Yifan Fan

• PhD
• Zhejiang University

Cities experience the most severe hot and polluted environment under calm conditions. To understand how complex urban terrain affects the wind and thermal environment, a city scale simulation was conducted with CFD (Computational Fluid Dynamics) and field transformation method to analyze the urban heat island circulations. A multi-layer refinement...

The Kowloon Peninsula, an urban area of Hong Kong, might be one of the most studied cities in terms of urban climate in the world. Both annual mean urban air temperature and humidity have been on the rise following the continual increase in the building volume and continual reduction in the average wind speed in the urban canopy layer. The observed...

Light-framed timber structure (LTS) buildings have been highly valued in recent years due to their low-carbon characteristics. However, the applicability of the building envelope is closely related to indoor and outdoor conditions. The hot summer and cold winter (HSCW) climate zone in China has high humidity and great temperature variation througho...

High-resolution urban surface information, e.g., the fraction of impervious/pervious surface, is pivotal in studies of local thermal/wind environments and air pollution. In this study, we introduced and validated a domain adaptive land cover classification model, to automatically classify Google Earth images into pixel-based land cover maps. By com...

There is growing evidence of the high transmission potential of COVID-19 through virus-laden aerosols. Because aerosols are inhaled in various concentrations, an overall assessment of transmission risks at different indoor scales is crucial. However, a comprehensive risk assessment method that evaluates the direct link between short-range and room-...

Changed urban surface and human activities in urban areas have led to serious environmental problems globally, including deteriorated local thermal/wind environments and air pollution. In this study, we proposed and validated a domain adaptive land cover classification model, to automatically classify Google Earth images into pixel-based land cover...

The outbreak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has caused an unparalleled disruption to daily life. Given that COVID-19 primarily spreads in densely populated indoor areas, urban public transport (UPT) systems pose significant risks. This study presents an analysis of the air change rate in buses, subways,...

The characteristics of energy balance and heat transfer on building walls are important for building energy consumption and outdoor thermal/wind environment. The in-situ measurement of energy balance and wall flows during clear days on a 16-story building in Guangzhou, China is introduced and analyzed in this paper. The velocity along the wall was...

Experimental investigations using wind and water tunnels have long been a staple of fluid mechanics research for a large number of applications. These experiments often single out a specific physical process to be investigated, while studies involving multiscale and multi-physics processes are rare due to the difficulty and complexity in the experi...

The availability of high spatio-temporal resolution of urban air temperature is paramount for understanding urban heat island (UHI) and developing effective mitigation strategies, in particular for local-scale mitigations. Obtaining high spatial resolution of air temperature at city-scale is challenging as the quantity of weather stations is often...

Urban areas are experiencing excessive heating. Addressing the heat is a challenging but essential task where not only engineering and climatic knowledge matters but also a deep understanding of social and economic dimensions. We synthesize the state of the art in heat mitigation technologies and develop an 'ITE index' framework that evaluates the...

Beating excessive urban heat calls for a whole-system approach, where several individual mitigation measures have to be implemented together. We assess the use of green walls, green roofs, reflective roofs, thermally efficient buildings, high-efficiency indoor cooling, urban forestry, evaporative pavement, and constructed shade for directly reducin...

Urban heat dome flow forms under calm background conditions, which has large impacts on urban ventilation, building energy consumption and pollutants dispersion. With ongoing rapid and intense urbanisation, an increasing number of megacities have emerged. The hydraulic diameter of megacities can reach beyond than 20 km, leading to the Coriolis forc...

A significant portion of the cooling or heating load of buildings is contributed by relatively large heat flux through thermal bridges. Water vapour concentration significantly alters thermal conductivity and heat transfer characteristics within the thermal bridges, affecting building energy consumption, particularly in humid climates. Moreover, th...

Moisture in building envelopes increases the energy consumption of buildings and induces mould growth, which may be amplified within the area of thermal bridges due to their different hygrothermal properties and complex structures. In this study, we aimed to (1) reveal the moisture distribution in the typical thermal bridge (i.e., wall-to-floor the...

The hygric performance of building envelopes determines the degradation progress. Multiple factors, including the climate parameters (e.g., solar radiation and wind-driven rain) and building structure (e.g., thermal bridges), significantly affect the hygrothermal conditions in building envelopes. Inappropriate thermal insulation measures may exacer...

The urban heat island (UHI) phenomenon has gained increasing attention as it not only affects the energy consumption of buildings but also threatens the health of urban dwellers. In this study, we calculated the UHI intensity in major China cities across different climates based on the measured weather data of year 2019. The influences of UHI inten...

Under calm conditions where the background synoptic wind is weak or absent, the difference between city and rural temperature allows natural convection to develop. The turbulent circulation is also referred as urban heat island circulation or urban heat dome flow. The coupling of buoyancy, inertia, and vertical stability induces a natural periodici...

Urban heat island (UHI) draws more attention as it affects not only the health of residents but also the energy consumption of buildings at the city scale. To achieve carbon neutrality goals, it is crucial to better understand the mechanism of the UHI influences on building energy consumption. The characteristics of urban heat island intensity (UHI...

Moisture in the building envelopes increase the energy consumption of buildings and induce mould growth, which may be amplified within the area of thermal bridges due to their different hygrothermal properties and complex structures. In this study, we aimed to (1) reveal the moisture distribution in the typical thermal bridge (i.e., wall-to-floor t...

Moisture in the building envelopes increase the energy consumption of buildings and induce mould growth, which may be amplified within the area of thermal bridges due to their different hygrothermal properties and complex structures. In this study, we aimed to (1) reveal the moisture distribution in the typical thermal bridges (i.e., wall-to-floor...

The moisture modifies the characteristics of heat transfer in building envelopes. Multiple factors, including the distinct hygric properties of various material, gravity, etc ., affect the moisture content, resulting in a non-uniform distribution of water vapour in different parts of the envelope (e.g. column, beam, the main part of exterior walls)...

Natural convection arising over vertical and horizontal heated flat surfaces is one of the most ubiquitous flows at a range of spatiotemporal scales. Despite significant developments over more than a century contributing to our fundamental understanding of heat transfer in natural convection boundary layers, certain “hidden” characteristics of thes...

With increasing urbanisation, the fraction of built-up areas and human activities increase, deteriorating the urban thermal environment and air quality. To improve the urban environment, wind corridors have attracted much research attention in recent years. In this study, a sky-view factor (SVF)-based method is proposed and verified for the potenti...

Urban surface composition is key information for global carbon emission estimation, mesoscale numerical simulations, and outdoor environment studies at both city and neighborhood scales. High spatial-resolution satellite imagery can provide accurate urban surface data. Due to the large volume of data, it is time-consuming to extract manually inform...

Effective infection prevention and control measures are required in the intensive care units of hospitals, as these areas have a high incidence of nosocomial infections. Adopting proper ventilation pattern that is efficient in pollutant removal is important for controlling the spread of infectious diseases. In this study, the computational fluid dy...

Severe haze episodes and extreme heat events are both related to the strong inversion in the atmospheric boundary layer. Inversion breakup is the main mechanism to alleviate the accumulation of heat or pollutants, especially in urban areas. However, the physical process and turbulent flow structures of inversion breakup remain unclear. In this stud...

The amount of heat loss through thermal bridges increases with the improvement of the thermal insulation performance of the building exterior wall, making thermal bridges vulnerable points of thermal insulation. The wall-to-floor thermal bridge (WFTB) takes the most considerable fraction on the building envelope and has the largest heat flux. In th...

Natural convection flow above a heated horizontal area plays a major role in energy utilisation, indoor/outdoor thermal environment, city ventilation and pollutant dispersion. Such natural convection can present different flow patterns, and identifying the type of flow pattern is crucial for determining the bulk heat transfer coefficient. Water tan...

The severity of urban air pollution problems in China increases with the city's size and population density. Outdoor air pollution not only affects indoor air quality but also increases building energy consumption. We analyzed the characteristics of urban air pollution in China based on long-period monitoring data with high temporal resolution (hou...

When background wind is moderate, urban environment may face great challenges as removal ability of airborne pollutants, anthropogenic heat and moisture reduces. Under this condition, buoyancy-driven flow can break the dominant role of the background wind and affect the urban environment greatly. Knowledge of buoyant flow dynamics is essential for...

The adverse environmental impacts of the urban heat island (UHI) phenomenon have been known amid rapid urbanization in many parts of the world. UHI-induced circulation (UHIC) can affect pollutant dispersion and heat exchange. An UHIC can transform into an urban plume (or perturbed UHIC) in the presence of regional wind. To understand the urban plum...

Natural convection over an isolated horizontal plate in a stably stratified background condition is fundamental and challenging in industrial, atmospheric, geographical, and oceanic environmental studies, which, however, is still lack of investigation. In this study, the water tank modelling experiment with two main techniques, Thermal Image Veloci...

Air pollution and extreme heat waves are among the major environmental challenges faced by modern cities. Stable stratification and temperature inversion help to trap urban airborne pollutants and produce a strong urban heat island intensity. Such adverse effects can disappear when the buoyancy flows introduced by the city heat is sufficiently stro...

Extreme heatwaves and air pollution in urban areas often occur in calm and stable background conditions. In such situations, urban heat dome flows are induced by the urban heat island (UHI) effect, which has a strong influence on the urban thermal and wind environment. Cities have various shapes, but most studies of urban heat island circulation ha...

This paper presents a numerical study of two interacting urban heat island circulations (UHICs) in the presence of weak background wind. The Weather Research and Forecasting (WRF) model was used with ideal settings without the Earth's rotation effect. UHICs were simulated over circular cities of the same size arranged in tandem or side by side with...

The paper performs an investigation on multi-scale coherent structures that exist in different flow patterns of triple interacting plumes. Time-averaged and turbulent flow characteristics are first obtained by the two-dimensional (2-D) particle image velocimetry (PIV) technique. Proper orthogonal decomposition (POD) method is then applied to extrac...

The mean and random components of the velocity field at very low wind speeds in a convective boundary layer (CBL) over a wide urban area are dominated by large eddy structures—either turbulent plumes or puffs. In the mixed layer at either side of the edges of urban areas, local mean recirculating flows are generated by sharp horizontal temperature...

This paper presents a systematic experimental study on stream-wise flow development and spatial structure of triple buoyant plumes. Two-dimensional Particle Image Velocimetry (2-D PIV) is employed to resolve velocity fields. Stream-wise axial velocity profiles, flow structure, flow region parameters, and self-similarity properties are analyzed at d...

The Weather Research and Forecasting (WRF) Model is used to study the interaction between urban heat island circulation (UHIC) and its background wind. Two distinct wind regimes are found depending on the ratio of the horizontal convective scale velocity to the background velocity, which is referred to as the buoyancy velocity ratio. When the buoya...

High-rise deep street canyons usually experience poor ventilation and large vehicular pollutant exposure to residents in near-road buildings. Investigations are still required to clarify the flow and dispersion mechanisms in deep street canyons and explore techniques to reduce such large pollutant exposure. By conducting computational fluid dynamic...

Sustainable urban design is an effective way to improve urban ventilation and reduce vehicular pollutant exposure to urban residents. This paper investigated the impacts of urban open space and ‘lift-up’ building design on vehicular CO (carbon monoxide) exposure in typical three-dimensional (3D) urban canopy layer (UCL) models under neutral atmosph...

Urban heat island-induced circulation, or urban heat dome flow, significantly influences urban thermal environments and air quality in calm wind conditions with stable stratification. An urban heat dome is characterized by convergent inflow at the ground level, divergent outflow at the upper level and upward flow over the city center in calm condit...

Urban heat island circulation (UHIC), commonly established under calm background conditions, is important for understanding the accumulation of pollutants and heat in a city. In a city cluster in which multiple cities exist in proximity, the resulting multiple UHICs can interact. As many city clusters continue to grow in size and in number, particu...

Urban heat dome flow, which is also referred to as urban heat island circulation, is important for urban ventilation and pollutant transport between adjacent cities when the background wind is weak or absent. A “dome-shaped” profile can form at the upper boundary of the urban heat island circulation. The horizontal extent of the heat dome is an imp...

The natural convective wall flows along an exterior wall of a 16-story high-rise building were measured in Guangzhou city, China. The Rayleigh number reached as high as 10¹⁴. The correlation between the vertical velocity along the wall and the temperature difference between the wall surface and ambient air was analyzed. The diurnal variation of the...

In the buoyancy and turbulence-driven atmospheric circulations (BTDAC) that occur over urban areas where the approach means wind speeds are very low (less than turbulent fluctuations and typically <. 3. m/sec), the surface temperatures are significantly higher than those in the external rural areas, and the atmosphere above the mixing layer is stab...

Urban heat island circulation establishes an urban dome under stable stratification and no background wind conditions. Small-scale water models have been a very useful tool in the exploration of the mechanisms by which urban domes and their associated wind flows are formed. Data are available from a number of water-tank heat island models. Data fro...

The flow caused by natural convection adjacent to a heated vertical wall (wall flow) is an important mechanism in the creation of wind flows in a city when the background wind is weak. The wall flows along a 16-storey building were measured in Guangzhou, China. Fourteen three-dimensional ultrasonic anemometers were installed on three floors to stud...