Fluid Dynamics Model Research Articles

Experimental and Computational Investigation of the Emission and Dispersion of Fine Particulate Matter (PM2.5) During Domestic Cooking

As the wealth of evidence grows as to the negative impact of indoor air quality on human health, it has become increasingly urgent to investigate and characterise sources of air pollution within the home. Fine particulate matter with a diameter of 2.5 µm or less (PM2.5) is a key cause for concern, and cooking is known to be one of the most significant sources of domestic PM2.5. In this study, the aim was to demonstrate the efficacy of combining experimental techniques and cutting-edge High-Performance Computing (HPC) to characterise the dispersion of PM2.5 during stir-frying within a kitchen laboratory. This was carried out using both experimental measurement with low-cost sensors and high-fidelity Computational Fluid Dynamics (CFD) modelling, in which Lagrangian Stochastic Methods were used to model particle dispersion. Experimental results showed considerable spatio-temporal variation across the kitchen, with PM2.5 mass concentrations in some regions elevated over 1000g/m3 above the baseline. This demonstrated both the impact that even a short-term cooking event can have on indoor air quality and the need to factor in such strong spatio-temporal variations when assessing exposure risk in such settings. The computational results were promising, with a reasonable approximation of the experimental data shown at the majority of monitoring points, and future improvements to and applications of the model are suggested.

An Evaluation of the Sensitivity of a Source Term Estimation Methodology of Sensor Configuration in an Urban-like Environment

Identifying unknown sources of air pollutants is vital for protecting public health, especially in cases involving the emission of toxic substances. The efficiency of this process depends highly on the accuracy of Source Term Estimation (STE) methods and the availability of robust measurements. Therefore, it is important to examine how sensor network characteristics affect STE accuracy. This study investigates the impact of different sensor configurations on STE results for a stationary point source in a complex, urban-like environment. The STE methodology employs the Metropolis–Hastings Markov Chain Monte Carlo (MCMC) algorithm alongside numerical simulations of a Computational Fluid Dynamics (CFD) model. The STE algorithm is applied across several sensor configurations in three distinct release scenarios and real sensor observations from the Michelstadt wind tunnel experiment, assessing both the number of sensors used and the agreement between measured and modeled concentrations. In general, the results indicate that increasing the number of sensors and the model’s accuracy improves the source parameters estimations. However, there is a specific number of sensors in each release scenario where STE outcomes from randomly selected, high-accuracy, and low-accuracy sensors converge to similar solutions. Overall, the findings provide valuable information for designing sensor configurations in urban areas.

The Effect of Barrel Configurations on the Porosity During HVAF Thermal Spray Ni-Based Amorphous Coatings: Numerical Simulation and Experiment

The relationship between barrel configurations and porosity of a Ni-based amorphous coating (AM) that is fabricated using a high-velocity air fuel (HVAF) process was revealed by both numerical and experimental methods. A computational fluid dynamics model was applied to investigate the gas-flow field and the behavior of in-flight particles with various barrel configurations. It is found that barrel length obviously affects the particle velocity and temperature while it has a slight influence on the particle velocity and temperature. The longer the barrel length (diameter), the higher the flame (particle) velocity and temperature. By analyzing both particle velocity and temperature, the optimal barrel configuration (4E) to achieve low-porosity coatings was predicted. These calculations were experimentally verified by the production of a low-porosity (2.09%) Ni-based AM that was fabricated by HVAF using the predicted optimal barrel configuration.

Comparison between Compartment and Computational Fluid Dynamics Models for Simulating Reactive Crystallization Processes

Comparison between Compartment and Computational Fluid Dynamics Models for Simulating Reactive Crystallization Processes

Real-time lava flow forecasting during the 2022 Mauna Loa eruption response

On November 27, 2022, Mauna Loa (Hawai‘i) erupted for the first time in ∼38 years, initially producing lava flows that covered the floor of its summit caldera, Moku‘āweoweo. Over the first 12 h following the summit eruption, four main fissures opened on Mauna Loa’s Northeast Rift Zone, with “fissure 3” quickly becoming the dominant source of lava flows. For the next 12 days, fissure 3 produced a 19-km-long lava flow to the north, crossing the Mauna Loa Weather Observatory access road and coming within 2.8 km of inundating the Daniel K. Inouye Highway (Saddle Road). Within 40 min of fissure 3 opening, inundation modeling efforts had begun. For the duration of the eruption, the computational fluid dynamics model Lava2d was run in real time, using flow front locations and other field observations to make sequential forecast improvements, eventually producing a set of models which accurately predicted the routing and arrival times of lava from fissure 3. These models were used to inform timing estimates of possible future inundation of the Saddle Road. As the eruption progressed, almost 4000 Lava2d models were made using high-performance computing resources, providing critical information on uncertainty in multi-week forecasts. To our knowledge, this was the first ever real-time physics-based ensemble lava flow modeling and forecasting effort. Here, we present a chronology of these real-time efforts, focusing on the successes and limitations of this approach.

Research on water flow characteristics and stress around bridges during floods

ABSTRACT Due to the frequent threat of floods to structures and engineering constructions near rivers, this study examines the impact characteristics of river hydrodynamics on structures under excessive flow during floods, using Jiefang Bridge as an example. We employ the fluid volume two-phase flow model (volume of fluid) in computational fluid dynamics, combined with advanced geometric reconstruction techniques such as the isoAdvector method, to simulate the dynamic changes of the gas–liquid interface in the river. On the premise of ensuring grid independence, high-precision structural grids were used to finely divide the study area and numerical simulations were conducted. The research results indicate that when a flood contacts a bridge, the force on the bridge rapidly increases and fluctuates, reaching a significant peak of over 6,000,000 N. Bridge piers have a significant hindering effect on floods and their impact gradually expands over time. Vorticity and turbulence energy analysis indicate the presence of strong flow disturbances around the bridge pier. In addition, the characteristics of the contact surface between water flow and bridges also significantly affect the stress and flow characteristics of bridges. Especially at a 45° angle of attack, the force on the bridge decreases, but the wake velocity increases.

Considerations Regarding High Oil Density Bioreactor-Scale Fermentations of Yarrowia lipolytica Using CFD Modeling and Experimental Validation.

Hydrophobic feedstocks such as waste cooking oil have recently been considered for microbial biotransformation due to their abundance, low cost, and unique advantage for lipid-derived fermentation products. Most fermentations with hydrophobic substrates are conducted at the tube or flask scale (less than 1 L total volume) or with the hydrophobic substrate comprising a small fraction of the media. Low substrate concentrations require additional feeding. Alternatively, high concentrations do not require significant dilution of the oil feedstock, which reduce volumetric requirements for larger scale fermentations. However, high-oil-density fermentations complicate efficient mixing and mass transfer challenges which are exacerbated at larger scales. To address this, computational fluid dynamics (CFD) models were explored to simulate three-phase (hydrophobic, hydrophilic, and gaseous) bench (3 L) and pilot scale (4000 L) bioreactors, highlighting challenges and potential considerations. Bioreactor fermentations of Yarrowia lipolytica strain L36DGA1 with substrate loadings of 5%, 10%, 20%, 30%, 40%, and 50% (v/v) waste cooking oil were also conducted, representing one of the highest concentrations in the reported literature. This work supports future research into and implementation of high-oil-density fermentations at the bench and pilot bioreactor scale.

Study on simulated airflow dynamics of children with obstructive sleep apnea treated by different surgical methods

Objective:To analyze the effects of adenoidectomy, tonsillectomy and tonsillectomy combined with adenoidectomy on obstructive sleep apnea children by computational fluid dynamics numerical simulation. Methods:A case of typical tonsil with adenoid hypertrophy was selected. Mimics 21.0 software was used to establish the original preoperative model, adenoidectomy, tonsillectomy and virtual surgical models of tonsillectomy combined adenoidectomy, and the computational fluid dynamics model of the upper airway was established by ANSYS 2019 R1 software, and then the pressure and velocity of the internal flow field of the CFD model were numerically simulated. Seven planes perpendicular to the flow trace were selected as the observation planes, including the cross section of the sinusostoma complex, the anterior end of the adenoid body, the narrowest cross section of the nasopharyngeal cavity, the pharyngostoma tube, the narrowest cross section of the oropharyngeal cavity, the lower pole of the tonsil and the glottis section. The comparison indexes included pressure, flow velocity and flow distribution. Results:Compared with the original model before operation, after the adenoids were removed only, the pressure drop between the section of the ostiomeatal complex and the section of the eustachian tube decreased, the high velocity peak at the anterior end of the adenoids disappeared, and the flow trace through the middle nasal canal increased. When only bilateral tonsils were removed, the pressure drop between the eustachian tube and the glottis slowed down and the flow velocity between the eustachian tube and the glottis slowed down. Combined tonsillar-adenoidectomy resulted in the most uniform pressure distribution, the most gentle pressure change and flow rate in the upper airway, and the most ignificant increase in airflow trace through the middle nasal canal among the three operations. Conclusion:Adenoidectomy, tonsillectomy and combined tonsillar adenoidectomy can make the airflow velocity and pressure of upper respiratory tract uniform to different degrees, but there are obvious differences in the specific anatomical location and degree. The application of CFD can intuitively predict the improvement of upper airway flow field in OSA children by different surgical methods, which helps clinicians to make surgical decision.

Numerical investigation on the effect of ignition timing on a low-temperature hydrogen-fueled Wankel rotary engine with passive pre-chamber ignition

Adopting the low-temperature hydrogen evaporated from the liquid hydrogen is capable of improving volumetric efficiency for the Wankel rotary engine (WRE). Considering the difficulty in ignition and slow flame propagation of low-temperature hydrogen-air mixtures, the passive pre-chamber is used to improve ignition and combustion. A three-dimensional computational fluid dynamics model for a turbulent jet ignition (TJI) WRE fueled by low-temperature hydrogen was established. The effects of low temperature and TJI on the in-cylinder flow field, combustion, emissions and leakage in the TJI-WRE fueled by low-temperature hydrogen were studied under different ignition timings. The results indicated that low-temperature tends to suppress the flame propagation, whereas TJI can accelerate the flame speed and promote flame propagation to the unburned zone in the combustion chamber. Combining low-temperature hydrogen with the passive pre-chamber can achieve high engine thermal efficiency and power while significantly reducing leakage. With the ignition timing set at 18 °CA before the top dead center, the indicated thermal efficiency reached 39.49% and the indicated mean effective pressure peaked at 0.77 MPa. Compared to the original engine, fresh mixture leakage through spark plug cavities and adjacent chambers was reduced by 72.13% and 78.79%, respectively.

A computational fluid dynamics-based girth welding model for large-diameter pipeline to reveal vertical weld formation mechanism

Welding quality significantly impacts the safety of large-diameter, long-distance pipelines. The molten pool flow, influenced by gravity, results in variations in the girth weld seam at different circumferential orientations. A three-dimensional transient computational fluid dynamics model was developed to study the multi-layer, multi-pass welding process of X80M pipeline, incorporating arc heat, droplet heat, gravity, and fluid flow in the molten pool. The model also simulates dual-torch automatic welding to examine heat transfer and flow characteristics. Notably, it reveals the morphological evolution of the girth weld seam from the 2 to 3 o'clock positions during continuous welding, an area lacking prior research. The results, validated by experiments, show good agreement between the simulation and thermal cycle curves. The weld pool solidifies from the sides toward the center, creating a concave shape due to downward metal flow, with dual-torch welding intensifying this effect. The second torch increases the concavity of filler layers, with depths rising by 21.81% and 32.20%. These findings offer new insights into pipeline girth welding.

On the Numerical Investigation of Two-Phase Evaporative Spray Cooling Technology for Data Centre Applications

Two-phase evaporative spray cooling technology can significantly reduce power consumption in data centre cooling applications. However, the literature lacks an established methodology for assessing the overall performance of such evaporation systems in terms of the water-energy nexus. The current study develops a Lagrangian–Eulerian computational fluid dynamics (CFD) modelling approach to examine the functionality of these two-phase evaporative spray cooling systems. To replicate a modular system, a hollow spray cone nozzle with Rosin–Rammler droplet size distribution is simulated in a turbulent convective natural-air environment. The model was validated against the available experimental data from the literature. Parametric studies on geometric, flow, and climatic conditions, namely, domain length, droplet size, water mass flow rate, temperature, and humidity, were performed. The findings indicate that at elevated temperatures and low humidity, evaporation results in a bulk temperature reduction of up to 12 °C. A specific focus on the climatic conditions of Dublin, Ireland, was used as an example to optimize the evaporative system. A new formulation for the coefficient of performance (COP) is established to assess the performance of the system. Results showed that doubling the injector water mass flow rate improved the evaporated mass flow rate by 188% but reduced the evaporation percentage by 28%, thus reducing the COP. Doubling the domain length improved the temperature drop by 175% and increased the relative humidity by 160%, thus improving the COP. The COP of the evaporation system showed a systematic improvement with a reduction in the droplet size and the mass flow rate for a fixed domain length. The evaporated system COP improves by two orders of magnitude (~90 to 9500) with the reduction in spray Sauter mean diameter (SMD) from 292 μm to 8–15 μm. Under this reduction, close to 100% evaporation rate was achieved in comparison to only a 1% evaporation rate for the largest SMD. It was concluded that the utilization of a fine droplet spray nozzle provides an effective solution for the reduction in water consumption (97% in our case) for data centres, whilst concomitantly augmenting the proportion of evaporation.

Prediction of transient thermal stress distribution in SOFC based on coupled computational fluid dynamics and thermodynamics modeling

Long-term stability and safety are two key factors for the application of solid oxide fuel cell (SOFC) technology, with thermodynamics playing a central role in influencing this stability. Thus, understanding the thermodynamic behavior within SOFC and how it will depend on the stack structure are very important, especially at the start and stop stages. In this study, a 3D calculated fluid dynamics model and thermomechanical coupling model based on the actual component structures are established. We place emphasis on understanding how these factors evolve during dynamic phases, shedding light on the transient thermal stress behavior of the SOFC. The influence of different interconnect structures on the thermal stress distribution is studied. The coupling calculation results show that the first principal stress of the electrolyte is significantly affected by the specific interconnect structure. Adopting cylindrical ribs instead of rectangular ribs, the thermal stresses of the SOFC components can be reduced by 13–25 %, respectively.

Simulation of Fluid Flow through Orifice Meter

The modeling of fluid flow using an orifice meter is an engineering endeavor aimed at thoroughly investigating and optimizing fluid flow measurement in various industrial applications. Orifice meters are highly regarded for their accurate measurement of fluid flow rates as they pass through a specifically designed orifice plate, utilizing the principles of fluid dynamics. The primary objective of this project is to develop a computational fluid dynamics (CFD) model capable of simulating the intricate fluid flow through an orifice meter. The simulation encompasses detailed geometric features of the orifice meter, including the precise dimensions of the orifice plate, pipe diameter, and any relevant taper angles. Additionally, the model takes into account various fluid parameters, boundary conditions, and factors such as velocity and pressure at different points within the system. The comprehensive study visualizes and quantifies key fluid properties, such as velocity profiles, pressure differentials, and flow velocities, across the entire length of the orifice meter using CFD analysis. This in-depth analysis provides crucial insights into the dynamic performance of the orifice meter. The obtained information holds significant potential to revolutionize flow rate measurement accuracy, efficiency, and cost-effectiveness in diverse industries, including water management, chemical processing, and oil and gas. The project's methodology for simulating fluid flow through orifice meters can bring about substantial improvements in the understanding and optimization of fluid flow in industrial processes.

Computational Fluid Dynamics Modeling and Analysis of Lime Slurry Drying in a Laboratory Spray Dry Scrubber

Computational Fluid Dynamics Modeling and Analysis of Lime Slurry Drying in a Laboratory Spray Dry Scrubber

CFD simulation of liquid nitrogen flow inside a cryogenic chamber used for micromachining of soft polymer

Cryogenic-assisted micromachining is seen as a possible solution to fabricate microchannel directly on soft polymer, by increasing the stiffness of the workpiece surface by reducing cryogenic chamber temperature. However, because of large temperature difference at various position of the cooling area inside the chamber, under cryogenic cooling condition, determination of workpiece temperature at machining time is very difficult. Unfortunately, very limited research work has investigated the complicated physical phenomena of cryogenic cooling responsible for temperature distribution occurring inside the chamber during machining process. These phenomena may affect the cryogenic flow characteristics in over or under-cooling of soft polymer as workpiece, thus the performance of the cryogenic machining. In this work, computational fluid dynamic (CFD) model is developed and applied to investigate the liquid nitrogen (LN2) flow inside the cryogenic chamber under direct cooling (DC) and novel perforated wall cooling (PWC) techniques. The major objective is to evaluate the influence of several parameters (temperature and pressure) on the LN2 flow inside the chamber and role of the innovative PWC technique in temperature distribution with comparison to DC approach. Results of this study offer two important conclusions for reliable cryogenic micromilling of soft polymer. First, uniform temperature distribution inside the chamber is possible by novel PWC approach and second, peripheral temperature of the chamber shows less fluctuation with surface temperature of the workpiece.

A Baroclinic Fluid Model and Its Application in Investigating the Salinity Transport Process Within the Sediment–Water Interface in an Idealized Estuary

Understanding the salinity transport process around the sediment–water interface is important for water resources management in the upper reach of an estuary. In this study, we developed a baroclinic fluid dynamic model for investigating the flow and salt transport characteristics within the sediment–water interface under tidal forcing. The validation showed robust model performance on the salinity transport within the sediment–water interface. The results revealed that the turbulent kinetic energy, dissipation rate, and kinetic energy production rate exhibited periodic variations within the seabed boundary layer. The thickness of the viscous sublayer and the mean flow showed an inverse relationship. Water and salinity exchange within the sediment–water interface occurred predominantly via turbulent diffusion, with extreme turbulent kinetic energy production rates appearing during the tidal reversal, flood, and ebb stages. The sediment acted as a source of salinity release during ebb tides and a sink for salinity absorption during flood tides. As the sediment depth increased, fluctuations in salinity were weakened. These results clearly illustrated that the sediment layer is important in modulating the salinity transport in the upper reach of an estuary. However, such an important process was usually excluded by previous studies. The model developed in this study can be used as a sediment–water interface module that, coupled with other hydrodynamic models, can evaluate the contributions of the sediment layer to the salinity exchange in coastal water.

Numerical Investigation of Combustion and Emission Characteristics of the Single-Cylinder Diesel Engine Fueled with Diesel-Ammonia Mixture

This study proposes a dual-fuel approach combining diesel and ammonia in a single-cylinder compression ignition engine to reduce harmful emissions from internal combustion. Diesel is directly injected into the combustion chamber, while ammonia is introduced through the intake manifold with intake air. In this study, injection timing and the percentage of ammonia energy fraction was varied. A computational fluid dynamics (CFD) model simulates the combustion and emission processes to assess the impact of varying diesel injection timings and ammonia energy contributions. Findings indicate that as ammonia content increases, the engine experiences reductions in peak in-cylinder pressure, temperature, heat release rate, as well as overall efficiency and power output. Emission results suggest that greater ammonia usage leads to a reduction in soot, carbon monoxide, carbon dioxide, and unburned hydrocarbons, though a slight increase in nitrogen oxides emissions is observed. This analysis supports ammonia’s potential as a low-emission alternative fuel in future compression ignition engines.

Innovative Approaches to Windcatcher Design: A Review on Balancing Tradition Sustainability and Modern Technologies for Enhanced Performance

This review investigates the role of windcatchers in modern architecture, exploring their optimization through the integration of traditional designs with contemporary technologies. Historically utilized in hot and arid climates for passive cooling, windcatchers offer energy-efficient solutions for improving indoor air quality (IAQ). This study examines the sustainability of traditional windcatcher designs and their relevance in preserving heritage structures. Using advanced tools like computational fluid dynamics (CFD) modeling, modern adaptations of windcatchers can be optimized for urban environments. This review also explores hybrid systems, combining windcatchers with solar chimneys, evaporative cooling, or heat pumps, to enhance performance in low-wind conditions by balancing natural and mechanical ventilation. Additionally, it addresses the role of artificial intelligence (AI) in heritage planning, facilitating the design and integration of windcatchers into contemporary architecture. The findings suggest that windcatchers, combined with modern design strategies and hybrid systems, continue to be viable and sustainable solutions for passive cooling, contributing to energy-efficient and climate-resilient buildings across different environmental and urban contexts.

Evaluation of flow and heat transfer behavior in parallel flow copper electro-refining cell with different inlet arrangements

Parallel flow copper electro-refining cell technology has been developed for over a decade, and the flow field in these cells is significantly influenced by the arrangement of the electrolyte inlets. Four computational fluid dynamics models were developed to compare the flow and heat transfer characteristics of the electrolyte under varying electrolyte inlet arrangements. These models include bi-directional parallel flow (BPF), staggered parallel flow (SPF), top inlet unidirectional parallel flow (UPF-T), and bottom inlet unidirectional parallel flow (UPF-B). Flow and heat transfer simulations were conducted for each model. The simulation results indicate that the BPF and SPF electro-refining cells exhibit varying degrees of kinetic energy loss, which leads to lower volume-weighted average velocities and impacts the rapid circulation of the electrolyte. The UPF-B is the most effective in terms of both flow uniformity and flow velocity, with the UPF-T following closely behind. The temperature in the inter-pole area is elevated when the SPF and UPF-T are arranged, which is more conducive to the diffusion of copper ions. The copper cathode production efficiency and deposition uniformity are enhanced by the UPF-B arrangement, which enables the liquid to be supplied to the inter-pole area more rapidly and uniformly.

Design and performance evaluation of the snowflake slope composite flow field based on a biomimetic principle

To address the problems of uneven mass distribution and hydrothermal management imbalance in flow fields, this study proposes a snowflake slope composite flow field (SSCFF). A three-dimensional multiphase computational fluid dynamics (CFD) model was developed to analyze the differences between the SSCFF and traditional flow fields, and to investigate the effects of gas inlet and outlet configurations, height ratios (Ld/D), and the number of main channels (N) on the performance. The study shows that the SSCFF excels in gas distribution and temperature control, with a maximum power density 35.5% higher than the honeycomb structure. The diagonal inlet and outlet configuration effectively reduces the risk of local hotspots and flooding. With Ld/D of 0.9, the uniformity of oxygen distribution improves significantly and the current density reaches 1.168 A cm−2. Additionally, with 6 main channels, the proton exchange membrane (PEM) achieves a higher hydration level, which boosts catalytic activity and working efficiency.