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The application of turbulators to improve thermal performance and thermal enhancement in heat exchangers because of the significance of energy management and optimization is one of the interesting topics for researchers. Analysis of aerodynamic turbulator in internal flow has been less discussed in previous studies. Therefore, the present work focuses on the effect of a perforated sphere turbulator in a circular pipe with square, circular, oval, and hexagonal geometry holes on turbulent flow characteristics and thermal performance. These turbulators are placed with equal obstruction against the flow of air passing inside the pipe at Re = 6000–24000 in wall conditions of constant heat flux. Ansys Fluent software is used for numerical solutions, and the results are validated with an experimental paper. According to the results, the hexagonal geometry creates less pressure drop than other geometries. The thermal performance in the pipe with innovative aerodynamic turbulators is improved compared to the smooth pipe and the pipe equipped with conventional turbulators. The highest thermal performance of 1.256 is obtained for the turbulator with an oval hole. Also, the range of Nusselt number compared to the plain pipe for turbulator with circular, hexagonal, square, and oval holes increases by 1.97–2.46, 2.24–2.65, 1.58–1.89, and 2.48–2.81 times, respectively. The effect of the proposed new turbulators was compared with previous studies in this field, and the results are promising. [ABSTRACT FROM AUTHOR]

Large-span arch greenhouse has gained widespread application in fruit and vegetable production in recent years, due to the convenient facility operation, high land use efficiency, suitability for multiple coverings, and external heat preservation. However, internal turbulence can often occur in the expansion of the span and height of the large-span arch greenhouse. The resulting uniformity of the greenhouse environment can then affect the efficient production of greenhouse crops. In this study, a multi-field coupled computational fluid dynamics (CFD) model was constructed to integrate the facility structure and tomato plant aerodynamics, according to agricultural industry demand. The research object was selected as the 20 m span large-span arch greenhouse in Laiwu district, Jinan City, Shandong province (36.14° N, 117.28° E), China. A systematic investigation was carried out to explore the influence of the height of the arch greenhouse on the spatial and temporal distribution and evolution of the turbulent structure inside the large-span arch greenhouse. An analysis was also made to clarify the relationship between the wind and the temperature distribution, turbulence intensity, summer ventilation, and cooling efficiency, and the height of the arch greenhouse. Seven kinds of large-span arch greenhouse were established with 4.5, 5.0, 5.5, 6.0, 6.5, 7.0 and 7.5 m heights. The results show that there was turbulent behavior in the large-span arch greenhouses, indicating the mostly double vortex in the section. The air-flow entered the greenhouse via the bottom vent on the windward side, then ascended along the lower side of the greenhouse film, and finally descended towards the roof area. There was a tendency for the stabilization in the position of the inflection point, as the ridge height increased beyond 6.0 m. Therefore, the better uniformity of air flow and temperature distribution were, the higher the uniformity of the greenhouse was. The large-span arch greenhouse with a height of 6.0 m shared the highest average flow velocity at the crop canopy, which was in the appropriate range and relatively high. The average temperatures were also relatively low, which were 0.404 ℃ and 0.026 ℃ lower than those of the arch greenhouse with a height of 5.5 and 6.5 m, respectively. The turbulence intensity of the large-span arch greenhouse with a height of 4.5-5.5 m was significantly higher than that with a height of more than 6.0 m. There was a small difference, after the ridge height exceeded 6.0 m. Once the height of the greenhouse was 4.5 m, the ventilation efficiency was 2.24. After that, the efficiency of ventilation decreased with the increase in the height of the greenhouse. There was a relatively high value when the ridge height reached 6.0 and 6.5 m. The ridge height of 7.0 m corresponded to the lowest ventilation efficiency of 1.60. The large span greenhouse with a 4.5 m ridge height exhibited the higher ventilation efficiency, but the lower air change rate. The large span greenhouse with a 7.5 m ridge height shared the lower air change rate and ventilation efficiency. The outstanding ventilation and cooling performance of the large-span arch greenhouse in summer was determined by many factors. In a 20 m long-span arch greenhouse with shoulder, a better structure was achieved with the ridge height of 6.0-6.5 m and the ridge height of 6.0 m, in order to better consider the factors of economy and safety. The finding can provide a strong reference to optimize a similar greenhouse configuration in the construction of the large-span arch greenhouse. [ABSTRACT FROM AUTHOR]

To address the challenge of uneven and inadequate deposition within the canopy and on the lower side of the leaves in vineyards spraying operations, the performance of new prototype air-disturbance sprayers was evaluated. Firstly, the optimal parameter combination under the swing type disturbance mode (SW) was determined through orthogonal analysis. Then, a multivariate variance analysis was employed to compare the performance indicators of SW with those found under the rotating type disturbance modes (anticlockwise rotating AR, and clockwise rotating CR), as well as with the blank control group. It has been confirmed that SW could increase the penetration of droplets within the canopy and obtain the optimal deposition uniformity (58.72%). This mode did not affect the canopy deposition, but it decreased the coverage of droplets on the lower side of the leaves (11.82%). AR achieved a deposition uniformity of 62.06% and could consistently ensure that the coverage of both sides of the leaf was over the threshold of 30%. However, it decreased the canopy deposition. Generally speaking, CR not only significantly increased the canopy deposition, but also improved the deposition uniformity to 60.94% (second only to SW). Although the coverage on the lower side of the leaf for CR (25.41%) has not yet reached the threshold requirement of 30%, it could be anticipated that the implementation of two-sided spraying could effectively solve this deficiency. Therefore, the future positioning of a clockwise rotating turbulence system at the airflow outlet of the air-assisted sprayer will be a valuable choice. • Exploring the effect of novel airflow disturbance methods on canopy deposition. • Spray quality assessed by field orthogonal experiment and multiple comparisons. • Modelling airflow characteristics using CFD to help understand deposition results. • Discussed the effect of airflow turbulence intensity on droplet deposition. [ABSTRACT FROM AUTHOR]

The goal of the current study is to determine how the SST k−ω$$ k-\omega $$ and the standard k−ɛ$$ k-\varepsilon $$ turbulence models prediction on PCM with cylindrical configuration affect AC performance and PCM discharging when coupled with an AC unit. For simulation, 308.15 K and 318.15 K, the inflow air temperature has been considered with a fixed 33.6 L/s intake air flow rate. The low outside temperature charges the PCMs during the night. During the daytime, heated ambient air is cooled by the PCM heat exchanger before passing over the unit condenser. The present outcomes show that using the standard k−ε$$ k-\varepsilon $$ model, the cylindrical PCM has the lowest time of complete melting. The temperature contours demonstrate that turbulence occurs, particularly at higher temperatures, in the PCM melting zone within the solid region. This implies that there is increased convection in this area. The maximum improved percentage in COP increases as the rising input air temperature for both turbulence models increases. The average power saving of AC at 308.15 K of an input air temperature for 83.33 min is predicted by both the standard k−ɛ$$ k-\varepsilon $$ and the SST k−ω$$ k-\omega $$ to be 14.0905 W and 14.1089 W, respectively. [ABSTRACT FROM AUTHOR]

In order to determine the most suitable turbulence model for studying the aerodynamic performance of bus, the effects of different turbulence models on the aerodynamic characteristics of bus were investigated. A comparative analysis was conducted on five turbulence models (IDDES, DDES, DES, LES, URANS). The pressure distribution on the cross section at x=0 and y=0 is also analyzed for each model. The results reveal that IDDES accurately captures the negative pressure at the rear of the bus and predicts the pressure gradients more effectively than other models. IDDES also captures more vortices at the head of the bus and predicts the wake flow more widely than other models. DDES has obvious shedding phenomenon in the wake flow, while IDDES provides a relatively smooth airflow trajectory, but its prediction of airflow trajectory at a distance is less clear. Through quantitative and qualitative analyses of the aerodynamic characteristics of bus under different turbulence models, it can be concluded that IDDES is the most suitable turbulence model to study the aerodynamic characteristics of bus. [ABSTRACT FROM AUTHOR]

Abrupt section changes are a classic problem in the study of flow in cylindrical ducts or pipes. For its analysis, there are a wide set of exiting data from previous studies, among which some authors stand out and will be mentioned. Those previous works have been used to obtain reliable results for the resolution of section changes along a pipe, either due to cross area increases or reductions on a 1D basis. It is also known that a numerical 2D axisymmetric simulation (CFD) could find a consistent result compared to experimental data in almost all fluid flow fields. The main novelty of the present study is the development of a simple numerical approach used to solve the minor loss calculation. Firstly, a theoretical analysis is developed, and then the results of the numerical simulations carried out on the behavior that affects the water and air flow rate in an abrupt section change, for both contraction and expansion problems, are presented. In both cases, the results are analyzed with different meshes (discretizations) and turbulence models. Finally, the obtained numerical results are compared with those in the technical literature. Also, a theoretical approach is shown in order to show a whole frame of the discussion. The core results are the loss coefficient evolution as a function of the section change both for the sudden contraction and the expansion of a pipe flow. As the results follow the existing experimental values, it is concluded that the developed model provides a feasible and quick design tool to analyze possible geometrical changes without the need for further experiments. [ABSTRACT FROM AUTHOR]

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]

Physics-informed neural network (PINN) has aroused broad interest among fluid simulation researchers in recent years, representing a novel paradigm in this area where governing differential equations are encoded to provide a hybrid physics-based and data-driven deep learning framework. However, the lack of enough validations on more complex flow problems has restricted further development and application of PINN. Our research applies the PINN to simulate a two-dimensional indoor turbulent airflow case to address the issue. Although it is still quite challenging for the PINN to reach an ideal accuracy for the problem through a single purely physics-driven training, our research finds that the PINN prediction accuracy can be significantly improved by exploiting its ability to assimilate high-fidelity data during training, by which the prediction accuracy of PINN is enhanced by 53.2% for pressure, 34.6% for horizontal velocity, and 40.4% for vertical velocity, respectively. Meanwhile, the influence of data points number is also studied, which suggests a balance between prediction accuracy and data acquisition cost can be reached. Last but not least, applying Reynolds-averaged Navier–Stokes (RANS) equations and turbulence model has also been proved to improve prediction accuracy remarkably. After embedding the standard k–ε model to the PINN, the prediction accuracy was enhanced by 82.9% for pressure, 59.4% for horizontal velocity, and 70.5% for vertical velocity, respectively. These results suggest a promising step toward applications of PINN to more complex flow configurations. [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]

The role of coherent airflow structures capable of setting gravel‐sized particles in motion is studied theoretically and experimentally. Specifically, a micromechanical model based on energy conservation is proposed to describe the incipient motion of large‐particles ranging from rocking (incomplete entrainment) to incipient rolling (full entrainment). Wind tunnel experiments were conducted on an aerodynamically rough bed surface under near‐threshold airflow conditions. Synchronous signals of airflow velocities upwind of the test particles and particle displacement are measured using a hot film anemometer and a laser distance sensor, respectively, from which coherent airflow structures (extracted via quadrant analysis) and particle movements are interlinked. It is suggested that the incipient motion of gravel‐sized particles (rocking and rolling) may result from sufficiently energetic sweep events corresponding to aerodynamic drag forces in excess of the local micro‐topography resistance. However, full entrainment in rolling mode should satisfy the presented work‐based criterion. Furthermore, using an appropriate probabilistic frame, the proposed criterion may be suitable for describing processes of energy transfer from the wind to the granular soil surface, ranging from the creep transport of gravels to the "mechanical sieving" of mega‐ripples, as well as the transport of light anthropogenic debris (such as plastics). Plain Language Summary: Entrainment of particles from a particle bed is a key problem in wind‐driven sediment transport. Most existing models define critical entrainment conditions as those at which a bed particle begins to move. Such conditions are typically met during the passing of turbulent flow structures. However, the energy transferred from the structure to the particle may not be sufficient to leapfrog over neighboring bed grains. In this case, the particle will eventually fall back into its bed pocket. Here, we experimentally evaluate an alternative work‐based criterion for particle entrainment during the passing of turbulent flow structures. Our results indicate that sweeps of sufficient turbulent energy are predominantly responsible for particle entrainment. Key Points: Coherent airflow sweep structures exerting sufficient drag force can set coarse particles in motionA work‐based criterion has been established to define the full aerodynamic entrainment of coarse particlesThe proposed criterion agrees with wind tunnel experimental observations [ABSTRACT FROM AUTHOR]

This paper presents the results of thermal performance study of a solar air heater having absorber plate with inclined fins fitted in equilateral triangular flow passages in parallel using the governing equations under transition to turbulent flow and compares the same with the conventional solar air heater having low aspect ratio rectangular air flow duct at equal pumping power condition. The equal pumping power condition for the equilateral triangular passages of width w and rectangular duct height H has been found to be w = 2.65 H. The finned absorber plate solar air heater has been found to provide 7.3-25.8% better thermal efficiency than the conventional air heater because of the substantial increase in the effective heat transfer surface area due to the fins. The effects of variation of design, ambient, and operating parameters on the performance of the finned solar air heater show that the triangular passage width w must be increased with the increase in the collector length L to satisfy the condition of equal pumping power according to the relation w³/L2.75 = constant. The results of the present study can be utilized for the development of enhanced-performance finned solar air heater with triangular passages. [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]

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]

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]

This study analyses Compound Fins (CFs) in turbulent airflows using numerical and experimental methods. CFs combine Novel Plate Fin Heatsinks (NPFHSs) [1] and Slotted fins (S8 and S9) [2] and are compared to plain plate fins. Numerical modelling of turbulent airflow is conducted using Reynolds-Averaged Navier-Stokes equations, and ANSYS is used for the analysis. The CFs are manufactured using selective laser melting and validated experimentally. CF variations are categorized as CF18, CF19, CF28 and CF29 as described in Table 1. CFs outperform plain fins, with CF18, CF19, CF28, and CF29 showing higher Nu numbers by 52.7%, 51.2%, 44.8%, and 47.9%, respectively. CF18 and CF19 have 22.9% and 21.7% higher heat transfer coefficients than NPFHS1, respectively. CF28 and CF29 have 19.1% and 22.4% higher heat transfer coefficients than NPFHS2, respectively. CF18 and CF19 have higher air pressure drops than plain fins, while CF28 and CF29 have lesser pressure loss. The study concludes that CFs perform better than plain fins and are lighter. The methodology ensures the accuracy and reliability of the findings, making the study a valuable contribution to electronic cooling. [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]

The article explores flow behavior around thick airfoils at low Reynolds numbers and the potential application of energy methods to manipulate the flow field for increased lift and reduced drag. The study relies on a set of propulsion airfoils calculated using a combined approach of solving the inverse problem of aerodynamics and applying stochastic global optimization methods. The calculations consider the transition from laminar to turbulent flow regimes, which significantly affects lift and airfoil drag. The suitability of different turbulence models for airfoil modeling in low Reynolds numbers is discussed, and numerical simulation results determine the lift coefficient dependence on angle of attack and the optimal air flow rate taken from the airfoil surface for each angle of attack. The accuracy of different turbulence models is analyzed by comparing numerical simulation results to physical experiment data. [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]

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]

In the present study, a new and efficient design of a double-pass solar air heater with converged air ducts is proposed and simulated numerically. In the designed solar collector, the inclined position of the absorber plate regarding the glass cover and bottom plate provides converged shapes for the upper and lower air ducts, in which the accelerated flows and extra turbulence generation cause an increased rate of convection heat transfer. This concept is evaluated by numerical solution of the governing equations for air turbulent flow consisting of the conservations of mass, momentum, and energy by the finite element method using the COMSOL Multi-physics. Besides, the conduction equation is solved to compute the temperature distributions inside all solid parts. Numerical findings reveal that the increased velocity of airflow inside the converged duct causes significant convection enhancement, especially in the downstream side of airflow with a thick thermal boundary layer. This behavior leads to a considerable decrease in the absorber temperature due to a higher convection coefficient. The air outlet temperature for the studied test case with the inclined angle of 3° is found 3.5 C° more than that obtained for the base model and the percentage of efficiency increase is calculated about 10% due to using a converged duct. [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]

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]

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]

Current investigation aims to introduce and analyze an oblique-finned corrugated to evaluate numerically an unique method for improving heat transfer. Vertical gap ratios (V) of 0.15, 0.20, and 0.25; horizontal gap ratios (H) of 0.03, 0.04, and 0.05 as well as oblique-angle (θ) values of 10°, 20°, and 40° are just a few of the design factors that are examined. The targeted channels are subjected to turbulent air flows that are simulated using the finite volume technique (FVM) and the κ- ε model under constant temperature circumstances (T = 300 K). The data show that the novel approach enhances fluid mixing, which enhances heat transfer and, ultimately, thermal-hydraulic performance (PEC). The outcomes also show that frictional loss was employed to stimulate the target system's overall performance in the way of reducing the impact of heat transfer. Additionally, the findings uncover that, in comparison to other gap ratios, a moderate vertical gap ratio and a large horizontal gap ratio have a greater impact on heat transfer rate and PEC, respectively. Accordingly, the Nusselt number enhances by 73 %, 74 %, and 72 % across the same range of Reynolds number at a group of gap ratios (V = 0.15, h = 0.04), (V = 0.2, h = 0.05), and (V = 0.25, h = 0.05), respectively. Besides, the design parameters V = 0.2, H = 0.05, and θ = 40° yielded the best PEC of 2.547. New correlations for the innovative oblique-finned corrugated model are also presented. [ABSTRACT FROM AUTHOR]

Vegetative windbreaks have a significant advantage in regulating microclimates and improving soil conditions. Some studies highlight the importance of turbulence and plant flexibility, but few has investigated the relationship between flexibility and the shelter effect of windbreaks. Therefore, we perform a series of 3D fluid‐structure interaction (FSI)‐large‐eddy‐simulation (LES) simulations to study the airflow passing through flexible single‐plant windbreaks. We first model the plants with branches according to their geometric features in the field, present a FSI solver to strongly couple the airflow velocity field and windbreak vibration, and then use a LES turbulent model to resolve the turbulent flows. Based on the simulations, the airflow fields around the plants (Plant #1 and Plant #2) with different flexibilities, evaluated by Young's modulus, were analyzed and compared. Afterward, the shelter effect of flexible plants is analyzed based on three indices, including turbulence intensity, surface shear stress and plant swing displacement. The peak turbulence intensity of the three plants follows the order Plant #1 > Plant #2 > rigid plant. Regardless of wind speed, the surface shear stress around the plants follows the order Plant #1 < Plant #2 < rigid plant. The swing displacement increases as the velocity and flexibility increase. It is concluded that the flexible plant has a better shelter effect than the rigid plant, and within a certain range, the stronger the flexibility of the plant is, the better its shelter effect. This study not only investigates the interaction mechanism between flexible plants and airflow, but also provides a theoretical reference for the application of flexible plants in wind protection engineering. Plain Language Summary: Flexibility refers to the property that an object is not easy to break after being deformed by force. The flexibility of a plant is determined by its internal tissue and it is a significant factor for shelter effect of the vegetative windbreaks. Branches of plant swing under the action of wind, which disturb the surrounding airflow, form turbulence, weaken the wind velocity, and finally settle sand particles. There is few research on the relationship between plant flexibility and the shelter effect of windbreak. In our study, we conduct a series of 3D numerical simulations to study the airflow passing through flexible single‐plant windbreaks. We compare both airflow and shelter effect of plants with different flexibility and find the flexible plant has a better shelter effect than the rigid plant (with lowest flexibility). Our research also provides a new reference for the application of plant flexibility in building windbreaks. Key Points: Simulating airflow around flexible plant with fluid‐structure interaction (FSI)‐large‐eddy‐simulation (LES) schemeComparing airflow fields around the plants with different flexibilities, evaluated by Young's modulusAnalyzing shelter effect of flexible plants based on turbulence intensity, surface shear stress and plant swing displacement [ABSTRACT FROM AUTHOR]

High-Froude-number flows become self-aerated when the destabilizing effect of turbulence overcomes gravity and surface tension forces. Traditionally, the resulting air concentration profile has been explained using single-layer approaches that invoke solutions of the advection-diffusion equation for air in water, i.e. bubbles' dispersion. Based on a wide range of experimental evidence, we argue that the complete air concentration profile shall be explained through the weak interaction of different canonical turbulent flows, namely a turbulent boundary layer (TBL) and a turbulent wavy layer (TWL). Motivated by a decomposition of the streamwise velocity into a pure wall flow and a free-stream flow (Krug et al., J. Fluid Mech., vol. 811, 2017, pp. 421-435), we present a physically consistent two-state formulation of the structure of a self-aerated flow. The air concentration is mathematically built upon a modified Rouse profile and a Gaussian error function, resembling vertical mass transport in the TBL and the TWL. We apply our air concentration theory to over 500 profiles from different data sets, featuring excellent agreement. Finally, we show that the turbulent Schmidt number, characterizing the momentum-mass transfer, ranges between 0.2 and 1, which is consistent with previous mass-transfer experiments in TBLs. Altogether, the proposed flow conceptualization sets the scene for more physically based numerical modelling of turbulent mass diffusion in self-aerated flows. [ABSTRACT FROM AUTHOR]

This work provides a comprehensive overview of various aspects of airfoil CFD simulations. The airflow around a 2D NACA 0012 airfoil at various angles of attack is simulated using the RANS SST turbulent flow model and compared to experimental data. The airfoil is then modified with a slotted flap and additionally the angle of the flap is altered. The flow model is subsequently coupled to a heat transfer model to compare the isothermal versus non-isothermal performance. The airfoil with the slotted flap shows increased C L and C D values compared to the standard NACA 0012. Larger flap angles further increase the C L and C D . The lift and drag coefficients show no difference in the non-isothermal model compared to the isothermal model, indicating the isothermal model is sufficient for this system. The 3D model without wingtips shows a similar C L to the 2D model as it effectively has an infinite span. Adding a wingtip reduces the lift coefficient, as the air can flow around the wingtip, increasing the pressure on top of the wing. Overall, these results match the behavior expected from wing theory well, showing how CFD can be effectively applied in the development and optimization of wings, flaps, and wingtips. [ABSTRACT FROM AUTHOR]

In this study, we simulate the cooling of a microprocessor by thermal convection in three different shapes: a square, a trapezoidal, and a triangular shape. The latter is improved by a variety of types of roughness, including square roughness, triangular roughness Type 1, triangular roughness Type 2, and triangular roughness Type 3. The microprocessors are kept at a constant temperature, the air flow is constant, and the geometry is fixed. The physical phenomenon is simulated by the ANSYS software. The numerical results reported in this study cover the ranges of the obstacle's angle of inclination, 0 ° ≤ θ ≤ 45 ° , (square obstacles, θ = 0 ° , trapezoidal obstacles, 0 ° < θ < 45 ° , triangular obstacles, θ = 45 ° ) and Reynolds number, 2500 ≤ R e ≤ 10 , 000 . The findings relate to streamlines, dynamic pressure (max), mean velocity, temperature field, mean Nusselt number (Nu/Nu0) profiles, local coefficient of friction (Cf/f0), mean coefficient of friction (f/f0) profiles, mean velocity field with roughness, and fluid temperature field with roughness. The aim of the study is to show the interaction between the roughness parameter and the obstacle geometry. In the case of a triangular obstacle, the contact between the cold air and the obstacle is significant downstream of the obstacle, which gives us good cooling, and the Nusselt number has an important value because the agitation of the flow increases convective heat transfer, and the coefficient of friction is low because the air flow is uniform. [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]

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]

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 purpose of this study was to investigate the natural ventilation potential in an apartment unit in a high-rise building. A corner unit of a two-bedroom apartment was selected for this study, where single-sided and cross ventilation occurred in the unit. This study employed a CFD simulation to model the indoor airflow of an apartment unit in West Jakarta. The units were modelled and simulated using CFD with a RANS k-ε turbulence model. The results were validated with the readings from the field measurements that had been conducted. Based on CFD results, the window position influences indoor airflow. In the case of cross ventilation, a windward opening is more beneficial, while in single-sided ventilation, a leeward opening creates more indoor airflow. Therefore, it is recommended that the characteristic of window design be considered in the early design stage not only to improve indoor air quality but also to maintain privacy and safety measures. [ABSTRACT FROM AUTHOR]

The two-fluid (Euler–Euler) model and large-eddy simulation are used to compute the turbulent two-phase flow of air and water in a cyclonic flotation device known as an Air-Sparged Hydrocyclone (ASH). In the operation of ASH, air is injected through a porous cylindrical wall. The study considers a 48 mm diameter hydrocyclone and uses a block-structured fine mesh of 10.5 million hexagonal elements. The air-to-water injection ratio is 4, and a uniform air bubble diameter of 0.5 mm is specified. The flow field in ASH was investigated for the inlet flow rate of water of 30.6 L/min at different values of underflow exit pressure. The current simulations quantify the effects of the underflow exit pressure on the split ratio and the overall flow physics in ASH, including the distribution of the air volume fraction, water axial velocity, tangential velocity, and swirling-layer thickness. The loci of zero-axial velocity surfaces were determined for different exit pressures. The water split ratio through the overflow opening varies with underflow exit pressure as 6%, 8%, 16%, and 26% for 3, 4, 5, and 6 kPa, respectively. These results indicate that regulating the pressure at the underflow exit can be used to optimize the ASH's performance. Turbulent energy spectra in different regions of the hydrocyclone were analyzed. Small-scale turbulence spectra at near-wall points exhibit f − 4 law, where f is frequency. Whereas for points at the air-column interface, the energy spectra show an inertial subrange f − 5 / 3 followed by a dissipative range of f − 7 law. [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]

Spraying liquid jets in the transverse airflow is suitable for creating tiny droplets in the combustion chamber. This paper numerically investigated the effect of airflow turbulence intensity on liquid jet penetration and breakup. The large-eddy simulation method is used for numerical solutions. The level set model and volume of fluid (VOF) model are combined for two-phase crossflow modeling. Elliptical and circular nozzles with different aspect ratios and diameters were used to obtain liquid jet trajectories. Other trajectory equations due to different nozzle shapes were obtained for laminar flow. It is shown that the liquid jet trajectory depends on momentum ratio and dimensionless length. For turbulence flow, as results show, when the turbulence intensity of the transverse airflow increases, the energy in the flow vortexes also increases, so the breakup point approaches the liquid jet location. Also, as the turbulence intensity of the transverse airflow increases, the liquid jet trajectory and its penetration depth are not affected significantly because the dynamic energy of turbulence fluctuations is negligible compared to the air main flow. i.e., at 10 %, turbulence intensity equals 1 percent of the primary energy dynamics of the main flow. [ABSTRACT FROM AUTHOR]

Melt blowing (MB) is a process for producing microfiber or nanofiber using high-velocity air to attenuate the polymer jet. Compared to research on the melt-blowing airflow field analysis, the melt blown die optimization, and new materials development, little work has been done on fiber attenuation and whipping in the melt-blowing process. In this study, the airflow field distribution and turbulence fluctuation of the melt-blowing die are investigated using numerical simulation. The fiber motion process is simulated with the bead-viscoelastic element model and obtained using the high-speed camera. The underlying mechanisms leading to melt-blowing fiber attenuation have been discussed. The results show that the airflow field can be separated into three regions. The turbulent fluctuations in Regions I are related to the fiber whipping in the melt-blowing process. The fiber motion in Regions II and III are unsteady, resulting in higher fiber attenuation. Region II is the main zone of fiber attenuation where the fiber whipping increases and the drawing ratio is the largest. The fluctuation of air velocity causes fiber whipping which plays an important role in fiber attenuation. Experimental results of fiber diameter reduction and fiber motion are consistent with the simulation results. [ABSTRACT FROM AUTHOR]

Among the several aspects of decay products behavior, deposition is of special significance because of its prominent role in the activity removal from the environment, which eventually results in the occurrence of decay product disequilibrium with the parent gas. This point is particularly important in case of thoron dosimetry where thoron progeny 212Pb accounts for the most of the radiological dose. The deposition depends on the size distribution of decay products and the structure of air turbulence at the air-surface interface. In the present work, the effect of varying air-flow (fan speed) and aerosol count median diameter (CMD) was studied on the deposition and distribution profile of 212Pb using computational fluid dynamics (CFD). The simulations have been carried out in a cubical calibration chamber of volume 8 m3, facilitated at RP&AD, BARC. Simulated results showed that the increase of total depositional loss rate of attached fraction of 212Pb due to increase of the fan speed was significant for CMD up to 400 nm, beyond which this effect started becoming less prominent with increasing diameter. Besides, a minimum of the total depositional loss rate curve was seen to be shifted to the higher CMD with increase of the fan speed. CFD results were found to be in good agreement with experimental observations obtained in the controlled conditions with thoron source. [ABSTRACT FROM AUTHOR]