Search

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]

In presence of baffle, the turbulent airflow phenomena as well as forced convective heat exchange characteristics in two-dimensional rectangular channel have been analyzed in this work. For variations in Reynolds number (Re), we have studied the variations in characteristics of thermal behavior due to the change in the shape of baffle. Computations have been done using finite volume method (FVM) and FLUENT software and the SIMPLE algorithm has been employed for solving the governing equations. Finally, the flow and thermal exchange characteristics viz., streamline flow, turbulence intensity (TE), axial velocity, turbulence kinetic energy (TKE), normalized friction factor (F), normalized average Nusselt number (Nuavg) and thermal enhancement factor (TEF) have been studied in details from numerical standpoint. It has been found that the triangular shaped baffle provides highest value of F at Re = 30,000 and at Re = 46, 000, the maximum value of the TEF is found for the same baffle implying that triangular shaped baffle is more suitable for overall purposes.

The numerical simulation of turbulent flow and heat transfer, when air moves around a thermal manikin sitting in a model room with mixing ventilation, has been carried out. The calculations were performed on the basis of the RANS approach using the standard k-ε turbulence model. The buoyancy effects were described in the Boussinesq approximation. The obtained calculated data were close to the experimental ones, although there were local differences in the temperature distribution near the surface of the room walls. The impossibility of correct determination of the integral heat removal from the surface of the body without taking into account the radiation heat transfer was established. Along with studies in the ventilation regime with predominant forced convection, corresponding to the experiment, the characteristics of the flow and heat transfer in the free convection regime were analyzed, where the flow structure being caused by an intensive thermal plume forming above the manikin, and the temperature field being stratified in height.

Background: The optimal type of ventilation in operating theatres for joint arthroplasty has been debated for decades. Recently, the World Health Organization changed its recommendations based on articles that have since been criticized. The economic and environmental impact of ventilation is also currently an important research topic but has not been well investigated.Aim: To compare how large, high-volume, laminar airflow (LAF) and turbulent airflow (TAF) ventilation systems perform during standardized simulated total hip arthroplasty (THA), as they pertain to colony-forming units (cfu), particle counts, and energy consumption.Methods: Two identical operating theatres were used to perform simulated THA. The only difference was that one was equipped with LAF and the other with TAF. Cfu and particles were collected from key points in the operating theatre, and energy was measured for each simulation. Thirty-two simulations were done in total.Findings: LAF had significantly reduced cfu and particle count when compared with TAF, at both 100% and 50% air influx. Furthermore, it was shown that lowering the air influx by 50% in LAF did not significantly affect cfu or particles, although reducing the fresh air influx from 100% to 50% significantly lowered the energy consumption. Most simulations in TAF did not meet the cleanroom requirements.Conclusion: Cfu were significantly lower in LAF at both 100% and 50% air influx. It is possible to reduce fresh air influx in LAF operating theatres by 50%, significantly reducing energy consumption, while still maintaining cfu and particle counts below the ISO classification threshold required for THA surgery. [ABSTRACT FROM AUTHOR]

Background: Preventing surgical site infections and prosthetic joint infections is crucial for patient safety after total joint arthroplasty. Microbial air contamination has been suggested as a risk factor. Therefore, the ventilation system that will reduce air contamination most effectively in operating theatres (OTs) has been discussed.Aim: To determine whether laminar airflow (LAF) ventilation is superior to turbulent airflow (TAF) ventilation by looking at the colony forming units (cfu) count during live total hip and knee arthroplasties. Furthermore, to explore whether the number of OT personnel, door and cabinet lock openings and technical parameters of the ventilation systems have an impact on the number of cfu.Methods: Active air sampling and passive sedimented bacterial load were performed in 17 OTs, equipped with either LAF or TAF ventilation, during 51 live surgeries while observations were noted.Findings: LAF OTs reduced cfu counts compared with TAF OTs during live surgery (P<0.001). All LAF OTs provided ultraclean air whereas TAF had nine procedures exceeding the threshold of 10 cfu/m3. Door and cabinet lock openings and number of personnel did not influence the cfu count, while it decreased with increasing volume and total air change per hour (P<0.05).Conclusion: All LAF OTs had cfu counts within recommendations and provided lower cfu counts compared with TAF OTs. The number of OT personnel and total openings did not have an influence on cfu counts. Increased volume of the OT and total air change per hour showed a decrease in active cfu counts. [ABSTRACT FROM AUTHOR]

In the present study, the turbulent flows inside a realistic model of the upper respiratory tract were investigated numerically and experimentally. The airway model included the geometrical details of the oral cavity to the end of the trachea that was based on a series of CT-scan images. The topological data of the respiratory tract were used for generating the computational model as well as the 3D-printed model that was used in the experimental pressure drop measurement. Different airflow rates of 30, 45, and 60 L/min, which correspond to the light, semi-light, and heavy activity breathing conditions, were investigated numerically using turbulence and transition models, as well as experimentally. Simulation results for airflow properties, including velocity vectors, pressure drops, streamlines, eddy viscosity, and turbulent kinetic energy contours in the oral-trachea airway model, were presented. The simulated pressure drop was compared with the experimental data, and reasonable agreement was found. The obtained results showed that the maximum pressure drop occurs in the narrowest part of the larynx region. A comparison between the numerical results and experimental data showed that the transition ( γ − R e θ ) SST model predicts higher pressure losses, especially at higher breathing rates. Formations of the secondary flows in the oropharynx and trachea regions were also observed. In addition, the simulation results showed that in the trachea region, the secondary flow structures dissipated faster for the flow rate of 60 L/min compared to the lower breathing rates of 30 and 45 L/min. [ABSTRACT FROM AUTHOR]

The paper presents the results of numerical modeling of turbulent airflow in a test room based on the vortex-resolving wall-modeled large eddy simulation approach. The room ventilation is provided by a plain air jet at Re = 5233. The jet is supplied from a slit placed at a side wall under the ceiling. The problem formulation reproduces the test experiment conditions (Nielsen et al., 1978, 1990) as completely as possible. Two configuration with various air supply slit width are considered. Calculations were carried out with the ANSYS Fluent software using the grid consisting of 48 million cells. The paper demonstrates that in the near-wall jet zone the computational results agree well with the experimental data, but visible disagreement is obtained in the recirculation flow region (occupied zone) with relatively low velocities.

The paper presents the methods and results of numerical modeling of turbulent airflow in a test room based on the vortex-resolving wall-modeled large eddy simulation approach. The room ventilation is provided by a plain air jet at Re = 5233. The jet is supplied from a slit placed at a side wall under the ceiling. The room geometry and airflow parameters correspond to the experimental benchmark test by Nielsen et al. (1978), but with the periodicity boundary conditions in the transverse direction. Calculations were carried out with the ANSYS Fluent software using fine grids consisting of up to 6x10^7 cells. The paper presents detailed analysis of parametric computations aimed at the evaluation of numerical simulation adequacy. In particular, the grid dependency study was performed and the Kolmogorov scale was estimated.

Insect-proof screens are a frequent passive method to restrict the entrance of insects into greenhouses. However, the installation of these screens also has a negative effect on natural ventilation, which is reflected in the turbulence and velocity of the airflow inside the greenhouse. The turbulent characteristics of airflow through an insect-proof screen installed in the greenhouse windows have not been studied thoroughly in the literature. The present work focuses on the use of two simultaneous 3D sonic anemometers to study the impact of the use of a 13 × 30 threads·cm−2 insect-proof screen on the turbulence properties of the micro and microscale airflow turbulence. Four tests have been carried out in windward-oriented side windows of a Mediterranean greenhouse. Results demonstrate that the approach of using two simultaneous 3D sonic anemometers for the first time allows one to observe that the effect is different for the three components of the velocity vector field, and there is a strong connection between the simultaneous conditions inside and outside of the greenhouse. Useful information and data on the effect of using a 13 × 30 threads·cm−2 insect-proof screen are also provided. To give details on the impact of screens in the turbulent properties of ventilation is essential for any commercial distribution, as well as providing important data in the design and development of more efficient insect-proof screens.

Solar Chimney Power Plant (SCPP) is a large-scale system which is designed to produce electricity from the solar energy. This thermal device is characterized by a high investment cost and a low thermodynamic efficiency. The optimization of these thermal systems is required. The solar collector is one of the important parts of the solar chimney power plant. The collector is considered as a heat generator by using the greenhouse effect. In this paper, a novel design of the collector is proposed in order to increase the overall efficiency of the SCPP. In fact, impact of the collector concavity on the system performance is studied. Using CFD method, two-dimensional steady simulations were performed while varying the concavity ratio of the collector (CC). The specific ratio is defined as the curvature radius of the collector roof divided by the collector radius. The airflow behavior is examined by analyzed the static temperature, the magnitude velocity, the static pressure and the overall percentage of the power output rise. The numerical simulations were validated using experimental data gathered from a small prototype build at the National School of Engineers of Sfax, Tunisia. The predicted outcomes showed that a concave collector could enhance the overall performance of the solar chimney power plant. [ABSTRACT FROM AUTHOR]

Abstract Dust particles deposited on a solar photovoltaic (PV) panel surface may influence its performance depending on the particle composition, size and origin. In this context, the mechanics of fine particle adhesion on solar panel surface was analyzed and the simulation and experiment on dust removal from solar panel surface by turbulent airflow were conducted. Firstly, a particle adhesion model on the solar panel surface in dry and wet conditions and a particle detachment model in turbulent flows were established. The critical shear velocity of airflow to remove the particles was calculated based on Monte Carlo method. Then, a multi-stage expansion nozzle was designed which had multiple expansion cavities in series. The flow field inside the nozzle was simulated in FLUENT to obtain the outlet airflow velocity. Finally, the dust removal system for solar panel was validated experimentally, and its feasibility was demonstrated. Highlights • The critical shear velocity of the airflow to remove the dust particles on the solar panel surface was related with the particle characteristics. • The capillary force generated in wet condition has a great influence on the adhesion between the dust particles and the surface. • The dust removal performance of the proposed multi-stage expansion nozzle in different environment conditions were tested. • The feasibility of dust particle removal from solar panel surface by turbulent airflows was demonstrated. [ABSTRACT FROM AUTHOR]

In order to explore the forming mechanism of the fiber whipping motion in slot-die melt blowing, the turbulent airflow in slot-die melt blowing was measured online with the approach of the Particle Image Velocimetry (PIV) technique. The PIV results visualized the structure of the turbulent airflow and provided the distributions of air velocity components (vx, vy, and vz). Moreover, the PIV results also demonstrated the evolutive process of turbulent airflow at successive time instants. By comparing the characteristics of the turbulent airflow with the fiber whipping path, the PIV results provide a preliminary explanation for the specific fiber whipping motion in slot-die melt blowing.

The problem of tracking a dynamic odor plume using a realistic odor sensor model was investigated in a computer simulation. A chemical sensor typically has a significant time response delay that can disturb its practical application. This characteristic presents a challenge in tracking a dynamic plume toward the source. A reliable plume tracking strategy in a dynamic turbulent environment was designed through this simulation, which exploits the transient response of the chemical sensor. In this simulation, a mathematical model derived from a semiconductor gas sensor for sensing ethanol gas was used to model the sensor response. The sensor model was embedded into a chemotaxis-anemotaxis-based plume tracking strategy using a single sensor node to localize the source. In essence, the localization strategy is to search for the plume centerline and then move upwind along the centerline. The plume edges are estimated by evaluating the gradient of the fitting model of the frame size of the latest data points of sensor response during tracking. The strategy was tested on a turbulent environment simulated using a computational fluid dynamics (CFD) software. Although the odor distribution was complicated owing to the turbulent airflow and the obstacles, evaluation of the plume tracking strategy to localize the source starting from 404 initial positions achieved a success rate of approximately 70%. [ABSTRACT FROM AUTHOR]

The intermittent nature of turbulent airflow interacting with the surface is readily observable in fluctuations of the surface temperature resulting from the thermal imprints of eddies sweeping the surface. Rapid infrared thermography has recently been used to quantify characteristics of the near-surface turbulent airflow interacting with the evaporating surfaces. We aim to extend this technique by using single-point rapid infrared measurements to quantify properties of a turbulent flow, including surface exchange processes, with a view towards the development of an infrared surface anemometer. The parameters for the surface-eddy renewal ( $$\alpha $$ and $$\beta )$$ are inferred from infrared measurements of a single-point on the surface of a heat plate placed in a wind tunnel with prescribed wind speeds and constant mean temperatures of the surface. Thermally-deduced parameters are in agreement with values obtained from standard three-dimensional ultrasonic anemometer measurements close to the plate surface (e.g., $$\alpha = 3$$ and $$\beta = 1/26~\hbox {(ms)}^{-1}$$ for the infrared, and $$\alpha = 3$$ and $$\beta = 1/19~\hbox {(ms)}^{-1}$$ for the sonic-anemometer measurements). The infrared-based turbulence parameters provide new insights into the role of surface temperature and buoyancy on the inherent characteristics of interacting eddies. The link between the eddy-spectrum shape parameter $$\alpha $$ and the infrared window size representing the infrared field of view is investigated. The results resemble the effect of the sampling height above the ground in sonic anemometer measurements, which enables the detection of larger eddies with higher values of $$\alpha $$ . The physical basis and tests of the proposed method support the potential for remote quantification of the near-surface momentum field, as well as scalar-flux measurements in the immediate vicinity of the surface. [ABSTRACT FROM AUTHOR]

A proper ventilation strategy in an isolation ward could promote better indoor air quality for the occupants. This could also reduce the risk of immunocompromised patients contracting healthcare-associated infections (HAI) or airborne diseases such as COVID-19, tuberculosis, and measles among others. This study aims to propose and examine appropriate ventilation strategies in a single-patient isolation ward that can reduce particle settlement in patients. A simplified CFD model of the isolation ward was developed and well-validated against established data. An RNG k-ε model and discrete phase model (DPM) were used to simulate airflow and particle transportation. The study examined the airflow and particle dispersion under a baseline case and four proposed ventilation strategies. Results showed that the baseline case study, which used the ceiling-mounted air curtain was insufficient to prevent the particles from dispersing into the vicinity of the patient. Likewise, the dilution effect under the baseline case and case 4 (wall-mounted air supply diffuser) were relatively weak due to the low air change rate (ACH) of 4/hr and 9/hr respectively. The ventilation strategy in case 4 has a negligible effect on reducing the particles (14%) settling on the patient although the ACH in case 4 was 2-times the baseline case. The present finding ascertains that utilising the combination of ceiling-mounted air diffuser and air curtain jet (case 3) results in zero particle settlement on both patient's and the patient's bed. It also reduced 57% of particles in the vicinity of the medical staff's breathing zone compared to the baseline case. • Ceiling-mounted air curtain was insufficient to prevent the particles from dispersing into the vicinity of the patient. • The dilution effect under the ceiling-mounted air curtain and wall-mounted air supply diffuser were relatively weak. • Utilising the combination of ceiling-mounted air diffuser and air curtain jet results in zero particle settlement. [ABSTRACT FROM AUTHOR]

The importance of accounting for the temperature dependence of air properties in numerical simulations of air flows over pinned heat sinks is demonstrated by comparisons with recently published experiments. Numerical simulations, based on a conjugate heat transfer analysis, using the RANS-based modified k-ω turbulence model, with temperature-dependent air properties, are shown to be in significantly better agreement with experimental measurements of pressure drop, heat transfer coefficient, and heat sink base temperature, than those which employ constant air properties. [ABSTRACT FROM AUTHOR]

Stably stratified turbulent boundary-layer flows over both a waved water surface and a flat smooth surface are investigated through direct numerical simulation (DNS) for the bulk Reynolds numbers, Re, from 15 000 to 80 000. DNS expose the following basic properties of the flow. A statistically stationary turbulent regime is sustained if the turbulent Reynolds number, ReL, based on the Obukhov length-scale and friction velocity, is larger than 10&#178. At ReL <10², turbulence over a flat surface degenerates completely, but over a waved surface it survives in the form of residual fluctuations, which are weaker for smaller wave slopes. In the stationary turbulent regime, at ReL >10&#178, vertical profiles of the mean-flow velocity and temperature have a log-linear shape, as predicted by the Monin-Obukhov similarity theory, with the same empirical dimensionless constants as in laboratory and field experiments. The velocity and temperature roughness lengths, vertical turbulent fluxes of momentum and heat, and root mean square turbulent velocity and temperature fluctuations increase with increasing slope of the surface waves. At the same time, vertical profiles of the mean velocity and temperature keep the self-similar shape predicted by the Monin--Obukhov theory, irrespective of the wave slope. [ABSTRACT FROM AUTHOR]

Summary Bluff-body obstacles interacting with turbulent airflows are common in many natural and engineering applications (from desert pavement and shrubs over natural surfaces to cylindrical elements in compact heat exchangers). Even with obstacles of simple geometry, their interactions within turbulent airflows result in a complex and unsteady flow field that affects surface drag partitioning and transport of scalars from adjacent evaporating surfaces. Observations of spatio-temporal thermal patterns on evaporating porous surfaces adjacent to bluff-body obstacles depict well-defined and persistent zonation of evaporation rates that were used to construct a simple mechanistic model for surface–turbulence interactions. Results from evaporative drying of sand surfaces with isolated cylindrical elements (bluff bodies) subjected to constant turbulent airflows were in good agreement with model predictions for localized exchange rates. Experimental and theoretical results show persistent enhancement of evaporative fluxes from bluff-rough surfaces relative to smooth flat surfaces under similar conditions. The enhancement is attributed to formation of vortices that induce a thinner boundary layer over part of the interacting surface footprint. For a practical range of air velocities (0.5–4.0 m/s), low-aspect ratio cylindrical bluff elements placed on evaporating sand surfaces enhanced evaporative mass losses (relative to a flat surface) by up to 300% for high density of elements and high wind velocity, similar to observations reported in the literature. Concepts from drag partitioning were used to generalize the model and upscale predictions to evaporation from surfaces with multiple obstacles for potential applications to natural bluff-rough surfaces. [ABSTRACT FROM AUTHOR]

The relief and roughness of natural surfaces interacting with airflows and with radiation affect rates and distributions of heat and vapor fluxes into the atmosphere. The study quantifies interactions of regular sinusoidal wavy porous surfaces (with different geometrical characteristics) affecting heat and vapor transport into prescribed turbulent airflows. A model for turbulent eddies interacting with an undulating evaporating surface with mean boundary layer that varies across sinusoidal wavy surfaces was developed and experimentally evaluated in a wind tunnel. The surface of a $$1\,\hbox {m}^{2}$$ shallow (0.3 m deep) sand-filled basin was imprinted with regular sinusoidal ridges and troughs; water content and temperature sensors were embedded in the sand, and the instrumented basin was placed on a balance in the wind tunnel. Detailed thermal signatures of the evaporating surface for different wind speeds and surface patterns were obtained using high-resolution infrared thermography. The evaporative mass loss measurements and observed thermal patterns were in good agreement with model predictions for turbulent exchange over various wavy sand surface geometries. Results suggest that evaporative fluxes can be either enhanced or suppressed (relative to a flat surface) due to complex interplay between local boundary layer thickness and internal limitations to water flow to the evaporating surface. For a practical range of air velocities (0.5-4.0 m/s), and for sinusoidal configurations studied (amplitudes of 50-100 mm), the evaporative mass loss (relative to the flat surface) was reduced by up to 60 % for low surface aspect ratio and high wind velocity, and enhanced by up to 80 % for high aspect ratio and low wind velocity. The study offers a framework for interpreting and upscaling evaporative fluxes from rough terrestrial surfaces. Ongoing work considers shortwave radiation and geometrical interactions for a more complete account of surface energy balance and fluxes from natural rough surfaces. [ABSTRACT FROM AUTHOR]

Insect-proof screens are a frequent passive method to restrict the entrance of insects into greenhouses. However, the installation of these screens also has a negative effect on natural ventilation, which is reflected in the turbulence and velocity of the airflow inside the greenhouse. The turbulent characteristics of airflow through an insect-proof screen installed in the greenhouse windows have not been studied thoroughly in the literature. The present work focuses on the use of two simultaneous 3D sonic anemometers to study the impact of the use of a 13 × 30 threads·cm−2 insect-proof screen on the turbulence properties of the micro and microscale airflow turbulence. Four tests have been carried out in windward-oriented side windows of a Mediterranean greenhouse. Results demonstrate that the approach of using two simultaneous 3D sonic anemometers for the first time allows one to observe that the effect is different for the three components of the velocity vector field, and there is a strong connection between the simultaneous conditions inside and outside of the greenhouse. Useful information and data on the effect of using a 13 × 30 threads·cm−2 insect-proof screen are also provided. To give details on the impact of screens in the turbulent properties of ventilation is essential for any commercial distribution, as well as providing important data in the design and development of more efficient insect-proof screens. [ABSTRACT FROM AUTHOR]

Objectives/Hypothesis: The purpose of this article is to analyze the effects of septal deviation on the aerodynamic air flow pattern compared with that of a normal nose by computational fluid dynamics (CFD) tools. Methods: Two 3-dimensional (3-D) models of nasal cavities were constructed from the magnetic resonance imaging and computed tomography scans of a healthy human nose and a nose with septal deviation, with the use of the software MIMICS 12.1 (The Materialise Group, Leuven, Belgium). Thereafter high-resolution 3-D volume meshes comprising boundary layer effect and computational domain exterior to the nose were constructed. Numerical simulations were carried out using FLUENT (ANSYS, Canonsburg, PA) for CFD simulations. The Reynolds-averaged Navier-Stokes equations were solved for the turbulence flow with the shear stress transport k − ω model. Results: In the nose model with septal deviation, major changes in the pattern of inspiratory airflow (e.g., flow partitioning and nasal resistance, velocity and pressure distributions, intensity and location of turbulence), wall shear stress, and increasing of total negative pressure through the nasal cavity were demonstrated qualitatively and quantitatively. In the healthy nose, the area with the highest intensity of turbulent flow was found in the functional nasal valve region, but it became less apparent or even disappeared in the septal deviation one. Conclusions: This CFD study provides detailed information of the aerodynamic effects of nasal septal deviation on nasal airflow patterns and their associated physiological functions. Laryngoscope, 2009 [ABSTRACT FROM AUTHOR]

Novel self-join winglet vortex generators (SWVGs) consisting of multiple pairs of connected V-shaped rectangular winglets were put forward for enhanced heat transfer of turbulent airflow in round tubes. Numerical results firstly confirmed the generation of longitudinal swirl flows, which improved the air mixing and reduced the synergy angle between flow and thermal fields in the tube. Besides, increasing the winglets' included angle (α) and height ratio (HR) resulted in more intense swirl flows and uniform temperature distributions. Additive manufacturing was applied to fabricate the vortex generators using nylon, and experimental tests were carried out. The results showed that the Nusselt number ratio was 1.50–3.49 over the smooth tube, demonstrating the high capability for enhanced heat transfer of the proposed SWVGs. However, pressure loss was accompanied meanwhile. The overall thermal performance in terms of thermal enhancement factor displayed a decreasing tendency with the Reynolds number. The maximum thermal enhancement factor value of 1.27 was found at HR = 0.05 and α = 120°. In addition, the empirical correlations for friction factor and Nusselt number regarding α, HR, and Reynolds number were achieved by nonlinear regression to reference industrial applications. • Novel self-join winglet vortex generators were proposed for heat transfer enhancement. • Longitudinal swirl flows improved the field synergy. • Additive manufacturing was applied to fabricate the vortex generators. • The maximum thermal enhancement factor value of 1.27 was achieved. [ABSTRACT FROM AUTHOR]

Abstract: A numerical study is dedicated to the influence of the different dynamic and geometrical parameters on the sealing efficiency of a downward-blowing air curtain device, which is installed between two contiguous rooms with distinct ambient temperatures. The numerical simulation is based on the two-dimensional solution of the differential equations for the conservation of mass, momentum and thermal energy, using the k–ɛ turbulence model with two-layer wall functions. The performance of the air curtain is expressed by two parameters, the sealing efficiency and effectiveness, which provide the assessment of the energy savings predicted. The results allow a global, yet detailed characterization of the airflow pattern and provide guidelines for the appropriate operation of such devices. [Copyright &y& Elsevier]