Climate change is intensifying urban heat stress, and microclimate simulation can support climate-responsive planning. Computational fluid dynamics (CFD) is the dominant approach at the microscale, but urban CFD studies are predominantly isothermal, neglecting buoyancy effects. Yet these effects become non-negligible under the low-wind, thermally active conditions that climate change is making more frequent. Coupled solvers such as urbanMicroclimateFoam (uMF), built on OpenFOAM, resolve airflow, heat and moisture transport, radiation, and vegetation interactions that wind-only formulations omit. However, it remains unclear under which conditions a wind-only simulation is sufficient and when the additional complexity of a coupled solver is justified. Addressing this question is hindered by three further gaps: published applications of uMF to realistic urban sites with complex terrain are scarce, its computational costs are not well characterised, and rigorous validation against field measurements is limited.

To address these gaps, this thesis asks three questions: whether uMF can be feasibly applied to realistic urban models with non-flat terrain; how its mesh requirements, solver parameters, and computational demands compare to those of the wind-only solver simpleFoam (SF) on the same case; and how the two solvers’ wind-speed predictions compare against street-level field measurements during a representative heatwave hour.

Applied to the Carnegie Mellon University campus in Pittsburgh during one hour of a heatwave on 27 August 2024, with a 3D model reconstructed in City4CFD from LiDAR and building footprints and validated against four MORICHI street-level stations, three findings emerge. First, applying uMF to realistic terrain is feasible but requires time-consuming, case-specific geometric adaptations compared to the geometry-robust SF. Second, on identical geometry and 20 cores, uMF took 3.6× longer than SF (6 h 28 min versus 1 h 49 min), which does not represent a barrier to the use of the solver. Third, uMF improved wind-speed agreement across every aggregate indicator: FB moved from +0.65 to −0.11, MG from 1.89 to 0.83, NMSE was reduced by 65%, and FAC2 rose from 0.50 to 0.75.

These results indicate that uMF merits adoption when buoyancy effects are non-negligible and the analyst can absorb the case-setup overhead. The findings are based on a single one-hour window under one inflow direction, with the observed wind speeds at three of the four stations falling below the anemometer accuracy threshold, and vegetation modelled as a porous medium. Addressing these limitations is identified as a priority for future work. ... Read more

This thesis investigated how SOLWEIG-derived urban microclimate data can be transformed and integrated into a fully open-source, scalable pedestrian routing tool that supports thermally conscious mobility decisions. Scalability is treated as a central design requirement because such a tool can only contribute to climate-adaptive urban mobility if it can be reproduced and extended to different areas without being limited by manual processing or computational bottlenecks.

The modular workflow prepares SOLWEIG input data, runs SOLWEIG_GPU to generate hourly UTCI outputs, samples these outputs onto an OpenStreetMap-derived pedestrian network as edge-level thermal-comfort attributes, and uses these in a modified, state-aware weighted Dijkstra algorithm with user-defined preferences. Interaction with the route planner is implemented using a locally deployable web interface. Evaluation with stratified origin-destination pairs shows that thermally conscious routes can reduce modelled UTCI exposure compared with the shortest path, particularly during hotter hours, while requiring only limited additional walking distance. The development process further shows that scalability depends not only on the routing algorithm, but also on data structures, file formats, network representation, and modular software design. ... Read more

Building geometry strongly influences pedestrian comfort and safety, especially in dense urban environments. As urbanization increases and cities continue to develop, understanding how building arrangement affects pedestrian-level wind conditions becomes increasingly important for creating safe and comfortable outdoor conditions. In this thesis, the TU Delft campus was used as a case study to investigate how modifications in the spatial arrangement of buildings affect pedestrian-level wind conditions. By relocating groups of buildings within the campus area, a set of four hypothetical modified layouts was created and steady-state RANS simulations were performed for each layout. To assess pedestrian wind comfort, a combined exceedance criterion based on wind velocity and turbulent kinetic energy was used rather than the standardized wind comfort guideline NEN 8100. The results show that building rearrangement mainly redistributes discomfort zones, following the regions of high wind velocity and turbulence kinetic energy. The strongest effects occur in the places where layout modifications took place. The relocation of high-rise buildings is the dominant factor that determines the probability and the extent of the discomfort zones, with more exposed placements generally leading to a larger area of discomfort. While most layouts mainly redistribute the zones of high discomfort risk, one modified configuration shows the clearest improvement in pedestrian wind comfort in the main central open area of the campus. For a critical wind direction that produces the highest wind speeds in the main open space of the campus, an additional blockage-ratio analysis was performed. The results indicate that local wind velocity in the region responds to upstream geometric blockage, with higher frontal blockage generally associated with lower wind velocity. Overall, these findings highlight the important role of building design in shaping pedestrian-level wind flow and provide useful insight for improving pedestrian comfort in urban spaces. ... Read more

Accurate urban Computational Fluid Dynamics (CFD) simulations require volumetric meshes whose boundary conforms to complex city geometry while maintaining cell quality and enabling adaptive mesh sizing. This thesis develops a Voronoi-based polyhedral meshing methodology tailored to the output of City4CFD, where the simulation domain is provided as a triangulated Piecewise Linear Complex (PLC) whose faces are grouped into semantic boundary patch types. The central goal is to generate a boundary-conforming polyhedral mesh without clipping Voronoi cells against the boundary, and to preserve patch information so that CFD boundary conditions can be transferred consistently to the mesh.

The method constructs a set of boundary (surface) Voronoi sites by intersecting triplets of spheres centered at the vertices of a refined surface triangulation. Building on the sphere-based sampling conditions of VoroCrust, sphere radii are initialized and iteratively adjusted to satisfy smooth-coverage, smooth-overlap, and Lipschitz-type size-transition constraints, while a shrinking step resolves "half-covered" seed configurations. The surface triangulation is refined by splitting triangles and protecting edges, then regularized with centroidal smoothing until the triangles associated with each facet intersect in two points, yielding paired sites on opposite sides of the boundary. These sites induce Voronoi facets that coincide with the input surface, producing triangular boundary faces and avoiding cell clipping. Patch-boundary preservation is enforced by identifying protected edges not only via dihedral-angle sharpness but also via changes in patch groups, ensuring that 1D interfaces between patch types are explicitly represented in the resulting Voronoi boundary.

To populate the mesh interior with Voronoi sites, the thesis evaluates several strategies (uniform random scattering, adaptive distance-based refinement, and structured lattices) to regulate cell density and promote larger cells away from geometric features. A prototype implementation in C++ using CGAL demonstrates feasibility for 2-manifold inputs and produces boundary-conforming Voronoi meshes compatible with OpenFOAM-style polyhedral representations. The approach assumes a valid 2-manifold boundary and does not repair non-manifold or overlapping input geometries. ... Read more

Long-term exposure to hazardous pollutants in the air is a problem in urban areas all over the world. In European countries, where regulations have been sharpened over the years, an estimated 200,000 to 300,000 people die prematurely every year due to bad air quality. Many more people experience negative health effects, like respiratory and cardiovascular diseases. In the Netherlands as well, air quality has improved over the years. Yet still, most of the country exceeds the WHO standards for most pollutants. In an effort to bring the negative impact of air pollution down to 0, many urban planners suggest planting trees as a potential mitigation strategy. However, the impact of trees on air quality is not fully understood.

This thesis investigates how the leaf area density, or LAD, of trees in a street canyon affects the dispersion of pollutants emitted in said canyon. It does so with a Reynolds-Averaged Navier-Stokes model in the OpenFOAM v7 software. A street canyon with an aspect ratio of 1:1 is considered, with a row of trees running through the middle. For four different LAD values, the impacts on canyon concentrations are examined. The results for mean concentrations on the facades and within the canyon are computed and visualised for three different wind directions: one parallel to the canyon, one perpendicular to the canyon, and one at a 45° angle. This was also done for multiple street lengths to investigate the impact of the street boundaries.

The results for this LAD investigation are used to determine monthly averages and seasonal effects. Therefore, the results are subjected to daily KNMI meteorological data. This method utilises wind parameters, direction and speed, to estimate canyon concentrations. Two different types of trees are considered: deciduous trees, which lose their leaves in winter, and coniferous trees, which are evergreens.

It is found that an increase in LAD causes an increase in pollution for parallel wind and angled wind, especially near the boundaries. This is mainly due to the reduced wind speeds within the canyon, limiting dilution. For parallel wind, recirculation zones caused by trees cause the canyon concentrations to accumulate. For perpendicular wind, lower pollutant concentrations are found with higher LAD, due to enhanced vertical transport and reduced accumulation resulting from limited lateral transport.

The seasonal impact of deciduous and coniferous trees is very LAD-dependent when taking yearly averages. Depending on the chosen LAD value, deciduous trees are up to 17-23% worse than a case with no trees, and coniferous trees are up to 28-36% worse, although for low LAD values the impact is small. ... Read more

While reconstructing urban environments, the accuracy of the model is strongly related to the quality of the input data. The initial type of input data for this process could be the footprints of the buildings, which are typically used to reconstruct the buildings, either through manual or automated methods. However, these data could be biased, and when we perform a Computational fluid dynamics (CFD) simulation, they could impact our results. An example of such bias could be either translation or rotation. In our case, simple building footprints were used to define these biases associated with the uncertainty of raw data. Additionally, statistical analysis for representing and quantifying this uncertainty was performed.
The Case C dataset from the Architectural Institute of Japan (AIJ) is an example of a canonical case for our simulations, in which the building footprints could play an important role in the calculation of our results. A CFD simulation on such a canonical case would typically involve the steps of preparing the geometry, generating the mesh, setting boundary and initial conditions, validating the results using experimental data and finally, performing uncertainty analysis. The last step involves various ways of representing the results, like scatter plots, box plots and contour plots. Important aspects of this analysis were the visualization of the flow patterns, the calculation of various quantities of interest such as velocity or turbulent kinetic energy, and the comparison of the simulation results with the experimental data from the AIJ dataset. The effects were examined across multiple wind directions and different footprint uncertainties. This approach could help us to improve the accuracy and reliability of the CFD simulations. ... Read more

As urbanization and climate change intensify, managing the urban microclimate becomes increasingly challenging, affecting outdoor thermal comfort. The practical integration of urban microclimate research into urban design remains limited, in part due to the complexity and inaccessibility of existing tools. To support early-stage, climate-sensitive urban design at the neighbourhood scale, I present SOLWEIG For Design (SOLFD): a computation framework that builds on the existing SOLWEIG tool. SOLFD enables urban designers to visualize current microclimatic conditions and assess the impact of design interventions on outdoor thermal comfort. In particular, it focuses specifically on (in)direct solar radiation and its effect as quantified by the mean radiant temperature. Key contributions include: (1) extending SOLWEIG’s 2.5D model to a layered 3D representation for improved accuracy in complex urban geometries; (2) automating the data pipeline using open Dutch geospatial datasets; (3) enabling the modification of the existing urban scene; (4) enhancing output usability through temporally grouped mean radiant temperature maps, derived physiological equivalent temperature maps, and comparison statistics; and (5) significantly reducing simulation time with GPU acceleration. The accuracy of SOLFD was validated using sensor data, achieving an RMSE of 5.39°C. Underneath structures, the RMSE increases to 5.83 °C. The potential of SOLFD is further demonstrated with a case study across various Dutch urban typologies. By laying the foundation for an accessible decision-support tool for outdoor thermal comfort, SOLFD takes a step toward integrating climate-responsive strategies into the urban design process. ... Read more

Wind behavior is complex and not intuitive. Despite its significant impact on urban environments, the topic remains underexplored in architectural design practice. Meanwhile, as cities continue to densify and buildings rise to increasing heights, designing with wind comfort in mind becomes increasingly more important. This thesis explores how wind behavior can be effectively integrated into early-stage high-rise design to improve outdoor comfort and safety.

Using Computational Fluid Dynamics (CFD) simulations, a series of design strategies were evaluated for their impact on local wind conditions in Rijnhaven, Rotterdam, a site facing both ambitious urban development and strict wind regulations. The study identifies how design interventions such as aerodynamic shaping, podiums, and open floors can significantly reduce wind discomfort at street level, particularly on the leeward side of buildings. The result is a workflow aimed at guiding architects in designing with wind more intuitively and effectively.

This research demonstrates that incorporating wind analysis early in the design process can not only improve environmental conditions but also support more coherent and informed architectural outcomes. ... Read more

Computational Fluid Dynamics (CFD) is widely used to analyse wind flow around buildings; however, creating detailed input geometries and corresponding meshes can be a time-consuming process. This thesis investigates voxelization as a means to simplify building models for their use in CFD and analyses the impact of voxel resolution on simulation accuracy.

Three building geometries with varying roof shapes and footprints were converted from detailed continuous models into voxel models with increasingly finer voxel resolutions. The voxelized models were compared to a non-voxelized LoD 3.2 model to assess accuracy under four key wind directions (90°, 45°, 22.5°, and 0°).

The CFD simulations were performed using OpenFOAM’s RANS solver with a $k–\epsilon$ turbulence model. Due to its higher computational efficiency compared to other turbulence-resolving frameworks, the RANS approach enabled a large number of simulations while maintaining sufficient accuracy for urban CFD applications. A grid-independence test was conducted using the Grid Convergence Index (GCI) method for one model. The resulting grid-independent mesh was then scaled for the other models, ensuring that all simulations remained grid-independent.

The results show that coarse voxel resolutions (1 m and 0.5 m) significantly increase the size of the building geometry and leads to large velocity differences compared to the non-voxelized model. Sloped roofs were most affected by voxelization, as these models showed greater velocity differences than those with rounded roofs.

Wind direction also plays a significant role in voxelization accuracy. While the 90°, 22.5°, and 0° wind directions showed similar results across voxel resolutions, the 45° direction produced notable velocity differences. An exception was observed for the model with a rounded roof, which showed more consistent results across all wind directions.

Overall, the velocity difference between non-voxelized and voxelized models decreases as voxel size decreases. However, below a voxel size of 0.1 m, the reduction in velocity difference stagnates, indicating that smaller voxel sizes offer limited additional benefit to CFD accuracy. ... Read more

In response to the WHO and UN’s call to ensure children’s right to breathe “clean” air and the challenges posed by the COVID-19 pandemic on maintaining healthy indoor air quality (IAQ), this PhD research explores ventilation and air cleaning strategies to control the spread of infectious respiratory particles (IRPs) in school classrooms.

The study follows four key steps: (1) a literature review bridging school ventilation regimes, IRP transmission, and advanced ventilation systems; (2) a field study to evaluate real-world ventilation and thermal conditions during the pandemic; (3) an experimental investigation of performance of mobile air cleaners (MACs) followed by an in-situ validation; and (4) a combined experimental and computational study to assess personalized air cleaners (PACs) as localized exhaust for IRP removal.
Findings reveal that most classrooms rely on natural ventilation, often failing to meet IAQ standards, especially when fully occupied. With windows and doors open, ventilation rates remained inconsistent, and thermal conditions were unsatisfactory. Hence, more controllable ventilation and air cleaning approaches are needed. MACs, when appropriately selected and positioned, offer effective protection against long-range IRP transmission at room scale, while PACs are effective at mitigating localized, short-range IRP exposure, improving IAQ at an individual level.

This research offers a comprehensive set of solutions for IRP control in classrooms, with actionable insights for a variety of stakeholders. It advocates for a shift from comfort-based to health-centered paradigms. Future research should explore hybrid systems, optimize designs, and validate interventions through real-world infection risk assessments to create healthier, more resilient classrooms. ... Read more

Computation Fluid Dynamics (CFD) simulations are used in a diverse set of fields such as aerodynamics, automotive, biomedical engineering and wind impact. With the advancements in technology the scale of these simulations has increased significantly. This has resulted in \textit{massive} CFD simulations --- simulations that do not fully fit within RAM. Due to the limitations in RAM, visualizing the results of \textit{massive} CFD simulations has become an issue, mainly on personal computers. Existing solutions necessitate either substantial external servers equipped with sufficient RAM, a costly and inefficient approach that struggles to accommodate increasingly larger CFD simulations, or reliance on manual intervention for data loading and unloading. However, manual intervention introduces potential for error.

This thesis proposes a solution to automatically load/unload data from memory based on real-time demand. To achieve the proposed solution the methodology is split into two main stages: \textbf{(a)} pre-processing and \textbf{(b)} visualization.

The pre-processing is required to efficiently manage the \textit{massive} amount of data during the visualization step. It involves segmenting the study area into smaller, more manageable regions. Furthermore, it generates multiple level of details for each region such that the desired level of detail can be used as required.

The visualization is performed within game engines --- Unity for this thesis. Game engines provide a solid starting platform as they include aspects such as read/write operations, rendering capabilities, and flexible code execution. During visualization, the relevant regions --- regions that are within the user's point of view --- are automatically loaded into memory. subsequently, regions that leave the user's point of view are automatically loaded out of memory. Utilizing iso-surfaces, volume rendering, and barbs, the loaded data is then presented to the user.

The results showcase that visualizing \textit{massive} CFD results within game engines is possible in real-time. However, through the data transformation performed in the pre-processing step the data has lost some accuracy. Thankfully, an downward trend can be seen in the loss of accuracy as the level of detail increases. The result show that for data used in the thesis the pre-processing takes between 390 seconds (6 minutes and 30 seconds) and 972 seconds (16 minutes and 12 seconds). Furthermore, a data size reduction of up to 84\% can be seen after the pre-processing has finished. ... Read more

Computational Fluid Dynamics (CFD) simulations for residential areas are becoming increasingly important as the urban population keeps growing and extreme weather conditions due to climate change are becoming more prevalent. Since CFD simulations simulate and visualise fluid flows, users can analyse and predict air flows in urban environments, giving insight in pollution, heat dissipation, and weather conditions. Performing these simulations demands expertise and time: 3D urban models must be prepared, and pre-run setups must be defined to obtain accurate results. Partial automation can streamline this process. Therefore, we developed a method that identifies geometric errors and defines mesh parameters for the open source CFD software OpenFOAM. This method follows the ISO19107 standard and recent CFD guidelines for urban areas, ensuring accurate simulation results. We validated algorithms with a variety of urban models and parameters, and analysed the workflow developed for the mesh parameters definition. Additionally, we created a prototype, in the form of a web application, in which these algorithms are implemented. Our prototype will simplify the use of CFD simulations for urban areas, making them more accessible to everyone. ... Read more

Urbanization has led to more than half of the world’s population living in cities. The design of sustainable and resilient urban environments is becoming increasingly critical to optimize the well-being of their inhabitants and the planet. One of the major challenges in achieving this is the complex wind flow patterns in densely built-up areas, which require accurate prediction and analysis to effectively harness the potential benefits of wind flow, such as natural ventilation and wind power generation. However, the unique features of urban landscapes, such as high-rise buildings, narrow streets, and irregular building shapes, make the analysis of wind flow within urban canopies complicated.

In recent years, Computational Fluid Dynamics (CFD) has become a vital tool for studying wind flow in urban areas. Still, the complex geometries of buildings can lead to challenges, including recirculation, reattachment, intense turbulence, and dead zones. Moreover, vegetation plays a crucial role in controlling wind flow in dense areas by acting as a physical barrier, significantly reducing the wind speed and alter the wind flow direction. Additionally, generating geometry for computa-tional fluid dynamics (CFD) simulation in complex urban environments is a chal-lenging and time-consuming process.

Hence, for this thesis, the City4CFD software will be used to automatically recon-struct a 3D model of Stanford University at LoD1.2, which will significantly reduce the time and effort required to generate the complex geometry necessary for com-putational fluid dynamics (CFD) simulations in urban environments. The results will be compared to those obtained from an already manually reconstructed model at LoD2.1 and real-world measurements conducted within the area of interest. This will allow me to determine the differences introduced by different level of detail.

The research will address several sub-questions, such as the steps needed to auto-matically reconstruct a 3D city model, the potential improvements in simulation accuracy by increasing LoD, and the impact of complex geometries on wind flow. The results of the thesis indicated that a more complex geometry Level of Detail (LoD) can enhance the accuracy of simulations by providing a more precise de-piction of wind flow patterns. In other words, a higher LoD geometry, such as LoD2.1, can more accurately predict wind patterns in urban environments based on real-world measurements. The study observed that the LoD2.1 model, which in-corporates more complex features, generated simulation outcomes that were closer to the measurements compared to the less detailed LoD1.2 model.


... Read more

Planting trees is widely considered an effective way to create a good urban wind environment, improve air quality, mitigate heat island effects, improve pedestrian wind comfort and reduce building energy consumption. To assess tree effects and find suitable tree setups in urban areas, Computational Fluid Dynamic (CFD) simulations can be used.
To handle trees in CFD simulations, the implicit tree modeling approach, i.e, the porosity model, is widely used where finite volume cells that roughly account for trees are marked as porous zones. Some studies have also attempted to model trees as obstacles rather than porous zones, which can be referred to as an explicit tree modeling approach. The difference between these two approaches deserves further study. Also, for practical purposes and lack of information, the geometric features of trees are usually oversimplified or even ignored in CFD simulations.
This thesis investigates the difference between implicit and explicit tree modeling approaches and analyzes the impact of tree Level of Detail (LoD) and shapes on the flow structure. For comparative analysis, several numerical test cases with different urban complexities, tree modeling approaches, tree LoDs, tree shapes, Leaf Area Density (LAD) values, and wind directions were used for CFD simulations.
The results show: (a) the implicit models always allow some of the wind flow into the porous cells no matter how high the LAD values are, resulting in smaller wind acceleration on the lateral sides of implicit tree models; (b) for the idealized street canyon and realistic urban geometry test cases simulated in this thesis, the velocity magnitude differences between the LoD2 cases and the LoD3 cases are rather limited, with maximum differences in the order of 0.5 m/s; (c) differences in tree shapes, LAD values, and wind directions will change the effects of tree modeling approaches and tree LoDs on wind. For instance, the case using an isolated explicit LoD2 conifer tree model has a different wake flow pattern from other explicit cases. Also, with the inflow direction perpendicular to buildings, the higher the LAD values, the larger the velocity magnitude difference between cases using LoD2 tree models and those using LoD3 tree models. ... Read more

Currently more than 4 billion people live in urban areas around the globe, a trend that is expected to be increased in the upcoming years. While urbanisation provides the space for innovation and new opportunities, in the meantime physical, technical and social challenges are rising and the cities’ vulnerability is increasing. A tool to tackle these issues are Computational Fluid Dynamics
(CFD) simulations, which can provide insight in various topics.

CFD simulations are valuable for modelling complex urban phenomena such as wind flow, microclimates and thermal comfort. A CFD requires as an input a 3D geometric dataset that represents objects in the urban environment which are most commonly buildings and then according to this input the air flow is simulated around it.

When creating geometries automatically for CFD simulations, several clean up tasks must be completed for them to be usable without any issues. One of the problems arising is related to the redundant faces shared between adjacent buildings, which have no purpose for outdoor flow simulations and cause complications when creating the mesh that is needed for the CFD. This
synthesis project focuses on addressing the aforementioned issue by removing the shared faces.

The ultimate goal of this project was to create an open-source product that can efficiently and in an automated way remove the adjacent faces between buildings. The benefits will be imminent during the meshing process, as we strive to reduce the time that consultancies spend fixing the input geometries before running a CFD simulation, along with an overall improved user experience.

This report is organised in four main sections. The first section is the general introduction of the issue that needs to resolved. The second section defines more in depth the problem and sets the research questions, in accordance to that, in the third section the research methodology is developed. In the fourth section the results of both methods are presented. The fifth sectionfocuses on a reflection of the project, while the sixth section presents the final conclusions. Finally, the seventh section contains the specifics of the project management itself.

The project was carried out in cooperation with Dassault Syst`emes and is developed in the context of the GEO1101 course in MSc Geomatics TU Delft. In addition to this report we have created a GitHub repository (https://github.com/Fabisser/facesBgone) that contains the source code of the two methods. ... Read more

Urban physics is a multi-scale and interdisciplinary field, that combines science and engineering for the study of physical processes in urban areas. Computational Fluid Dynamics (CFD) is considered a powerful tool for the study of these processes. In the context of microscale phenomena these processes refer to the transfer of heat and mass in the indoor and outdoor urban environment, and can be observed up to ≈1km above the surface of the Earth. Their development takes place inside the Atmospheric Boundary Layer (ABL), which for the case of urban areas is referred to as the Urban Boundary Layer (UBL), and is formed due to the interactions between the surface obstacles and the wind flows. In CFD simulations the surface of the Earth and the encountered obstacles are represented with the use of 3D models, as well as estimated values that are used to implicitly represent their roughness. In this thesis the aim is to investigate relevant to CFD parameters that could be used as 3D model semantics. For this purpose, a list of parameters was identified. From this list roughness length was selected and a methodology was developed for the assignment of roughness values for the open-source software OpenFOAM. The developed methodology that was built using built-in functions of OpenFOAM, is based on an octree data structure that is used to store the input triangulated model in obj format. The roughness length landuse names are stored in an mtl file that complements the input obj and the roughness length values are specified as a user defined parameter using the landuse names. The process is semi-automated and it entails the assignment of non-uniform roughness at the bottom of the computational domain. Additionally, a methodology to assign non-uniform roughness at the inlet of the domain was developed. The results showed that the assignment of non-uniform roughness at the bottom of the domain was successful for cases of flat terrain, however, under the restriction that the input geometry model abided by certain geometry guidelines, such as no self-intersections, no gaps. For the case of non-uniform roughness at the inlet the process also produced satisfactory results in terms of the assignment process, however the impact of multiple roughness values at the inlet on the calculated flow parameters requires further investigation. ... Read more

Wind has a profound impact on the meteorological and environmental conditions in cities. And so, by understanding wind flow behaviour within the urban environment, we can use the increasingly available open data to contribute to the design of healthy cities. This Master’s thesis presents a methodology to compute urban morphological parameters and its effect on potential wind velocity. The proposed method may serve as an complementary method to Computational Fluid Dynamics (CFD) simulation or scaled wind tunnel tests. The research question in this thesis is: Can we use urban morphology to automatically calculate potential increase in wind velocity? To answer this, first an introduction to wind flows in the urban environment
is presented. Then, several methodologies are presented to compute the urban morphological parameters, such as the Urban Canyon, wind- or leeward facade, Angle of Attack and terrain roughness length. The method relies on the use of a Voronoidiagram, with cells describing the morphology. After, the urban morphological parameters are related to potential wind velocity through a scoring method. Using two meteorological stations inside the area of interest, the mean wind velocity is compared to the scores. The result show that both stations show a higher mean wind velocity for higher scores. However, more research is necessary to validate this outcome and a recommendation is given to compare the result of this thesis to a CFD simulation. ... Read more

In 2017, the ‘Kustpact’, a Dutch national agreement, was signed to develop the Dutch coast without damaging its ecosystem nor its aesthetics. Consequently, the formation and protection of coastal dunes have become a focal point for research and development. For this reason, based on the idea of Performance-Based Design (PBD), this Master thesis aims to investigate the impact of certain geometric design parameters of beach house configurations on wind turbulence for the purpose of widening the dunes.

A parametric design space was set up to easily automate Computational Fluid Dynamics (CFD) simulations for different purposes throughout this study. The sediment mobility estimation was the objective function for all simulations conducted. It is based on the difference of transport rate between two lines from the beginning of the plateau to the foot of the dunes. To simplify the parametric model, a Sensitivity Analysis (SA) was conducted to statistically identify the most influential parameters in the model. Afterward, the filtered parameters from the SA are used to build a surrogate model to detect the trends that result from combining the most influential parameters. Finally, a Surrogate-Based Optimisation (SBO) is conducted based on the former surrogate and using a Genetic Algorithm (GA). Three generations were run and used to increase the accuracy of the surrogate and predict an optimum solution for widening the dunes.

The study concludes on a list of design criteria to respect in order to widen the dunes mainly pertaining to the consistent position of the configuration relative to the dunes, the important overlap between houses and the larger wind-facing direction of the configuration. ... Read more

In the Netherlands, the coastal dunes are essential to protect the country against flooding. However, the rising sea levels increase the risk of flooding along these sandy shores. Moreover, due to a combination of human and natural activities, dune erosion has increased and will continue to do so in the coming decades. Besides flood protection, the Dutch shoreline is important for preserving biodiversity, the generation of drinking water and recreation. In recent year, the number of recreational buildings on the beach, such as bars and holiday homes has increased. This is relevant because previous studies show that such beach buildings affect the wind flow and limit aeolian transport of sediment towards the dunes.

This research studies the impact of beach house configurations on dune-ward sediment transport to limit the adverse effects on dune development. We use CFD simulations to study the wind flow around a 3D model of a beach with holiday houses, based on a section of the Noordwijk beach in the Netherlands. We implement the CFD software OpenFOAM to solve the RANS equations for turbulent, steady-state flow. The sediment transport that occurs is calculated using the wind direction and speed near the ground surface of the solution.

The study consists of multiple 3D models in which the placement of the houses is varied systematically, to study the effects of beach house configurations. Variations are made by rotating houses, individually or within a row, and changing the distance between the houses and dunes. We determine the annual effect on sediment transport by applying varying wind conditions based on historical wind data from Noordwijk.
As we have many simulations to run, and all need different parameters and settings, we automated the process. First, a PostgreSQL database is used to store all requirements for the CFD simulations, the metadata and the results the simulations give. Then, a Python script links the information stored in the database to the correct settings in OpenFOAM. This way, many simulations are run in a row, and the results area to compare.

The results show that rotating the houses individually towards the prevailing wind direction appears to improve the amount of dune-ward sediment that takes place, compared to beach houses placed perpendicular to the shore. Rotating a row of houses as a whole has a limited effect on the amount of sediment transport. However, combining the rotation of the row of houses and the houses individually towards the prevailing wind direction shows the best improvement in sediment transport. Changing the distance between the houses and the dune foot so that a row of houses forms a funnel shape pointing towards the dunes also yields promising results.
Because we use a simplified model and do not take factors such as moisture levels or fetch distance into account, the results of this study overestimate the amount of sediment transport that takes place and might not quite resemble the reality. Further research using scale models or wind tunnels is necessary to confirm the suggestions made in this thesis.
... Read more

In current study, several fundamental and inherent problems in original Deardorff subgrid model are identified under stably stratified condition. It is found that the mixing length parameterization in this subgrid model is at the root of a long trouble problem of grid size sensitivity in large-eddy simulation (LES). A new formulation of mixing length is proposed under the consideration of some basic elements including the presence of surface, the dependence of grid size Δ and a smoothing interpolation. The performance of this modified scheme is remarkable regarding the improvement of the simulation quality and accuracy. In other words, not only is the convergence of the simulated results from a range of grid size achieved but also in the precise intensity of physical variables are modelled. The only discrepancies display in the variance of temperature in the middle of boundary layer and high turbulent kinetic energy near the surface.

To further experiment the performance of the new scheme under different scenarios, the cases of different stability condition, an independent LES code with same modification, the cases of different advection schemes and different prescribed parameters are explored. In very stable condition, the first order variables from the modified scheme are in reasonable range but with some spreads compared to the results from a dynamic code. The deviation of second order statistics shows that the proposed formulation of mixing length meets limitations due to the complex interaction between the surface and turbulent flow in shallower boundary layer. The modified scheme is model system independent based on the similar improvement of simulation results in an independent LES code system. The sensitivity of advection schemes is surprisingly hardly found in new proposed SGS model. The cases of tested parameters further verifies the limitation of original Deardroff subgrid model. ... Read more