Fluids

Wall-flow filters are used in exhaust gas after treatment systems to reduce particulate matter emissions from internal combustion engines. The particles accumulate on the filter surface during operation, forming a layer that progressively increases the flow resistance and thus the pressure drop. This layer consists mostly of combustible materials but also contains inert ash parts. The pressure drop increase leads to the necessity of regenerating the filter. Filter regeneration may cause particle structure fragments to rearrange within single-filter channels, leading to specific ash deposition patterns that modify the filter’s pressure drop, loading behavior, and separation efficiency. This work advances previous investigations toward application-relevant temperature and inflow-velocity conditions by extending the existing resolved-particle methodology with turbulence and reaction models, enabling temperature-dependent effects on particle-structure fragments to be considered. The rearrangement process is studied in detail. It can be shown that at high velocity, most gas crosses into the outlet channel at the end of the inflow channel, leading to a pressure spike. A fragment-local reaction model was introduced and shows qualitative agreement with the experimental results. These simulations also showed a temperature difference of about 15 K between particles at the beginning and end of the inlet channel, leading to faster oxidation close to the inlet. The presented modeling approach helps to assess the formation of deposition patterns and their influence on filter behavior, engine efficiency, fuel consumption, and long-term filter durability. Full article

This study investigates the effects of magnesium carbonate (MgCO₃) nanoparticles in addition to cottonseed biodiesel/diesel blends on diesel engine performance and emission characteristics. Experiments were conducted under various engine loads, and Response Surface Methodology (RSM) was employed for modeling and multi-objective optimization of operating parameters. Results showed that biodiesel blends increased brake-specific fuel consumption (BSFC) by up to 16.11% and reduced brake thermal efficiency (BTE) by up to 13.53% compared to diesel fuel, mainly due to lower calorific value and higher viscosity. However, the addition of MgCO₃ nanoparticles improved combustion performance, reducing BSFC by up to 5.25% and increasing BTE by up to 5.87% under optimal conditions. Emission analysis revealed that nitrogen oxide (NO_x) emissions increased by up to 49.06%, while hydrocarbon (HC) and carbon monoxide (CO) emissions decreased by up to 42.44% and 51.93%, respectively, indicating enhanced combustion efficiency. Carbon dioxide (CO₂) emissions increased by up to 17.67% due to improved oxidation reactions. RSM analysis confirmed the statistical significance of the developed models with high coefficients of determination (R² = 0.9178–0.9921). The optimal operating condition was determined to be 52.30 ppm MgCO₃ and 1.51 kW engine load. Validation experiments showed good agreement between predicted and experimental results, with errors ranging from 0.71% to 8.83%, all within acceptable limits. Overall, the study demonstrates that MgCO₃ nanoparticles can partially mitigate the performance drawbacks of biodiesel while improving combustion quality, and RSM is an effective tool for optimizing engine operating conditions. Full article

This paper systematically investigates the hydrodynamic and seabed dynamic responses around twin-pile groups under various wave–current combinations (current velocity $U_c=\pm 1.0,\pm 0.8,\pm 0.6,\pm 0.4,\pm 0.2, 0$ m/s) and flow skew angles ($\theta =0^{°},{30}^{°},{60}^{°},{90}^{°}$) using a 3D coupled model developed in OpenFOAM. Hydrodynamic results indicate that water surface profiles and gap vortex shedding are heavily modulated by wave–current superposition and pile arrangements. Specifically, strong following currents elongate separated shear layers and amplify gap vorticity, whereas increasing the flow skew angle ($\theta \ge {60}^{°}$) effectively mitigates upstream wake interference. Furthermore, pore water pressure escalates sharply from strong opposing to strong following currents, exhibiting significant attenuation with depth. Strong opposing currents drastically intensify lateral liquefaction risks around the upstream pile, while strong following currents induce irregular liquefaction distribution. Especially, the maximum pore water pressure and maximum liquefaction depths are induced under strong currents ($U_c=\pm 1.0$ m/s) at a ${60}^{°}$ staggered arrangement. These findings highlight the vulnerability of the lateral seabed regions, indicating that targeted asymmetric reinforcement strategies offer an effective approach for mitigating liquefaction risks in offshore twin-pile foundation designs. Full article

Severe fracturing-fluid retention and low post-fracturing flowback efficiency are common in the Lianggaoshan shale reservoirs of the Sichuan Basin. Liquid loading may also occur during late production. To address these problems, this study investigates a synergistic flowback technology that combines natural fracturing-fluid flowback with CO₂ gas lift. First, based on the complex fracture network characteristics of the Lianggaoshan shale reservoir, the interaction mechanisms between hydraulic fractures and natural fractures were investigated. An energy model for fracturing-fluid flowback under natural flowback conditions was established, revealing that reservoir gas expansion energy, hydromechanical energy, and rock elastic energy are the primary driving forces for fracturing-fluid flowback. Furthermore, considering fracture closure behavior, fluid leakoff, and wellbore flow dynamics, a calculation model for the natural flowback of fracturing fluid was developed, and a staged pressure-controlled flowback strategy was proposed. Subsequently, to address the decline in liquid unloading capacity caused by formation-energy depletion during the late stage of natural flowback, a gas-lift-assisted flowback multiphase flow model for the wellbore was established. The effects of the gas injection pressure, gas injection rate, and wellhead pressure on liquid unloading efficiency were systematically investigated. The results indicate that the liquid unloading rate increases with an increasing gas injection pressure and gas injection rate; however, a pronounced diminishing marginal effect is observed. For the Well H1 reference case, the central recommended gas injection pressure was 12 MPa, the gas injection rate was 8 × 10⁴–10 × 10⁴ m³/d, and the wellhead backpressure was maintained below 0.5 MPa. Furthermore, the CO₂-assisted flowback mechanisms were evaluated by distinguishing between the effects explicitly represented in the model and the potential reservoir-scale physicochemical effects. The reduction in wellbore mixture density and bottomhole flowing pressure was simulated directly, whereas CO₂–oil mass transfer, viscosity reduction, mineral dissolution, and changes in water-blocking behavior were interpreted with reference to published experimental studies. Based on these mechanisms, a three-stage synergistic optimized flowback scheme, consisting of “CO₂ soaking–natural flowback–CO₂ gas lift,” was established. A sequence of stagewise quasi-steady PIPESIM calculations was subsequently performed over the 30-day operating schedule. Under the adopted simulation conditions, the recommended soaking period is 5–7 days. The operation should be switched to gas lift when the wellhead pressure falls below 1.5 MPa or when daily liquid production declines continuously by more than 20%. Under the synergistic scheme, the 30-day cumulative flowback volume was predicted to reach 3492 m³. This value was substantially higher than those obtained by conventional natural flowback and standalone gas-lift processes. Moreover, the flowback curve exhibits a distinct “secondary surge” characteristic. These findings provide a theoretical basis and technical support for efficient fracturing-fluid flowback and stable long-term production in the Lianggaoshan Formation. They may also be applicable to other shale oil reservoirs with low porosity and ultra-low permeability. Full article

Agitator reactors are widely used in chemical production processes, and their structural design has a significant impact on power consumption. Therefore, this study performs numerical simulations of multi-stage cup-shaped paddle agitators with different geometric parameters, and discusses in detail the effects of the paddle spacing (S/H), the ratio of the upper paddle length to the reactor radius (L_s/R), the ratio of the lower paddle length to the reactor radius (L_x/R), and the ratio of the upper to lower paddle lengths (L_s/L_x) on the reactor’s power characteristics and internal flow field. Equations were derived to relate the power number (Np) to parameters such as Re, L_s/R, and L_x/R. The study found that, at the same Reynolds number, torque exhibits a slight upward trend as the paddle spacing increases; the best mixing effect is achieved when S/H is 0.333. Based on this pitch, when L_s/R, and L_x/R exceed 0.67, the mixing process fails to form a stable and complete radial circulation; when L_s/R and L_x/R are less than 0.53, the high-velocity zone in the flow field decreases, leading to the formation of dead zones. Therefore, selecting a multi-stage cup-shaped impeller with an L_s/R value of 0.53, an L_x/R value of 0.53, and L_s/L_x of 1 can achieve better mixing results with lower power consumption. These findings provide a reference for the energy-efficient optimization design of multi-stage cup-shaped impeller mixers in industrial applications. Full article

Tsunamis, though infrequent, pose catastrophic threats to coastal communities and infrastructure, underscoring the urgent need for effective mitigation strategies. This review provides a comprehensive evaluation of current engineered countermeasures, specifically seawalls, breakwaters, and water-filled canals, by synthesizing findings from post-tsunami field surveys. Evidence from major events, such as the 2011 Tohoku Tsunami, indicates that well-designed structural measures can substantially reduce tsunami wave energy and delay inland inundation, thereby improving the resilience of coastal infrastructure. However, their effectiveness depends heavily on proper geometric configuration, construction quality, regular maintenance, and integration with non-structural measures such as evacuation planning. Recent experimental and numerical investigations have also highlighted the potential of innovative countermeasures, in attenuating bore forces and protecting critical infrastructure. Despite advancements, significant knowledge gaps remain, particularly concerning the long-term reliability, cost-effectiveness, and adaptability of these systems under diverse tsunami conditions. This critical review aims to identify these gaps and outline key priorities for future research and development. The findings contribute to a deeper understanding of structural tsunami mitigation and support the advancement of integrated, resilient strategies for reducing disaster risk in tsunami-prone regions worldwide. Full article

The main objective of this study is to obtain the average parameters of gas-discharge plasma when controlling the steady position of the bow shock wave (BSW) using the combined action of a gas discharge initiated by a current from an external source and a magnetic field near the frontal surface of the model. The studies were carried out using both experimental and numerical methods in xenon and air. A comparison of the numerical and experimental dependences of the relative distance of the steady BSW from the model on the discharge power showed good agreement. Based on the conducted flow modeling, taking into account the dependence of the adiabatic index on the degree of ionization and the degree of nonequilibrium, and using the theory of Burm et al., gas-discharge plasma characteristics were obtained, such as the degree of ionization and the degree of nonequilibrium, the electron density and the electron temperature in the absence and presence of a magnetic field. By this way an integrated experimental–computational system was formed in which the measured characteristics of the discharge and BSW, as well as the numerically obtained averaged plasma parameters in the impact zone, are combined with the theory of Burm et al. to clarify the thermodynamic state of the medium and determine the corresponding characteristics of the gas-discharge plasma. The obtained results can be used for assessing the characteristics of plasma gas dynamic and magnetohydrodynamic phenomena in high-speed flows; for example, in the development of control systems that take into account the influence of plasma parameters and the electric and magnetic fields. Full article

An adaptive immersed boundary method (IBM) for simulating non-isothermal incompressible flows with convective heat transfer involving a rotating circular cylinder is developed. Both Dirichlet- (isothermal) and Neumann (zero heat flux)-type temperature boundary conditions are implemented. In addition to the discrete momentum forcing and energy forcing adopted to effectively satisfy the prescribed velocity and temperature boundary conditions, a mass source/sink term is introduced into the continuity equation to meet the mass conservation at the immersed boundary. The Navier–Stokes equations are solved using the fractional step method implemented on a staggered Cartesian grid system. Time stepping is performed using a second-order Adams–Bashforth/backward-differentiation method, while spatial derivatives are approximated with a second-order centered scheme. Testing of the flow induced by a rotating disk demonstrates that the spatial accuracy of the presented algorithm is second-order. Furthermore, the proposed method is validated by forced convective flow past a rotating isothermal circular cylinder. Finally, mixed Rayleigh–Bénard convection in a square cavity with an embedded adiabatic rotating circular cylinder is simulated, showing that heat transport can be greatly enhanced by increasing the rotating rate and radius of the cylinder at larger Prandtl numbers in the laminar regime. Full article

We study the unsteady mechanical response of an incompressible viscoelastic polymeric fluid in a flat channel, governed by the Vinogradov–Pokrovskii rheological model. The motion arises from an electrohydrodynamic reduction of Poiseuille type, after which the mechanical subsystem decouples from the electric field; the velocity then depends on time and on the transverse coordinate only. Treating the rheological parameter as small, we reduce the governing system in the leading-order approximation to a non-autonomous second-order evolution equation whose stiffness coefficient relaxes exponentially in time, so that the nonstationarity is driven by the internal relaxation of the normal stress rather than by an external force. For spatially homogeneous initial normal stress, we diagonalize the Galerkin system in the sine basis and obtain an explicit modal representation in which each mode satisfies a Bessel equation whose order depends on the mode number. This yields a critical index that splits the modes into three regimes—real order, zero order, and purely imaginary order—a structure absent from the classical UCM and Oldroyd-B solutions. Using the explicit representation, we prove convergence of the modal series and show that the solution decays in the long-time limit, so that the rest state is asymptotically stable in the natural energy phase space. The analytical solution is confirmed numerically. Full article

The main reason for limiting the working flow range of the compressor is the unstable flow phenomenon of the compressor working at a small flow rate, including stall, surge, and rotational instability. Among them, the rotating stall phenomenon is particularly prone to occur during the operation of centrifugal compressors. In this paper, a three-stage nitrogen centrifugal compressor is taken as the research object, and the dynamic development process of rotating stall in the diffuser is captured by full-channel numerical calculation. After research, the leading-edge vortex at the diffuser inlet is the cause of rotating stall. In the throttling process, the backflow in the diffuser causes the channel blockage and the stall phenomenon triggered by the leading-edge overflow. There are six stall channels in the first-stage diffuser and nine stall channels in the second-stage diffuser. The propagation direction is the same as the rotation direction of the blade, and the propagation speeds are 4.348% and 5.26%, respectively. Full article

The analysis of blood flow behavior has been studied in various aspects. Recently, these studies took a turn when they were developed using Computational Fluid Dynamics (CFD), thereby advancing understanding of fluid behavior. Artery geometries and the properties of flow offer a field of interest for developing studies in which the behavior of liquid and structures can be observed. Biomodel development has evolved to allow for greater ease and precision. With a geometry similar to the real one, mechanical properties can be used to conduct studies with greater precision, yielding greater results on the behavior of a fluid and a structure. This research focuses on developing a biomodel of the right carotid artery. CFD and structural analyses are performed using the generated arterial geometry and a control volume that simulates blood flow. The structural analysis was performed using the Finite Element Method (FEM) to obtain results that provide data on the effects on the arterial walls. The results presented focus on the velocity, pressure, and wall shear stress generated by the flow. In addition, a section on displacement and Von Mises stress results is presented, demonstrating how the structure of the arterial walls is affected by these effects. Full article

To address the cleaning requirements for marine growth on offshore platform jackets, an underwater cleaning robot featuring a combined “chassis + thruster-assisted adhesion + magnetic adhesion” mode is designed. The robot is equipped with four thrusters and a magnetic-adhesion wheeled chassis, enabling stable attachment and movement on varying-diameter pipes. Kinematic models in both inertial and body-fixed coordinate systems are established, and six-degree-of-freedom (6-DOF) dynamic equations are derived. These equations systematically incorporate key factors including added-mass forces, damping forces, hydrostatic restoring forces, ocean current disturbances, and thruster torques. Based on CFD simulations employing overset grids, moving reference frames, and simple harmonic motion techniques, the damping, added-mass, and thruster thrust and torque coefficients for each degree of freedom are identified. The obtained parameters demonstrate reasonable consistency with the CFD internal validation and preliminary external verification, providing a complete theoretical model and simulation data to support the motion control and operational stability analysis of the underwater cleaning robot. The established dynamic model addresses the free-navigation condition of the robot without cleaning operation. The additional hydrodynamic effects during cleaning operations will be considered in future work. Full article

A Laval nozzle is a pivotal component of supersonic separation technology for dehydration, but its performance is constrained by low separation efficiency due to intractable conflicts between droplet nucleation and growth rates. To address this issue, this work for the first time applied the Foelsch-MOC method to design an expansion section with a first-order differentiable and second-order continuous profile. A numerical model for pure water vapor condensation based on the ideal gas equation of state (EOS) was then established to optimize nozzle structures for droplet growth. Major findings revealed that the droplet radius of the Foelsch-MOC nozzle was 30.5% higher than that of the conical nozzle, while its outlet liquid mass fraction was 5.8% lower. The liquefaction capacity was found to increase first and then decrease with the expansion coefficient, peaking at 0.5. Moreover, increasing the axis shift from 9.3 mm to 25 mm promoted the outlet liquid mass fraction by 1.2% and decreased the droplet radius by 9.3%, thereby improving liquefaction capacity. These results highlight the droplet growth superiority of the novel expansion profile, providing a valuable guideline for designing nozzles that simultaneously ensure liquefaction efficiency and facilitate droplet development. Full article

This study presents a computationally efficient quasi-one-dimensional mathematical model based on the traveling wave method to investigate hydraulic shock attenuation using a gas-hydraulic damper in pipeline systems. Unlike conventional models, this formulation accounts for fluid compressibility and incorporates a non-linear boundary condition strictly satisfying gas mass conservation within the damper. The model was successfully validated against a MATLAB 2024 Simulink benchmark, demonstrating a maximum pressure amplitude discrepancy of only 5–8%. A parametric analysis evaluated the effects of damper volume, initial gas pressure, and pipe diameter on surge suppression. Results show that insufficient damper volume causes extreme negative pressure drops, risking severe cavitation and fluid column separation. Conversely, excessive volume induces “over-damping,” undesirably increasing system inertia and delaying steady-state recovery. Crucially, scaling analysis reveals that a damper optimized for a specific pipe diameter loses efficacy in larger pipes, as the flow’s kinetic energy scales with the diameter’s square. This model provides a robust, precise computational tool for the optimal and safe design of pipeline networks. Full article

Abdominal aortic aneurysm (AAA) is a critical condition with high rupture risk, and the maximum diameter alone is insufficient for prediction. Pulse wave velocity (PWV), a surrogate of aortic stiffness, can be estimated using 4D-Flow magnetic resonance imaging (MRI), but requires validation under dilated conditions. This in vitro study examined the relationship between PWV and stiffness by comparing healthy and aneurysmal compliant aortic models. Two latex phantoms were fabricated to represent normal and AAA geometries. A circulatory MRI-compatible system simulated physiological inlet flow, with flow rates measured across perpendicular planes using 4D- and 2D-Flow MRI. PWV was derived from transit times of the systolic upstroke and interplane distances. Complementary 1D numerical simulations and laboratory flowmeter measurements were performed. Although the wall elasticity and thickness were identical, PWV in the healthy model ranged from 6.2 to 7.7 m/s and in the aneurysmal model it ranged from 14.2 to 15 m/s. This increase was confirmed by temporal overlap of thoracic flow curves and reduced slope in the transit time–distance regression. Results were consistent across simulations, 2D-Flow, and flowmeter data. Findings highlight that indirect 4D-Flow assessment of thoracic stiffness in the presence of AAA must account for wave reflections introduced by dilation, which significantly alter PWV estimation. Full article

Heat loss in steam injection pipelines is one of the primary causes of low thermal efficiency in heavy oil steam injection. To investigate the heat loss and heat transfer variation patterns in steam injection pipelines, a three-dimensional numerical model was established using Fluent software. The effects of overhead pipeline insulation parameters and environmental factors on heat loss and radial temperature distribution were analyzed. This study systematically quantifies the effects of sunlight radiation for the first time and proposes a heat loss correction equation for sunlight conditions. Additionally, overhead and buried pipelines were compared within the same modeling framework. The results show that selecting insulation materials with low thermal conductivity and increasing the insulation thickness can effectively reduce steam pipeline heat loss. For overhead pipelines, as sunlight radiation intensity increased from 0 W/m² to 800 W/m², actual heat loss decreased from 68.43 W/m² to 58.03 W/m². A sunlight-dependent effective heat transfer coefficient, h_Sunlight (E, T), was fitted to extend surface temperature heat loss calculations under sunlightt conditions, in which determination (R²) is 0.9951 and the average error is 5.57%. Under the same operating conditions, the heat loss of the buried pipelines was 62.59 W/m², which was 8.5% lower than that of the overhead pipelines. The findings provide a theoretical basis for the insulation design, thermal efficiency assessment, and operational optimization under sunlight radiation conditions of steam injection pipelines. Full article