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This article presents a study on the capture velocity of local exhaust ventilation (LEV) using a specially designed workstation within a laboratory setting. The workstation featured a worktop with dimensions of 90 cm width and 45 cm depth, and the exhaust duct was positioned near the pollutant source, considering the intended operation of the LEV system. The worktop was divided into squares for precise documentation and remeasurement. A supply duct above the worktop provided controlled fresh airflow. Smoke was used to visualize airflow patterns. The measurements focused on air velocity and turbulence intensity, aiming to understand flow structures and vortices. Various capture rates were tested at specific measurement points. The study revealed that the central capture lines yielded the highest efficiency. To address air extraction from behind the exhaust duct, a back sheet panel was introduced. The results showed that installing a back sheet enhanced capture velocities. The findings contribute to understanding LEV efficiency and the importance of proper design and adjustments for effective containment of contaminants in the occupational environment. [ABSTRACT FROM AUTHOR]

Human airways represent a complex flow system with a spatially and temporally variable character of air flow during respiration. In this paper, we experimentally studied the oscillatory flow of air with monodispersed micron-sized liquid particles in a transparent, anatomically realistic model of human upper airways and several bronchi generations using phase-Doppler anemometry (PDA). The PDA provided point-wise high-frequency measurements of axial velocities of individual aerosol particles in multiple positions of the airways (in the trachea and the upper bronchi) for three breathing regimes with a sinusoidal course. Typical time-resolved velocity plots at several positions within the model were documented and analysed using dimensionless criteria. Local mean air velocity and turbulence time-lines disclosed specific flow dynamic features in the multiple bifurcation system, namely the transit of vortical structures, oscillations induced by flow reversals, and inspiratory flow separations behind bifurcations. The results elucidated the laminar, transitional and turbulent flows during inspiratory and expiratory breathing phases. The character of the flow varies significantly with position in the airways, while the breathing regime has a generally low effect on the flow character. Inspection of the flow in the terminal branches indicated the need to add further branches for more realistic results there. [ABSTRACT FROM AUTHOR]

In this research, an angular contact ball bearing with two‐half inner rings is used as a carrier. Considering the two‐phase flow characteristics of oil and air in the bearing, the flow characteristics of lubricating oil inside the bearing with under‐race lubrication are studied. Based on the volume of fluid (VOF) method and the standard k–ε turbulent flow model, the characteristics of oil and air two‐phase flow inside the ball bearing are analysed. The bearing internal pressure field distribution, streamline distribution, and other flow properties for the different radial working clearances, pocket clearances and guide clearances are determined. The distribution of the lubricating oil in key areas is observed. The oil phase volume fraction of the key lubrication areas, such as the cage pocket surface and the inner and outer ring surfaces is used to evaluate the influence of different structural parameters on the bearing lubrication performance. The lubrication influences of the inner and outer guides of the cage are evaluated, and the internal flow characteristics of the bearing are analysed with different guide clearances. The results show that with the radial working clearance range from 0.100 to 0.145 mm, the pressure in the working contact area of the bearing decreases 26%. The pocket clearance ranges from 0.48 to 0.28 mm, and the pressure in the working contact area of the bearing significant increases from 0.642 to 1.165 MPa. From this perspective, the larger the radial working clearance and pocket clearance are, the more favourable it is for bearing lubrication. For bearings with under‐ring lubrication, when the bearing adopts outer guidance, the distribution of lubricating oil in the key areas of the bearing is worse than that for internal guidance. However, the pressure in the working contact area of the bearing slightly increases from 0.642 to 0.759 MPa with the inner guide clearance increasing from 0.4 to 0.8 mm. [ABSTRACT FROM AUTHOR]

Air velocity is one of the key parameters affecting the sensation of thermal comfort. In mixing ventilation, the air is most often supplied above the occupied zone, and the air movement in a room is caused by jets that generate recirculating flows. An effective tool for predicting airflow in a room is CFD numerical modeling. In order to reproduce the air velocity distribution, it is essential to select a proper turbulence model. In this paper, seven Eddy–Viscosity RANS turbulence models were used to carry out CFD simulations of a sidewall air jet supplied into a room through a wall diffuser. The goal was to determine which model was the most suitable to adopt in this type of airflow. The CFD results were validated using experimental data by comparing the gross and integral parameters, along with the parameters of the quasi-free jet model. The numerical results obtained for Std k-ε and EVTM models were most consistent with the measurements. Their error values slightly exceeded 15%. On the contrary, the k-ω and RNG k-ε models did not reproduce the quasi-free jet parameters correctly. The research findings can prove beneficial for simulating air distribution in supplied air jets during the initial conceptual phases of HVAC system design. [ABSTRACT FROM AUTHOR]

An experimental investigation was performed to study the effect of the central air flow on the turbulent inverse diffusion flame height. The study conducted a series of experiments using two coaxial burners with different nozzle sizes in the atmospheric environment. The experimental results show that the central air flow influences the mixing process between the air/fuel jets and the flame morphology. The inverse diffusion flame height decreased with the increase in air flow rate under the same heat release rate due to the strengthening of air/fuel mixing. The flame height decreases sharply when the air flow is turbulence flow. The air–fuel momentum ratio was found to estimate the inverse diffusion flame height. The momentum flux and buoyancy flux of inverse diffusion flame have been analyzed. Considering the combinational effect of momentum flux and buoyancy flux on the inverse diffusion flame, a new correlation between the inverse diffusion flame height, air flow rate, and heat release rate has been established which provides a valuable resource for designing the inverse diffusion flame burners. [ABSTRACT FROM AUTHOR]

Computational rhinology is a specialized branch of biomechanics leveraging engineering techniques for mathematical modelling and simulation to complement the medical field of rhinology. Computational rhinology has already contributed significantly to advancing our understanding of the nasal function, including airflow patterns, mucosal cooling, particle deposition, and drug delivery, and is foreseen as a crucial element in, e.g., the development of virtual surgery as a clinical, patient-specific decision support tool. The current paper delves into the field of computational rhinology from a nasal airflow perspective, highlighting the use of computational fluid dynamics to enhance diagnostics and treatment of breathing disorders. This paper consists of three distinct parts—an introduction to and review of the field of computational rhinology, a review of the published literature on in vitro and in silico studies of nasal airflow, and the presentation and analysis of previously unpublished high-fidelity CFD simulation data of in silico rhinomanometry. While the two first parts of this paper summarize the current status and challenges in the application of computational tools in rhinology, the last part addresses the gross disagreement commonly observed when comparing in silico and in vivo rhinomanometry results. It is concluded that this discrepancy cannot readily be explained by CFD model deficiencies caused by poor choice of turbulence model, insufficient spatial or temporal resolution, or neglecting transient effects. Hence, alternative explanations such as nasal cavity compliance or drag effects due to nasal hair should be investigated. [ABSTRACT FROM AUTHOR]

Acquired subglottal stenosis is an unpredicted complication that can occur in some patients who have undergone prolonged endotracheal intubation. It is a narrowing of the airway at the level of the cricoid cartilage that can restrict airflow and cause breathing difficulty. Stenosis is typically treated with endoscopic airway dilation, with some patients experiencing multiple recurrences. The study highlights the potential of computational fluid dynamics as a noninvasive method for monitoring subglottic stenosis, which can aid in early diagnosis and surgical planning. An anatomically accurate human laryngeal airway model was constructed from computerized tomography (CT) scans. The subglottis cross-sectional area was narrowed systematically using ≈10% decrements. A quadratic profile was used to interpolate the transformation of the airway geometry from its modified shape to the baseline geometry. The numerical results were validated by static pressure measurements conducted in a physical model. The results show that airway resistance follows a squared ratio that is inversely proportional to the size of the subglottal opening (R ∝ A-2). The study found that critical constriction occurs in the subglottal region at 70% stenosis (upper end of grade 2). Moreover, removing airway tissue below 40% stenosis during surgical intervention does not significantly decrease airway resistance. [ABSTRACT FROM AUTHOR]

Jet flows have many applications in various technical processes such as temperature control, mixing, spraying and so forth. Along with wide usage in technology and manufacturing, jet flows are the object of fundamental scientific interest. In particular, a proper understanding of laminar‐turbulent transition in jets is highly important. In this experimental work, we study round laminar submerged jet flow of air and the evolution of controlled perturbations. First, the modal perturbation growth mechanism was under consideration. Thin metal rings were put into the jet at a small distance from the orifice to amplify unstable eigen modes of the jet by oscillating at different frequencies. Experimental and theoretically predicted wavelengths, radial distributions of velocity fluctuations and amplification curves of modal perturbations were compared and a good correspondence was found. Second, the non‐modal perturbation growth mechanism was under consideration. To excite algebraic perturbation growth, we put special wavy structures (deflectors) into the jet, which provide a roller‐like transverse motion in the perturbed jet. The features of the transition to turbulence caused by this non‐modal growth were considered. Based on obtained experimental results, we definitely identify the non‐modal 'lift‐up' growth mechanism of introduced disturbances. The development of perturbations qualitatively corresponds to the theoretically calculated optimal perturbations. [ABSTRACT FROM AUTHOR]

The effect of the boundary conditions of the first and second kind on the predicted characteristics of anomalous heat transfer intensification in the case of turbulent low-velocity air flow over an inclined groove in the hot wall of a narrow channel is numerically investigated. It is shown that the isothermality conditions lead to a considerable underestimation of the thermal efficiency of a surface structured with narrow grooves, compared with the conditions of heat flux constancy. [ABSTRACT FROM AUTHOR]

This study presents a numerical analysis of turbulent air flow through a rectangular duct fitted with two perforated vertical baffle plates, focusing on flow characteristics and pressure distribution. The analysis employs two-dimensional differential equations, solved using the finite volume method. The k-e turbulence model, implemented in Fluent software, elucidates the turbulence dynamics. Boundary conditions, including the entrance velocity field and exit atmospheric pressure, were varied to comprehensively evaluate the system. The model's validity was established against experimental data at a Reynolds (Re) number of 87300, demonstrating excellent comparability at a distance of 0.525 m from the duct entrance. The research aims to investigate the effects of different Re numbers (10,000, 20,000, and 30,000) on various parameters in a duct equipped with two perforated, nozzleshaped vertical baffles, each comprising eight trapezoidal sections forming seven nozzles. Parameters analyzed include the velocity profile, pressure drop, turbulent kinetic energy, dynamic pressure coefficient, and skin friction coefficient. The study finds that the insertion of perforated vertical baffles enhances mixing, particularly at higher Re numbers. Axial velocities attain maximum values above the bottom baffle and below the top baffle, with multiple re-circulation zones observed at strategic locations including above, below, and behind the baffles. Significant findings include the occurrence of maximum vertical velocity values at Re=30000 upstream of the bottom baffle, and a substantial re-circulation zone immediately upstream of the upper baffle. The channel's thermal enhancement factor is noted to improve with decreasing levels of skin friction as the Re number increases. Pressure values rise at the junctions where the duct's inner walls meet the upper surfaces of the baffles. Turbulent kinetic energy across the duct is categorized into three distinct zones based on the Re number: Zone 1, between the entry and the first baffle, exhibits minimal turbulence influence; Zone 2, located between the baffles, shows a peak turbulent kinetic energy of about 3 m²/s² near the nozzle exits and the bottom of the top baffle; Zone 3, extending from the second baffle to the outlet, records the highest turbulent kinetic energy rate at a Re number of 30,000. [ABSTRACT FROM AUTHOR]

Atmospheric image blur, "seeing", is one of the key parameters that influences the selection of observatory sites and the performance of ground-based telescopes. In this review, the common definition of seeing based on the Kolmogorov turbulence model is recalled. The ability of this model to represent real, non-stationary fluctuations of the air refractive index is discussed. Even in principle, seeing (a model parameter) cannot be measured with arbitrary accuracy; consequently, describing atmospheric blur by a single number, seeing, is a crude approximation. The operating principles of current seeing monitors are outlined. They measure optical effects caused by turbulence, sampling certain regions of spatial and temporal spectrum of atmosphreic optical disturbances, and interpret their statistics in the framework of the standard model. Biases of seeing monitors (measurement noise, propagation, finite exposure time, optical defects, wind shake, etc.) should be quantified and corrected using simulations, while instrument comparison campaigns serve as a check. The elusive nature of seeing follows from its uniqueness (a given measurement cannot be repeated or checked later), its non-stationarity (dependence on time, location, and viewing direction), a substantial role of the highly variable surface layer, and a potential bias caused by the air flow in the immediate vicinity of the seeing monitors. The results of seeing measurements are outside the scope of this review. [ABSTRACT FROM AUTHOR]

The improved delayed detached Eddy simulation (IDDES) approach used in the part I of this investigation to study the self-ignition and combustion of hydrogen jets in a high-speed transverse flow of hot vitiated air in a duct is extended in the following directions: (i) the wall boundary conditions are modified to take into account the optical windows employed in the experiments; (ii) the detailed chemical kinetic model with 19 reactions is used; (iii) a nonlinear turbulence model is implemented in the code to capture the secondary flows in the duct corners; (iv) the wall roughness model is adapted; (v) the synthetic turbulence generator is imposed upstream of the fuel injection. As a result of improving the mathematical and physical problem statements, a good agreement between the simulation and the experimental database obtained at the LAERTE workbench (ONERA) is achieved. [ABSTRACT FROM AUTHOR]

Surface waves and sea spray play a significant role in air–sea fluxes in high winds. The present study used a marine atmosphere surface layer (MASL), which couples the traditional Monin–Obukhov similarity theory, sea spray generation function, the balance of turbulent kinetic budget, and momentum/enthalpy conservation equations. Based on this model, the effects of wave states and spray injection velocities on air–sea momentum/enthalpy fluxes and near-surface wind/temperature profiles were theoretically investigated. Based on the assumption that the velocity of injected spray is the same as that of the ambient airflow, it was found that spray could increase the near-surface air turbulence intensity and inhibit air–sea fluxes at 10 m above the sea surface. Correspondingly, near-surface wind speeds and temperature increase in high winds. This phenomenon becomes prominent in cases of large wave ages or surface waves supporting a minority of air–sea fluxes. Based on the assumption that the velocity of the edges of breaking water bags is used to estimate that of spray injection, the opposite results were found: spray could weaken the near-surface air turbulence and increase total air–sea fluxes at 10 m above the sea surface. In this case, the near-surface wind speeds and temperature decreased. This reduction becomes remarkable when surface waves are full-developed or the majority of air–sea momentum fluxes are supported by waves. [ABSTRACT FROM AUTHOR]

In order to solve the inevitable instability problem of dandelion-like unpowered aircraft, transient simulations are carried out for the transition to turbulence of the wake from stable to unstable stage under different Reynolds numbers, and the vortex mode characteristics presented by the vortex structure as the Reynolds number increases are identified. Furthermore, by monitoring the velocity and lift and drag coefficients at different positions in dandelion flow field, the spectral characteristics of flow velocity and aerodynamic coefficients in the turbulent phase triggered by extreme aerodynamic environment are revealed. Compared with solid disk, it is found that the bandgap structure is more conducive to expanding the stable flight threshold of the dandelion-like aircraft, that is, the canopy configuration has weakening effect on airflow fluctuations. In addition, an evaluation method for unsteady boundary Reynolds number and load capacity of a dandelion-like aircraft is presented. The proposed method aims to plan a reasonable number of filaments (or porosity) for further designing dandelion-like aircraft with flight stability and high load capacity under aerodynamic conditions at different Reynolds numbers. [ABSTRACT FROM AUTHOR]

We investigate experimentally the phenomenon of turbulent thermal diffusion of micrometer-size solid particles in an inhomogeneous convective turbulence forced by one vertically oriented oscillating grid in an air flow. This effect causes the formation of large-scale inhomogeneities in particle spatial distributions in a temperature-stratified turbulence. We perform detailed comparisons of the experimental results with those obtained in our previous experiments with an inhomogeneous and anisotropic stably stratified turbulence produced by a one oscillating grid in the air flow. Since the buoyancy increases the turbulent kinetic energy for convective turbulence and decreases it for stably stratified turbulence, the measured turbulent velocities for convective turbulence are larger than those for stably stratified turbulence. This tendency is also seen in the measured vertical integral turbulent length scales. Measurements of temperature and particle number density spatial distributions show that particles are accumulated in the vicinity of the minimum of the mean temperature due to the phenomenon of turbulent thermal diffusion. This effect is observed in both convective and stably stratified turbulence, where we find the effective turbulent thermal diffusion coefficient for micrometer-size particles. The obtained experimental results are in agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

The modeling of atmospheric ice accretion on duplex cylinders received a limited attention, with modeling carried by Wagner and Qing et al. The publicly available experimental data about the ice accretion on the duplex cylinders is limited to experiments of Qing et al. and Veerakumar et al. When comparing the data of Wagner and Qing et al. with the results of Veerakumar et al., the major difference is the airflow behavior in the wake of the windward cylinder, the extent of the wake and recirculation bubble, and the velocity distribution in the wake. Thus, its needed to study the effect of the turbulence model on the airflow behavior of duplex cylinders, with focus being the behavior of the wake of the windward cylinder. This study reports the simulation results of the complex airflow behavior of duplex circular cylinder bundle obtained using several turbulence models employed by commercial CFD code. [ABSTRACT FROM AUTHOR]

The environment inside airliner cabins has attracted increasing attention. Instantaneous airflow, as one of the fundamental parameters of airflow field, affects aspects of the airliner cabin environment such as occupant comfort and airborne disease transmission. This study evaluated the characteristics of instantaneous airflow in airliner cabins with different ventilation systems (mixing ventilation and displacement ventilation) and focused on the region above passengers' heads, where complex turbulence characteristics are found. This investigation used ultrasonic anemometers for measurements at ten selected points above passengers' heads. The energy ratio on the low-frequency scale with mixing ventilation was greater than that with displacement ventilation. The instantaneous airflow with mixing ventilation was close to that of natural wind, while the instantaneous airflow with displacement ventilation was close to that of mechanical wind. Compared with mixing ventilation, displacement ventilation produced a smaller vortex length and a shorter residence time. Moreover, there was no long-term vortex in the flow field under displacement ventilation, and therefore, pollutants would be discharged more quickly from the cabin. In addition, this paper distinguishes the spatial and temporal turbulence scales of mixing and displacement ventilation, thus providing a reference for the selection of grid size and time steps in computational fluid dynamics simulations. [ABSTRACT FROM AUTHOR]

Reverse circulation (RC) drilling technology enables the rapid acquisition of coal seam samples, which is crucial in accurately measuring gas content. In addition, the design of the drill bit plays a key role in RC sampling. In this study, the turbulence model and simulation method applied during the RC drilling process is analyzed, and an annular jet flow bit is developed. An experimental laboratory setup is used to simulate the RC performance of the proposed drill bit, based on which an orthogonal design simulation of the structural parameters of the drilling bit studies was performed to investigate the effects of the RC drilling process. The experimental results show that annular jet flow moving up the central channel wall of the bit is conducive to the suction of annular airflow and results in the strong flow field created by the center channel of the bit generating negative pressure in the center channel of the bit, a comparison of the computational fluid dynamics data on negative pressure and suction rate shows that the annular jet flow RC bit is suitable for use in RC drilling. [ABSTRACT FROM AUTHOR]

Air-to-air fixed plate enthalpy membrane exchanger is considered one of the equipment used in energy recovery services. Thermal performance of air-to-air energy recovery ventilator is examined numerically using a 3D CFD simulation. Air flow inside the exchanger is tested using four numerical turbulence models: Standard k-ε, k-ε renormalization group (RNG), k-ε realizable and k-ω shear-stress transport (SST) models. The adopted heat and mass exchange element within the ventilator (membrane) is a thin 98 μm porous 60 gsm Kraft paper. A user defined function (UDF) has been developed to enable the CFD model to estimate amounts of mass exchanged between the two sides of the membrane. Grid dependency study is conducted and results have shown that a perpendicular distance of 50 μm or less from the membrane surface would result in a negligible variation in the ERV thermal effectiveness. The validated CFD model and UDF code against experimental measurement resulted in a maximum difference in thermal effectiveness of 3.6%. Results have shown that the SST k-ω turbulence models under enhanced wall treatment showed more sensitivity to flow at all Re values when compared with the k-ε simulated models. [ABSTRACT FROM AUTHOR]

In this work, a parametric two‐dimensional computational fluid dynamics (CFD) analysis of solar chimney power plant was performed to describe the physical mechanism in order to establish realistic predictions for the operation of such plants in different location in Algeria. The developed numerical model includes a solar radiation model within the collector; an energy storage model; an air flow and heat transfer model, and a turbine model. It is based on the solution of the Navier‐Stokes equation for turbulent flow using the standard k − ϵ model. The Boussinesq model was adopted in this simulation for the density of the fluid. The boundary conditions were adapted according to the selected sites and the effect of this on the SCPP performance was studied. The numerical simulation was performed using the commercial computational fluid dynamics (CFD) code "Ansys Fluent 19.2". [ABSTRACT FROM AUTHOR]

The idea of "Nanoval technology" origins in the metal injection molding for gas atomization of metal powders and the knowledge of spunbond technologies for the creation of thermoplastic nonwovens using the benefits of both techniques. In this study, we evaluated processing limits experimentally for the spinning of different types of polypropylene, further standard polymers, and polyphenylene sulfide, marked by defect-free fiber creation. A numerical simulation study of the turbulent air flow as well as filament motion in the process visualized that the turnover from uniaxial flow (initial stretching caused by the high air velocity directed at the spinning die) to turbulent viscoelastic behavior occurs significantly earlier than in the melt-blown process. Modeling of the whole process showed that additional guide plates below the spinneret reduce the turbulent air flow significantly by regulating the inflow of secondary process air. The corresponding melt flow index of processible polymer grades varied between 35 g·10min−1 up to 1200 g·10min−1 and thus covering the range of extrusion-type, spunbond-type, yarn-type, and meltblown-type polymers. Hence, mean fiber diameters were adjustable for PP between 0.8 and 39.3 μm without changing components of the process setup. This implies that the Nanoval process enables the flexibility to produce fiber diameters in the typical range achievable by the standard meltblown process (~1–7 μm) as well as in the coarseness of spunbond nonwovens (15–30 μm) and, moreover, operates in the gap between them. [ABSTRACT FROM AUTHOR]

The aim of the work is to describe the air flow in an enclosed space, which is ventilated by a diffuser, to select an appropriate turbulence model, to solve the problem using the ANSYS Fluent, to study the effect of heat sources in a room on air flow under various conditions and to simulate the movement of particulate matter. As a result, the distribution of PM2.5 particles in the room was shown, which enter the room through the diffuser. According to the data obtained, the temperature value increases with an increase in the area of the heat source, that is, with an increase in the number of batteries. The maximum temperature corresponds to a room with a warm floor, the minimum temperature is observed in a room with one battery. The obtained numerical data can be used when installing ventilation or heating devices inside buildings, when simulating the movement of harmful particles in the air, when determining the optimal ways to clean the air. [ABSTRACT FROM AUTHOR]

There exists an ongoing need to improve the validity and accuracy of computational fluid dynamics (CFD) simulations of turbulent airflows in the extra-thoracic and upper airways. Yet, a knowledge gap remains in providing experimentally-resolved 3D flow benchmarks with sufficient data density and completeness for useful comparison with widely-employed numerical schemes. Motivated by such shortcomings, the present work details to the best of our knowledge the first attempt to deliver in vitro–in silico correlations of 3D respiratory airflows in a generalized mouth-throat model and thereby assess the performance of Large Eddy Simulations (LES) and Reynolds-Averaged Numerical Simulations (RANS). Numerical predictions are compared against 3D volumetric flow measurements using Tomographic Particle Image Velocimetry (TPIV) at three steady inhalation flowrates varying from shallow to deep inhalation conditions. We find that a RANS k-ω SST model adequately predicts velocity flow patterns for Reynolds numbers spanning 1'500 to 7'000, supporting results in close proximity to a more computationally-expensive LES model. Yet, RANS significantly underestimates turbulent kinetic energy (TKE), thus underlining the advantages of LES as a higher-order turbulence modeling scheme. In an effort to bridge future endevours across respiratory research disciplines, we provide end users with the present in vitro–in silico correlation data for improved predictive CFD models towards inhalation therapy and therapeutic or toxic dosimetry endpoints. Author summary: The dispersion and ensuing deposition of inhaled airborne particulate matter in the lungs are strongly influenced by the dynamics of turbulent respiratory airflows in the mouth-throat region during inhalation. To cirumvent costly in vitro experimental measurement resources, fluid dynamics (CFD) simulations are widely sought to predict deposition outcomes but often lack detailed experimental data to first validate the three-dimensional (3D) flow structures anticipated to arise in the upper respiratory tract. In an effort to reconcile such data scarcity, we deliver experimental-numerical correlations of 3D respiratory airflows in an idealized 3D printed mouth-throat model against two widely-established numerical schemes with varying computational costs, namely coarse RANS and finer LES technique. Our time-resolved 3D flow data underline the complexity of these physiological inhalation flows, and discuss advantages and drawbacks of the different numerical techniques. With an outlook on future respiratory applications geared towards broad preclinical inhaled aerosol deposition studies, our open source data are made available for future benchmark comparisons for a broad range of end users in the respiratory research community. [ABSTRACT FROM AUTHOR]

In this paper, a 2D numerical simulation of a solar chimney with a top V cap was performed to evaluate the induced air flow degradation. Dimensions including the width of the cap and the cap offset from the top of chimney are specified as key parameters. Meanwhile, height and width of the chimney are fixed. The numerical model was confirmed to be accurate compared to the published data. The results showed that reducing the offset and increasing the width reduces airflow through the chimney. The effect of offset on chimney intake air is significant. When considering the addition of the top V cap, the airflow is reduced by about 20% compared to the chimney without a cap. This is because the cap forms three primary vortices including one vortex below the cap and two ones above the cap. The vortex under the cap in the direction from the absorber plate to the glass cover increases the air flow out of chimney at the side of the glass cover. The region with great turbulent kinetic energy forms at upper side of the cap. The air flow correlation as a function of the heat flux to the absorber plate, cap offset and cap width have been developed with errors of less than 2.5%. [ABSTRACT FROM AUTHOR]

The paper deals with the self-ignition and combustion of hydrogen jets in a high-speed transverse flow of hot vitiated air in a duct. The Improved Delayed Detached Eddy Simulation (IDDES) approach based on the Shear Stress Transport (SST) model is used, which in this paper is applied to a turbulent reacting flow with finite rate chemical reactions. An original Adaptive Implicit Scheme for unsteady simulations of turbulent flows with combustion, which was successfully used in IDDES simulation, is described. The simulation results are compared with the experimental database obtained at the LAERTE experimental workbench of the ONERA—The French Aerospace Laboratory. Comparison of IDDES with experimental results shows a strong sensitivity of the simulation results to the surface roughness and temperature of the duct walls. The results of IDDES modeling are in good agreement with experimental pressure distributions along the wall and with the results of videoregistration of the excited radical chemiluminescence. [ABSTRACT FROM AUTHOR]

Coughing and sneezing are the main ways of spreading coronavirus-2019 (SARS-CoV-2). People sometimes need to work together at close distances. This study presents the results of the computational fluid dynamics (CFD) simulation of the dispersion and transport of respiratory droplets emitted by an infected person who coughs in an indoor space with an air ventilation system. The resulting information is expected to help in risk assessment and development of mitigation measures to prevent the infection spread. The turbulent flow of air in the indoor space is simulated using the k-ε model. The particle equation of motion included the drag, the Saffman lift, the Brownian force and gravity/buoyancy forces. The innovation of this study includes A: Using the Eulerian–Lagrangian CFD model for the simulation of the cough droplet dispersion. B: Assessing the infection risk by the Wells–Riley equation. C: A safer design for the ventilation system (changing the ventilation supplies and exhausts in the indoor space and choosing the right location for air ventilation). The droplet distribution in the indoor space is strongly influenced by the air ventilation layout. The air-curtain flow pattern significantly reduces the dispersion and spreading of virus-infected cough droplets. When the ventilation air flow occurs along the room length, it takes about 115 s for the cough droplets to leave the space. However, when the ventilation air flow is across the width of the indoor space and there are air curtain-type air flow patterns in the room, it takes about 75 s for the cough droplets to leave the space. [ABSTRACT FROM AUTHOR]

To date, a backflow phenomenon that occurs in subsonic zero-pressure-gradient and adverse-pressure-gradient turbulent boundary layers has been well studied and its existence in such flow types is beyond doubt. In the present investigation, focusing on a turbulent air flow in a duct with adjustable cross section, for the first time we provide experimental evidence for the existence of backflow events in a converging channel and demonstrate the possibility of their occurrence in a favorable-pressure-gradient turbulent boundary layer. Taking into account that the backflow events are characterized by the low probability of their occurrence and spatio-temporal extent at the level of the Kolmogorov scale, we pay special attention to the use of high-speed particle image velocimetry with high spatio-temporal resolution. The measurement results revealed a general tendency in the backflow formation mechanism in the considered flow regimes and channel configurations. In conjunction with the findings of other studies, we suggest that the backflow events are induced by transversely oriented vortices located in the buffer region of the turbulent boundary layer and formed as a result of the interaction of large-scale high-momentum and low-momentum flow regions. [ABSTRACT FROM AUTHOR]

In-flight airflow and temperature distributions are key parameters for the thermal design of aircraft cockpit. In real working conditions, the effect of gravitational acceleration on flow and heat transfer characteristics is crucial but has long been ignored in the cockpit study. Gravitational acceleration also induces buoyant force and inhomogeneous thermal transport, which gives rise to thermal challenges of aircraft cockpit. To address this challenge, an SST k-ω turbulence model was well validated with 94% prediction accuracy to evaluate the inhomogeneous characteristics. The results indicated that the buoyancy-driven temperature distribution became progressively more inhomogeneous as gravitational acceleration increased. It was also found that the nonlinear variations in temperature were observed in the vertical direction from 0 to 1.5 m. Besides, a dimensionless parameter Gr* (∝107) was used to quantitatively assess the buoyant force. The results showed that the buoyancy force was considerably similar at 2.0 g and 4.0 g, and largely different from the trend at 1.0 g. Indeed, a common characteristic of these three conditions is the presence of a large inhomogeneity coefficient R in the top region of the cockpit. Therefore, an important limitation when designing the thermal structure of cockpit is the inhomogeneous feature of which the follow-up study needs to be carried out. [ABSTRACT FROM AUTHOR]

The purpose of this experimental study is to provide a detailed analysis of the transition to turbulence in an airflow channel perturbed by a delta winglet pair vortex generator. Measurements of instantaneous velocity are carried out by a laser Doppler anemometry technique. Experiments are conducted for Reynolds numbers (based on the hydraulic diameter) ranging from Re = 400 to R e = 12 000 and at several axial position downstream of the vortex generator. The flow behavior is characterized in each regime by means of a frequency analysis. We identified the inlet conditions corresponding to laminar weakly unsteady, transitional, and fully turbulent flow regimes. Furthermore, we have constructed a correlation between the Strouhal number and the Reynolds number that characterizes the vortex instability mechanism. Finally, under turbulent flow conditions, the dissipation rate was estimated, which showed an increase followed by an exponential decrease with the distance downstream of the vortex generator. [ABSTRACT FROM AUTHOR]

Arrays of buildings with pitched roofs are common in urban and suburban areas of European cities. Large-eddy simulations are performed to predict the boundary-layer flows over flat and pitched-roof cuboids to gain a greater understanding of the impact of pitched roofs on urban boundary layers. The simulation methodology is validated for an array of flat roof cuboids. Further simulations show that changes in the type of grid conformity have a negligible effect on the mean flow field and turbulent stresses, while having a visible, but small, effect on the dispersive stresses for a given packing density. Comparisons are made for flat and 45 ∘ pitched roof cuboid arrays at packing densities of 16.7% and 33.3%. The interactions between pitched-roof buildings and their effect on the urban boundary layer are considerably different to those of flat-roof buildings. The pitched roofs at a packing density of 33.3% leads to significant changes in the mean flow field, the Reynolds stresses, and the aerodynamic drag. Further work investigates the effects of changes in turbulence level and atmospheric thermal stratification in the approaching flow. Importantly, in comparison to a flat-roof array, the pitched-roof one at a packing density of 33.3% evidently increase the friction velocity and greatly reduces the effects of stable stratification conditions and changes in inflow turbulence level. [ABSTRACT FROM AUTHOR]

While the air lubrication by bubble injection and superhydrophobic (SHPo) surfaces have been investigated vigorously for flow control, for example, underwater drag reduction, further advancement seems to be delayed. For the former, large air flow rate is required for the meaningful performance, and furthermore, the injected bubbles do not stay over the surface willingly. Depletion (diffusion) of the trapped air pockets on the SHPo surface is a critical issue for the latter. In the present water-tunnel experiments, we show that the above-mentioned challenges can be successfully overcome by combining the two methods; that is, the plastron on SHPo surfaces can be replenished in turbulent flows with a very small amount of air, even after the surface is fully wetted. To analyze the phenomena, the bubble–plastron interaction is visualized and quantified while introducing bubbles over the SHPo surfaces (with random roughness or longitudinal grooves) in the turbulent boundary layer flow of R e L = 0.3 − 1.1 × 10 6 . The plastron on SHPo surfaces with longitudinal grooves is retained in a film-like shape with a quite smaller amount of air than that with random roughness. By quantifying the light intensity from the surface, we suggest a scaling relation between the effective plastron thickness and surface light intensity, which would serve as a criterion for the successful plastron replenishment. Finally, the morphology of the plastron is classified into different regimes, depending on the Reynolds number, air flow rate, and surface roughness types. [ABSTRACT FROM AUTHOR]

A numerical methodology has been developed to analyze the thermo-hydrodynamic aspect of airflow occurring in solar chimney power plants (SCPP) according to some dominant parameters. The general curvilinear coordinates finite volume method (GCCFVM), which is necessary in the case of turbulent flow through complex geometries, is used in this work. The governing equations describing the steady state turbulent fluid flow are solved numerically using this technique. It is shown that the chimney tower dimensions control directly the hydrodynamic field. However, the collector dimensions control directly the thermal field and indirectly the hydrodynamic field. It is demonstrated that the solar radiation influences strongly and positively the thermo-hydrodynamic field by increasing the mass flow rate. The mass flow decreases with the increase of the ambient temperature and then the system is more efficient with low ambient temperature. Indeed, the mass flow rate increases from 0.8 kg/s up to approximately 2 kg/s when the solar radiation varies between 200 W/m2 and 1000 W/m2 for fixed ambient temperature value of 30 °C. When ambient temperature increases from 10 °C up to 50 °C, the mass flow rate decreases slightly and in a linear manner from 1.7 kg/s to 1.5 kg/s for fixed solar radiation intensity value of 600 W/m2. Contrasting to other studies, conclusion based on simplified analytical models, ambient temperature affects adversely the performance of a SCPP in decreasing the mass flow rate. This conclusion should be taken into consideration when analyzing models dedicated to the prediction of solar chimney power plant performance. [ABSTRACT FROM AUTHOR]

The gas-dynamic and heat-exchange behaviours of air flows in gas-dynamic systems have a significant impact on the efficiency and environmental performance of most technical equipment (heat engines, power plants, heat exchangers, etc.). Therefore, it is a relevant task to obtain reliable experimental data and physical laws on the influence of cross-sectional shape and initial turbulence intensity on gas dynamics and the level of heat transfer. In this study, data were experimentally obtained on the instantaneous values of the local velocity and local heat transfer coefficients of stationary air flows in straight pipes with circular, square, and triangular cross-sections at different initial values of the turbulence intensity. The measurements were carried out with a constant temperature hot-wire anemometer, thermocouples, and pressure sensors. Based on the research results, data on the turbulence intensity and averaged local heat transfer along the length of pipes with different cross-sections were summarised. It has been established that turbulence intensity in a square pipe is up to 40% higher than in a round channel; in a triangular channel, on the contrary, it is up to 28% lower. After the air flow's initial turbulence, the relaxation of the flow in square and triangular pipes occurs faster than in a round channel. It is found that the initial intensity of turbulence leads to an increase in the averaged local heat transfer, which is typical of all investigated pipe configurations and initial conditions. [ABSTRACT FROM AUTHOR]

The characteristics of a flow formed behind a large particle moving in a descending turbulent air flow in a duct was measured using the PIV method, which makes it possible to record the instantaneous velocity fields. Data on deformation of the field of the instantaneous air velocity in a turbulent wake behind a large particle are presented and analyzed. [ABSTRACT FROM AUTHOR]

COVID-19 virus, which is a member of the coronavirus family, is a virulent virus that is transmitted by physical contact or air and results in death in infected people. People infected by the COVID-19 virus must be kept in quarantine in a closed area. Therefore, it is very important for the health of the individuals (patient, doctor, nurse, etc.) in the isolation room that, where the area kept closed is completely free of virus. This study was conducted to examine the flow dynamics of the air in the isolation chamber. With the simultaneous operation of the sanitized air machine and the ventilation in the room, it is aimed to investigate the virus killing effect of the air mixed with each other. The flow dynamics, velocity, temperature and turbulence kinetic energy of the air in the isolation chamber were examined. Investigations were carried out to ensure that the mixture of the two air in the room was better and distributed throughout the room. [ABSTRACT FROM AUTHOR]

In this study, the role of the shape, size and position of the windows, which play an important role in the natural ventilation of the buildings, in the ventilation of the buildings were examined. By using a blower providing constant velocity airflow, the best window model and position were determined for a total of ten window conditions, five wind directions, three wall inclination angles, and three wall thickness conditions. In addition, the system was also tested in the prevailing wind direction in the outer atmosphere. From the results obtained, it was found that the amount of air fed into the building increases in cases where the window size expands in an outward sloping way, the angle of inclination and the wall thickness increase, and the wind blows directly into the window. It has been observed that the air flow entering the building increased by 16-23% and 3-6% with the increase of the lateral slope and wall thickness of windows, respectively, but the air flow decreased rapidly with the increase of the angle of blowing the wind towards the window, and the air flow became zero when the wind blew parallel to the window opening. It has been seen that it is important for effective natural ventilation of buildings that window openings are constructed in the prevailing wind direction and on the opposite side of the building, that the interior partitions of the building are constructed to facilitate the linear flow of air, and that the indentations and projections that will cause turbulence outside the building are reduced as much as possible. [ABSTRACT FROM AUTHOR]

The small size of Unmanned Aerial Vehicles (UAVs) incurs many challenges, including concerns of flight stability during turbulence. To address this issue, birds as their natural counterparts have been studied in depth. This paper presents a biologically inspired Gust Mitigation System (GMS) for a flapping wing UAV (FUAV), inspired by the covert feathers of birds. The GMS uses electromechanical (EM) covert feathers that sense the incoming gust and mitigate it through deflection of these feathers. A multibody dynamic model of gust mitigating FUAV is developed by appending models of the subsystems including rigid body, propulsion system, flapping mechanism, and GMS installed to the wings, by using a bond graph modeling approach. The dynamic wing flexibility is modeled with a Euler-Bernoulli beam for realism. The simulation results show that wing flexibility enhances aerodynamic efficiency, and moreover, the performance of the proposed GMS for flexible wings is better than that of rigid wings during gusty airflows. A good agreement between experimental results with these simulations validates the proposed design as well as accuracy of the developed model. [ABSTRACT FROM AUTHOR]

This work presents the conformation of a hybrid model aimed at forecasting the wind speed one step ahead. The model comprises the Multiplicative Cascade and Persistence. To couple both techniques, a transition point was used, in this case, 6.6 m/s, defined from the spectrum of wind speed near the ground. The Multiplicative Cascade was used when speeds were higher than the transition point, while Persistence was used when lower. Two time series measured in Tamaulipas and Veracruz, Mexico, were used to build the hybrid model. The performance of the individual models concerning the hybrid model was compared, finding that the adjustment of the hybrid model exceeds that of the Multiplicative Cascade and Persistence models for both series. Different error metrics were used in the quantitative analysis, where the hybrid model was the most competitive. For example, in Mean Absolute Percentage Error, the difference in performance between the hybrid model and Persistence is 2.72% points for the 10-min time series. In contrast, this difference is 27.89% points for the hourly time series. Finally, this work shows that for the cases analyzed, differentiating the effects of turbulent from non-turbulent flows and modeling with the proper techniques improves forecasting accuracy. [ABSTRACT FROM AUTHOR]

The supersonic airflow and injected fuel stream mixing process is complicated for a scramjet combustor because of little supersonic air resident time and high airflow stream momentum. The direction of fuel injection into a supersonic airflow stream plays a significant role in mixing enhancement with turbulence generation. This study investigates the effect of strut-based parallel (primary) and inclined fuel injection in the strut flame holder wake region. The primary strut with parallel injection is derived from the open literature. The base model strut consists of parallel injection, whereas in the new models, the fuel is injected at an angle of θ for both the upward and downward directions. By computing the Reynolds averaged Navier-Stokes equations, finite-rate eddy dissipation turbulence chemistry, and SST k-ω turbulence models, the mixing and combustion behavior for various fuel injections were investigated. The impact of different fuel injections on the downstream wake region is assessed by evaluating the distribution of H 2 and H 2 O species in the radial and axial directions. The turbulence intensity and turbulent kinetic energy are also considered to evaluate the cross-impact of the air stream and fuel stream for inclined fuel injection. Numerical results found that inclined injection significantly impacts the mixing phenomenon with the development of enriched re-circulation zones in the vicinity of the flame keeper. The mixing and combustion efficiencies performance parameters are evaluated for different fuel injection schemes and found the average increased mixing efficiency of 13% and combustion efficiency of 12%, respectively, for inclined fuel injection. From the analysis of mixing efficiency, it is observed that complete mixing has been found after 235 mm, whereas for inclined injection, the complete mixing happened within a 175 mm distance. The maximum of 75% and 62% combustion efficiency has been observed at a 225 mm and 285 mm distance for inclined and parallel fuel injection, respectively. • Scramjet mixing and combustion are investigated for parallel and inclined fuel injection. • The impact of inclined fuel injection in the strut wake region is assessed using the recirculation regions. • Inclined fuel injection improves the fuel penetration in the radial direction. • The shear mixing layer in the strut wake region intensifies with inclined fuel injection. • Mixing and combustion performance is improved with negligible impact of pressure losses. [ABSTRACT FROM AUTHOR]

With the involvement of sinusoidal containers of phase change material (PCM) inside the duct, new configuration for the ventilation system has been achieved in the current paper. Mixture of TiO2 and RT25 was assumed as PCM, and the temperature of domain is fixed at 25°C at the start of the process. Owing to the radiation of the sun, air becomes warmer up to 35°C and with entering the air into the domain with Re = 6000, the melting process starts. The cold air at the outlet section can be utilized for ventilating the room. Homogeneous model for NEPCM and K‐ɛ approach for turbulent air flow has been incorporated. ANSYS FLUENT was applied for simulating this unsteady mechanism, and verification of the model was done according to previous experimental work. To control the air gap among tanks, the factor "b" was utilized and the influence of the fraction of titanium oxide (ϕ) was analyzed in results. As nano‐sized material has been added, more heat can be received to RT25 and the completed process can be reached in lower time. With considering the highest "b," as nano‐sized material, the required time reduces from 20,672 to 19705 s. When ϕ = 0, growth of b leads to a reduction of time of about 42.57%. [ABSTRACT FROM AUTHOR]

Turbulent flow past a radiator contributes to noise emission when interacting with a downstream cooling fan. This study examines turbulent flow characteristics downstream of a radiator, focusing on turbulence production, dissipation, non-homogeneity, and anisotropy. We assess turbulence models based on isotropy and homogeneity for noise prediction in real applications. Results show significant non-homogeneity due to the radiator grid's wakes, extending downstream to a region where the fan would be located. Flow in this region trends toward isotropy, especially when considering a downstream circularly-holed wood panel mimicking the flow contraction caused by a fan casing. The radiator core's fins and louvers break down vortical structures more than generating large eddies, as reported in studies involving heat exchangers with larger gaps between cooling pipes. The von Kármán turbulence model approximates the experimental spectrum, but caution is needed with rapid flow acceleration. This investigation enhances our understanding of turbulence characteristics in the vicinity of radiators with implications for noise spectrum prediction and modeling in such systems. • Automotive Noise Emissions: Radiators alter the noise emitted by cooling fans. • Turbulence Analysis: Flow past a radiator is characterized in realistic conditions. • Evaluation of Turbulence Models: For noise prediction in automotive cooling systems. • Experimental Technique: Stereo PIV to study the airflow downstream of radiators. [ABSTRACT FROM AUTHOR]

For remotely piloted aircraft systems (RPAS) operating in the urban environment, the flight path will most likely pass through the turbulent airflow of building wakes. To attenuate or reject instabilities caused by the turbulent airflow, control systems strategies are being developed in preparation for increased demand on the smaller urban air mobility vehicles. In this paper, results from urban airflow measurements of four 1:300 scaled Canadian city model flow fields are examined to provide detailed understanding of flow characteristics that can be found in typical Canadian cities. The results show common patterns for the range of inner city wind speed and turbulence intensity but that within the urban boundary layer (UBL) the variation of flow characteristics does not have a gradient with respect to altitude and that flow characteristics are highly variable along representative flight paths. For the purpose of simulation of RPAS response to the complex urban airflow, methods for using real urban flows data as inputs to simulations is presented. Demonstration of an Advancing Fourier Series (AFS) method, using the measured city data, shows successful preservation of the spatial- and temporal-correlations for reconstruction of a flow time series offering a novel, efficient and flexible approach for implementation of a time-based simulation of RPAS response in complex flow environments such as the urban environment. • For Canadian cities, a relationship between wind speed and turbulence has been found. • Wind speed and turbulence intensity are variable along an urban RPAS flight path. • A novel method that generates spatially/temporally correlated flow is validated. [ABSTRACT FROM AUTHOR]

We perform an experimental study of transport of nanoparticles in convective turbulence with the Rayleigh number ∼ 10 8 in the air flow. We measure a temperature field in many locations by a temperature probe equipped with 11 E-thermocouples. Nanoparticles of the size ∼ 70 nm in diameter are produced by an advanced electrospray aerosol generator. To determine the number density of nanoparticles, we use a condensation particle counter. The joint action of turbulent effects and the large-scale circulations in convective turbulence, which are important in the core flow, and molecular effects, which are essential near the boundaries of the chamber, results in an effective accumulation of nanoparticles at the cold wall of the chamber. The turbulent effects are characterized by turbulent diffusion and turbulent thermal diffusion of nanoparticles, while the molecular effects are described by the Brownian diffusion and thermophoresis, as well as the adhesion of nanoparticles at the cold wall of the chamber. In different experiments in convective turbulence in a chamber with the temperature difference Δ T between the bottom and top walls varying between Δ T = 29 and Δ T = 61 K, we find that the mean number density of nanoparticles decreases exponentially in time. For instance, the characteristic decay time of the mean number density of nanoparticles varies from 12.8 min for Δ T = 61 K to 24 min for Δ T = 29 K. For better understanding of experimental results, we perform one-dimensional mean-field numerical simulations of the evolution of the mean number density of nanoparticles for conditions pertinent to the laboratory experiments. The obtained numerical results are in agreement with the experimental results. [ABSTRACT FROM AUTHOR]