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The authors regret that Fig. 9b in this article incorrectly repeated the RANS results already shown in Fig. 9a, instead of displaying the LES results. Corrected figure below. The authors would like to apologise for any inconvenience caused. [Figure presented]

The objective of this study is to investigate the urban wind power potential from the proper arrangement of high-rise buildings in a complex and dense urban environment. There is great prospective in the formulation of the building design at early stages to maximize wind power production in dense urban areas. We employed the 3D steady Reynolds-averaged Navier-Stokes computational fluid dynamics (CFD) simulations to investigate the impact of the arrangement of high-rise buildings on the wind energy potential . Two arrays of high-rise buildings with height = 90 m and aspect ratio (height/width) of 4.5 is studied, which focuses on different distances between the side façades of the upstream buildings, ranging from 3 to 21 m. The findings of the study support the high-rise buildings design with respect to integrated urban wind energy harvesting and the concept of sustainable urban development.

Knowledge of convective heat transfer at ground surfaces around buildings is required for urban canyon models and for research on asphalt and road collectors, heat stresses in urban areas, etc. However, while many studies of convective heat transfer around buildings have been performed in the past, the focus of most of these studies was on rather simple building geometries and external surfaces of buildings. This paper, therefore, presents computational fluid dynamics (CFD) simulations and wind-tunnel measurements of convective heat transfer at ground surfaces around complex building models. The 3D Reynolds-averaged Navier Stokes equations are solved with a combination of the high-Re number realizable k- model and the low-Re number Wolfshtein model. The evaluation is based on validation with wind-tunnel measurement of ground surface temperature around a complex building model acquired through infrared thermography.

The urban population has reached the highest number ever recorded. Based on recent studies, this number is going to increase even further, with strong consequences for the urban microclimate. In this perspective, the analysis of microclimatic conditions in the urban environment is getting more significant. This study analyzes microclimatic conditions in a real urban area. The real compact inhomogeneous urban area under study is located in Nicosia old town, in Cyprus. High-resolution Computational Fluid Dynamics (CFD) simulations are performed based on the 3D unsteady Reynolds-Averaged Navier-Stokes equations to assess the air temperature, surface temperatures and wind speed distributions. The CFD results are compared with on-site measurements for the same area. The results show that CFD can predict air temperatures in compact real urban areas, with an average deviation of approximately 7%. Based on the results, conclusions are going to be made regarding microclimatic conditions in the case study area.

Vertical axis wind turbines (VAWTs) are promising for wind energy harvesting in the urban environment mainly because of their omnidirectional capability. However, currently their aerodynamic performance is not comparable with horizontal axis wind turbines (HAWTs). Therefore, to make them an ideal candidate, they need to be further improved. The aerodynamic performance of VAWTs depends on several geometrical parameters, such as solidity. However, the impact of solidity on blade aerodynamics and turbine wake has not yet been comprehensively investigated. Therefore, the current study intends to systematically study the effect of solidity on aerodynamic performance of VAWTs with different number of blades operating at various tip speed ratios to provide a deeper insight into its impact on dynamic loads on blades, turbine performance and wake. High-fidelity unsteady Reynolds-averaged Navier-Stokes (URANS) simulations extensively validated with experimental data are employed. The results show that for fixed-rotational-speed urban VAWTs, which frequently operate at high tip speed ratios, a low solidity value is more favorable. On the other hand, an optimal VAWT is a high-solidity variable-rotational-speed (fixed λ) rotor operating at a low tip speed ratio regime.

Because of the rapid trend toward urbanization around 54% of the world’s population currently live in urban areas (UNFPA, 2007). The urbanized population is projected to increase and reach up to 66% by 2050 (United Nations, 2014). In addition, due to climatic changes phenomena like the Urban Heat Island (UHI) effect and heat waves are becoming more severe, with dramatic consequences for the urban population (Toparlar et al., 2015; Montazeri et al., 2017). Considering this trend, problems related to urban overpopulation are expected to get more intense in the next years, hence in this perspective, the analysis of microclimatic conditions in urban areas is getting more significant. Through the detailed literature review, it appears that most of the studies focusing on the analysis of microclimatic conditions use observational approaches such as on-site measurements, since this method provides information about the real complexity of the microclimatic conditions in urban areas, without any similarity issues. While computational power is radically increasing, the use of numerical simulation approaches is getting more popular. Most of the numerical studies use the Energy Balance Model which is based on the law of energy conservation. However, the use of Computational Fluid Dynamics (CFD) is considered advantageous since it can provide information of both temperature and velocity fields, and can be used in higher resolution scales. In this perspective, this study analyzes microclimatic conditions in a real compact urban area, with the use of CFD simulations, and results are compared with on-site measurements of the same area. The real compact inhomogeneous urban area under study is located in Nicosia old town, in Cyprus. High-resolution Computational Fluid Dynamics (CFD) simulations are performed based on the 3D unsteady Reynolds-Averaged Navier-Stokes equations to assess the air temperature and wind speed distributions. The on-site measurements took place as a part of the European funded project with code name TOPEUM (Neophytou et al., 2011), with collected data of air and surface temperature. The results show that CFD can predict air temperatures in compact real urban areas, with an average deviation of 6.8%, and surface temperatures with average deviation of approximately 6 to 7%. Based on the results, conclusions are going to be made regarding thermal comfort in the case study area.

The urban environment constitutes a promising potential for wind energy harvesting where the wind turbines can be integrated in the existing buildings and city infrastructures or renovation projects. While several studies have been performed to investigate the urban wind energy potential, the impact of the arrangement of high-rise buildings has not yet investigated in detail. In this paper, therefore, the impact of the arrangement of high-rise buildings on the wind energy potential (defined as high mean wind speed and low turbulence intensity (Ti 18%)) is investigated using 3D steady Reynolds-averaged Navier-Stokes (RANS) simulations. A 2×2 array of high-rise buildings with height = 90 m and aspect ratio (height/width) of 4.5 is studied. The evaluation is based on validation with wind-tunnel measurements of mean wind speed for a generic urban area. The study focuses on two building orientations,  = 0 and 45, and seven distances, ranging from 3 to 21 m, between the side façades of the upstream buildings. The results show that for cases with  = 45 and D  9 m, the wind power potential between the buildings significantly increase (29%). The findings of the study support the design of high-rise buildings with respect to integrated wind energy harvesting.

The surface-averaged forced Convective Heat Transfer Coefficient (CHTC) distribution across the facades of a building is influenced by the complex interplay between a wide range of parameters including building geometry, position on the building facade, wind speed and wind direction. Existing CHTC expressions, however, consider the impact of these parameters either incompletely or not at all. Earlier studies have shown that this shortcoming can lead to significant errors in Building Energy Simulations. This paper, therefore, systematically investigates the combined effects of wind speed, building height and width, and wind direction on the surface-averaged forced CHTC for the windward facade of buildings and presents a new generalized CHTC expression as a function of these parameters. This expression is derived from high-resolution CFD simulations of wind flow and forced convective heat transfer for 70 different building geometries, 8 wind directions and 4 reference wind speed values. The 3D steady Reynolds-averaged Navier-Stokes equations are solved combining the high-Re number realizable k-ε model and the low-Re number Wolfshtein model. The CFD simulations are based on a validation study with wind-tunnel measurements of surface temperature for a reduced-scale cubic model. The accuracy of the expression is confirmed by detailed in-sample and outof-sample evaluations.

Wheels account for about 10% of the total aerodynamic drag of a cyclist. While different types of wheels are commercially available, spoked wheels are commonly used in cycling races. This paper presents computational fluid dynamics (CFD) simulations of spoked wheels, and systematically evaluates different boundary conditions that are usually used for rotation modelling of wheels, namely (i) rotational moving wall, (ii) moving reference frame (MRF) and (iii) sliding mesh. Steady and unsteady Reynolds-Averaged Navier-Stokes (RANS) CFD simulations are thus performed for an isolated wheel. Moreover, the impact of the volume enclosing the wheel, where the MRF is applied, on the predicted wheel drag is evaluated. The evaluation is based on validation with wind-tunnel measurements of force coefficients. The results of this study can be used for accurate CFD simulations of cyclist aerodynamics. 1Introduction In the 2017 Tour de France, 10 different manufacturers provided the wheels for the 22 teams in the race (Arthur, 2017), while each manufacturer had several wheels in their catalogue. The wheels are selected among the large variety of commercially available options based on their performance in terms of aerodynamic drag, weight, inertia and stiffness (Kyle, 1995). The aerodynamic performance of wheels is of significant importance since the drag of both wheels is responsible for about 10% of the total cyclist resistance (Greenwell et al., 1995). It is usually evaluated using wind-tunnel tests (Greenwell et al., 1995; Kyle, 1995, 1991; Tew and Sayers, 1999) and more recently using CFD simulations (Godo et al., 2010). CFD is capable of computing forces and moments acting on each single wheel’s component (rim, tyre, spokes and hub) and providing fundamental information that can be used by designers to improve the aerodynamic performance of wheels. Nevertheless, one critical aspect in the CFD simulations of wheels is appropriate rotation modelling approaches. To the best of our knowledge, the impact of different rotation modelling approaches on the accuracy of CFD simulations of cycling wheel aerodynamics has not yet been investigated. 2Methodology In this study, CFD simulations are first validated with the wind-tunnel measurements by Tew and Sayers (1999). The Campagnolo Shamal wheel has a 19 mm rim width and a 61 mm depth, spanning from the tyre to the rim edges (Fig. 1a). The spoke’s cross section is approximated to a rectangle of 3 mm  1 mm (Fig. 1b). The computational domain has a cross-section of 8.6 m  7.8 m. The upstream and downstream length of the domain are 3.9 m and 7.4 m, respectively. The computational grid consists of about 13.2 million cells, while about 246,000 surface cells are used on the wheel (Fig. 1b). The mean velocity inlet boundary condition is a uniform profile (48 km/h), accordingly to the experiment (Tew and Sayers, 1999). The 3D RANS equations are solved in combination with the k-ω SST turbulence model. It should be noted that the good performance of the k-ω SST turbulence model has been already shown in previous studies on cycling aerodynamics, e.g. Defraeye et al. (2010). Three approaches are evaluated to model the rotation of the wheel: (i) the rotational wall approach (RW), (ii) the moving reference frame approach (MRF) and (iii) the sliding mesh approach (SM). The latter two methods are applied on a volume surrounding the wheel, as shown in Fig. 1a and Fig. 1c. Moreover, the impact of the volume enclosing the wheel, where the MRF is applied, on the predicted wheel drag is evaluated. (Fig. 1c). 3Results The CFD results show a good agreement with the wind-tunnel results in terms of the drag coefficient with a deviation of about 1.8 % at 0˚ yaw angle. Further and more detailed information about the different approaches will be provided in the full paper.

Considering the radical increase of urban population and the trend toward urbanization, the analysis of microclimatic conditions in the urban environment is getting more significant. In this perspective, this study analyzes microclimatic conditions in a real urban area. The real compact inhomogeneous urban area under study is located in Nicosia old town, in Cyprus. High-resolution Computational Fluid Dynamics (CFD) simulations are performed based on the 3D unsteady Reynolds-Averaged Navier-Stokes equations to assess the air temperature and wind speed distributions. The CFD results are compared with on-site measurements for the same area. The results show that CFD can predict air temperatures in compact real urban areas, with an average deviation of 6.8%. Based on the results, conclusions are going to be made regarding thermal comfort in the case study area.

Knowledge of the pressure distributions on building surfaces is essential for a complete understanding of infiltration, wind-induced ventilation and wind loads. Earlier studies have shown the influence of different façade appurtenances like balconies on the wind-induced pressure on building facades. However, a detailed investigation of the impact of facade appurtenances on the pressure distribution on building facade has not yet been performed. This is especially the case for high-rise buildings. This paper, therefore, presents a detailed study on mean wind pressure distributions on the windward façade of a high-rise building with and without façade appurtenances at wind direction of 0°. The realizable k-ɛ turbulence model in 3D steady Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) is used for predicting. The evaluation is based on validation with wind-tunnel measurements. The results show that the presence of balconies can significantly influence the Cp distributions on the windward façade. This influence greatly depends on the size and geometry of balconies.

Given the rapid increase of urbanization and urban population worldwide, the urban air quality, wind and thermal comfort have become increasingly important matters. In this perspective, accurate prediction of the ventilation conditions in complex urban areas is of significant importance. CFD has been used in different occasions in the past to investigate the pedestrian-level wind conditions in urban areas. The 3D steady Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulations (LES) approach have been widely used. However, a detailed evaluation of the two approaches for this application has not yet been performed. This paper presents a systematic evaluation of 3D steady RANS and LES CFD simulations of wind flow in a compact heterogeneous urban area in the city of Nicosia, Cyprus. The ventilation conditions are investigated by assessing the distribution of the age of air at pedestrian height. The evaluation is based on validation with wind-tunnel measurements of mean wind speed and turbulence intensity for the same urban area, performed in an atmospheric boundary layer wind-tunnel at scale 1:250. The results show that the average deviations of the obtained results by steady RANS and LES with the experiments are about 10% and 7.3% for the mean wind speed. For turbulence intensity, this deviation is 42% and 20%, respectively.

Cross-wind can strongly influence the results of a cycling stage. Indeed, in stages characterized by cross-wind, echelons formations are assumed by the cyclists. The reason is that the presence of the cross-wind can modify the forces acting on the cyclists both in term of magnitude and direction. Echelons are able to reduce the negative effects of the generated side force and still allow to benefit of drafting, thus reducing wind resistance. Previous investigations on the impact of cross-wind on cycling aerodynamics have been performed considering isolated wheels and single cyclists and more recently with a couple of cyclists without bike. However, to the best of our knowledge, the impact of cross wind on a couple of cyclists including bike has not yet been investigated. In this paper, therefore, Computational Fluid Dynamics (CFD) is used to investigate the impact of cross wind on the aerodynamic resistance of a couple of cyclists. Two different configurations are considered: (i) in-line; when the trailing cyclist is placed in line with the leading cyclist and (ii) echelon; when the trailing cyclist is staggered from the leading cyclist. For each configuration, the impact of different spacing and yaw angles are also assessed. The evaluation is based on validation with wind-tunnel measurements of drag force performed at several yaw angles. For the CFD simulations, the cyclist geometry has been obtained by means of 3D laser scanning of an elite cyclist while the bike geometry has been created using 3D CAD modelling. The 3D steady Reynolds-Averaged Navier-Stokes equations (RANS) are solved in combination with the standard k-ε turbulence model and with low-Reynolds number modelling. The results show that the leading cyclist is only slightly affected by the position of the trailing cyclist. Drag and side forces reduction occur to the trailing cyclist when he is located in the wake of the leading cyclist, i.e. moving from an in-line to a staggered position when cross wind is present. Further results and discussions on the interaction of the two cyclists under influence of cross-wind will be presented in the full paper.

The success of combination antiretroviral therapy is limited by the evolutionary escape dynamics of HIV 1. We used Isotonic Conjunctive Bayesian Networks (I CBNs) a class of probabilistic graphical models to describe this process. We employed partial order constraints among viral resistance mutations which give rise to a limited set of mutational pathways and we modeled phenotypic drug resistance as monotonically increasing along any escape pathway. Using this model the individualized genetic barrier (IGB) to each drug is derived as the probability of the virus not acquiring additional mutations that confer resistance. Drug specific IGBs were combined to obtain the IGB to an entire regimen which quantifies the virus' genetic potential for developing drug resistance under combination therapy. The IGB was tested as a predictor of therapeutic outcome using between 2185 and 2631 treatment change episodes of subtype B infected patients from the Swiss HIV Cohort Study Database a large observational cohort. Using logistic regression significant univariate predictors included most of the 18 drugs and single drug IGBs the IGB to the entire regimen the expert rules based genotypic susceptibility score (GSS) several individual mutations and the peak viral load before treatment change. In the multivariate analysis the only genotype derived variables that remained significantly associated with virological success were GSS and with 10 fold stronger association IGB to regimen. When predicting suppression of viral load below 400 cps/ml IGB outperformed GSS and also improved GSS containing predictors significantly but the difference was not significant for suppression below 50 cps/ml. Thus the IGB to regimen is a novel data derived predictor of treatment outcome that has potential to improve the interpretation of genotypic drug resistance tests.

Given the rapid increase of urbanization and urban population worldwide, the urban air quality, wind and thermal comfort have become increasingly important matters. In this perspective, an accurate prediction of urban wind flow is of high importance. The 3D steady Reynolds-Averaged Navier-Stokes (RANS) approach is widely used in CFD simulations of wind flow in urban areas. However, there is a lack of basic knowledge on the performance of 3D steady RANS for this application. This paper presents a systematic evaluation of 3D steady RANS CFD simulations of wind flow in a compact heterogeneous urban area, most commonly encountered in old historical city centers. In addition, the impact of different turbulence models is investigated. The study area selected for this investigation is the old city of Nicosia, Cyprus. The evaluation is based on validation with wind-tunnel measurements of mean wind speed performed in an atmospheric boundary layer wind-tunnel at scale 1:250. The results show that steady RANS, in spite of its limitations, can accurately reproduce the mean wind speed distributions. For all of the turbulence models the average deviations of all the measuring points, from the wind-tunnel measurements are within 10%, where none of the models is superior.