THE EFFECT OF SOURCE TREATMENT ON POLLUTANT DISPERSION IN AN IDEALISED URBAN ROUGHNESS IN NUMERICAL SIMULATIONS USING THE STANDARD k-ε TURBULENCE CLOSURE MODEL

The need for accurate model predictions in urban air quality assessment studies during the past decade has led to the ever increasing use of Computational Fluid Dynamics (CFD) models in order to resolve the various local scale inhomogeneities which dominate flow and dispersion and are usually encountered in urban areas. Towards the aim of improving model predicted dispersion via the use of CFD models, a numerical study was undertaken in order to investigate the effect of different techniques applied for treating the sources of emissions on the near source behaviour of the models, as well as on the actual predicted concentrations at locations away from the vicinity of the sources under consideration. A series of 3D numerical simulations were performed for the wind tunnel model geometry of the Mock Urban Setting Test (MUST) field experiment of the University of Hamburg, Meteorological Institute, Division of Technical Meteorology, which was made available within the frame of COST Action 732. Overall in conclusion, results show that depending on the type of source, the intensity of the vertical component of the emissions exit velocity at the source and the mesh refinement close to source boundaries predicted concentrations can deviate significantly from the wind tunnel measurements. However, it is possible to partially improve the performance of a CFD model in urban dispersion problems, mainly via the application of the proper combination of these parameters

Improving Resilience of Transport Instrastructure to Climate Change and other natural and Manmande events based on the combined use of Terrestrial and Airbone Sensors and Advanced Modelling Tools

The project PANOPTIS, funded by the European Commission under the H2020 Programme, aims at increasing the resilience of the transport infrastructures (focusing on roads) and ensuring reliable network availability under unfavourable conditions, such as extreme weather, landslides, and earthquakes. The main target is to combine downscaled climate change scenarios (applied to road infrastructures) with structural and geotechnical simulation tools and with actual data from a multi-sensor network (terrestrial and airborne-based), so as to provide the operators with an integrated tool able to support more effective management of their infrastructures at planning, maintenance and operation level. During the first stage of the project, the consortium will develop advanced technologies to monitor and control transport infrastructures, such as a Geotechnical and Structural Simulation Tool (SGSA) to predict structural and geotechnical risks in road infrastructures; drone-technologies applied to road upkeep and incident management; improved computer vision and machine learning techniques for damage diagnosis of infrastructure, and early warning systems to help operators identify and communicate emerging systemic risks. At the same time, experts in climate modelling, will analyse the possible short and long term effects of climate change on transport infrastructure (e.g. flooding, heavier snows). All the information from the different sensors, models and applications will be integrated and processed through a unique Resilience Assessment Platform that will support operators in the introduction of adaptation and mitigation strategies based on multi-risk scenarios. During the second stage of the project, ACCIONA Engineering will implement the developed technologies and methodologies in a section of the Spanish A-2 motorway, in the province of Guadalajara. PANOPTIS integrated Platform will help optimize the management and maintenance of the Ministry of Public Works' concession for a 77.5-km section, all in collaboration with ACCIONA Infrastructure Maintenance (AMISA) and ACCIONA Concessions. In parallel, PANOPTIS platform will also be implemented in a section of 62 Km of a Greek motorway, renowned for its seismic activity. The trials in Greece hosted by the operator Egnatia Odos will integrate the motorway that serves the Airport of Thessaloniki. So the scenario will integrate a modal transfer segment.Le projet PANOPTIS, financé par la Commission européenne dans le cadre du programme H2020, vise à accroître la résilience de l'infrastructure de transport et à permettre une disponibilité fiable du réseau dans des conditions défavorables, telles que les conditions météorologiques extrêmes, les glissements de terrain et les tremblements de terre. L'objectif principal doit être associé à un réseau multi-capteurs (terrestre et aéroporté) pour permettre une gestion plus efficace de leurs infrastructures au niveau de la planification, de la maintenance et de l'exploitation. Au cours de la première phase du projet, le consortium développera des technologies avancées pour surveiller et contrôler les infrastructures de transport, telles que l'outil de simulation géotechnique et structurelle (SGSA) permettant de prévoir les risques structurels et géotechniques dans les infrastructures routières; technologies de drones appliquées à l'entretien des routes et à la gestion des incidents; la vision par ordinateur et les techniques d'apprentissage automatique pour le diagnostic des infrastructures et les systèmes d'alerte précoce. Dans le même temps, des experts en modélisation du climat analyseront le potentiel du changement climatique sur les infrastructures de transport (par exemple, les inondations, les neiges plus lourdes). Toutes les informations provenant des différents capteurs, modèles et applications seront intégrées dans un scénario unique comportant plusieurs risques. Au cours de la deuxième phase du projet, ACCIONA Engineering mettra en oeuvre les technologies et les méthodologies dans une section de l'autoroute espagnole A-2, dans la province de Guadalajara. La plate-forme intégrée PANOPTIS contribuera à optimiser la gestion et la maintenance de la concession du ministère des Travaux publics pour une section de 77,5 km, le tout en collaboration avec ACCIONA Infrastructure Maintenance (AMISA) et ACCIONA Concessions. Parallèlement, la plate-forme PANOPTIS sera également mise en oeuvre dans une section de 62 Km d'une autoroute grecque réputée pour son activité sismique. Les essais en Grèce organisés par l'opérateur Egnatia Odos vont rejoindre l'aéroport de Thessalonique. Le scénario intégrera donc un segment de transfert modal

A nested multi-scale system implemented in the large-eddy simulation model PALM model system 6.0

Large-eddy simulation (LES) provides a physically sound approach to study complex turbulent processes within the atmospheric boundary layer including urban boundary layer flows. However, such flow problems often involve a large separation of turbulent scales, requiring a large computational domain and very high grid resolution near the surface features, leading to prohibitive computational costs. To overcome this problem, an online LES-LES nesting scheme is implemented into the PALM model system 6.0. The hereby documented and evaluated nesting method is capable of supporting multiple child domains, which can be nested within their parent domain either in a parallel or recursively cascading configuration. The nesting system is evaluated by first simulating a purely convective boundary layer flow system and then three different neutrally stratified flow scenarios with increasing order of topographic complexity. The results of the nested runs are compared with corresponding non-nested high-and low-resolution results. The results reveal that the solution accuracy within the high-resolution nest domain is clearly improved as the solutions approach the non-nested high-resolution reference results. In obstacle-resolving LES, the two-way coupling becomes problematic as anterpolation introduces a regional discrepancy within the obstacle canopy of the parent domain. This is remedied by introducing canopy-restricted anterpolation where the operation is only performed above the obstacle canopy. The test simulations make evident that this approach is the most suitable coupling strategy for obstacle-resolving LES. The performed simulations testify that nesting can reduce the CPU time up to 80 % compared to the fine-resolution reference runs, while the computational overhead from the nesting operations remained below 16 % for the two-way coupling approach and significantly less for the one-way alternative. © 2021 Antti Hellsten et al

A nested multi-scale system implemented in the large-eddy simulation model PALM model system 6.0

Large-eddy simulation (LES) provides a physically sound approach to study complex turbulent processes within the atmospheric boundary layer including urban boundary layer flows. However, such flow problems often involve a large separation of turbulent scales, requiring a large computational domain and very high grid resolution near the surface features, leading to prohibitive computational costs. To overcome this problem, an online LES–LES nesting scheme is implemented into the PALM model system 6.0. The hereby documented and evaluated nesting method is capable of supporting multiple child domains, which can be nested within their parent domain either in a parallel or recursively cascading configuration. The nesting system is evaluated by first simulating a purely convective boundary layer flow system and then three different neutrally stratified flow scenarios with increasing order of topographic complexity. The results of the nested runs are compared with corresponding non-nested high- and low-resolution results. The results reveal that the solution accuracy within the high-resolution nest domain is clearly improved as the solutions approach the non-nested high-resolution reference results. In obstacle-resolving LES, the two-way coupling becomes problematic as anterpolation introduces a regional discrepancy within the obstacle canopy of the parent domain. This is remedied by introducing canopy-restricted anterpolation where the operation is only performed above the obstacle canopy. The test simulations make evident that this approach is the most suitable coupling strategy for obstacle-resolving LES. The performed simulations testify that nesting can reduce the CPU time up to 80 % compared to the fine-resolution reference runs, while the computational overhead from the nesting operations remained below 16 % for the two-way coupling approach and significantly less for the one-way alternative.publishedVersio

Development of a methodology for assessing the potential abatement of air pollution with the use of photocatalytic coatings

Within the frame of this Ph.D. thesis an integrated methodology for the assessment of the efficiency of innovative photocatalytic covering materials as a viable means for the abatement of the adverse effects of air pollution on human health and the improvement of the aesthetics of the building sector is developed, validated and applied. To this purpose, as a first step a thorough literature review of existing numerical methodologies is performed in order to select the optimum one, by taking into consideration the need for resolving all urban elements in an area of interest in relation to the computational cost. Based on the findings of this review the RANS (Reynolds Averaged Navier Stokes) – URANS approach of the classical Computational Fluid Mechanics (CFD) discipline is selected. The suggested methodology, which is based on the aforementioned RANS approach, can take into account the combined complex effect of the most prominent environmental parameters on the de-pollution effectiveness of the photocatalytic materials under consideration such as the humidity, the temperature, the initial concentration and the presence of other pollutants and oxygen. The proposed methodology adopts a meta-modelling logic in order to produce estimations for the expected de-pollution efficiency of selected air pollutants in the urban areas of interest for selected periods of time. The basic tools for the assessment and the validation of the adopted holistic approach are the experimental measurements from a field trial and a series of wind tunnel simulations. The field trial measurements proved that the materials under consideration preserve their photocatalytic properties under real atmospheric conditions. At the same time their de-pollution effectiveness remains unaffected from the prevailing meteorological conditions. Considering the fact that field trial measurements are by definition characterized by low representativeness in space and time, a series of measurements in an environmental wind tunnel were conducted to support the findings of the aforementioned field trial. In addition, these measurements were used to generate a quality assured database consisting of really detailed experimental data for the verification and validation of the suggested numerical methodology, through rigorous comparisons between numerical results and experimental data. Having validated the proposed numerical methodology, it was then applied for a series or real life applications, including an extensive field trial in the Sir John Cass Primary School in Central London as a follow up activity of the PICADA project. The main aim of this activity was to assess whether it would be possible to reduce the exposure of children which are classified as the most vulnerable part of the population to air pollution. The findings of this trial further proved the de-pollution potential of the photoctalytic materials as well as the validity of the methodology which was developed within the frame of this thesis.Στα πλαίσια της παρούσας εργασίας αναπτύσσεται, πιστοποιείται και εφαρμόζεται μια ολοκληρωμένη μεθοδολογία για την αποτίμηση της αποδοτικότητας καινοτόμων φωτοκαταλυτικών δομικών υλικών επικαλύψεων ως ενός βιώσιμου εναλλακτικού τεχνικού μέτρου για την ανάσχεση των αρνητικών επιπτώσεων της αέριας ρύπανσης στην υγεία του πληθυσμού και την αισθητική αναβάθμιση του κτιριακού τομέα στις αστικές περιοχές, με έμφαση σε ιδιαίτερα βεβαρυμμένες περιοχές. Για το σκοπό αυτό πραγματοποιείται επισκόπηση των διαθέσιμων υπολογιστικών εργαλείων για την επιλογή της καταλληλότερης αριθμητικής προσέγγισης λαμβάνοντας υπόψη την ανάγκη για υψηλή διακριτοποίηση των αστικών δομών σε σχέση με το απαιτούμενο υπολογιστικό κόστος και υιοθετείται η προσέγγιση RANS - URANS της κλασικής υπολογιστικής ρευστομηχανικής ως η καταλληλότερη. Η προτεινόμενη μεθοδολογία, που βασίζεται στην ως άνω προσέγγιση, συνυπολογίζει με ακρίβεια τις επιδράσεις όλων των βασικών περιβαλλοντικών παραμέτρων όπως η υγρασία, η θερμοκρασία, η αρχική συγκέντρωση, η παρουσία άλλων ρύπων και η παρουσία οξυγόνου στην απόδοση των υπό μελέτη υλικών σε εφαρμογές πραγματικής κλίμακας σε αστικές περιοχές. Η μεθοδολογία επιστρατεύει τη λογική του μετα-μοντέλου για την εξαγωγή αποτελεσμάτων σχετικά με την σε βάθος χρόνου αναμενόμενη απομείωση επιλεγμένων αέριων ρύπων στην περιοχή ενδιαφέροντος. Βασικά στοιχεία της ολιστικής θεώρησης που υιοθετείται για την αποτίμηση της απόδοσης των υπό μελέτη υλικών και την πιστοποίηση της προτεινόμενης αριθμητικής μεθοδολογίας αποτελούν κατάλληλα προγράμματα επιτόπιων μετρήσεων και φυσικών προσομοιώσεων. Μέσω των επιτόπιων μετρήσεων καταδεικνύεται ότι τα συγκεκριμένα υλικά διατηρούν τις φωτοκαταλυτικές τους ιδιότητες σε πραγματικές ατμοσφαιρικές συνθήκες. Τα αποτελέσματα δείχνουν επίσης ότι η απόδοση των φωτοκαταλυτικών υλικών παραμένει ανεπηρέαστη από τις επικρατούσες μετεωρολογικές συνθήκες. Με δεδομένη τη χαμηλή διακριτότητα και την αμφισβητήσιμη αντιπροσωπευτικότητα των επιτόπιων μετρήσεων, οι φυσικές προσομοιώσεις είναι αυτές που διαφωτίζουν πλήρως τους μηχανισμούς που καθορίζουν το φυσικό αερισμό και τη διασπορά της αέριας ρύπανσης στην υπό μελέτη διάταξη. Με τις μετρήσεις αυτές δημιουργείται παράλληλα μια ποιοτικά διασφαλισμένη βάση πειραματικών δεδομένων για την επικύρωση και επαλήθευση της προτεινόμενης μεθοδολογίας με τη βοήθεια συγκρίσεων ανάμεσα στις αριθμητικές προσομοιώσεις και τις πειραματικές μετρήσεις, επιτόπιες και στην αεροσήραγγα. Η προτεινόμενη μεθοδολογία αξιοποιείται σε σειρά πρακτικών εφαρμογών. Σε αυτές περιλαμβάνεται το διάδοχο του PICADA πρόγραμμα επιτόπιων μετρήσεων για την εφαρμογή φωτοκαταλυτικών υλικών τοιχοποιίας στο Sir John Cass Primary School του κεντρικού Λονδίνου. Τα αποτελέσματα του προγράμματος αυτού, που αποσκοπούσε στην προστασία της υγείας του πιο ευάλωτου μέρους του πληθυσμού από τις επιπτώσεις της αέριας ρύπανσης, αποδεικνύουν ότι η μεθοδολογία που αναπτύχθηκε στην παρούσα διατριβή οδηγεί σε πολύ ικανοποιητικά αποτελέσματα

Development of an Algorithm for Prediction of the Wind Speed in Renewable Energy Environments

The aim of this work is to develop an algorithm that is able to provide predictions of wind speed statistics (WSS) in renewable energy environments. The subject is clearly interesting, as predictions of storms and extreme winds are important for decision makers and emergency response teams in renewable energy environments, e.g., in places where wind turbines could be located, including cities. The goal of the work is achieved through two phases: (a) During the preparation phase, the construction of a big WSS database based on computational fluid dynamics (CFD) is carried out, which includes flow fields of different wind directions in all grid numerical points; (b) In the second phase, the algorithm is used to find the records in the WSS database with the closest meteorological conditions to the meteorological conditions of interest. The evaluation of the CFD model (including both RANS and LES turbulence methodologies) is performed using the experimental data of the MUST (Mock Urban Setting Test) wind tunnel experiment

A nested multi-scale system implemented in the large-eddy simulation model PALM model system 6.0

Large-eddy simulation (LES) provides a physically sound approach to study complex turbulent processes within the atmospheric boundary layer including urban boundary layer flows. However, such flow problems often involve a large separation of turbulent scales, requiring a large computational domain and very high grid resolution near the surface features, leading to prohibitive computational costs. To overcome this problem, an online LES–LES nesting scheme is implemented into the PALM model system 6.0. The hereby documented and evaluated nesting method is capable of supporting multiple child domains, which can be nested within their parent domain either in a parallel or recursively cascading configuration. The nesting system is evaluated by first simulating a purely convective boundary layer flow system and then three different neutrally stratified flow scenarios with increasing order of topographic complexity. The results of the nested runs are compared with corresponding non-nested high- and low-resolution results. The results reveal that the solution accuracy within the high-resolution nest domain is clearly improved as the solutions approach the non-nested high-resolution reference results. In obstacle-resolving LES, the two-way coupling becomes problematic as anterpolation introduces a regional discrepancy within the obstacle canopy of the parent domain. This is remedied by introducing canopy-restricted anterpolation where the operation is only performed above the obstacle canopy. The test simulations make evident that this approach is the most suitable coupling strategy for obstacle-resolving LES. The performed simulations testify that nesting can reduce the CPU time up to 80 % compared to the fine-resolution reference runs, while the computational overhead from the nesting operations remained below 16 % for the two-way coupling approach and significantly less for the one-way alternative

PLOTO: Improved IWW resilience using predictive modelling, environmentally sustainable and emerging digital technologies and tools

editorial reviewed13. Climate action11. Sustainable cities and communitie