Search Results (1,708)

The objectives of reducing and increasing pollutant emissions during the glass production process also apply to the glass industry, meaning that the accurate modeling of a glass furnace is of critical strategic value. In the available literature, several CFD studies have proposed various models with different levels of complexity. Two basic aspects are shared by the existing models, limiting their accuracy and their impact on furnace design: the combustion space is usually solved with reliance on simplified models (e.g., Flamelet and global kinetic mechanisms); and the glass tank is solved separately, using an iterative approach to couple two (or more) simulated domains. This work presents the development of an innovative CFD model to overcome these limitations and to perform accurate simulations of industrial glass furnaces. The reactive flow is solved using a reduced chemical kinetic mechanism and the EDC (eddy dissipation concept) turbulence–chemistry interaction model to properly reproduce the complex combustion development. The glass bath is solved as a laminar flow with the appropriate temperature-dependent glass properties. The two domains are simulated simultaneously and thermally coupled through an interface. This procedure allows for the more accurate calculation of the heat flow and the temperature distributions on the glass bath, accounting for their subsequent influence on the glass convective motions. The simulation of an existing glass furnace, along with selected comparisons with experimental data, are presented to demonstrate the validity of the proposed model. The developed model provides a contribution that allows us to advance the wider understanding of glass furnace dynamics. Full article

Hydrogen has been presented as a promising energy vector in decarbonized economies. Its singular properties can affect important aspects of industrial flames, such as the temperature, emissions, and radiative/convective energy transfer balance, thus requiring in-depth studies to optimize combustion processes using this fuel isolate or in combination with other renewable alternatives. This work aims to conduct a detailed numerical analysis of temperatures and gas emissions in the combustion of biomethane enriched with different proportions of hydrogen, with the intent to contribute to the understanding of the impacts of this natural gas surrogate on practical combustion applications. RANS k-$\omega$ and k-$ϵ$ turbulence models were combined with the GRI Mech 3.0, San Diego, and USC mechanisms using the ANSYS-Fluent 2024-R2 softwareto evaluate its performance regarding flame prediction. The Moss–Brookes model was adopted to predict soot formation for the methane flames by solving transport equations for normalized radical nuclei concentration and the soot mass fraction. The Discrete Ordinates (DOs) method with gray band model was applied to solve the Radiation Transfer Equation (RTE). The results of the experiments and numerical simulations highlight the importance of carefully selecting turbulence and chemical kinetics models for an accurate representation of real-scale industrial burners. Relative mean errors of 1.5% and 6.0% were registered for temperature and pollutants predictions, respectively, with the USD kinetics scheme and k-$omega$ turbulence model presenting the most accurate results. The operational impacts of hydrogen enrichment of biomethane flames were accessed for a practical combustion system. With 15% of hydrogen blending, the obtained results indicate a 73% penalty in CO emissions, an increase of 6% in NO emissions, and a 34 K flame temperature increase. Also, a reduction in flame radiation due to hydrogen enrichment was observed for hydrogen concentrations above 20%, a behavior that can affect practical combustion systems such as those in glass and other ceramics industries. Full article

The wind and slope are deemed to be the determinant factors driving the extreme or erratic spread behavior of wildfire, which, however, has not been fully investigated, especially to elaborate the mechanism of fire spread associated with heat transfer and fluid dynamics. A systematic study is therefore carried out based on a physical-based simulation and proper orthogonal decomposition (POD) analysis. Results show that compared to the wind, the slope plays a more profound effect on the fire structure; with the increase in slope, the fire line undergoes a transition from a W-shape to the U- and pointed V-shape, accompanied by stripe burning zones, indicating a faster spread but incomplete combustion. The wind effect is distinguished by mainly inducing a turbulent backflow ahead of the fire front, while the slope effect promotes convective heating via the enhanced slant fire plume. Different mechanisms are also identified for the heat transfer ahead of the fire line, i.e., the radiative heat is affected by the combined effects of the flame length and view angle, and in contrast, the convective part of the heating flux is dominated by the action of the flame attachment, which is demonstrated to play a crucial role for the fire spread acceleration at higher slopes (>20°). The POD analysis shows the distinct pattern of flame pulsating for the respective wind and slope effects, which sheds light on modeling the unsteady features of fire spreading and reconfirms the necessity of considering the different effects of these two environmental factors. Full article

The aviation sector faces a significant challenge in balancing the rising demand for air travel with the need to reduce its environmental impact. Because air travel accounts for approximately 2.5% of global carbon emissions, there is a need to find sustainable solutions to reduce its environmental impact. Improving aerodynamic performance is a crucial area for reducing fuel consumption and emissions. Nowadays, more focus is given to commercial aviation, which contributes to global aviation emissions. The A380 is the largest passenger aircraft in the world at the moment. It was observed in real life that the wake turbulence from the A380 led to a sudden loss of the Challenger aircraft’s control and a rapid descent of more than 10,000 feet. This Challenger incident is a wake-up call to address the A380’s wake turbulence. Hence, this research focuses on designing and analysing blended winglets for the Airbus A380 to reduce wake turbulence. With the use of modern computational fluid dynamics tools, the current A380 winglets’ performance was evaluated to identify the level of lift, drag and wake vortex patterns. To address these challenges, the performance of newly designed blended winglets with different cant angles, i.e., 0, 15, 45 and 80, was analysed computationally using the K-ω SST turbulent model in the software ANSYS Fluent 2024 R1. It resulted in a decrease in the wake vortex size accompanied by a 1.724% decrease in drag. This research project evidenced that addressing the wake turbulence issue on a large aircraft could improve aerodynamic performance and thus contribute towards sustainable aviation. Full article

This study investigates the seabed response induced by wave shoaling and breaking on a sloping seabed through numerical modeling. A coupled approach is employed, integrating a Reynolds-Averaged Navier–Stokes (RANS) wave model with a poro-elastic soil model based on Biot’s consolidation theory. The wave model incorporates a stress-$\omega$ turbulence model to mitigate the tendency to overestimate turbulence intensity during wave breaking. The numerical simulations capture key hydrodynamic processes such as wave transformation, breaking-induced turbulence, and the evolution of pore pressure and soil stress within the seabed. Model validation against analytical solutions and experimental data confirms the reliability of the numerical framework. The study simulates two types of breaking waves: spilling and plunging breakers. The results indicate that wave breaking significantly alters the spatial and temporal distribution of pore pressures and effective stresses in the seabed. In particular, the undertow generated by breaking waves plays an important role in modulating seabed responses by inducing asymmetric pore pressure and stress distributions. The influence of soil permeability and the degree of saturation on wave-induced responses is investigated, showing that higher permeability facilitates deeper pore pressure penetration, while under lower permeability conditions, a higher degree of saturation significantly enhances pore pressure transmission. Additionally, different breaker types exhibit distinct seabed response characteristics, with plunging breakers causing stronger nonlinear effects. These findings provide valuable insights for the design and stability assessment of marine and coastal infrastructure subjected to dynamic wave loading. Full article

In order to study the influence of split blades on the turbine force characteristics and fluid–structure coupling characteristics of pumps, this paper selected the IS 80-50-315 centrifugal pump, used as a reverse-acting hydraulic turbine, as the research object, optimized the original pump-acting turbine impeller, and adopted different combinations of long and short blades. Based on the SIMPLE algorithm and RNG k–ε turbulence model, a complete three-dimensional unsteady numerical simulation was conducted on the internal flow field of the pump-turbine. The results show that the split blades reduce the radial and axial forces. The deformation patterns of rotor components in the two pump types used as turbine models were similar, with deformation gradually decreasing from the inlet to the outlet of the impeller. The equivalent stress distribution law of the rotor components of the two pump turbine models has also been found to be similar, with the maximum stress occurring at the connection between the blades and the front and rear cover plates and the minimum stress occurring at the outlet area of the impeller and the maximum shaft diameter of the pump shaft. The maximum deformation and stress of the rotor components in the split blade impeller model were smaller than those in the original impeller model. Full article

This study analyzes the feasibility of using pressure swirl atomizers at scale as energy generators. Likewise, the Ansys Fluent numerical simulation tool was used, configured based on the Volume of Fluid (VOF) multiphase model and six DOF motion for rigid bodies. In turn, three configurations of feeding flow were tested: upper manifold, lower manifold, and dual manifold. The numerical results show that it is possible to produce mechanical energy with 29.4% and 32.9% efficiency (using the SST k-$\omega$ and k-$\epsilon$ turbulence model, respectively), while generating a uniform spray effect at the outlet of the atomizer, even though this has certain ovoid-type deformities. Likewise, it was found that the addition of an internal rotor to the swirl chamber caused the generation of a very low-pressure contour, leading to an increase in the mass flow consumption of the atomizer. Also, four cases were analyzed, considering a hydraulic supply of both manifolds: 250 kPa, 300 kPa, 350 kPa, and 400 kPa, in order to obtain the characteristic curve of the turbine depending on the mass flow obtained for each case. Finally, this research proves how viable the use of this type of technology is in the field of renewable energy generation and the impact on its performance under different configurations of hydraulic supply. Full article

Bubble–particle collisions in turbulent flows are fundamental to flotation processes, yet their complex dynamics remain challenging to characterize accurately. In this study, a comparison study of a particle–bubble collision system in homogeneous isotropic turbulence was performed using the particle-resolved method and point-particle method. Direct numerical simulations of turbulent flows were achieved using the lattice Boltzmann method (LBM). The effects of hydrodynamics on the collision particles were compared between Lagrangian tracking and directly resolving the disturbance flows around finite-size solid particles using an interpolated bounce-back scheme. The differences between point-particle and particle-resolved simulations are evaluated, highlighting their respective strengths and limitations. These findings enhance the understanding of turbulence-driven bubble–particle interactions and provide guidance for improving the accuracy of flotation modeling and process optimization. Full article

Turbulence and instability problems are unavoidable challenges for fluid film bearings as rotation speed continues to rise. This paper investigates the effect of turbulence on the dynamic characteristics of two non-circular journal bearings, hybrid two-lobe bearing (TLB) and hybrid three-step recess bearing (TSRB), under large Sommerfeld number conditions. The linear perturbation method and nonlinear trajectory method are employed in this work. The bearing stiffness coefficients, damping coefficients, and threshold speed are determined by solving the perturbed Reynolds equation using the finite element method. Additionally, the bearing nonlinear trajectories are obtained by solving the motion equation and the dynamic Reynolds equation simultaneously. The threshold speed and trajectory spectrum are utilized to evaluate the bearing dynamic characteristics, and the results derived from laminar and turbulence models are compared. The research on those two different types of bearings has yielded a consistent conclusion: under large Sommerfeld number conditions, the onset of turbulence significantly enhances both the stiffness and damping coefficients of the bearings, as well as the onset speed for the appearance of half-frequency components in the trajectory. The findings suggest that turbulence lubrication is beneficial for improving the dynamic characteristics of these non-circular bearings. Full article

As resources are extracted from the deeper sections of a mine, the ventilation network becomes increasingly complex. Consequently, determining the optimal installation location for speed-measuring equipment that accurately reflects the average wind speed along the roadway remains a challenging task. In this study, two three-dimensional geometric models, smooth and rough, were developed based on field conditions. The cross-sectional widths, heights, and flow velocities of the model channels were processed dimensionlessly. The dimensionless velocity distributions of the smooth and rough models were then analyzed for different Reynolds numbers. It was observed that the dimensionless average velocity ring distributions for the rough model were smaller than those for the smooth model. Additionally, the maximum values of dimensionless flow velocities were negatively correlated with the flow velocities under laminar flow conditions, whereas they largely overlapped under turbulent flow. The dimensionless distances of the average velocity rings from the top and sidewalls of the channel were studied and determined for both models across different flow regimes. Specifically, the dimensionless distance values $d(-)$ were found to be 0.111 for the smooth model and 0.101 for the rough model under the laminar regime. Under the turbulence regime, the corresponding values were 0.106 and 0.108. Likewise, the values of $h(-)$ were 0.135 and 0.135 for the smooth and rough models in the laminar flow regime, while under turbulent flow, the values were 0.131 and 0.162, respectively. The largest dimensionless velocity value was identified at the center of the velocity distribution circle. For corners that did not maintain simple parallelism with the walls, these regions were incorporated into the circle equation using the Least Squares Method, providing a theoretical basis for the placement of velocity-measuring equipment in practical applications. By using the sidewall as the reference coordinate, an appropriate mathematical model was employed to establish the functional relationship between the centerline velocity of the roadway and the dimensionless horizontal coordinate. The fitting results showed good agreement, and this model can be used to back-calculate and expand the potential installation locations for a mine anemometer. Full article

On steep-sloped watersheds, high-intensity, short-duration rainfall events are the leading causes of flash floods. Typical overland flow analysis assumes sheet-like flow with a shallow water depth. However, the natural creek beds in steep watersheds produce complex and intense flows with a shallow depth and high velocity. According to the hydrodynamical modeling processes for open channel turbulent flow, calculating rainfall-induced overland flow becomes a complex task. Steep topography requires a highly refined numerical mesh, which demands a more complex simulation process. Depth-integrated models with distributed parameters provide useful methods to capture the behavior of steep watersheds. This study investigates the watershed’s overland flow behavior by varying turbulent flow parameters and monitoring possible model errors. The refined modeling places a heavy demand on numerical solvers used for simulating the overland flow motion. This paper examines different depth-integrated model solvers applied to artificial watersheds and compares results produced by the different solver types. This study found that the Shallow Water Equation solutions produced the most consistent and stable results, with the Local Inertia Approximation solutions performing adequately. Adding Large Eddy Simulation to these solutions tended to overcomplicate Shallow Water solutions but generally improved Large Eddy solutions. The Diffuse Wave Equation solutions produced erratic results, losing stability and accuracy as watershed slopes steepened and flow paths became complex. 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

Urban heat islands (UHIs) constitute one of the most conspicuous anthropogenic impacts on local climates, characterized by elevated land surface temperatures in urban areas compared to surrounding rural regions. This study represents a novel and comprehensive effort to characterize the spectral signature of SUHI through the lens of the two-dimensional (2D) turbulence theory, with a particular focus on identifying energy cascade regimes and their climatic modulation. The theory of two-dimensional (2D) turbulence, first described by Kraichnan and Batchelor, predicts two distinct energy cascade regimes: an inverse energy cascade at larger scales (low wavenumbers) and a direct enstrophy cascade at smaller scales (high wavenumbers). These cascades can be detected and characterized through spatial power spectra analysis, offering a scale-dependent understanding of the SUHI phenomenon. Despite the theoretical appeal, empirical validation of the 2D turbulence hypothesis in urban thermal landscapes remains scarce. This study aims to fill this gap by analyzing the spatial power spectra of land surface temperatures across 14 cities representing diverse climatic zones, capturing varied urban morphologies, structures, and materials. We analyzed multi-decadal LST datasets to compute spatial power spectra across summer and winter seasons, identifying spectral breakpoints that separate large-scale energy retention from small-scale dissipative processes. The findings reveal systematic deviations from classical turbulence scaling laws, with spectral slopes before the breakpoint ranging from ~K^−1.6 to ~K^−2.7 in winter and ~K^−1.5 to ~K^−2.4 in summer, while post-breakpoint slopes steepened significantly to ~K^−3.5 to ~K^−4.6 in winter and ~K^−3.3 to ~K^−4.3 in summer. These deviations suggest that urban heat turbulence is modulated by anisotropic surface heterogeneities, mesoscale instabilities, and seasonally dependent energy dissipation mechanisms. Notably, desert and Mediterranean climates exhibited the most pronounced small-scale dissipation, whereas oceanic and humid subtropical cities showed more gradual spectral transitions, likely due to differences in moisture availability and convective mixing. These results underscore the necessity of incorporating turbulence theory into urban climate models to better capture the scale-dependent nature of urban heat exchange. The observed spectral breakpoints offer a diagnostic tool for identifying critical scales at which urban heat mitigation strategies—such as green infrastructure, optimized urban ventilation, and reflective materials—can be most effective. Furthermore, our findings highlight the importance of regional climatic context in shaping urban spectral energy distributions, necessitating climate-specific urban design interventions. By advancing our understanding of urban thermal turbulence, this research contributes to the broader discourse on sustainable urban development and resilience in a warming world. Full article

The toothless oil stirring disk is vital in modern transmission technology, particularly in fields like aviation, aerospace, and nuclear power, significantly impacting equipment performance. Oil-stirring lubrication is widely used in internal systems due to its simplicity and high reliability, but oil-stirring losses during lubrication contribute to increased system temperatures, affecting lifespan and performance. Accurate simulation of the two-phase flow during the lubrication process of high-speed toothless oil stirring disks is crucial for extending the lubrication system service life. This paper proposes a dynamic modeling approach for the lubrication of high-speed toothless oil stirring disks, integrating the volume of fluid (VOF) model and the RNG k-ε turbulence model, alongside spring smoothing and dynamic mesh reconstruction techniques. The model explores fluid flow and oil distribution in high-speed, toothless oil stirring pans, investigating the effects of different stirring pan speeds and oil heights on lubrication performance. Results indicate that stirring pan speed and oil height are key to improving lubrication efficiency. At high speeds, centrifugal force and gravity cause the lubricating oil to detach from the stirring pan surface, continuing to splash due to inertia. At 3200 r/min and an oil level of 20 mm, a stable oil film forms in the gearbox. Higher stirring pan speeds generate greater turbulence, enhancing lubrication effectiveness. The findings offer theoretical insights for dynamic lubrication system modeling and support gearbox design and optimization in aerospace and similar fields. Full article

The trailing edge of gas turbine blades encounters concentrated heat loads, necessitating cooling techniques distinct from those used in mid-chord regions. Narrow cooling channels in these areas typically incorporate pin fins or dimples for internal cooling. In contrast, external cooling relies on cutback film cooling configurations, which differ significantly from mid-chord designs. Large eddy simulation (LES) has emerged as a powerful tool for investigating heat transfer in these challenging environments, capturing intricate flow phenomena and turbulence effects that Reynolds-Averaged Navier–Stokes (RANS) simulations often cannot resolve. This review synthesizes findings from 54 LES-based studies on trailing edge cooling, focusing on three key configurations: pin fin arrays, dimpled surfaces, and cutback film cooling. LES consistently demonstrated higher accuracy in predicting heat transfer and cooling effectiveness, outperforming RANS by resolving complex flow structures such as horseshoe vortices, shear layer vortices, and unique flow interactions inherent to these geometries. Furthermore, LES provided detailed turbulence statistics and local heat transfer distributions, offering critical insights for optimizing and improving predictive models. Beyond its demonstrated capabilities, this review underscores the future potential of LES in advancing shape optimization, transient flow analysis, and multi-physics simulations, including conjugate heat transfer and flow-structure interactions. Full article