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The present study investigated the transmission of exhaled particles generated by coughing inside a car cabin, considering eleven different window opening configurations. The results indicated that particle dispersion and removal were mainly affected by the airflow, which was largely determined by the window opening configurations. Notably, efficient ventilation and a large number of open windows did not necessarily result in lower infection risk. Given the complex structure and formation of intricate airflow patterns within the cabin, airborne particles could spread throughout the cabin and deposit on the interior walls. As particles tended to escape or deposit rapidly within the first 10 s, precautionary measures were necessary during this time frame following a passenger's coughing activity. Furthermore, closing the window adjacent to the driver effectively reduced the proportion of exhaled particles passing through the driver's breathing zone due to the rear-in and front-out airflow pattern, thus mitigating the risk of infection. [ABSTRACT FROM AUTHOR]

The cleaning system is a critical component of the sugarcane chopper harvester, facing challenges such as high impurity rate, elevated power consumption, and an inadequate understanding of the cleaning mechanism. This study aims to simulate the process of removing extraneous matter (represented by sugarcane leaves) from the cleaning system by employing a coupling approach of computational fluid dynamics (CFD) and the discrete element method (DEM) to determine the speed of the extractor fan. Initially, a CFD model was established to analyze the airflow field within the extractor, and its accuracy was verified on a test bench for the cleaning system. Subsequently, a DEM model was developed for sugarcane billets and leaves, which was then integrated with the CFD model to form a gas–solid coupling model. The efficacy of this integrated model was confirmed through experimental measurements of impurity rate. Furthermore, a ternary quadratic regression orthogonal combination design was utilized in the gas–solid coupling simulation to assess the impacts of feed rate, leaf–stalk ratio, and extractor fan speed on impurity rate. Finally, the extractor fan speeds were obtained for various feed rates and leaf–stalk ratios under impurity rates of 5%, 6%, 7%, and 8%. This research can guide in controlling the extractor fan speed during sugarcane chopper harvester field operations and can serve as a foundation for extractor fan design. [ABSTRACT FROM AUTHOR]

Flexible psammophytes play an important role in controlling soil wind erosion and desertification, owing to their characteristics. Although flexibility of psammophytes has been considered in previous studies, the interaction between flexible psammophytes and the surrounding airflow field still remained unclear. In this study, we used the Young's modulus to describe plant flexibility and conducted a 3D computational fluid dynamics simulation using a standard k-e model and a fluid-structure interaction model. Taking Caragana korshinskii (Caragana), a typical psammophyte, as the research object, we constructed 3D geometric models with different diameters to simulate the airflow field around the flexible psammophytes. By comparing with the simulation results of rigid plants and simulation results of flexible plants at different wind speeds, we could verify the rationality of the simulation method. Based on the simulation results, the maximum swing amplitude of the model and the Young's modulus were found to have a negative correlation, presenting an exponential functional relationship with good fitting. The relationship between the actual Young's modulus of the plant branches and that of different diameter models in the numerical simulation was also established. This study is expected to improve our basic understanding of the interaction between flexible psammophytes and the surrounding airflow field, and provide some qualitative reference for the numerical simulation of the airflow field around flexible psammophytes. [ABSTRACT FROM AUTHOR]

To provide reference for the design of the air-suction tea sorting device, the coupled numerical simulation model was established by the coupling method of computational fluid dynamics (CFD) and discrete element method (DEM) with tea of different quality as test objects, and the model was verified experimentally. Regarding tea particles of different quality, when the test tea particle mass was 0.215, the test value was located in the simulation value with a minimum error of 9 mm, which an error rate of 3.33%, and maximum error of 19 mm, with an error rate of 7.03%. When the test tea particle mass was 0.145, the minimum error of the test value was 5 mm and the error rate was 1.54%, and the maximum error was 9 mm and the error rate was 3.33%. The verification results established the accuracy of the model. During the suspension test and simulation, tea particles were affected by the air flow field of the observation tube, and tea particles fluctuated. During suspension, tea particles were attached to the inner wall of the observation tube under the action of the air flow field. An in-depth study showed that the relationship between the different distances from the initial position of the particles during suspension and the simulation time was a peak function. The extreme function is used to fit the actual trajectory, and the fitting degree is good. The fitting degree of the particle closest to the initial position was 0.9455, and the fitting degree of the particle farthest from the initial position was 0.9981. [ABSTRACT FROM AUTHOR]

To study the characteristics of nasal airflow in the presence of nasal cycle by computational fluid dynamics. CT scan data of a healthy Chinese individual was used to construct a three-dimensional model of the nasal cavity to be used as simulation domain. A sinusoidal airflow velocity is set at the nasal cavity entrance to reproduce the breathing pattern of a healthy human. There was a significant difference in the cross-sectional area between the two sides of the nasal cavity. Particularly, the decongested side is characterized by a larger cross-section area, and consequently, by a larger volume with respect to the congested side. The airflow velocity, pressure, and nasal resistance were higher on the congested narrow side. The temperature regulation ability on the congested narrow side was stronger than that on the decongested wider side. During the nasal cycle, there are differences in the nasal cavity function between the congested and decongested sides. Therefore, when evaluating the impact of various factors on nasal cavity function, the nasal cycle should be considered. [ABSTRACT FROM AUTHOR]

A new type of gust generator generates the airflow oscillation in the wind tunnel through the Coanda effect of the unsteady trailing edge blowing, which has been shown to have strong potential for accurately simulating discrete gusts. It is necessary to study the relationship between the generated gust characteristics and the control parameters of such devices in order to optimize the design performance and improve gust simulation capabilities. By solving the compressible unsteady Reynolds-averaged Navier–Stokes (URANS) equations, the computational fluid dynamics model of the subsonic airflow past the gust generator in the wind tunnel was presented. The effects of jet momentum, frequency, and spanwise blowing ratio on gust intensity, shape, and spatial uniformity were investigated. Results indicate that the intensity of gusts is positively correlated with jet momentum and frequency. The gust shape matches well with the normalized jet momentum coefficient curve. However, when the frequency increases to above 10 Hz, the gust shape differs significantly from expectation due to the appearance of reverse wave peaks. In addition, the mechanism of the impact of the sidewall and partial spanwise blowing on gusts was revealed. In the three-dimensional situation, streamwise vortices are formed on the sidewall and at the spanwise position where the blowing stops, respectively. This results in an increase and noticeable nonuniformity in gust amplitude. When the blowing with a 15% spanwise length near the sidewall is turned off, the gust amplitude at the symmetry plane increases by nearly 40% due to the main vortex being closer to the main flow. The result provides a physical explanation for the availability of this operation to reduce gust attenuation. [ABSTRACT FROM AUTHOR]

To improve its cleaning performance, the peanut sheller's air–screen cleaning device was used as the research object, and a numerical simulation was carried out. A scheme was proposed to optimize the installation angle of the screen surface of the air–screen cleaning device, and the influence of the airflow velocity of the sieve surface before and after the structural improvement of the machine on the airflow distribution of the whole chamber was evaluated. At the same time, the computational fluid dynamics–discrete element method (CFD–DEM) of coupling simulation was used to carry out single-factor simulation tests on the improved air–screen cleaning device, analyze the movement trajectory, velocity, and displacement of the extrudates in the cleaning chamber, characterize the separation law of extrudates, and determine the parameter ranges for each factor. In addition, based on the central composite Box–Behnken design, an orthogonal simulation test was carried out with three factors, including fan speed, amplitude, and vibration frequency, and the influence of each factor on the kernel loss rate and impurity rate was investigated. Furthermore, the influencing factors were optimized, and the optimal parameter combination was obtained; when the fan speed was 1682.72 r/min, the amplitude was 3.74 mm, and the vibration frequency was 492.86 Hz, it was more conducive to the cleaning of kernels. Finally, the accuracy of the simulation and optimization methods was verified via the machine test, and the optimal parameter combination was obtained: at a fan speed of 1680 r/min, an amplitude of 3.7 mm and a vibration frequency of 490 Hz were achieved, and the kernel loss rate and impurity rate were 2.01% and 2.42%, 3.71 and 4.42 percentage points lower than those before optimization, respectively. [ABSTRACT FROM AUTHOR]

With the spread of sustainability concepts, due to the global energy crisis and the unrestrained consumption of natural resources, the importance of rational use and reduction of energy consumption has been intensified, albeit in short steps. This concern has taken up bioclimatic concepts in buildings, especially housing buildings for low-income people, aiming at improving the quality of housing production in terms of its habitability. The objective of this research is to theoretically and experimentally study the natural ventilation in a housing building, which fits into the low-cost pattern. The use of Computational Fluid Dynamics to predict natural ventilation was adopted as a tool to perform these analyses. Experiments were carried out by visiting the study area to collect data on air velocity, temperature, and relative humidity in all rooms of the residence in order to carry out the intended analyses. Computer simulation of natural ventilation considering the building with the doors and windows open and with fixed geometry was performed. Results proved that the proposed mathematical model was able to reproduce, with rich details and physical coherence, the internal and external air flow inside the building, indicating better internal ventilation performance in environments that have door and window openings, with recesses, revealing the importance of cross ventilation to reduce the internal temperature and consequent improvement in thermal comfort. The idea is to help civil engineers and specialists in the economically viable design of low-cost buildings from the economic, social, and thermal comfort points of view. [ABSTRACT FROM AUTHOR]

Background and Objectives: This paper presents a unique study that links the physical conditions in the nasal passage with conditions that favour the development of bacterial strains and the colonization of the mucous membranes of the nose and paranasal sinuses. The physical parameters considered were air flow, pressure, humidity, and temperature. Materials and Methods: Numerical models of the human nose and maxillary sinus were retrospectively reconstructed from CT images of generally healthy young subjects. The state-of-the-art numerical methods and tools were then used to determine the temperature, humidity, airflow velocity, and pressure at specific anatomical locations. Results: The results were compared with optimal conditions for bacterial growth in the nose and sinuses. Conclusions: Temperature, humidity, air velocity, and pressure were shown to play critical roles in the selection and distribution of microorganisms. Furthermore, certain combinations of physical parameters can favour mucosal colonisation by various strains of bacteria. [ABSTRACT FROM AUTHOR]

Featured Application: In this study, a computational fluid dynamics (CFD) model was developed for a pregnant sow piggery with centralized ventilation to reveal the distribution of temperature, humidity, and airflow velocity. After verifying the CFD model, the location of the air outlets and the velocity at the air inlets was also examined to obtain the optimal structure and control parameters. The average values, non-uniformity coefficient, and comfort levels were used to evaluate the performance of the piggery under these different parameters. (1) Background: The thermal environment in a pregnant sow piggery is affected by physical parameters such as air temperature, relative humidity, and airflow velocity. However, it is challenging to conduct experimental studies due to the high cost. (2) Methods: Computational fluid dynamics (CFD) was used to study the distribution characteristics of airflow in a pregnant sow piggery with centralized ventilation. (3) Results: The results show that the maximum difference between the simulated and experimental temperature was less than 1.54 °C, and the simulated and tested relative humidity difference was less than 10% RH. Incorporation of a middle air outlet is beneficial for increasing the uniformity of temperature distribution, as studied by comparing the temperature and humidity uniformity coefficient of the two air outlet locations, but the uniformity of humidity distribution will be reduced. With an increase in velocity, the temperature shows a downward trend and the relative humidity shows an upward trend. (4) Conclusions: The most suitable position for the outlet is the middle, with an associated airflow velocity of 0.5 m/s. This study revealed the variation in flow field distribution and air distribution in the pregnant sow piggery as a consequence of changes in ventilation structure, which has certain significance as a reference for the optimization of airflow in intensive pregnant sow piggeries. [ABSTRACT FROM AUTHOR]

Background: The truncation level of human airways is an influential factor in the analysis of respiratory flow in numerical simulations. Due to computational limitations and limited resolution of diagnostic medical imaging equipment, a truncated geometry of airways is always investigated. Objective: This study aimed to employ image-based geometries with zero generation and 5th-generation truncation levels and assess bronchial airways truncation's effect on tracheal airflow characteristics. Material and Methods: In this numerical study, computational fluid dynamics was employed to solve the respiratory flow in a realistic human airway model using the large eddy simulation technique coupling with the wall-adapting local eddy-viscosity (WALE) sub-grid scale model. The accuracy of numerical simulations was ensured by examining the large eddy simulation index of quality and Kolmogorov's K-5/3 law. Results: The turbulent kinetic energy along the trachea has increased abnormally in the geometry with the zero-generation truncation level, and more severe fluctuations occurred in the velocity field of this geometry, which increased the tendency of each point to rotate. Compared to the extended model, the airflow's more chaotic behavior prevented larger-scale vortices from forming in the geometry with the zero-generation truncation level. Larger-scale vortices in the extended model caused the primary flow passing next to the vortices to accelerate more intensely, increasing the wall shear stress peaks in this geometry. Conclusion: Eliminating the bronchial airways caused changes in tracheal airflow characteristics. [ABSTRACT FROM AUTHOR]

Purpose. Due to the poor ventilation and air stagnation in the radiation therapy ward, it is easy to cause respiratory disease transmission, which brings about the public health safety problem of infection. In order to alleviate this problem, we propose a research method based on computational fluid dynamics (CFD). Method. A three-dimensional model of a radiation therapy ward is established, and the CFD software framework is used to numerically simulate the air flow field in the constrained radiation therapy ward environment. We computed the influence of the spray speed, particle size, and inlet content of respiratory droplets on the flow and spread of multidrug-resistant bacteria. Results. In the range of the horizontal transmission line X from 0 to 3 meters, when the transmission speed (V) is 35 m/s, the multidrug-resistant bacteria concentration reaches the highest value. In the range of the vertical transmission line Y from 0 to 3 meters, when V is 35 m/s, the multidrug-resistant bacteria concentration reaches the highest value. Conclusion. A large amount of data shows that there is a positive correlation between the respiratory droplet spray velocity, inlet content, and the multidrug-resistant bacteria flow propagation speed and concentration distribution. The respiratory droplet size mainly affects the peak concentration of the multidrug-resistant bacteria flow propagation. [ABSTRACT FROM AUTHOR]

Achieving an optimal cooling of the generator unit is indispensable for high working performance. In this work, computational fluid dynamics analysis on the flow field of the conventional type and silent type of the S688CCS series generator unit is conducted, and design optimization of the generator unit with poor cooling is studied based on flow field analysis results. Flow field simulation results indicate that the total cooling air quantity of the silent type generator unit is lower than that of the conventional type generator unit, and the cooling air quantity of the radiator is also lower than that of the conventional type generator unit, which is not conductive for the cooling of the silent type generator unit. The flow field optimization is achieved by adopting the single variable control method to improve the structure of the fan cover, silent components for silence, adjacent structure, and air inlet grille. The corresponding structure optimization scheme is put forward. After optimization, the air quantity for the cooling radiator of the silent type generator unit is 44.33% higher than that of its original structure, and the total cooling air quantity is higher than that of the conventional type generator unit. The research results in this work can provide a theoretical basis for the design of the cooling air flow path of generator units for achieving an optimal cooling performance. [ABSTRACT FROM AUTHOR]

Most of the sprayers used in fruit trees are of the type of jet transported, which use an air flow produced by a fan to transfer the pesticide drop to the tree. In the energy balance of agricultural sprayers assisted by air flow, it is proposed that between 50 and 65% of the power in these equipment is used by the fan that produces the air flow. Air stream sprayers produce high pollution due to high levels of drift. Using the Computer Modeling of Fluids (CFD) the aerodynamics of the air flow is analyzed based on the geometric and kinematic parameters of the fan, which allows to determine the air flow with better characteristics. The selected regimens assess the quality of the plant cover, using image treatment methods. In this case, a work regime is achieved that decreases the amount of power required, maintaining the quality of the treatment. [ABSTRACT FROM AUTHOR]

• Wind towers incorporated to a greenhouse to provide wind driven natural ventilation. • Natural ventilation performance of the wind towers was assessed by CFD simulations. • CFD model was validated by flow visualization, point measurement, and PIV measurement. • At a wind speed of 3 m/s, the wind towers provided the recommended air change rate. • At a wind speed of 3 m/s, air velocity at crop height was within recommended values. In this study, the air change rate and airflow distribution inside a greenhouse equipped with wind towers were analyzed using Computational Fluid Dynamics (CFD) simulations, considering different wind speeds (1–5 m/s) and incident angles (0–45°). The validation methods included smoke visualization, hot wire velocity point measurements, and Particle Image Velocimetry (PIV) measurements. The visualized and simulated flow regimes exhibited fair agreement. The average discrepancy between the hot wire velocity point measurements and simulated results was about 7.96%. The predicted vector fields in the inlet and outlet wind towers demonstrated good qualitative agreement with the corresponding PIV measurements. The discrepancy between the predicted and measured maximum air velocity in the inlet tower was 15%, while it was 3% in the outlet wind tower. At an external wind speed of 3 m/s and normal incidence angle, the average velocity of the airflow entering the greenhouse was 0.65 m/s (about one air change per minute), while the average air velocity in the greenhouse was 0.44 m/s. The average air velocity inside the greenhouse at a crop height (1 m) ranged from 0.3 to 1.8 m/s, which is within the optimum range of recommended air velocities for greenhouses. [ABSTRACT FROM AUTHOR]

A system with optimum thermal control and noise control is proposed to allow placement of servers at workspace for low operation office cost. A computational fluid dynamics (CFD) model is developed to predict the air flow and temperature distribution of the system. To improve the accuracy of the simulation, the geometry of the axial-flow fan is reproduced in detail and the rotor region is treated with the multiple reference frame model. A porous model is applied to describe the hydraulic and thermal behavior of the evaporator. The integrated system simulation model is validated by measurements. Four layouts of fans are proposed to analyze the airflow organization and temperature distribution. The inhomogeneity of the temperature field is quantitatively evaluated via information entropy and variance. The results reveal that the airflow organization scheme avoids the occurrence of an evident stagnant zone or a hot spot. There are low-velocity zones with insufficient heat transfer in the evaporator. Increasing the number of fans can improve the heat transfer and result in a more uniform temperature distribution. Setting up ventilation fans to increase the ventilation rate of the server is an effective way to meet the challenges of higher heat density. [ABSTRACT FROM AUTHOR]

In this study, some of the optimal parameters for a new-style marine axial flow fan are defined by using numerical simulation and experimental tests with a large marine axial flow fan, based on the analysis of the blade perforation’s influences on its internal flow field and aerodynamic noise characteristics. Test result shows that the noise reduction for the axial flow fan with perforated blade is about 3 dB when the blade perforation diameter D is 10 mm and its deflection angle α is 45°. The results of the study show that there is an inhibitory effect on the discrete noise of axial flow fan with perforated blade on the tip area, and its total noise level emerged as the fluctuated distribution characteristics with the increase in the perforation diameter D and reduced along with the increase in the deflection of perforation angle α, at the same time varied as a linear characteristics, which can be reasonably explained by the acoustic interference theory. The results of the study have also further confirmed that the improvement of the flow of axial flow fan with perforated blade helps to reduce the pressure pulsation amplitude caused by the turbulence of the blade surface boundary layer, thereby suppressing the back-flow and vortex from the pressure surface to the suction surface efficiently. It is indicated that the improved vortex shedding phenomenon at the blade trailing edge after perforation on the area of blade tip is the main reason for the aerodynamic noise reduction of axial flow fan. [ABSTRACT FROM AUTHOR]

To keep pace with the growing energy demand, legacy air-cooled data centers begun implementing energy efficiency strategies: Perfecting air flow management, enhancing cooling air delivery and collecting (re-using) waste heat. However, one may wonder: What is the magnitude of these energy savings? Is it worth the effort? The second law of Thermodynamics offers unique insights about energy wasteful practices by estimating the Exergy Destruction in a system. Exergy is equivalent to the “available energy”, hence the presence of inefficiencies “Destroys Exergy”. In this work, we numerically modeled the behavior of the airside in an existing data center laboratory (CEETHERM) using the commercial Finite Volume software 6SigmaDCX TM . The collected numerical data were used to post-process two Exergy Destruction approaches (Direct and Indirect method), whose behavior was tested against: (1) A simplified study case and (2) Actual data center flow. Both approaches worked well against the study case, although for case (2) the Indirect Method–which neglects turbulence effects–predicted zones of artificial negative Exergy Destruction. The Direct Method permitted associating large inefficiencies in the airflow to hot–cold airstream pre-mixing and important pressure drops in the raised floor. The airside Exergy Destruction encompassed a significant amount of the total irreversibilities in the system, suggesting that mitigating (or eliminating) it, can substantially improve energy saving efforts, especially in legacy data centers. [ABSTRACT FROM AUTHOR]

Click here and insert your abstract text. A numerical simulation of the airflow and thermal field for a quiet power vehicle (QPV) compartment was presented in order to regulate the airflow and dissipation. A general three-dimension computational fluid dynamics (CFD) model, based on the Navier-Stokes equations and Realizable k−ɛ turbulence model, was applied to study the airflow and heat dissipation in the QPV compartment. The airflow fields and pathlines of the airflow in the QPV compartment, the temperature fields of generator sets and diesel exhaust mufflers were calculated. The simulation results showed that the airflow moved fast and intensively at the place that was close to diesel generator radiator fan, which was useful for improving cooling effect of the generator sets and radiator; the temperature of generator sets and mufflers was relatively high, which would be beyond to 80°C, and an axial fan was designed on the gen-set chamber wall to improve its ventilation for cooling, the results showed the temperature dropped about 2°C-8°C. Moreover, experiments were conducted to measure the temperatures referring to some testing standards for QPV, and comparable results were obtained between the simulation and measurements, which showed that the addition of the axial fan was reasonable. [ABSTRACT FROM AUTHOR]

In this study, a fully unsteady computational fluid dynamics (CFD) model was used and the transient airflow properties during the entire breathing cycle, including inhalation and exhalation in a human nasal cavity, were evaluated. Unsteady particle tracking was performed to find the particle motion and deposition in the nasal airway using a Lagrangian approach. In most of earlier computer simulations, the assumption of quasi-steady or steady airflows averaged over the inhalation cycle were typically used to reduce the computational cost. In the present work particular attention was given to assessing the accuracy of these assumptions and their consequence on particle deposition in a human nasal cavity with paranasal sinuses. The simulation results for the airflow field showed significant differences between the unsteady and quasi-steady cases at low breathing rates near the beginning and end of the inspiration cycle. For breathing under a rest condition with a frequency of 0.25 Hz, the quasi-steady airflow assumption in the nasal cavity was found to be reasonable when the instantaneous Strouhal number was smaller than 0.2. The instantaneous deposition of micro-particles was also studied, and the effects of unsteady accelerating and decelerating flows on the deposition fraction were examined. The simulation results showed that the deposition fractions were affected by the accelerating and decelerating airflows during the inhalation phase. The simulated micro-particle depositions under the cyclic breathing condition were compared with those for steady breathing with an equivalent mean airflow rate. It was found that while the general trend was similar, the steady breathing simulation with the mean airflow rate during inhalation cannot accurately predict the total micro-particle deposition for cyclic breathing, particularly for 1–5 µm particles. Furthermore, the predicted regional depositions by the steady breathing were markedly different from those obtained under cyclic breathing. [ABSTRACT FROM AUTHOR]

This study established the three-dimensionally random structures of fibrous filters, with fiber diameters in the range of 10 to 20 μm and solid volume fractions (SVFs) in the range of 12 to 19%, in order to explore the filtration process inside the fibrous filters. The computational fluid dynamics (CFD), coupled with the discrete element method (DEM), was applied to simulate the airflow, the motion of particles, and the interactions between particles, fibers and fluid. The filtration efficiency and pressure drop of the filters were calculated and analyzed in CFD-DEM and the results were validated by the semi-analytical models. In addition, the correlations between filtration performance and fiber structures, particle parameters and fluid properties were investigated. It was found that the changes in key parameters (e.g., particle diameter, fiber diameter and fluid velocity) had significant effects on filtration performance. [ABSTRACT FROM AUTHOR]

Particle deposition in two-dimensional turbulent duct air flows with uniform, expanding or contracting cross-section was studied by CFD simulation. The Reynolds stress turbulent model (RSM) with UDF correction and discrete particle model (DPM) were adopted to predict air flow fields and particle deposition rate. After numerical validation of air velocity profiles and particle deposition velocity in uniform duct, the air flow field structures, flow drag and particle deposition behaviors in expanding and contracting ducts with different air velocities and particle sizes were investigated and compared with uniform duct case. It was found that particle deposition velocity is overall reduced in expanding duct while enhanced in contracting duct. However, the modification magnitude of deposition velocity is significant discrepant for different particle sizes due to the role of near-wall turbulent eddies. For expanding duct cases, the particle deposition velocities are reduced about one or two orders of magnitude for large particles ( d p > 3 μ m ) but less than 5 times for small particles ( d p < 3 μ m ), compared with uniform duct cases. For contracting duct cases, the particle deposition velocities are increased less than 7 times for large particles while about 20–60 times for small particles. Besides, the deposition mechanisms of particles in expanding and contracting duct were also studied and discussed. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulations are conducted to investigate the impact of the blockage of vehicles in tunnel on the performance of semi-transverse smoke control system. Two well-known CFD tools, i.e., FDS 6.0.1 and ANSYS FLUENT 14, are used for mutual verification. The smoke pattern in tunnel without blockage is studied as a benchmark and the proposed semi-transverse smoke control system can maintain tenable conditions for safe egress. The scenarios with blockages of 2m and 4m high are studied respectively. The simulation results demonstrate the presence of blockage significantly changes the flow pattern in tunnel. The bulk mass flow rates are reduced from the blocked side while increased from the unblocked side. The unbalanced airflow drives more smoke to the blocked side and makes this side impassable for evacuation within a few minutes. The scenarios with symmetric blockages of the same heights are further studied for comparison and smoke is well confined within the defined smoke zone. Tentative simulations are conducted to improve the environment in tunnel by increasing the smoke extraction rate. For a blockage ratio of 26.6%, even a 50% increase in the smoke extraction rate can hardly maintain tenable condition throughout the tunnel. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the transient 3D numerical simulations of natural convection of air around a circular finned tube (24.9 mm OD ) kept in a small chimney. The annular plain fins are considered in this study. The effects of fin spacing to fin diameter ratio (0.057 mm ⩽ S / D f ⩽ 0.24 mm), chimney height (400–1000 mm) and ambient to surface temperature difference (10 K ⩽ T s ⩽ 65 K) on the heat transfer and the driving force have been investigated. The results are presented in terms of the temperature contours, velocity vectors, heat transfer and the driving force. It has been found that the heat transfer coefficient increases with an increase in the fin spacing upto an optimum value ( S = 8 mm) for all the fin geometries, and beyond S = 8 mm, the heat transfer coefficient decreases. The separation of the thermal boundary layer with a variation in the fin spacing and its effects on the heat transfer and driving force has been shown. For a fixed fin spacing, the heat transfer rate, heat transfer coefficient and the driving force increases with an increase in the fin diameter, however, for D f > 41 mm, the rate of increase in the heat transfer coefficient reduces. The heat transfer coefficient increases with an increase in the chimney height and it has been found that the effect of chimney height on the heat transfer coefficient is a resultant effect of the air outlet temperature and the driving force generated by the chimney. The base to ambient temperature difference has been varied to observe the temperature sensitivity on the heat transfer coefficient and flow patterns. In the last section, various circular and elliptical tube designs have been investigated, and it is found that, the elliptical tube with minimum ellipticity ( b / a = 0.33) and circular tube with smallest diameter (7 mm) provides better heat transfer coefficient than the other circular and elliptical designs. [ABSTRACT FROM AUTHOR]

An accurate prediction of flow and thermal fields around an human body provides valuable information in designing an efficient ventilation system. This study tries to address this issue by investigating the flow structure around an human body subjected to a displacement ventilation system through the computational fluid dynamics (CFD). For this purpose, both the large eddy simulation (LES) and hybrid LES–RANS methods are employed. The RAST one-equation model (OEM) and the dynamic Smagorinsky model (DSM) are utilized as a sub-grid scale (SGS) modeling for the LES while for the hybrid LES–RANS method, the SST–SAS version is applied. Predicted results are compared with available experimental measurements in the literature. Comparisons show that the OEM has a better performance in reproducing the correct level of velocity and temperature fields around the body as well as in other locations of the room while the SST–SAS model fails to predict these quantities accurately, especially around the occupant's body. Above all, the OEM provides a good compromise between accuracy and robustness in predicting the airflow and temperature fields in an indoor environment. [ABSTRACT FROM AUTHOR]

We investigate the average turbulent wind field over a barchan dune by means of Computational Fluid Dynamics. We find that the fractional speed-up ratio of the wind velocity over the three-dimensional barchan shape differs from the one obtained from two-dimensional calculations of the airflow over the longitudinal cut along the dune's symmetry axis - that is, over the equivalent transverse dune of same size. This finding suggests that the modeling of the airflow over the central slice of barchan dunes is insufficient for the purpose of the quantitative description of barchan dune dynamics as three-dimensional flow effects cannot be neglected. [ABSTRACT FROM AUTHOR]