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This study explores the development and validation of an airflow model to support climate prediction for Citrus Under Protective Screens (CUPS) in California. CUPS is a permeable screen structure designed to protect a field of citrus trees from large insects including the vector that causes the devastating citrus greening disease. Because screen structures modify the environmental conditions (e.g., temperature, relative humidity, airflow), farm management and treatment strategies (e.g., pesticide spraying events) must be modified to account for these differences. Toward this end, we develop a model for predicting wind speed and direction in a commercial-scale research CUPS, using a computational fluid dynamics (CFD) model. We describe the model and validate it in two ways. In the first, we model a small-scale replica CUPS under controlled conditions and compare modeled and measured airflow in and around the replica structure. In the second, we model the full-scale CUPS and use historical measurements to back test the models accuracy. In both settings, the modeled airflow values fall within statistical confidence intervals generated from the corresponding measurements of the conditions being modeled. These findings suggest that the model can aid decision support and smart agriculture solutions for farmers as they adapt their farm management practices for CUPS structures.

POREnet, a novel approach to model effective properties of thin porous media, TPM, is presented. The methodology allows the extraction of local effective property tensors by volume averaging from discrete pore networks, PNs, built on the tessellated continuum space of a TPM. The gradient theorem is used to describe 3D transport in bulk tessellated space, providing an appropriate metric to normalize network fluxes. Implemented effective transport properties include diffusivity, permeability, solid-phase conductivity, and entry capillary pressure and contact angle under two-phase conditions, considering multi-component materials with several solid phases and local contact resistances. Calculated property tensors can be saved on 3D image stacks, where interfacial and sub-CV scale features can be added before exporting data to CFD meshes for simulation. Overall, POREnet provides a general-purpose, versatile methodology for modeling TPM in an ample range of conditions within a single CFD framework. Among other advantages, coupling of PN and continuum models at TPM-channel interfaces is simplified, interfacial contact resistances can be included using robin boundary conditions, and transient multiphysics simulations can be implemented more easily using CFD. The code is tested against a miscellaneousness of examples extracted from electrochemical applications.

In this work, large-eddy simulations of hydrogen dispersion from turbulent subsonic hydrogen-gas emissions in a 5.8 × 0.9 × 0.8 m 3 open-ended channel are described. Such numerical modeling of hydrogen-related processes can provide new insights into the safety aspects of hydrogen, an increasingly more common energy carrier, particularly related to explosion hazards. Ten simulations, with jet mass flow rates ranging from 0.08 g/s to 1.27 g/s, have been simulated using the open-source OpenFOAM® 10 suite. The predicted concentrations in the channel are compared to corresponding experimental data, generally showing good agreement. Two distinct dispersion regimes are observed from the numerical data; a strongly stratified "filling box" regime is found for hydrogen mass flows ≲ 0. 15 g/s, whereas a more homogenized "fading box" regime emerges for higher mass flows. Based on the local Froude number in the channel, a novel model for the momentum length scale of the hydrogen jet is proposed, applicable to downward, strongly buoyant (i.e., non-Boussinesq) jets. It is demonstrated that the ratio of this length scale to the vertical length scale of the geometry can be used to predict the dispersion regime, which may benefit simplified predictive models for hydrogen concentrations and, consequently, ignition risks. • Experimental and numerical study of hydrogen dispersion in an open-ended channel. • Subsonic, turbulent jets with mass flows from 0.09 to 1.27 g/s. • Predicted concentrations compared to experimental measurements at 29 locations. • Two dispersion regimes, "filling box" and "fading up box", identified. • A new jet momentum-length model for strongly buoyant, downward jets is proposed. [ABSTRACT FROM AUTHOR]

This study develops a precise and cost-effective method for reducing the complexity of cryogenic hydrogen unintended release. For this purpose, the dominant modes of a well-characterised cryogenic hydrogen jet (Sandia National Laboratories), with stagnation pressure and temperature fixed at 5 bar and 50 K, are extracted using the proper orthogonal decomposition (POD) method. Building on validating the large eddy simulation (LES) against experimental measurements, the velocity field within the LES results is analysed near the release point. The mass fraction half-width of cryogenic hydrogen jets grows linearly with a slope of 0.1115 against the downstream distances, resembling room-temperature jets. The first 10 extracted modes from 500 LES snapshots demonstrate dominance over the remaining modes. In addition, this study evaluates the flammable gas dispersion using LES and 10-mode POD, showing POD effectively identifies high-risk areas within hydrogen's flammability range. Minor deviations (2.1–3.3%) confirm POD's reliability for hazard assessment compared with LES. Furthermore, an in-depth analysis is performed on the radial distributions of hydrogen mass fraction and centreline hydrogen mole fraction. [Display omitted] • Integrating LES and POD to extract dominant modes in Sandia's cryogenic jet release. • Processing 500 LES snapshots to extract dominant modes in hydrogen dispersion. • Evaluating fire risk with LES and 10-mode POD, highlighting POD's effectiveness. • Confirming POD's reliability with minor deviations in fire hazard assessment. • Detailed analysis of radial hydrogen mass fraction and centreline mole fraction. [ABSTRACT FROM AUTHOR]

Cogasification as energy conversion procedure is gradually gaining grounds in the biomass thermal conversion industry. Valorization of sewage sludge by gasification with all its energy potential also comes with some problems like high ash which is known for system instability but blending with coal has proving to be more beneficiary. In this study, a vertical lab-scale continues feed updraft gasification reactor is used to assess the parametric effect on blending sludge and coal at various ratios using air, carbon dioxide, and steam as gasifying agent. The experimental assessment is first conducted to validate a two-dimensional Eulerian computational fluid dynamics numerical simulation by solving the governing equations of mass phases, turbulence, energy, and momentum on a high-resolution mesh model. The validated updraft model is further used to assess the entire gasification process performance by evaluating steam-to-fuel ratio, carbon dioxide-fuel ratio, equivalent ratio and gasification temperature on blending ratios of sewage sludge and coal on syngas composition, yield and quality. There was high hydrogen production during steam gasification, whiles carbon monoxide was favored at higher equivalent ratio. Synergistic analysis indicated a higher synergy coefficient for a mixing ratio of 30% sewage sludge. The tar dynamics showed a counter trend for light and heavy tars as the reactor temperature increase in relation to the blending ratios. • Experimental and CFD model was studied. • Effects of steam/fuel ratio, CO 2 /fuel ratio and ER were well evaluated. • Light and heavy tars depicted counter trend against temperature change. • SS-30% recorded the highest Synergy coefficient. [ABSTRACT FROM AUTHOR]

Axisymmetric diffusers find wide applications in various industrial processes, including combustion systems, pneumatic conveying, and fluidized bed reactors. Understanding and accurately modeling the behavior of two-phase flows in these devices are critical for optimizing their performance and efficiency. Various aspects of the two-phase gas-solid flow, including particle-particle and particle-wall interactions, interphase momentum transfer, and phase segregation, are investigated. Our currently developed technique, which uses a cut-cell technique, is an established new method to handle the inclined wall of an axisymmetric diffuser. The near-wall cells are treated as five faces for the new grid; one is the inclined wall. This helps treat the boundary condition at the wall in an accurate physical way. The code FORTRAN, developed in-house, was used to solve the axisymmetric diffuser using a cut-cell technique. The results of this study will provide valuable insights into the behavior of gas-solid two-phase flows in axisymmetric diffuser. A parametric study of the impact of particles diameters (100 , 200 , and 300 μ m ), the solid volume loading ratios (0.005 , 0.008 , 0.01) , and cant angle (4.5 ∘ , 7 ∘ , 9.5 ∘) effect of axisymmetric diffuser on the local skin friction, pressure, velocity, turbulent kinetic energy, and separation zone. [ABSTRACT FROM AUTHOR]

This study presents a simplified numerical modeling approach that estimates the local scour depths around bridge supports based on the bed shear stresses. It is developed using 3D computational fluid dynamics and coding through ANSYS workbench scripting along with C++ language. The proposed model is called SCFDS (Simplified Computational Fluid Dynamics Scour). The model's main idea is to lower the bed bathymetry at the locations affected by flow obstruction until the shear stresses reach stable target values. The developed model is assessed by applying it to a complex pier of a real bridge over the Nile-River, and its scour data is calculated using the Hec-18 empirical equations. The outcomes of the model's assessment show that it can depict the local scour around complex bridge supports. The developed approach is a novel and efficient tool that can help the designers in simulating local scour in the vicinity of flow obstructions. However, more verification studies are necessary to reach a generalized conclusion. [ABSTRACT FROM AUTHOR]

Cavitation jet technology is extensively applied in fields such as mechanical processing, rock fragmentation, and energy development. To deeply understand the motion characteristics of the submerged jet and evaluate the influence mechanism of cavitation number on cavitation characteristics, the factors of boundary conditions, grid size, and turbulence model were taken into account. In this study, based on CFD numerical simulation technique, the SBES turbulence model was used to analyze the evolution mechanism of the cavitation cloud and the effects of time and jet pressure on the cavitation characteristics. The results show that the SBES turbulence model can better capture the small-scale turbulent details in jet flow and predict the shedding phenomenon of the cavitation cloud downstream. Moreover, when the downstream cavitation cloud collapses, a local high pressure of very short duration is generated and transmitted around, which affects the morphology of the cavitation cloud at the nozzle outlet. And the increase of the jet pressure has a positive effect on the length of the outlet bubble, the vapor volume fraction of the shed cavitation cloud, and the number of small bubbles generated at the gas-water interface at the tail of the cavitation cloud. Besides the effect of cavitation number on the cavitation characteristic of the jet is mainly in the early stages of cavitation, while the effect in the later stages of development is weak. The research can provide theoretical reference for improving nozzle structure and selecting working parameters to improve cavitation performance in engineering applications. [ABSTRACT FROM AUTHOR]

In recent years, the radiative forcing of aircraft contrails and aircraft-induced contrail cirrus have been highlighted as a serious short-term climate impact of the aviation industry. Greater understanding of factors influencing contrail properties are required if routes to mitigation are to be explored. In this work, a parametric turbofan powered aircraft model has been created to study the impact that aircraft design, in particular the interaction between the jet and wingtip vortex, can have on ice crystal formation, growth, and dynamics within a contrail. To investigate this, a contrail microphysics module has been developed and integrated within Rolls-Royce in-house Hydra computational fluid dynamics code. Three-dimensional Reynolds-averaged Navier-Stokes simulations are conducted over the jet and early vortex regime, covering an area which is often simplified in most contrail modeling approaches. It is found that the position of the engine along the wing of an aircraft can impact the formation of the wingtip vortex, altering the contrail properties and distribution downstream of the aircraft. The effect of multi-engine architecture is also assessed and shown to influence the magnitude of exhaust entrainment into the vortex. [ABSTRACT FROM AUTHOR]

This study is dedicated to the development of a mathematical model based on shape optimal control of the inlet domestic frost-free refrigerator in the context of energy consumption reduction. A three-dimensional thermofluid model is established for the numerical studies. As the physical system (with shelves and fruits) can be seen as a porous medium, the coupled state equations of the transport mechanism (for velocity and temperature fields) are governed by Navier–Stokes–Forchheimer/Fourier equations. Then, based on the finite element method, the numerical scheme computation is made with FreeFem++ software (Version 4.6). Numerical results are shown for three different cases: empty without shelves, empty with shelves, and loaded with foods. For each case, the velocity and temperature fields' results are discussed for the optimal configurations. The characterization of these physical parameters would help engineers in domestic frost-free refrigerator design. [ABSTRACT FROM AUTHOR]

This paper aims to compare the thermal performances of the conical solar collector (CSC) system and the spot Fresnel lens system (SFL) using water and CuO nanofluid as the working fluids. The studied CFD models for both systems were validated using experimental data. At an optimal flow rate of 6 L/min, the SFL system showed higher optical and thermal performance in comparison with that of the CSC system. In the case of the SFL system, the availability of a greater amount of solar energy per unit collector area caused an increase in thermal energy. Moreover, in the case of the CSC system, the non-uniform distribution of solar flux on the absorber's outer surface leads to an increase in temperature gradient and heat losses. As a heating medium, the CuO nanofluid outperformed the water in terms of higher thermal conductivity and heat capacity. The average thermal efficiencies of 64.7% and 61.2% were achieved using SFL with and without CuO nanofluid, respectively, which were 2.4% and 0.5% higher than those of the CSC with and without nanofluid. CFD simulations show a 2.80% deviation for SFL and 2.92% for CSC, indicating acceptable accuracy compared to experimental data. [ABSTRACT FROM AUTHOR]

An auxiliary structure can significantly improve the wind-trapping capacity of the Savonius wind turbine. In this study, a novel auxiliary structure called a wind energy gathering structure (WEGS) is proposed, and its five parameters, namely the lengths of the shrinkage and diffusion tubes, the length of the centerboard, the length of the throat, the length of the wind board, and the shrinkage and diffusion angles, are investigated using computational fluid dynamics (CFD) and Taguchi's method. Meanwhile, Taguchi's method and ANOVA reveal that among the studied parameters, the shrinkage and diffusion angles, the length of the centerboard, and the lengths of the shrinkage and diffusion tubes have a more significant influence on the performance of the WEGS. At a tip speed ratio (TSR) value of 1 and a wind speed of 7 m/s, the optimized combination of the WEGS parameters obtained by Taguchi's method improves the mean torque coefficient of the turbine by 42.1%. Moreover, at other TSRs (0.6–1.2), the turbine with the WEGS also outperforms an open turbine in terms of aerodynamic (increases of 20.1–53%) and lifetime performance. [ABSTRACT FROM AUTHOR]

Gas evolution and flow patterns inside an alkaline electrolyzer cell strongly affect efficiency, although such effects have not been explored in detail to date. The present study aims to critically analyze the dependence of cell performance on the multiphase flow phenomena, defining some key metrics for its assessment using CFD. Six performance indicators, involving gas accumulation, bubble coverage, and flow uniformity, are applied to a 3D CFD model of an alkaline cathodic cell, and possible optimizations of the cell geometry are evaluated. The results demonstrate the complexity of defining the optimal indicator, which strictly depends on the case study and on the analysis at hand. For the cell analyzed herein, the parameters linked to the electrode volume fraction were indicated as the most influential on the cell efficiency, allowing us to define the best geometry case during the optimization. Furthermore, a sensitivity analysis was conducted, which showed that higher mass flow rates are generally preferable as they are linked to higher bubble removal. Higher current densities, allowing enhanced gas production, are instead associated with slightly lower efficiencies and stronger nonuniformity of the electrolyte flow inside the cell. [ABSTRACT FROM AUTHOR]

In this work, the influence of plenum and port geometry on the performance of the intake process in a four-stroke spark ignition engine for ultralight aircraft applications is analyzed. Three intake systems are considered: the so-called "standard plenum", with a relatively small plenum volume, the "V1 plenum", with a larger plenum volume, and the "standard plenum" equipped with a large curvature manifold called the "G2 port". Both measurements and 3D CFD simulations, by using Ansys® Academic Fluent, Release 20.2, are performed to characterize and analyze the steady-flow field in the intake system for selected valve lifts. The experimental data and the numerical results are in excellent agreement with each other. The results show that at the maximum valve lift, i.e., 12 mm, the V1 plenum allows an increase in the air mass flow rate of 9.1% and 9.4% compared to the standard plenum and the standard plenum with the "G2 port", respectively. In addition, the volumetric efficiency has been estimated under unsteady-flow conditions for all geometries at relatively high engine rpms. The difference between numerical results and measurements is less than 1% for the standard plenum, thus proving the accuracy of the model, which is then used to study the other configurations. The V1 plenum shows a fairly constant volumetric efficiency as the engine speed increases, although such an efficiency is lower than that of the other two geometries considered in this work. Specifically, the use of the "G2 port" leads to an increase of 1.5% in terms of volumetric efficiency with respect to the configuration with the original manifold. Furthermore, for the "G2 port" configuration, higher turbulent kinetic energy and higher swirl and tumble ratios are observed. This is expected to result in an improvement of air–fuel mixing and flame propagation. [ABSTRACT FROM AUTHOR]

The melting of scrap and hot briquetted iron (HBI) in an AC electric arc furnace (EAF) is simulated by an advanced 3D computational fluid dynamics (CFD) model that captures the arc heating, the scrap/HBI melting process, and the solid collapse mechanisms. The CFD model is used to simulate a scenario where charge layering and EAF power profiles are provided by a real EAF operation. CFD simulation of the EAF operation shows proper prediction of the charge melting when compared with standard industry practice. Namely, the CFD model predicts a 32.5%/67.5% ratio of solid/liquid steel at the beginning of refining, which approaches the 30%/70% ratio used in standard practice. Based on this prediction, the melting rate in the CFD results differs by 8.3% from actual EAF operation. The impact of charge layering on melting is also investigated. CFD results show that distributing charge material into a greater number of layers in the first bucket (10 layers as compared to 4) enhances the melting rate by 12%. However, including dense material at the bottom of the furnace deteriorates melting performance, reducing the impact of the number of layers of the charge. The CFD platform can be used to optimize the use of HBI/scrap in real EAF operations and to determine best recipe practices. [ABSTRACT FROM AUTHOR]

This paper explores the effects of egg orientation and yolk position during thermal processing using computational fluid dynamics simulation and experimentation. A carboxymethyl cellulose suspension was used to simulate the egg white, and a two‐dimensional model incorporated an air cell near the larger end. The simulation included four cases: two focused on vertical orientation with the yolk at the rear shell and the geometric center, and two on horizontal orientation with similar yolk positions. Repositioning the yolk in a horizontal orientation near the eggshell resulted in significant temperature variations. The findings show that a horizontal egg position, especially with the yolk near the eggshell, led to a significant 8%–16% reduction in heating times. This configuration also improved pasteurization efficiency, assessed by the F value, by about 13.8%. The study also revealed distinct flow patterns influenced by buoyancy forces, significantly related to temperature distribution inside the egg. [ABSTRACT FROM AUTHOR]

In this paper, the friction properties of the port pair with non‐smooth surface in the pump were studied. The lubrication film was modelled and simulated to analyse dynamic pressure, velocity vector and friction coefficient. Tests were made for studying the effects of pit shape and revolution speed on friction properties of glass fibre epoxy resin (GFER) samples under seawater lubrication, with the wear of the surface and friction coefficient discussed. The results show that GFER is mainly manifested as adhesive and abrasive wear during the tests. The simulations and tests suggest that the hydrodynamic lubrication effect is improved by increasing revolution speed and using non‐smooth surfaces, with the friction coefficient being decreased. Moreover, a roughness test was conducted, and it was found that the Ra value of the 316L sample decreased, whereas the Ra value of the GFER sample increased. [ABSTRACT FROM AUTHOR]

Flow field organization significantly influences the performance criterion of a scramjet combustor. Recently, DLR scramjet combustor with strut injector has been mostly used to alter the flow field. Researchers have used innovative strut injectors to enhance the performance of the DLR scramjet combustor. However, the effect of utilizing a strut with both parallel and normal injections of air and fuel in the DLR scramjet combustor has not been investigated till date. Hence, in this study, the DLR combustor is numerically investigated using a modified strut injector with both parallel and normal injections of air and fuel. The 2D numerical solver is validated with the experimental results having a maximum deviation of 7.3%. The analysis shows that the combustors with modified strut injectors produce better turbulence mixing compared to the DLR combustor, resulting in higher combustion performance. The modified strut combustors, i.e., CMSI-1, CMSI-2, and CMSI-3 produced a combustion efficiency of 76%, 79%, and 81%. In contrast, the maximum combustion efficiency produced by the DLR combustor is 50%. This improvement in the combustion performance of the combustors with modified strut injectors resulted in higher thrust force than the DLR combustor. The thrust force produced by CMSI-1, CMSI-2 and CMSI-3 are 3160 Pa.m2, 3200 Pa.m2 and 3216 Pa.m2, respectively. Finally, it has been found that the CMSI-3 has produced the maximum combustion efficiency and better thrust force among all the scramjet combustor models considered in the study. [ABSTRACT FROM AUTHOR]

The effect of the seabed on the hydrodynamics of three-dimensional autonomous underwater vehicles (AUVs) varies according to the physical conditions of the place where AUVs interact with the environmental conditions. This study examines the hydrodynamics of an AUV resembling a torpedo model while taking the influence of the seabed surface as a function of the dimensionless distances (G/D) between the torpedo and the seabed. Reynolds numbers, varying from 1 × 104 to 8 × 104, were considered. These Reynolds numbers were associated with various seabed distances falling within 0.25 ≤ G/D ≤ 1.5. To perform the simulations, governing equations were utilized and incorporated with the k–ω SST turbulence model. It has been observed that when AUVs or torpedo models operate in close proximity to the seabed surface, several key hydrodynamic parameters and flow characteristics are affected. These include the pressure coefficient (Cp), drag coefficient (CD), overall flow structures, maneuverability, and performance of the torpedo model. As the AUV or torpedo model approaches the seabed surface, the symmetrical flow pattern deteriorates. This deterioration is associated with changes in vortical flow structures under the influence of seabed surfaces. Additionally, the intensity of the shear stress (τ) near the seabed surface gradually increases as the AUV or torpedo model gets closer to it. In summary, the proximity of AUVs or torpedo models to the seabed surface causes disruptions in the flow patterns, increased shear stress, and alterations in key hydrodynamic parameters, ultimately affecting the system's performance and behavior. [ABSTRACT FROM AUTHOR]

The current study explores the thermal performance and geometric optimization of radial heat sinks manufactured through selective laser melting process of AlSi10Mg material, primarily intended for cooling applications in light-emitting diodes (LEDs). Few studies have systematically approached the geometric optimization of radial heat sink designs, particularly considering variable fin heights (both fin outer and fin inner height), in conjunction with other geometric parameters like fin length, fin thickness, and the number of fins tested across a broad spectrum of heat flux values. Through comprehensive experimentation and numerical simulations, the independent and combined impact of these considered key geometric parameters was investigated on the heat sink performance. The experimental design, guided by Response Surface Methodology, encompasses a wide range of heat flux levels, varying from 300 to 1800 W/m2, to ensure the broad applicability of the findings. The results underscore the significance of fin thickness, which notably influences the base temperature of the heat sink, particularly at higher heat flux levels. The interaction between heat flux and fin length also plays a pivotal role in base temperature control, with additional fins contributing to lower temperatures. Furthermore, it was revealed that higher fin outer heights, combined with lower fin inner heights, lead to superior heat sink performance, aligning with practical LED cooling requirements. The optimization process results in configurations that consistently maintain base temperatures below the critical 70 °C threshold, thus contributing to effective thermal management in LED devices. [ABSTRACT FROM AUTHOR]

An airlift pump is a vertical tube that utilizes the buoyant effects of a gas to lift a liquid. Unlike a standard mechanical pump, the liquid flow rate through the airlift pump is not directly controlled; rather, it depends on the supplied gas flow rate, the tube length and diameter, and the relative height of the liquid supply free surface (submergence ratio). The present study uses the commercial CFD code ANSYS CFX to model the isothermal, 3D, transient flow in an airlift pump using water and air. The model applies pressure boundary conditions at both ends of the tube and specifies the mass flow rate of air through multiple openings in the side of the tube. The bottom of the tube is an inlet of water only and the outlet is a two-phase flow opening. A time-dependent, homogeneous, VOF two-phase RANS CFD modelling approach is used with the air treated as an ideal gas. This work found that a complete 3D domain was necessary for consistent prediction of the airlift performance and physically realistic two-phase flow structures. Statistical analysis of the two-phase flow structures was applied to characterize airlift pump instability and better understand the physics of the airlift pump. [ABSTRACT FROM AUTHOR]

Direct absorption solar collectors (DASCs) typically achieve high efficiency due to the volumetric heat absorption process facilitated by the working fluids. In this study, carbon black (CB) nanofluids were utilized as the working fluid to experimentally and numerically investigate the thermal performance of a rectangular DASC. The findings suggest that the nanoparticles have the potential to enhance the efficiency of the DASC. Direct absorption solar collectors (DASCs) are known for their high efficiency, which is achieved through the volumetric heat absorption process provided by the working fluids In this study, carbon black (CB) nanofluids were used as these working fluids to study the thermal performance of a rectangular DASC. The experiments were conducted using water and nanofluids with 0.05 wt.% nanoparticle concentration, at different flow rates and tilt angles, under a concentrated simulated solar power source. Our results show that the efficiency of the DASC increased as the flow rate increased. The DASC was more efficient when the receiving surface was facing downwards (tilt angle of 0°), and the efficiency was 35% higher than when the receiving surface was facing upwards (tilt angle of 180°). A computational fluid dynamics (CFD) model, which was validated against our experimental results, analyzed the DASC performance under different CB concentrations. According to the simulations, the highest efficiency occurred at a concentration of 0.05 wt.%. The study also highlighted the distribution of temperature and velocity of the nanofluids, as well as the volume fraction of carbon black during the flow process. [ABSTRACT FROM AUTHOR]

Prefilming airblast atomisers are commonly used in gas turbine combustion system fuel injectors. As the film propagates across the prefilmer it interacts with the high velocity gas stream above it. In this paper a numerical investigation into this interaction is presented. A Coupled Level Set & Volume of Fluid method is used to simulate the development of the film along the KIT-ITS planar prefilmer (Gepperth et al., in: 23rd European conference on liquid atomization and spray systems (ILASS-Europe 2010), Brno, Czech Republic, September, 2010). Initial results showed the importance of correctly specifying the contact angle as too high a value leads to the formation of rivulets instead of a continuous film. An analysis of the film and air showed two-way coupling. The presence of the film increases the growth rate of the gas phase boundary layer, and the strength and size of the turbulent structures within it. Surface waves form in the film, initially driven by the turbulent fluctuations, but developing into transverse waves. These waves are shown to be independent, stochastic events instead of a periodic wave system. At the trailing edge of the prefilmer the increased turbulence level in the air, the variations in the film thickness and the associated change in fuel mass flow and momentum will have large implications for the atomisation process and subsequent fuel spray. These will also impact simulation of the atomisation, as the boundary condition complexity is much greater than commonly used, and the variations will require larger domains and longer simulation times to obtain fully converged atomisation statistics. [ABSTRACT FROM AUTHOR]

In this work, numerical investigations were performed using large eddy simulations and validated against detailed measurements in the CeCOST swirl stabilised burner. Both cold and reactive flow have been studied and the model has shown a good agreement with experiments. The verification of the model was done using the LES index of quality and a single grid estimator. The cold flow simulations predicted results closely to experiments setting baseline for the reactive simulations. Coherent structures like the vortex rope above the swirler and a precessing vortex core in the combustion chamber were identified. The reactive conditions were modelled with the Flamelet generated manifold and artificially thickened flame models. Simulations were performed for an experimental syngas composition from black liquor gasification at three different CO2 dilution levels. Three different Reynolds numbers were investigated with the model matching closely to experimentally detected 2D flow field and OH for the most CO2 diluted mixture. It was found that the opening angles of the flames differ by a maximum of 13% between experiments and simulations. The most diluted fuel investigated experienced a liftoff distance of 23.5 mm at the Re 25 k. This was also the highest liftoff distance experienced in this cohort of fuels. The same fuel also proved to have the thickest flame annulus at 78.5 mm. Overall, in cases with no experimental data available the predictions made by the model follow the same trends which hints its applicability to higher Re cases. [ABSTRACT FROM AUTHOR]

Featured Application: To contain the diffusion of pathogens through air, a UV-C filter is optimized by CFD and ray tracing analysis guided by an MDO platform. Because of the recent COVID-19 pandemic, the problem of preventing and containing the diffusion of pathogens spread through air has become a main topic of research. The problem is particularly important for specific environments, such as dental or other medical practices, where the aerosol treatments in open-mouth patients, combined with closed and crowded rooms, raise the risk of infection. As an efficient countermeasure, in this study we propose a solution that is able to remove the risk at the source, through the aspiration of the aerosol and the neutralization of the bacterial load by means of a UV-C LED filter, which releases the sterilized air in the environment. To maximize the efficiency of the solution, in this study we performed a numerical multi-disciplinary optimization (MDO) of the filter, coupling numerical simulations of multiple disciplines (CFD and electromagnetics) by the process automation and optimization environment modeFRONTIER of ESTECO. Geometrical parameters of the filter are updated for each candidate solution proposed by the optimization algorithm, and their performance in terms of viral neutralization efficiency and air mass flow rate are evaluated by the simulations, until the optimal solution is found. The methodology and results of the study are presented. [ABSTRACT FROM AUTHOR]

The search for alternative, more environmentally friendly coolants to replace mineral oils in power transformers represents a relevant challenge for the power industry. In this frame, a CFD analysis is carried out by means of an open-source, conjugate heat transfer Finite Volume solver to assess the heat transfer performance of different coolants in a disc-type winding of an oil-immersed power transformer, whose geometry is taken from a reference case in the literature. Four different oils are considered: two mineral oils widely established among power transformer manufacturers, a synthetic ester and a natural ester. The latter two represent environmentally friendly alternatives to mineral oils, of great interest for the specific sector. The influence of temperature-dependent thermophysical properties on the overall flow and on the location and value of the hot spots in the copper conductors is discussed, highlighting the strength and weaknesses of the four oils as transformer coolants. In particular, the natural ester exhibits the best heat transfer performance, whereas high hot-spot temperatures and strong fluctuations are found for both mineral oils and the synthetic ester. [ABSTRACT FROM AUTHOR]

Considering the presence of airborne viruses, there is a need for renovation in refuse chutes, regarded as the first step in recycling household waste in buildings. This study aimed to revise the design of existing refuse chutes in light of the challenging experiences in waste management and public health during the coronavirus pandemic. This research primarily focused on the risks posed by various types of coronaviruses, such as the novel coronavirus (COVID-19) and acute respiratory syndrome (SARS and SARS-CoV), on stainless steel surfaces, with evidence of their survival under certain conditions. Refuse chutes are manufactured from stainless steel to resist the corrosive effects of waste. In examining the existing studies, it was observed that Casanova et al. and Chowdhury et al. found that the survival time of coronaviruses on stainless steel surfaces decreases as the temperature increases. Based on these studies, mechanical revisions have been made to the sanitation system of the refuse chute, thus increasing the washing water temperature. Additionally, through mechanical improvements, an automatic solution spray entry is provided before the intake doors are opened. Furthermore, to understand airflow and clarify flow parameters related to airborne infection transmission on residential floors in buildings equipped with refuse chutes, a computational fluid dynamics (CFD) analysis was conducted using a sample three-story refuse chute system. Based on the simulation results, a fan motor was integrated into the system to prevent pathogens from affecting users on other floors through airflow. Thus, airborne pathogens were periodically expelled into the atmosphere via a fan shortly before the intake doors were opened, supported by a PLC unit. Additionally, the intake doors were electronically interlocked, ensuring that all other intake doors remained locked while any single door was in use, thereby ensuring user safety. In a sample refuse chute, numerical calculations were performed to evaluate parameters such as the static suitability of the chute body thickness, static compliance of the chute support dimensions, chute diameter, chute thickness, fan airflow rate, ventilation duct diameter, minimum rock wool thickness for human contact safety, and the required number of spare containers. Additionally, a MATLAB code was developed to facilitate these numerical calculations, with values optimized using the Fmincon function. This allowed for the easy calculation of outputs for the new refuse chute systems and enabled the conversion of existing systems, evaluating compatibility with the new design for cost-effective upgrades. This refuse chute design aims to serve as a resource for readers in case of infection risks and contribute to the literature. The new refuse chute design supports the global circular economy (CE) model by enabling waste disinfection under pandemic conditions and ensuring cleaner source separation and collection for recycling. Due to its adaptability to different pandemic conditions including pathogens beyond coronavirus and potential new virus strains, the designed system is intended to contribute to the global health framework. In addition to the health measures described, this study calls for future research on how evolving global health conditions might impact refuse chute design. [ABSTRACT FROM AUTHOR]

Wind energy resources play an important role in sustainable development, and the accelerating effect of wind has been found in V-shaped hills, which informs the siting of wind turbines in this type of terrain. The wind field around the V-shaped hill was simulated using the CFD method. The impact of wind angle, hill pinch angle, and the distance between the hills on the wind field around the V-shaped hill was investigated. Wind acceleration effects at specific locations were studied and analyzed, and these findings were compared with established codes. It was observed that the wind speed at the hill's top under each wind angle is significantly higher compared to other areas. Additionally, the acceleration ratio at the top generally exhibits a decreasing trend with increasing height. If the wind angle is 15° and the pinch angle is greater than or equal to 15°, or if the distance between the hills is less than or equal to 50 m, the wake zone will gradually transition from two to one. The distance between the hills minimally affects the acceleration ratio at the mid-height and top of the hill. Several codes exhibit inconsistency in specifying acceleration effects in hilly terrain. The findings in this paper align most closely with the American code at the base of the hill. At the hill's top, the American code is the lowest above 100 m, while the Chinese code is the highest below 100 m. The findings in this paper fall between those of the Japanese and Australian codes. The formulas for the variation in wind speed acceleration ratio at typical locations with respect to height and the angle between the hills are provided. [ABSTRACT FROM AUTHOR]

The complement cascade is an ancient and highly conserved arm of the immune system. The accumulating evidence highlights elevated activity of the complement cascade in cancer microenvironment and emphasizes its effects on the immune, cancer, and cancer stroma cells, pointing to a role in inflammation-mediated etiology of neoplasms. The role the cascade plays in development, progression, and relapse of solid tumors is increasingly recognized, however its role in hematological malignancies, especially those of myeloid origin, has not been thoroughly assessed and remains obscure. As the role of inflammation and autoimmunity in development of myeloid malignancies is becoming recognized, in this review we focus on summarizing the links that have been identified so far for complement cascade involvement in the pathobiology of myeloid malignancies. Complement deficiencies are primary immunodeficiencies that cause an array of clinical outcomes including an increased risk of a range of infectious as well as local or systemic inflammatory and thrombotic conditions. Here, we discuss the impact that deficiencies in complement cascade initiators, mid- and terminal-components and inhibitors have on the biology of myeloid neoplasms. The emergent conclusions indicate that the links between complement cascade, inflammatory signaling, and the homeostasis of hematopoietic system exist, and efforts should continue to detail the mechanistic involvement of complement cascade in the development and progression of myeloid cancers. [ABSTRACT FROM AUTHOR]

In this work, the propulsive characteristic of an auto-propelled 2D NACA0015 foil undergoing traveling wave motion is numerically investigated. The effects of typical motion parameters, i.e. traveling amplitude, traveling frequency (f), and geometric parameters (thickness, d) on the propulsive property of auto-propelled foil are systematically investigated. The numerical results reveal that the moving velocity of foil can be significantly enhanced by the enlargement of the traveling amplitude and traveling frequency, while it presents a sharp decrease when the foil thickness increases. As for the propulsive efficiency, the effects of a1, f and d on the magnitude of η are similar to each other, that is, the magnitude of η will ascend to the peak value and then decrease, and there exists an optimum value corresponding to the highest magnitude of η. The flow structures in the wake of the auto-propelled foil under typical calculation conditions are also analysed. [ABSTRACT FROM AUTHOR]

The error introduced by the integration method is an important factor affecting the measurement accuracy of the multipath ultrasonic flowmeter. An adaptive weighted integration method (adaptive weighted integration method for velocity profile of circular section) is proposed to reduce the integration error, taking a DN400 double-side eight-path ultrasonic flowmeter as an example. This method is based on the velocity distribution information in the full flow range and the integration weights are determined by the principle of minimum error. The applicability of this method is verified by numerical simulation and actual fluid flow experiments. The results show that the integration error of the proposed method is superior to the Gauss–Jacobi and optimized weighted integration method for circular section integration methods, and the maximum integration error is reduced from 0.0877% and −0.0355% to 0.0220% in the flow range of 125–2500 t h−1. [ABSTRACT FROM AUTHOR]

The hydraulic turbocharger plays a vital role in harnessing the energy stored in brine within reverse osmosis desalination plants. To optimize the efficiency and durability of this equipment, it is crucial to develop accurate dynamic models of the turbocharger rotor. An improved understanding of rotor dynamics enables the integration of innovative technologies such as Hydraulic Energy Management Integration, effectively enhancing efficiencies in systems characterized by small capacities and high rotational speeds. This study presents a dynamic modeling methodology for the hydraulic turbocharger. The analysis involves approximating the turbocharger rotor with an equivalent finite element shaft line model. Verification of the model's natural frequency is conducted using three-dimensional finite element analysis, employing the ANSYS modal analysis module. Computational fluid dynamics is employed to evaluate the fluid forces, while the Reynolds equation is utilized to assess the journal bearing forces. The resulting model is employed to investigate the nonlinear dynamics of the rotor, examining the impact of various system parameters, including rotational speed, unbalance forces, and shaft geometrical parameters. The results highlight the significance of balancing the turbine and pump disks for optimal performance. Furthermore, the research demonstrates that increasing the shaft length reduces the rotor's threshold speed, while increasing the shaft diameter initially raises the threshold speed until it reaches a critical value. Beyond this critical value, further increases in shaft diameter lead to a decrease in the threshold speed. [ABSTRACT FROM AUTHOR]

We develop a computational fluid dynamics (CFD) framework to design a feedback circulation control system to compensate for fluctuations in the fixed-wing aircraft caused by wind gusts. Circulation control actions are realized using dynamic boundary conditions in the CFD simulations. The dynamic flow responses with the circulation control are obtained by solving the unsteady Reynolds-averaged Navier-Stokes equations. The dynamic lift responses at several oscillation frequencies of wind gusts and the plenum chamber pressure, which controls the circulation, are also obtained. A system identification algorithm from control theory establishes the transfer functions corresponding to the frequency responses. Based on the transfer functions and the aerodynamic characteristics of circulation control, a feedback circulation control algorithm is designed. The performance of the feedback control system is verified by the CFD simulation coupled with the controller as time-varying boundary conditions. At each time step, the controller determines the parameters in the boundary condition according to the instantaneous lift calculated in the previous time step. The simulation results show that the circulation control effectively compensates for the lift perturbations caused by vertical directional wind gusts. The proposed unsteady CFD simulation frameworks provide high-fidelity evaluations of feedback control systems, and it will save costly efforts to set up unsteady wind-tunnel experiments. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) method is a common method to obtain the temperature field distribution within the furnace. However, in order to reduce computational complexity, the numerical simulation involve simplifications in boundary conditions and model parameters. As a result, the temperature field distribution deviates from the actual operating conditions. This paper proposes a numerical temperature field modification method based on flame images. Flame images corresponding to the operational conditions are collected using the Industrial Flame Monitoring System (IFMS). The flame images are preprocessed, and the contour of the flame's core region is extracted using the Mask Region-based Convolutional Neural Network (Mask R-CNN) method. The geometric features of the flame are extracted, and matrix calculations are applied to modify the numerical temperature field. The modified temperature field exhibits a deviation in the combustion center, aligning with the actual operation of the boiler. A comparison between the modified temperature field and the temperature measurements from flue gas shows consistent temperature trends. The absolute error (AE) under different operating conditions is under 8.8 K, and the relative error (RE) remains below 1.3%. The analysis results demonstrate that it can enhance the accuracy of temperature field calculations by the modification from flame image features. [ABSTRACT FROM AUTHOR]

Researchers demonstrated that implementing new combustion technology and optimising fuel quantity results in a significant reduction in traditional fossil fuel usage and emission levels. The Reactivity Controlled Compression Ignition (RCCI) combustion strategy is one of the low temperature combustion technologies, and it is used to reduce the overall combustion temperature while also providing better combustion control. This study looks into RCCI combustion technology, which uses conventional diesel fuel as the high reactivity fuel (HRF) injected through the injector and acetylene gas as the low reactivity fuel (LRF) injected into the cylinder via a modified inlet manifold alongside air. The modified engine setup was tested for performance, emissions, and combustion under various load conditions, as well as different mass flow rates of acetylene gas, a low reactivity fuel that is injected with air. The flow field of the low reactivity fuel at the inlet manifold is analysed using the Computational Fluid Dynamics principle, which is used to determine the best flow rate for improving combustion quality. According to the simulation results, the optimal acetylene flow rate is 3 Litres Per Minute (LPM), and experimentation shows that at 3 LPM acetylene injection, the brake thermal efficiency (BTE) improves by about 3.2%, and emissions such as carbon monoxide (CO), hydrocarbon (HC), smoke intensity, and oxides of nitrogen (NOx) are reduced by about 35%, 17%, 10%, and 21%, respectively. [ABSTRACT FROM AUTHOR]

Turbulators are used in heat exchangers to increase the contact surfaces of fluids and enhance heat transfer rates by promoting turbulence flow. This is particularly important in applications that require high productivity and capabilities. The use of turbulators can lead to maximum energy efficiency, resulting in high efficiency and lower costs. This investigation presents a comprehensive experimental and computational fluid dynamics (CFD) approach into the influence of turbulator-induced disturbances on heat transfer characteristics in a double pipe heat exchanger. In this study, two innovative turbulators (named TY and TZ) were designed to enhance the performance of heat exchangers. The turbulators are inserted into the inner pipe of the double pipe heat exchanger. According to the experimental and numerical results, compared to the plain pipe condition (without turbulator), it was observed that maximum temperature differences were reached with a 28% increase at velocity of 2.5 m/s with TY and 118% increase at velocity of 3 m/s with TZ. Nusselt numbers increased by 32% with TY and by 157.9% with TZ compared to the plain pipe condition. Therefore, TZ turbulator with a simple structure can significantly enhance the heat transfer performance of double-pipe heat exchangers, making it an ideal option for use in these exchangers. [ABSTRACT FROM AUTHOR]

AbstractSteam condensation in the presence of a noncondensable gas is of vital importance for passive cooling containment systems. The noncondensable gas causes a significant reduction in the condensation rate and heat transfer across the containment, which is important for postulated loss-of-coolant accidents in a nuclear reactor.In this work, computational fluid dynamics models of condensation and the adjacent single-phase steam-air mixture flow are developed for laminar and turbulent flow in vertical channels by two distinct wall condensation modeling approaches using the commercial code STAR-CCM+. The first is the fluid film model available in STAR-CCM+, which solves liquid layer governing equations with connections to the adjacent gas mixture flow. The second is a user-defined wall condensation model that neglects the fluid film and instead accounts for mass, momentum, and heat transfer via user-defined volumetric sink terms adjacent to the cold wall.The condensation models are assessed by first comparing the calculated results with the numerical solution of laminar flow, solved using a complete two-phase model that solves parabolic equations based on conservation of mass, momentum, energy, and species for each phase. Next, the results of a two-dimensional analysis are compared with COPAIN experiments and existing numerical solutions from three-dimensional analyses. The comparisons include new, detailed results that have not been reported in previous analyses of a COPAIN case. These new results include local field profiles of velocity, temperature, and air mass fraction, and local mass flux. [ABSTRACT FROM AUTHOR]

In the genesis and progression of cardiovascular and metabolic diseases (CVMDs), adipose tissue plays a pivotal and dual role. Complement factor D (CFD, also known as adipsin), which is mainly produced by adipocytes, is the rate-limiting enzyme of the alternative pathway. Abnormalities in CFD generation or function lead to aberrant immune responses and energy metabolism. A large number of studies have revealed that CFD is associated with CVMDs. Herein, we will review the current studies on the function and mechanism of CFD in CVMDs such as hypertension, coronary heart disease, ischemia/reperfusion injury, heart failure, arrhythmia, aortic aneurysm, obesity, insulin resistance, and diabetic cardiomyopathy. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive hemodynamic evaluation of two endovascular techniques for treating cerebral aneurysms. Using the finite volume method, we simulated pulsatile blood flow and heat transport dynamics in two saccular aneurysms of varying sizes and shapes. We assessed hemodynamic factors under two coiling conditions with different porosities and deformation stages to identify the most effective treatment for each case. Our computational analysis reveals that stent and coiling applications are more efficient for aneurysms with low-sac volume. Notably, stent placement proves to be more effective than coiling in treating saccular aneurysms. Our findings indicate that stent-induced deformation sufficiently diverts the main blood flow, thereby reducing the risk of aneurysm rupture near the ostium region. [ABSTRACT FROM AUTHOR]

This study suggests a combustion strategy and introduces a new geometry for the combustor of a micro gas turbine fed by ammonia as fuel. Ammonia is essential for making the energy supply chain more eco-friendly because it is seen as an excellent way to transport green hydrogen and as a renewable, carbon-free fuel. This study has considered different cases with a wide range of overall and primary equivalence ratios to find the optimum geometry regarding lower NO X emission, lower unburned NH 3 , lower unburned H 2 , and temperature distribution. A comprehensive case study of CFD simulation was conducted considering earlier research that showed the NO reduction level in an NH 3 -air swirl burner is dependent on the equivalence ratio of the primary combustion zone. The CFD simulation's boundary conditions were set by running a one-dimensional cycle simulation of the micro gas turbine at various loads. Results indicate that by modifying the geometry to include a staged rich-lean strategy with a primary equivalence ratio of 1.07, the NO mole fraction in the combustor can be reduced to one-third of its original level despite the significantly higher Combustor Inlet Temperature (CIT) compared to previous studies. The study found that the unburnt NH 3 and H 2 levels are low enough in the modified design, which shows the fuel is completely consumed and the overall combustion efficiency is optimized. Also, the analysis of the fluid dynamic behavior of the combustor shows that streamlines are uniform, leading to improved heat transfer and better overall system performance. These findings highlight the staged rich-lean strategy's potential by tuning the combustion stages' equivalence ratio as a promising approach to mitigate NO X emissions in ammonia combustion systems while maintaining high energy efficiency. • Study of ammonia combustion in a 3 kWe MGT's combustor. • Proposing a novel design approach for the combustor. • Higher combustor inlet temperature investigation in smaller combustor. • Implementation of a staged rich-lean combustion strategy to reduce NOx emissions by one-third. • Investigation of various primary ERs and identification of the optimal value at 1.07. [ABSTRACT FROM AUTHOR]