Jonas Allegrini

Plants modify the climate and provide natural cooling through transpiration. However, plant response is not only dependent on the atmospheric evaporative demand due to the combined effects of wind speed, air temperature, humidity, and solar radiation, but is also dependent on the water transport within the plant leaf-xylem-root system. These intera...

As cities and their population are subjected to climate change and urban heat islands, it is paramount to have the means to understand the local urban climate and propose mitigation measures, especially at neighbourhood, local and building scales. A framework is presented, where the urban climate is studied by coupling a meteorological model to a b...

Street trees are more and more regarded as an effective measure to reduce excessive heat in urban areas. However, the vast majority of mesoscale urban climate models do not represent street trees in an explicit manner and, for example, do not take the important effect of shading by trees into account. In addition, urban canopy models that take inte...

A computational fluid dynamics (CFD) model was developed in the open-source CFD toolbox OpenFOAM for studying microscale urban flows during periods of weak synoptic forcing. The OpenFOAM model is coupled to the regional atmospheric model COSMO to provide boundary conditions for atmospheric variables. The urban canopy model DCEP is used to calculate...

Street trees are more and more regarded as an effective measure to reduce excessive heat in urban areas. However, the vast majority of mesoscale urban climate models do not represent street trees in an explicit manner and for example do not take the important effect of shading by trees into account. In addition, urban canopy models that take intera...

In the face of an increasing number of urban climate modelling studies performed at sub‐kilometre resolution, systematic investigations of the performance of high‐resolution urban climate simulations and their dependency on spatial resolution are still very sparse. This study investigates the impact of the scale of representation of the urban area...

Plant response is not only dependent on the atmospheric evaporative demand due to the combined effects of wind speed, air temperature, humidity, and solar radiation, but is also dependent on the water transport within the leaf-xylem-root system. Therefore, a detailed understanding of such dynamics is key to the development of appropriate mitigation...

The influence of trees in urban areas is typically assessed using urban microclimate models. These models rely on wind tunnel experiments using small-scale tree models to verify and validate their predictions of the flow field. However, it is not known sufficiently to which extent small model trees used in wind tunnel studies can recreate the behav...

In this presentation I introduced a newly developed urban climate model with explicit representation of street trees. The model is first evaluated against field measurements and then applied to study the citywide impact of street trees.

The assessment of the aerodynamic forces acting on transmission towers is of crucial importance for their design. These predictions are mainly based on an extrapolation of wind tunnel measurements done on simple structures which are the base of the present design codes. This extrapolation results in an uncertainty which often leads to insufficientl...

Higher temperatures are measured in urban areas compared to surrounding rural areas due to the urban heat island effect. One of the most efficient ways of removing heat from urban areas is wind-driven ventilation. Building configurations have a strong impact on the wind flow patterns and therefore on the heat removal from urban areas. Buoyancy can...

The Poster shows the Mesoscale Climate Modelling Workflow to investigate the Urban Heat Island Effect

Vegetation can provide transpirative cooling in cities and is therefore being increasingly integrated as an essential part of Urban Heat Island (UHI) mitigation strategies. However, the behaviour of vegetation must be accurately understood to determine the effectiveness of vegetation based solutions. In this study, vegetation is modelled as a porou...

The study of wind driven rain is an important design consideration in the built environment. Numerical prediction of this phenomenon requires knowledge of wind speed, rain drop sizes and rain fall intensity among others. The wind speed and rain drop sizes are usually calculated from field measurements. Rainfall intensity is usually assumed to follo...

Wind-flow field around a semi-outdoor structure can differ significantly from the one around a building. As a result, the design of such a structure can have a strong impact on the rain exposure. This paper studies the wind-driven rain (WDR) sheltering for a prototype of a small railway station shelter designed for rural areas. Computational fluid...

The temperatures in cities are increased due to the urban heat island effect. Heat can be removed from urban areas by wind and buoyancy driven ventilation. Building geometries have a strong impact on the wind flow patterns and heat removal in urban areas. The microclimate is analysed for a generic urban area with 23 buildings. Six different urban t...

free to download till 11 July 2017 under https://authors.elsevier.com/a/1V5BZ4s9Hvq7DQ As technology has advanced, the increasing pressure on energy usage reduction and expectations of consumers regarding comfort have made the requirements posed on clothing and control of the indoor climate more demanding. These goals, in turn, require advanced and...

Shelters, instead of buildings, are used at small railway stations in Switzerland to protect waiting passengers from environmental loading such as wind, rain and sun. As they are mostly located on open terrain, small railway stations are exposed to wind and therefore require wind comfort analysis. Generally, the same shelter design is used for a la...

A nested Large Eddy Simulation (LES) is used to compute the multiscale interaction between the Atmospheric Boundary Layer (ABL) and an existing cluster of buildings over the real topography. A Neutral ABL (NBL) and a Convective ABL (CBL) are simulated. As the ABLs develop over a no-flat terrain with heterogeneous roughness elements, standard ABL-LE...

Due to the urban heat island (UHI) effect the air temperatures in urban areas are most of the time higher compared to the temperatures in rural areas. Further the wind speeds are lower due to wind sheltering. In the past decades cities and therefore also the urban heat islands have been continuously growing. The local microclimate has a strong impa...

Understanding flows in urban areas is important for a wide range of research areas. In this study the influence of different angular configurations of two buildings on the local wind climate is analysed. PIV (particle image velocimetry) measurements are conducted in an atmospheric boundary layer wind tunnel. Blocken et al. (2008a) showed that, coun...

Large Eddy Simulation (LES) of obstacle-resolved flow over extended urban areas is still extremely costly, compared to the common practice of modeling obstacles with a rough wall-function. In the current study we investigate whether a one-way nesting procedure, consisting of a highly-resolved, small-scale LES embedded inside a low-resolution, large...

There is worldwide a trend towards urbanization, and cities try to improve their sustainability by saving natural resources and energy, and to mitigate the impact of climate change. Therefore growing cities need to optimize the energy demand of their new and existing buildings. There are a large number of urban scale phenomena that influence the en...

An experimental setup was developed to perform wind tunnel measurements on a unit-ratio, 2D open cavity under perpendicular incident flow. The open cavity is characterized by a mixing layer at the cavity top, that divides the flow field into a boundary layer flow and a cavity flow. Instead of precisely replicating a specific type of inflow, such as...

The mesoscale weather and climate model COSMO in Climate Mode (CCLM) is used in this study to investigate the impact of model resolution and urban parametrization on urban climate modeling. Two urban parameterizations with a different level of complexity are used, the urban land surface model TERRA-URB and the Double-Canyon Radiation Scheme (DCEP)....

We present a comprehensive review of modelling approaches and associated software tools that address district-level energy systems. Buildings play an important role in urban energy systems regarding both the demand and supply of energy. It is no longer sufficient to simulate building energy use assuming isolation from the microclimate and energy sy...

This work focuses on substituting a computationally expensive simulator by a cheap emulator to enable studying applications where running the simulator is prohibitively expensive. The procedure consists of two steps. In a first step, the emulator is calibrated to closely mimic the simulator response for a number of pre-defined cases. In a second st...

In the past decades the portion of the population living in urban areas has continuously increased. Due to the high building density, the microclimate in urban areas changes significantly compared to rural areas. The temperatures measured in urban areas are higher compared to the rural temperatures due to the urban heat island (UHI) effect. Further...

In the past decades cities have been continuously growing. The microclimate in urban areas differs significantly from the microclimate in rural areas. The temperatures in urban areas are most of the time higher due to the urban heat island (UHI) effect and the wind speeds are lower due to wind sheltering. The local microclimate strongly influences...

Computational fluid dynamics (CFD) is often used to predict flow structures in urban areas for the determination of pollutant dispersion, human comfort or heat fluxes. During daytime building façades and ground surfaces are heated by solar radiation and thereby induce buoyancy, which changes the flow field around buildings significantly. The CFD mo...

At day-times building façades and ground surfaces are heated by solar radiation. Due to the increased surface temperatures, buoyancy is induced which changes the flow field around buildings significantly. Wind tunnel measurements were conducted to study the influence of buoyancy on the flow in a scaled urban street canyon with heated surfaces. Part...

The urban microclimate (UMC) can strongly affect the building energy demand. In this paper, the impact of the UMC on the space heating and cooling energy demand of buildings is analysed for typical office buildings in street canyon configurations, using detailed building energy simulations (BES). Convective aspects of the UMC are modelled using com...

An urban microclimate model including air flow, heat and moisture transport in porous urban surfaces and solar and longwave radiation is presented, validated with wind tunnel experiments and used to study the effect of evaporative cooling on the thermal comfort in a street canyon.

An important part of the world's energy is used for space cooling and heating of buildings. Its minimization has great energy saving potential. An important part of the heat exchange between buildings and the ambient surrounding is due to convective and radiative heat flows. In this study detailed building energy simulation (BES) is used to analyse...

An important part of the world’s energy is used for space cooling of buildings. Minimisation of space cooling, especially in hot urban environments, has great energy-saving potential. An important part of the heat exchange between buildings and the ambient surrounding is due to convective and radiative heat flows. The impact of these heat flows on...

For computational fluid dynamics (CFD) simulations of large urban areas the air flow near surfaces is normally modelled using Wall Functions (WFs). This study aims at improving the accuracy of WFs, in terms of heat transfer predictions. Turbulent boundary layers at heated building surfaces in a street canyon were analysed with low-Reynolds number m...

A consistent method to derive the parameterized NO source term from a given flamelet library is presented. The approach was tested by conducting PDF simulations and comparing computed solutions of the Sandia D flame with measurements. The parameterization is based on laminar flamelets with additional parameters for NO formation and radiation. To ob...

A new approach to NO modelling for non-premixed turbulent flames with transported joint probability density function (PDF) methods was developed. The NO formation rate obtained using a full mechanism is tabulated as a function of mixture fraction, scalar dissipation rate and NO concentration, thus taking into account backward reactions. The formati...