Search Results (759)

In slab continuous casting, the internal hydrodynamics of the submerged entry nozzle (SEN) play a determining role in mold flow stability and product quality, particularly when external electromagnetic flow-control technologies are not employed. This study analyzes a novel bifurcated SEN design intended to promote stable, highly symmetric outlet jets under asymmetric inlet flow conditions produced by typical flow-control devices. The proposed configuration combines three geometric modifications: a square-section bore, a flow-divider bottom wall derived from a rotated mountain-type geometry, and two bell-shaped protrusions that act as flow modulators positioned immediately above the outlet ports. The hydrodynamic behavior inside the nozzle was investigated using complementary experimental and numerical approaches. Physical modeling was conducted in a scaled water model using particle image velocimetry (PIV) to characterize time-averaged velocity fields and flow fluctuations. In parallel, three-dimensional large-eddy simulations (LESs) were performed to resolve transient flow structures and quantify jet characteristics at the nozzle exits. Both approaches show consistent results. The combined action of the flow modulators and the flow-divider bottom wall robustly induces the formation of two nearly identical counter-rotating vortices in the lower region of the SEN. This flow structure suppresses stagnation and recirculation zones near the outlet ports, mitigates inlet-induced asymmetries, and enhances flow evacuation efficiency. Quantitative analysis of the outlet jets indicates a significant reduction in angular dispersion and a flow-rate imbalance below 0.2%, markedly lower than that observed in conventional SEN configurations. The results demonstrate that appropriate internal geometric design can effectively stabilize SEN hydrodynamics without active control systems, offering a feasible and scalable strategy for improving mold flow stability in industrial continuous casting operations. Full article

Salt-bearing foreland fold–thrust belts represent a critical tectonic system for ultra-deep hydrocarbon exploration. In the Kalasu structural belt of the Kuqa Depression—characterized by the “four extremes” of ultra-high temperature, pressure, salinity, and stress—conventional single-detachment models fail to adequately resolve the complex subsalt structures. To address this challenge, this study integrates high-resolution 3D seismic data, field outcrop observations, well logs, balanced cross-sections, and particle image velocimetry (PIV)-monitored physical modeling to propose a ramp–flat multi-detachment model. Our results demonstrate that deformation is governed by four regional detachment horizons: gypsum-salt layers, thick mudstones, coal-bearing strata, and the basement, which vertically partition the basin into six tectonic units: supra-salt, salt, subsalt, supra-coal, coal, and sub-coal basement. The structural architecture is controlled by five key factors: (1) paleo-uplift geometry, (2) distance from the South Tianshan orogenic front, (3) orientation of basin-bounding faults, (4) regional stress regime (pure compression versus transpression), and (5) rheological contrasts among detachment layers. The kinematic evolution follows a progressive sequence: basement-involved thrusting → multi-level ramp–flat detachment folding → cover detachment. Three primary trap levels are identified—subsalt, supra-coal, and sub-coal—hosting six distinct trap styles: pop-up anticlines, imbricate faulted anticlines, structural triangle zones, fault-bend fold anticlines, supra-coal anticlines, and inter-coal/sub-coal anticlines. Notably, under transpressional stress, oblique paleo-uplifts control the formation of enigmatic “fish-scale” arcuate trap belts composed of fault-bend fold anticlines. Full article

Bubble bursting at liquid surfaces was investigated experimentally using high-speed imaging at 25,000 fps and micro-particle image velocimetry (µ-PIV) at up to 4000 flow fields per second. Three fluids with distinct rheological properties were studied: a viscous Newtonian fluid (Emkarox, η₀ = 0.072 Pa·s) and two non-Newtonian fluids (highly viscous Carboxymethyl Cellulose, HV CMC, η₀ = 0.53 Pa·s, and viscoelastic Polyacrylamide, PAAm, η₀ = 57.17 Pa·s). Bubble radii ranged from 1.2 to 4.0 mm, with corresponding lifetimes spanning from O(10⁻²) to O(10¹) s depending on fluid properties. The relationship between bubble size and lifetime at the air–liquid interface was quantified for the non-Newtonian fluids, using the Newtonian fluid as a reference. µ-PIV measurements further captured the rapid dynamics of bubble bursting beneath the interface in the liquids. These findings provide new insight into the complex interfacial mechanisms governing bubble rupture and fluid motion. Full article

Computational fluid dynamics (CFD) plays a crucial role in optimizing micro-centrifugal pump geometries; however, conventional workflows often suffer from fragmentation, manual intervention, and poor interoperability among software tools. In this study, an integrated CFD-based simulation–optimization platform was developed to establish a closed-loop workflow covering parametric modeling, automated meshing, steady CFD analysis, and multi-objective optimization. Using a micro-centrifugal pump as a case study, optimal Latin hypercube sampling, a Kriging surrogate model, and a multi-objective genetic algorithm were combined to quantify the relationships between key structural parameters and hydraulic performance and to identify Pareto-optimal designs. Sensitivity analysis showed that blade count and volute throat height were the dominant factors affecting pump head and efficiency. Compared with the baseline design, the optimized schemes achieved average improvements of 40.36% in head and 22.89% in hydraulic efficiency, with Scheme 1 showing the best overall balance. Experimental validation using hydraulic performance testing and particle image velocimetry showed that the deviation between predicted and measured heads was within 10%, and the measured flow-field trends agreed well with the CFD results. The proposed framework provides a reproducible method for the design optimization of micro-centrifugal pumps and other small-scale turbomachinery. Full article

Flood discharge observations in Japan are shifting from the conventional float-based methods to unmanned techniques such as radio-wave current meters. These approaches differ fundamentally in their measurement principles: the former is based on a Lagrangian framework, whereas the latter relies on a Eulerian framework. In this study, surface velocity fields obtained using particle image velocimetry (PIV) were used to track virtual tracers and derive Lagrangian surface velocities, providing a basis for examining the characteristics of Lagrangian and Eulerian measurements in an actual river under flood conditions. The uncertainties associated with the two frameworks were quantitatively compared, and the principal sources of uncertainty in Lagrangian measurements were identified. To achieve accurate discharge observation based on Eulerian measurements, the influences of measurement duration, subsection configuration, and vertical velocity distribution were investigated. The results suggest that measuring many points over a short duration is more effective than measuring a few points over a long duration. In a fixed-point measurement of subsurface velocity, a velocity dip was observed. Furthermore, the results quantitatively demonstrate the effects of bridge-pier wakes on the required averaging time and subsection configuration, highlighting the practical advantage of conducting observations on the upstream side of bridges. Full article

Servo valves are critical components in hydraulic control systems; their performance directly affects the accuracy and reliability of systems used in aerospace and construction machinery. In service, micron-scale solid contaminants in hydraulic oil tend to deposit within the narrow clearances between spool and sleeve, causing spool sticking and accelerated wear that degrade system stability and lifetime. This study combines fluid–particle coupling analysis, numerical simulation, and experiments to examine particle motion and migration in representative valve-like flow fields. A force model for particles in viscous hydraulic oil is derived from fluid- and particle-dynamics principles, and two-dimensional CFD–DPM models are constructed for laminar, jet-like, and swirling flow conditions. Parametric simulations explore the influence of flow velocity, particle size, and particle density on particle trajectories and displacement. Results indicate that particle size has the strongest effect on migration behavior, with particle displacement increasing from 0.35% to 30.65% in laminar flow, from 2.31% to 67.08% in jet-like flow, and from 1.93% to 145.09% in swirling flow. Fluid velocity also significantly affects particle displacement, while particle density has a relatively minor influence. Swirling flow produces the largest displacement, followed by jet-like and laminar flow. Finally, a Particle Image Velocimetry (PIV)–style experimental platform on scaled models is used to validate key simulation trends. Findings clarify dominant mechanisms of particle contamination in servo valves and offer guidance for gap optimization and anti-contamination design. Full article

This work presents an experimental aerodynamic study of a Mars rover model, aimed at characterizing its flow behavior under Martian environmental conditions. Due to the extremely low Reynolds numbers associated with Mars’ thin atmosphere, the experiments were conducted using a scaled model of the rover manufactured via additive techniques. The study first focuses on understanding how the geometry of the rover influences the overall flow field, identifying key aerodynamic features such as separation zones, vortical structures, and flow reattachment regions driven by the complexity of the vehicle. A comprehensive investigation of the flow around the model was performed using both a hydrodynamic towing tank with dye injection for qualitative visualization, and particle image velocimetry (PIV) for quantitative flow field analysis in wind tunnel tests. After the general flow characterization, a more detailed local analysis was conducted using laser Doppler anemometry (LDA). This phase of the study targeted precise velocity measurements at specific locations corresponding to the MEDA (Mars Environmental Dynamics Analyzer) wind sensors onboard the rover. Quantitative results indicate that the central body induces a local flow acceleration of 20% to 40% relative to the free stream while severe turbulence was recorded in specific angular sectors, with velocity fluctuations reaching up to 120% for Sensor 1 and 90% for Sensor 2. Full article

Micro-scale counter-rotating wind turbines (CRWTs) offer enhanced potential for wake energy recovery. This study proposes an integrated cascade–coupling design framework for high-solidity CRWTs, in which rear rotor geometry and rotor coupling are co-designed based on stereoscopic particle image velocimetry measurements of the front rotor wake. Experiments are conducted at a tip-speed ratio of $\lambda =1.0$, solidity $\sigma =1.25$, spacing ratios of $d=0.6R_T$, $1.0R_T$, and $3.0R_T$, and a tip radius of $R_T=70$ mm. At the physical limit spacing of $d=0.6R_T$, the integrated design increases the system power coefficient by 24.1% while limiting front rotor power reduction to 17.2%, compared to a 10.3% system gain and 34.5% front rotor suppression for the baseline mirrored configuration. Wake measurements confirm near-complete absorption of rotational kinetic energy from the front rotor wake without exacerbating upstream interference. These results demonstrate that cascade-based energy extraction and coupling-based interference mitigation can operate synergistically, enabling compact, high-performance micro-scale CRWTs suitable for space-constrained and urban energy applications. Full article

Pressure fluctuations caused by a jet in crossflow (JICF) can induce cavitation and potentially damage wall surfaces. In mercury targets for a pulsed spallation neutron source, where cavitation damage progresses due to thermal shock, mercury is confined within a vessel that incorporates a double-wall structure—comprising a narrow channel and a main flow channel—to form parallel flows and suppress damage. However, as the damage progressed, penetration holes were formed in the inner wall separating these flows, and characteristic damage patterns were observed that suggest accelerated damage progression caused by JICF, in which a jet flows from the narrow channel into the main channel. The mechanism underlying this phenomenon has not been fully clarified. Therefore, the flow field and pressure fluctuations around the penetration hole were evaluated using PIV measurements in a water loop and numerical simulations of single-phase flow, with varying jet velocity and jet width. The results revealed that inflow through the penetration in the inner wall generates JICF, which produces vortices downstream of the inflow jet and induces pressure fluctuations that may be associated with cavitation. Full article

This study experimentally investigates the dynamics of air bubble plumes in water under varying thermal and hydrodynamic conditions using a two-dimensional Particle Image Velocimetry (PIV) system. The experimental setup consists of a transparent acrylic tank equipped with a bubble generator, a controlled heating system, and a synchronized PIV arrangement to capture both bubble motion and the induced liquid flow field. Experiments were conducted over a range of water temperatures (21–60 °C), air flow rates, and water depths (200–600 mm) to systematically quantify their coupled influence on bubble plume behavior. The results demonstrate that bubble rising velocity (defined here as the mean vertical, buoyancy-driven component of bubble motion measured in the fully developed plume region) increases with water temperature, gas flow rate, and water depth. For a fixed gas flow rate and water depth, increasing the water temperature from 40 °C to 60 °C resulted in an approximately twofold increase in bubble rising velocity, primarily due to reduced liquid viscosity and enhanced buoyancy forces. Bubble velocity also increased with gas flow rate and water depth, reflecting stronger momentum input and extended acceleration distances within taller water columns. PIV-resolved velocity fields further reveal that the surrounding fluid velocity increases proportionally with bubble rising velocity and temperature, confirming a strong coupling between bubble motion and plume-induced circulation. The surrounding liquid velocity reached approximately 30–60% of the corresponding bubble rising velocity, depending on operating conditions. These findings provide quantitative experimental insight into the coupled effects of thermal conditions, gas injection rate, and liquid depth on bubble–liquid interactions. The results contribute valuable validation data for multiphase flow modeling and offer practical relevance for thermal–hydraulic, chemical, and environmental engineering applications involving bubble-driven transport processes. Full article

Entrained gas in hydraulic oil undermines system stability. A rapid engineering method for predicting the separation efficiency of gas–liquid cyclone separators is still lacking. This study proposes an engineering-oriented predictive framework by combining the split ratio, the characteristic scale of the locus of zero vertical velocity envelope, and the axial residence time. A relative migration index, derived from maximum tangential velocity and axial residence time, is coupled with a relative overflow-pipe insertion indicator to characterize the interaction between swirl intensity and effective separation space. The separation-capability transition is described using a coupled logistic mapping. Model coefficients are identified via Eulerian–Eulerian simulations on a calibration set. The model was evaluated on isolated simulation validation sets with varying geometries and inlet gas volume fractions, yielding an R² of 0.762 and a root mean square error (RMSE) of 0.07. Particle Image Velocimetry validation tests on one representative prototype geometry gave RMSE values of 0.061 for simulation versus test and 0.108 for prediction versus test. The framework captures the macroscopic trend of separation efficiency within the investigated range, with the caveat that part of the model coefficients and intermediate inputs remain conditioned by simulation-derived quantities. Full article

Biological reactions are widely applied in processes such as bioenergy production, raw material manufacturing, and resource recovery from waste. As a main reactor type, the stirred-tank bioreactor exhibits prominent advantages of high mixing efficiency and strong adaptability. At present, the optimization of bioreactors mainly focuses on rigid impellers, and the research on flexible impellers is insufficient. Identifying the influence of flexible materials on bioreactor performance is of great significance. In this work, a stirred-tank bioreactor equipped with flexible blades was designed. In addition, a performance detection method coupling Particle Image Velocimetry (PIV) and image recognition was proposed to systematically study the effects of stirring speed, liquid environment, and impeller type. The results indicated that compared with rigid impellers, flexible impellers could reduce 7.7% low-velocity zones and save 15% mixing time. Velocity could be distributed more uniformly, and the suitable velocity ratio was increased by 7.88%. Moreover, the power consumption had been reduced by 7.49%. Taking into account the mixing efficiency and the impact of shear stress, the optimized structural combination and operating parameters were a pitched blade turbine (PBT)-propeller impeller type and a stirring speed of 300 rpm. This work provides important references for the design and optimization of stirred-tank bioreactors. Full article

In this study, systematic experiments are conducted on a vertical rigid cylinder with two degrees of freedom in the subcritical Reynolds-number regime. The selected flow conditions cover the excitation stage, the lock-in stage, and the post-lock-in stage of vortex-induced vibration. Structural displacements, hydrodynamic forces, and wake vorticity fields are measured simultaneously using laser displacement sensors, force transducers, and particle image velocimetry. The results show that the cross-flow motion remains dominant throughout the investigated range, while the in-line motion is activated through phase coupling within the lock-in region. A stage-dependent redistribution of hydrodynamic loading is identified. The loading first concentrates in the cross-flow direction during synchronization, then partially shifts toward the in-line direction under coupled motion, and finally becomes spatially dispersed as desynchronization develops. This directional redistribution moderates the peak cross-flow amplitude, broadens the lock-in region, and alters the sequence of force-coefficient peaks. The synchronized wake measurements reveal that the flow evolves from incoherent structures to organized vortex streets and then to fragmented and irregular patterns, directly reflecting the formation and collapse of directional load concentration. These findings establish a consistent linkage between hydrodynamic loading, structural response, and wake evolution, and provide experimental evidence for the coupled dynamics of two-degree-of-freedom vortex-induced vibration, offering physical insight for the design and assessment of realistic marine cylindrical structures. Full article

To investigate the evolution of turbulent-structure scales in decelerating open-channel flow, this study uses a high-frequency particle image velocimetry system in combination with a 28 m high-precision variable-slope flume to conduct controlled flume experiments. The analysis includes cross-sectional specific energy, velocity profiles, turbulence intensity, Reynolds stress, cross-correlation, and power spectral density. The study examines the turbulent statistical characteristics of decelerating flow and the evolution of turbulent-structure scale distributions during streamwise development. The results show that the velocity profile within the decelerating-flow region generally follows a logarithmic distribution, whereas the outer-region velocity profile gradually deviates from the logarithmic law as water depth increases. Compared with uniform open-channel flow, decelerating flow exhibits significantly higher turbulence intensities and Reynolds-stress levels. During flow development, turbulent structures maintain stronger spatial coherence, with spatial correlation increasing as water depth increases. As the nonuniformity coefficient γ increases, the turbulent-structure scale distribution shifts from bimodal to unimodal. Across the measured sections, the dominant turbulent-structure scales range approximately from λ/H = 2.5 to 20, over the ranges Re_τ = 596–849 and γ = 1.2–2.8. During downstream development, turbulent kinetic energy increases progressively and is redistributed from large and small scales toward intermediate scales. These results provide new insight into turbulence-scale redistribution in decelerating open-channel flow. Full article

The interaction between circular piers and turbulent open-channel flow generates complex three-dimensional structures, including horseshoe vortices at the pier base and wake vortices downstream. These structures increase vertical velocities, pressure fluctuations, and shear stresses, contributing to erosion and structural instability. Although these phenomena have been widely studied, limited attention has been given to surface geometric modifications as a flow-control strategy. This study employs Large Eddy Simulation (LES) to evaluate the influence of a hexagonal dimple pattern on circular piles in a free-surface channel. The dimples were defined by varying diameter, depth, and spacing to reduce vertical velocity and alter vortex formation. The computational domain represents a 0.40 m wide, 12 m long, and 1.2 m high rectangular channel, with an inlet mass flow of 9.4 kg/s and 0.10 m water depth. Model validation against particle image velocimetry (PIV) data showed 99% correlation, confirming numerical accuracy. Results demonstrate that textured surfaces modify flow dynamics by enhancing kinetic energy dissipation and generating micro-vortices that weaken dominant structures. The optimal configuration (6 mm diameter, 2 mm depth, 1 mm spacing) reduced downward vertical velocity by 42% and wake vortex shedding frequency by 24%, indicating improved hydraulic stability and erosion mitigation potential. Full article