Oscillating-wing power extractors (OWPEs) are an alternative to rotary wind turbines for small- and medium-scale renewable energy applications. However, the aeroacoustic response of such systems remains largely unexplored. In this study, the power extraction performance and near-field aeroacoustic characteristics of an OWPE are numerically investigated using transient computational fluid dynamics (CFD) simulations coupled with the Ffowcs Williams–Hawkings (FW–H) acoustic model at a Reynolds number Re of 8.58 × 104. Two important operating parameters, namely the pitching amplitude θo and reduced frequency f*, are varied systematically, and the corresponding near-field sound pressure level (SPL) is measured at 20 receiver locations surrounding the OWPE. The results show that the reduced frequency f* has a strong influence on the near-field overall sound pressure level (OSPL), whereas the effect of pitching amplitude is comparatively less significant. Increasing the reduced frequency broadens the acoustic spectrum and increases the predicted near-field acoustic levels, while the acoustic response remains dominated by low-frequency components. Flow-field analysis reveals that the formation, growth, and shedding of the leading-edge vortex (LEV) strongly influence both the power extraction performance and the near-field aeroacoustic characteristics. The Technique for Order Preference by Similarity to Ideal Solution (TOPSIS)-based multi-criteria analysis identified θo = 80° and f* = 0.16 as the optimal operating condition, providing the best compromise between power extraction and near-field acoustic levels.
A computational fluid dynamic (CFD) numerical framework is established in this article to comprehensively uncover the flow evolution laws and gas-liquid phase-change heat transfer mechanisms of vertical falling film with high Reynolds numbers (Re). Systematic numerical analysis are carried out to characterize the liquid film spatial distribution, flow velocity field, internal turbulent vortex structures and comprehensive heat transfer behaviors. The swirl-induced coherent structures are identified using velocity vectors and vortex-detection criteria, and the influences of swirl angle, channel width, and platform height on film thickness distribution and thermal performance are examined. Model validation is performed through comparison with published numerical and experimental data, showing good agreement. The results indicate that, under high Re conditions, swirling motion significantly disrupts the liquid film and intensifies interfacial turbulence, thereby enhancing heat transfer. The inlet region exhibits the highest thermal performance, driven by strong vortex activity. Increasing the swirl angle leads to a reduction in liquid film thickness and an overall enhancement of heat transfer. However, turbulent kinetic energy and dissipation rate exhibit nonlinear responses to changes in swirl angle. An optimal configuration is identified at a swirl angle of 60°, where the average film thickness is approximately 4.03 mm and interfacial fluctuations remain most stable. In addition, a coupled optimal range is observed for channel width and platform height, highlighting their combined influence on flow stability and thermal efficiency. The underlying two-phase transport mechanisms are interpreted in terms of vortex dynamics and energy transfer processes. Based on the simulation results, a heat transfer correlation valid for high Re conditions is developed. The maximum heat transfer coefficient reaches approximately 700 W/m2·K. Furthermore, fitting of the dimensionless heat transfer coefficient (h+) demonstrates excellent predictive capability for heat transfer trends in gas–liquid two-phase internal flows, with a coefficient of determination (R2) of 0.999.
Underwater bio-inspired robots have emerged as a promising alternative to conventional propeller-driven autonomous underwater vehicles and remotely operated vehicles because of their potential for high propulsive efficiency, superior maneuverability, reduced acoustic signatures, and enhanced environmental adaptability. Unlike rigid propellers operating under approximately steady inflow conditions, bio-inspired propulsion relies on strongly unsteady hydrodynamic mechanisms, including vortex generation and shedding, added-mass effects, boundary-layer evolution, and flexible fluid–structure interaction (FSI). These processes fundamentally govern thrust production, energy conversion, and maneuvering performance, yet a systematic synthesis connecting hydrodynamic mechanisms with engineering implementation remains limited. This review addresses that gap from a hydrodynamic perspective. First, the major propulsion modes of aquatic organisms, including body and caudal fin (BCF), median and paired fin (MPF), and jet propulsion, are summarized together with their characteristic wake structures. Key unsteady flow mechanisms are then discussed, including reverse Kármán vortex streets, leading-edge vortex dynamics, dynamic stall, boundary-layer behavior, wake instabilities, and biomimetic drag-reduction strategies. Particular attention is given to flexible FSI, including modeling frameworks, passive deformation–active actuation coupling, stiffness and morphology effects, and energy-transfer pathways. Representative studies report propulsive efficiencies of approximately 50–70% for optimized flexible flapping foils and above 70% for phase-tuned dual-foil systems, while biomimetic surface designs have achieved approximately 5–10% drag reduction under specific flow conditions. However, these gains remain strongly condition-dependent, and their practical transfer is still limited by scale effects, propulsor interference, model uncertainty, material degradation, biofouling and insufficient marine validation. Future directions are proposed in real-environment hydrodynamics, multi-robot flow coordination, interdisciplinary modeling, and advanced materials. This review provides a mechanism-to-design framework for understanding, designing, and optimizing next-generation underwater bio-inspired robots.
This study presents an integrated multi-scale framework for predicting gas entrainment and flow behavior in coalbed methane production systems under gas-liquid two-phase flow conditions. The approach combines three-dimensional computational fluid dynamics simulations, reduced-order modeling, and machine-learning-based prediction to achieve both high physical fidelity and computational efficiency. Such an improved strategy stems from a specific need. As coalbed methane extraction increasingly encounters complex multiphase flow conditions, accurate characterization of gas entrainment has become essential for improving production stability and optimizing downstream gathering and separation systems. In practice, the flow entering rod pumps frequently deviates from the conventional assumption of a purely aqueous phase, leading to strongly coupled gas-liquid interactions that are difficult to capture using traditional modeling approaches. At the same time, the computational cost associated with full three-dimensional simulations limits their applicability to real-time field operations. The present approach is introduced to map the three-dimensional flow dynamics onto a one-dimensional numerical manifold while retaining the dominant physical characteristics of the system. Building upon this reduced representation, a Stacking ensemble learning framework is developed using Support Vector Regression, Back-Propagation Neural Networks, and Random Forests as base learners, combined through an Adaptive Neuro-Fuzzy Inference System meta-learner for rapid field-scale prediction. The results show that the suction effect generated by the rod pump is the dominant mechanism governing gas entrainment. Notably, the proposed prediction model achieves high predictive accuracy, with a root mean square error of 1.75 L/min, a mean absolute error of 0.82 L/min, and a coefficient of determination of 0.98. Furthermore, analysis of the surface pipeline network indicates that terminal flow rates are characterized by low-frequency pulsations that promote stable gas-liquid interface formation within downstream separators.
Injection damage in the M tight oil reservoir is controlled by the coupled effects of inorganic scaling and organic fouling at the pore scale. To clarify the governing mechanisms, this study combines long-duration core flooding, water-chemistry compatibility analysis, and thermodynamic scale prediction with NMR T2 spectroscopy, mercury intrusion capillary pressure, SEM-EDS characterization, and factor-controlled microfluidic visualization that reproduces reservoir pore geometry and wettability. Core flooding tests reveal permeability reductions of 61 to 73 percent after 12 to 24 hours of injection, indicating progressive contraction of effective flow channels. NMR T2 spectra demonstrate strong pore-size selectivity: small pores largely retain their porosity, 99.43 and 89.48 percent, whereas medium and large pores experience substantial losses. SEM imaging and elemental mapping show Ca and Ba co-located with carbon within pore spaces, consistent with CaCO3 and BaSO4 precipitation induced by mixing sulfate-rich injection water with formation brine. Microfluidic experiments further decouple the roles of oil presence, hydrocarbon type, wettability, and asphaltene content. In the presence of oil, injection pressure increases from 20.4 to 93.6 kPa, compared with 1.3 to 13.4 kPa without oil, while pore-space retention decreases to 73 percent versus 92 percent. Inorganic scale alone causes only moderate injectivity impairment, whereas oil-mediated deposition raises total pore blockage to approximately 27 percent, accounting for nearly two-thirds of the overall injectivity decline. Heavier n-tetradecane generates larger aggregates and higher pressures than n-hexane. Oil-wet surfaces promote more continuous deposits, faster pressure escalation, and greater loss of open flow area than hydrophilic substrates. Increasing the asphaltene surrogate concentration from 2 to 6 percent accelerates inlet bank formation and early throat occlusion, reducing pore-space retention from 98.0 to 67.9 percent and increasing pressure from 59.09 to 78.23 kPa.
To address the short peak-production period and limited incremental recovery commonly encountered during chemical flooding of high water-cut reservoirs, this study investigates the dynamic evolution of displacement fronts and their controlling factors through laboratory experiments and numerical simulation. Two-dimensional plate flooding experiments were first conducted to characterize the evolution of the oil bank in homogeneous and heterogeneous reservoirs, revealing a four-stage process of formation, enrichment, mobilization, and residual depletion. Based on water-cut behavior, the flooding process was further classified into early-response, peak-response, and late-response stages. A three-dimensional heterogeneous reservoir model was subsequently developed to quantify the spatiotemporal evolution of the pressure, oil-bank, and chemical-agent fronts. The results show a clear displacement-front sequence, with the pressure front leading, the oil bank occupying the intermediate zone, and the chemical-agent front trailing behind. Sensitivity analyses demonstrate that the flooding system, chemical concentration, and slug size significantly influence oil-bank development. Compared with polymer flooding and polymer-surfactant flooding, the heterogeneous flooding system increases the maximum oil-bank magnitude by 72% and 43%, respectively. Higher chemical concentrations promote oil-bank enrichment, although the incremental benefit gradually diminishes. In addition, a critical slug size of approximately 0.4 PV is identified, beyond which further increases yield limited improvement.
Internal cooling galleries are widely employed to mitigate piston thermal loads in gasoline engines, where their configuration plays a critical role in temperature distribution and component durability. In this study, Cradle CFD was coupled with the Conjugate Heat Transfer (CHT) and Volume of Fluid (VOF) multiphase approaches to investigate the effects of inlet angle and guide vane geometry on piston thermal performance. The SST k-ω turbulence model was adopted to resolve the transient flow behavior associated with reciprocating motion, while the Box-Behnken design methodology was applied to develop empirical correlations for optimization. The results demonstrate that an inlet angle of 10° delivers the most effective thermal performance, reducing the maximum and minimum piston temperatures by 1.69°C and 28.34°C, respectively, while also producing the highest heat transfer coefficient. In contrast, a 15° inlet angle promotes excessive turbulence and flow instability, leading to diminished cooling effectiveness. For the inlet geometry, the configuration defined by L1 = 1.15 mm and L2 = 16.3 mm achieves the highest area-averaged heat transfer coefficient of 1755.13 W/(m2·K) at 270°CA. Subsequent response surface optimization identifies L1 = 2.3 mm and L2 = 14.0 mm as the optimal design parameters, corresponding to a time-averaged heat transfer coefficient of 1928.513 W/(m2·K).
This study investigates the leakage and dispersion behavior of high-pressure CO2 in long-distance pipelines using computational fluid dynamics (CFD) coupled with a regional-scale modeling framework. The influence of key operational and environmental parameters, including transport temperature, pressure, pipeline diameter, leak orifice size, and ambient wind speed, is systematically examined, with particular emphasis on their role in governing the spatial extent of solid CO2 formation. The results indicate that the evolution of the leakage flow field is governed by a strong coupling between thermodynamic effects and fluid dynamic processes. Elevated temperatures delay the formation of the Mach disk structure, while higher pressures enhance jet momentum, suppress turbulent mixing, and consequently slow the decay of CO2 concentration. Smaller pipeline and leak diameters promote the development of deep, localized low-temperature cores due to reduced thermal inertia. In contrast, increased wind speeds significantly enhance convective heat and momentum exchange, accelerating both dispersion and warming of the CO2 plume. Overall, the temperature and pressure state of the transported CO2 emerges as the primary internal control on dry ice formation, whereas geometric constraints and atmospheric conditions govern the accumulation and transport of cold energy. The findings highlight critical risk conditions associated with low transport temperatures, high operating pressures, small leak diameters, and low-wind environments, which collectively favor the formation of extended solid CO2 deposition zones.
To overcome the inherent limitations of conventional post-cementing acidification, including limited acid penetration into the formation and the potential impairment of zonal isolation, a novel pre-cementing acidification approach is proposed. This method aims to remove near-wellbore formation damage before cementing operations. Its feasibility, however, critically depends on the physicochemical compatibility between residual acid and the subsequent cementing fluids, namely spacer fluids and cement slurries. In this study, a comprehensive series of laboratory experiments was conducted to evaluate the effects of residual acid on flushing efficiency, rheological compatibility, and thickening time. The results show that residual acid significantly enhances the ability of spacer fluids to remove drilling fluid filter cakes, increasing the flushing efficiency from 82.61% to 91.90%. In the presence of 2% corrosion inhibitor, increasing the acid dosage further improves flushing performance. Although mild rheological incompatibility is observed between the spacer fluid and the cement slurry, residual acid effectively reduces the R-value, thereby improving fluid compatibility, with a 50% acid concentration providing greater improvement than a 25% concentration. High-temperature and high-pressure tests conducted at 80°C and 150°C show that the thickening times of mixtures containing different acid concentrations and dosages are comparable to, or longer than, that of the neat cement slurry, indicating no risk of flash setting or excessive retardation. These findings demonstrate that the proposed pre-cementing acidification process is compatible with subsequent cementing fluids under the investigated conditions, providing experimental evidence supporting its technical feasibility.
This study develops a particle-fiber-powder composite temporary plugging system and systematically investigates the dynamic plugging behavior of single-component, binary, and ternary formulations to elucidate the mechanisms governing plug formation and optimize material composition for diversion fracturing applications. Conventional temporary plugging materials often exhibit inadequate plug formation, limited pressure-bearing capacity, and poor plugging stability, compromising stimulation effectiveness in heterogeneous reservoirs. Experimental results show that neither the particle-only nor the particle-powder system can establish a stable load-bearing structure, resulting in poor plugging performance. In contrast, fiber incorporation fundamentally transforms weak particle bridging into a mechanically stable plug, with a distinct concentration threshold governing this transition. The addition of powder to the particle-fiber system further accelerates plug formation and enhances plug compactness by reducing pore connectivity. Among the formulations investigated, the ternary system containing 1 wt% particles, 0.5 wt% fibers, and 4 wt% powder exhibits the highest pressure-bearing capacity, achieving a maximum plugging pressure of 13.97 MPa, whereas increasing the powder concentration to 5 wt% produces the shortest plug formation time. Based on these findings, a synergistic plugging mechanism is proposed in which particles form the primary load-bearing skeleton, fibers reinforce and stabilize the particle framework, and powder densifies the pore structure to improve sealing integrity.
The utilization of water-cooled electric furnace ferronickel slag (EFFS) in concrete remains constrained by its intrinsically low pozzolanic reactivity as a supplementary cementitious material (SCM) and its inadequate volumetric stability when employed as aggregate. This study systematically investigates the compositional characteristics of this slag across different particle-size fractions and proposes a wet-grinding activation strategy to enhance its pozzolanic performance. In particular, cement pastes incorporating 10%, 30%, and 50% ultrafine EFFS derived from three original size fractions are comprehensively evaluated in terms of rheological behavior, compressive strength, hydration characteristics, and microstructural evolution. The results demonstrate pronounced size-dependent differences in phase composition. The amorphous phase content of EFFS particles smaller than 1.0 mm (EFFS0) reaches 54.04%, which is 19.72% higher than that of particles larger than 1.8 mm (EFFS2). The higher amorphous content leads to enhanced pozzolanic activity and improved mechanical performance. Mortars containing 30% ultrafine EFFS0 exhibit favorable strength development, with the 28-day compressive strength reaching 96% of that of the plain cement control and showing a 29% increase relative to the corresponding EFFS2 mixture. Based on these findings, a graded utilization strategy for water-cooled EFFS is proposed: The finer and more reactive fractions are suitable for SCM applications after activation, whereas the coarser fractions are more appropriate for non-cementitious applications, such as aggregate utilization.
