Local Airflow Research Articles

Effects of window view and local airflow on human thermal comfort in a sudden change environment

Transitioning from outdoors to indoors involves a sudden environmental change. However, current thermal comfort standards and design guidelines focus on steady-state environments, which do not fully address the urgent need for comfort during dynamic recovery periods. This study uses a climate chamber experiment to investigate the effects of window view and local airflow on thermal recovery under sudden environmental changes. Twenty participants, after exercising in a 34°C environment for 10 minutes, sat for 60 minutes in a 28°C room (with a microenvironment featuring window view/local airflow). Physiological parameters and subjective responses were measured during this period. The results indicate that under sudden environmental changes, window view significantly positively affects thermal recovery through psychological effects, while local airflow mainly accelerates convective heat exchange. The influence on thermal sensation recovery and recovery speed is as follows: window view and local airflow coupling > local airflow > window view. In terms of physiological parameters, both of them only had a significant effect on skin temperature but not on heart rate and blood pressure. The results of the study not only reveal the key role of indoor microenvironment on the effect and speed of thermal sensation recovery under the sudden change environments, which enriches the theory of dynamic thermal comfort, but also provides a scientific basis for the control strategy of indoor environments under sudden change environments.

Numerical Simulation and Parameter Optimization of a New Slant Insertion-Opening Combination Sand Fence

This paper presents a new slant insertion-opening combination sand fence designed to reduce the hazards of traditional railway sand damage along the line. This new fence aims to decrease the disturbance caused by lateral wind on the high-speed railway and minimize the deposition of track sand particles. Numerical modeling and wind tunnel testing were employed to examine the structure’s defensive capabilities. Using the computational fluid dynamics (CFD) method and the Eulerian–Eulerian two-fluid model, the wind protection effect and airflow characteristics of the new sand fence with different slant insertion angles and spacings were simulated, and the optimal configuration parameters were selected. The study found that the new mechanical sand fence exhibits similar performance to the traditional sand fence. Since there is a “narrow tube effect”, the leeward side of the inclined plate generates a local high-speed airflow zone. In the top acceleration zone, the new mechanical sand fence efficiently lowers air velocity, thereby enhancing its protective capabilities. Moreover, the optimal protective performance of the new mechanical sand fence is achieved with an inclination angle of 15°, with improved protection observed as the angle increases. Additionally, the protective performance of double rows of these fences is influenced by the spacing between them. Increasing the distance between the two rows enhances protective performance, with the optimal protection achieved at a spacing of 25H. Beyond this distance, protective performance decreases.

Evaluating the impact of human movement-induced airflow on particle dispersion: A novel real-time validation using IoT technology

Human movement significantly influences local airflow and particle dispersion in indoor environments. Therefore, this study integrates the dynamics of human walking into the analysis of airborne infection risks in a positive pressure isolation ward designed for the protection of immunocompromised patients. Real-time data collection was performed using an anemometer and IoT-based PM sensors to measure airflow velocities and particulate matter (PM) concentrations within a full-scale experimental chamber. Computational Fluid Dynamics (CFD) was used for the numerical simulations, and a User-Defined Function (UDF) code simulated the translational movement of a manikin. The results demonstrated strong agreement with the experimental data, thereby validating the airflow turbulence and Lagrangian-based Discrete Phase Model (DPM) in predicting the airflow velocities and particle transport. The study revealed that human walking substantially enhanced particle dispersion distance by 10-fold compared to static conditions, primarily attributed to intensified air mixing induced by the body movement. Furthermore, the CFD analysis underscored that the direction of walking plays a crucial role in airborne transmission. Specifically, walking away from a patient did not elevate infection risk, whereas approaching a patient significantly increased particle deposition in the patient-occupied region. This study highlights the critical need to consider both movement patterns and directional flow in managing airborne infection risks, contributing to the development of more effective infection control strategies in healthcare settings.

Head-neck local ventilation mode for long-narrow mine working face

To improve the thermal health state of workers in mines facing heat hazards and enhance cooling capacity utilization efficiency of mine ventilation, this study proposes a suitable air distribution for mine workers’ local cooling, taking into account the characteristics of long-narrow underground space and workers. The suggested air distribution involves harnessing underground cold air jets along with the mine’s crossflow (mainstream ventilation) to create a localized safeguard airflow around the worker’s head-neck, known as jet ventilation in crossflow (JVIC). The flow visualization experiment identified five flow patterns within a confined space. The study explores the impact of the velocity ratio (R) and confinement scale (C) on the evolution of JVIC flow patterns and presents a parametric description of the resulting flow field. Drawing on the microclimate control scope around mine workers’ head-neck, the study defines the effective cooling zone and the ineffective cooling zone as the boundaries for controlling JVIC air distribution within confined mine spaces. This clarifies the applicability of the air distribution form and introduces an evaluation model for assessing the cooling effect and the efficiency of cooling capacity utilization to manage the non-uniform underground environment.

Impact of Intra-Phenotypic Nasal Vestibular Variation on Local Airflow Dynamics.

Many individuals with healthy normal nasal anatomy and function exhibit a prominent notch indentation at the junction of the ala and sidewall, specifically around the anterior-superior region of the unilateral nasal vestibule up to the internal nasal valve. This study evaluates the influence of various sizes of notched indentations at the anterior nasal airway on local airflow pattern. A retrospective study involving 25 healthy individuals, each exhibiting at least one unilateral notched indentation (40 total airways). Each individual's notched indentation was quantified after subject-specific three-dimensional nasal airway reconstruction from radiographic images. Computational fluid dynamics modeling was used to simulate nasal inspiratory airflow in each nasal airway at 15 L/min. Localized airflow distributions passing through the inferior, middle, and superior regions were calculated at 15 cross sections. Notched indentation size ranged 1.75-86.84 mm2 (average = 22.37 mm2). At the anterior airway, notched size significantly correlated with inferior airflow volume (R = 0.32, p = 0.04) but not in the middle (R = 0.21, p = 0.20) or superior (R = 0.06, p = 0.70) regions, whereas middle and superior regional resistance values were significantly correlated with notched size (middle: R = 0.54, p < 0.001; superior: R = 0.41, p = 0.009). Medially, resistance at the middle region significantly correlated with notched size (R = 0.56, p < 0.001). At the posterior airway, airflow distributions through the inferior, middle, and superior regions demonstrated weak correlation with notched size (inferior: R = 0.24, p = 0.14, middle: R = 0.24, p = 0.13; superior:R = 0.03, p = 0.83), whereas resistance was significantly correlated in the middle and inferior regions (middle: R = 0.56, p < 0.001;inferior: R = 0.43, p = 0.006). Anterior nasal airway notched indentation size had significantly stronger influence on localized airflow volume through the anterior-inferior airway than other regions of the nasal passage. N/A Laryngoscope, 2024.

Analysing urban local cold air dynamics and climate functional zones using interpretable machine learning: A case study of Tianhe district, Guangzhou

Deterioration of the thermal environment in built-up areas poses a serious threat to human health, comfort, and urban infrastructure, while also increasing energy consumption and carbon emissions. This underscores the need to optimize wind environments as a key mitigation strategy for urban areas. This paper analyzed the effects of human activities and natural factors on local cold air in Tianhe District, Guangzhou, from the perspective of local ventilation systems. The KLAM_21 (Kaltluft Abfluss Modell) was used to simulate local cold air flow and delineate climate functional zones. A random forest model, interpreted with the SHapley Additive exPlanation (SHAP) method, assessed the impact of various factors on local cold air dynamics. The study found that: (1) The northern mountainous area is a crucial cold source; (2) Some open spaces in the built environment fail to function as effective local cold air corridors; (3) High-intensity urban development hinders local cold air transmission; (4) Water bodies are more effective than green spaces in collecting and transmitting local cold air. This study provided technical methods for identifying climate functional zones and understanding local cold air dynamics, as well as theoretical support for the construction of local ventilation systems in urban areas.

Experimental research on the flow flied of the nacelle and inlet of a civil aircraft with wind-mounted engines at low speed

Abstract Modern civil transport aircraft with wing-mounted engines are exposed to the upwash induced by the wing, resulting in the local angle of attack at the nacelle leading edge, notably greater than that of aircraft. Large local angles of attack can be combined with different engine airflow conditions, causing adversary aerodynamic phenomena to occur at different locations. Total and static pressures obtained in a wind tunnel test using a full-span aircraft model and simulating required engine airflow with an ejector indicate that during the around with landing configuration, the high suction peak will form on the bottom of the inlet with local air flow being supersonic and could lead to inlet distortion. In contrast, the engine that fails during takeoff climb will have a significant suction peak form on the top of the nacelle and might experience external separation and additional drag. Test results also demonstrate that well-designed nacelles can postpone these adversary phenomena until the aircraft stalls first.

Monitoring air fluxes in caves using digital flow metres

Precise measurements of airflow within caves are increasingly demanded to assess heat and mass transfers and their impacts on the karst environment, including subsurface ecosystems, hydrochemistry of karst water and secondary mineral precipitates. In this study, we introduce a new, low-cost and lightweight device adapted to monitoring air fluxes in caves which addresses the need for reliable measurements, low power consumption, durability and affordability. The device was calibrated in a wind tunnel, showing the high accuracy and precision of the device. Field-related uncertainties were further investigated in a ventilated cave to determine the effect of local airflow conditions on the inferred mass flux. Comparing measured values with a 3-D air velocity distribution modelled on a surveyed cave section suggests that most of the uncertainties in estimating the airflow result from the relative position of the instrument in the streamlines rather than from the accuracy of the device.

Influence of topography and synoptic weather patterns on air quality in a valley basin city of Northwest China

To clarify the mechanism underlying the effects of weather patterns and topography on air pollution, this study conducted the obliquely rotated principal component analysis in the T-mode to analyze ERA5 reanalysis data and categorize typical weather patterns at a 700-hPa geopotential height from 2015 to 2022. The probability of worsened air pollution attributable to weather patterns was quantitatively assessed using a generalized additive model. The results indicated that due to the influence of topography, Lanzhou was affected by an extended period of downdraft (with weak convective intensity) and the delayed formation of a convective boundary layer during the daytime by 1–2 h relative to other areas. Under the combined effect of low trough patterns (south low pressure type [SL] and south low weak pressure type [SL−]) and topography, the formation of a stable layer above the planetary boundary layer (PBL) would weaken the vertical exchange of the local airflow and inhibit the development of the PBL. The type of SL led to the most severe pollution, causing a 61.9 % (95 % confidence interval [CI]: 46.3 %–79.3 %) increase in PM2.5 concentration. For southwest high pressure patterns (south high [SH], southwest weak high [SWH−], southwest high [SWH], and southwest strong high [SWH+] pressure types), the prevailing northwest wind was the main transport path for pollutants. For the high pressure patterns (north high [NH] and northwest high [NWH] pressure types) and south wind patterns (southeast weak high [SEH−], southeast high [SEH], and northeast high [NEH] pressure types), the enhancement of vertical convection, deepening of the PBL, and reduction of pollution transport led to improved air quality. The NH, NWH, and NEH pressure types caused PM2.5 concentration to decrease by 18.4 % (95 % CI: 8.8 %–27.1 %), 14.9 % (95 % CI: 4.7 %–24.0 %), and 35.9 % (95 % CI: 9.7 %–54.6 %), respectively.

Reducing direct exposure to exhaled aerosol through a portable desktop fan

Vulnerable individuals close to infected people emitting a respiratory cloud containing infectious load can inhale a pathogen dose, experiencing a more severe impact on their health compared to other individuals breathing the mixed air in the same room. In crowded spaces, this issue is crucial. Employing local airflow patterns can reduce the proximity risk of inhalation and subsequent transmission across short distances. This study proposes an experimental and numerical analysis of a novel personal and portable device creating a short-range air barrier to transmitting airborne pathogens in proximity. The portable device adopts V-shaped air blades affecting the trajectory of the particle-laden respiratory cloud emitted by the respiratory system of the infected individual. Experimental results, supported by CFD analysis, indicate that controlling local airflow through the V-shaped jet significantly reduces local particle concentrations by more than 60%, compared to typical scenarios without a local airflow control.

Impact of human walking on the pollutant removal effectiveness of direction air supply considering environmental disturbances: Dynamic simulation study

Direction air supply (DAS) is a computer vision-assisted ventilation mode designed to address the challenge of respiratory protection during human movement. The DAS parameter design is based on ideal, steady-state air distribution results, but it cannot reflect the dynamic protection performance. This work investigates the effect of human walking on the pollutant removal effectiveness of DAS through computational fluid dynamics simulation with the dynamic mesh method. This work formulates an occupant's movement pattern and implements walking and turning motions using the overset mesh method. To verify the feasibility of the dynamic simulation method, a walking experiment was conducted in an experimental chamber equipped with a DAS system. The evolution of concentration isosurfaces, as well as the concentration, velocity, and static pressure at breathing-zone height are revealed. The negative impacts of three common industrial environmental disturbances: localized high-temperature pollutants, ambient airflow, and distance between the DAS nozzle and the breathing zone, on the protective zone and the DAS barrier against pollutants are analyzed. To comprehensively evaluate the effectiveness of DAS, four assessment indexes are determined: inhalation exposure, protection factor, protective zone area, and effective protective ratio. The inconsistency between the protective zone area and the effective protective ratio needs to be noted. This work confirms the effectiveness of DAS within the protective zone and supports its further application in industrial settings.

METHOD OF ESTIMATING THE DANGEROUS RANGE OF TRANSONIC NUMBERS M OF THE FLIGHT OF SUPERSONIC AIRCRAFT AND AEROSPACE SYSTEMS

Ensuring flight safety of supersonic aircraft and aerospace systems in the transonic range of flight M numbers still remains an ac- tual scientific and applied problem. This is due to the occurrence of various dangerous aeroelasticity phenomena in these flight modes. Such phenomena include transonic flutter, the occurrence of which has repeatedly resulted in the destruction of aircraft structural elements and, first of all, of aerodynamic control surface structural elements. Many publications are devoted to the theoretical and experimental research of this phenomenon, in which various approaches are proposed to substantiate the causes of intense oscillations of the aerodynamic control surfaces of modern supersonic aircraft in these flight modes, the conditions of their occurrence, the influence of various factors on the level of oscillations. It is noted that there are still no reliable theoretical methods for estimating the non-stationary forces of aerodynamic control surfaces that oscillate in a transonic flow, so the use of linear mathematical similarity models does not always allow transferring the results of blowing models in wind tunnels to full-scale aircraft designs. The paper proposes a method for estimating the dangerous range of M numbers in which transonic flutter of the aerodynamic control surfaces of supersonic aircraft and aerospace systems is possible. The method is based on the analysis of regularities of the adiabatic expansion of the local supersonic air flow on the surface of the airfoil in the range of transonic numbers M. Calculations have proven that for typical aerodynamic surfaces of modern supersonic aircraft, the occurrence of transonic flutter is possible in a narrow range of numbers M = 0.9…0.94. The obtained results can be used to substantiate the safe flight modes of supersonic aircraft both at the stage of flight tests and at the stage of operation. Further studies of this problem should be devoted to the analysis of methods for reducing the level of oscillations of aerodynamic control surfaces when transonic flutter occurs.

Local control of near-field diffusion of infected respiratory cloud in a room by air-blades

The respiratory cloud of an infective subject contains droplets of mucosalivary fluid carrying pathogens. As this cloud spreads at a certain distance from the emission point, the droplets accumulate and their volume concentration increases in the room unless dilution, adequate ventilation, or filtration reduce it. A susceptible subject, standing a short distance away can be exposed more easily to the infected respiratory cloud, thus inhaling a higher dose of pathogens than someone breathing the mixed air in the room. A local airflow pattern can be employed to reduce this short-distance risk of inhalation and potential contagion. We present experimental and numerical investigations of a novel device acting as a barrier to airborne pathogen diffusion at a short distance. This portable device generates V-shaped air blades in front of the subjects, shifting the respiratory clouds. The air blades are generated by 12 small fans, three on each side of the cube. The air is sucked into the small plenum inside the device body through the bases. By being positioned obliquely on a meeting table, the device acts as a direct barrier to virus-laden aerosols without any filtration. The experimental tests show that the system can reduce the local concentration of aerosol by 63 to 84% at the respiratory position of a subject sitting at a table in front of an infective person. CFD simulation outputs using the Multiphase Eulerian-Lagrangian model show a good agreement with the experimental results. The validated model will be used to extend the range of investigation to different settings and to perform a parametrical analysis of the main design conditions.

Investigating the impact of gaspers on airborne disease transmission in an economy-class aircraft cabin with personalized displacement ventilation

Overhead gaspers provide directional fresh airflow, and thus affect the local airflow pattern and contaminant distribution. To investigate the impact of gaspers on airborne disease transmission in an aircraft cabin with a personalized displacement ventilation system, numerical calculations were conducted in a seven-row, single-aisle, fully occupied, economy-class aircraft cabin with the computational fluid dynamics (CFD) simulation method. We first investigated the impact of source gasper direction and flow rate on the airborne transmission near the contaminant source. We then investigated the protective effect of the receptor's gasper. For a source passenger's gasper, the direction and flow rate of the gasper flow either increased or decreased the air contaminant transmission to other passengers. Directing the source gasper to the abdomen with a medium flow rate performed best by reducing the receptors' mean exposure index by at least 45%, as this approach minimized the contaminant circulation in the cabin. Turning on a receptor passenger's gasper could be an effective strategy to protect the receptor, and the working mechanism was revealed. The gasper-induced jet flow entrained the surrounding air into the jet region, and the protective effect was related to the contaminant concentration at ceiling level. With a suitable gasper direction and flow rate, the gasper jet formed a virtual barrier between the source passenger and the receptor. When the contaminants were transported upwards to a receptor's breathing zone, turning on the receptor's gasper reduced the contaminant concentration, since the downward gasper jet altered the airflow pattern in front of the receptor.

Droplet dispersion characteristics during human walking in a queue

The dispersion of respiratory droplets is strongly influenced by the complex airflow induced by human activities, such as walking in a queue. Understanding the relationship between local airflow disturbances during queue walking and droplet dispersion is crucial. This study investigates the effects of following distance (1.0, 1.5, 2.0, and 2.5 m), walking speed (0.8, 1.0, 1.2, and 1.4 m/s), and droplet diameter (1, 10, 50, 80, and 120 μm) on droplet dispersion. The findings reveal that the interaction between wake vortex and forward airflow provides a foundation for cross-infection among individuals. An increased following distance leads to an initial rise and subsequent decrease in the concentration in the breathing zone of the susceptible individual. The social distances of 1.0 and 1.5 m are insufficient to mitigate the risk of cross-infection, warranting a recommended following distance of at least two meters. The effect of walking speed on droplet dispersion varies depending on the scenario. In cases involving standing and walking cycles, the infection risk of the susceptible individual gradually increases with higher walking speeds. Conversely, when individuals walk continuously in a queue, the infection risk of the susceptible individual decreases with increased walking speed. Moreover, intermediate-sized droplets play a critical role in the transmission of respiratory infectious diseases and demand heightened attention. This study expounds the intricate airflow dynamics during queue walking and emphasizes the significance of following distance, walking speed, and droplet diameter in minimizing the risk of cross-infection.

Synthesis of hetero-site nucleation twisted bilayer MoS2 by local airflow perturbations and interlayer angle characterization

Synthesis of hetero-site nucleation twisted bilayer MoS2 by local airflow perturbations and interlayer angle characterization

The Effects of Various Maxillary Sinus Antrostomy Techniques on Modifying the Ventilation and Air-Conditioning Characteristics of the Maxillary Sinus: A Numerical Study

Background and Objectives: Endoscopic sinus surgery is commonly performed for maxillary sinus (MS) disease, and the surgical extent of the MS medial wall or ostium varies. We examined the effect of MS surgery on nasal airflow and air-conditioning using computational fluid dynamics in five nasal cavity numerical models.Methods: Four types of unilateral virtual MS surgery were conducted on the right MS based on computed tomography images of a 49-year-old man with normal anatomy. The five models were as follows: baseline (normal), middle meatal antrostomy (MMA), MMA with inferior meatal antrostomy (MMA+IMA), mega-antrostomy (MEGA), and endoscopic medial maxillectomy (EMM). Virtual simulator software and a stereoscopic display with haptic device were used for virtual surgery. Meshing software and computer fluid dynamics software were used to generate meshes and analyze airflow.Results: The MMA and MMA+IMA results were similar to the baseline model. However, EMM and MEGA exhibited some physiological changes. The amount of airflow moving into the MS was largest in the EMM model, followed by the MEGA model. The distributions of wall shear stress and surface water-vapor increased near the enlarged MS ostium in EMM and MEGA. Skewed airflow partition and different airflow rates between the operated and unoperated sites of the nose also changed the air-conditioning characteristics. EMM substantially reduced the relative humidity in the nasopharynx, and MEGA showed a smaller reduction.Conclusion: Among four surgery techniques, EMM produced the largest increase in wall shear stress and surface water vapor flux on the posterior surface of the MS and the greatest deterioration in the nasal cavity’s air-conditioning capacity. MEGA reduced the local airflow disturbance inside the MS and prevented excessive degeneration of the cavity’s overall air-conditioning capacity. In conclusion, MEGA and modified EMM approaches have physiological advantages over EMM, while securing a sufficient spatial extent of resection for surgery.

Design, Analysis and Testing of Mechanism to Reduce The Impact on Drones in Failure

This work aims at proving the concept of an autorotation-based crash prevention system for drones. The work focuses on quadcopters, whereas the concept can be used for all multi-copters in general with slight modification in design. The system works on the principle of autorotation which is a commonly used method in helicopters for unpowered landing. The autorotation system causes a gyroscopic effect preventing the quadcopter from changing its orientation during fall and also provides drag that helps in reducing the fall velocity. This technique reduces the energy that needs to be absorbed by the quadcopters structure during impact by converting a part of the kinetic energy of fall to the rotational kinetic energy and also creating a profile normal to the local airflow to produce drag. To prove this concept, the terminal velocity of the fall is obtained by mathematical modelling and this is compared with practical results in order to verify the theoretical results. Experimentally, a substantial reduction in velocity was found and this proves that the autorotation mechanism indeed reduces impact during failure in drones.

Numerical investigation on the effect of porosity distribution on the flame characteristics

The low velocity filtration combustion of a lean methane/air mixture in the fixed bed reactors is numerically investigated using the system scale method. The effect of porosity on the flame characteristics, such as temperature profile, flame displacement speed and flame shape is examined in this study. For comparison, porosity is considered in two forms, i.e., volumetric average porosity (VAP) and porosity spatial distribution function (PSDF). The simulation results show that, local distribution of porosity primarily affects the flame shape, while having minimal impact on the peak flame temperature and mean flame displacement velocity. Quantitative analysis indicates that the flame displacement velocity obtained using VAP is closer to the experimental data compared to the PSDF. However, the simulation with PSDF explicitly captures the flame front bending caused by local porosity variation. Velocity and temperature fields suggests that flame front bending predominantly depends on the local flame displacement speed (LFDS), which is the vector sum of local interstitial airflow speed and the laminar flame speed of the combustible gas. The radial difference in LFDS, which is associated with uniformity in velocity and temperature fields, serves as the main driving force for flame front instability. The inclusion of PSDF enables a more accurate prediction of flame front development by capturing the preferential flow near the wall.

Influence of Pulsatility and Inflow Waveforms on Tracheal Airflow Dynamics in Healthy Older Adults.

Tracheal collapsibility is a dynamic process altering local airflow dynamics. Patient-specific simulation is a powerful technique to explore the physiological and pathological characteristics of human airways. One of the key considerations in implementing airway computations is choosing the right inlet boundary conditions that can act as a surrogate model for understanding realistic airflow simulations. To this end, we numerically examine airflow patterns under the influence of different profiles, i.e., flat, parabolic, and Womersley, and compare these with a realistic inlet obtained from experiments. Simulations are performed in ten patient-specific cases with normal and rapid breathing rates during the inhalation phase of the respiration cycle. At normal breathing, velocity and vorticity contours reveal primary flow structures on the sagittal plane that impart strength to cross-plane vortices. Rapid breathing, however, encounters small recirculation zones. Quantitative flow metrics are evaluated using time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI). Overall, the flow metrics encountered in a real velocity profile are in close agreement with parabolic and Womersley profiles for normal conditions, however, the Womersley inlet alone conforms to a realistic profile under rapid breathing conditions.