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Vortex shedding in the wake flow generated by moving bodies exerts considerable influence on pollutant dispersion. This study investigated the effects of different body shapes using scaled models 1/5th of realistic size, including thin and wide shapes, standing and walking poses. The airflow from moving bodies was simulated using computational fluid dynamics (CFD) with dynamic meshing to account for the manikin movement. Experimental data from a smoke visualisation technique provided validation data for computational simulations which included flow separation angle over the head computed through image processing. Vortex structures were visualised using an Omega vortex identification method and compared with experimental visualisations. The main objective of this study is to verify the CFD simulations with smoke visualisation in terms of predicting motion-induced vortex structures, thus helping identify contaminant transport around different shaped bodies during walking and when coming to a stop. The results showed matching locations and patterns of vortex structures between the smoke visualisation and CFD simulations. After the manikin came to a stop, the flow induced by the larger body was characterised by a longer residence time for airborne contaminants in the breathing region while a reduced flow residence time for the thinner bodied manikin. [ABSTRACT FROM AUTHOR]

Due to the fast development of high-speed rail (HSR) around the world, high-speed trains (HSTs) are becoming a strong competitor against airliners in terms of long-distance travel. Compared with airliner cabins, HST cabins have much larger window sizes. When the big windows provide better lighting and view of the scenery, they also have significant effects on the thermal conditions in the cabins due to the solar radiation through them. This study presents a numerical study on the solar radiation on the thermal comfort in a typical HST cabin. The effect of solar radiation was discussed in terms of airflow pattern, temperature distribution and thermal comfort indices. Parametric studies with seven different daytime hours were carried out. The effect of using the roller curtain was also studied. The overall cabin air temperature, especially near passengers, was found to have significantly increased by solar radiation. Passengers sitting next to windows were recorded to have an obvious thermal comfort variation at different hours of the day. To improve the passengers' comfort and reduce energy consumption during hot weather, the use of a curtain could effectively reduce the solar radiation effect in the cabin environment. [ABSTRACT FROM AUTHOR]

Abstract Maintaining a high level of thermal comfort and indoor air quality for occupants while minimizing the system energy consumption is crucial for the long-haul High-speed train cabins. The traditional way of handling the multi-objective problem relies on the "trial and error" design which involves lengthy manual design parameter adjustment and performance evaluation based on on-site measurements or analytical and empirical models. To shorten design optimization process, a multi-objective optimization platform has been developed using the nondominated sorting-based particle swarm optimization (NSPSO) algorithm for searching the trade-off optimal design of the ventilation system in a fully occupied high-speed train (HST) cabin. A computational model of the HST cabin occupied by four full rows of passengers was constructed using ANSYS Fluent. To ensure the accuracy of the CFD model, high resolution computational thermal manikins were adopted to simulate the thermal and pollutant dispersion under influence of the passengers. Different combinations of ventilation operation parameters were evaluated against its performance in terms of thermal comfort, air quality and energy consumption. Furthermore, to reduce the computational cost of constructing the training sample, a Multi-fidelity Kriging technique is also proposed a surrogate method in replacing the time-consuming CFD simulations while maintaining acceptable accuracy. The result demonstrates that the presented approach is capable to perform a multi-objective optimization for indoor ventilation system design and yield accurate Pareto-front result with up to 35.61% saving of computational time. Highlights • We use CFD to simulate fully occupied HST cabin. • We use very fine 3D-scanned thermal manikin models in the simulation. • We use Multi-objective optimization algorithm to provide generative solutions. • We develop a Multi-fidelity surrogate algorithm to save computational resources. [ABSTRACT FROM AUTHOR]

Understanding the inhalation, transport and deposition of smoke particles during fire missions are important to evaluating the health risks for firefighters. In this study, measurements from Underwriters Laboratories' large-scale fire experiments on smoke particle size distribution and concentration in three residential fire scenes were incorporated into models to investigate the fate of inhaled toxic ultrafine particulates in a realistic firefighter nasal cavity model. Deposition equations were developed, and the actual particle dosimetry (in mass, number and surface area) was evaluated. A strong monotonic growth of nasal airway dosages of simulated smoke particles was identified for airflow rates and fire duration across all simulated residential fire scene conditions. Even though the "number" dosage of arsenic in the limited ventilation living room fire was similar to the "number" dosage of chromium in the living room, particle mass and surface area dosages simulated in the limited living room were 90–200 fold higher than that in the ventilated living room. These were also confirmed when comparing the dosimetry in the living room and the kitchen. This phenomenon implied that particles with larger size were the dominant factors in mass and surface area dosages. Firefighters should not remove the self-contained breathing apparatus (SCBA) during fire suppression and overhaul operations, especially in smoldering fires with limited ventilation. [ABSTRACT FROM AUTHOR]

Abstract This study numerically investigated the thermal effect of human body on the time-dependent dispersion of cough droplets with evaporation process. The thermal flow of human body was imitated using a 3D thermal manikin with real body features, while a recent developed multi-component Eulerian-Lagrangian approach was used to address the effects of inhomogeneous temperature and humidity fields on droplet evaporation. By comparing the results yielded without and with the human body heat, the outcomes demonstrated strong impact of human body heat on the droplets mass fraction and local air velocity distributions. Inspirable droplets could potentially drop into respirable droplets by evaporation, although the evaporation rate was not significantly affected by body heat. The thermal effect of human body revealed its vital impacts on the time-dependent droplets dispersion. Due to the buoyancy driven thermal flow, both the vertical velocity and displacement of small droplets (≤20 μm) were completely reversed from descending to ascending, while the deposition time of large droplets (≥50 μm) were significantly delayed. With the reduced droplet size by evaporation and droplets lifted into breathing zone by human thermal effect, the inhalability and infection risks of cough droplets would be much higher in real occupied indoor spaces. Highlights • Inspirable droplets could drop into respirable droplets through evaporation process. • Human body heat strongly affects the local droplets mass fraction. • Evaporation rate is not sensitive to human body heat but to the RH and droplet size. • Cough droplets could be lifted to breathing zone by buoyancy driven thermal flow. • Human thermal effect promotes evaporation process by delaying droplets deposition. [ABSTRACT FROM AUTHOR]

Abstract The theoretical models of Surface-to-Surface (S2S) thermal radiation, including the Monte Carlo model, Discrete Transfer model, Modest model and Heat-Flux-Split approach, are evaluated in terms of the predictive accuracy and CFD computational cost when simulating indoor thermal flows. It is demonstrated that the inclusion of thermal radiation in the CFD model is vital as the air temperature in the lower levels can be underpredicted while the heater surface temperature can be significantly overpredicted if the radiative effects are ignored. In addition, the predicted temperature distribution on the heat-receiving solid surfaces is highly sensitive to the selected radiation model. The comparisons demonstrate that the Monte Carlo model and Discrete Transfer model have comparable predictive capabilities while the latter requires less CPU time and is more computationally efficient. The appropriate number of the representative photons and rays are also recommended for the Monte Carlo model and Discrete Transfer model, respectively. Highlights • Predictive models/approaches of S2S thermal radiation are evaluated. • Importance of indoor radiative heat transfer is demonstrated. • Monte Carlo and Discrete Transfer models are comparably accurate. • Discrete Transfer models are computationally more efficient. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) is an important and effective tool to study the airflow field and contaminant distribution in aircraft cabins. The accuracy of numerical simulation using the CFD approach could be significantly affected by configurations of the inlet boundary conditions, turbulence model, etc. The core of this study was to assess whether conclusions achieved in simulation of airflow on usual surfaces in buildings like in commercial offices could be applicable to aircraft cabins. Comparative studies involving turbulence models or air supply opening models in aircraft cabin environment are still absent in the literature. Therefore, in this study, two turbulence models (the renormalization group (RNG) k-ɛ model and Reynolds-stress model) and three types of air supply opening models (simple open model, basic model and momentum model) were applied to simulate the airflow and contaminant concentration fields in a mockup seven-row cabin section. Our simulation results were compared with the experimental data. Six indexes based on different criteria were used to quantitatively evaluate the agreement between measurements and modelled results given by turbulence models and air supply opening models. The results show that the RNG k-ɛ and RSM turbulence models have similar accuracy in airflow and contaminant fields in the mockup cabin, and the momentum model has the best accuracy among the three air supply opening models for the aircraft cabin environment. [ABSTRACT FROM AUTHOR]

Rats have been widely used as surrogates for evaluating the health effects of inhaled airborne particulate matter. To provide a thorough understanding of particle transport and deposition mechanisms in the rat nasal airway, this article presents a computational fluid dynamics (CFD) study of particle exposure in a realistic rat nasal passage under a resting flow condition. Particles covering a diameter range from 1 nm to 4 µm were passively released in front of the rat’s breathing zone, and the Lagrangian particle tracking approach was used to calculate individual particle trajectories. Detailed particle deposition analysis shows the deposition of inertial particles >2 µm is high in the rat nasal vestibule and more than 70% of all inhaled inertial particles were trapped in this region. While for diffusive nanoparticles, the vestibule filtration effect is reduced, only less than 60% of inhaled nanoparticles were blocked by the anterior nasal structures. The particle exposure in the olfactory region only shows notable deposition for diffusive nanoparticles, which peaks at 9.4% for 5 nm particles. Despite the olfactory deposition remains at a low level, the ratio between the olfactory and the main passage is kept around 30-40% for 10-800 nm particles, which indicates a particle-size-independent distribution pattern in the main nasal passage and olfactory. This study provides a deep understanding of particles deposition features in a rat nasal passage, and the research findings can aid toxicologist in inter-species exposure-response extrapolation study. [ABSTRACT FROM AUTHOR]

Simplified computational thermal manikins are beneficial to the computational efficiency of computational fluid dynamics simulations. However, the criterion of how to simplify a computational thermal manikin is still absent. In this study, three simplified computational thermal manikins (CTMs 2, 3 and 4) were rebuilt based on a detailed 3D scanned manikin (CTM 1) using different simplification approaches. Computational fluid dynamics computations of the human thermal plume in a quiescent indoor environment were conducted. The predicted airflow field using CTM 1 agreed well with the experimental observations from the literature. Although the simplified computational thermal manikins did not significantly affect the airflow predictions in the bulk regions, they strongly influenced the predicted airflow patterns near the computational thermal manikins. The predictive error of the computational thermal manikin was strongly related to the simplification approach. The computational thermal manikins generated from the surface-smoothing approach (CTM 2) was very close to CTM 1, while the required mesh elements for a stable numerical solution dropped by over 75%. Comparatively, the predictive errors of CTMs 3 and 4 were considerable in the near-body regions. This study has illustrated the importance of keeping the key body features when simplifying a computational thermal manikin. The surface-smoothing-based simplification method was shown to be a promising approach. [ABSTRACT FROM AUTHOR]

An urgent demand of assessing passengers' exposure risks in airliner cabins was raised as commercial airliners are one of the major media that carrying and transmitting infectious disease worldwide. In this study, simulations were conducted using a Boeing 737 cabin model to study the transport characteristics of airborne droplets and the associated infection risks of passengers. The numerical results of the airflow field were firstly compared against the experimental data in the literature to validate the reliability of the simulations. Airborne droplets were assumed to be released by passengers through coughing and their transport characteristics were modelled using the Lagrangian approach. Numerical results found that the particle travel distance was very sensitive to the release locations, and the impact was more significant along the longitudinal and horizontal directions. Particles released by passengers sitting next to the windows could travel much further than the others. A quantifiable approach was then applied to assess the individual infection risks of passengers. The key particle transport information such as the particle residence time yielded from the Lagrangian tracking process was extracted and integrated into the Wells-Riley equation to estimate the risks of infection. Compared to the Eulerian-based approach, the Lagrangian-based approach presented in this study is more robust as it addresses both the particle concentration and particle residence time in the breathing zone of every individual passenger. [ABSTRACT FROM AUTHOR]

Environment control system of the near-space capsule is of great importance to maintain a comfortable environment and working conditions for crew members as well as onboard equipments. Temperature and humidity, as two main parameters, are controlled by the phase change cool storage device in crew capsule. To improve the design of environment control system, a numerical study of the thermal environment based on a crew capsule suspending in the stratosphere was conducted in this paper. The main structure and thermodynamic parameters of the phase change cool storage device were calculated. Under the way of nozzle outlet air supply, a numerical modelling of the temperature and humidity distribution inside a crew capsule is performed. This research will contribute a better solution for an advanced environment control system design of crew capsules. [ABSTRACT FROM AUTHOR]

Micron-sized particle deposition in anatomically realistic models of a rat and human nasal cavity was numerically investigated. A steady laminar inhalation flow rate was applied and particles were released from the outside air. Particles showing equivalent total particle deposition fractions were classified into low, medium and high inertial particle. Typical particle sizes are 2.5, 9 and 20 μm for the human model and 1, 2 and 3 μm for the rat model, respectively. Using a surface-mapping technique the 3D nasal cavity surface was “unwrapped” into a 2D domain and the particle deposition locations were plotted for complete visual coverage of the domain surface. The total surface area comparison showed that the surface area of the human nasal model was about ten times the size of the rat model. In contrast, the regional surface area percentage analysis revealed the olfactory region of the rat model was significantly larger than all other regions making up ∼55.6% of the total surface area, while that of the human nasal model only occupying 10.5%. Flow pattern comparisons showed rapid airflow acceleration was found at the nasopharynx region and the nostril region for the human and rat model, respectively. For the human model, the main passage is the major deposition region for micro-particles. While for the rat model, it is the vestibule. Through comparing the regional deposition flux between human and rat models, this study can contribute towards better extrapolation approach of inhalation exposure data between inter-subject species. [ABSTRACT FROM PUBLISHER]

Airflow in the cockpits of commercial airliners could be substantially different and more complex than it in passenger cabins, while simply referring to the standard of passenger cabin may not effectively achieve optimum ventilation or ensure a comfortable working environment for pilots. This study numerically investigated the ventilated Boeing 737 cockpit by analysing its airflow and thermal distribution inside, especially in pilots' micro-environments, under various in-flight conditions (number of personalised jet-inlets, window heat exchange, etc.). Gaseous contaminant CO 2 released from pilots was analysed in relation to its concentration distribution and potential lock-up phenomena in pilots' micro-environments, followed by quantitative analysis of pilots' thermal comfort and air quality. The outcomes demonstrated that the window heat exchange had significant impacts on pilots' thermal sensation and could induce severe thermal stratification around pilots' head level. The most effective CO 2 removal rate was achieved by initiating windshield inlets in combination of the side diffusers. Further adding personal gaspers did not significantly alleviate the CO 2 concentration in pilots' micro-environment but may potentially compromise their thermal comfort. Also, the overwhelming numbers of personalised inlets could hardly provide superior ventilation performance or ensure consistent air quality and could be impractical to use sometimes. It is suggested that future optimisation of the environmental control system could rely more on the global airflow circulations induced by larger or wider diffusers rather than the local complex jet flows from high number of personal gaspers. [Display omitted] • Pilots' micro-environments in terms of thermal comfort and air quality are assessed. • Window heat exchange is a vital factor and may propel thermal stratification. • Air change efficiency and age of air in the upper region is seemingly unsatisfactory. • Contaminants removal is ineffective in pilots' breathing zone with diffuser open only. • Adding windshield inlets significantly improve air exchange and contaminants remove. [ABSTRACT FROM AUTHOR]

Abstract: The inhalation of micron particles by a manikin standing in a ventilated indoor environment was numerically investigated using Computational Fluid Dynamics (CFD). Computations were conducted with various combinations of the free stream velocity (0.05–0.25 m/s representing typical indoor wind speeds.), occupant orientation relative to the free stream (back-to-the-wind or facing-the-wind) and heat transfer (isothermal or thermal flow). It was found that the body heat has a significant impact on the airflow field in the vicinity of the manikin by causing an upwards airflow on the downstream side of the manikin. It was also found that the effect of body heat on particle inhalation depends on the manikin orientation relative to the free stream. When the manikin is facing-the-wind, body heat has a little effect on particle inhalation and can be neglected. However for a back-to-the-wind orientation, the situation is much more complicated as the source height of inhaled particles depends on the speed of free stream. When the wind speed is low (0.05 m/s), the critical area is located near the floor level. The central height of the critical area then increases with increasing free stream speed until it reaches the nose height when the wind speed rises up to 0.25 m/s. This indicates that the body heat is an important consideration when investigating contaminant inhalation by human occupants in low-speed (typically less than 0.2 m/s) indoor environment. [Copyright &y& Elsevier]

Abstract: Steam-jet vacuum pump is widely used in a range of applications. This paper evaluated the performance of four well-known turbulence models for predicting and understanding the internal flow of a steam-jet vacuum pump first. With the help of a commercial computational fluid dynamics (CFD) code ANSYS-Fluent 6.3, the simulation results obtained from the concerned turbulence models were compared with experimental values, the k-omega-SST model was chosen as a tool model for carrying out numerical simulations. Then, based on the simulation results obtained from specific operating conditions, a method for locating the shock-mixing layer was put forward. The shape of the shock-mixing layer shows that the secondary steam does not mix with the primary steam immediately after being induced into the mixing chamber of the pump; actually, they maintain their independence till the shocking position instead. After the shock happens, the shock-mixing layer disappear, the two fluid in the pump begin to mix with each other and discharge to the next stage with almost the same state. Based on the shape of the shock-mixing layer and the supersonic region of the secondary steam, a detailed analysis for the flow duct of the secondary steam was carried out. It is found that the throat of the secondary steam flow duct plays a crucial role in maintaining a stable operating state and the length of the throat reflects the back pressure endurance for the pump. [Copyright &y& Elsevier]

Abstract: CFD computations of particle flows in a human nasal cavity were conducted, using two types of inlet velocity profiles at the nostril openings respectively. One type is the widely used uniform inlet velocity profile while the other is a realistic inlet velocity profile extracted from the external environment that is influenced by facial features. The latter type of inlet velocity profiles were obtained through CFD computations of indoor gas-particle flows around a human head geometry containing detailed facial features in an enclosed space. Comparisons were made between the predicted results of airflow field, particle tracks and particle deposition efficiency in the nasal cavity. It was revealed that although the effects of facial features exist only in a small region (10–20 mm) in front of the face, they lead to complicated, and non-uniform velocity profiles at the nostril openings. This discrepancy leads to different predictions of airflow fields and local particle deposition efficiency in the nasal cavity, especially in the anterior regions such as the vestibule and nasal valve. The results may further lead to discrepant health-risk assessments associated with particle inhalation. Therefore, for CFD simulations of particle deposition in the nasal cavity, the inlet velocity profiles induced by facial features are important for more realistic results. [Copyright &y& Elsevier]

Urgent demands of assessing respiratory disease transmission in airliner cabins had awakened from the COVID-19 pandemics. This study numerically investigated the cough flow and its time-dependent jet-effects on the transport characteristics of respiratory-induced contaminants in passengers' local environments. Transient simulations were conducted in a three-row Boeing 737 cabin section, while respiratory contaminants (2 μm–1000 μm) were released by different passengers with and without coughing and were tracked by the Lagrangian approach. Outcomes revealed significant influences of cough-jets on passengers' local airflow field by breaking up the ascending passenger thermal plumes and inducing several local airflow recirculation in the front of passengers. Cough flow could be locked in the local environments (i.e. near and intermediate fields) of passengers. Results from comparative studies also revealed significant increases of residence times (up to 50%) and extended travel distances of contaminants up to 200 μm after considering cough flow, whereas contaminants travel displacements still remained similar. This was indicating more severe contaminate suspensions in passengers' local environments. The cough-jets was found having long and effective impacts on contaminants transport up to 4 s, which was 8 times longer than the duration of cough and contaminants release process (0.5 s). Also, comparing to the ventilated flow, cough flow had considerable impacts to a much wider size range of contaminants (up to 200 μm) due to its strong jet-effects. • Cough-jets could break up thermal plume and induce local air recirculation. • Contaminant residence time and travel distance increase with cough flow. • More severe contaminant suspensions are caused by strong cough-jet effects. • Cough-jets has long impacts on contaminants transport up to four seconds. • Cough flow has considerable impacts to large contaminants up to 200 μm. [ABSTRACT FROM AUTHOR]

As an essential emergency management strategy, innovative emergency ventilation schemes that can quickly remove infectious and fatal contaminants without further spreading are highly demanded for public and commercial buildings. This study numerically investigated a vortex flow driven ventilation in a model room to explore the dynamic characteristics and 3D visualisation of vortex-driven indoor tornados. Four approaches to identify the core region of the indoor tornado were developed and compared against each other. By successfully capturing the continuously changing centre of the vortex and significant core region size variations at different heights, the swirl vector method was recommended as a quantifiable approach to identify the core region of indoor tornados. The numerical outcomes also revealed a strong connection between the lift angle, vortex intensity, overall size of indoor tornado and maximum size of core region. The best contaminants control and removal was achieved at lift angle of 20° in this study and an optimum lift angle ranging from 10° to 20° was recommended for future study. • Swirl vector based method is proposed to identify the core region of indoor tornado. • Centre of indoor tornado keeps changing along the vertical travel direction. • Tornado core region size changes significantly along the vertical travel direction. • The best contaminants removal is achieved at lift angle of 20° in this study. • Optimum lift angle range from 10° to 20° is recommended for future study. [ABSTRACT FROM AUTHOR]

Highlights: • The SST k-ω model performs best for convection-radiation hybrid thermal airflows. • Surface radiation affects airflow pattern via heating up surfaces. • Surface radiation affects VOC emission and dispersion. Abstract This study presents a computational fluid dynamics (CFD) study on the effects of surface radiation on the emission and dispersion of gaseous contaminants in indoor spaces. Mathematical models are firstly validated against experimental data reported in the literature. It demonstrates that the Shear Stress Transport (SST) k-ω model performs best among other turbulence models when modelling convection-radiation hybrid heat transfer. The study also reveals that surface radiation accounts for 37%–71% of the heat dissipation from the heat sources in a typical office room, which remarkably alters the indoor airflow pattern through cooling and heating the solid surfaces. Beyond that, the emission rate of volatile organic compounds (VOCs) from solid surfaces is also changed due to its dependence on the temperature. Consequently, the VOCs exhibit different dispersion characteristics and distribution patterns in the air, which ultimately results in different evaluations of the indoor air quality (IAQ). This study demonstrates that even in high-momentum indoor spaces such as those equipped with mixing ventilation systems, surface radiation still plays an important role in shaping the overall indoor environment quality (IEQ). [ABSTRACT FROM AUTHOR]

Abstract Intranasal drug delivery has attracted significant attention because of the opportunity to deliver systemic drugs directly to the blood stream. However, the mucociliary clearance poses a challenge in gaining high efficacy of intranasal drug delivery because cilia continuously carry the mucus blanket towards the laryngeal region. To better understand mucus flow behaviour on the human nasal cavity wall, we present computational model development, and evaluation of mucus motion on a realistic nasal cavity model reconstructed from CT-scans. The model development involved two approaches based on the actual nasal cavity geometry namely: (i) unwrapped-surface model in 2D domain and (ii) 3D-shell model. Conservation equations of fluid motion were applied to the domains, where a mucus production source term was used to initiate the mucus motion. The analysis included mucus flow patterns, virtual saccharin tests and quantitative velocity magnitude analysis, which demonstrated that the 3D-shell model results provided better agreement with experimental data. The unwrapped-surface model also suffered from mesh-deformations during the unwrapping stage and this led to higher mucus velocity compared to experimental data. Therefore, the 3D-shell model was recommended for future mucus flow simulations. As a first step towards mucus motion modelling this study provides important information that accurately simulates a mucus velocity field on a human nasal cavity wall, for assessment of toxicology and efficacy of intranasal drug delivery. [ABSTRACT FROM AUTHOR]

Human-induced wake flow characteristics and its interaction with thermal conditions was investigated by performing CFD simulations with dynamic-meshing of a moving manikin model. The manikin motion with and without swinging limbs was achieved by the re-meshing method to update the grid with each time step. The results focused on determining what discrepancies are produced in the flow field by a simplified geometry in the form of a cylinder, swinging limbs and thermal conditions; and whether such assumptions can be made for larger multi-body analysis. Using a cylinder showed differences in the velocity field behind the head and leg gap. The flow field between the rigid motion and swinging limb motion, showed significant discrepancies which corresponded to the gait phase. There were increased airflow disturbances at the hands and ankles (furthest body parts from the pivot point). The influence of thermal plume on the wake flow was minor during walking motion because of the walking speed of 1.2 m/s which dominated the buoyant thermal plume velocity. However, after the manikin stopped moving the thermal plume velocity became comparable to the residual wake. [ABSTRACT FROM AUTHOR]

Particle diffusional losses in confined flows such as pipes are important for identification of erosion or accretion build-up. Its applications are varied and prominent in industrial and biomedical applications where essentially, tubular geometries transport fluid-particle flows. Computational modelling of dilute suspensions of ultrafine and nano-scale particles dispersing in a fluid often use the Lagrangian particle tracking approach. The Euler Implicit scheme in FLUENT v16 was evaluated for tracking such particles through a standard pipe geometry. It was found that the particles’ Brownian dispersion was dependent on the computational mesh, and the integration time step for a given particle size. For the pipe geometry well established analytical solutions for particle deposition efficiency are available to directly compare the simulated results. For irregular geometries (such as human respiratory anatomy) there are no analytical solutions and experimental deposition data is scarce and an alternative method is required to verify the simulation setup. In this case the computational models were set with zero velocity and the nanoparticles released from rest. The particle motion was then initiated purely by Brownian motion. The root mean square displacement was used to compare the time step size selector (either by the Length Scale Factor, L S , or the Step Length Factor SLF approach in FLUENT ; and a fixed time step using an in-house code ‘PARTICLE’ ). This provides a modelling verification framework to determine the most appropriate time step selection that reproduces the particle Brownian dispersion behaviour correctly. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new visualization technique that transforms 3D nasal cavity into a 2D domain. [•] Pressure distribution and wall shear stresses mapped onto a 2D domain. [•] Regions hidden by the curved airway geometry are revealed through the 2D domain. [•] Applications of technique include inter-individual geometry and particle inhalation. [ABSTRACT FROM AUTHOR]

Abstract: Effective management of asthma is dependent on achieving adequate delivery of the drugs into the lung. Inhalers come in the form of dry powder inhalers (DPIs) and metered dose inhalers (pMDIs) with the former requiring a deep fast breath for activation while there are no restrictions on inhalation rates for the latter. This study investigates two aerosol medication delivery methods (i) an idealised case for drug particle delivery under a normal breathing cycle (inhalation–exhalation) and (ii) for an increased effort during the inhalation with a breath hold. A computational model of a human tracheobronchial airway was reconstructed from computerised tomography (CT) scans. The model''s geometry and lobar flow distribution were compared with experimental and empirical models to verify the current model. Velocity contours and secondary flow vectors showed vortex formation downstream of the bifurcations which enhanced particle deposition. The velocity contour profiles served as a predictive tool for the final deposition patterns. Different spherical aerosol particle sizes (3–10μm, 1.55g/cm3) were introduced into the airway for comparison over a range of Stokes number. It was found that a deep inhalation with a breath hold of 2s did not necessarily increase later deposition up to the sixth branch generation, but rather there was an increase in the deposition in the first few airway generations was found. In addition the breath hold allows deposition by sedimentation which assists in locally targeted deposition. Visualisation of particle deposition showed local “hot-spots” where particle deposition was concentrated in the lung airway. [Copyright &y& Elsevier]

Abstract: Nasal physiology is dependent on the physical structure of the nose. Individual aspects of the nasal cavity such as the geometry and flow rate collectively affect nasal function such as the filtration of foreign particles by bringing inspired air into contact with mucous-coated walls, humidifying and warming the air before it enters the lungs and the sense of smell. To better understand the physiology of the nose, this study makes use of CFD methods and post-processing techniques to present flow patterns between the left and right nasal cavities and compared the results with experimental and numerical data that are available in literature. The CFD simulation adopted a laminar steady flow for flow rates of 7.5L/min and 15L/min. General agreement of gross flow features were found that included high velocities in the constrictive nasal valve area region, high flow close to the septum walls, and vortex formations posterior to the nasal valve and olfactory regions. The differences in the left and right cavities were explored and the effects it had on the flow field were discussed especially in the nasal valve and middle turbinate regions. Geometrical differences were also compared with available models. [Copyright &y& Elsevier]

Studying thermal hydraulics in reactor cores is essential for ensuring the safe operation of nuclear power plants and advancing the development of reactors and fuel. In the CASL program initiated by the US Department of Energy, they selected the advanced nuclear reactor's numerical simulation method to establish a high-fidelity numerical reactor system, VERA. The thermal–hydraulic part of the VERA program's software system uses the subchannel program CTF for precise calculations and comprehensive analysis. Based on synthesizing and mapping more than 170 papers, this study provides a concise review of the present state in thermal hydraulics for light water reactors using the subchannel code CTF. The analysis method of the subchannel is discussed thoroughly, and the chronology of the development process of the subchannel program are provided. The physical model and simulation studies of CTF are also introduced, together with the investigations on the important phenomenon of thermal hydraulic treatment of the subchannel by CTF are summarized. For each of the above issues, the latest study results, existing difficulties and future trends will be presented. While subchannel analysis procedures have made great progress over the past few decades, existing subchannel codes' performance still faces challenges. We provide discussions and suggestions for further study of the CTF subchannel program to address these challenges. For CASL, CTF is the preferred program for analyzing thermal–hydraulic problems in subchannels of light water reactors. This review may potentially provide a useful reference for subchannel thermal–hydraulic analysis and improvement of CTF program. [ABSTRACT FROM AUTHOR]

A major issue among computational respiratory studies is the wide variety of nasal morphologies being studied, caused by both inter-population and inter-subject variations. Six nasal cavity geometries exhibiting diverse geometry variations were subjected to steady inhalation flow rate of 15 L/min. to determine if any consistent flow behaviour could be found. Despite vastly different geometries we were able to identify consistent flow patterns including relatively high velocity in the nasal valve region, followed by flow continuing predominantly in the inferior half of the airway. We also found conformity among models where the inhaled air reached a near-conditioned state by the middle of the nasal cavity. Air from the front of the face reached the olfactory regions while air from the lateral sides of the face moved through the inferior half of the nasal cavity. The ability to predict gross flow features provides a baseline flow field to compare against. This contributes towards establishing well defined flow predictions and be used as a comparison for future larger studies. [ABSTRACT FROM AUTHOR]

Abstract The patterns of primary flow jet core in steam ejector were investigated using computational fluid dynamics (CFD) method. Simulations based on ideal gas model at different operating conditions were performed. The results demonstrate the pattern of primary pseudo-shock flow was affected by the operating conditions obviously when value of operating condition was bigger than that of the critical condition. Compared with the results generated from ideal gas modelling, the primary pseudo-shock flow predicted by wet steam model has a similar pattern and almost the same effective area. But the wet steam model based simulation gives a further downstream choking position and a higher secondary fluid flow velocity at choking position. The above two factors lead to improved entrainment ratio (E m) and increased critical back pressure of steam ejector compared to the results generated from ideal gas modelling. More importantly, the wet steam model predictions show better agreement with the experimental data. Highlights • Study the pumping mechanism of ejector by primary pseudo-shock flow pattern. • The primary pseudo-shock flow pattern affected by the operating conditions. • Secondary fluid flow divided into three modes based on flow pattern analysis. • Operating condition less than critical parameter sustains a stable entrainment process. • Wet steam model captures primary pseudo-shock flow pattern more accurately. [ABSTRACT FROM AUTHOR]

Inhalation exposure to smoke particles emitted from fire grounds could induce respiratory and cardiovascular diseases to firefighters and emergency responders. Understanding the detailed smoke-particle deposition distribution and dosages in nasal airway is of significant value to inhalation risk assessment. In this study, a realistic firefighter nasal airway model, accounting for facial features and external environment was employed to study the inhalation and deposition of smoke particles emitted from a composite deck fire. Particle size distribution and concentration used in the simulation were from the Underwriters Laboratories’ large-scale fire experimental data. Deposition patterns and a method for calculating particles dosimetry (in number, mass and surface area) were analyzed. The dosages in the firefighter nasal cavity, middle turbinate, middle meatus, onto the face and penetrated under various inspiration rates were discussed. The aspiration ratio was also considered in the exposure inhalation risk assessments. Three deposition hot spots were identified in the nasal cavity: nasal vestibule, nasopharynx and middle meatus. The breathing flow rate did not affect the aspiration ratio significantly, while the particle density was an obvious impact factor to aspiration ratio of larger size of micron particles (> 5 µm). Greater than 97% of number dosages were from nanoparticles in all simulated areas, yet the nanoparticle mass dosages and surface dosages only took up around 50%. In addition, majority (about 98%) of particles in composite deck fire scenario penetrated into lower airways or even into the lungs. Meanwhile, the dosages in all metrics onto the face were less than those in nasal cavity, but higher than those in the middle meatus and turbinate. Smaller sized particles (such as nanoparticles) were more likely to deposit onto the face than being inhaled into nasal cavity at high flow rate due to the intensive diffusion. Mass carrier (larger sized) particles tended to run into middle turbinate than to middle meatus. [ABSTRACT FROM AUTHOR]

The interaction of bubbles with flow boundaries has been of high interest for marine engineering; for example, when a propeller is cavitating or air is entrained in the wake of a maneuvering ship, the strong interaction with the boundary layer will lead to the formation of a bubbly wake. To be able to develop the best mitigation strategy, a deep understanding of the associated physics is required. Only a few articles published in open literature address this two-phase fluid system. In the present study, a 3D numerical simulation has been performed to model a bubbly two-phase flow around the DARPA SUBOFF, in which exhaust gas is discharged into the flow around the object to provide a platform for investigating the distribution of the bubbles around a curved body. The two-phase flow is modelled using the Eulerian-Eulerian approach coupled with the MUSIG model. The bubble distribution is characterized based on different gas discharge configurations. It has been found that the boundary layer flow has a strong effect on bubble formation process, particularly encourages the bubble fragmentation. As a result, many small bubbles will be trapped at the aft of the vehicle. [ABSTRACT FROM AUTHOR]

While simplified computational thermal manikins (CTMs) are widely employed in CFD models of occupied indoor spaces in order to save the computational cost, a criterion of simplification is still absent and the effects of CTM simplification are yet not clear. In this study, six CTMs including a 3D scanned CTM and five simplified CTMs generated from various simplification approaches were employed to analyse the impact of CTM simplification on the prediction of airflow field and contaminant transport. Comparison of the predicted airflow field against the published data in the literature demonstrated that CTM simplification has a strong effect on the thermal airflow field prediction in the vicinity of manikin surfaces. For densely occupied indoor spaces such as a train cabin, the error induced by CTM simplification could be enlarged and further cause significant global error to the prediction of contaminant transport. This is especially true when contaminants are released from the CTMs. This study demonstrated that the mesh decimating algorithm is promising to simply CTMs that is not only able to reduce considerable computational cost but capable of maintaining an acceptable predictive error. [ABSTRACT FROM AUTHOR]

The impact of haze-fog on surface temperature, flow pattern, pollutant dispersion and pedestrian thermal comfort are investigated using computational fluid dynamics (CFD) approach based on a three-dimensional street canyon model under different haze-fog conditions. In this study, light extinction coefficient ( K ex ) is adopted to represent haze-fog pollution level. Numerical simulations are performed for different K ex values at four representative time events (1000 LST, 1300 LST, 1600 LST and 2000 LST). The numerical results suggest that the surface temperature is strongly affected by the haze-fog condition. Surface heating induced by the solar radiation is enhanced by haze-fog, as higher surface temperature is observed under thicker haze-fog condition. Moreover, the temperature difference between sunlit and shadow surfaces is reduced, while that for the two shadow surfaces is slightly increased. Therefore, the surface temperature among street canyon facets becomes more evenly distributed under heavy haze-fog conditions. In addition, flow patterns are considerably altered by different haze-fog conditions, especially for the afternoon (1600 LST) case, in which thermal-driven flow has opposite direction as that of the wind-driven flow direction. Consequently, pollutants such as vehicular emissions will accumulate at pedestrian level, and pedestrian thermal comfort may lower under thicker haze-fog condition. [ABSTRACT FROM AUTHOR]

The effects of primary steam superheating on steam condensation in nozzle and the performance of steam ejector were investigated using CFD (computational fluid dynamics) method. Using a wet steam model being proposed in our previous study, simulations based on the primary steam with five superheated levels were performed, and the results demonstrate the superheating operation of the primary steam weakens the spontaneous condensation intensity and postpones its occurrence within the nozzle vicinity. Due to the droplets nucleation refinement for the condensation of superheated steam, the mixing process between the primary and the secondary fluids is improved. Consequently, a higher entrainment ratio is achieved. However, the superheating operation may not exceed 20 K, as its contribution on entrainment ratio improvement is not as significant as 0 K–20 K superheating, and too much superheating will requires more energy as input, which is not a practical solution to further improve the steam ejector pumping performance. [ABSTRACT FROM AUTHOR]

Social distance will remain the key measure to contain COVID-19 before the global widespread vaccination coverage expected in 2024. Containing the virus outbreak in the office is prioritised to relieve socio-economic burdens caused by COVID-19 and potential pandemics in the future. However, "what is the transmissible distance of SARS-CoV-2" and "what are the appropriate ventilation rates in the office" have been under debate. Without quantitative evaluation of the infection risk, some studies challenged the current social distance policies of 1–2 m adopted by most countries and suggested that longer social distance rule is required as the maximum transmission distance of cough ejected droplets could reach 3–10 m. With the emergence of virus variants such as the Delta variant, the applicability of previous social distance rules are also in doubt. To address the above problem, this study conducted transient Computational Fluid Dynamics (CFD) simulations to evaluate the infection risks under calm and wind scenarios. The calculated Social Distance Index (SDI) indicates that lower humidity leads to a higher infection risk due to weaker evaporation. The infection risk in office was found more sensitive to social distance than ventilation rate. In standard ventilation conditions, social distance of 1.7 m–1.8 m is sufficient distances to reach low probability of infection (PI) target in a calm scenario when coughing is the dominant transmission route. However in the wind scenario (0.25 m/s indoor wind), distance of 2.8 m is required to contain the wild virus type and 3 m is insufficient to contain the spread of the Delta variant. The numerical methods developed in this study provide a framework to evaluate the COVID-19 infection risk in indoor environment. The predicted PI will be beneficial for governments and regulators to make appropriate social-distance and ventilation rules in the office. • In standard ventilation conditions, 1.7 m-1.8 m is sufficient to reach low infection. • A social distance of 2.8 m is required to contain the wild virus type. • A social distance of 3 m is not insufficient for the Delta variant. • The infection is higher in a dryer environment due to a stronger evaporation effect. [ABSTRACT FROM AUTHOR]

Abstract: The water-intake temperature is a key factor affecting the system energy efficiency of an open-loop surface water source heat pump system (SWHPS). In addition to the conventional single-pipe water-intake design, we proposed two new design options that can improve SWHP efficiency. The numerical model that pertains to a SWHPS is presented and parameters such as the fluid-intake temperature and energy-saving rate of the heat pump system are analyzed and compared with experimental measurements. Our results demonstrate that on the basis of energy-saving rate, reducing the velocity of the water delivery has no significant influence while intake via multiple ports delivers superior efficiency. In conclusion, the water-intake design impacts on the SWHPS energy-saving rate because of its efficiency in drawing lower temperature water from a water retention body during summer. The method presented in this paper can provide a reference for a more detailed improvement on the energy performance of an open-loop SWHPS. [Copyright &y& Elsevier]

The aqueous humor (AH) flow in the anterior chamber (AC) due to saccadic movements is investigated in this research. The continuity, Navier-Stokes and energy equations in 3D and unsteady forms are solved numerically and the saccadic motion was modeled by the dynamic mesh technique. Firstly, the numerical model was validated for the saccadic movement of a spherical cavity with analytic solutions and experimental data where excellent agreement was observed. Then, two types of periodic and realistic saccadic motions of the AC are simulated, whereby the flow field is computed for various saccade amplitudes and the results are reported for different times. The results show that the acting shear stress on the corneal endothelial cells from AH due to saccadic movements is much higher than that due to normal AH flow by buoyancy induced due to temperature gradient. This shear stress is higher on the central region of the cornea. The results also depict that eye saccade imposes a 3D complicated flow field in the AC consist of various vortex structures. Finally, the enchantment of heat transfer in the AC by AH mixing as a result of saccadic motion is investigated. [ABSTRACT FROM AUTHOR]

Abstract: A computational model was developed for studying the flow field and particle deposition in a human upper airway system, including: nasal cavity, nasopharynx, oropharynx, larynx and trachea. A series of coronal CT scan images of a 24 year old woman was used to construct the 3D model. The Lagrangian and Eulerian approaches were used, respectively, to find the trajectories of micro-particles and concentration of nano-particles. The total and regional deposition fractions of micro/nanoparticles were evaluated and the major hot spots for the deposition of inhaled particles were found. [Copyright &y& Elsevier]

Abstract: The inhalation of toxic particles such as asbestos fibres through the nasal airway has been found to cause harmful damage to the respiratory system. This study made use of CFD techniques to investigate deposition of fibrous particles in a human nasal cavity. A 3D computational model was created from CT scans which provided the framework to study the flow and deposition of fibres at a constant flow rate of 7.5L/min. The effects of the fibres’ elongated shape, density and size were incorporated into empirical drag correlations and the fibre trajectories were recorded through a Lagrangian tracking scheme. In general, good agreement was found in the right cavity and an overprediction in the left cavity. The major cause of deposition differences was in the geometrical variations between subjects as well as the left and right cavities. The dominant mechanism of deposition was by inertial impaction, with a majority of the particles depositing in the anterior region. It was found that asbestos had a very low deposition, , and was independent of fibre length. In comparison, the carbon fibre exhibited increases in deposition as the fibre length increased. A parameter which represents the mass per unit length was used to equate the for different fibre lengths. [Copyright &y& Elsevier]

Inhaled viral droplets may immediately be expelled and cause an escalating re-transmission. Differences in the deposition location of inhaled viral droplets may have a direct impact on the probability of virus expelling. This study develops a numerical model to estimate the region-specific deposition fractions for inhalable droplets (1–50 μ m) in respiratory airways. The results identified a higher deposition fraction in the upper airways than the lower airways. Particularly for droplets larger than 10 μ m, the relatively high deposition fraction in the oral/laryngeal combined region warns of its easy transmission through casual talking/coughing. Moreover, considering droplet sizes' effect on virus loading capacity, we built a correlation model to quantify the potential of virus expelling hazards, which suggests an amplified cascade effect on virus transmission on top of the existing transmission mechanism. It therefore highlights the importance of considering the instant expelling possibilities from inhaled droplets, and also implies potentials in restricting a rapid secondary transmission by measures that can lower down droplet deposition in the upper airways. • The rapid re-transmission of COVID-19 via close contact people is probable. • 1–50 μ m particles account for most of particles from a cough. • The high deposition rate in the oral/laryngeal region for droplets larger than 10 μ m warns of the easy expelling for re-transmission. • The re-transmission potential is estimated as 14.9% in the oral–nasal inhalation scenario. [ABSTRACT FROM AUTHOR]