Search Results (1,541)

Conventional particle image velocimetry (PIV) techniques face an inherent trade-off between temporal resolution and single-pulse laser energy, limiting their performance in shock wave measurements. This study develops a multi-channel parallel PIV system with programmable timing control to address this constraint. By distributing laser pulses across eight independent optical channels, the system decouples single-pulse energy from the repetition rate, enabling continuous velocity field measurements at microsecond temporal resolution with high signal-to-noise ratio. Experiments were conducted on a planar shock wave propagating over a trapezoidal step in a shock tube facility. The system captured velocity fields at seven consecutive time instants with a 1 μs pulse interval, revealing the curved evolution of diffracted shock fronts and transient flow separation induced by shock–boundary-layer interaction. Comparison with unsteady Reynolds-averaged Navier–Stokes simulations demonstrated that the PIV system resolves fine-scale post-shock perturbations and turbulent fluctuations that were numerically dissipated in computational fluid dynamics. The results verify that the parallel-channel architecture accurately captures unsteady flow structures during shock reflection and diffraction, offering a reliable diagnostic technique for investigations of shock wave dynamics. Full article

The primary objective of this study is to model the velocity distribution in the near-field of a tornado-like flow using computational fluid dynamics (CFD) simulations conducted in ANSYS Fluent 2025 R1. A complementary goal is to develop a computational framework capable of analyzing tornado-induced velocity fields while maintaining a simplified model structure that minimizes computational cost and processing time. The paper begins by introducing the phenomenon of extreme wind events, their classification, and representative cases, with particular emphasis on tornado characteristics and the inherent challenges in accurately capturing their dynamics through numerical modeling. Several Reynolds-Averaged Navier–Stokes (RANS) turbulence models were applied and compared with an analytical Rankine-type vortex profile. The methodological section presents the model development process and the comparative evaluation of simulation results. Various modeling approaches were analyzed to minimize numerical errors, with particular attention paid to mesh refinement and grid sensitivity analysis. The results include a comprehensive investigation of velocity distributions across different model configurations, initial wind speeds, computational domain geometries, and radial distances from the tornado core. Based on these analyses, a representative wind velocity profile was formulated. The findings demonstrate that both the selected RANS turbulence model and the computational domain geometry significantly influence the predicted velocity field in the tornado near-field. The study emphasizes the comparative performance of the Spalart–Allmaras, Realizable k–ε, and SST k–ω models, which showed the closest agreement with the analytical vortex profile. Full article

Background: Patients with type 2 diabetes (T2D) frequently exhibit impaired erythrocyte deformability, which contributes to microvascular dysfunction. We previously reported that imeglimin, a mitochondrial-targeted antidiabetic agent, prolongs erythrocyte lifespan. This study investigated the effects of imeglimin on whole-blood fluidity and its clinical implications in patients with T2D. Methods: This post hoc analysis of the INFINITY study included 25 patients with T2D who completed 6 months of imeglimin treatment (2000 mg/day) followed by a 3-month follow-up. Whole-blood fluidity was assessed by measuring whole-blood passage time using a microchannel array flow analyzer (MC-FAN). Hematological parameters, glycemic markers, and vascular indices, including brachial-ankle pulse wave velocity (baPWV) and toe-brachial index (TBI), were also assessed. Results: Whole-blood fluidity, assessed by 3-month averages of whole-blood passage time, showed an improvement trend at Months 1–3 (p = 0.058) and a significant improvement at Months 4–6 (p = 0.016) compared with baseline; this effect was reversed after discontinuation. Erythrocyte lifespan significantly increased by 10–20% during treatment and remained prolonged after discontinuation. Conversely, red blood cell count, hemoglobin, and hematocrit decreased during treatment and returned toward baseline post-discontinuation. At Month 6, baPWV increased, and TBI decreased, both showing reversibility after treatment cessation. Conclusions: In this exploratory post hoc analysis, imeglimin treatment was associated with reduced whole-blood passage time measured using the MC-FAN system, suggesting improved whole-blood fluidity in patients with T2D. The clinical and mechanistic significance of this observation requires confirmation in future controlled prospective studies incorporating direct assessments of erythrocyte rheology and microvascular function. Full article

Overpressure is widely developed in the Enping Formation of the Baiyun Sag, Pearl River Mouth Basin, yet its origin has long remained controversial. Previous studies, based on the acoustic velocity-effective stress crossplot, concluded that undercompaction is the dominant overpressure mechanism in this area; however, the significant influence of high total organic carbon (TOC) in the thick mudstone intervals on sonic transit time was not effectively eliminated. In this paper, geochemical logging data are used to perform TOC correction on the sonic transit time of Well BY-X1. Combined with log-curve assemblages and the effective-stress crossplot, the overpressure origin is re-identified, and the development characteristics and quantitative patterns of overpressure are clarified. The results show that the maximum TOC of mudstones in the overpressure intervals of the Enping Formation in the Baiyun Sag reaches 5.8%, exhibiting a strong positive correlation with sonic transit time. After TOC correction, the reduction in sonic transit time ranges from 6.8% to 29.8%, with an average reduction of 16.8% in the lower Enping Formation. Before correction, data points fall within the loading curve region, leading to a potential misinterpretation of undercompaction as the dominant mechanism; after correction, all data points plot along the unloading curve. Combined with the absence of significant shifts in density logs, the maximum formation pressure coefficient of 1.53, and the lack of anomalously high porosity, it is confirmed that the dominant origin of overpressure in this area is fluid expansion driven by hydrocarbon generation, rather than undercompaction. The sonic transit-time correction method for organic-rich mudstones established in this study can significantly improve the accuracy of formation-pressure prediction, providing a quantitative reference for the study of overpressure mechanisms in source-rock systems with high heat flow and hydrocarbon-rich sags. Full article

In the current work, pulsating airflow and an external heat source are proposed to improve the evaporation performance of falling films. A volume of fluid (VOF) multiphase flow model is established based on the commercial software ANSYS Fluent 2023 R1 (ANSYS, Inc., Canonsburg, PA, USA) to simulate the falling film evaporation process. Numerical simulations are conducted under combined working conditions with variable average inlet velocity (u₀), relative pulsating amplitude (A), and wall heat flux (q_w). The spatial and temporal distributions of physical fields are visualized via numerical contours and characteristic curves, and the heat and mass transfer enhancement mechanism is revealed from three aspects, namely, the promotion of driving potential difference by wall heat flux, the increase in heat and mass transfer gradients induced by pulsating airflow, and the synergistic effect of the above two factors. The results indicate that the evaporation ratio (Ψ) increases monotonically with the rise of u₀, with a maximum growth rate of 83.8%. By contrast, under the condition of fixed A₀ = 1 m/s while varying u₀, the evaporation ratio exhibits a convex variation with the relative amplitude A = A₀/u₀, and the global optimal value is achieved at A = 1/6, corresponding to u₀ = 6 m/s and A₀ = 1 m/s. Comparative analysis demonstrates that wall heat flux exerts a more significant influence on evaporation performance than pulsating airflow. Specifically, the evaporation ratio at q_w = 10,000 W/m² is 3~4 times higher than that under the adiabatic wall condition. The reliability of the numerical model is first confirmed by comparing the predictions with published experimental data for vertical falling film evaporation. Based on this validated model, the quantified parametric effects and optimal operating conditions provide practical design references for falling film evaporators in seawater desalination and related thermal separation applications. Full article

Reducing aerodynamic drag on medium-duty freight trucks is essential for improving fuel efficiency; however, the relationship between local flow modification, aerodynamic loads, and propulsion-power demand has not yet been sufficiently quantified. This study evaluates the aerodynamic influence of a front deflector on a Chevrolet NQR 1015 box truck using steady RANS CFD with the k–ω SST turbulence model under zero-yaw conditions from 50 to 120 km/h. The numerical setup included near-wall inflation layers and mesh characterization, as well as grid-independence assessments based on C_D, and the Grid Convergence Index. The deflector produced consistent aerodynamic improvements, reducing average drag coefficient by 14.1%, while the average lift coefficient decreased by 73.5%. These aerodynamic changes reduced the average required propulsion power from 53.86 kW to 50.39 kW, corresponding to a 6.4% reduction, with a maximum saving of 8.1% at 120 km/h. Pressure, velocity, and pressure-coefficient C_P distributions indicate that the deflector promotes smoother flow redirection at the cab–box transition, attenuates suction peaks, and suggests lower pressure losses associated with the separated-flow and wake regions. Full article

Affected by moisture cohesion, wet rice seeds exhibit poor flowability and frequent arching blockage during silo discharging, which seriously restricts stable grain storage and conveying. To address this issue and reveal its intrinsic flow mechanism, this study establishes a discrete element method (DEM) model for wet rice seed-silo systems adopting the Hertz-Mindlin with Johnson-Kendall-Roberts (JKR) contact model, which incorporates surface energy to reflect moisture-induced cohesive effects. The model is verified via physical silo discharge tests, with consistent flow patterns, wall pressure error below 3.7% and discharge time error of 2.14%. EDEM parametric simulations are conducted to analyze velocity fluctuation at different silo heights. Coordination number and normalized contact force distribution are adopted to assess micro-contact force distribution in discharge areas, and a force chain extraction algorithm is used to explore variations in force chain length and orientation. Results demonstrate that during discharge, average particle velocity drops from silo bottom to top with growing fluctuation amplitude, presenting obvious stratified flow and intense upper-layer velocity pulsation. Weak contacts dominate wet rice seed groups and conform to exponential decay distribution. The force chain network undergoes three evolution phases: formation, force arch generation and collapse. Quantitative analysis reveals long force chain proportion falls steadily from 81.40% to 3.68% throughout discharge. Short force chains rise to 60.54% in the arch-forming stage and reach 96.32% after arch collapse. Horizontal force chains account for a maximum of 71.09% during arch formation, while vertical ones decline from 99.52% initially to 61.57% post collapse. This research offers mechanical references and quantitative parameters for the design and operation of silos for wet granular farm grains like rice seeds, and is particularly relevant to post-harvest engineering, grain storage safety, and agricultural machinery design. Full article

Debris flows pose significant threats to people and infrastructure in mountainous regions. Their destructive potential largely arises from the deep, dry granular front, followed by a progressively thinner and increasingly watery tail. This phase separation behaviour has been rigorously described in previous work using a depth-averaged theory that accounts for the vertical structure of the flow, velocity shear and relative motion between grains and fluid. This paper numerically solves these equations using a high-resolution shock-capturing scheme to investigate the case of dry and wet granular inclined flows onto a horizontal run-out pad. In this case, comparisons between numerical results and experimental data reveal that the shear-induced grain forward transport, which is completely missed by other debris flow models, exerts stronger influence on debris flows than mobility difference-driven transport that is assimilated into many debris flow models. This shear-induced grain forward transport is responsible for the formation of phase separation and crucial to quantitatively describe the feedback of phase separation on the overall dynamics. The mobility difference-driven transport indeed leads to phase separation, but it does not adequately describe the feedback of phase separation on the debris flow dynamics. Full article

Small unmanned aerial vehicles (UAVs) are widely used in civil and military fields, and their noise problem has always been the industry’s focus. Compared with a traditional propeller fan, a ducted fan offers higher aerodynamic efficiency, lower aerodynamic noise, and greater safety. It has become the key power component of small UAVs. However, due to the rigid restriction on tip clearance, the traditional integral ducted fan is prone to generating a tip leakage vortex, which produces high-intensity aerodynamic noise and significantly reduces propulsion efficiency. To address the above key problem restricting the quiet flight of small UAVs, this paper designs a segmented ducted fan (SDF). It preliminarily explores the influence of the segmented clearance on the fan’s flow field structure and acoustic radiation characteristics. Specifically, the k-ω SST (shear stress transport) turbulence model and the broadband noise source model were used to establish a computational fluid dynamics model, and the effects of fan speed (20,000–40,000 rpm) and duct spacing (0–20 mm) on its aeroacoustic characteristics were systematically studied. The results showed that the SDF’s acoustic power level maximum (APL_max) was significantly higher than that of the traditional integral structure, especially at high speed. At 40,000 rpm, increasing the duct spacing to 20 mm resulted in a sudden increase in APL_max to 194.5 dB, 61.3 dB higher than that of the integral type. Its essence was derived from the three-stage chain amplification mechanism: (1) strong tip leakage vortex induced by geometric clearance; (2) broadband noise caused by vortex impacting the duct wall; (3) resonant coupling of leakage vortex harmonic frequency and duct cavity standing wave. Based on this, a collaborative noise reduction path was proposed: compressing the spacing to ≤10 mm to suppress the intensity of leakage vortex, designing the periodicity of failure vortex combined with the serrated blade tip/inner wall rubber strip, and blocking the acoustic cavity resonance with non-uniform wall stiffness or 8–10 kHz Helmholtz resonator, providing a solution for the low-noise design of UAV propulsion system. Unfortunately, our study cannot currently resolve transient characteristics; only time-averaged velocity/pressure flow-field contours and total acoustic power distribution are obtained for qualitative analysis of macroscopic noise variation laws and flow-sound correlation. Full article

The lubrication performance of high-speed transmission systems directly affects mechanical power consumption and operational reliability. During high-speed oil-stirring lubrication, strong gas–liquid interfacial shear, liquid-film deformation, droplet splashing, and oil-mist transport generate an unsteady multiphase turbulent flow field. Conventional continuum-based numerical methods often face difficulties in resolving interface breakup and transient turbulent dissipation under high-speed rotational excitation. To address this problem, this study develops a coupled Lattice Boltzmann–Large Eddy Simulation (LBM–LES) method for oil–air two-phase flow in a high-speed oil-stirring lubrication system. The D3Q27 discrete velocity model, cumulant collision operator, WALE subgrid-scale model, free-surface tracking, and local grid refinement are integrated to analyze free-surface deformation, oil-mist evolution, and power-loss characteristics. Taking a notched toothless oil-stirring disk as the reference configuration, the effects of oil immersion depth and disk topology on gas–liquid phase distribution, oil-mist coverage, power consumption, and vortex-induced energy dissipation are investigated. The results indicate that oil immersion depth has a nonlinear influence on lubrication performance and power loss. Among the investigated cases, an immersion depth of 20 mm provides a favorable balance between upper-region oil-mist coverage and lower-region oil-pool stability. At this depth, the notched disk exhibits directional oil delivery and relatively low power consumption, whereas the double-rhombus structure expands the oil-mist coverage but increases the average power consumption to approximately 175 W. These findings provide numerical support for balancing oil-mist coverage, mechanical power consumption, and disk topology design in high-speed transmission lubrication systems. Full article

Hypertension is a major risk factor for primary stroke; however, reliable noninvasive physiological biomarkers for early stroke warning in hypertensive patients remain elusive. To characterize the dynamic evolution of cerebral arterial blood conductivity—from the earliest hypertensive stages through to imminent stroke onset—we developed four physiologically grounded numerical models: normotension, borderline hypertension, established hypertension, and pre-stroke hypertension. These models were constructed based on empirically validated correlations between in vivo cerebral arterial blood conductivity and key hemodynamic parameters. All input physiological data were rigorously sourced from peer-reviewed clinical studies. Each model was coupled with standardized geometries constructed using population-averaged templates. Using the finite element method, we simulated blood conductivity across a full cardiac cycle under realistic in vivo physiological conditions. Crucially, we performed quantitative decomposition analysis to isolate and assess the individual contributions of specific physiological parameter changes—such as systolic pressure, dynamic viscosity of blood, hematocrit, and blood flow velocity—to the observed shifts in conductivity during hypertensive progression. Results revealed a biphasic, stage-dependent evolutionary pattern: conductivity initially rises slightly in borderline hypertension, then declines markedly as hypertension advances toward the pre-stroke stage. Relative to the normotensive baseline, conductivity in the pre-stroke model decreased by 17.61%—a reduction strongly associated with hypertension-induced reductions in cerebral blood flow velocity and concurrent increases in hematocrit. Comprehensive mesh independence and time-step sensitivity analyses confirmed the numerical robustness and computational reliability of all simulations. Collectively, these findings demonstrate that cerebral arterial blood conductivity undergoes quantifiable, pre-symptomatic deviation prior to stroke onset, establishing it as mechanistically grounded. The research findings demonstrate substantial theoretical significance and translational potential, grounded in a rigorously validated modeling framework and serving as a robust basis for generating and refining novel scientific hypotheses. Full article

Electric ducted fans (EDFs) have emerged as promising propulsion systems due to their compact design, high thrust density, and enhanced operational safety. Accurate prediction of aerodynamic thrust is essential for EDF design and performance evaluation; however, existing numerical studies have not yet provided a systematic comparison of the thrust-prediction capability of different k−ω-based turbulence models in micro-EDF applications. In this study, a dedicated thrust-measurement platform was developed for a 120 mm EDF, and experimental thrust data were obtained under three representative hover operating conditions. Based on these measurements, six turbulence models, including SST, SK$\omega$, BSL, GEKO, EARSM, and SST-$\gamma$(alg.), were evaluated using three-dimensional CFD simulations. The numerical model was assessed through thrust validation, centerline velocity comparison, power-consistency analysis, grid independence verification, and qualitative flow-field interpretation. A two-factor full-factorial analysis was further conducted to quantify the effects of rotational speed and turbulence model on prediction accuracy and computational cost. The results show that the turbulence model has a stronger influence on the normalized thrust-prediction error than the rotational speed factor over the investigated operating range. The SST-$\gamma$(alg.) model achieves the highest thrust-prediction accuracy, with an average relative deviation of 0.47%, but requires the highest computational cost. In comparison, the SST model provides a favorable balance between accuracy and efficiency, with an average relative deviation of 1.79% and an average computation time of 184.33 min, approximately 33% lower than that of the SST-$\gamma$(alg.) model. The centerline velocity and power-consistency results further support the comparative model assessment. Overall, this study provides an experimentally validated comparative reference for turbulence model selection in simulations of similar 120 mm EDF under hover conditions. Considering both prediction accuracy and computational efficiency, the SST model can serve as a practical turbulence model choice for engineering parameter optimization of similar micro-EDF configurations. Full article

Pin arrangement significantly affects rubber-melt mixing and extrusion in pin-barrel cold-feed extruders. However, internal flow details are difficult to observe experimentally, and efficient prediction of flow-field parameters remains unavailable. This study used a finite-element model preliminarily validated against measured temperatures, together with particle tracing, to compare configurations with 0, 2, 4, and 6 pins per group. A dataset of 140 pin arrangements was generated by Latin hypercube sampling and numerical simulation. A mind evolutionary algorithm-optimized back-propagation neural network (MEA-BP) was then developed to predict melt volume-averaged temperature and average shear rate. Pins increased melt velocity and shear heating and improved cross-sectional temperature uniformity. Among the four uniform configurations, the 4-pin-per-group configuration showed the fastest reduction in segregation scale with a moderate residence time, achieving a favorable balance between mixing adequacy and processing efficiency. Particle tracing indicated repeated fluid splitting and recombination, whereas further increases in the number of pins yielded limited benefits. Under identical data partitions, network settings, and evaluation conditions, MEA-BP achieved R² values of 0.957 and 0.872 for temperature and shear-rate prediction, respectively, outperforming GA-BP, PSO-BP, and conventional BP. Full article

Currently, Computational Solid Mechanics (CSM) and Computational Fluid Dynamics (CFD) simulations are not enough to correctly estimate the different physical characteristics found in the human cardiovascular system. As an alternative to individual simulations, Fluid Structure Interaction (FSI) simulations can yield more accurate physical quantities. In this study a comparison between rigid-wall CFD of a thoracic aorta affected by an aneurysm and the FSI of the Descending Thoracic Aortic Aneurysm (DTAA) itself was performed. The 18-year-old patient-specific geometry of the aorta and its branches was based on the National Institutes of Health public database. A patient-specific pulsatile blood flow waveform and a pressure three-element Windkessel model were set for boundary conditions. Parameters such as wall pressure, velocity distribution, Wall Shear Stress (WSS), Time-averaged Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), wall displacement and Von Mises Stress (VMS) were investigated. The research shown that blood flow in the aorta is strongly affected by the onset of the aneurysm, which causes recirculation and uneven flow within the aneurysmal bulge. The results highlight that rigid-wall CFD, which cannot capture wall deformation and aneurysm compliance, leads to an overestimation of velocity, WSS, and TAWSS by 15, 21, and $32\%$ respectively, compared to FSI during the systolic peak; furthermore, a key novelty is represented by the slight underestimation of pressure during the systolic peak, an aspect not previously detailed in the DTAA literature. Full article

Multi-scale vortex structures constitute the intrinsic skeleton of turbulent flows and govern the energy cascade process in oceanic turbulence. Elucidating their evolutionary dynamics is crucial for understanding turbulent mixing and transport. In this study, we develop an innovative Energy Cascade Multilayer Directed Network (ECMDN) framework grounded in complex network theory to directly characterize nonlinear energy coupling pathways and directional transfers among multi-scale vortices in real marine environments. By integrating multi-parameter fusion node definitions, multi-scale interaction detection, and energy transfer direction identification, the ECMDN reconstructs the nonlinear turbulent system into a topologically interpretable structure. The emergent network properties enable quantitative characterization of intermittency and inhomogeneity in the energy cascade, offering new insights into vortex interactions and cross-scale energy transfer mechanisms. Compared with conventional cascade diagnostics including spectral flux, third-order velocity structure functions, multifractal analysis and shell models that require homogeneity and local equilibrium assumptions and only output global averaged energy flux, the proposed ECMDN multilayer network retains point-wise depth coordinates of each vortex interaction, separates directed forward/inverse energy edges, and quantifies intermittency via topological metrics. Analysis of the single Shenhu thermocline shear segment demonstrates these differentiated analytical capabilities of the proposed framework. Application to shear measurements from the Shenhu Sea reveals the simultaneous occurrence of forward and inverse energy cascades, manifesting a synchronous dual-energy-cascade pattern. This indicates that vortices at a given scale can concurrently transfer energy to larger- or smaller-scale structures and receive energy from larger- or smaller-scale counterparts during the cascade process. Our findings observe a typical synchronous dual-energy-cascade pattern in the strong thermocline of the Shenhu Sea, providing a novel theoretical and methodological framework for investigating the spatiotemporal evolution of stratified ocean turbulent mixing and advancing our understanding of geophysical fluid dynamics. Full article