Low Wind Conditions Research Articles

Prehospital Use of Ultrathin Reflective Foils.

Ultrathin reflective foils (URFs) are widely used to protect patients from heat loss, but there is no clear evidence that they are effective. We review the physics of thermal insulation by URFs and discuss their clinical applications. A conventional view is that the high reflectivity of the metallic side of the URF is responsible for thermal protection. In most circumstances, the heat radiated from a well-clothed body is minimal and the reflecting properties of a URF are relatively insignificant. The reflection of radiant heat can be impaired by condensation and freezing of the moisture on the inner surface and by a tight fit of the URF against the outermost layer of insulation. The protection by thermal insulating materials depends mostly on the ability to trap air and increases with the number of covering layers. A URF as a single layer may be useful in low wind conditions and moderate ambient temperature, but in cold and windy conditions a URF probably best serves as a waterproof outer covering. When a URF is used to protect against hypothermia in a wilderness emergency, it does not matter whether the gold or silver side is facing outward.

Spatiotemporal distribution of paralytic shellfish poisoning (PSP) toxins in Beagle Channel (South America) during 2005–2017

Toxigenic algal blooms have been reported since 1886 in the Beagle Channel, at the southern limit of South America, mainly associated with the occurrence of paralytic shellfish poisoning (PSP) toxins produced by dinoflagellates of the genus Alexandrium. Toxic outbreaks have serious impacts on marine wildlife and ecosystem services, particularly on fisheries and mussel aquaculture. Within the framework of the Shellfish Toxicity Monitoring Program carried out close to Almanza in Beagle Channel eastern coastal waters, here we analyzed the spatiotemporal patterns of PSP toxins in the Magellan mussel Aulacomya ater and the blue mussel Mytilus edulis, measured by the mouse bioassay for 12 years, between 2005 and 2017. PSP outbreaks occurred mostly during summer and their duration was significantly longer than for outbreaks detected during spring and winter. A marked interannual variability in their magnitude was also evident. The largest outbreaks were detected in summers 2010–2011, in extreme warm and low-wind conditions, reaching up to 5600 µg saxitoxin equivalent per 100 g of tissue, causing a closure of shellfish fisheries of up to 200 days. Small scale spatial variability in PSP was also found, the highest values being observed in the main mussel culture areas, and the lowest in the natural mussel beds. PSP toxicities for the Magellan mussel were significantly higher than for the blue mussel. Natural detoxification in mussels from Beagle Channel followed an exponential decay, with mean detoxification rates of 3.5% toxin day−1, lower than those from elsewhere in the world for similar PSP toxin concentrations, which means a longer time to attain concentration limits safe for human consumption. Understanding PSP dynamics is important to avoid large economic losses related to halting mussel production.

Comparison between oil spill images and look-alikes: an evaluation of SAR-derived observations of the 2019 oil spill incident along Brazilian waters.

Three SAR-derived observations of dark surface patches along the Northeastern Brazilian coastline by the end of 2019 were misreported in the Brazilian media as oil spill-related. Unfortunately, these observations were misled by false positives or look-alikes. Therefore, this paper aims to technically evaluate these look-alike classes by analyzing image attributes found to be helpful to the identification of ocean targets, including oil spills, rain cells, biofilms, and low wind conditions. We use image augmentation to extend our dataset size and create the probability density function curves. The processing includes image segmentation, optimal attribute extraction, and classification with random forest classifiers. Our results contrast with the open-source oil spill detection system and patch classifier methodology called "RIOSS." Analysis of the feature probability density functions based on optimal attributes is promising since we could capture most of the false positive targets in the three SAR-reported images in 2019. The only exception was the biofilm slick observed on October 28th, where the RIOSS mistakenly classified this organic patch as a low wind region with oil spots. This pitfall is acceptable at this project stage since we had only five biogenic film samples to train the algorithm.

Measurement and analysis for the improvement of efficiency and power of Savonius vertical axis wind turbines without dimples and fins

Energy effective approaches to improve the extraction of work from different sources of renewable energy are still appreciated in this energy starved world. Wind energy is one such widely used source. Wind energy is one of the world's most rapidly expanding electricity industries and most exciting alternative energy sources. A. Crespo, J. Hernandez, and S. Frandsen, “Survey of modelling methods for wind turbine wakes and wind farms Wind turbine technology is a method for converting wind kinetic energy into electrical energy. Efforts have been made in recent years to increase the capacity and reliability of standard Savonius VAWTs, which are not only easy to create but can also be used as a renewable energy source to meet the needs of rural areas with low power consumption. A.J. Alexander, B.P. Holownia Wind tunnel tests on a Savonius rotor; Journal of Industrial Aerodynamics In this present research paper, we analysis for the improvement of Efficiency and the power of the Savonius type wind turbine without using dimples on their blades and fins for more pressure generation Akwa, J. V., Vielmo et al., Review on the Performance of Savonius Wind Turbines“, Renewable and Sustainable Energy. the Savonius vertical axis wind turbine could be a safer alternative because it can also work in low wind conditions The aim of this model is to demonstrate its performance in varying wind conditions as opposed to the conventional horizontal axis wind turbine, and to contribute to its steady increasing popularity as a reliable source of power generation in the near future.

Enhancement of PV Panel Power Production by Passive Cooling Using Heat Sinks with Perforated Fins

This paper presents a numerical model regarding the passive cooling of PV panels through perforated and non-perforated heat sinks. A typical PV panel was studied in a fixed position, tilted at 45 degrees from the horizontal with the wind direction towards its backside. A challenging approach was used in order to calibrate the base case of the numerical model according to the NOCT conditions. Further validation of the accuracy of the numerical simulation consisted of a comparison between the results obtained for the base case, or heat sink, with horizontal non-perforated fins and the experiments presented in the literature. Six types of heat sink attached to the backside of the PV panel were numerically studied. The analyzed configurations focused on heat sinks with both perforated and non-perforated fins that were distributed horizontally and vertically. The CFD simulation was also conducted by modeling the air volume around the PV panel in real wind conditions. The main output parameters were the average temperature and the convective heat transfer coefficient on the front and back of the PV panel. The most important effect of cooling was achieved in low wind conditions and high levels of solar radiation. For vair = 1 m/s, G = 1000 W/m2 and ambient temperature tair = 35 °C, the percentage of maximum power production achieved 83.33% for the base case, while in the best cooling scenario it reached 88.74%, assuring a rise in the power production of 6.49%.

No Consistent Link Between Dust Storms and Valley Fever (Coccidioidomycosis).

Dust storms, such as those associated with haboobs and strong regional winds, are frequently assumed to cause increases in cases of Valley fever (coccidioidomycosis). The disease is caused by inhaling arthroconidia of Coccidioides fungi that, after being disturbed from semi‐desert subsoil, have become airborne. Fungal arthroconidia can be transported in low‐wind conditions as well as in individual dust events, but there is no reliable evidence that all or most dust storms consistently lead to subsequent increases in coccidioidomycosis cases. Following a review of the relevant literature, this study examines the relationship between dust storms and coccidioidomycosis cases to determine if there is a consistent and general association between them. All recorded dust storms from 2006 to 2020 in and near the Phoenix area of Maricopa County, Arizona and the Bakersfield area of Kern County, California were used in a compositing analysis (superposed epoch analysis) of subsequent coccidioidomycosis cases in each area. Analyses of monthly and weekly disease case data showed no statistical differences in the patterns of coccidioidomycosis cases following dust storms versus non‐dust storm conditions, for the entire data set as well as for seasonal subsets of the data. This study thoroughly analyzes post‐dust storm coccidioidomycosis cases for a large set of dust storms, and it confirms and expands upon previous literature, including a recent study that measured airborne arthroconidia and found no consistent links connecting wind and dust conditions to increases in coccidioidomycosis.

A review of the effectiveness of operational curtailment for reducing bat fatalities at terrestrial wind farms in North America.

Curtailment of turbine operations during low wind conditions has become an operational minimization tactic to reduce bat mortality at terrestrial wind energy facilities. Site-specific studies have demonstrated that bat activity is higher during lower wind speeds and that operational curtailment can effectively reduce fatalities. However, the exact nature of the relationship between curtailment cut-in speed and bat fatality reduction remains unclear. To evaluate the efficacy of differing curtailment regimes in reducing bat fatalities, we examined data from turbine curtailment experiments in the United States and Canada in a meta-analysis framework. We used multiple statistical models to explore possible linear and non-linear relationships between turbine cut-in speed and bat fatality. Because the overall sample size for this meta-analysis was small (n = 36 control-treatment studies from 17 wind farms), we conducted a power analysis to assess the number of control-treatment curtailment studies needed to understand the relationship between fatality reduction and change in cut-in speed. We also identified the characteristics of individual curtailment field studies that may influence their power to detect fatality reductions, and in turn, contribute to future meta-analyses. We found strong evidence that implementing turbine curtailment reduces fatality rates of bats at wind farms; the estimated fatality ratio across all studies was 0.37 (p < 0.001), or a 63% decrease in fatalities. However, the nature of the relationship between the magnitude of treatment and reduction in fatalities was more difficult to assess. Models that represented the response ratio as a continuous variable (e.g., with a linear relationship between the change in cut-in speed and fatalities) and a categorical variable (to allow for possible non-linearity in this relationship) both had substantial support when compared using AICc. The linear model represented the best fit, likely due to model simplicity, but the non-linear model was the most likely without accounting for parsimony and suggested fatality rates decreased when the difference in curtailment cut-in speeds was 2m/s or larger. The power analyses showed that the power to detect effects in the meta-analysis was low if fatality reductions were less than 50%, which suggests that smaller increases in cut-in speed (i.e., between different treatment categories) may not be easily detectable with the current dataset. While curtailment is an effective operational mitigation measure overall, additional well-designed curtailment studies are needed to determine precisely whether higher cut-in speeds can further reduce bat fatalities.

Quantifying the impacts of urban morphology on modifying microclimate conditions in extreme weather conditions

It is well-known that the morphology of urban areas modifies the variations of climate variables at microscale; known as microclimate conditions. The complexity of urban morphology can lead to undesired wind conditions or excessive air temperature; particularly in extreme weather conditions. This study attempts to quantify the impacts of urban morphology on the evolution of wind speed and air temperature at the urban canopy layer using Computational Fluid Dynamic (CFD) simulations. In this regard, three urban neighbourhoods are generated based on a novel urban morphology parameterization method and assessed in two extreme low and high wind conditions. Results showed that wind speed (up to 75%) and air temperature (up to 28%) at the microscale can get amplified or dampened in extreme conditions. A negative correlation was observed between wind speed and air temperature variations indicating a great potential to reduce outdoor air temperature through heat removal in urban canyons. The findings of the study are categorized based on the morphological parameters to present a series of design-based strategies for the newly-built urban neighbourhoods.

Performance Analysis of Multi Rotating Savonius Turbines for Exhaust Air Energy Recovery Through CFD Simulations

Wind energy generation in adverse conditions has always been a challenge for the energy industry, especially at low wind speeds. Vertical axis wind turbines (VAWT) are promising solutions for low and turbulent wind conditions; however, their low efficiency has been a problem for their application and requires further research initiatives. In this research, a multi-Savonius VAWT arrangement is tested to use an unnatural wind source, a cooling tower exhaust, to improve the turbine performance. The analysis method was done by a series of two-dimensional computational fluid dynamics (CFD) simulations using Ansys FLUENT. A grid sensitivity test was performed, and the numerical model was validated against published numerical and experimental results. Test cases with single and multi-turbine configurations at six different tip speed ratios were then performed to calculate the turbine performance. The multi-turbine configuration improved the power coefficient by up to 19.29%. The multi- turbine arrangement has proven to be an effective means of increasing the performance of the Savonius turbine for the exhaust energy recovery system.

The Imprint of Primary Production on High-Frequency Profiles of Lake Optical Properties.

Water inherent optical properties (IOPs) contain integrative information on the optical constituents of surface waters. In lakes, IOP measurements have not been traditionally collected. This study describes how high-frequency IOP profiles can be used to document short-term physical and biogeochemical processes that ultimately influence the long-term trajectory of lake ecosystems. Between October 2018 and May 2020, we collected 1373 high-resolution hyperspectral IOP profiles in the uppermost 50 m of the large mesotrophic Lake Geneva (Switzerland-France), using an autonomous profiler. A data set of this size and content does not exist for any other lake. Results showed seasonal variations in the IOPs, following the expected dynamic of phytoplankton. We found systematic diel patterns in the IOPs. Phases of these diel cycles were consistent year-round, and amplitudes correlated to the diurnal variations of dissolved oxygen, clarifying the link between IOPs and phytoplankton metabolism. Diel amplitudes were largest in spring and summer under low wind condition. Wind-driven changes in thermal stratification impacted the dynamic of the IOPs, illustrating the potential of high-frequency profiles of water optical properties to increase our understanding of carbon cycling in lake ecosystems.

Effect of the wind acceleration magnitude during the first stages of the wind-wave generation process

A comprehensive analysis of the wavefield evolution under accelerated wind conditions provides an essential contribution to understanding the wind-wave generation process. A set of experiments was carried out in a large wind-wave facility where it is possible to reproduce high wind speed conditions to study the wind acceleration effect in the wind-wave development. The facility was equipped with high-frequency sampling devices that provide accurate air turbulence and water surface displacement measurements. From this deployment, it was possible to describe the evolution of the wave characteristics under different magnitudes of constant wind acceleration in detail. This study analyzes the wind acceleration effect in the early stages of wind-wave generation and evolution. The increase of spectrum energy saturation level and the downshift of the peak frequency are processes associated with the spectral shape evolution under low acceleration wind conditions. Under high wind acceleration conditions, the spectral shape did not vary with wind speed and fetch. Despite under low acceleration wind conditions, the wavefield is more developed than under high acceleration wind conditions; there was no direct relation between wind acceleration and the wavefield efficiency to grow. Besides, during these early instants, it was observed that a more developed wave field, associated with low acceleration wind conditions, could slow down the increase of drag coefficient with wind speed.

Atmospheric CO2 Exchange of a Small Mountain Lake: Limitations of Eddy Covariance and Boundary Layer Modeling Methods in Complex Terrain

AbstractLakes receive and transform significant amounts of terrestrial carbon and are often considered a source of atmospheric carbon dioxide (CO2). Yet, continuous direct measurements of lake‐atmosphere CO2 exchange with high temporal resolution are sparse. In this study, we measured the CO2 exchange of a mountain lake in the eastern Austrian Alps continuously for one year using the eddy covariance (EC) and the boundary layer model (BLM) approaches. Results from both the EC and the BLM methods indicated the lake to be a small source of atmospheric CO2 with highest emissions in fall. EC flux measurements were affected by low‐frequency contributions especially during low wind conditions. The CO2 concentration gradient at the air‐water interface decreased during night‐time due to an increase in atmospheric CO2 above the lake, likely caused by cold and CO2‐rich air draining from the surrounding land. Consequently, BLM fluxes were lower during night‐time than during daytime. This diel pattern was lacking in the EC flux measurements because the EC instruments deployed at the shore of the lake did not capture low nocturnal lake CO2 fluxes due to the local wind regime. Overall, this study illustrates the effect of the surrounding landscape on lake‐atmosphere flux measurements. We conclude that estimating CO2 evasion from lakes situated in complex topography needs to explicitly account for biases in EC flux measurements caused by low‐frequency contributions and local wind regimes.

Assessment of emission-source contribution to spatial dispersion for coal crusher agglomeration using prognostic model

The emission of inhalable particulates (PM 10 ) from coal comminution processing is detrimental to the air quality. However, limited works have been carried out for the estimation of emission and dispersion of PM 10 from coal crushers and its ancillary operations. In this study, field-based measurements and regulatory dispersion model coupled with Weather Research Forecasting (WRF) were applied to investigate the assimilative capacity (AC) of a region with operational coal crushers. The model run was found ‘acceptable’ when compared with measured values according to set performance criteria. Furthermore, the validated model parameterization was used to forecast the dispersion effects by various emission control alternatives recommended by regulators viz. covering of conveyor belts, paving of the unpaved road, reducing feed rate, etc. Results suggested that the major contribution of PM 10 was from transportation and loading of coal after crushing, while PM 10 levels from crushing dissipated in a smaller area. Paving of transport roads and bunker/silo-based loading were effective control measures as emissions reduced by 30.67%–52.51%. The relationship between distance and emission load revealed that PM 10 concentrations below 100 μg/m 3 were achieved at approximately 750 m away from emission sources in the present study. Crusher's operations with existing emissions of 23.43 g/day/m 2 were detrimental for the region's AC and needed to be stepped down to 11.71 g/day/m 2 . In particular, using modeled meteorological data provided reasonable forecasts for allowable emissions and planning to site crusher operations. Correction to the low-wind conditions resulted in a better simulation of mean annual estimates than daily estimates of PM 10 . Such visualization of spatially explicit frameworks will guide policymakers in strengthening regulations. • Emissions from coal crushers and linked transport roads evaluated for spatial dispersion. • Transport bottlenecks are formed at feed point of crushers resulting in lower dispersion. • Emission reduction vis-à-vis dispersion by adopting controls recommended by regulators forecasted. • Paved roads and bunker/silo based loading enhanced available assimilative capacity. • Wind speed was key variable with low wind correction resulted in better mean annual estimates.

Sampling Constraints and Variability in the Analysis of Bacterial Community Structures in the Sea Surface Microlayer

The sea surface microlayer (SML) is a thin surface film located at the interface between oceans and the atmosphere. In this study, three SML samplers—polycarbonate membrane (PC), glass plate (GP), and drum sampler (DS)—were used to collect microbiological DNA samples for molecular analysis. Among the three samplers, DS only took half the time to sample the SML compared to GP while PC were able to sample the thinnest SML depth. Biological matter and distinct bacterial communities in the SML were apparent during low wind conditions in samples collected by three samplers. Signs of biological matter [transparent exopolymer particles (TEP) and chlorophyll-a concentrations] depletion, and an increased similarity in the biological communities of the SML and underlying water (UW), were more pronounced during high wind speed conditions in samples collected by GP and DS. GP samples had lower biological matter enrichment than DS samples compared with UW. The depletion of biological matter in GP samples were more apparent during periods of high chl-a concentrations in the SML. In contrast, PC was able to consistently sample an SML community distinct from that of the UW, regardless of wind conditions. Bacterial community DNA samples obtained by the three SML samplers showed relatively consistent patterns of community structure, despite large fluctuations between seasons (summer vs. winter) and layers (SML vs. UW) being observed. Although no SML-specific taxon was detected in this study, a comparison of the representation of taxonomic groups in each sample suggested that certain taxa (15 orders) were specifically enriched or depleted in the SML, especially taxa belonging to Actinobacteria, Cyanobacteria, Deferribacteria, and Proteobacteria. This trend was consistent regardless of sampling method, implying that these bacterial groups are key taxa in the biogeochemical processes occurring at the air-sea interface.

Determining Optimum Rotary Blade Design for Wind-Powered Water-Pumping Systems for Local Selected Sites

The design of a windmill rotor is critical for harnessing wind energy. In this work, a study is conducted to optimize the design and performance of a rotor blade that is suitable for low wind conditions. The windmills’ rotor blades are aerodynamically designed based on the SG6043 airfoil and wind speed data at local selected sites. The aerodynamic profile of the rotor blade that can provide a maximum power coefficient, which is the relation between real rotor performance and the available wind energy on a given reference area, was calculated. Different parameters, such as blade shapes, chord distributions, tip speed ratio, geometries set angles, etc., were used to optimize the blade design with the objective of extracting maximum wind power for a water pumping system. Windmill rotor of 10.74 m, 7.34 m, and 6.34 m diameter with three blades were obtained for the selected sites at Abomsa, Metehara, and Ziway in south-east Ethiopia. During the rotary blades performance optimization, blade element momentum (BEM) theory and solving iteration by MATLAB® coding were used.

Determining Optimum Rotary Blade Design for Wind-Powered Water-Pumping Systems for Local Selected Sites

The design of a windmill rotor is critical for harnessing wind energy. In this work, a study is conducted to optimize the design and performance of a rotor blade that is suitable for low wind conditions. The windmills’ rotor blades are aerodynamically designed based on the SG6043 airfoil and wind speed data at local selected sites. The aerodynamic profile of the rotor blade that can provide a maximum power coefficient, which is the relation between real rotor performance and the available wind energy on a given reference area, was calculated. Different parameters, such as blade shapes, chord distributions, tip speed ratio, geometries set angles, etc., were used to optimize the blade design with the objective of extracting maximum wind power for a water pumping system. Windmill rotor of 10.74 m, 7.34 m, and 6.34 m diameter with three blades were obtained for the selected sites at Abomsa, Metehara, and Ziway in south-east Ethiopia. During the rotary blades performance optimization, blade element momentum (BEM) theory and solving iteration by MATLAB® coding were used.

Effects of different wind directions on ventilation of surrounding areas of two generic building configurations in Hong Kong

This study investigated effects of incident wind angles on wind velocity distributions in wakes of two generic building configurations, namely, ‘T’- and ‘+’-shaped, and the air pressure distributions along their leeward walls by using computational fluid dynamics simulations. Results show that when the wind approaches laterally (90°) (vs. when the wind is direct (0°)), the downwind length and maximum bilateral width of the low-wind velocity zone in the wake of ‘T’-shaped building decrease by 11.5% and 37.9%, respectively. When the incident wind is oblique (45°) (vs. when it is direct), the length and width of this low-wind velocity zone in the wake of ‘+’-shaped building decrease by 15.0% and 30.9%, respectively. Furthermore, results show that the air pressure on the leeward walls of the ‘T’- and ‘+’-shaped buildings gradually decreases along with the building height. The resulting low-wind conditions on upper floors of buildings reduce the fresh air intake of their leeward units utilizing natural ventilation. It is particularly apparent in the case of direct approaching wind. Thus, the appropriate selection of building configurations and their orientations allows for the most effective use of wind to enhance ventilation in indoor and urban environments.

Performance analysis of natural convection correlations for spheres at high Rayleigh numbers

There are industrial applications, such as spherical tanks under very low wind conditions, in which natural convection from spheres at high Rayleigh numbers can be of great importance. Due to different limitations, this problem has been studied either experimentally or numerically for Rayleigh numbers smaller than 1011, approximately. Furthermore, just a few correlating equations are available in scientific literature beyond that limit. Thus, a CFD model has been developed to estimate the overall heat transfer to large spheres with Rayleigh numbers ranging from 4·108 to 2·1014. A set of 48 cases of spheres with different diameters (1m–40 m) and under different air and sphere surface temperatures were numerically simulated. Besides, the results of the average Nusselt number provided by the CFD model and the available correlating equations were compared and deviations quantified. At the model validation stage, CFD estimations of the overall Nusselt number showed good agreement with experimental observations (7.1% of average relative error) while correlating equations deviated up to more than 28% on average. From the cases studied, CFD results suggest that Kitamura et al.‘s correlating equation could be extended beyond its reported limits of validity. A comparison analysis has also shown high discrepancies, up to 40%, among correlations.

Factors determining the occurrence of floret sterility in rice in a hot and low-wind paddy field in Jianghan Basin, China

• High temperature (<36.5 °C) and low wind induced floret sterility in the paddy field. • High temperatures increased the sterility through processes after pollen germination. • Wind lessened the sterility through stable pollination and probably via cooling. • Positive effects of low and erect panicle, and short anther were newly demonstrated. • Positive effects of long basal anther dehiscence and early flowering were confirmed. Global warming may increase the occurrence of heat-induced floret sterility (HIFS) in rice. The effects of meteorological factors and plant traits on the occurrence of floret sterility have only been examined independently and under controlled or simplified conditions. The aim of this study was to comprehensively clarify the role and impact of these factors in HIFS in rice under practical field conditions. We observed pollination and seed set of 12 rice cultivars with wide variation in traits potentially related to HIFS for 3 years in a paddy field in the Yangtze Valley in China where HIFS sometimes occurs. Floret sterility increased as temperature increased under moderately high temperatures (32–36.5 °C) and low-wind conditions (<3.5 m s −1 at flowering time). Path analysis with multiple regression revealed that high temperatures increased the occurrence of floret sterility through processes after pollen germination on the stigma and that wind lessened the occurrence of floret sterility; the magnitude of the wind effect was equivalent to that of high temperature. Multiple regression analysis estimated that low and erect panicles, and short anthers have positive effects on tolerance to HIFS and known heat tolerance traits, e.g., long anther dehiscence at the base of the anther and early morning flowering. The results clarified the factors that control HIFS in the paddy field and identify the processes and traits that scientists and breeders should focus on to mitigate HIFS under global warming.

Enlightenment of re-entry airflow: The path of the airflow and the airborne pollutants transmission in buildings

Viable aerosols in the airflow may increase the risk of occupants contracting diseases. Natural ventilation is common in buildings and is accompanied by re-entry airflow during the ventilation process. If the re-entry airflow contains toxic or infectious species, it may cause potential harm to residents. One of the Covid-19 outbreaks occurred in a public residential building at Luk Chuen House (LC-House) in Hong Kong. It is highly suspected that the outbreak of the disease is related to the re-entry airflow. The study attempts to explain and discuss possible causes of the outbreak. In order to understand the impact of airflow on the outbreak, a public residential building similar to LC-House was used in the study. Two measurements M − I and M − II with the same settings were conducted for a sampling unit in the corridor under low and strong wind conditions respectively. The sampling unit and the tracer gas carbon dioxide (CO2) were used to simulate the index unit and infectious contaminated airflow respectively. The CO2 concentrations of the unit and corridor were measured simultaneously. Two models of Traditional Single-zone model (TSZ-model) and New Dual-zone model (NDZ-model) were used in the analysis. By comparing the ACH values obtained from the two models, it is indicated that the re-entry airflow of the unit is related to the corridor wind speeds and this provides a reasonable explanation for the outbreak in LC-House, and believes that the results can help understand the recent frequent cluster outbreaks in other residential buildings.