Search Results (32)

This paper investigates the influence of coarse particle size on pressure characteristics through horizontal pipe transportation experiments of coarse particles and sand-laden water. As particle size increases, the thin and long grain accumulation layer forming at the pipe bottom and particle clusters above the layer vanish, most grains roll and bounce more quickly, the instantaneous pressure fluctuation intensity increases exponentially, and the time-averaged pressure decreases linearly along the flow direction. The fluctuating pressure probability density tends to obey a Gaussian distribution, and the turbulence power below 16 Hz increases. After adding fine sand constituting sand-laden water flows, the instantaneous pressure fluctuation intensity, transportation energy loss speed and fluctuating pressure amplitudes increase. With increasing particle size, the fitted Gaussian distribution of the fluctuating pressure probability density changes from thin to short and wide, and the spectral power of the measured pressure fluctuations increases within the resolvable frequency range, especially in the range from 8 to 10 Hz. Full article

Solid–liquid transport pumps are widely used in slurry conveying, deep-sea mining, and sediment-laden water delivery, where suspended particles substantially modify internal flow behavior, energy transfer, and operational stability. This review systematically summarizes recent progress on flow evolution and stability issues in centrifugal pumps and related particle-laden pump systems. The fundamental mechanisms of particle dynamics are first discussed, including single-particle transport and force response, particle collision and agglomeration, turbulence modulation by particle assemblies, and wake-induced local disturbances. On this basis, the review further examines particle-induced changes in global flow topology, local separation and backflow, leakage shear layers, and the evolution of representative vortex structures, with particular attention to the enhancement of flow unsteadiness. In addition, the influences of particle size, concentration, density, and shape on hydraulic performance, wear failure, and operational reliability are summarized, together with recent advances in stability evaluation and fault diagnosis. Although substantial progress has been achieved, current studies still show limitations in cross-scale correlation, unified mechanism interpretation, and life-cycle coupled analysis. This review provides a useful reference for understanding solid–liquid two-phase flow mechanisms and for improving anti-wear design and stable operation control of transport pumps. Full article

Accurate modeling of the burning rate of char particles in particle-laden flows is essential. However, because of the strong inhomogeneity and nonlinearity of the process, accurately resolving the surface burning rate of char particles remains challenging. In this study, an eXtreme Gradient Boosting (XGBoost)-based framework is developed to reformulate the conventional char oxidation rate model, namely the Baum&Street (B&S) model, resulting in a modified model referred to as the XGB-B&S model. In this model, a correction term ${\beta }_{\mathrm{turb}}$ is incorporated and formulated using the particle Reynolds number together with a dimensionless temperature. A turbulent mixing layer with char particle combustion is simulated by means of particle-resolved direct numerical simulation with three-dimensions, generating a high-fidelity dataset for model training and validation. To assess the predictive capability of the XGBoost model, its results are benchmarked against those obtained from an Artificial Neural Network model. The comparison indicates that XGBoost provides better overall accuracy, as reflected by a larger coefficient of determination (${\mathrm{R}}^2$) and smaller values of both the root mean square error and the mean absolute error. Finally, the XGB-B&S model is validated against the test dataset. The ${\mathrm{R}}^2$ between the XGB-B&S predictions and the PR-DNS results is significantly higher than that between the conventional B&S model and the PR-DNS results, confirming the strong predictive capability of XGBoost for modeling char particle oxidation rate. Full article

Semi-open impeller sewage pumps are widely used for transporting solid-laden fluids due to their anti-clogging properties. However, unlike extensive research on clear water conditions, the specific mechanisms governing pressure instabilities under solid–liquid two-phase flows remain underexplored. This study investigates the unsteady flow field and pulsation characteristics of a Model 80WQ4QG pump using unsteady CFD simulations based on the Standard k−ϵ turbulence model and the Eulerian–Eulerian multiphase model. The effects of flow rate, particle size, and volume fraction were systematically analyzed. Results indicate that the blade-passing frequency (95 Hz) dominates the pressure spectra, with the volute tongue and impeller outlet identified as the most sensitive regions. While increased flow rates weaken fluctuations at the volute tongue, the presence of solid particles significantly amplifies them. Specifically, compared to single-phase flow, the pulsation amplitudes at the volute tongue increased by 68.15% with a 3.0 mm particle size and by 97.73% at a 20% volume fraction. Physically, this amplification is attributed to the intensified momentum exchange between phases and the enhanced turbulent flow disturbances induced by particle inertia at the rotor–stator interface. These findings clarify the particle-induced flow instability mechanisms, offering theoretical guidelines for optimizing pump durability in multiphase environments. Full article

This study investigates the wear characteristics and optimization of a centrifugal pump (Q = 25 m³/h, H = 50 m, n = 2900 r/min) applied in sediment-laden waters of Southern Xinjiang irrigation systems. A numerical framework integrating the Realizable $k-\epsilon$ turbulence model, Discrete Phase Model (DPM), and Oka erosion model was established to analyze wear patterns under varying parameters (particle size, density, and mass flow rate). Results indicate that the average erosion rate peaks at 0.92 kg/s mass flow rate. Subsequently, a Response Surface Methodology (RSM)-based optimization was implemented: (1) Plackett–Burman (PB) screening identified the inlet placement angle (A), inlet diameter (C), and outlet width (E) as dominant factors; (2) Full factorial design (FFD) revealed significant interactions (e.g., A × C, C × E); (3) Box–Behnken Design (BBD) generated quadratic regression models for head, efficiency, shaft power, and wear rate (R² > 0.94). Optimization reduced the average erosion rate by 31.35% (from 1.550 × 10⁻⁴ to 1.064 × 10⁻⁴ kg·m⁻²·s⁻¹). Experimental validation confirmed the numerical model’s accuracy in predicting wear localization (e.g., impeller outlet). This work provides a robust methodology for enhancing the wear resistance of centrifugal pumps for agricultural irrigation in water with high fine sediment concentration environments. Full article

Sediment-laden seawater (1.4 kg/m³) under controlled flow velocities (1.5 m/s and 3.0 m/s) was employed to evaluate degradation mechanisms in static anti-fouling coatings. Exposure to 1.5 m/s sediment-laden flow induced a 49% reduction in adhesion strength, a 4.9–5.2° decrease in water contact angle, and an elevation in surface roughness from 0.32 μm to 0.88 μm after 30 days. Concurrently, antibacterial rate and anti-algal rate declined by 11.9% and 14.6%, respectively. In comparison, pure seawater scouring at equivalent velocity reduced adhesion by 30% and contact angle by merely 1.1°. Low-flow (1.5 m/s) conditions accelerated abrasive wear, driving severe surface roughening, whereas higher flow velocity (3.0 m/s) disrupted sustained particle–coating contact through turbulence generation, attenuating roughness progression. Crucially, low-flow conditions intensified abrasive wear and promoted severe surface roughening, whereas higher flow velocities generated sufficient turbulence to disrupt sustained particle–coating contact, thereby slowing the progression of roughness. These findings reveal a previously unrecognized, flow-velocity-dependent erosion mechanism: lower velocities encourage particle deposition and progressive surface damage, while higher velocities unexpectedly produce a protective, turbulence-mediated buffering effect that mitigates surface roughening. These findings establish a theoretical foundation for developing advanced anti-fouling coatings with enhanced resistance to sediment erosion. Full article

This study utilizes the Standard k-ε turbulence model and ANSYS CFX software to tackle silt erosion in the top cover clearances of guide vane of the Francis turbine at Genda Power Station (Minjiang River Basin section, 103°17′ E and 31°06′ N) under sediment-laden flow conditions. A numerical simulation of a solid–liquid two-phase flow along the whole flow route was performed under rated operating circumstances to examine the impact of varying guide vane end clearance heights (0.3 mm, 0.5 mm, and 1.0 mm) on internal flow patterns and sediment erosion characteristics. The simulation parameters employed an average sediment concentration of 2.9 kg/m³ and a median particle size of 0.058 mm, indicative of the flood season. The findings demonstrate that augmenting the clearance height intensifies leaky flow and secondary flow, resulting in a 0.49% reduction in efficiency. As the gap expanded from 0.3 mm to 1.0 mm, the leakage flow velocity notably increased to 40 m/s, exacerbating flow separation, enlarging the vortex structures in the vaneless space, and augmenting the sediment velocity gradient and concentration, consequently heightening the risk of erosion. An experimental setup was devised based on the numerical results, and the dynamic resemblance between the constructed test section and the prototype turbine was confirmed for flow velocity, concentration, and Reynolds number. Tests on sediment erosion revealed that the erosion resistance of the anti-sediment erosion material 04Cr13Ni5Mo markedly exceeded that of the base cast steel, especially in high-velocity areas. This study delivers a systematic, quantitative analysis of clearance effects on flow and erosion, along with an experimental wear model specifically for the Gengda Power Station, thereby providing direct theoretical support and engineering guidance for its wear protection strategy and maintenance planning. Full article

The presence of solid particles (or droplets) in a flow leads to a significant increase in heat fluxes, the occurrence of chemical reactions, and erosive surface wear of various aircraft moving in the dusty (or rainy) atmosphere of Earth or Mars. A review of computational, theoretical, and experimental work devoted to the study of the characteristics of the boundary layers (BL) of gas with solid particles was performed. The features of particle motion in laminar and turbulent boundary layers, as well as their inverse effect on gas flow, are considered. Available studies on the stability of the laminar boundary layer and the effect of particles on the laminar–turbulent transition are analyzed. At the end of the review, conclusions are drawn, and priorities for future research are discussed. Full article

Centrifugal irrigation pumps in Southern Xinjiang face severe performance degradation due to high fine-sediment loads in canal water. This study combines Eulerian multiphase simulations with experimental validation to investigate the coupled effects of sediment size (0.05~0.8 mm) and concentration (5~20%) on hydraulic performance. Numerical models incorporating Realizable k–ε turbulence closure and discrete phase tracking reveal two critical thresholds: (1) particle sizes ≥ 0.4 mm trigger a phase transition from localized disturbance to global flow disorder, expanding low-pressure zones by 37% at equivalent concentrations; (2) concentrations exceeding 13% accelerate nonlinear pressure decay through collective particle interactions. Velocity field analysis demonstrates size-dependent attenuation mechanisms: fine sediments (≤0.2 mm) cause gradual dissipation via micro-scale drag, while coarse sediments (≥0.6 mm) induce “cliff-like” velocity drops through inertial impact-blockade chains. Experimental wear tests confirm simulation accuracy in predicting erosion hotspots at impeller inlets/outlets. The identified synergistic thresholds provide critical guidelines for anti-wear design in sediment-laden irrigation systems. Full article

To investigate the impact of sand-laden flow on energy loss in Francis turbines, this study integrates entropy generation theory with numerical simulations conducted using ANSYS CFX. The mixture multiphase flow model and the SST k-ω turbulence model are employed to simulate the solid–liquid two-phase flow throughout the entire flow passage of the turbine at the Gengda Hydropower Station (Minjiang River Basin section, 103°17′ E and 31°06′ N). The energy loss characteristics under different off-design conditions are analyzed on the basis of the average sediment concentration during the flood season (2.9 kg/m³) and a median particle diameter of 0.058 mm. The results indicate that indirect entropy generation and wall entropy generation are the primary contributors to total energy loss, while direct entropy generation accounts for less than 1%. As the guide vane opening increases, the proportion of wall entropy generation initially rises and then decreases, while the total indirect entropy generation exhibits a non-monotonic trend dominated by the flow pattern in the draft tube. Entropy generation on the runner walls increases steadily with larger openings, whereas entropy generation on the draft tube walls first decreases and then increases. The variation in entropy generation on the guide vanes remains relatively small. These findings provide technical support for the optimal design and operation of turbines in sediment-rich rivers. Full article

Developing efficient water-saving irrigation technologies that utilize high sand-laden water is an important approach to alleviating agricultural water scarcity in the Yellow River Basin. This study aims to investigate sedimentation patterns and fluid movement characteristics in drip irrigation emitters under such challenging water conditions. The dynamic changes in Dra and Cu were determined through short-period intermittent clogging tests to evaluate the anti-clogging performance of four different emitter types. The distribution and particle size composition of the deposited sediments inside the emitters were analyzed using a high-resolution electron microscope and a laser particle size analyzer. Additionally, the RNG k-ε turbulence model was used to simulate the fluid movement inside the emitters. The results showed that the B drip irrigation belt had better sediment tolerance and operational stability. The anti-clogging capacity of drip irrigation can be improved by optimizing the combination of emitter channel structure and sediment content. The fluid in the channel was divided into mainstream zone and vortex zone. Sediment particles increased in the backing-water zone and vortex center, where particles of 0.05–0.1 mm were more prone to settling due to reduced transport capacity. Energy dissipation primarily took place at the curvature of the emitter channel, and within each channel unit, gradually decreasing along the vortex flow direction, with the lowest dissipation aligning with sediment deposition zones. These findings provide a theoretical basis for mitigating clogging in high sand-laden water drip irrigation systems, offering valuable insights for improving the effective utilization of water resources in the Yellow River Basin. Full article

In current transportation hubs, passengers travelling with wheeled luggage or suitcases is a common phenomenon. Due to the fact that most luggage occupies a certain space in dense passenger crowds with high mass inertia, its abnormal motion, such as drifting, can frequently trigger unavoidable local disturbances and turbulence in the surrounding pedestrian flows, further increasing congestion risk. Meanwhile, there still is a lack of quantitative disturbance propagation analysis, since most state-of-the-art achievements rely on either scenario-based experiments or the spatial characteristics of crowd distribution assessed qualitatively. Therefore, this study considers the luggage-laden passenger as a deformable particle. The resulting disturbance on surrounding non-luggage-carrying passengers is analyzed and quantified into a nonlinear pressure term. Subsequently, the disturbance propagation model of passenger-owned luggage is developed by adapting the classical Aw–Rascle traffic flow model with a pressure term. Simulation experiments of disturbances caused by luggage drifting and retrograding were conducted in Pathfinder 2022 Software. Experimental results showed that the disturbing force of a left-sided crowd can reach a peak of 238 N with a passenger density of 3.0 $\mathrm{p}/{\mathrm{m}}^2$, and the maximum force difference between the left- and right-sided disturbing force can reach 153 N, as confirmed by a case study in an L-shaped corridor of a transportation hub. Furthermore, it is recommended that the proposed model can be applied in crowd flow analysis and intelligent decision-making for passenger management in transportation hubs. Full article

This work investigates the dynamics of heavy particles dispersed in turbulent channel flows under unstable thermal stratification conditions using point-particle direct numerical simulations (PP-DNS), to quantify the influence of large-scale coherent vortex rolls, arising from the combined effects of shear and buoyancy, on the spatial distribution and preferential sampling behavior of inertial particles. We examined three particle Stokes numbers (${\mathrm{St}}^{+}=0.6,60,120$) and two friction Richardson numbers, ${\mathrm{Ri}}_{\tau }=0.272$ and ${\mathrm{Ri}}_{\tau }=27.2$, which exemplify the regimes below and above the critical condition for vortex roll formation, respectively. The results indicate that the flow reorganization into large-scale longitudinal vortices significantly alters the topological features of small scales in the near-wall region impinged by the thermal plumes, resulting in a prevalence of vorticity-dominated topologies. The interplay between this phenomenon and the tendency of particles to preferentially sample strain-dominated topologies leads to a distinctive asymmetric particle distribution in the near-wall planes. Inertial particles markedly accumulate in the strain-dominated regions where the coherent thermal plumes emerge from the walls, while avoiding the vorticity-dominated impingement zones. This peculiar particle response to the vortex rolls is most pronounced when the particle response time matches the characteristic timescale of the large-scale coherent motions in the cross-stream planes. Full article

Preferential concentration, observed in turbulent flows when particle response times are of the same order of the flow’s characteristic timescales, manifests as non-uniform particle distributions in space. Unraveling its governing mechanisms holds crucial implications for both natural and industrial processes reliant on particle-laden flows. Focusing on particles with small inertia, this study employs Direct Numerical Simulations coupled with Lagrangian particle tracking to investigate the influence of the added-mass factor on the preferential concentration of particles denser than the fluid in the one-way coupling regime. It is shown how the added-mass factor $\beta$ affects particle distribution within the channel through the statistical correlations between particle concentration and typical descriptors of the flow topology. The results suggest that increasing values of $\beta$ (corresponding to lighter particles) significantly reduce the effectiveness of turbophoresis in producing particle accumulation in the near-wall region. Resulting in a gradual decorrelation between particle concentration and both the strain-rate and the vorticity tensors, higher values of $\beta$ lead to a more uniform particle distribution, regardless of the Stokes number. Full article

We present an analysis of the effect of particle inertia and thermal inertia on the heat transfer in a turbulent shearless flow, where an inhomogeneous passive temperature field is advected along with inertial point particles by a homogeneous isotropic velocity field. Eulerian–Lagrangian direct numerical simulations are carried out in both one- and two-way coupling regimes and analyzed through single-point statistics. The role of particle inertia and thermal inertia is discussed by introducing a new decomposition of particle second-order moments in terms of correlations involving Lagrangian acceleration and time derivative of particles. We present how particle relaxation times mediate the level of particle velocity–temperature correlation, which gives particle contribution to the overall heat transfer. For each thermal Stokes number, a critical Stokes number is individuated. The effect of particle feedback on the attenuation or enhancement of fluid temperature variance is presented. We show that particle feedback enhances fluid temperature variance for Stokes numbers less than one and damps is for larger than one Stokes number, regardless of the thermal Stokes number, even if this effect is amplified by an increasing thermal inertia. Full article