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With the increasing popularity of hydrogen fuel cell vehicles (HFCV), the risk of hydrogen leakage is becoming increasingly prominent. The closed nature in the vehicle structure may lead to rapid accumulation of hydrogen in the cabin when a leak occurs, creating a high concentration that can threaten passengers' respiratory safety and even their lives, as well as potentially triggering an explosion accident. Therefore, this study focuses on hydrogen fuel cell vehicles (HFCVs) with a hydrogen storage pressure of 70 MPa, applying computational fluid dynamics (CFD) methods to simulate the diffusion of hydrogen leakage at different locations, and discusses the impact of leakage rates, leakage hole shapes, and ventilation conditions. This study reveals how hydrogen concentration and distribution change with time in the vehicle under different leakage scenarios, providing important theoretical support for improving the safety of HFCVs. The results indicate that hydrogen leaks at different positions lead to different concentration distributions. Specifically, leaks at position one can accumulate hydrogen between the driver and co-driver, increasing the flammable risks for the front seats. Leaks at position two gather around the seats and spread outward, with the area around the vehicle's roof edge prone to hydrogen accumulation. Leaks at position three, due to the confined space of the trunk, lead to a rapid increase in hydrogen concentration. Further analysis indicates that the higher the leakage rate, the faster the hydrogen diffuses, and the broader the range of concentration distribution becomes; the irregular rectangular shape of the leakage hole accelerates the diffusion speed of hydrogen in both horizontal and vertical directions, expanding the diffusion range. The location of the vent plays a significant role in controlling hydrogen diffusion under different leakage positions. At position one, the vent at the front of the car can effectively reduce the hydrogen concentration on the hood and driving position. At position two, the vents at the front and rear of the car can more rapidly decrease the hydrogen concentration inside the vehicle, reducing the time personnel are in danger. At position three, the vent at the rear can effectively promote the quick exhaust of hydrogen, lowering the concentration inside the car and reducing the risk of ignition. • Focusing on the hydrogen leakage at different positions in the car, the state of hydrogen leakage on the concentration distribution inside the car is analyzed. • The shape of the leak hole has a significant effect on hydrogen diffusion in the vehicle. The irregular rectangular shape of the leak hole spreads the fastest and most widely in both horizontal and vertical directions, increasing the risk of hydrogen explosion in the car. • The location of the vents is critical to controlling the spread of hydrogen leaks，and the position of the vent determines the path of hydrogen control and diffusion. • This paper analyzes the impact of different leakage rates on the speed and range of hydrogen diffusion. [ABSTRACT FROM AUTHOR]

Wind energy is essential for sustainable energy development, providing a clean and reliable energy source through the wind turbine. However, the vortices and turbulence generated as wind passes through turbines reduce wind speed and increase turbulence, leading to significant power losses for downstream turbines in wind farms. This study investigates wake characteristics in wind turbines by examining the effects of different scale ratios on wake dynamics, using both experimental and numerical approaches, utilizing scaled-down models of the Aeolos H-20 kW turbine at scales of 1:33, 1:50, and 1:67. The experimental component involved wind tunnel tests in an open-circuit tunnel with adjustable wind speeds and controlled turbulence intensity. Additionally, Computational Fluid Dynamics (CFD) simulations were conducted using STAR-CCM+ (Version 15.06.02) to numerically analyze the wake characteristics. Prior to the simulation, a convergence test was performed by varying grid density and y+ values to establish optimized simulation settings essential for accurately capturing wake dynamics. The results were validated against experimental data, reinforcing the reliability of the simulations. Despite minor inconsistencies in areas affected by tower and nacelle interference, the overall results strongly support the methodology's effectiveness. The discrepancies between the experimental results and CFD simulations underscore the limitations of the rigid body assumption, which does not fully account for the deformation observed in the experiment. [ABSTRACT FROM AUTHOR]

This review paper provides an overview of recent advances in computational fluid dynamics (CFD) simulations of ejector pumps for vacuum generation. It examines various turbulence models, multiphase flow approaches, and numerical techniques employed to capture complex flow phenomena like shock waves, mixing, phase transitions, and heat/mass transfer. Emphasis is placed on the comprehensive assessment of flow characteristics within ejectors, including condensation effects such as nucleation, droplet growth, and non-equilibrium conditions. This review highlights efforts in optimizing ejector geometries and operating parameters to enhance the entrainment ratio, a crucial performance metric for ejectors. The studies reviewed encompass diverse working fluids, flow regimes, and geometric configurations, underscoring the significance of ejector technology across various industries. While substantial progress has been made in developing advanced simulation techniques, several challenges persist, including accurate modeling of real gas behavior, phase change kinetics, and coupled heat/mass transfer phenomena. Future research efforts should focus on developing robust multiphase models, implementing advanced turbulence modeling techniques, integrating machine learning-based optimization methods, and exploring novel ejector configurations for emerging applications. [ABSTRACT FROM AUTHOR]

The cochlea, situated within the inner ear, is a spiral-shaped, liquid-filled organ responsible for hearing. The physiological significance of its shape remains uncertain. Previous research has scarcely addressed the occurrence of transverse flow within the cochlea, particularly in relation to its unique shape. This study aims to investigate the impact of the geometric features of the cochlea on fluid dynamics by characterizing transverse flow induced by harmonically oscillating axial flow in square ducts with curvature and torsion resembling human cochlear anatomy. We examined four geometries to investigate curvature and torsion effects on axial and transverse flow components. Twelve frequencies from 0.125 Hz to 256 Hz were studied, covering infrasound and low-frequency hearing, with mean inlet velocity amplitudes representing levels expected for normal conversation or louder situations. Our simulations show that torsion contributes significantly to transverse flow in unsteady conditions, and that its contribution increases with increasing oscillation frequency. Curvature alone has a small effect on transverse flow strength, which decreases rapidly with increasing frequency. Strikingly, the combined effect of curvature and torsion on transverse flow is greater than expected from a simple superposition of the two effects, especially when the relative contribution of curvature alone becomes negligible. These findings may be relevant to understanding physiological processes in the cochlea, including metabolite transport and wall shear stress. Further studies are needed to investigate possible implications for cochlear mechanics. [ABSTRACT FROM AUTHOR]

A self-exchange aquaculture vessel stands as an environmentally sustainable solution for fish farming, capitalising on seawater utilization and minimising the risk of fish escapes through the implementation of perforated culture tanks. This research aims to lay the groundwork for the conceptual design, modelling, and simulation analysis of such vessels, focusing on how near-bottom perforation placement affects flow field characteristics within the culture tank. This paper presents a computational study using Computational Fluid Dynamics (CFD) to analyse self-exchange aquaculture vessels under both head and beam current conditions. The solution of conservation equations governing tank hydrodynamics is achieved using an implicit unsteady second-order Eulerian (finite volume) technique on optimised trimmed meshes. Experimental and predicted values for the vessel model's total resistance were evaluated using uncertainty analysis, validating the numerical model. It was found that proper positioning of perforations near the bottom significantly enhances the synergistic effect of fluid within the culture tank and the mixing characteristics of the flow field. To enhance water circulation, it is recommended to install two or more rows of perforations on the sides of self-exchange aquaculture vessels. The coordination between perforation placement and vessel structure should be considered to determine the optimal layout. By offering valuable insights into the effects of perforation placement, this study contributes to the development of more efficient and environmentally friendly aquaculture practices. • Hydrodynamics of a tank on the self-exchange aquaculture vessel studied by numerical methods. • The jet-like effect in the perforated culture tank was explored. • The influence mechanism of perforation placement on tank hydrodynamics was revealed. • Well-placed perforations boost fluid linkage inside and outside the tank. [ABSTRACT FROM AUTHOR]

A nanofluid is a solution of nanoparticles with diameters fewer than 100 nanometers suspended in a base fluid such as water, ethylene glycol, or oil. In the nanofluid, these nanoparticles are suspended. The goal of this research is to look at the functioning of a twin-pipe heat exchanger that uses counter flow arrangements and two different nanofluids as cooling fluids. Alkaline water is a basic fluid made up of silicon carbide (SiC) and carbon nanotubes (CNT). The goal of this research was to see how different compositions of SiC and CNT nanoparticles dispersed in water affected the heat transfer capacities of a twin pipe heat exchanger developed with a counterflow arrangement. The flow rate of the nanofluid and the particle volume concentration of alkaline water were (0.02) and (0.04), respectively. Fluids with constant intake temperatures of 60°C for water and 30°C for nanofluid flow at the same input velocity via a heat exchanger. Both fluids are traveling at the same rate. According to the findings, nanofluid absorbs more heat than water at a range of flow speeds. Because of the improved thermal properties of nanoscale fluids, this results in increased thermal efficiency in heat exchangers. [ABSTRACT FROM AUTHOR]

Analysis of various accident scenarios is vital for the safety assessment of nuclear fuel storage facilities. The accidents in the storage vault due to loss of cooling are generally considered highly uncertain since the accident progression is slow (in comparison to reactors) and allows time for remedial activities to the operator. In the present work, numerical simulations of different accident scenarios have been carried out for a short duration to understand the situation better. Thermal aspects of accident conditions such as failure of the suction blower, drying of cooling water at the chiller, and combined effect of both accidents were investigated. The airflow inside the ventilated enclosures due to the failure of the blower and the rise in inlet air temperature is analyzed numerically. The temperature distributions inside the vault and the rise in temperature of the sub-assemblies and magazines have been studied. The key mechanisms of heat transfer, which take part in nuclear fuel storage vault for post-accident conditions, were identified. The study will be helpful to classify various accident conditions based on their thermal implications and the model developed can be used to design passive cooling systems. [ABSTRACT FROM AUTHOR]

The interflat cross-contamination of air pollutants such as coronavirus disease 2019 (COVID-19) in built environments has become a growing concern. This study investigates the effect of the geometrical details of building facades on wind-induced airborne pollutant transmission routes in high-rise buildings. Parametric studies of different external-shading elements of buildings, wind speeds, and wind directionality are considered. A high-resolution computational fluid dynamics (CFD) using a realizable k-epsilon turbulence closure model is employed to analyze the airflow field. For the windward single-sided ventilation case, the reentry ratio from the source room to the other unit under prevailing, 45°, and 90° wind directions are quantified, and the possible interflat cross-contamination routes are simulated. The transmission route is highly dependent on a building's architectural features, wind speed, wind directionality, and location of the source room. The result shows that external shading plays a crucial role in mitigating or accelerating airborne pollutant transmissions. A building with horizontal shadings restricts vertical cross-contamination between flats, but it allows horizontal interflat cross-contamination. However, buildings with vertical shadings reduce the risk of horizontal cross-contamination but increase the probability of vertical cross-contamination. The egg-crate shading minimizes the risk of both horizontal and vertical cross-contamination. A smooth facade building is highly susceptible to cross-contamination for a wide range of wind directionality. Therefore, this study is helpful for architecture and building science for the analysis of airborne pollutants, for tracing the routes of cross-contamination in residential buildings, and for reducing the risk of transmission of respiratory diseases such as COVID-19. [ABSTRACT FROM AUTHOR]

The effect of side holes morphology changes in double J stent (DJS) on encrustation was analyzed using computational fluid dynamics (CFD). We analyzed DJS side holes with inner diameter of 1 mm and outer diameters of 1 (type A), 1.2 (type B) and 1.4 (type C) mm, respectively. Concentric stenosis with three intraureteral degree (0%, 12%, and 88%) was analyzed. The flow rate, shear stress and wall shear stress (WSS) distribution were investigated. Urine flow through SH1 before the ureteropelvic junction (UPJ) differed based on the ureteral stenosis degree. The sum of flow rates through the SHs increased with diameter. In the stented ureter with 12% stenosis, the flow rate through SH1 approximately doubled than that without ureteral stenosis, and the flow rate through SH1 was maximal for the type 'C' stent in both 12% and 88% ureteral stenosis. The mean shear stress in the SHs increased with the degree of stenosis. The WSS around the SHs was higher for type 'C' than types A and B. From the flow rates and shear stresses in and around the SHs, the larger SH diameter of the DJS from the UPJ to mid-ureter is expected to induce encrustation reduction, especially in patients with urinary lithiasis. [ABSTRACT FROM AUTHOR]

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The formation of double-emulsions or core/shell microdroplets in microchannels, essential for various chemical applications, traditionally relies on costly and time-consuming laboratory methods. In this regard, computational fluid dynamics (CFD) and artificial neural network (ANN) techniques were employed. The present study developed ANN models to predict the relationship between shell thickness and double-emulsion size in a double-T microchannel, using two datasets comprising 180 experimental and CFD data points. Assessing this relationship involved analyzing various input factors, including the Capillary, Weber (case A), and Reynolds numbers (case B) of the core, shell, and continuous phases. Among twelve training algorithms and four activation functions, the Levenberg–Marquardt (LM) algorithm with sigmoidal activation functions (Tansig and Logsig), in contrast to the linear activation functions (Poslin and Purelin), achieved the highest predictive accuracy. Additionally, the predictive accuracy of ANN models was found to be significantly improved when trained using a combination of capillary and Weber numbers, as opposed to models trained only using capillary, Weber, and Reynolds numbers. The optimal neural network architectures were [10 5] neurons for case A (tansig and logsig) and [8] neurons for case B (tansig), yielding coefficients of determination (R2) of 0.99 and 0.98, respectively. These models demonstrated high precision and effective generalization, evidenced by statistical measures such as R2, MSE, RMSE, AAD, %AARD, and computational time. Moreover, their ability to generalize within the training dataset further substantiates their predictive capacity. [ABSTRACT FROM AUTHOR]

A compelling solution to the issue of high heat flux generated by flexible electronic devices has been found in liquid-based microfluidic cooling devices. It has been earlier realized that the varying microchannel hydrodynamics influences the overall heat transfer in these devices. However, microfluidic cooling devices that incorporate intricate microchannels have not been explored to their full potential. In this study, we investigate the use of 3-D intricate microchannel geometries in microfluidic heat sinks, their generated hydrodynamics, and their profound impact on the overall heat transfer process. Utilizing 3D-printed scaffold removal technology, three distinct microfluidic devices were fabricated, each distinguishable by its cross-sectional shape of the microchannel designs (coil, square, and triangle). These microfluidic devices, based on Polydimethylsiloxane-Graphene oxide (PDMS-GO) as substrate material, have been examined experimentally and numerically for their heat dissipation capacities under constant temperature heat source of 358 K at flow rates ranging from 40 to 400 μL/min. Experimental observation illustrates that the coil-microchannel configuration exhibited superior heat dissipation capabilities, outperforming both the square and triangle microchannels across all flow settings. Furthermore, numerical simulations corroborated this experimental finding by providing insights into through-plane temperature distribution, heat transfer coefficient, pressure drop, and channel hydrodynamics. Our study intends to advance the understanding of microchannel cooling, as well as emphasizes the importance of geometrical configuration towards optimal electronic hotspot cooling. [ABSTRACT FROM AUTHOR]

The impact of tropical cyclones on the operation of bridges and railways are mostly dependent on the forecast wind speed trend (upward, downward or staying steady) at present in Hong Kong. There are requests to forecast the exceedance of wind speed thresholds for such operations with a lead time of many hours ahead. This study considers the technical feasibility of forecasting the wind speed along a recently built bridge in Hong Kong with a coupled mesoscale numerical weather prediction (NWP)–computational fluid dynamics (CFD) model. This bridge features numerous anemometers where the coupled model can be verified. It is found that these two tropical cyclone cases are very challenging, especially in representing the wind structure of the cyclone because of its relatively small circulation. As such, the timing of the maximum wind could be 2 to 4 h earlier than the actual observation. The maximum wind speed from CFD modeling could be higher than that from the NWP model alone by 5 to 10 m/s, which shows that CFD modeling could add value in the forecasting of wind speed exceedance, although the maximum simulated value is still lower than the actual observation by as much as 10 m/s. As a result, while the general wind speed trend may be forecast, the exceedance of definite values of wind speed limits is still practically rather challenging, given the present two cases of tropical cyclones. [ABSTRACT FROM AUTHOR]

Wind resistance optimization is crucial for enhancing the rotational speed of supergravity centrifuges. We conducted a study using computational fluid dynamics on the Centrifugal Hypergravity and Interdisciplinary Experiment Facility (CHIEF) under construction at Zhejiang University and validated it experimentally using a ZJU400gt centrifuge. Our findings indicate significant reductions in wind resistance through structural modifications of the CHIEF. Reducing the outer radius from 4650 to 4150 mm decreased wind resistance by 16%, primarily due to reduced effective viscosity in the wake region's gases. More substantial reductions were achieved by lowering the height of the outer wall from 2200 to 1400 mm, which cut wind resistance by 25%. This height reduction suppressed vortex shedding and Kármán vortex street development via the Venturi effect. Adjustments to the roughness height of wall surfaces further decreased wind resistance, with minimal impact from arm roughness. A critical roughness height was identified, below which no further reductions in wind resistance could be attained. Notably, using disc-shaped arms reduced wind resistance by approximately 73% because of their minimal pressure–resistance components and predominant frictional resistance, highlighting their potential in future high-speed centrifuge designs. [ABSTRACT FROM AUTHOR]

"Gray space", also known as transitional space, focuses on the connection and transition between indoor and outdoor spaces in architecture. With its unique diversity of forms and functional inclusiveness, gray space reasonably integrates architectural spaces' hierarchical construction with innovative ecological energy-saving concepts. Existing research mainly analyzes and interprets the design techniques of gray space from a visual perception perspective but needs more analysis of classification and design interpretation of the gray spaces in traditional gardens based on climate adaptability. This paper studied the gray spaces in traditional Jiangnan gardens, summarizing five common types of gray space in architectural spaces and their responses to the climate. Subsequently, we selected a typical representative for each of the five types of spaces and used "height-to-depth ratio (HDR), open space ratio (OSR), and direction (DIR)" as variables to conduct wind environment simulations. The simulation results help to determine the optimal climate adaptability scheme for each type of space. Through this research on the gray spaces of traditional gardens, we aimed to contribute to the conservation and utilization of classical gardens from an ecological energy-saving perspective and also provide ideas for passive energy-saving design in small public spaces and garden landscape spaces. [ABSTRACT FROM AUTHOR]

The occurrence of fluid flow near a wellhead is the major concern of the petroleum industry, as pressure drop, loss of formation, and other variables of interest are mostly affected in this region. The fluid flows from the hydrocarbon reservoir to the wellbore can be characterized as laminar to turbulent; thus, it is important to model this phenomenon with the integrated wellbore-reservoir model. Using 3D Navier–Stokes equations, an integrated wellbore-reservoir model is created in this study, and it incorporates the formation damage zone. For the porous-porous and porous-fluid interfaces, the General Grid Interface (GGI) approach is applied in conjunction with the conservative mass flux interface model. Model equations are solved using a velocity-pressure coupling solver that is pressure-based. For reliable and quick results, the system of equations is solved using an algebraic multigrid approach. The pressure diffusivity equation's analytical solution under steady-state flow circumstances is used to validate the model. The integrated wellbore-reservoir model is applied to different reservoir scenarios, for example, different production rates, formation zones, and reservoir formation conditions. The results indicate that the present Computational Fluid Dynamics (CFD) model can be extended to simulate the real field scale model. integrated wellbore-reservoir modeling based on 3D Navier–Stokes equations with efficient computational techniques can lead the field of petroleum industries to advance current knowledge. [ABSTRACT FROM AUTHOR]

Vertical axis wind turbine (VAWT) has a rotating axis perpendicular to the wind direction. This type of wind turbine that is suitable for urban environments has low wind direction dependency and noise. In this research, a novel surrogated approach for optimizing a VAWT is proposed, used, tested, and verified, which is not reported in literature. The proposed method consisted of 3D computational fluid dynamics (CFD) analysis of wind flow through the wind turbine with FLUENT software by solving the unsteady turbulent equations. However, 3D CFD analysis was time and cost consuming to obtain the output result (power coefficient) from input values (airfoil chord length, pitch angle, and tip speed ratio as turbine design variables). Thus, artificial neural network (ANN) was applied to obtain weight functions to correlate FLUENT software inputs and outputs after learning process. Finally, genetic algorithm was used for maximizing the turbine power coefficient considering three defined design variables. The optimum value of power coefficient was improved to 0.244, and the optimum values of design variables for blade chord length, blade pitch angle, and blade tip speed ratio were 0.218, −0.453, and 1.24, respectively. This novel surrogated method reduced the computational time and cost of VAWT optimizing considerably. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the impacts of roof ridges and semi-cylindrical tiles on the wind loading on traditional single-eave hip roofs. To the best of the authors' knowledge, the semi-cylindrical tiles have been considered in the simulation of ancient Chinese architecture for the first time. Several roof models with various ridges and semi-cylindrical tiles are simulated by solving the Reynolds-averaged Navier-Stokes equations (RANS) using the computational fluid dynamics (CFD) technique. The results reveal that the addition of roof ridges and semi-cylindrical tiles has a considerable structural protection effect, which can significantly reduce the suctions, as well as the turbulence fluctuation, on both the windward and leeward sides: the average of negative mean wind pressure coefficients is reduced by 33% on the leeward surface, and approximately 48% on the windward surface one. When the number of protruding ridges and semi-cylindrical tiles increases (decreasing the diameter of them by 40%), the average of area mean wind pressure coefficient for all the wind directions decreases by about 30% on the windward side and about 50% on the leeward side. The average of maximum spatial wind pressure coefficient decreases by about 25% on the windward side and about 40% on the leeward side. [ABSTRACT FROM AUTHOR]

Due to the low insertion speed and poor weft motion stability with single round-hole relay nozzle in the air jet loom, this study is aims to investigate the characteristics of transient intersecting airflow from a main nozzle and tri-elliptical hole relay nozzles. The turbulent intersecting airflow was simulated based on a large eddy simulations (LES). The correctness of the LES model was evaluated by comparing the time-averaged axial velocity with experimental and the Reynolds-averaged Navier–Stokes (RANS) results. The LES simulation has shown that only one potential-core arose its height about 4 mm for single round hole relay nozzle, whereas three potential-core arouse its height about 4 mm for tri-elliptical hole relay nozzles. It is possible to enhance the mean axial velocity of the intersecting airflow by up to 10% and decrease fluctuation magnitude by 25% using a new type of tri-elliptical center array relay nozzle. [ABSTRACT FROM AUTHOR]

Summary: This study investigates the impact of different positions of two limbs on the structural response of a rectangular building model to wind forces. The building's geometry assumes Z and + shapes based on specific limb configurations. Computational fluid dynamics (CFD) simulations are performed to quantify wind‐induced pressures, resulting in wind force coefficients. These coefficients are used to develop predictive machine learning models through Gene Expression Programming, Group Method of Data Handling‐combinatorial (GMDH‐Combi), Model Tree, and Artificial Neural Network (ANN) techniques. The ANN analysis explores various combinations of training algorithms, adaptation functions, activation functions, and performance functions to enhance model accuracy. Among these, the Levenberg–Marquardt (LM) with gradient descent with momentum (GDM) adaptation function and sigmoid activation function exhibit superior performance with high R‐squared values. These predictive models are then employed for a comprehensive comparative assessment of the maximum wind force coefficient (CF, max) concerning different limb positions and angles of attack (AOA). For CF, max vs Limb position, variations of limb position are examined for most critical cases of AOA. Similarly, the study of CF, max vs AOA involves an exhaustive investigation into the variation of AOA for the building with the worst limb position. The analysis reveals that changes in AOA have a more pronounced effect on CF, max compared to alterations in limb position. Interestingly, within the AOA range of 1.5 to 2.5, the CF, max consistently reaches a minimum across all models. However, the relationship between CF, max and the critical structural parameter 'S' (representing limb position) remains less conclusive for the most significant AOAs. [ABSTRACT FROM AUTHOR]

In order to solve the problem of the lack of maneuverability of the conventional underwater glider, this paper proposes a hybrid-driven underwater glider equipped with a Kappel tip rake propeller, analyzes the propulsion performance of different types of Kappel tip rake propellers in the wake field of the hybrid-driven underwater glider, optimizes the overall propulsion performance of the hybrid-driven underwater glider, and realizes self-propulsion and gliding with high efficiency and low energy consumption. In the research process, the Schnerr–Sauer cavitation model and the cavitation simulation strategy of VOF two-phase flow were adopted, coupled with the SST k-ω and γ transition turbulence model, and the control calculation error was not more than 3%. Based on the hydrodynamic performance study of the Kappel tip rake propeller, the self-propelled simulation was carried out under the working conditions of 6 kn, 5 kn, 4 kn, and 3 kn, and the gliding simulation was carried out under the working conditions of 1 kn, 0.5 kn, and a glide angle of 12°. The propulsion performance of the hybrid-driven underwater glider with different models of Kappel tip rake propellers was analyzed. It was found that the maximum open water propulsion efficiency of the propeller Kap05 had the largest improvement, which was 3.07% higher than that of the reference base propeller. Under the self-propelled condition, the hybrid-driven underwater glider with the propeller Kap05 had the lowest wake fraction, and the propellers Kap04 and Kap05 had the best propulsion performance in the wake field of the hybrid-driven underwater glider. In the gliding condition, the form of the folding paddle can reduce the gliding resistance generated by the propeller by more than 45% and the gliding negative lift by more than 68%. A moderate tip rake can effectively improve the propulsion efficiency of the Kappel tip rake propeller in the wake field of the hybrid-driven underwater glider, reduce energy loss, and improve the overall performance of the hybrid-driven underwater glider. [ABSTRACT FROM AUTHOR]

Indoor air quality (IAQ) has a significant impact on human health, as people spend 90% of their time in various indoor environments. Therefore, research on IAQ is extremely necessary. However, current research on traditional Qiang residences in western Sichuan mainly focuses on the indoor thermal environment and heritage protection, with relatively little attention paid to IAQ. This study investigates the IAQ of traditional Qiang residences in western Sichuan, which have open fire pits as the core of daily life, exploring the impact of passive renovation strategies on the indoor air quality. Using simulation methods, this study employs passive strategies, such as increasing the size of windward windows, changing ventilation methods, relocating the fire pit, and enlarging interior partition openings, to improve and optimize the IAQ through natural ventilation. The results show that when the windward window sizes are 0.8 m × 1.9 m and 0.7 m × 1.55 m, the reduction in the indoor CO2 concentration is the greatest, with a maximum decrease of 0.024% at the 1.5 m plane. This paper proposes passive renovation strategies to improve the indoor air quality of Qiang residences in western Sichuan. These strategies effectively enhance the indoor air quality of Qiang residences and address the research gap on indoor air quality in regional Qiang residences in western Sichuan. The insights and methods presented contribute to the improvement of the indoor air quality in traditional buildings and support the sustainable development of traditional architecture. [ABSTRACT FROM AUTHOR]

The research investigates converting carbon dioxide through methanation using computational fluid dynamics (CFD) in a baffled straight microchannel. The study considers different reactant distribution scenarios, including 'CO 2 Side,' 'H 2 Side,' and 'No side' streams. After finding the optimal catalyst mesh density, the model performance was validated against experimental microchannel reactor data. Results indicated that the microchannel with "CO 2 Side with Baffles" provides higher carbon dioxide conversion while maintaining the reactor temperature at a lower level. Finally, the influence of operational conditions, including feed temperature (450-400-350 °C), GHSV (120-90-60 NL/g cat/h), and H 2 /CO 2 (3.5-4.0-4.5) in the feed, was evaluated using a response surface methodology (RSM) based on the design of experiment (DOE) with carbon dioxide distribution. Multi-objective optimization results demonstrate that the optimal feed temperature, GHSV, and hydrogen-to-carbon dioxide ratio are 380 °C, 60 NL/g cat/h, and 4.43, respectively. Under these conditions, the methane yield is 60.95%, and the reactor exit temperature is around 520 °C. [Display omitted] • Reducing CO 2 emission was performed through methanation in a microchannel reactor. • CFD was used for studying the different feed distributions from side streams. • The Microchannel with Baffles and distributing CO 2 provides higher CO 2 conversion. • Adding CO 2 side streams reduces the microchannel reactor temperature. • Multi-objective optimization results in T = 380 °C, GHSV = 60 Nl/gcat/h, and H 2 /CO 2 = 4.43. [ABSTRACT FROM AUTHOR]

Access to potable water is essential for human existence. This work aims to enhance the performance of single-slope solar still. Two solar stills were employed: A conventional solar still (CSS)served as a reference, and a modified solar still (MSS) which featured a novel design with a floating absorber surface. The objective is to increase the productivity and efficiency of solar still by enhancing the evaporation surface area using wick materials. Multiple ratios of wick material (25%, 50%, 75%, and 100%) with and without an external condenser were examined to assess their influence on production. Computational Fluid Dynamics (CFD) program was employed to numerically simulate solar distillation under natural and forced convection circumstances, therefore confirming the accuracy of the experimental findings. Based on the outcomes, the increase in productivity reached 25%, 50%, 75%, and 100% wick coverage for the MSS were around 33%, 66%, 45%, and 16% higher than the productivity achieved with the CSS, respectively. With the external condenser, the enhancements increased to 35%, 75%, 50%, and 27% compared to the CSS. Daily efficiency of the MSS with wick was 19.19%, while the efficiency increased to 27.13% when both the wick and condenser were used. [ABSTRACT FROM AUTHOR]

In the present study, the principal objective is to investigate the role of multiple tuned mass damper (MTMD) to reduce aerodynamic effect of wind force on "V" plan-shaped high-rise buildings with the various internal limb angle. Distinct cases have been made by considering the angle between the limbs is 90° which is gradually increased from 90° to 150° with 15° regular interval and decreased from 90° to 40° with 10° regular interval maintaining same plan area and limb width subjected from 0° to 180° wind incidence angle with 30° regular interval. Computational fluid dynamics (CFD) is adopted to determine the aerodynamic coefficients by numerical simulation. A polynomial expression has been proposed to compute force, moment, and torsional coefficient along X, Y, and Z direction from the entire result for avoiding rigorous calculation. Dynamic wind time history in along and crosswind is obtained using maximum force coefficient. The dynamic response analysis such as peak displacement, acceleration is obtained for selected models with MTMD and effectiveness of MTMD is computed. Finally, the influence of MTMD and internal angle variation on the wind-induced response of "V" plan-shaped buildings have been observed to determine suitability of internal angle variation based on the numerical result. [ABSTRACT FROM AUTHOR]

This paper develops and verifies a multiscale computational fluid dynamics (CFD) model to investigate the airflow and heat transfer in kiwifruit cold storage under forced-air cooling (FAC). The CFD model incorporates the material properties, geometry, position of kiwifruit and ventilated packaging box, and the detailed structure of the cooling unit. For the multiscale modeling, the material characteristics are described using three interconnected sub-models, focusing each on different spatial scales: the warehouse-scale, packaging-scale, and kiwifruit-scale. In the FAC experiment, the measured airflow and temperature on these three spatial scales were obtained and compared with the simulated results. The data analysis shows that the environmental fluctuations at different scales weaken significantly in a stepwise manner with the cushioning of packaging and fruit flesh, indicating coupling between the spatial scales, which is well reflected in the numerical simulation. The average kiwifruit temperature decreases from 20 to 6 °C in 14.5 h (experimental) and 15.6 h (simulated). Specifically, the average mean absolute error, mean absolute percentage error, and root mean squared error of the predicted airflow and kiwifruit temperature were 0.116 m s−1, 1.26 °C; 26.8%, 14%; and 0.124 m s−1, 1.54 °C, respectively. These results indicate that the multiscale CFD model accurately and efficiently simulates the airflow and spatiotemporal temperature distribution in the given kiwifruit FAC system. Finally, this study provides a reference for accurately simulating large-scale industrial FAC systems and supports optimal decision-making for the design of sustainable kiwifruit cold chains. • Multiscale CFD modeling of warehouse-packaging-kiwifruit under forced-air cooling. • The established model is verified to be accurate through FAC experimental data. • Fine perception of product-scale in large-scale industrial FAC process. • Analysis of spatiotemporal coupling characteristics of multiscale environments. [ABSTRACT FROM AUTHOR]

The rotating stall generated by the centrifugal pump impeller reduces efficiency and causes severe flow fluctuations and noise due to surging. In the present work, the six-bladed impeller in the centrifugal pump was simulated by RANS, LES, and Hybrid RANS/LES turbulence models using ANSYS CFX. The turbulence models considered were the Shear Stress Transport (SST), Detached Eddy Simulation (DES), Stress-Blended Eddy Simulation (SBES), Scale Adaptive Simulation (SAS), and Wall-Adapted Local Eddy-viscosity (WALE). The design load condition and the quarter-load condition were applied for the boundary conditions, and the experimental results were compared and analyzed using velocity profile and turbulent kinetic energy at the impeller mid-height. Under the design load condition, all turbulence models predicted results similar to the experimental results. In the off-design load condition, LES predicted the experimental value most accurately, followed by SST-RM of RANS with high accuracy, and the hybrid RANS/LES model showing lower prediction accuracy; SBES predicted excessive recirculation flow. However, if sufficient grid resolution is achieved, hybrid RANS/LES model can simulate the rotating stall under the off-design flow condition than RANS models. Both DES and SAS model show relatively low mesh dependent results with acceptable accuracy. [ABSTRACT FROM AUTHOR]

By improving the understanding of fluid behaviour and allowing the development of cutting-edge technologies that enhance fluid-related processes in various sectors, advances in fluid dynamics serve a crucial role in both science and engineering. Sequel to the broad applicability of fluid dynamics leading to more efficient, sustainable, and innovative solutions for real-world challenges associated with the motion of liquids and gases, reviews of the recent advancements are far-fetched. The scope of the review was structured to focus on recent published facts on lift generation and drag reduction of aeroplanes, Computational Fluid Dynamics, turbulence modelling, and multiphase flow. Research synthesis which focuses on summarizing the state of the art of research facts on fluid dynamics was adopted. It is worth concluding that fluid dynamics principles stand as a cornerstone, unequivocally driving the relentless advancement of aerospace and automotive engineering, crucially contributing to the development of drag reduction techniques, precision control of lift generation, streamlined shapes for drag minimization, innovative wing profiles for enhanced lift, and effective boundary layer control for drag reduction. Recent advancements in Computational Fluid dynamics have revolutionized engineering simulations, providing unparalleled accuracy and efficiency in modelling complex fluid flow phenomena, from aerodynamics to hydrodynamics, thereby significantly accelerating the design and optimization processes across various industries. Studying of multiple fluid phases moving through a system simultaneously causes complicated interactions, phase transition events, and a variety of flow patterns, making it a complex but essential research topic. Experts face challenges validating Computational Fluid Dynamics results due to insufficient experimental data. [ABSTRACT FROM AUTHOR]

Endovascular treatment has become the standard therapy for cerebral aneurysms, while the effective treatment for middle cerebral artery (MCA) bifurcation aneurysms remains a challenge. Current flow-diverting techniques with endovascular coils cover the aneurysm orifice as well as adjacent vessel branches, which may lead to branch occlusion. Novel endovascular flow disruptors, such as the Contour device (Cerus Endovascular), are of great potential to eliminate the risk of branch occlusion. However, there is a lack of valid comparison between novel flow disruptors and conventional (intraluminal) flow-diverters. In this study, two in silico MCA bifurcation aneurysm models were treated by specific Contour devices and flow-diverters using fast-deployment algorithms. Computational fluid dynamic simulations were used to examine the performance and efficiency of deployed devices. Hemodynamic parameters, including aneurysm inflow and wall shear stress, were compared among each Contour device, conventional flow-diverter, and untreated condition. Our results show that the placement of devices can effectively reduce the risk of aneurysm rupture, while the deployment of a Contour device causes more flow reduction than using flow-diverters (e.g. Silk Vista Baby). Besides, the Contour device presents the flow diversion capability of targeting the aneurysm neck without occluding the daughter vessel. In summary, the in silico aneurysm models presented in this study can serve as a powerful pre-planning tool for testing new treatment techniques, optimising device deployment, and predicting the performance in patient-specific aneurysm cases. Contour device is proved to be an effective treatment of MCA bifurcation aneurysms with less daughter vessel occlusion. [ABSTRACT FROM AUTHOR]

Objective: To review the existing literature on the application of computational fluid dynamics methods to study nasal particle deposition and to summarize and analyze the factors affecting nasal particle deposition in order to provide theoretical references for the development of future transnasal drug delivery devices and the prevention of respiratory‐related diseases. Data Source: PubMed and CNKI databases. Methods: A search of all current literature (up to and including February 2023) was conducted. Search terms related to the topic of factors influencing nasal particle deposition were identified, and queries were conducted to identify relevant articles. Results: Both the properties of the particles themselves and the environmental conditions external to the particles can affect particle deposition in the nasal cavity, with particle deposition showing a positive correlation with particle size, particle density, and airflow velocity, with increasing subject age leading to a decrease in deposition, and with the relationship between airflow temperature and humidity still requiring more research to further explore. Conclusions: With the popularity of computational fluid dynamics, more and more scholars have applied computational fluid dynamics technology to explore the influence of different parameters on particle deposition. By summarizing and analyzing the influence law of various factors on deposition, it can provide a theoretical basis for the future development and application of transnasal drug delivery devices and the prevention of respiratory‐related diseases, which makes a significant contribution to the optimization of clinical disease prevention and treatment. Level of Evidence: NA. [ABSTRACT FROM AUTHOR]

Manual welding operations are performed inside the engine room of a liquefied natural gas carrier under construction. The welders are at risk of exposure to welding fumes in case of poor ventilation. Therefore, ventilation fans are installed at shipbuilding sites to improve indoor air quality. Although ensuring the respiratory health of welders is important, studies focusing on ventilation in the ship engine room have not been conducted. Therefore, the ventilation efficiency was evaluated herein based on the placement of ventilation fans to alleviate air stagnation using a computational fluid dynamic (CFD) model operating on Fluent. The mean age of air (MAA) was computed to assess the ventilation efficiency. In addition, particles with size and physical properties similar to welding fumes were sourced assuming 30 welders in the engine room. Results revealed that ventilation fan and/or exhaust in enclosed spaces contributes significantly to alleviating the MAA level. MAA and particle distribution did not correlate well due to the different properties of air and the iron oxide particle. Therefore, to determine the optimal ventilation fan displacement, particle motion should be studied along with performing MAA analysis. The proposed CFD model potentially guides to improvement of the working environments and respiratory health of welders. [ABSTRACT FROM AUTHOR]

Purpose: To enhance the performance of machine learning (ML) models for the post-embolization recanalization of cerebral aneurysms, we evaluated the impact of hemodynamic feature derivation and selection method on six ML algorithms. Methods: We utilized computational fluid dynamics (CFD) to simulate hemodynamics in 66 cerebral aneurysms from 65 patients, including 57 stable and nine recanalized aneurysms. We derived a total of 107 features for each aneurysm, encompassing four clinical features, 12 morphological features, and 91 hemodynamic features. To investigate the influence of feature derivation and selection methods on the ML models, we employed two derivation methods, simplified and fully derived, in combination with four selection methods: all features, statistically significant analysis, stepwise multivariate logistic regression analysis (stepwise-LR), and recursive feature elimination (RFE). Model performance was assessed using the area under the receiver operating characteristic curve (AUROC) and precision-recall curve (AUPRC) on both the training and testing datasets. Results: The AUROC values on the testing dataset exhibited a wide-ranging spectrum, spanning from 0.373 to 0.863. Fully derived features and the RFE selection method demonstrated superior performance in intra-model comparisons. The multi-layer perceptron (MLP) model, trained with RFE-selected fully derived features, achieved the best performance on the testing dataset, with an AUROC value of 0.863 (95% CI: 0.684– 1.000). Conclusion: Our study demonstrated the importance of feature derivation and selection in determining the performance of ML models. This enabled the development of accurate decision-making models without the need to invade the patient. [ABSTRACT FROM AUTHOR]

Multiscale agent-based modeling frameworks have recently emerged as promising mechanobiological models to capture the interplay between biomechanical forces, cellular behavior, and molecular pathways underlying restenosis following percutaneous transluminal angioplasty (PTA). However, their applications are mainly limited to idealized scenarios. Herein, a multiscale agent-based modeling framework for investigating restenosis following PTA in a patient-specific superficial femoral artery (SFA) is proposed. The framework replicates the 2-month arterial wall remodeling in response to the PTA-induced injury and altered hemodynamics, by combining three modules: (i) the PTA module, consisting in a finite element structural mechanics simulation of PTA, featuring anisotropic hyperelastic material models coupled with a damage formulation for fibrous soft tissue and the element deletion strategy, providing the arterial wall damage and post-intervention configuration, (ii) the hemodynamics module, quantifying the post-intervention hemodynamics through computational fluid dynamics simulations, and (iii) the tissue remodeling module, based on an agent-based model of cellular dynamics. Two scenarios were explored, considering balloon expansion diameters of 5.2 and 6.2 mm. The framework captured PTA-induced arterial tissue lacerations and the post-PTA arterial wall remodeling. This remodeling process involved rapid cellular migration to the PTA-damaged regions, exacerbated cell proliferation and extracellular matrix production, resulting in lumen area reduction up to 1-month follow-up. After this initial reduction, the growth stabilized, due to the resolution of the inflammatory state and changes in hemodynamics. The similarity of the obtained results to clinical observations in treated SFAs suggests the potential of the framework for capturing patient-specific mechanobiological events occurring after PTA intervention. [ABSTRACT FROM AUTHOR]

In 2021, the Ingenuity helicopter performed the inaugural flight on Mars, heralding a new epoch of exploration. However, the aerodynamics on Mars present unique challenges not found on Earth, such as low chord-based Reynolds number flows, which pose significant hurdles for future missions. The Ingenuity's design incorporated a Reynolds number of approximately 20,000, dictated by the rotor's dimensions. This paper investigates the implications of flows at a Reynolds number of 50,000, conducting a comparative analysis with those at 20,000 Re. The objective is to evaluate the feasibility of using larger rotor dimensions or extended airfoil chord lengths. An increase in the Reynolds number alters the size and position of Laminar Separation Bubbles (LSBs) on the airfoil, significantly impacting performance. This study leverages previous research on the structure and dynamics of LSBs to examine the flow around a cambered plate with 6% camber and 1% thickness in Martian conditions. This paper details the methods and mesh used for analysis, assesses airfoil performance, and provides a thorough explanation of the results obtained. [ABSTRACT FROM AUTHOR]

Launching underwater gliders by aircraft could greatly expand the application of underwater gliders. However, during the process of the glider entry into the water, it will be subjected to significant impact loads, especially during the process of wing entry into the water. In this paper, a foldable wing module is proposed to reduce the water entry impact loads of the glider caused by the wings entering into the water. The effect of the foldable wing module on impact loads reduction and the influence of the foldable wing module on the water entry trajectory are studied by numerical method. The results show that the differences in mass and gravity center position caused by the foldable wing module have little effect on the water entry impact loads of the glider until the wings impact the water. When the glider enters the water obliquely, the wing module reduces the peak radial acceleration of the glider. In addition, the trajectory and time of the glider to reach the horizontal attitude are also reduced. These conclusions will be helpful for the designing of the wings of air-launched underwater gliders. [ABSTRACT FROM AUTHOR]

Critical flow Venturi nozzles (CFVNs) are a state-of-the-art secondary standard widely used for gas flow measurements with high precision. The flow rate correlates with the type and thickness of the boundary layer (BL) inside the nozzle throat. In the cylindrical type—one of the two standard designs of CFVNs—the nozzle throat encompasses a defined axial length in which the BL develops. This numerical study is concerned with the BL effects in a cylindrical CFVN by means of two turbulence models. Compared to experimental data, the k- ω SST model predicts the discharge coefficient well for high and low Reynolds numbers, but not in the intermediate regime. The γ - R e θ model, on the contrary, agrees well with experimental data in the entire flow range. Relevant quantities and profiles of the BL are separately investigated in the laminar, turbulent, and transitional region. The calculated laminar and turbulent BL thicknesses correspond to predictions based on integral methods for solving the BL equations. Simple representations are proposed for the Zagarola-Smits scaled laminar and turbulent deficit BL profiles removing the effects of axial position, Reynolds number, and pressure gradient. Furthermore, the shape factor is investigated as a characteristic parameter for determining the transitional region. [ABSTRACT FROM AUTHOR]

The aerodynamic behavior of a square-shaped formation of four quadcopter UAVs flying in a swarm is investigated in detail through three-dimensional computer simulations utilizing Computational Fluid Dynamics (CFD) methodology. The swarm configuration comprises four UAVs positioned with two in the upper row and two in the lower row along the same propeller axes. The flow profile generated by the UAV propellers rotating at 10,000 revolutions per minute is analyzed parametrically using the Multiple Reference Frame (MRF) technique. UAVs within the swarm are positioned at 75 cm from the motion centers of adjacent propellers. This distance, the effects of horizontally and vertically positioned UAVs on each other, and the collective behavior of the swarm are thoroughly examined. Pressure, velocity, and turbulent kinetic energy values are meticulously analyzed. This research represents a milestone in understanding the aerodynamic characteristics of UAV swarms and the optimization of swarm performance. The findings highlight effective factors in swarm flights and their consequences for UAVs. Additionally, the article describes the "near-UAV phenomenon". Furthermore, the methodology developed for CFD simulations provides an approach to analyzing close flight scenarios and evaluating their performance in various swarm configurations. These achievements contribute to the future development of UAV technology. [ABSTRACT FROM AUTHOR]

In‐transit quality loss and wastage of perishables, during cold chain export, is a critical issue faced globally. Owing to increasing population, reducing food wastages by enhancing the efficacy of supply chain is imperative to meet the increasing demand. This paper presents a virtual cold chain‐based approach to model quality loss of horticultural produce prior to actual logistics operations. It is a combination of different models for predicting the temperature heterogeneity among the perishables, its related quality decay and remaining shelf‐life. An innovative simulation‐based approach is also presented which predicts the temperature of perishables inside a domain based upon its storage conditions, at a reduced computational expense. The proposed approach is demonstrated for Indian mango cold chain export. The simulation results are validated with an experimental setup, using mangoes and a standard refrigerated (reefer) container. Different metrices shows a RMSE and MAPE of 0.8 K and 10.02%, respectively. The calculated remaining quality is also found to be in accordance with experimental findings. The results report uneven air circulation and hence, heterogeneity in temperature distribution of about 3–4 K after 15 days of sea transport. This induces variations in remaining quality and shelf‐life among the mangoes placed at different locations. The maximum variation in quality is found to be 19% at 25th day of export at a location near the door of the reefer. The export transit time should be less than or equal to 26 days, to avoid spoilage, as it is the minimum shelf life of mangoes inside the container under given conditions. Practical applications: This study is concerned with managing the loss in quality and wastage of perishables, during cold chain export. Predicting the storage temperature, prior to actual logistics operations, can aid the decision makers in appropriate planning of export mode so as to minimize the loss and wastage during real export process. A virtual or simulation‐based approach is proposed to analyze the cooling behavior of individual mangoes and hence predict the evolution of its various quality attributes, passing through different stages of the cold chain. To illustrate this approach, a case study of Indian mango export is presented. [ABSTRACT FROM AUTHOR]

For a climate-neutral future mobility, the so-called e-fuels can play an essential part. Especially, oxygenated e-fuels containing oxygen in their chemical formula have the additional potential to burn with significantly lower soot levels. In particular, polyoxymethylene dimethyl ethers or oxymethylene ethers (PODEs or OMEs) do not contain carbon-carbon bonds, prohibiting the production of soot precursors like acetylene (C2H2). These properties make OMEs a highly interesting candidate for future climate-neutral compression-ignition engines. However, to fully leverage their potential, the auto-ignition process, flame propagation, and mixing regimes of the combustion need to be understood. To achieve this, efficient oxidation mechanisms suitable for computational fluid dynamics (CFD) calculations must be developed and validated. The present work aims to highlight the improvements made by developing an adapted oxidation mechanism for OME1−6 and introducing it into a validated spray combustion CFD model for OMEs. The simulations were conducted for single- and multi-injection patterns, changing ambient temperatures, and oxygen contents. The results were validated against high-pressure and high-temperature constant-pressure chamber experiments. OH*-chemiluminescence measurements accomplished the characterization of the auto-ignition process. Both experiments and simulations were conducted for two different injectors. Significant improvements concerning the prediction of the ignition delay time were accomplished while also retaining an excellent agreement for the flame lift-off length. The spatial zones of high-temperature reaction activity were also affected by the adaption of the reaction kinetics. They showed a greater tendency to form OH* radicals within the center of the spray in accordance with the experiments. [ABSTRACT FROM AUTHOR]

Computational techniques can be applied to numerically assess key parameters influencing the biotechnological process to better predict the essential features governing macroalgae growth and nutrient removal in aerated tanks, e.g., integrated into multitrophic aquaculture systems. Recent advances in computational hardware and software, such as the discrete element method (DEM) coupled with computational fluid dynamics (CFDs) codes, have enabled flow simulations in biotechnological systems. Here, we perform CFD-DEM simulations of macroalgae motion within aerated tanks to assess the light–dark cycle period as one of the most critical abiotic conditions governing the growth of photosynthetic organisms. This proof-of-concept study, which deals with the challenging problem of the fluid–structure interaction in aerated (bubbled) tanks with a highly flexible solid phase, includes a set of detailed 2D CFD simulations for two types of settings differing in the presence or absence of an inner cylinder assembly. Consequently, corresponding regression models for the cycle period are derived, and the initial hypothesis of the assembly's beneficial role is confirmed. Eventually, the CFD results are verified using an image processing technique on the laboratory scale tank with Ulva sp. and specific 3D CFD-DEM simulations. [ABSTRACT FROM AUTHOR]

Coronary artery disease is the leading global cause of mortality and Fractional Flow Reserve (FFR) is widely regarded as the gold standard for assessing coronary artery stenosis severity. However, due to the limitations of invasive FFR measurements, there is a pressing need for a highly accurate virtual FFR calculation framework. Additionally, it’s essential to consider local haemodynamic factors such as time-averaged wall shear stress (TAWSS), which play a critical role in advancement of atherosclerosis. This study introduces an innovative FFR computation method that involves creating five patient-specific geometries from two-dimensional coronary angiography images and conducting numerical simulations using computational fluid dynamics with a three-element Windkessel model boundary condition at the outlet to predict haemodynamic distribution. Furthermore, four distinct boundary condition methodologies are applied to each geometry for comprehensive analysis. Several haemodynamic features, including velocity, pressure, TAWSS, and oscillatory shear index are investigated and compared for each case. Results show that models with average boundary conditions can predict FFR values accurately and observed errors between invasive FFR and virtual FFR are found to be less than 5%. [ABSTRACT FROM AUTHOR]

In this paper, the effects of an ultrasonic power and the intensity of mechanical agitation for pulp on alkaline pretreatment of gold-bearing arsenopyrite were investigated. The effect of pulp temperature on leaching efficiency in alkaline pretreatment of arsenopyrite was investigated under ultrasound and non-ultrasound conditions. Pre-treatment was followed by gold leaching tests with a cyanide solution. Compared with the nonultrasound condition at the temperature of 60 ○C, arsenic extraction and gold extraction was increased 20 %, 14.4 %, respectively, in the presence of ultrasound at ambient temperature. The characteristics of the ultrasonic power level as a function of the intensity of mechanical agitation were evaluated by a numerical simulation with CFD software – Ansys Fluent. The simulation results demonstrated that the stronger intensity of mechanical agitation, the lower ultrasonic power level. These results were proved through leaching experiments at different rotation speeds of impeller and ultrasonic powers. The study results demonstrate that the ultrasound is an effective factor for pretreatment of gold bearing arsenopyrite and gold extraction is related to an ultrasonic power and the intensity of mechanical agitation. [ABSTRACT FROM AUTHOR]

Cardiovascular disease (CVD), a global health concern, particularly coronary artery disease (CAD), poses a significant threat to well-being. Seeking safer and cost-effective diagnostic alternatives to invasive coronary angiography, noninvasive coronary computed tomography angiography (CCTA) gains prominence. This study employed OpenFOAM, an open-source Computational Fluid Dynamics (CFD) software, to analyze hemodynamic parameters in coronary arteries with serial stenoses. Patient-specific three-dimensional (3D) models from CCTA images offer insights into hemodynamic changes. OpenFOAM breaks away from traditional commercial software, validated against the FDA benchmark nozzle model for reliability. Applying this refined methodology to seventeen coronary arteries across nine patients, the study evaluates parameters like fractional flow reserve computed tomography simulation (FFRCTS), fluid velocity, and wall shear stress (WSS) over time. Findings include FFRCTS values exceeding 0.8 for grade 0 stenosis and falling below 0.5 for grade 5 stenosis. Central velocity remains nearly constant for grade 1 stenosis but increases 3.4-fold for grade 5 stenosis. This research innovates by utilizing OpenFOAM, departing from previous reliance on commercial software. Combining qualitative stenosis grading with quantitative FFRCTS and velocity measurements offers a more comprehensive assessment of coronary artery conditions. The study introduces 3D renderings of wall shear stress distribution across stenosis grades, providing an intuitive visualization of hemodynamic changes for valuable insights into coronary stenosis diagnosis. [ABSTRACT FROM AUTHOR]

Surface-patterned membranes are becoming increasingly attractive for reducing fouling in membrane processes for water treatment. In this review article, literature on simulations of physically surface-patterned membranes is reviewed, with emphasis on the various factors affecting their anti-fouling performance. Associated computational techniques, including computational fluid dynamics and Brownian dynamics, are discussed. Key parameters discussed in the literature include the dimensions of the membrane (height, width), the velocity and direction of the fluid flow, the size of the particles, and the pattern size (height, width, and pitch). The key observables are the shear stress and velocity streamlines at various points, especially the pattern apex and valley regions, with an un-patterned membrane as a point of comparison in studies. The review concludes that the pattern dimensions have the most significant influence on the anti-fouling performance. Also, the effect of particle size to membrane pattern ratio on the extent of particle deposition on the membrane (fouling activity) can be explained by understanding the shear stress distribution around the membrane. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) simulations have been extensively used in designing air distribution systems for controlled environment agriculture (CEA). In recent years, more application studies using CFD simulations can be found for vertical farms due to the increasing interest in indoor vertical farming systems. However, it is well-known that CFD simulations are sensitive to many computational parameters and settings. The requirement of a crop response model in the CFD simulation for a vertical farm makes it even more complicated. Despite increased interest, guidelines for CFD simulations in vertical farms are scarce based on a literature study. Therefore, a systematic sensitivity analysis is conducted for a small generic multi-layer vertical farm with sole source lighting, which was the object of study in the literature before. The impact of a wide range of computational and physical parameters is investigated, including grid resolution, turbulence model, turbulence intensity, discretisation scheme, drag coefficient of the crops and computational time. The analysis shows that in this case (inlet Re = 46,923, Ar = 0.078, cultivated with lettuce), the RNG k-ε turbulence model outperforms other commonly used two-equation turbulence models. Compared to the experimental results from the literature, the simulation results from the first-order upwind scheme show large discrepancies, especially on the coarse grid. Although the influence of drag coefficient on the airflow inside the crop canopy is pronounced, little difference is observed in the air distributions in the vertical farm away from the crops. • Literature review on computational settings in CFD simulations of indoor farming. • Validation of RANS CFD simulations including a crop response model. • RNG k-ε turbulence model outperforms the other two-equation turbulence models. • First-order upwind discretisation scheme shows large discrepancies. • Influence of the momentum sink of lettuce canopy on the air distributions is limited. [ABSTRACT FROM AUTHOR]

The study investigated how variations in pressure ratio affect the leakage flow of a brush seal for both contact and clearance structures, in which the clearance is measured as the distance between the bristles tip and the rotor surface. This investigation utilized the Reynolds-Averaged-Navier–Stokes (RANS) equations alongside a two-dimensional axisymmetric anisotropic porous medium model. To verify the model's accuracy and dependability, the obtained results were compared with previous numerical results and experimental observations, showing a satisfactory level of agreement. The results indicate that the predominant pressure drop occurs downstream of the bristle pack with the clearance model exhibiting a higher leakage rate compared to the contact model. Leakage increases proportionally with the pressure ratio, while axial velocity gradually rises and radial velocity experiences a significant increase. In conclusion, the leakage in the brush seal contact structure is significantly lower than in the clearance structure, resulting in the best performance. [ABSTRACT FROM AUTHOR]

Fluid jet polishing (FJP) is a non-contact polishing technology that can fabricate free-form optical surfaces with sub-micron-level form accuracy and nano-level surface roughness, especially for hard and brittle materials. The surface generation model of FJP can be used to guide the determination and optimization of process parameters and is of great significance for understanding the evolution mechanism of surface microtopography. However, predictive models for the microscopic topography of polished surfaces are still lacking. This study established a macroscopic surface profile model for predicting 3D material removal characteristics and surface texture by combining the 3D computer fluid dynamics (CFD) simulation model and single-particle erosion mechanism. A fractal theory-based erosion model has been built to calculate the material removal caused by the erosion of a single abrasive particle on the rough surface; thus, it predicts the micro-topography and surface roughness of the polished samples. A series of polishing experiments were conducted to analyze the feasibility and accuracy of the model quantitatively and study the influence mechanism of process parameters on the material removal characteristics and surface quality. Results indicated that the models could well predict material removal and surface roughness. The prediction accuracy of the surface roughness Ra and maximum removal depth is better than 91.6% and 90%, respectively. It is also found that the material removal rate of FJP could reach 0.517 mm3/min, and the surface roughness convergence rate could reach 62.9%. [ABSTRACT FROM AUTHOR]

The reliable functioning of next-generation electronic devices within their temperature limits is contingent upon the efficient removal of high heat flux. Interfaces between the device, heat spreaders, and heat sink contribute significantly to thermal resistance in conventional chip packages. The elimination of interface resistances can lead to a noteworthy decrease in overall thermal resistance by incorporating the heat sink directly into the heat-generating device. The current study involved the manufacturing, simulation and experimentation of a micro channel heat sink. The micro channel assembly is manufactured with dimensions of 50 × 50 × 3 mm. The length of micro channel is 35 mm having height and width of 0.2 mm with 58 channels. The experimentation and numerical simulation was done with considering the various parameters like mass flow rate, heat flux, and inlet temperature of nanofluid. The microchannel heat sink improved electronic device thermal performance in fabrication, experimentation, and numerical simulation. The heat sink lowered device temperatures and prevented overheating. Nanofluid at 0.3% volume and at a mass flow rate of 8 m/s, the heat transfer coefficient reaches a maximum value of 13,693.00 W/m2 K at input temperature of 35 °C. The comprehension of the heat sink's performance was enhanced subsequent to the simulations, which unveiled the fluid flow characteristics and heat transfer mechanisms within the microchannels. [ABSTRACT FROM AUTHOR]

For energy-assisted compression ignition (EACI) engine propulsion at high-altitude operating conditions using sustainable jet fuels with varying cetane numbers, it is essential to develop an efficient engine control system for robust and optimal operation. Control systems are typically trained using experimental data, which can be costly and time consuming to generate due to setup time of experiments, unforeseen delays/issues with manufacturing, mishaps/engine failures and the consequent repairs (which can take weeks), and errors in measurements. Computational fluid dynamics (CFD) simulations can overcome such burdens by complementing experiments with simulated data for control system training. Such simulations, however, can be computationally expensive. Existing data-driven machine learning (ML) models have shown promise for emulating the expensive CFD simulator, but encounter key limitations here due to the expensive nature of the training data and the range of differing combustion behaviors (e.g. misfires and partial/delayed ignition) observed at such broad operating conditions. We thus develop a novel physics-integrated emulator, called the Misfire-Integrated GP (MInt-GP), which integrates important auxiliary information on engine misfires within a Gaussian process surrogate model. With limited CFD training data, we show the MInt-GP model can yield reliable predictions of in-cylinder pressure evolution profiles and subsequent heat release profiles and engine CA50 predictions at a broad range of input conditions. We further demonstrate much better prediction capabilities of the MInt-GP at different combustion behaviors compared to existing data-driven ML models such as kriging and neural networks, while also observing up to 80 times computational speed-up over CFD, thus establishing its effectiveness as a tool to assist CFD for fast data generation in control system training. [ABSTRACT FROM AUTHOR]

This work outlines a method for characterizing flexible polyurethane foam (FPF) for use as a filter material, particularly for personal protective equipment. Two different FPF samples were tested experimentally to establish their geometric and flow resistance properties, which were then used to calibrate a geometric idealization of the foam created using a discrete element modeling software. The idealized model was then used to conduct pore-level numerical simulations to estimate the filtration efficiency of the foam for particles with average of diameters in the range 0.2–200 µm for various airflow velocities. A parametric study was then done to estimate the particle penetration rate of a facile mask made of FPF under different breathing conditions. The results indicate that during inhalation, pressure and velocity variations on the inner surface of the mask are not significant and that estimates of the filtration efficiency can be made by considering the time-dependent filter velocity combined with prior results for filter effectiveness as a function of velocity and particle size. The results also show that a non-medical FPF mask can drastically reduce the risk of particle penetration for particles larger than 0.2 µm. The process demonstrated in this work can be used to estimate the overall effectiveness of an FPF mask when exposed to clouds of different sized particles and to study the impacts of mask shape and fit on filtration effectiveness. [ABSTRACT FROM AUTHOR]