% for the most eccentric vertical case and by about 87% for the most eccentric corner-approach case. Force decomposition and pressure-field analysis show that this increase is governed primarily by pressure-induced inertial effects, whereas viscous shear plays a secondary role under the conditions considered. From a practical standpoint, the immersed-boundary method reduced the computational time by approximately 92% in the most demanding case. Full article

Fluid flow in fractured-vuggy carbonate reservoirs is characterized by extreme multiscale heterogeneity, where the coexistence of tight matrix rock and macroscopic cave challenges traditional Darcy-based continuum models. This paper presents a semi-analytical solution for two-phase immiscible displacement in a one-dimensional composite porous–cavernous–porous (PCP) system. The main feature of the model is that the cave region is treated separately from the porous domains: classical Darcy flow is used in the surrounding matrix, whereas an idealized free-flow representation is introduced for open caves based on a simplified one-dimensional treatment of the cave momentum balance. To elucidate the impact of distinct flow regimes on displacement dynamics, three physical models are compared for the cave region: (1) an open-cave model represented by a simplified free-flow formulation; (2) a filled-cave non-Darcy model governed by the Forchheimer equation using the Ergun correlation; and (3) a creeping-flow model governed by Darcy’s law. A piecewise semi-analytical solution procedure is established to enforce flux continuity, characterize interfacial state remapping, and determine the downstream front under global water-balance closure. The results show that both cave geometry and internal cave-flow mechanism critically control water-front advancement. While the open-cave model exhibits piston-like displacement behavior with high local displacement efficiency but stronger preferential flow, the Forchheimer model shows that inertial resistance can modify the saturation profile and delay breakthrough relative to the Darcy prediction. The proposed framework provides an idealized theoretical reference for benchmarking numerical simulators and for interpreting waterflooding behavior in complex vuggy reservoirs under one-dimensional, incompressible, gravity-free, and capillarity-free conditions. Full article

The responses of a very large floating structure (VLFS), which is modeled as a thin viscoelastic plate floating on a fluid of finite depth, are analytically studied within the framework of the nonlinear potential flow theory. We use the Laplace equation with the dynamical boundary condition to express a balance among the hydrodynamic, inertial, and viscoelastic forces. For the case of steady-state incident waves, we obtain convergent series solutions for plate deflection and velocity potential by choosing the optimal convergence-control parameter $C_0$ and proper auxiliary linear operators in the homotopy analysis method (HAM). The strain relaxation time for the viscoelastic plate is studied, and the result shows that the plate deflection decreases when the retardation time increases. The influences of other physical parameters on the viscoelastic plate are also discussed. The nonlinearity of dispersion relation and the retardation time of the plate have important and non-negligible effects on the responses of the VLFS. The results obtained here may be helpful in understanding the different physical parameters to model hydroelastic responses of a VLFS in the real ocean. Full article

With the rapid development of technologies for scramjet and combined-cycle engines, the efficient mixing of supersonic airflow and fuel within the combustor has become a key factor limiting engine performance improvement. Existing research has predominantly focused on Mach number and compressibility effects, while systematic analysis of the influence of Reynolds number remains scarce. In this study, the large eddy simulation (LES) method is employed to investigate the effects of inflow Reynolds number on the flow structures, growth characteristics, and modal evolution of a supersonic mixing layer. By adjusting the inlet pressure, three different Reynolds number conditions are established, and the evolution of vortex structures, development of mixing layer thickness, turbulence statistics, and dynamic mode decomposition (DMD) characteristics are analyzed. The results indicate that under high Reynolds numbers, the transition in the mixing layer occurs earlier, vortex breakdown intensifies, three-dimensional features become more pronounced, and the mixing layer centerline shifts significantly toward the low-speed side. The energy spectrum in the self-similar region exhibits approximate isotropy, and the inertial subrange expands with increasing Reynolds number. Moreover, DMD analysis reveals that flow field reconstruction at high Reynolds numbers requires higher-order modes, reflecting richer dynamic scales. Our study elucidates the influence of Reynolds number on the multi-scale evolution mechanisms of supersonic mixing layers, providing a theoretical basis for the prediction and control of mixing processes in high-speed propulsion systems. Full article

Top Submerged Lance (TSL) technology is widely used in non-ferrous smelting, yet in-situ bath dynamics remain challenging to quantify because the process operates in a closed, high-temperature, highly turbulent and optically inaccessible environment. The absence of direct diagnostics limits the ability to relate operating conditions to bubble dynamics, gas penetration and bath agitation and constrains validation of multiphase CFD models under realistic conditions. This study introduces a multimodal sensing framework that combines spectral acoustic analysis with lance-mounted inertial motion sensing to characterize dynamic bath behavior across cold-model, laboratory-scale and pilot-scale systems. Water-glycerin experiments establish repeatable acoustic signatures of individual bubble-collapse events, with dominant emission bands in the 300–900 Hz range and higher-frequency components extending into the kilohertz domain. High-temperature laboratory trials using fayalitic slag reproduce these frequency regions while exhibiting depth-dependent attenuation and clear spectral separation between submerged and non-submerged lance operation. Power Spectral Density (PSD) and cumulative spectral power analyses resolve the influence of gas flow rate and lance submersion depth on acoustic spectral power distribution, while inertial measurements capture corresponding increases in vertical lance acceleration associated with back-pressure fluctuations. Pilot-scale trials at 120 Nm³/h air and 13 L/h diesel confirm that shallow lance submersion substantially increases measured acoustic spectral power below 3 kHz, whereas deeper penetration enhances periodic vertical acceleration response measured by the inertial sensor. The combined acoustic-inertial methodology provides a physically interpretable and cross-scale framework for assessing bubble collapse activity, plume interaction and bath agitation under high-temperature TSL conditions. The approach enables frequency-based diagnostics that can be systematically compared with CFD predictions of plume oscillation and collapse-related dynamics. Once baseline frequency ranges are established for a given slag system, the method can support process monitoring and may provide indirect indicators related to changes in surface agitation or foaming tendency, enabling structured data-driven analysis. The framework thus provides a practical bridge between cold-model experiments, high-temperature measurements, multiphase modeling and industrial TSL operation. Full article

In this study, we present a novel microfluidic platform for tunable size-based particle separation within a straight microchannel using symmetrical viscoelastic sheath flows. The device incorporates two pairs of symmetrical microchannels for sheath fluid injection: the first pair facilitates particle focusing and separation, while the second pair enables dynamic regulation of the separation distance between particle streams. Experimental results demonstrate that a 50 ppm polyethylene oxide (PEO) solution focuses 1 μm polystyrene particles toward the channel centerline via elastic forces, whereas 5 μm particles migrate toward the channel sidewalls under dominant inertial forces, effectively overcoming the elastic effects. The interplay between inertial and elastic forces thus achieves size-dependent particle separation. Furthermore, by adjusting the flow rate of the PEO sheath in the second pair of microchannels, the separation distance between the two particle populations can be modulated in real time. Higher PEO concentrations (500 and 1000 ppm) exhibit enhanced capabilities to deflect particle flow streams. By contrast, the lower PEO concentrations like 50, 100 and 200 ppm are more versatile in adjusting the separation distance. The biological applicability of this platform is further demonstrated through the tunable separation of Escherichia coli (E. coli) and Chlorella vulgaris (C. vulgaris). This microfluidic device demonstrates significant potential for downstream particle processing applications, including real-time particle detection and targeted drug delivery. Full article

Existing low-dimensional cavity element models developed under the lumped-parameter assumption, which neglect cavity geometric parameters and inertial effects within the cavity, cannot meet the simulation requirements of aircraft-engine secondary air systems (SAS) during the fast transient response processes. To address this gap, this study proposes a modular modeling methodology for a fast transient cavity low-dimensional model. The cavity is partitioned into modules according to the internal flow features during the fast transient response, and the partition ratios are determined by evaluating how different geometric parameters affect these flow characteristics. Using this method, low-dimensional models are constructed for single-port cavities and dual-port cavities under various geometric parameters, and the fast transient depressurization response is investigated. In parallel, corresponding three-dimensional models are established using a validated simulation approach, and three-dimensional computations are performed. Comparison between the low-dimensional and three-dimensional results confirms that the proposed method effectively reproduces the key flow phenomena in the cavity during the fast transient events with credible predictive accuracy. This work optimizes existing low-dimensional simulation algorithms for air systems and provides technical support for studying fast transient responses in aircraft-engine SAS. Full article

Gondolas are a useful mode of transportation in the mountainous regions. In regions located at high altitudes, atmospheric icing is a significant safety hazard to gondola infrastructure. In this study, multiphase numerical simulations of ice accretion on the monopole gondola tower were performed and validated against experimental and analytical model results. An analytical model has limitations for calculating ice loads on large cylinder diameters, and conducting experiments on large cylinders is also challenging due to practical constraints. Ansys FENSAP-ICE 2025 R2, as the primary numerical simulation tool, appears to be an attractive alternative for better estimation of ice loads on structures with larger diameters. The numerical analysis demonstrates that the ice accretion on the access ladder of the gondola tower is more critical than its main structure. This is because the ice growth on the smaller components is higher than on the larger components. A solution based on passive structural design is suggested, in which a semi-circle-shaped wind shield is introduced along the windward side of the tower which successfully diverts the flow by creating a protective droplet shadow on the trailing components, significantly reducing the accreted ice loads. It can also serve as a safety barrier for maintenance personnel. The study also showed that increasing the shield diameter ultimately reduced overall ice accretion, due to the dominant droplet drag forces over inertial forces. Full article