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Understanding hydrogen dispersion in a semi-confined space is crucial for the safe operation of hydrogen-related systems, such as hydrogen fuel cell vehicles. Analyzing hydrogen release and its subsequent dispersion can be effectively conducted using computational models, which necessitate experimental measurements for validation. For safety reasons, accidental scenarios are frequently replicated using helium as a hydrogen simulant in experiments, despite some concerns about the comparability of helium and hydrogen dispersions. Hence, this study conducts a comprehensive parametric numerical analysis of the similarities between hydrogen and helium dispersion when released in a semi-confined space. The model is based on the Macquarie Dispersion Chamber and the simulation results are first validated against the measurements. The study focuses on the impact of the leakage rate and ventilation velocity. Three release models were analysed: equal concentration (Method A), equal volumetric flow rate (Method B), and equal buoyancy (Method C). This study extends previous research on Method B, used for gas release in open spaces, to environments where flow-wall interactions become important. It also compares Methods A and C for a few scenarios, examining variations in concentration distribution, purge time, and activation time under different conditions. In the absence of ventilation, Method B effectively compares hydrogen and helium flow rates by accounting for volumetric flow rates, regardless of buoyancy effects. However, under increased ventilation velocities, Method A and Method C exhibit superior agreement across sensors, highlighting the necessity of choosing detection methods according to prevailing environmental conditions. [Display omitted] • A CFD model for gas release in semi-confined space equipped with ventilation is established. • Three release models are studied to investigate similarity between hydrogen and helium gas dispersion. • Purge time and activation time are analysed with the aim of safe hydrogen infrastructure development. • Influence on gas dispersion by various ventilation velocity and flow rate at leakage are analysed. [ABSTRACT FROM AUTHOR]

Mixing elbows are widely used in various industrial processes to mix two different Newtonian or non-Newtonian fluids under turbulent flow conditions. This study numerically investigates the fluid flow and mixing characteristics in 90-degree elbows with different bend curvatures (curvature ratios of 3, 6, and 9) and Reynolds numbers ranging from 1 × 104 to 5 × 105 for both fluid types. The Reynolds-Averaged Navier–Stokes equations are solved using the turbulent k-epsilon model in ANSYS Fluent. Results show that the bend curvature creates an adverse pressure gradient that drives secondary flows, which become more pronounced with higher Reynolds numbers and lower curvature ratios. Higher Reynolds numbers improve mixing quality, as indicated by velocity and temperature variations quantified using standard deviations. For Reynolds numbers in the range of 104, velocity fluctuations initially increase, but at higher values (~ 105), they decrease, even by up to 64% as the Reynolds number rises from 1 × 105 to 5 × 105. Similarly, increasing the curvature ratio enhances mixing efficiency, with a 32% reduction in velocity fluctuations when the curvature ratio increases from 6 to 9. Furthermore, shear-thinning fluids ( n = 0.6 ) exhibit superior mixing performance, with a standard deviation of velocity fluctuations at the outlet of 0.32, compared to 0.54 for shear-thickening fluids ( n = 1.4 ). In terms of temperature fluctuations also, a similar trend is observed. These findings are valuable for optimizing mixing and fluid transport in industries such as chemical processing and food production, where effective mixing of complex fluids is critical. This study provides insights for improving the design of mixing systems that handle fluids with various rheological characteristics. [ABSTRACT FROM AUTHOR]

Patient-specific studies on vascular flows have significantly increased for hemodynamics due to the need for different observation techniques in clinical practice. In this study, we investigate aortic aneurysms in terms of deformation, stress, and rupture risk. The effect of Ascending Aortic Diameter (AAD) was investigated in different aortic arches (19.81 mm, 42.94 mm, and 48.01 mm) via Computational Fluid Dynamics (CFD), Two-way coupling Fluid–Structure Interactions (FSI) and deep learning. The non-newtonian Carreau viscosity model was utilized with patient-specific velocity waveform. Deformations, Wall Shear Stresses (WSSs), von Mises stress, and rupture risk were presented by safety factors. Results show that the WSS distribution is distinctly higher in rigid cases than the elastic cases. Although WSS values rise with the increase in AAD, aneurysm regions indicate low WSS values in both rigid and elastic artery solutions. For the given AADs, the deformations are 2.75 mm, 6. 82 mm, and 8.48 mm and Equivalent von Mises stresses are 0.16 MPa, 0.46 MPa, and 0.53 MPa. When the rupture risk was evaluated for the arteries, the results showed that the aneurysm with AAD of 48.01 mm poses a risk up to three times more than AAD of 19.81 mm. In addition, an Artificial neural network (ANN) method was developed to predict the rupture risk with a 98.6% accurate prediction by numerical data. As a result, FSI could indicate more accurately the level of rupture risk than the rigid artery assumptions to guide the clinical assessments and deep learning methods could decrease the computational costs according to CFD and FSI. [ABSTRACT FROM AUTHOR]

Although flow mixing and cooling can be greatly enhanced when considering the use of fluidic oscillators (FOs), they are more commonly employed in active flow control (AFC) applications where the injected pulsating flow interacts with the boundary layer, usually in order to delay its separation. In fact, prior to any FO implementation in a given application, it is essential to study the range of frequencies and amplitudes it can generate as a function of the incoming mass flow and its dimensions. This is what is being performed in the present manuscript for a rather novel FO configuration. A numerical study of a standard three-dimensional (3D) FO configuration, and also using a two-dimensional (2D) approach, is initially presented. After comparing the 3D and the 2D results and analyzing the main differences, we modified some of the internal dimensions of the FO in order to evaluate the variation in its dynamic performance. The present results clarify which internal dimensional modifications are more effective in generating larger output frequencies and velocity field variations. Care is taken to analyze the origin of self-sustained oscillations. This paper links, for the first time, the origin of the pressure force oscillations at the feedback channel's outlet, with the interaction of the mixing chamber central jet and the reverse feedback channel flow at the mixing chamber's converging walls. A novel equation relating the FO outlet mass flow frequency with the time-averaged FC reverse flow is presented and discussed. In fact, the present study needs to be seen as the continuation of a former one, recently published by authors, where the effects of several Reynolds numbers as well as some different internal dimensions were considered. [ABSTRACT FROM AUTHOR]

Introduction: The relationship between carotid artery stenosis (CAS) and ipsilateral silent brain ischemia (SBI) remains unclear, with uncertain therapeutic implications. The present study, part of the TAXINOMISIS project (nr. 755,320), aimed to investigate SBIs in patients with asymptomatic CAS, correlating them with clinical, carotid ultrasonographic data, and CFD analyses. Methods: The TAXINOMISIS clinical trial study (nr. NCT03495830) involved six vascular surgery centers across Europe, enrolling patients with asymptomatic and symptomatic CAS ranging from 50 to 99%. Patients underwent carotid ultrasound and magnetic resonance imaging (MRI), including brain diffusionweighted, T2-weighted/FLAIR, and T1-weighted sequences. Brain MRI scans were analyzed for the presence of SBI according to established definitions. Ultrasound assessments included Doppler and CFD analysis. Only asymptomatic patients were included in this substudy. Results: Among 195 asymptomatic patients, the mean stenosis (NASCET) was 64.1%. Of these, a total of 33 patients (16.9%) had at least one SBI detected on a brain MRI scan. Specifically, 19 out of 33 patients (57.6%) had cortical infarcts, 4 out of 33 patients (12.1%) had ipsilateral lacunar infarcts, 6 out of 33 patients had (18.2%) subcortical infarcts, 1 out of 33 patients (3.0%) had both cortical and lacunar infarcts, and 3 out of 33 patients (9.1%) both cortical and subcortical infarcts. Patients with SBIs exhibited significantly higher risk factors, including a higher body mass index (28.52  ±  9.38 vs. 26.39  ±  3.35, p  =  0.02), diastolic blood pressure (80.87  ±  15.73  mmHg vs. 80.06  ±  8.49  mmHg, p  =  0.02), creatinine levels (93.66  ±  34.61  μmol/L vs. 84.69  ±  23.67  μmol/L, p  =  0.02), and blood triglycerides (1.8  ±  1.06  mmol/L vs. 1.48  ±  0.78  mmol/L, p  =  0.03). They also had a higher prevalence of cardiovascular interventions (29.6% vs. 13.8%, p  =  0.04), greater usage of third/fourth-line antihypertensive treatment (50%vs16%, p  =  0.03), and anticoagulant medications (60% vs. 16%, p  =  0.01). Additionally, the number of contralateral cerebral infarcts was higher in patients with SBIs (35.5% vs. 13.4%, p  <  0.01). Moreover, carotid ultrasound revealed higher Saint Mary’s ratios (15.33  ±  12.45 vs. 12.96  ±  7.99, p  =  0.02), and CFD analysis demonstrated larger areas of low wall shear stress (WSS) (0.0004  ±  0.0004  m2 vs. 0.0002  ±  0.0002  m2, p  <  0.01). Conclusion: The TAXINOMISIS clinical trial provides valuable insights into the prevalence and risk factors associated with SBIs in patients with moderate asymptomatic carotid stenosis. The findings suggest that specific hemodynamic and arterial wall characteristics may contribute to the development of silent brain infarcts. [ABSTRACT FROM AUTHOR]

Self‐supporting concrete shell structures are highly efficient in distributing loads, which can result in very reduced thicknesses (ultra‐thin), giving them remarkable slenderness. Due to their geometric complexity, it is difficult to predict how they interact with wind action. The main aim of the present study is to assess the mean surface pressure coefficient distribution in a shell with a triangular plan shape and three supports for different angles of wind incidence. To determine the distribution of surface pressure coefficients and lift and drag force coefficients, an experimental study was carried out in a wind tunnel, and a numerical simulation study was performed through computational fluid dynamics. The experimental and numerical results were analyzed and compared, and making it possible to identify the most critical surface zones and wind incidences when the shell is under the wind action. [ABSTRACT FROM AUTHOR]

This study presents a physics-based reduced-order model (ROM) to assess the mixing behavior of hydrogen and natural gas in pipelines, facilitating the integration of hydrogen into natural gas networks—a key strategy for reducing carbon emissions. The methodology consists of dimensional analysis to identify crucial dimensionless parameters, CFD simulations for data collection, and statistical analysis for effective data modeling. This approach enables rapid evaluation of injection strategies and operational conditions, reducing the computational demands of traditional CFD simulations. The model correlates reduced-order parameters with key dimensionless numbers like Reynolds number, and diameter and velocity ratios, to develop a predictive tool for assessing mixture quality. Validated through extensive simulations, the model accurately predicts gas mixing, using beta distributions for statistical representation to enhance data interpretability and applicability. • Developed a reduced-order model based on CFD data for hydrogen-natural gas mixing. • Used dimensional analysis to simplify the model and reduce computational demand. • Applied beta distributions to analyze mass fractions and improve mixture prediction. [ABSTRACT FROM AUTHOR]

In the rapidly advancing field of 5G technology, efficient thermal management is essential for enhancing the performance and reliability of high-power-density integrated circuits (ICs). This paper introduces an innovative approach to cooling these critical components, significantly surpassing traditional methods. Our design optimizes heatsink and fan configurations through systematic experimentation, varying fin shapes, heatsink dimensions, and fan speeds. The results demonstrate that fan velocity is the most critical factor in reducing IC temperatures, as increased airflow dramatically lowers thermal output. Expanding the heatsink surface area further improves heat dissipation by enhancing airflow interaction, while a larger copper heatsink boosts thermal conduction, effectively reducing the final IC temperature. These optimizations streamline the cooling process, minimizing the need for more complex and expensive equipment. This research sets a new benchmark in thermal management, fostering the development of more efficient and reliable electronic systems in the era of advanced wireless communications. Our approach brings a new dimension to existing research by focusing on the optimization of heatsink and airflow designs specifically for ICs. While previous studies have explored broader thermal management strategies, our work addresses specific challenges in heat dissipation by refining geometric configurations and fan speed adjustments. These optimizations result in measurable improvements in both efficiency and scalability, particularly within the context of high-power 5G systems. [ABSTRACT FROM AUTHOR]

A validated computational fluid dynamic (CFD) model was developed to conduct a detailed examination of particle distribution within a burn patient ward. The indoor airflow was simulated using an RNG k–epsilon turbulence model, and particle dispersion was tracked employing a discrete phase model (DPM) that utilizes the Lagrangian framework. The primary objective is to assess the impact of a thermal-guided mobile air supply (MAS) unit, used in conjunction with an air curtain jet and localized exhaust grilles, on controlling particle dispersion. The focus on burn patient wards is critical, given the heightened vulnerability of burn patients to environmental contaminants, coupled with their impaired thermoregulatory and fluid balance capabilities. By integrating temperature control through the MAS unit, this study explores a novel approach to maintaining a sterile environment, achieving 0 BCP/m3 within the laminar airflow region around patients. The analysis reveals that the MAS unit significantly reduces particle penetration into the patient's protective zone by 82% relative to the baseline scenario without the activation of MAS unit. The thermal-guided MAS unit also effectively maintains ambient air temperatures within the optimal 21–24 °C range for burn patient recovery zone. However, the study also uncovers a temperature distribution around healthcare workers who do not meet satisfactory conditions, indicating areas for further improvement. In addition, the particle dispersion outside the protective zone was exacerbated when the MAS unit was activated, which demonstrated its contradictory effect. This underscores the importance of selecting optimal operating temperatures and configurations in clinical practice, emphasizing the need for extensive clinical testing and verification of the MAS device in varied room layouts and ventilation schemes. This research contributes significantly to the field by focusing on an underexplored area of patient care technology during critical times, providing insights into the efficacy of thermal-guided MAS units in enhancing environmental control in burn patient wards. [ABSTRACT FROM AUTHOR]

Introduction: Nasal airway obstruction (NAO) could be a common symptom that influences a person's quality of life. It can be assessed by patient perception or by physical measurements. Computational fluid dynamics (CFD) can be used to analyze nasal function. There is a need of comparative studies for assessment of airflow regimes using CFD. Assessment of the different CFD utilities as an objective method for evaluation of nasal airflow characteristics was our main goal. Studied were collected from MEDLINE (Ovid), Google Scholar, Cochrane Library and EMBASE using a combination of the MeSH terms "septal deviation", "nasal obstruction", "Computational fluid dynamics (CFD)". Methods: We investigated all the results obtained by the authors with respect to the CFD parameters and the evaluation of nasal obstruction (clinical or physical). Results: To compare nasal obstruction with CFD parameters, most studied used heat flow, Wall Shear Stress (WSS), pressure drop, velocity and streamlines. We found that heat flux appeared to be the CFD parameter which most strongly correlated with patient perception. Pressure drop, wall shear stress and velocity were moreover valuable and appeared a great relationship. Conclusion: More and more research on CFD on the nasal cavity has caused a better understanding of nasal obstruction. Further studies need to be done, including temperature and humidity exchange. [ABSTRACT FROM AUTHOR]

The train operates in special environments such as large bridges and elevated viaducts. The fluctuations of the aerodynamic loads of the high-speed train (HST) are more intense and the possibility of the train derailment and overturning will increase when the train is running on the bridge under the crosswind. Thus, it is of utmost importance to study both the aerodynamic characteristics and the running safety of the train in this situation. This study uses the IDDES method to investigate the aerodynamic characteristics of the train running on the double track bridge in both up and down train directions at different speeds. The differences in the impact of aerodynamic loads on the train's dynamic response indicators are discussed using the wind-vehicle coupling dynamic response calculation method. Based on these researches, the operational safety of the train under different operating conditions is evaluated from both flow field and dynamic perspectives. The results show that large-scale vortices fall off from the nose of the train and form a larger vortex structure on the leeward side and when the train is running under the crosswind. Its aerodynamic loads fluctuate intensely with time due to the complex wake flow of the train. The dominant frequencies of the unsteady aerodynamic loads are mostly concentrated in the range of 0–5Hz, which is close to the natural modal frequencies of the train. This will lead to the overturning of the train due to vehicle resonance. The derailment coefficient and wheel load reduction rate of the train increase with the speed. Their peak values exceed the limit of 0.8 while the peak duration of the derailment coefficient is less than 0.05s, which means the state of the leeward wheel will recover from a short derailment. However, the duration of derailment increases with speed. Therefore, appropriate measures should be taken to prevent accidents when the train is running at higher speed on the bridge to guarantee the operational safety of the HST. [ABSTRACT FROM AUTHOR]

Background/Objectives: Cerebrovascular events, such as strokes, are often preceded by the rupture of atherosclerotic plaques in the carotid arteries. This work introduces a novel approach to predict the occurrence of such events by integrating computational fluid dynamics (CFD), structural analysis, and machine learning (ML) techniques. The objective is to develop a predictive model that combines both imaging and non-imaging data to assess the risk of carotid atherosclerosis and subsequent cerebrovascular events, ultimately improving clinical decision-making. Methods: A multidisciplinary approach was employed, utilizing 3D reconstruction techniques and blood-flow simulations to extract key plaque characteristics. These were combined with patient-specific clinical data for risk evaluation. The study involved 134 asymptomatic individuals diagnosed with carotid artery disease. Data imbalance was addressed using two distinct approaches, with the optimal method chosen for training a Gradient Boosting Tree (GBT) classifier. The model's performance was evaluated in terms of accuracy, sensitivity, specificity, and ROC AUC. Results: The best-performing GBT model achieved a balanced accuracy of 88%, with a ROC AUC of 0.92, a sensitivity of 0.88, and a specificity of 0.91. This demonstrates the model's high predictive power in identifying patients at risk for cerebrovascular events. Conclusions: The proposed method effectively combines CFD, structural analysis, and ML to predict cerebrovascular event risk in patients with carotid artery disease. By providing clinicians with a tool for better risk assessment, this approach has the potential to significantly enhance clinical decision-making and patient outcomes. [ABSTRACT FROM AUTHOR]

This paper represents a detailed investigation of tall hexagonal buildings in the presence of a similar type of single-interfering buildings and double-interfering buildings. The building models are analysed using CFD in ANSYS CFX module. The k-ε turbulence model is used to carry out the numerical simulations. For two buildings case (single interfering building), the wind incidence angles (WIA) vary from 0° to 90° at an interval of 15° and from 90° to 360° at an interval of 30°. The variable spacing of 200 mm, 300 mm, 500 mm and 800 mm has been kept apart for two building case. For the three building case (double interfering buildings), the orientation of the interfering buildings kept varying from 15° to 90° with a regular interval of 15°. The variable spacing between the principal building and interfering buildings is kept 300 mm and 500 mm apart. The model height for both cases is 500 mm in 1:300 length scale. The variation of interference factors for both pressure and force coefficients are evaluated and graphically represented to investigate the hexagonal building model. The interference Factor is found to be minimum at 90° WIA in each of the faces irrespective of spacing between buildings. [ABSTRACT FROM AUTHOR]

The impact of drug delivery and particulate matter exposure on the human respiratory tract is influenced by various anatomical and physiological factors, particularly the structure of the respiratory tract and its fluid dynamics. This study employs computational fluid dynamics (CFD) to investigate airflow in two 3D models of the human air conducting zone. The first model uses a combination of CT-scan images and geometrical data from human cadaver to extract the upper and central airways down to the ninth generation, while the second model develops the lung airways from the first Carina to the end of the ninth generation using Kitaoka's deterministic algorithm. The study examines the differences in geometrical characteristics, airflow rates, velocity, Reynolds number, and pressure drops of both models in the inhalation and exhalation phases for different lobes and generations of the airways. From trachea to the ninth generation, the average air flowrates and Reynolds numbers exponentially decay in both models during inhalation and exhalation. The steady drop is the case for the average air velocity in Kitaoka's model, while that experiences a maximum in the 3rd or 4th generation in the quasi-realistic model. Besides, it is shown that the flow field remains laminar in the upper and central airways up to the total flow rate of 15 l/min. The results of this work can contribute to the understanding of flow behavior in upper respiratory tract. [ABSTRACT FROM AUTHOR]

• Critical releasable charges (CRCs) are modeled by mechanism analysis. • Predicted CRCs are generally within 16 % compared with measured and simulated values. • Effect of air speed on concentration field under CRCs is studied by CFD. • Transition value of air speed is 0.1 and 0.2 m/s for 8 g and 14.2 g CRC respectively. Propane (R290) is a promising refrigerant for split-type household air conditioners with the advantages of energy saving, environmentally friendliness and low charge. Nevertheless, the large scale use of R290 has been hindered by its high flammability. The potential fire hazards can be relieved by reducing R290 releasable charge, and numerous methods have been put forward. In the authors' previous papers, the method of refrigerant pump-down was proposed and a mathematical model of critical releasable charge (CRC, ignition threshold of leakage) was developed by dimensional analysis, but it is difficult to reflect the actual physical process of R290 dispersion. To reveal the leakage and dispersion mechanism of R290, a new numerical model of CRC is developed based on mechanism analysis in this work, in which the turbulent jet model, Coanda effect and dimensional analysis are involved. The predicted CRCs agree well with experimental and simulated data. Besides, the influence of indoor air speed with its direction parallel to the IDU panel on R290 concentration field is investigated by computational fluid dynamics (CFD) under different releasable charges. It is found that there is a transition value of air speed, below which the fire hazards decrease greatly with the increase of air speed, on the contrary, when the air speed is above the transition value, raising air speed has little impact on fire hazards. [ABSTRACT FROM AUTHOR]

Heat exchangers are widely studied in energy and production processes. There are various techniques available to enhance the performance of heat exchangers, but in recent years, vortex generators have gained significant attention. Vortex generators (VGs) is a passive control method that can improve heat transfer if properly designed. Vortex generators achieve heat exchange enhancement by creating transverse, longitudinal, or normal twiddle flows, disrupting the flow field, and improving transport phenomena. The improvement in convective heat transfer coefficient is achieved by increasing fluid mixing, breaking down the thermal boundary layer, and improving mean velocity and temperature gradient. In this paper, a coaxial counter-flow heat exchanger was considered. Prism shape vortex generators were installed on the outer surface of the inner tube of the heat exchanger and resulting performance was compared to that of the same heat exchanger without vortex generators. RANS CFD study (SST k-ω turbulence model was used) demonstrated a 13% improvement in heat transfer rate when using a heat exchanger with vortex generators as compared to the case without VGs. [ABSTRACT FROM AUTHOR]

In hot and arid regions like the Saharan area, effective methods for cooling and humidifying intake air are essential. This study explores the utilization of a water trickle cooler as a promising solution to meet this objective. In particular, the HASSI MESSAOUD area is considered as a testbed. The water trickle cooler is chosen for its adaptability to arid conditions. Modeling results demonstrate its effectiveness in conditioning air before it enters the compressor. The cooling system achieves a significant temperature reduction of 6 to 8 degrees Celsius, enhancing mass flow rate dynamics by 3 percent compared to standard cases without cooling. Moreover, the cooling system contributes to a remarkable 10 percent reduction in power consumption of gas turbines and a notable 10 percent increase in turbine efficiency. These findings highlight the potential of water trickle coolers in improving the performance and efficiency of gas turbine systems in hot and dry climates. [ABSTRACT FROM AUTHOR]

This study presents a computational fluid dynamics (CFD) analysis of the performance of counter-rotating impeller systems in mixed-flow pumps. The analysis evaluates the impact of varying rotor velocity ratios and blade geometry on head rise, efficiency, and hydraulic losses. Through detailed CFD simulations, the counter-rotating system demonstrates significant improvements in head and efficiency at low flow rates, with model B achieving up to 20% higher efficiency near the best efficiency point (BEP). However, increased hydraulic losses offset efficiency gains at higher flow rates. While the findings provide valuable insights for optimizing the design of counter-rotating systems in mixed-flow pumps, experimental validation is needed to confirm the results and ensure real-world applicability. The study lays the groundwork for future work in refining counter-rotating pump designs to minimize hydraulic losses and slippage. [ABSTRACT FROM AUTHOR]

Short‐circuiting in secondary clarifiers is a well‐known problem that can occur through up‐flow or underflow routes. The underflow short‐circuiting is not as visible as up‐flow short‐circuiting but can affect clarifier performance. The energy‐dissipating inlet (EDI) is a type of inlet structure that is used in secondary clarifiers to dissipate the energy of larger influent volumes, allowing clarifiers to operate at higher treatment capacities. The underflow short‐circuiting is encountered particularly in clarifiers equipped with EDIs. As influent volume increases, conventional draw‐off pipes cannot handle high sludge capacities, deforming the sludge blanket and leading to lower concentration of solids being withdrawn. Retrofitting the design of draw‐off pipes is an effective way to mitigate underflow short‐circuiting and enhance treatment performance. In this study, a snail‐shaped sludge draw‐off pipe was designed and tested in two types of EDIs using computational fluid dynamics tools, showing a 20% increase in withdrawn sludge concentration and mitigating underflow short‐circuiting potential. The optimal retrofit option was identified as equipping the clarifier with a snail‐shaped draw‐off pipe and an innovative EDI, known as multilayer EDI column, which would save almost half of the energy and operational costs of the biological processes while meeting discharge limits. [ABSTRACT FROM AUTHOR]

Ti6Al4V alloy has wide range of applications in various fields of engineering such as aerospace, marine and medical due to its high strength to weight ratio and high temperature stability. The demand for Laser Powder Bed Fusion (LPBF) is driven by its exceptional capability to produce intricate shapes and components that pose challenges in traditional manufacturing techniques. LPBF is an additive manufacturing process which deals with the powder bed fusion of metallic, polymer as well as ceramic powder particulates. The present study investigates the melt pool behaviour and its characteristics with the help of a computational fluid dynamics (CFD) based numerical model, in case of a single-track analysis. The developed high-fidelity CFD model solves the conservation equations of mass, momentum and energy adopting finite volume method. It is found that the convective heat transfer serves as the dominant heat transfer mode while laser beam travels across the powder bed. The simulation findings include temporal evolution of melt pool geometry such as bead height, bead width, cooling rate and solid fraction of the simulated track deposition. The accuracy of the developed coupled DEM–CFD model is confirmed from experimental validation of single-track deposition of Ti6Al4V alloy, which closely matches the numerical prediction of cylindrical bead profile in the longitudinal direction and hemispherical bead profile in the bead cross section. Along with qualitative validation of bead profile, experimental results match reasonably well with the simulation findings in terms of bead width and its height. [ABSTRACT FROM AUTHOR]

This research analyses the flow patterns in an Oscillatory Central Baffled Reactor (OCBR) using Computational Fluid Dynamics (CFD) simulations under various oscillation conditions. Frequency (f and amplitude (x0) are examined as critical parameters for enhancing fluid mixing and energy efficiency in high viscosity fluids, such as biofuels. The findings highlight the significant impact of the Strouhal number (St) on the flow behavior, showing improved fluid mixing with an increase in the oscillatory Reynolds number (Re0) from 125.6 f = 2 Hz, x0 = 2 mm) to 392.7 f = 2.5 Hz, x0 = 5 mm), corresponding to a decrease in the St from 0.2 to 0.08. The simulations indicated the appearance of stable vortices and a better distribution of the Weibel dead zones at an oscillation cycle (t/T) of 0.5. During the course of the study, the pressure distribution within the OCBR and its dependence on oscillation amplitude were shown, which significantly impacted the pressure drop from 8.8 to 123 Pa as Re0 was raised. In order to alleviate the endpoints for high resistance of sharp edged baffles, two modified baffle designs (semi-central and smooth- edge central baffles) were used. The findings showed that the performance of the semi-central baffle design in terms of dead zone reduction and shear stress was superior to those of the other designs for both upward and downward flows, indicating its suitability for enhancing the performance of the OCBR. This research offers important developments in the efficient mixing processes needed in industrial applications and indicates some areas for effective testing and validation of the models developed. [ABSTRACT FROM AUTHOR]

The mechanisms underlying the effects of wind and buoyancy on ventilation in urban street canyons are unclear. This study investigated the effects of facade heating on ventilation and pollutant transport in an idealized street canyon with a 1.67 aspect ratio through computational fluid dynamics simulations. The dispersion pattern of discharged hot pollutants was also studied. A primary recirculation was observed when facade heating was not applied; this recirculation was promoted in leeward-wall and ground heating cases. However, the recirculation was bifurcated into two recirculations in windward-wall heating cases, restricting ventilation. Enhanced recirculation increased the ventilation and decreased the pollution level; by contrast, air pollution increased considerably when the recirculation was bifurcated and ventilation was restricted. In the hot-pollutant case, similar results to those in the ground-heating case were observed. The hot discharged pollutant enhanced ventilation, reducing pollution. The pollutant transport mechanism was determined through an analysis of pollutant fluxes. For the one-recirculation pattern, air convection transported the pollutant from the ground level to the top boundary, and turbulent diffusion then caused pollutant removal. For the two-recirculation pattern, turbulent diffusion contributed substantially to pollutant transport both in the junction between the recirculations and through the top boundary of the street canyon. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the interaction between the free surface and a semi/shallowly submerged underwater vehicle, especially when the submergence depth h is smaller than 0.75D (D: submarine maximum diameter). In this respect, the straight-ahead simulations of the generic SUBOFF underwater vehicle geometry are conducted with constant forward velocities using the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations with a Shear-Stress Transport (SST) k−ω turbulence model in commercial code Fluent, at submergence depths and Froude numbers ranging from h = 0 to h = 3.3D and from Fn = 0.205 to Fn = 0.512, respectively. The numerical models are verified against the existing experimental data. The analysis of the obtained results indicates that in the case of the semi and shallowly submerged underwater vehicle (UV), both the submergence depth and forward velocity have a great effect on the behaviors of hydrodynamic forces acting on the UV. The magnitude of maximum total resistance may reach almost five times the value of resistance exerted on the totally submerged hull. Both the forces acting on the UV and the generated waves when the submergence depth h is smaller than 0.75D are significantly different from those whenr h is larger than 0.75D. The conclusions can be used as reference for future research on near free surface motions of underwater vehicles and the design of small water-plane area twin hull. [ABSTRACT FROM AUTHOR]

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]

Oil-filled motors (OFMs) are widely used in deep-sea exploration and oil well extraction. During motor operation, the rotor stirs the oil in the air gap, causing viscous loss. Viscous loss affects the temperature distribution inside the motor. Accurately calculating the viscous loss and temperature rise in OFMs can provide a basis for optimizing the motor's structural design. Motor structural parameters, including the rotor's outer diameter, air gap, and slot opening, have a significant impact on viscous loss. The working conditions of OFMs, such as rotor speed and environmental temperature, also affect viscous loss. The viscosity of hydraulic oil is highly influenced by temperature, and changes in viscosity can lead to changes in viscous loss. These changes in viscous loss, in turn, alter the temperature distribution. Therefore, the coupling relationship between viscous loss and temperature must be considered. Additionally, when Taylor vortices occur in the fluid, the surface roughness of the rotor also has a significant influence on viscous loss. Currently, both domestic and international research on viscous loss and thermal analysis struggle to simultaneously consider the coupling of viscous loss and the temperature field, rotor surface roughness, and the effect of motor structure. This paper summarizes the methods used in recent years for studying viscous loss and thermal analysis, and puts forward some suggestions for future research on the coupling of the OFM temperature field and viscous loss. [ABSTRACT FROM AUTHOR]

Atherosclerosis involves an inflammatory response due to plaque formation within the arteries, which can lead to ischemic stroke and heart disease. It is one of the leading causes of death worldwide, with various contributing factors such as hyperlipidemia, hypertension, obesity, diabetes, and smoking. Wall shear stress (WSS) is also known as a contributing factor of the formation of atherosclerotic plaques. Since the causes of atherosclerosis cannot be attributed to a single factor, clearly understanding the mechanisms and causes of its occurrence is crucial for preventing the disease and developing effective treatment strategies. To better understand atherosclerosis and define the correlation between various contributing factors, computational fluid dynamics (CFD) analysis is primarily used. CFD simulates WSS, the frictional force caused by blood flow on the vessel wall with various hemodynamic changes. Using apolipoprotein E knockout (ApoE-KO) mice subjected to partial ligation and a high-fat diet at 1-week, 2-week, and 4-week intervals as an atherosclerosis model, CFD analysis was conducted along with the reconstruction of carotid artery blood flow via magnetic resonance imaging (MRI) and compared to the inflammatory factors and pathological staining. In this experiment, a comparative analysis of the effects of high WSS and low WSS was conducted by comparing the standard deviation of time-averaged wall shear stress (TAWSS) at each point within the vessel wall. As a novel approach, the standard deviation of TAWSS within the vessel was analyzed with the staining results and pathological features. Since the onset of atherosclerosis cannot be explained by a single factor, the aim was to find the correlation between the thickness of atherosclerotic plaques and inflammatory factors through standard deviation analysis. As a result, the gap between low WSS and high WSS widened as the interval between weeks in the atherosclerosis mouse model increased. This finding not only linked the occurrence of atherosclerosis to WSS differences but also provided a connection to the causes of vulnerable plaques. [ABSTRACT FROM AUTHOR]

This study analyzes the turbomachinery flow of a gas turbine using OpenFOAM, an open-source CFD code. While foam-extend, a version of OpenFOAM, includes tools for turbomachinery analysis, some of its codes are incomplete, resulting in incorrect results. Consequently, this study required the investigation and correction of the solvers and libraries. Specifically, foam-extend-4.1 and a compressible multi-reference-frame solver were utilized. Two primary errors related to temperature calculation were identified. The first error involved temperature discontinuity at the interface between the stator and rotor domain when using the mixingPlane. The second error was related to temperature rising at the wall. To address the temperature discontinuity problem, the rothalpy jump equation in the enthalpyJump code was modified from a scalar product to an inner product of vectors. To resolve the high-temperature problem at the wall, modifications were made to the energy equation code in iEqn.H. A rothalpy separation was introduced, and the rothalpy equation was adjusted to mimic the enthalpy equation. The results obtained with the corrected codes were consistent with those from the commercial code, demonstrating the effectiveness of the modifications. [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]

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]

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]

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]

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]

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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 presents a comprehensive three-dimensional computational fluid dynamics (CFD) analysis of abrasive fluid flow and its erosive effects on the active components of the WUXI YCWJ-380-1520 water jet cutting machine. The research investigates the behavior and impact of abrasive particles within the fluid, determining the erosion rates for particles with diameters of 0.19 mm, 0.285 mm, and 0.38 mm (dimensions resulting from the granulometry of the experimentally established sand), considering various abrasive flow rates. The methodology includes a detailed granulometric analysis of the abrasive material, identifying critical particle sizes and distributions, with a focus on M50 granulation (average particle size of 0.285 mm). Additionally, the study employs the Wadell method to determine the shape factor (Ψi = 0.622) of the abrasive particles, which plays a significant role in the erosion process. Experimental determination of the abrasive flow rate is conducted, leading to the development of a second-order parabolic model that accurately predicts flow variations based on the control settings of the AWJ machine. The maximum erosion occurs at the entry surface of the mixing tube's truncated zone, with a higher intensity as the particle size increases. For the 0.19 mm particles, the erosion rates range from 1.090 × 10−6 kg/m2·s to 2.022 × 10−6 kg/m2·s and follow a parabolic distribution. The particles of 0.285 mm show erosion rates ranging from 2.450 × 10−6 kg/m2·s to 6.119 × 10−6 kg/m2·s, also fitting the second-order parabolic model. The largest particles (0.38 mm) exhibit erosion rates ranging from 3.646 × 10−6 kg/m2·s to 7.123 × 10−6 kg/m2·s, described by a third-order polynomial. The study concludes that larger particle sizes result in higher erosion rates due to their increased mass and kinetic energy. Therefore, the present investigation demonstrates a significant relationship between particle size, abrasive flow rate, and erosion rate, highlighting critical wear points in the machine's components. The findings contribute to optimizing the design and operational parameters of water jet cutting machines, thereby enhancing their efficiency and lifespan. [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]

The occurrence of cavitation in marine propellers is a major source of noise in ships. Consequently, the occurrence and noise characteristics of cavitation must be better understood to control this issue. This study focuses on identifying the occurrence and noise characteristics of cavitating flow around two-dimensional (2D) hydrofoils. Using the commercial computational fluid dynamics software STAR-CCM+, a numerical analysis was conducted on the partial cavity flow occurring around 2D hydrofoils at specific angles of attack. In addition, the cavitation noise characteristics were analyzed by conducting a frequency analysis using the predicted pressure data obtained via a fluctuating pressure sensor positioned vertically above the hydrofoil. Consequently, the numerical results were compared with existing experimental data to validate the accuracy of the simulation. This study identifies the limitations of the Reynolds-averaged Navier–Stokes (RANS) method by closely comparing it with the large eddy simulation (LES) method for assessing noise characteristics in unsteady cavitating flow. Although RANS has limitations in qualitatively assessing periodic behavior compared to LES, it effectively predicts cavitation extent and is valuable for relative assessments in practical applications. [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]

Abstract Mixing elbows are widely used in various industrial processes to mix two different Newtonian or non-Newtonian fluids under turbulent flow conditions. This study numerically investigates the fluid flow and mixing characteristics in 90-degree elbows with different bend curvatures (curvature ratios of 3, 6, and 9) and Reynolds numbers ranging from 1 × 104 to 5 × 105 for both fluid types. The Reynolds-Averaged Navier–Stokes equations are solved using the turbulent k-epsilon model in ANSYS Fluent. Results show that the bend curvature creates an adverse pressure gradient that drives secondary flows, which become more pronounced with higher Reynolds numbers and lower curvature ratios. Higher Reynolds numbers improve mixing quality, as indicated by velocity and temperature variations quantified using standard deviations. For Reynolds numbers in the range of 104, velocity fluctuations initially increase, but at higher values (~ 105), they decrease, even by up to 64% as the Reynolds number rises from 1 × 105 to 5 × 105. Similarly, increasing the curvature ratio enhances mixing efficiency, with a 32% reduction in velocity fluctuations when the curvature ratio increases from 6 to 9. Furthermore, shear-thinning fluids ( $$n = 0.6$$ n = 0.6 ) exhibit superior mixing performance, with a standard deviation of velocity fluctuations at the outlet of 0.32, compared to 0.54 for shear-thickening fluids ( $$n = 1.4$$ n = 1.4 ). In terms of temperature fluctuations also, a similar trend is observed. These findings are valuable for optimizing mixing and fluid transport in industries such as chemical processing and food production, where effective mixing of complex fluids is critical. This study provides insights for improving the design of mixing systems that handle fluids with various rheological characteristics.

ABSTRACT 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.

ObjectivesThis study calculates and analyzes the flow field around the hull of a 210 000 DWT bulk carrier in order to perform hull line optimization with resistance and wake non-uniformity as the optimization objectives. MethodsComputational Fluid Dynamics (CFD) is used to evaluate the initial hull lines, calculate the flow field around the ship and obtain flow field characteristics such as the wave pattern, pressure distribution, velocity distribution, etc. According to the CFD calculation results, an optimization strategy is constructed to form the modified hull lines. CFD calculation is then carried out on the modified lines to evaluate the optimization effects on resistance and wake non-uniformity. Finally, a model test of the optimized hull form's power delivery performance is carried out to verify the optimization effects. ResultsThe CFD calculation results show that compared with the initial hull form, the effective power of the modified hull form is reduced by 2.46% and the wake non-uniformity is reduced by 8.48%, while the model test results show that compared with the initial hull form, the delivered power of the modified hull form is reduced by 3.49%.ConclusionsThe proposed optimization method can obtain hull lines with excellent resistance performance and good wake field uniformity, giving it strong engineering applicability.