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Microfluidic paper-based analytical devices (µPADs) are a promising technology to enable accurate and quantitative in situ assays. Paper’s inherent hydrophilicity drives the fluids without the need for external pressure sources. However, controlling the flow in the porous medium has remained a challenge. This study addresses this problem from the nature of the paper substrate and its design. A computational fluid dynamic model has been developed, which couples the characteristics of the porous media (fiber length, fiber diameter and porosity) to the fluidic performance of the diffusion-based µPAD sensor. The numerical results showed that for a given porous membrane, the diffusion, and therefore the sensor performance is affected not only by the substrate nature but also by the inlets’ orientation. Given a porous substrate, the optimum performance is achieved by the lowest inlets’ angle. A diffusion-based self-referencing colorimetric sensor was built and validated according to the design. The device is able to quantify the hydronium concentration in wines by comparison to 0.1–1.0 M tartaric acid solutions with a 41.3 mM limit of detection. This research showed that by proper adjustments even the simplest µPADs can be used in quantitative assays for agri-food applications.

By combining computational fluid dynamics (CFD) and surrogate model method (SMM), the relationship between turbine performance and airfoil shape and flow characteristics at low flow rate is revealed. In this paper, the flow velocity tidal energy airfoil model is designed based on the Kriging model, and the original airfoil with a relative thickness of 12% and a relative curvature of 2.5% is obtained. The parameter optimization is carried out by setting the 4th CST equations through the surrogate model; the maximum lift-drag ratio is the optimization goal, the optimization design variable is 10, the maximum number of iterations is 100, and the maximum number of sub-optimization iterations is 200. The results show that the hydrodynamic performance of the airfoil with thinner thickness and more curvature is better, the maximum thickness part is shifted forward by 4.58%, and the lift-drag ratio is improved by 4.03%. The flow field and the efficiency are more stable, which provides an engineering reference for the optimal design of hydraulic turbine airfoils under low flow velocity. It supplements the research on the performance of turbine blades in low velocity. [ABSTRACT FROM AUTHOR]

It is important to marine ecology research that plankton samples are collected without damage, especially for time series samples. Usually, most fixed-point plankton samplers are made using a pump with paddle blades in order to increase the flow rate. But it can easily injure soft plankton. In this paper, a shaftless hollow sampling pump is designed, which can provide a highly efficient driving component for the plankton sampler. The numerical model of the sampling pump is established, and the flow rate of the sampling pump at different rotational speeds is simulated by the computational fluid dynamics method. In order to obtain a higher flow rate, the influence of internal and external cavity size, blade angle, and blade number on the flow rate of the sampling pump with a constant rotational speed of the blade was simulated and discussed. The results show that the flow rate at the internal cavity is positively correlated with the inlet and outlet pressure differences of the internal cavity, and the greater the negative pressure at the outlet of the internal cavity, the greater the flow rate. When the internal and external cavity sizes are h = 14 mm, d = 52 mm, blade angle θ = 45°, and number of blades s = 5, the flow rate of the sampling pump internal cavity reaches the maximum. Finally, the feasibility of the shaftless hollow sampling pump is verified by experiments. The shaftless hollow sampling pump can realize non-destructive sampling of plankton. This paper presents a theoretical design foundation for a new non-destructive siphon sampling method for marine plankton, which is of great significance for marine plankton sampling and subsequent research. [ABSTRACT FROM AUTHOR]

The catalytic combustion has the advantage of lower auto-ignition temperature and helps to expand the combustible limit of lean premixed gas. However, the intake needs to be preheated to certain temperature commonly through an independent heat exchanger. Similar to the principles of non-catalytic RTO combustion, this paper presents a similar approach whereby the combustion chamber is replaced by a catalytic combustion bed. A new catalytic reactor integrated with a heat recuperator is designed to enhance the heat recirculation effect. Using a two-dimensional computational fluid dynamics model, the performance of the reactor is studied. The reaction performances of the traditional and compact reactors are compared and analyzed. Under the same conditions, the compact reactor has better reaction performance and heat recirculation effect, which can effectively decrease the ignition temperature of feed gas. The influences of the inlet velocity, the inlet temperature, the methane concentration, and the thermal conductivity of porous media on the reaction performance of integrated catalytic reactor are studied. The results show that the inlet velocity, inlet temperature, methane concentration, and thermal conductivity of porous media materials have important effects on the reactor performance and heat recirculation effect, and the thermal conductivity of porous media materials has the most obvious influence. Moreover, the reaction performance of multiunit integrated catalytic reactor is studied. The results show that the regenerative effect of multiunit integrated catalytic reactor is further enhanced. This paper is of great significance to the recycling of low calorific value gas energy and relieving energy stress in the future. [ABSTRACT FROM AUTHOR]

With the reliance on ocean resources, the nuclear power powers have set their sights on marine nuclear power plants to break through the bottleneck of energy supply for the development of ocean resources. In this paper, the computational fluid dynamics software ANSYS CFX 2021 is used to simulate the TOSQAN benchmark experiment. Three different turbulence models, the k − ε model, R N G   k − ε model, and S S T model, are selected to analyze the adaptability of the turbulence model. The simulation results are compared with the benchmark experimental results, and the selected numerical calculation model is used to analyze the influence of vapor on the pressure, temperature, hydrogen distribution, and hydrogen risk in the containment space when a hypothetical serious accident occurs in a marine nuclear power plant. The results show that the results simulated with the k − ε turbulence model are closer to the benchmark experimental results. Vapor has no obvious effect on the response speed of pressure balance at each position in the closed containment space, and the condensation of the vapor wall can effectively reduce the pressure peak in the closed containment space. The existence of vapor and the increase in vapor concentration will increase the temperature in the closed containment space. The condensation of vapor on the wall surface will cause the temperature in the containment space to have a peak value, which can effectively reduce the temperature in the containment space. Vapor will promote the mixing of gas in the containment space and make the hydrogen distribution tend to be uniform. The presence of vapor and the increase in vapor concentration can reduce the hydrogen risk in the containment space, but the condensation of vapor may increase the hydrogen risk in the containment space. [ABSTRACT FROM AUTHOR]

A passive wedge screen, thanks to its many functional and environmental advantages, has recently become a popular type of surface water intake for municipal and industrial purposes. The design solutions proposed in this paper for a passive wedge wire screen intake model and two different deflectors have been experimentally tested under conditions that can be considered as no-flow conditions at the hydraulic flume. There was only a slight flow associated with the operation of the screen, while there was almost no flow in the hydraulic channel itself, such that it would be considered a watercourse. A hydraulic analysis was carried out, including velocity distribution around the screen as well as the determination of head losses with or without deflectors installed inside the screen. Lower inlet and inflow velocities to the surface of the water intake reduce the risk of injury or death to small fish and fry as well as attracting pollutants understood as sediments, debris, and plant remains floating in the river. In order to achieve the lowest possible maximum inlet and inflow velocities at the highest possible intake capacity, it was necessary to equalize the approach velocity distributions. It was shown that by using the proposed deflectors, the approach velocity distributions were equalized and the maximum values of inflow and inlet velocities were reduced. A water intake screen with a deflector with an uneven porosity distribution equalized the approach velocities better than a deflector with equal openings, but the differences were small. Installing the wedge screen model reduced the maximum inlet velocity from exceeding 2 m/s to a value of 0.08 m/s, and after installing deflectors with equal and unequal openings to values of 0.06 m/s and 0.05 m/s, respectively. In addition to laboratory tests, the paper describes the numerical simulations performed in ANSYS Fluent software. The results of the simulations made it possible to obtain a broader study, as well as to compare the velocity values obtained at the measuring points during the laboratory tests. [ABSTRACT FROM AUTHOR]

In order to assess whether condensation will occur on the shipside of a bulk grain cargo hold during transportation at sea, this paper has established a ventilation model for the bulk cargo hold of the ship, and optimized the model according to the characteristics of the solid bulk grain stowed on a moving ship at sea. The temperature field, micro-airflow field and relative humidity field of the bulk grain in a cargo hold are simulated by using fluent software (v.2020). Incorporating the impact of grain moisture exchange, the Equilibrium Relative Humidity (ERH) method is introduced alongside the Dew Point (DP) method to determine the condensation on the shipside of the cargo hold. The results of simulation are in agreement with the practical observation results obtained from an actual ship with a heavy cargo damage claim. Conclusively, this paper finds that the risk of the condensation on the shipside of a bulk grain cargo hold always exists if the inner part of the shipside is directly in contact with the grain. Meanwhile, when the grain temperature near the shipside decreases, the moisture in the cargo hold will migrate to the shipside due to the temperature gradient. Furthermore, the longer the voyage, the more obvious the migration of moisture from the central part of the bulk grain to the shipside, and the greater the risk of condensation. [ABSTRACT FROM AUTHOR]

For high-speed railway sound barriers, determining the aerodynamic pressure generated by high-speed trains is crucial for their structural design. This paper investigates the distribution of aerodynamic pressure on the sound barrier caused by high-speed trains with different nose lengths, utilizing the computational fluid dynamics (CFD) simulation method. The accuracy of the numerical simulation method employed is verified through comparison with field test results from the literature. Research findings reveal that when a high-speed train passes through a sound barrier, significant "head wave" and "wake wave" effects occur, with the pressure peak of the "head wave" being notably greater than that of the "wake wave". As the distance between the sound barrier and the center of the train gradually increases, the aerodynamic pressure on the sound barrier gradually decreases. The nose length of the train has a considerable impact on the aerodynamic pressure exerted on the sound barrier. The streamlined shape of longer-nose trains can significantly reduce the aerodynamic effects on the sound barrier, resulting in a notably smaller pressure peak compared to shorter-nose trains. Finally, by establishing the relationship between the train nose length and the aerodynamic pressure peak, a calculation formula for the train-induced aerodynamic pressure acting on the sound barrier is proposed, taking into account the nose length of the high-speed train. [ABSTRACT FROM AUTHOR]

Motion in waves is a crucial issue for planing craft safety and human comfort. Practically, a boat at sea may navigate in any heading angle with respect to wave directions. In this paper, the planing craft motion in regular oblique waves in a range of heading angles is investigated using computational fluid dynamics (CFD). The simulation is performed on two prismatic hulls in which slamming occurs on one hull, and the other one is in non-slamming condition. The simulation results are validated in comparison with the experiment in the head wave condition. Findings show that as the wave direction changes from the head to the oblique, heave, pitch and acceleration rapidly decrease while roll increases. Additionally, the impact acceleration becomes a quasi-periodic, and its amplitude drops at the same time. It is observed that the aforementioned influences are much more pronounced for the craft in slamming condition. [ABSTRACT FROM AUTHOR]

Reasonable coolant flow distribution and its heat transfer coefficient (HTC) distribution are of great significance to the cooling performance of water-cooled engine. Therefore, the present paper proposes a coolant transport path analysis method aiming at analyzing coolant velocity distribution and optimizing the coolant flow characteristics of water jacket based on Computational Fluid Dynamics (CFD), with particular emphasis on the assessment of coolant flow velocity distributions of hightemperature area of engine head water jacket. First, the coolant flow characteristics of a single-cylinder water jacket is investigated and it is found that coolant velocity of exhaust bridge is less than 1.5 m/s and the HTC distribution of water jacket under three flow conditions of 15 L/min, 25 L/min and 35 L/min have a small area reaching 5000 W/(m2·K). Some areas have no coolant flow and the mass flowrate distribution of each gasket hole is unreasonable, proving that original water jacket structure has some shortcomings and need to be optimized. Based on coolant transport analysis, an improved design of the single cylinder water jacket is proposed and HTC distribution of improved water jacket meet cooling requirements that HTC in high heat load area are above 5000 W/(m2·K). The coolant transport path analysis method for optimizing coolant flow characteristics of water jacket proves to be an effective way through successful application and remarkable achievement in the other single-cylinder water jacket and two-cylinder water jacket that coolant flow distribution become more reasonable and coolant velocity of high-temperature areas are bigger than 1.5 m/s. [ABSTRACT FROM AUTHOR]

Supplying homogenous and suitable airflow schemes were explored in Chinese solar greenhouses, which had a positive impact on the crop yield and quality. This paper provided a multifunctional fan–coil unit system (FCU) to assist in circulating air. This system could collect the surplus heat of daytime air and release it to heat the greenhouse at nighttime. However, the main problem to be faced was the nonuniform airflow distributions. Thus, this paper aimed to optimize and analyze the placement strategy of the FCU system for a Chinese solar greenhouse using the numerical methodology. The computational fluid dynamics model was constructed to evaluate the effect of the FCU system on the airflow field and to uphold its validation. The complex structure of the FCU system was simplified to a fan model by fitting the pressure jump and the air velocity to enhance the practicality of the simulation model. Finally, the coefficient of variation was used to optimize four parameters: the tilt angle, swing angle, height above the ground, and shape of the outlet baffle. The effective disturbance velocity percentage was proposed as the evaluation index to improve the turbulence characteristics. The mean absolute error (MAE) between the measured and simulated values of the air velocity for the two planes was 0.06 m/s and 0.09 m/s, and the root mean square error (RMSE) was 0.08 m/s and 0.11 m/s. The simulated results showed that the coefficient of variation before optimization was 0.76, and the effective disturbance velocity percentages of the planes at 0.7 m and 1.0 m from the ground were 42.73% and 41.02%, respectively. After optimization, the coefficient of variation was reduced to 0.33, and the effective disturbance velocity percentages of the two planes increased to 58.68% and 43.73%, respectively. These results significantly improved the uniformity of the interior airflow field. This paper provides a reference for the design and installation of the FCU system. [ABSTRACT FROM AUTHOR]

Horizontal wells are more likely than vertical wells to have enlarged wellbore sections due to borehole instability. However, there is scarce research on borehole cleaning of horizontal wells with enlarged wellbore sections. In this paper, we establish a horizontal wellbore model with a breakout enlargement section using field borehole diameter data. We used the three-dimensional computational fluid dynamics (CFD) method and the Realizable k-ε turbulence model with the Euler–Euler approach to simulate the effects of the drilling fluid circulation return speed and the spinning speed of the drill pipe on the cutting movement of conventional horizontal wells and horizontal wells with a breakout enlargement section. The simulation results demonstrate that increasing the drilling fluid circulation return speed and the spinning speed of the drill pipe does not significantly improve the hole cleaning impact for horizontal wells with a breakout enlargement section. We analyzed the effects of the enlargement ratio, ellipticity, and principal axis orientation on the borehole cleaning effect of horizontal wells with a breakout enlargement section. The results show that the cleaning impact is better when the enlargement ratio is lower; moreover, the ellipticity is larger and the principal axis orientation is perpendicular to the gravity direction. This paper fills a gap in the existing theory of hole cleaning in horizontal wells and provides a theoretical basis for improving the hole cleaning effect in actual drilling processes. [ABSTRACT FROM AUTHOR]

The existence of defects in the enclosure structure is the primary cause of water and sand leakage in foundation pits, as well as being a significant source of danger in pit construction, but current research lacks an in-depth investigation of the generation mechanism and gestation process. In this paper, which comprehensively considers the microscopic particles and macroscopic level, the development mechanism of a water and sand leakage disaster in a foundation pit with a water-rich sand layer was studied using the principle of computational fluid dynamics and discrete element method coupled analysis (CFD–DEM); moreover, based on the anisotropy of the particle force and fluid energy analysis, the deformation of the stratum and ground stress field were analyzed. The results show that the stress field will produce a plugging effect at a certain distance from the defect, and the strata exhibit a dominant displacement tendency in the vertical direction, resulting in the emergence of a gradually concave stress relaxation zone and an elliptical contour in the strata displacement map near the defect. The fluid energy describes the displacement of the sand layer very well, and it is separated into the sand layer's centralized loss region and the major loss area based on the high and low levels of the fluid energy class. The impact of fluid at the defect reaches the maximum kinetic energy, which penetrates the structural weakness and causes the loss of sand particles, and the cross-section of the water influx near the defect gradually expands with the loss of particles, indicating that there is a danger of further expansion of the defect under the impact of water flow. These results have technical implications for the management of water and sand leakage disasters in foundation pit engineering. [ABSTRACT FROM AUTHOR]

Wing smarting and eliminating conventional control surfaces are fundamental parameters for improving aircraft aerodynamic performance in future aviation. Twist is a well-known tool that, along with the development of morphing technology, can play a crucial role in controlling next-generation aircraft. However, wing twisting with a control approach requires many aerodynamic studies, particularly at the high aft-swept angle; this is more noticeable in the flying wing configuration. In this paper, a control strategy based on twist morphing has been evaluated aerodynamically at the Swing, a flying wing configuration. Extraction of aerodynamic coefficients and flow field on the wing have been performed using the computational fluid dynamics (CFD) method in an incompressible flight regime. To comprehensively cover the control needs, two control concepts have been introduced, called independent and nonindependent twist. Within the concept of independent twist, a co-oriented twist arrangement (Co-OTA) and counteroriented twist arrangement (Cun-OTA) are applied to the wings, which are used to produce pitching and rolling moments, respectively. The results show these control arrangements have high efficiency at low angles of attack (AoAs), but as the AOA increases, their aerodynamic performance will gradually decrease. In this regard, a significant challenge for Cun-OTA is producing the yawing moment during roll maneuvering. Attempts to solve this problem have led to the idea of a compound twist arrangement (CTA). The existence of a control arrangement to generate yawing moment is beyond the capacity of the independent twist concept. The nonindependent twist has been introduced as a solution to this issue. Conventional control surfaces have various weaknesses, one of the most important of which is the unfavorable effects on aerodynamic efficiency; the reduction of aerodynamic efficiency leads to a drop in flight endurance and an increase in fuel consumption. At a step forward, with the approach of wing smarting and morphing technology, the tasks of conventional control surfaces can be delegated to the wing itself. Therefore, it will be possible to remove the control surfaces and integrate the wing. In this article, according to the mentioned approach, an attempt was made to introduce a control strategy based on the geometric twist. In this strategy, the value and direction of the twist applied to each wing produces a specific control arrangement. Control arrangements (three types of arrangements) are involved in producing longitudinal and lateral and modified lateral moments. The results indicate that the use of twisting in aircraft control is efficient for a wide range of flight conditions, and this capability exists to be used in the next generation of aircraft. In this way of control, challenges are deliberately related to the design of the operating mechanism, safety issues, and weight. [ABSTRACT FROM AUTHOR]

Industries across the world are making the transition to net-zero carbon emissions, as government policies and strategies are proposed to mitigate the impact of climate change on the planet. As a result, the use of hydrogen as an energy source is becoming an increasingly popular field of research, particularly in the aviation sector, where an alternative, green, renewable fuel to the traditional hydrocarbon fuels such as kerosene is essential. Hydrogen can be stored in multiple ways, including compressed gaseous hydrogen, cryo-compressed hydrogen and cryogenic liquid hydrogen. The infrastructure and storage of hydrogen will play a pivotal role in the realisation of large-scale conversion from traditional fuels, with safety being a key consideration. This paper provides a review on previous work undertaken to study the characterisation of both unignited and ignited hydrogen jets, which are fundamental phenomena for the utilisation of hydrogen. This includes work that focuses on the near-field flow structure, dispersion in the far-field, ignition and flame characteristics with multi-physics. The safety considerations are also included. The theoretical models and computational fluid dynamics (CFD) multiphase and reactive flow approaches are discussed. Then, an overview of previous experimental work is provided, before focusing the review on the existing computational results, with comparison to experiments. Upon completion of this review, it is highlighted that the complex near-field physics and flow phenomena are areas lacking in research. The near-field flow properties and characteristics are of significant importance with respect to the ignition and combustion of hydrogen. [ABSTRACT FROM AUTHOR]

Precise ventilation rate estimation of a naturally ventilated livestock building can benefit the control of the indoor environment. Machine learning has become a useful technique in many research fields and might be applied to ventilation rate prediction. This paper developed a machine-learning model for ventilation rate prediction from batch computational fluid dynamics (CFD) simulation results. By comparing deep neural networks (DNN), support vector regression (SVR), and random forest (RF), the best machine learning algorithm was selected. By comparing the modeling scheme of direct single-output (ventilation rate) and indirect multiple-output (predict averaged air velocities normal to the openings, then calculate the ventilation rate), the performances of the machine learning models widely applied in ventilation rate prediction were evaluated. In addition, this paper further evaluated the impact of adding indoor air velocity measurement in ventilation rate prediction. The results showed that the modeling performance of the DNN algorithm (Mean Absolute Percentage Error (MAPE) = 20.1%) was better than those of the SVR (MAPE = 23.2%) and RF algorithm (MAPE = 21.0%). The scheme of multiple-output performed better (MAPE < 8%) than the single-output scheme (MAPE = 20.1%), where MAPE was the mean absolute percentage error. Additionally, the comparison of modeling schemes with different inputs showed that the predictive accuracy could be improved by adding indoor velocities to the inputs. The MAPE decreased from 7.7% in the scheme without indoor velocity to 4.4% in the scheme with one indoor velocity, and 3.1% in the scheme with two indoor velocities. The location of the additional air velocity affected the accuracy of the predictive model, with the ones at the bottom layer performing better in the prediction than those at the top layer. This study enables a real-time and accurate prediction of the ventilation rate of a barn and provides a recommendation for optimal indoor sensor placement. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to study the heat transfer effect of copper sensor and skin simulant on skin. Design/methodology/approach: For the sensor, the physical and mathematical models of the thermal sensors were used to obtain the definite conditions in the heat transfer process of the sensor, and the heat transfer models of the two sensors were developed and solved respectively by using ANSYS WORKBENCH 19.0 software. The simulation results were compared with the experimental test results. For the skin, the numerical model of the skin model was developed and calculated. Finally, the heat transfer simulation performance of the two sensors was analyzed. Findings: It is concluded that the copper sensor is more stable than the skin simulant, but the material and structure of the skin simulant is more suitable for skin simulation. The skin simulant better simulates the skin heat transfer. For all the factors in the model, the thermal properties of the material and the heat flux level are the key factors. The convective heat transfer coefficient, radiation heat transfer rate and the initial temperature have little influence on the results, which can be ignored. Research limitations/implications: The results show that there are still some differences between the experimental and numerical simulation values of the skin simulant. In the future, the thermal parameters of skin simulant and the influence of the thermocouple adhesion should be further examined during the calibration process. Practical implications: The results suggest that the skin simulant needs to be further calibrated, especially for the thermal properties. The copper sensor on the flame manikin can be replaced by the skin simulant with higher accuracy, which will be helpful to improve the accuracy of performance evaluation of thermal protective clothing. Social implications: The application of computational fluid dynamics (CFD) technology can help to analyze the heat transfer simulation mechanism of thermal sensor, explore the influence of thermal performance of thermal sensor on skin simulation, provide basis for the development of thermal sensor and improve the application system of thermal sensor. Based on the current research status, this paper studies the internal heat transfer of the sensor through the numerical modeling of the copper sensor and skin simulant, so as to analyze the effect of the sensor simulating skin and the reasons for the difference. Originality/value: In this paper, the sensor itself is numerically modeled and the heat transfer inside the sensor is studied. [ABSTRACT FROM AUTHOR]

Concrete remains a widely used material in construction. As structures become more optimised, a deeper understanding of the rheology of the concrete mixture is necessary. This paper aims to numerically simulate the flow of fresh concrete in the L-box apparatus, with the objective of gaining insights into its rheological behaviour and predicting its properties. The fresh concrete flowing through the L-box test is simulated from the moment that the gate is lifted until the stoppage and the material takes its final shape. The flow in this tool occurs on a free surface. In this work, a three-dimensional model has been developed using the computational fluid dynamics technique for simulation. The flow behaviour of fresh concrete was assumed to be non-Newtonian following the Bingham law, characterised by a non-linear shear stress–shear rate ratio, yield stress and plastic viscosity. A set of numerical simulations by varying workability were conducted. Furthermore, a parametric study was conducted to examine the impact of introduced parameters in the concrete flow, including the effect of yield stress, viscosity and density. [ABSTRACT FROM AUTHOR]

To achieve maximum efficiency in organic photovoltaics (OPV), functional layers with uniform and exactly predefined thickness are required. An in-depth understanding of the coating process is therefore crucial for an accurate process control. In this paper, the meniscus-guided blade coating process, which is the most commonly used process for the manufacturing of organic electronics, is investigated by experimental and numerical methods. A computational fluid dynamics (CFD) model is created to simulate the coating behaviour of P3HT:O IDTBR, an industrial state-of-the-art active material system used in OPV, and its results' independence of numerical parameters is ensured. In particular, the influence of the coating velocity and the initially injected fluid volume on the resulting wet film thickness is studied. The developed CFD analysis is able to reproduce the experimental results with very high accuracy. It is found that the film thickness follows a power law dependence on the velocity (~v2/3) and a linear dependence on the ink volume (~V). Accordingly, an analytical expression based on our theoretical considerations is presented, which predicts the wet film thickness as a function of the coating velocity and the ink volume only based on easily accessible ink properties. Consequently, this CFD model can effectively substitute time-consuming and expensive experiments, which currently have to be performed manually in the laboratory for a multitude of novel material systems, and thus supports highly accelerated material research. Moreover, the results of this work can be used to achieve homogeneous large-area coatings by utilising accelerated blade coating. [ABSTRACT FROM AUTHOR]

The dynamic characteristics of the pumped storage unit (pump-turbine runner) make it highly susceptible to vibrations. Previous studies seldom addressed the clearance variation due to runner vibration, largely because of two challenges: the integration of the moving grid with the clearance and governing equations, and the intricacy of factoring in the entire shaft system's influence on vibration. By employing user-defined functions (UDF), kinematic equations for the pump-turbine runner's rotation and translation were formulated and integrated with computational fluid dynamics results. This paper introduces a computational method to simulate clearance-induced vibration displacement. The study examines the impact of clearance vibration displacement on the pump-turbine's transient flow field and runner vibrations under various operating conditions. Notably, deviations from the rated load condition led to an expansion-contraction trajectory of the runner axis, culminating in chaotic behaviour in the "S" characteristic zone. The correlation between runner vibrations and pressure fluctuations strengthened with the clearance displacement model, especially in narrow labyrinth seal clearances. Simulations also provided a refined estimation of the secondary rotational speed increase during load rejection. The method's reliability is confirmed through field test data comparison, offering a fresh perspective to identify the vibration characteristics of the pump-turbine runner. [ABSTRACT FROM AUTHOR]

This paper investigated the effect of the changed albedo of colored pavement on the urban temperature. The surface albedo of different conventional and colored pavement slabs was measured in the laboratory. Numerical simulations were conducted to determine the relationship between pavement albedo and the temperatures of pavement and its surrounding environment in the local urban. Results showed that colored porous portland cement concrete (PPCC) slabs have higher albedo values than conventional gray PPCC and black asphalt concrete, but conventional dense portland cement concrete (DPCC) has the highest albedo value owing to its smooth surface. The temperature of colored PPCC (except black PPCC) slabs at 1-cm depth was about 1°C–6°C lower than that of conventional gray PPCC due to the high albedo, and the green PPCC slab had the best cooling effect among all PPCCs. The simulated temperature profiles of the PPCC slab were found to be in good agreement with the laboratory test results. The local urban simulation showed that the colored pavement has a noticeable effect on reducing pavement surface temperature and nearby air temperature. Compared with open-graded friction course, which had an albedo value of 0.058, conventional gray DPCC with an albedo value of 0.32 had a temperature at 0.2 m below the pavement surface that was 0.83°C lower at 3:00 p.m. of a typical summer day. [ABSTRACT FROM AUTHOR]

The special surface appearance of complex surfaces restricts the coating film quality of spraying. The study of the atomization and film formation characteristics of typical complex surfaces, as well as the spraying mechanism, is essential for planning the spraying robotic trajectory and improving the spraying efficiency. In this paper, modeling and characteristics of the atomization and film formation process, based on CFD numerical simulations in previous studies, are systematically reviewed, focusing especially on airless spraying. In addition, the advantages and disadvantages of the existing research from the perspective of numerical models and methods are discussed. Finally, a further research direction for spraying on complex surface is prospected. Overall, a comprehensive and up-to-date review of spray atomization and film formation characteristics is considered valuable to practitioners and researchers in these fields, and will facilitate the further application of robotic spraying in the mechanical, automotive, marine, aerospace, petrochemical and other industries. [ABSTRACT FROM AUTHOR]

Effective and reliable slipstream numerical simulation methods are important for propeller-driven aircraft design. This paper presents a high-precision and efficient momentum source method (HPE-MSM) based on a novel actuator disk load prediction model established by the frozen rotor method and blade element momentum theory. The simulation results of two benchmark test cases of an isolated propeller and a typical turboprop airliner show that the accuracy of the HPE-MSM proposed in this paper is close to the time-averaged unsteady results of the sliding mesh method (SMM), with a maximum error of 5% in aircraft lift and drag coefficients compared with experimental values. Meanwhile, the calculation efficiency of the HPE-MSM is comparable to quasi-steady methods, with only about 3.4% of the computation resources of the SMM in the whole aircraft simulation. This novel approach achieves high-precision and efficient simulation of the slipstream, which has the potential to improve the design level of propeller-driven aircraft. [ABSTRACT FROM AUTHOR]

Supercritical hydrothermal combustion, as a quick homogeneous oxidizing process, offers a promising treatment option for industrial wastewater. This paper established a computational fluid dynamics model of a water-cooled hydrothermal combustion burner to investigate the thermal flame characteristics. The effects of the fuel mass flow rate, fuel concentration, initial reactor temperature, reaction pressure, and oxidant temperature on the thermal combustion ignition were revealed. The results indicate that the fuel concentration (from 10 wt% to 60 wt%) and initial reactor temperature (from 623 to 773 K) had less effect on the ignition temperature. In contrast, the ignition temperature increases by 398 K with increasing fuel mass flow rate (from 24 kg h−1 to 1080 kg h−1). As the oxygen temperature increases (from 273 to 673 K), the ignition temperature gradually decreases to 573 K and then increases. An increase in reaction pressure can facilitate a decrease in ignition temperature to a certain extent, and the optimal reaction pressure is 25 MPa. This study provides a vital reference for a hydrothermal burner's scale-up design and ignition operation. [ABSTRACT FROM AUTHOR]

This paper investigates the heat transfer properties of liquefied natural gas (LNG) in a corrugated plate heat exchanger and explores its application in cold energy recovery for enhanced energy efficiency. The study aims to integrate this technology into a 500 MW gas-fired power plant and a district cooling system to contribute to sustainable city development. Using computational fluid dynamics simulations and experimental validation, the heat transfer behaviour of LNG in the corrugated plate heat exchanger is examined, emphasising the significance of the gas film on the channel wall for efficient heat transfer between LNG and water/ethylene glycol. The study analyses heat exchange characteristics below and above the critical point of LNG. Below the critical point, the LNG behaves as an incompressible fluid, whereas above the critical point, the compressible supercritical state enables a substantial energy recovery and temperature rise at the outlet, highlighting the potential for cold energy recovery. The results demonstrate the effectiveness of cold energy recovery above the critical point, leading to significant energy savings and improved efficiency compared to conventional systems. Optimal operational parameters, such as the number of channels and flow rate ratios, are identified for successful cold energy recovery. This research provides valuable insights for sustainable city planning and the transition towards low-carbon energy systems, contributing to the overall goal of creating environmentally friendly and resilient urban environments. [ABSTRACT FROM AUTHOR]

With the increase of coal mining depth, the gas content in coal seams could also become larger and larger, which could suddenly cause an inrush of gas into the longwall mining face. It is very dangerous for miners' safety in the underground. The U-shaped ventilation pattern of longwall mining face that underground coal mines currently use is not enough to deliver sufficient air quantities to dilute gases in mining faces, which could result in the gas concentration over the required celling limit by government laws. Thus, the mine must stop production. In this paper, the high level roadway (HLR) is designed and the U + HLR new ventilation pattern is proposed to control gas emission in a longwall mining face. using computational fluid dynamics simulation (CFD) software, the flow field and gas transportation in the mine gob are studied. The optimized ventilation parameters are summarized. It is found that the best vertical distance of the HLR is 35 m over the coal seam and the horizontal distance is 25 m from the air return roadway. It is recommended that the negative suction pressure design of the high level roadway should be ranged from 9000 pa to 10000 pa. Based on the study outcomes, the gas emission could be well controlled in mining faces and avoid any gas disaster accidents. [ABSTRACT FROM AUTHOR]

A vehicle exposed to flooding may lose its stability and wash away resulting in potential injuries and fatalities. Traffic disruption, infrastructure damage, and economic losses are also additional effects of the washed vehicles. Therefore, understanding the responses of passenger vehicles during flood events is of the utmost importance to reduce flood risks and develop accurate safety guidelines. Previously, flooded vehicle stability was investigated experimentally, theoretically, and numerically. However, numerical investigations are insufficient, of which only a few studies have been published since 1967. Furthermore, coupled motion simulations have not been employed to investigate the hydrodynamic forces on flooded vehicles. In this paper, a numerical framework was proposed to assess the response of a full-scale medium-size passenger vehicle exposed to floodwaters through three-dimensional computational fluid dynamic modelling. The vehicle was simulated under subcritical and supercritical flows with the Froude number ranging between 0.09 and 2.46. The results showed that the vehicle experienced the floating instability mode once the flow depth reached 0.38 m, while the sliding instability mode was observed once the d e p t h × v e l o c i t y threshold function exceeded 0.36 m2/s. In terms of hydrodynamic forces, it was noticed that the drag force decreased with the increment of the Froude number and flow velocity. On the other hand, the fraction and buoyancy forces are mainly governed by the flow depth at the vehicle vicinity. The drag coefficient was noticed to be less than 1 for supercritical flows and more than 1 for subcritical flows. The numerical results obtained through the framework introduced in this study demonstrate favorable agreement with three different previously published experimental outcomes. [ABSTRACT FROM AUTHOR]

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In this paper, an improved RSM-CFD method is used to optimally design a mixed turbine of non-equilibrium condensing steam (NECS) and hydrogen (H2), of which the response surface method (RSM) and computational fluid dynamics (CFD) are coupled to take into account the effects of the wet steam non-equilibrium condensation process of the multimixed working fluid. A single-stage H2/Steam (NEC)-mixed turbine was developed based on the improved RSM-CFD, and the effect mechanism of the H2 component ratio (ωH2) on the flow characteristics, internal power, and isentropic efficiency within the turbine stage were investigated. The results show that the isentropic efficiency (η) increases with the increase in the hydrogen component ratio (ωH2), since hydrogen, as a non-condensable component, can inhibit the nucleation and growth of steam, reducing the pressure pulsation on the blade surface; furthermore, it accelerates the transport and diffusion of liquid droplets, inhibits the flow separation, and reduces the flow loss in the flow channel. However, the internal power of the turbine (P) tends to decrease with increasing ωH2, since the increase in hydrogen reduces the pressure difference on the blade and lowers the torque of the fluid acting on the blade, and at the same time, the vortex and radial flow intensify, and the enthalpy drop inside the stage decreases. On this basis, the optimum operating conditions are found where the hydrogen component ratio (volume percent) ωH2 = 53%. Accordingly, the hydrogen component ratio should be maintained in the range of 38–68%, considering the work capacity and hydrogen yield of the mixed working fluid. [ABSTRACT FROM AUTHOR]

Local scouring might result in the spanning of submarine cables, endangering their mechanical and electrical properties. In this contribution, a three-dimensional computational fluid dynamics simulation model is developed using FLOW-3D, and the scouring process of semi-exposed submarine cables is investigated. The effects of the sediment critical Shields number, sediment density, and ocean current velocity on local scouring are discussed, and variation rules for the submarine cables' spanning time are provided. The results indicate that three scouring holes are formed around the submarine cables. The location of the bottom of the holes corresponds to that of the maximum shear velocity. The continuous development of scouring holes at the wake position leads to the spanning of the submarine cables. The increase in the sediment's critical Shields number and sediment density, as well as the decrease in the ocean current velocity, will extend the time for maintaining the stability of the upstream scouring hole and retard the development velocity of the wake position and downstream scouring holes. The spanning time has a cubic relationship with the sediment's critical Shields number, a linear relationship with the sediment density, and an exponential relationship with the ocean current velocity. In this paper, the local scouring process of semi-exposed submarine cables is studied, which provides a theoretical basis for the operation and maintenance of submarine cables. [ABSTRACT FROM AUTHOR]

Gas-liquid two-phase swirling flow is widely used for gas-liquid separation in the power, chemical, petroleum, and nuclear industries. However, the majority of current research on swirling flow focuses on identifying flow patterns and does not pay more attention to topics such as the boundary where swirling flow forms. The length and diameter of the central gas core are the main focus of the current studies as well as the distribution patterns of gas-liquid two-phase. Comparative studies on the gas-liquid distribution morphology, such as whether the gas phase is separated and the separation mode, are lacking. In this paper, a combination of visual experimental observations and numerical simulations of Computational Fluid Dynamics (CFD) is used to investigate the formation conditions of gas-liquid two-phase swirling flow in three types of cyclonic components. The results show that the minimum superficial liquid velocity for the formation of swirling flow in the horizontal tube is about 0.375~0.82 m/s when the superficial gas velocity is less than 10 m/s. The formation of swirling flow is almost independent of the geometric swirl number and superficial liquid velocity when the superficial gas velocity is greater than 10 m/s. At low inlet superficial velocities, the tangential velocity determines the transition from swirling flow to stratified flow. However, at higher inlet superficial velocities, the decay of the cyclonic field is mainly affected by the wave amplitude of the gas-liquid interface. In both co-current and counter-current horizontal inline gas-liquid cyclone separators, the flow split is related to the vortex core breakdown of the central gas core. In addition, the numerical simulation results show that the breakdown of the vortex core is related to the pressure distribution inside the separator. This work enriches the study of swirling flow and provides a basis for the performance improvement of inline gas-liquid cyclone separators. [ABSTRACT FROM AUTHOR]

Based on the computational fluid dynamics (CFD) theory, this paper proposes a film formation model and a numerical simulation method that can be used in thickness prediction of airless spraying robots. The spraying flow field and the film formation process in the airless spraying process were simulated by the Eulerian–Eulerian approach, and the airless spraying film formation model including the paint expansion model and the wall hitting model was established. To verify the correctness of the model, numerical simulations of static spraying and dynamic spraying were carried out on the plane and arc surfaces. The simulation results showed that the width of the spraying flow field on the far wall increased linearly with the longitudinal distance in the major-axis direction. The busbar spraying on the outer surface of the arc surface showed the similar characteristics to the plane in the major-axis direction. Besides, the annular spraying was similar to the plane spraying in the minor-axis direction, but the inner surface spraying was completely opposite. When spraying the outer surface, the film thickness increased with the increase of the inner diameter but was smaller than that of the plane spraying, while the inner surface spraying was completely opposite. In the spraying experiment, the plane dynamic spraying and the arc plane inner and outer surface translation spraying were selected for verification. The experimental results were in good agreement with the simulation results, indicating that the film formation model of airless spraying established in this paper is basically correct. As a result, this model can be used for thickness prediction of spraying robots. [ABSTRACT FROM AUTHOR]

The use of grain refiners plays a crucial role in the casting of Al alloys, and ultrasonic treatment is increasingly applied. This paper focuses on the numerical simulations of 2219, an Al–Cu alloy, using different processes for introducing Al–5Ti–1B grain refiner, along with mechanical stirring and ultrasonic treatment. The multiphase Computational Fluid Dynamics (CFD) model considers turbulent fluid flow, heat transfer, solidification, and the complex interaction between the 2219 Al alloy and TiB2 particles. Ansys's fluent dense discrete phase model (DDPM) and a particle engulfment and pushing (PEP) model are utilized for this purpose. The study investigates the fluid flow patterns and the distribution of TiB2 particles. Additionally, four control experiments are designed to correspond with the numerical simulations, enabling the investigation of the variations in α-Al grains and Al2Cu precipitation phases. The findings demonstrate that direct introduction of Al–5Ti–1B into the ultrasonic sonotrode results in uniform dispersion of TiB2 particles in the Al melt, reduction in α-Al grain size, and decreased area fraction of Al2Cu precipitated phase. The numerical simulation results are successfully validated through experimentation. Al–5Ti–1B ultrasonic sonotrode along with ultrasonic treatment has a good effect on 2219 Al alloy. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to develop a numerical model of bead spreading architecture of a viscous polymer in fused filament fabrication (FFF) process with different nozzle geometry. This paper also focuses on the manufacturing feasibility of the nozzles and 3D printing of the molten beads using the developed nozzles. Design/methodology/approach: The flow of a highly viscous polymer from a nozzle, the melt expansion in free space and the deposition of the melt on a moving platform are captured using the FLUENT volume of fluid (VOF) method based computational fluid dynamics code. The free surface motion of the material is captured in VOF, which is governed by the hydrodynamics of the two-phase flow. The phases involved in the numerical model are liquid polymer and air. A laminar, non-Newtonian and non-isothermal flow is assumed. Under such assumptions, the spreading characteristic of the polymer is simulated with different nozzle-exit geometries. The governing equations are solved on a regular stationary grid following a transient algorithm, where the boundary between the polymer and the air is tracked by piecewise linear interface construction (PLIC) to reconstruct the free surface. The prototype nozzles were also manufactured, and the deposition of the molten beads on a flatbed was performed using a commercial 3D printer. The deposited bead cross-sections were examined through optical microscopic examination, and the cross-sectional profiles were compared with those obtained in the numerical simulations. Findings: The numerical model successfully predicted the spreading characteristics and the cross-sectional shape of the extruded bead. The cross-sectional shape of the bead varied from elliptical (with circular nozzle) to trapezoidal (with square and star nozzles) where the top and bottom surfaces are significantly flattened (which is desirable to reduce the void spaces in the cross-section). The numerical model yielded a good approximation of the bead cross-section, capturing most of the geometric features of the bead with a reasonable qualitative agreement compared to the experiment. The quantitative comparison of the cross-sectional profiles against experimental observation also indicated a favorable agreement. The significant improvement observed in the bead cross-section with the square and star nozzles is the flattening of the surfaces. Originality/value: The developed numerical algorithm attempts to address the fundamental challenge of voids and bonding in the FFF process. It presents a new approach to increase the inter-bead bonding and reduce the inter-bead voids in 3D printing of polymers by modifying the bead cross-sectional shape through the modification of nozzle exit-geometry. The change in bead cross-sectional shape from elliptical (circular) to trapezoidal (square and star) cross-section is supposed to increase the contact surface area and inter-bead bonding while in contact with adjacent beads. [ABSTRACT FROM AUTHOR]

We investigated the impact of exhaust emissions from hydraulic support transporters on the air quality in roadways in mines. The dispersion distribution of diesel exhaust pollutants emitted by hydraulic support transporters was simulated with a dynamic mesh and computational fluid dynamics (CFD) simulations. More specifically, the dispersion and distribution of the main exhaust pollutants CO, HC, and NOx emitted by vehicles under the influence of the roadway wind flow were simulated with CFD simulations; in addition, the dispersion characteristics of exhaust pollutants from hydraulic support transporters during multiple driving phases in an alleyway (from transporting material, being unloaded at idle speed, to driving off without load) were predicted. The simulation results show that exhaust pollutants emitted by moving hydraulic support transporters can pollute the air in roadways and negatively affect the performance of gas monitoring devices in the roadway. Therefore, coal mining companies should optimize the ventilation design scheme to improve the air quality in roadways: they should increase the ventilation volume to dilute the emitted pollutants; in addition, the positions of underground gas monitoring devices should be adjusted to prevent interference from exhaust pollutants emitted by vehicles. This paper provides the theoretical basis and results of a preliminary investigation of the dispersion and transportation characteristics of exhaust pollutants emitted by vehicles in roadways. The results in this paper can serve as guidance for reducing the risk of occupational diseases. [ABSTRACT FROM AUTHOR]

Solid asperity interactions are common and inevitable under severe loading conditions for any lubricated contact. Heavy-duty machine components (gears, bearings, etc.) generally operate under Mixed Lubrication (ML), where uneven surface features contact each other when the generated fluid pressure is not enough to support the external load. The Reynolds equation is commonly used to simulate smooth lubricated contacts numerically. In rough lubricated interfaces where opposite surface asperities make contact, the Reynolds equation alone cannot accurately predict pressure using the traditional numerical simulation method. In this paper, lubrication–contact interface conditions (LCICs) have been implemented and extended to solve the multiple asperity contact problem using the full-multigrid approach. The developed novel algorithm has significantly accelerated the solution process and improved the accuracy and efficiency of pressure calculation for fluid–solid sub-interactions that can occur in ML regions. The results of the finite difference method (FDM) results have been compared with those of computational fluid dynamics (CFD) simulation to validate the newly developed model. Hence, the proposed optimized solution method will provide valuable insight to researchers and industry engineers interested in simulating the ML problem where the effect of the fluid–solid interface can be captured effectively to improve reliability in the calculation of the life expectancy of the lubricated parts. [ABSTRACT FROM AUTHOR]

This article deals with a thermal energy storage system in the form of a water tank with a thermocline. The well-known thermocline phenomenon is modeled using computational fluid dynamics (CFD). However, the reservoir model proposed in this article is zero-dimensional. This is due to the fact that the aim of this article is to build a mathematical model that will be more useful in mathematical models of complex energy systems in which a hot water tank is one of many elements of the system. In such a zero-dimensional mathematical model, the hot water tank will be modeled using equations describing heat transfer, and the thermocline itself will be treated as a heat transfer surface with known dimensions and heat transfer coefficient. A novelty of this paper is that it addresses heat loss across the thermocline as defined in this manner. A CFD model of a thermal storage tank is created, validated with available experimental data, and used to obtain the heat transfer coefficient U. The resulting value is then analyzed quantitatively and qualitatively and the changes in the thickness of the thermocline are accounted for in the equation. The results from this groundbreaking work can be used to analyze heat storage in the form of thermocline water tanks at the level of system modeling, e.g., for the purpose of configuring the structure of other devices and control systems. [ABSTRACT FROM AUTHOR]

Microfluidic paper-based analytical devices (µPADs) are a promising technology to enable accurate and quantitative in situ assays. Paper's inherent hydrophilicity drives the fluids without the need for external pressure sources. However, controlling the flow in the porous medium has remained a challenge. This study addresses this problem from the nature of the paper substrate and its design. A computational fluid dynamic model has been developed, which couples the characteristics of the porous media (fiber length, fiber diameter and porosity) to the fluidic performance of the diffusion-based µPAD sensor. The numerical results showed that for a given porous membrane, the diffusion, and therefore the sensor performance is affected not only by the substrate nature but also by the inlets' orientation. Given a porous substrate, the optimum performance is achieved by the lowest inlets' angle. A diffusion-based self-referencing colorimetric sensor was built and validated according to the design. The device is able to quantify the hydronium concentration in wines by comparison to 0.1–1.0 M tartaric acid solutions with a 41.3 mM limit of detection. This research showed that by proper adjustments even the simplest µPADs can be used in quantitative assays for agri-food applications. [ABSTRACT FROM AUTHOR]

To increase launching frequency and decrease drag force of underwater projectiles, a serial multiprojectiles structure based on the principle of supercavitation is proposed in this paper. The drag reduction and supercavitation characteristics of the underwater serial multi-projectiles are studied with computational fluid dynamics (CFD) and machine learning. Firstly, the numerical simulation model for the underwater supercavitating projectile is established and verified by experimental data. Then the evolution of the supercavitation for the serial multi-projectiles is described. In addition, the effects of different cavitation numbers and different distances between projectiles are investigated to demonstrate the supercavitation and drag reduction performance. Finally, the artificial neural network (ANN) model is established to predict the evolution of drag coefficient based on the data obtained by CFD, and the results predicted by ANN are in good agreement with the data obtained by CFD. The finding provides a useful guidance for the research of drag reduction characteristics of underwater serial projectiles. [ABSTRACT FROM AUTHOR]