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The proper choice of insulation materials contributes to the long and reliable operation of the envelope of a whole building. This paper presents the results of moisture-content determination in materials used for internal thermal insulation under different hygrothermal conditions. In this study, surface and internal moisture contents were measured. Moisture sensors that enable constant monitoring of material moisture content but with different operational characteristics, were used in the analysis. The operating principle of the first method involves the conversion of the amount of infrared radiation reflected in an electric signal, and the second method involves the analysis of the electric impulse propagation velocity. The measurement results of both methods are used to determine the drying-out characteristics of components used in internal thermal insulation and the sorptive properties of the selected materials. The results of comparative studies are also presented for these proposed methods as well as the gravimetric method to determine the usability of the proposed methods in determining the dampness level. The overall measurement results helped determine the relationship between the internal and surface moisture contents and the time needed for the moisture content in different parts of the selected materials to equalize.

Previous studies have revealed significant differences between the theoretical and real energy consumption of buildings. These differences can be associated with the use of space heating and ventilation systems. The main difficulty is to simulate manual operation of the heating and ventilation system and to achieve results that approximate reality. The aim of this paper is to present the initial stage of the generation of a calculation model based on the space heating energy use. The generated model, works with free temperature (floating). It incorporates some of its occupants practices related to the use of energy systems. Subsequently, the results are compared with the information obtained in dwellings studied. This paper presents the model and its validation with the first 7 houses. Using a classical model, significant differences were obtained. By contrast, with the proposed model the difference is much smaller, when compared with experimental data. In the future, it is expected to identify the variables and parameters that have the min influence on the model. Thus, it is expected to achieve the calibration of the model and future generalization to other dwelling types.

Mixing ventilation in airplane cabins is driven by overhead supply jets, which may be directed towards each other, interact and merge before entering the passenger area. Although many studies already investigated airplane cabin mixing ventilation, detailed knowledge on the fundamental flow components (i.e. supply jets, interaction zone, merged jet and secondary flows) is rather scarce, but can be useful to obtain new insights into mixing ventilation design optimisation. This paper presents time-averaged 2D particle image velocimetry (PIV) measurements of the flow driven by isothermal opposing plane jets in a reduced-scale water-filled generic airplane cabin. Two configurations of opposing jets, i.e. ceiling jets and lateral jets, are examined with inlet Reynolds numbers ranging from 3,450 to 4,650. The analysis focuses on the mean velocity and Reynolds stresses of the whole flow field and the aforementioned fundamental flow components. Decay rates of the supply jets and decay and growth rates of the merged jet are analysed and the size of the interaction zone is assessed. The supply jet velocity decays very fast due to the interaction with the opposing jet. Within the interaction zone, the turbulence levels are high and turbulence is highly anisotropic. A comparison between the merged jet and a self-similar turbulent plane free jet is presented as well. The measurement data is also valuable for (sub-configuration) computational fluid dynamics (CFD) validation purposes.

Aerodynamic drag is the main resistive force in cycling at high speeds and on flat terrain, so reducing it is critical to improving cyclist performance. Aerodynamic comparisons have been made in the past between different types of wheels, and disk wheels were often the best performers. However, to the best of our knowledge, there are no studies in the available literature on how modifications to the disk wheel geometry can improve its performance. Therefore, this paper studies and compares the aerodynamics of disk wheels with flat side disks and with curved side disks (lenticular). Moreover, semilenticular front wheels with an asymmetrical shape are introduced. All but one of the simulated (semi-)lenticular wheels perform better than the flat disk wheels at all yaw angles, e.g., the maximum CD reduction was 5.5%, 10.9%, and 87.5% at 0 deg, 4 deg, and 8 deg yaw angle, respectively. Semilenticular wheels provide a lower CD at medium and large yaw angles compared to corresponding symmetric lenticular wheels. Moreover, the large influence of the ratio of tire width to wheel width on the aerodynamic drag of cycling wheels is confirmed. These results will help riders in their wheel choice and will help manufacturers to design future disk wheels.

Thunderstorm is a severe phenomenon which can produce downburst winds capable for causing significant damage or even the collapse of low-rise structures. Experimental tests and numerical simulations are widely used by the Wind Engineering (WE) community for gaining increased understanding of complex winds like downbursts. In this paper, the accuracy of the Unsteady Reynolds-averaged Navier-Stokes (URANS) and Scale-Adaptive Simulation (SAS) to reproduce a vertical downburst wind - previously tested in the WindEEE Dome wind-simulator facility - was investigated. CFD results were first validated with the experiments and then used to study the dynamics of the phenomenon. The most suitable CFD setting (i.e. SAS case based on the k-ω SST turbulence model) was able to reproduce the development of the primary vortex ring, shedding of secondary rings induced by Kelvin-Helmholtz (KH) instabilities and the periodic detachments of smaller secondary vortices ahead the primary vortex. The superposition of these three contributions has shown to determine the temporal variation of the characteristic nose-shaped vertical profile which was found in the experiments. The performed simulations were also compared to field measurements from the NIMROD project showing a high level of agreement.

Wind flows inside complex urban environments are determined by the mutual effect of large-scale (i.e., wind above the urban boundary layer, UBL) and local-scale forcing (i.e. constraints into the urban canopy layer, UCL). Usually, when the wind field above the UBL is known (e.g. by on-site measurements, OsM), high-resolution microscale models (e.g. CFD) are used to predict the wind inside the UCL. However, standard procedures to map the wind field from an undisturbed position to the UCL are not available yet and several technical aspects need to be investigated. A downscaling method, so-called “static downscaling”, of the wind from mesoscale to microscale is innovatively adopted here to evaluate the performance of two CFD microscale models when predicting the flow in a UCL. The methodology is based on OsM transferred into the UCL by means of so-called “transfer coefficients” calculated by 3D steady RANS simulations for two different spatial extents of the explicitly modeled urban texture (Case A and B). It is discussed in detail the way the transfer coefficients work, how they can be used to understand the correlations between wind above and within the UCL as well as to identify the major limitations of the RANS approach. Results are discussed in qualitative terms and quantified using standard metrics. It is also shown that too high flow rates can occur at the entrance of the waterway of the area of interest and in the outer part of the explicitly modeled urban area, which can be mitigated by “buffer zones”.

Air infiltration and exfiltration that occur at open building entrances are of concern as these have been repeatedly associated with increased energy demand in buildings. Therefore, air curtains are often used to restrict air infiltration/exfiltration through busy building entrances, thereby limiting the exchange of heat and mass between indoor and outdoor environments. Air curtains are fundamentally turbulent plane impinging jets (TPIJs). This paper presents an experimental analysis of the fluid dynamics of TPIJs under parameters that are representative of air-curtain systems in buildings. Experiments are conducted at reduced scale in a water channel where measurements are taken via particle image velocimetry (PIV). Experimental data is subsequently used to validate computational fluid dynamics (CFD) simulations of the TPIJs based on steady Reynolds-averaged Navier-Stokes (RANS) approximation that is commonly used in air-curtain studies. The validation study shows that RANS simulations are capable of resolving the mean velocity field with reasonable accuracy, especially when employing the renormalization group k-ε turbulence model.

The present study investigates the impact of building façade geometrical details on the pollutant transport mechanism in long street canyons. Large-eddy simulations (LES), extensively validated with experiments, are performed for four cases: (i) street canyon without façade balconies, (ii) street canyon with balconies at both windward and leeward façades, (ii) street canyon with balconies only at the windward façade and (iv) street canyon with balconies only at the leeward façade. The results show that the building balconies can strongly affect the wind flow field and pollutant dispersion in long street canyons. The most significant impact is observed for the two street canyon cases with balconies at the windward façade, which strongly obstruct the airflow from penetrating deep into the bottom of the canyon. The presence of balconies only at the windward façade and at both façades can increase the area-weighted mean pollutant concentration in the vertical center plane inside the canyon by 80% and 106%, respectively, and reduce the mean pollutant exchange velocity (Ue) by 46% and 54%, respectively. The analysis of the vertical mean convective and turbulent mass fluxes indicates that the presence of balconies mainly decreases the convective contribution to Ue, while the impact on the turbulent contribution is smaller.

Understanding the effects of climate change on building indoor thermal conditions is of importance for providing a comfortable thermal environment for occupants. Some multi-family dwellings have already been listed as heritage in China (hereinafter referred to as heritage apartments), limiting modifications to the building envelope. However, the effect of climate change on thermal comfort in heritage apartments with a compact interior (i.e. without a living room) built before the 1980s in different Chinese climate zones has seldom been studied. This study focuses on the current and future thermal comfort in two-bedroom heritage apartments in China. The study was conducted for two different Chinese climate zones, that is, a cold climate zone (Beijing), and a hot summer and cold winter climate zone (Shanghai) and both current climate scenarios (typical meteorological years) and future climate scenarios (2050) were used. The results indicate, among other things, increases of 58%–60% and 41%–44% in the predicted average number of overheating hours in 2050 compared to the current climate for the studied bedrooms on the first floor in dwellings in Beijing and Shanghai, respectively.

Infiltration of unconditioned air through access openings and entrance doors with high recurrence can cause detrimental impacts to the energy performance, air quality and thermal comfort of buildings. Air curtains are of strategic importance to attenuate these negative impacts. In addition, air curtains are relevant in specialized HVAC applications for which the impediment of infiltration is also essential (e.g., reduction of smoke propagation in fire events, decrease of contamination hazard in clean rooms, preservation of refrigeration properties in cold rooms). A common performance indicator of an air-curtain system is the separation efficiency, which relates to the rate of heat or mass transfer between the two environments that are separated by the air curtain. The jet parameters have a large influence on the momentum and mixing/entrainment processes that take place in the jet, ultimately affecting the separation efficiency of air curtains. However, to the best of our knowledge, information in the scientific literature is focusing mostly on the analysis of air curtains with single jets. Therefore, this study addresses a preliminary investigation of the implementation of secondary co-flowing jets in air curtains as an approach to modify the jet characteristics to restrict jet entrainment and improve the separation efficiency of air curtains. Reynolds-averaged Navier-Stokes (RANS) simulations are performed to analyze the effect of modifying one of the major parameters of secondary jets (i.e., velocity ratio R) on the air-curtain separation efficiency. The simulation results indicate that reasonable improvements of 4.3% in the air-curtain separation efficiency based on infiltration can be obtained with the incorporation of secondary jets under certain jet discharge conditions.

Accurate computational fluid dynamics (CFD) simulations of the ventilation flow in airplane cabins are important for ventilation design optimisation regarding passenger health, thermal comfort and energy efficiency. The complex unsteady flow phenomena inside the cabin are challenging in numerical modelling and therefore dedicated validation of the simulation outcomes is required. The majority of airplane ventilation studies performed steady Reynolds-averaged Navier-Stokes (RANS) simulations and focused mainly on global flow field characteristics. This paper presents both steady RANS and transient simulations, including unsteady RANS and large eddy simulations (LES), of the flow driven by opposing plane wall jets in a reduced-scale isothermal water-filled generic airplane cabin. A detailed analysis of the mean velocity and turbulence characteristics (including Reynolds stresses) of the cabin flow is outlined, encompassing a thorough investigation of the fundamental flow components such as the opposing jets and the merged jet. Specific attention is devoted to LES grid sensitivity and the performance of different RANS turbulence and LES subgrid-scale (SGS) models is assessed by comparison with particle image velocimetry (PIV) measurements. It is shown that LES in general performs much better than RANS, the latter being incapable of providing accurate mean flow characteristics within the interaction zone and merged jet due to the underlying dynamic opposing jet interaction. Unsteady RANS partly covers the unsteadiness, however, turbulence levels remain systematically underpredicted and LES is required for a correct representation. Differences between the LES SGS model predictions are limited to the SGS kinetic energy budget of the total turbulent kinetic energy.

Inlet boundary conditions at the supply opening play an important role in the accuracy and reliability of computational fluid dynamics (CFD) simulations for indoor airflow. A non-exhaustive overview of past CFD simulations of ventilation flow in generic enclosures indicates that uniform hypotheses of inlet boundary conditions are commonly used. However, due to thermal effects and a complex air supply system geometry, constant values of inlet airflow quantities can be insufficient for an accurate simulation of non-isothermal ventilation flow. In addition, this can lead to biased conclusions on the performance of turbulence models and other computational settings. To assess this issue, a well-documented experiment on non-isothermal mechanical ventilation with detailed information of inlet conditions from the literature is used in this study. Different turbulence models and inlet boundary conditions are validated, including seven steady Reynolds-averaged Navier-Stokes (RANS) models, six methods of imposing inlet air velocity, three methods of specifying air temperature, and a wide range of turbulence quantities. The parametric study demonstrates that in this particular case, i.e., cold air supply from a single round nozzle diffuser close to the ceiling, ω-based turbulence models perform better than the ε-based turbulence models. The impacts of different methods to specify inlet air temperature profile and turbulence quantities on the simulation results are not significant. However, if the inlet airflow direction is not taken into account appropriately, significant deviations are observed between CFD simulations and experimental data.

We applied data-based recurrence CFD (rCFD) to model pollutant dispersion in near-field flow configurations. In case of complex topologies, the global-domain version of rCFD fails to account for local recurrent flow features. We therefore developed a novel island-based version of rCFD, which partitions the computational domain to isolate islands of high recurrence prominence, and subsequently defines a distinct recurrence path for each of these islands. We applied island-based rCFD to pollutant dispersion for two side-by-side cubical buildings with three different gap widths in between them and a real urban environment. We showed that numerical predictions of pollutant dispersion by island-based rCFD were in excellent agreement with full CFD simulations, thus outperforming the global-domain version of rCFD. In both applications, island-based rCFD simulations ran three orders of magnitude faster than corresponding full CFD simulations. In the second application, this speed-up enabled real-time simulations on a computational grid of 10 million cells.

Some teams aiming for victory in a mountain stage in cycling take control in the uphill sections of the stage. While drafting, the team imposes a high speed at the front of the peloton defending their team leader from opponent’s attacks. Drafting is a well-known strategy on flat or descending sections and has been studied before in this context. However, there are no systematic and extensive studies in the scientific literature on the aerodynamic effect of uphill drafting. Some studies even suggested that for gradients above 7.2% the speeds drop to 17 km/h and the air resistance can be neglected. In this paper, uphill drafting is analyzed and quantified by means of drag reductions and power reductions obtained by computational fluid dynamics simulations validated with wind tunnel measurements. It is shown that even for gradients above 7.2%, drafting can yield substantial benefits. Drafting allows cyclists to save over 7% of power on a slope of 7.5% at a speed of 6 m/s. At a speed of 8 m/s, this reduction can exceed 16%. Sensitivity analyses indicate that significant power savings can be achieved, also with varying bicycle, cyclist, road and environmental characteristics.

Cycling races contain a multitude of motorcycles for various activities including television broadcasting. During parts of the race, these motorcycles can ride in close proximity of cyclists. Earlier studies focused on the impact of a nearby motorcycle on cyclist drag for in-line arrangements. It was shown that not only a motorcycle in front of a cyclist but also a motorcycle closely behind a cyclist can substantially reduce cyclist drag. However, there appears to be no information in the scientific literature about the impact of the motorcycle on cyclist drag for parallel and staggered arrangements. This paper presents wind tunnel measurements of cyclist drag for 32 different parallel and staggered cyclist-motorcycle arrangements. It is shown that the parallel arrangement leads to a drag increase for the cyclist, in the range of 5 to about 10% for a lateral distance of 2 to 1 m. The staggered arrangement can lead to either a drag increase or a drag decrease, where the latter is about 2% for most positions analyzed. For one of the parallel arrangements, computational fluid dynamics simulations were performed to provide insight into the reasons for the drag increase. A cyclist power model was used to convert the drag changes into potential time gains or losses. Compared to a lone cyclist riding at a speed of 46.8 km/h (13 m/s) on level road in calm weather, the time loss by a drag increase of 10%, 4% and − 2% was 2.16, 0.76 s and − 0.80 s per km, respectively. These time differences are large enough to influence the outcome of cycling races.

Pollutant dispersion in urban street canyons has been widely investigated by large-eddy simulation (LES). Many LES studies focused on generic street canyons under a wind direction perpendicular to the street axis. Accurate LES simulations require a sufficiently large domain size to minimize the effects of the artificial boundary conditions at the domain faces on the results. As opposed to RANS simulations, there is a lack of guidelines for an appropriate domain size for LES simulations of wind flow and pollutant dispersion in street canyons. The present study systematically investigates the effect of the domain width, domain height and upstream and downstream domain lengths on the wind flow and pollutant dispersion within a generic 2.5D street canyon with spanwise periodic boundary conditions. Following a validation study, 16 LES simulations are performed for different domain sizes. The results show that the minimum requirement for the domain width is 2.5H, where H is the roof height of the street canyon. For the domain height, upstream domain length and downstream domain length, 7.5H, 5H and 10H are recommended, respectively. These guidelines should help to reduce the computational costs of this type of simulation without significantly compromising the accuracy.

This paper introduces a novel snow transport model for the analytical simulation of wind-induced snow transport on flat roofs. In the novel model, the differences between precipitation and deposited snow particles on roofs, including the differences in threshold friction velocity and fetch distance for saturated drifting state, are considered. Thus, snow drifting on a roof is divided into drifting without and during snowfall. The effects of terrain category and roof height are also considered using the friction velocity on roofs to compute snow transport rate instead of directly using the wind speed data reported by weather stations. Parametric analysis and case study are conducted to explain the novel model in detail and compare the results with those obtained from the model developed by O’Rourke et al. (2005). The estimated fetch distance for saturated snow drifting by the proposed approach in this study ranges from zero to thousands of meters, which is consistent with field measurement results and more reasonable than the use of constant values. Results of the case study indicate that the proposed snow transport model might be more reasonable because the effects of more factors are considered.

Aerodynamic drag is the main resistive force in cycling at high speeds and on flat terrain. In wind tunnel tests or computational fluid dynamics simulations, the aerodynamic drag of cycling wheels is often investigated isolated from the rest of the bicycle, and sometimes in static rather than rotating conditions. It is not yet clear how these testing and simulating conditions influence the wheel aerodynamic performance and how the inclusion of wheel rotation influences the overall measured or computed cyclist drag. This study presents computational fluid dynamics simulations, validated with wind tunnel tests, that indicate that an isolated static spoked front wheel has a 2.2% larger drag area than the same wheel when rotating, and that a non-isolated static spoked front wheel has a 7.1% larger drag area than its rotating counterpart. However, rotating wheels are also subjected to the rotational moment, which increases the total power required to rotate and translate the wheel compared to static conditions where only translation is considered. The interaction with the bicycle frame and forks lowers the drag area of the front wheel by 8.8% for static and by 12.9% for the rotating condition, compared to the drag area of the isolated wheels. A different flow behavior is also found for static versus rotating wheels: large low-pressure regions develop from the hub for rotating wheels, together with a lower streamwise velocity region inside the circumference of the wheel compared to static wheels. The results are intended to help in the selection of testing/simulating methodologies for cycling spoked wheels. ispartof: Sports Engineering vol:24 issue:1 status: Published online

Air curtains (ACs) are plane turbulent impinging jets that are used to separate two environments in terms of heat and mass transfer while still allowing traffic between these environments. The many applications of ACs across a wide variety of industries makes the evaluation of their performance an important but difficult task. The aim of this paper is to introduce a performance indicator, called the adapted separation efficiency, that is suitable for different types of systems that may involve different AC configurations (downward blowing, upward blowing, lateral blowing, multiple jets, etc.) at multiple scales, different transported quantities (heat, water vapor, particles, gases, etc.) subjected to various transport mechanisms (advection, molecular and turbulent diffusion) and varying environmental conditions (gradients in environmental pressure and/or density). It is defined using a conventional efficiency formula. The principle of this performance indicator is illustrated with a generic case study where the performance is evaluated for two basic AC configurations involving cross-jet pressure and density gradients, as well as different jet momentum fluxes. The case study is conducted based on computational fluid dynamics employing validated large eddy simulations.

Motorcycles are present in cycling races for reasons including television broadcasting. During parts of the race, these motorcycles ride in front of individual or groups of cyclists. Concerns have been expressed in the professional cycling community that these motorcycles can provide aerodynamic benefits in terms of drag reduction for the cyclists drafting behind them. However, to the best of our knowledge, no information about the extent of these benefits is present in the scientific literature. Therefore, this paper analyses the potential drag reduction for a cyclist by drafting behind a motorcycle. Wind tunnel measurements and numerical simulations with computational fluid dynamics were performed. It was shown that drafting at separation distances d = 2.64, 10, 30 and 50 m can reduce the drag of the cyclist down to 52, 77, 88 and 93% of that of an isolated cyclist, respectively. A cyclist power model is used to convert these drag reductions into potential time gains. For a non-drafting cyclist at a speed of 54 km/h on level road in calm weather, the time gains by drafting at d = 2.64, 10, 30 and 50 m are 12.7, 5.4, 2.7 and 1.6 s per km, respectively. These time differences can influence the outcome of cycling races. The current rules of the International Cycling Union do not prevent these aerodynamic benefits from occurring in races.

Within a time span of only a few months, the SARS-CoV-2 virus has managed to spread across the world. This virus can spread by close contact, which includes large droplet spray and inhalation of microscopic droplets, and by indirect contact via contaminated objects. While in most countries, supermarkets have remained open, due to the COVID-19 pandemic, authorities have ordered many other shops, restaurants, bars, music theaters and indoor sports centers to be closed. As part of COVID-19 (semi)lock-down exit strategies, many government authorities are now (May-June 2020) allowing a gradual re-opening, where sometimes indoor sport centers are last in line to be permitted to re-open. This technical note discusses the challenges in safely re-opening these facilities and the measures already suggested by others to partly tackle these challenges. It also elaborates three potential additional measures and based on these additional measures, it suggests the concept of a certificate of equivalence that could allow indoor sports centers with such a certificate to re-open safely and more rapidly. It also attempts to stimulate increased preparedness of indoor sports centers that should allow them to remain open safely during potential next waves of SARS-CoV-2 as well as future pandemics. It is concluded that fighting situations such as the COVID-19 pandemic and limiting economic damage requires increased collaboration and research by virologists, epidemiologists, microbiologists, aerosol scientists, building physicists, building services engineers and sports scientists. ispartof: BUILDING AND ENVIRONMENT vol:180 ispartof: location:England status: published

© 2018 Elsevier Ltd In the past, computational fluid dynamics (CFD) simulations have been successfully applied for the prediction of snow drift around buildings and on building roofs. A literature study indicates that a wide range of influential computational and physical parameters exist for snow drifting predictions in CFD, while the impact of these parameters is unclear, resulting in a lack of available CFD simulation guidelines. Therefore, this study presents a systematic and generic analysis with emphasis on the fundamentals of snow transport prediction techniques. Snow transport over flat, uniformly rough, open terrain, including snow saltation and snow suspension is successfully simulated using CFD and the results are compared to field measurements of snow concentrations for validation. This paper investigates the impact of grid resolution, falling velocity of snow, turbulent Schmidt number, threshold friction velocity of snow and turbulence model on the CFD simulation results. The results show that the falling velocity and the turbulent Schmidt number have the largest impact. A slight change in the falling velocity or the turbulent Schmidt number significantly impacts the predicted snow concentration in the air. In addition, the turbulence model mainly affects the turbulent kinetic energy, another key factor that influences the numerical predictions of snow transport. ispartof: JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS vol:177 pages:213-226 status: published

The surface-averaged forced Convective Heat Transfer Coefficient (CHTCavg) at a windward building facade is influenced by the complex interaction between a wide range of parameters. 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. In this paper, therefore, the combined impacts of wind speed (U10), building height (H) and width (W), and wind direction (θ) on the CHTCavg for the windward facade of buildings are systematically investigated. High-resolution CFD simulations of wind flow and forced convective heat transfer, validated with wind-tunnel measurements, are performed for 64 building geometries (10 m ≤ H and W ≤ 80 m), 8 wind directions (0° ≤ θ ≤ 78.75°) and 4 reference wind speeds (1 m/s ≤ U10 ≤ 4 m/s). The 3D steady RANS equations with the realizable k-ε turbulence model and the low-Re number Wolfshtein model are used. The results show that for a given building geometry and U10, the CHTCavg decreases as θ increases from 0° to 78.75°. The maximum reduction of about 42% occurs for the building with H = 8W = 80 m. In addition, for a given θ and U10, by increasing H, the CHTCavg increases, while increasing W has the opposite impact on the CHTCavg. Finally, a new generalized CHTC expression is presented as a function of U10, H, W and θ and its accuracy is confirmed by detailed in-sample and out-of-sample evaluations.

On-site renewable energy generation in the built environment can be achieved by incorporating wind turbines in the integral design of buildings. Passages through buildings are considered promising to strengthen the local wind resource availability but information concerning their design and performance is scarce. Therefore, two key design parameters that can enhance the wind energy performance of ducted openings in high-rise buildings are addressed and optimized via CFD simulations: the fillet radius (r) of the opening and the duct diameter (d0). 3D steady RANS simulations are performed and validated with wind tunnel data from the literature. Fillets are shown to suppress flow separation, thereby enhancing the magnitude and uniformity of the wind speed in the duct and reducing the turbulent kinetic energy. With a reference diameter d0 = D, the best-performing configuration has a normalized fillet radius r/d0 = 0.2, which increases the average wind speed in the duct by 65% and the wind power by 354%. Modifying the duct diameter alone has limited influence. However, combining a larger duct diameter d0 = 1.5D with fillets with r/d0 = 0.4, can yield up to 78% increase in average wind speed and 650% in wind power density. Findings indicate that the dimensionless wind speed in the duct (U/U0) scales closely in proportion to the normalized fillet radius (r/d0). With these results, the present study demonstrates the aerodynamic advantage of ducted openings in buildings and identifies relevant design conditions required to improve the wind resource availability for the prospective implementation of wind turbines.

© 2018 The Authors Vertical axis wind turbines (VAWTs) have received growing interest for off-shore application and in the urban environments mainly due to their omni-directional capability, scalability, robustness, low noise and costs. However, their aerodynamic performance is still not comparable with their horizontal axis counterparts. To enhance their performance, the impact of operational parameters such as tip speed ratio (λ), Reynolds number (Re c ) and turbulence intensity (TI) on their power performance and aerodynamics needs to be deeply understood. The current study, therefore, intends to systematically investigate the effect of these parameters in order to provide a deeper insight into their impact on the aerodynamic performance of VAWTs. For this investigation, a Darrieus H-type VAWT has been employed. A wide range of the parameters is considered: λ = 1.2-6.0, Re c = 0.3 × 10 5 -4.2 × 10 5 and TI = 0%-30% to analyze the turbine performance, turbine wake and dynamic loads on blades. High-fidelity computational fluid dynamics (CFD), extensively validated with experimental data, are employed. The results show that (i) variable-speed operation maintaining the optimal λ at different wind speeds improves the turbine power coefficient, e.g. up to 168% at 4 m/s, while keeping an almost constant thrust coefficient, (ii) the turbine performance and wake are Re-dependent up to the highest Re c studied, (iii) large TI (> 5%) improves the turbine performance in dynamic stall by promoting the laminar-to-turbulent transition and delaying stall on blades, however it deteriorates the optimal performance by introducing extra skin friction drag. The findings of the current study can support more accurate performance prediction of VAWTs for various operating conditions and can help the improvement of the aerodynamic performance of VAWTs. ispartof: Energy Conversion And Management vol:169 pages:45-77 status: published

Museums are dedicated to protect their artwork collection and to display the collection as safely as possible. Amongst other things, the indoor climate is of utmost importance to minimize collection degradation. Many museums employ tight climate guidelines, allowing only small fluctuations of indoor temperature and relative humidity, resulting in the following problems: huge energy consumption, the need for high-capacity HVAC systems, additional stress on historical buildings. This simulation study investigates the energy-saving potential of different setpoint strategies. Damage functions were used to assess the degradation risk of the collection and an Adaptive Temperature Guideline was used to assess thermal comfort. A state-of-the-art museum in the Netherlands was modeled and the indoor climate and energy consumption were simulated, including heating, cooling, humidification and dehumidification. Maximum savings, compared to a reference situation, of 82% may be achieved. However, the optimum strategy yields a saving of 77%, significantly improves thermal comfort and decreases chemical degradation.

Thermal comfort models can be used to gain insight into important building design variables and predict whether a given design will provide satisfactory thermal conditions. There is a need for better industry standards and awareness towards thermal comfort as a multi-domain construct is increasing. However, despite the research efforts of academics, research outcomes in the field of thermal comfort do not live up to their full potential because they are difficult to scale. In this review, scalability is presented as a construct which characterizes the ability of a thermal comfort model to aid in the understanding and prediction of thermal comfort conditions in real-world practice, and more specifically the design of office buildings. A literature search of recent scientific publications is conducted, resulting in 77 articles on multi-domain thermal comfort modelling. The scoping review identifies current scalability challenges associated with implementing existing thermal comfort models in practice and seeks to steer the research field towards generating more reliable models that contribute to the assessment of thermal comfort in office buildings, with particular focus on the design stage. We propose to do that by identifying potential avenues for future research that are related to several aspects of model scalability, namely, model scope, resolution, and portability.

Atmospheric wind may affect mechanically-induced depressurization in asbestos containment zones set to prevent escape of hazardous fibers. The associated health risks necessitate investigation of wind effects on internal depressurization. This can be achieved by experiments in atmospheric boundary layer wind tunnels utilizing relatively large geometrical scaling ratios (e.g., 1:40), suitable for accommodating all components of the reducedscale mechanical ventilation system. However, physical constraints in the wind-tunnel cross-section limit replicating large-scale turbulent structures, thus mispredicting exceedances of pressures responsible of containment breaches. Investigating the latter is the innovative goal of present study, for which external pressure characteristics and duration of a certain threshold pressure exceedance have been analyzed for an idealized lowrise cubic building with two geometrical scaling ratios (1:40 and 1:300). The 1:300 scaling ratio allows to represent turbulent structures of almost all relevant sizes of the ABL; whereas, with the 1:40, large-scale turbulent structures are missing. Overall, findings suggest that a larger scaling ratio of 1:40 can be effectively used for mechanical ventilation studies in scenarios where ventilation inlets or outlets are not installed on the roof. However, with the caution that the containment breach probability can be underpredicted at regions of flow reattachment and recirculation.

Construction with cementitious materials via 3D printing requires a highly thixotropic behavior, which is a challenge for construction industry. In this work a facile and low-cost gelatin-modified thermal responsive smart cement paste formulation was developed for extrusion-based 3D printing in cold environments The paste's temperature-dependent rheological properties were characterised, and the underlying mechanism was explored. At room temperature, the modified paste presents similar rheological properties as the reference cement paste. After resting for 10 min at 5 °C, the modified cement paste has a yield stress of 1900 Pa which is 10 times that of the reference paste. Moreover, the mechanical properties of the modified paste are comparable to or higher than that of the reference paste at later age. Our approach may inspire a facile manipulation of paste rheology through temperature, which facilitates smartly controlled 3D concrete printings.

© 2017 The Author(s) Generating economical, high-resolution and high-quality computational grids for Large Eddy Simulation (LES) of wind flow and convective heat transfer (CHT) around surface-mounted obstacles is not straightforward. When the grid size is used as filter, LES grids should ideally consist of cubic cells, while CHT requires a very high near-wall resolution to resolve the thin viscous sublayer and buffer layer that represent the largest resistance to CHT. To avoid very high cell numbers and the need for excessive computational resources, non-conformal grids can be considered. This paper provides a detailed evaluation of the performance of non-conformal grids with cubic cells, for wind flow and CHT around a wall-mounted cubic obstacle. LES results on non-conformal versus conformal grids are compared with each other and with wind-tunnel measurements of wind speed and surface temperature. Moreover, sensitivity analysis is performed concerning the impact of overall grid resolution, subdomain size and grid refinement ratio. Average absolute deviations between LES on non-conformal versus conformal grids are about 0.9% (0.5 °C) for surface temperature on all cube surfaces. Comparison with experiments shows for the non-conformal grid an average and maximum absolute deviation for surface temperature of 2.0% (1.1 °C) and 7.6% (3.6 °C), respectively. The sensitivity analysis shows minor impact of subdomain size on convective heat transfer coefficients (CHTC) where, on average, absolute deviations of less than 2.2% are observed. This study shows that non-conformal grids can strongly reduce the total cell count (here by a factor up to 30.2) without significantly compromising the accuracy of results. ispartof: Building and Environment vol:119 pages:44-61 status: published

One of the under-represented groups in participatory urban research is very young children (0–3 years old). Very young children from disadvantaged neighbourhoods, particularly in global cities, such as Istanbul, often have to negotiate unfriendly urban spaces in their daily routines. These routines consist of intertwined events of caregivers and children, as care duties of caregivers frame their joint daily lives. Based on questionnaires and participatory mapping with full-time mothers from Istanbul, we argue that a compact design of neighbourhoods, which merges public spaces relevant to families with young children in combined destinations, is critical towards creating inclusive urban environments.

This paper presents finite-volume-based scale-adaptive simulations of single paceline configurations up to eight cyclists for three different postures. In cycling, drag reduction by drafting in pacelines is a key strategy to limit energy expenditure. The drag reductions of individual cyclists and of the paceline as a whole are determined by several factors, including cycling posture. To the best of our knowledge, a systematic study on the effect of cyclist posture on the drag in single pacelines has not yet been published in the scientific literature. In this study, drag reduction and flow field data were computed while validation was performed by wind tunnel measurements. The three investigated postures concern a road race dropped posture with either a large or small sagittal torso angle and a time trial posture. For the considered pacelines in which all cyclists have the same posture, the drag of a cyclist could be reduced by changing either the posture, or the position, or both. Changing posture can yield a maximum drag reduction of about 15% for the leading cyclist. The position in the paceline with minimum drag was the one but last, independent of the investigated cycling postures. For the pacelines containing eight cyclists, maximum drag reductions up to 63% were found. The largest drag reduction was 68%, obtained by riding in penultimate position in an eight cyclist paceline in dropped position with a small sagittal torso angle.

Promoting the sustainability of the building industry is one of the major approaches to addressing energy depletion and climate change. Here, we developed scalable cementitious cooling composites (CCCs) with superior energy-free cooling performance and environmental applicability. Optical properties, phase composition, microstructure, and silica reactivity of composites are characterized and analyzed. Onsite measurements are conducted to evaluate the surface/internal cooling capacities and validate the cooling principles and such composites’ climatic applicability. Results show that calcite, C[sbnd]S[sbnd]H phases (especially tobermorite), and a higher water-to-powder ratio can increase the solar reflectivity (Rsun). Meanwhile, C[sbnd]S[sbnd]H and calcite can also increase the spectral emissivity in the atmospheric window (εaw). Optimal sizes of 0.5 μm (particles) and 1.0 μm (pore size) for Mie scattering are determined by Finite-Difference Time-Domain simulations. The Rsun of 0.90 and εaw of 0.88 are simultaneously achieved, which are comparable to exquisitely designed polymer-based coatings, metamaterials, and multi-layer composites. The surface cooling of 17.3 ℃, internal cooling of 9.2 ℃ by solar reflection, internal cooling of 4.8 ℃ by evaporative cooling, and internal cooling above 2.8 ℃ by mid-infrared (MIR) emission are observed. CCCs are proven to provide efficient cooling in different conditions, with low investment, facile production, and high environmental resistance.

Applying high temperature cooling concepts, i.e. high temperature cooling (T(supply) is 16-20 degrees C) HVAC systems, in the built environment allows the reduction in the use of (high quality) energy. However, application of high temperature cooling systems can result in whole body and local discomfort of the occupants. Non-uniform thermal conditions, which may occur due to application of high temperature cooling systems, can be responsible for discomfort. Contradictions in literature exist regarding the validity of the often used predicted mean vote (PMV) index for both genders, and the index is not intended for evaluating the discomfort due to non-uniform environmental conditions. In some cases, however, combinations of local and general discomfort factors, for example draught under warm conditions, may not be uncomfortable. The objective of this study was to investigate gender differences in thermophysiology, thermal comfort and productivity in response to thermal non-uniform environmental conditions. Twenty healthy subjects (10 males and 10 females, age 20-29 years) were exposed to two different experimental conditions: a convective cooling situation (CC) and a radiant cooling situation (RC). During the experiments physiological responses, thermal comfort and productivity were measured. The results show that under both experimental conditions the actual mean thermal sensation votes significantly differ from the PMV-index; the subjects are feeling colder than predicted. Furthermore, the females are more uncomfortable and dissatisfied compared to the males. For females, the local sensations and skin temperatures of the extremities have a significant influence on whole body thermal sensation and are therefore important to consider under non-uniform environmental conditions.

Knowledge of indoor ventilation airflow is essential for creating a healthy, comfortable and energy-efficient indoor climate in buildings, airplanes, cars, ships, etc. In the past decades, numerical methods such as Computational Fluid Dynamics (CFD) have become primary tools to assess indoor airflow. However, validation of numerical simulations by high-quality experimental data is imperative. Although a lot of studies have focused on experimental data for turbulent ventilation flow, there is a lack of experimental data for transitional ventilation flow. Transitional ventilation flow is in general associated with relatively low air velocities inside the enclosure. This paper presents detailed Particle Image Velocimetry (PIV) measurements and an analysis of transitional flow in a ventilated enclosure. The isothermal forced mixing ventilation flow is driven by a transitional plane jet. The measurements are performed in a reduced-scale water-filled model for slot Reynolds numbers ranging from 800 to 2,500. Flow visualizations indicate that this range of Reynolds numbers results in transitional flow, including the development of large coherent structures in the outer region of the jet. The measurements are analyzed in terms of mean velocity near the inlet and in the entire flow domain, and in terms of turbulence intensity and vorticity. Specific attention is given to the Coanda effect by which the free plane jet develops into a wall jet. The experimental data and analysis are specifically intended to support the development and validation of numerical models for ventilation flow.

Wind catcher as a natural ventilation system is increasingly used in modern buildings to minimize the consumption of non-renewable energy and reduce the harmful emissions. Height, cross section of the air passages and also place and the number of openings are the main factors which affect the ventilation performance of a wind catcher structure. In this study, experimental wind tunnel, smoke visualization testing and computational fluid dynamic (CFD) modeling were conducted to investigate ventilation performance of wind catchers with different number of openings to find how the number of opening affects hydrodynamic behavior of wind catchers. To achieve this particular aim, five cylindrical models with same cross section areas and same heights were employed. The cross sections of all these wind catchers were divided internally into various segments to get two-sided, three-sided, four-sided, six-sided and twelve-sided wind catchers. The experimental investigations were conducted in an open circuit subsonic wind tunnel. For all these five shapes, the ventilated air flow rate into the test room was measured at different air incident angles. Numerical solutions were used for all these five configurations to validate the proposed measuring techniques and the corresponding wind tunnel results. The results show that the number of openings is a main factor in performance of wind catcher systems. It also shows that the sensitivity of the performance of different wind catchers related to the wind angle decreases by increasing the number of openings. Moreover, comparing with a circular wind catcher a rectangular system provides a higher efficiency.

Application of the exergy concept to research on the built environment is a relatively new approach. It helps to optimize climate conditioning systems so that they meet the requirements of sustainable building design. As the building should provide a healthy and comfortable environment for its occupants, it is reasonable to consider both the exergy flows in building and those within the human body. Until now, no data have been available on the relation between human-body exergy consumption rates and subjectively assessed thermal sensation. The objective of the present work was to relate thermal sensation data, from earlier thermal comfort studies, to calculated human-body exergy consumption rates. The results show that the minimum human body exergy consumption rate is associated with thermal sensation votes close to thermal neutrality, tending to the slightly cool side of thermal sensation. Generally, the relationship between air temperature and the exergy consumption rate, as a first approximation, shows an increasing trend. Taking account of both convective and radiative heat exchange between the human body and the surrounding environment by using the calculated operative temperature, exergy consumption rates increase as the operative temperature increases above 24 °C or decreases below 22 °C. With the data available so far, a second-order polynomial relationship between thermal sensation and the exergy consumption rate was established. © 2010 Elsevier B.V. All rights reserved.

Convective heat transfer at exterior building surfaces has an impact on the design and performance of building components such as double-skin facades, solar collectors, solar chimneys and ventilated photovoltaic arrays, and also affects the thermal climate and cooling load in urban areas. In this study, an overview is given of existing correlations of the exterior convective heat transfer coefficient (CHTC) with the wind speed, indicating significant differences between these correlations. As an alternative to using existing correlations, the applicability of CFD to obtain forced CHTC correlations is evaluated, by considering a cubic building in an atmospheric boundary layer. Steady Reynolds-averaged Navier-Stokes simulations are performed and, instead of the commonly used wall functions, low-Reynolds number modelling (LRNM) is used to model the boundary-layer region for reasons of improved accuracy. The flow field is found to become quasi independent of the Reynolds number at Reynolds numbers of about 105. This allows limiting the wind speed at which the CHTC is evaluated and thus the grid resolution in the near-wall region, which significantly reduces the computational expense. The distribution of the power-law CHTC-U10 correlation over the windward and leeward surfaces is presented (U10= reference wind speed at 10 m height). It is shown that these correlations can be accurately determined by simulations with relatively low wind speed values, which avoids the use of excessively fine grids for LRNM, and by using only two or three discrete wind speed values, which limits the required number of CFD simulations. © 2010 Elsevier Ltd. All rights reserved. ispartof: Energy Conversion and Management vol:52 issue:1 pages:512-522 status: published

Wind flow in urban environments is an important factor governing the dispersion of heat and pollutants from streets, squares and buildings. This paper presents a coupled CFD modelling approach for urban wind flow and indoor natural ventilation. A specific procedure is used to efficiently and simultaneously generate the geometry and the high-resolution body-fitted grid for both the outdoor and indoor environment. This procedure allows modelling complex geometries with full control over grid quality and grid resolution, contrary to standard semi-automatic unstructured grid generation procedures. It also provides a way to easily implement various changes in the model geometry and grid for parametric studies. As a case study, a parametric analysis of natural ventilation is performed for the geometrically complex Amsterdam ArenA stadium in the Netherlands. The turbulent wind flow and temperature distribution around and inside the stadium are solved with the 3D steady Reynolds-averaged Navier-Stokes equations. Special attention is given to CFD solution verification and validation. It is shown that small geometrical modifications can increase the ventilation rate by up to 43%. The coupled modelling approach and grid generation procedure presented in this paper can be used similarly for future studies of wind flow and related processes in complex urban environments.

Heat and mass transfer modelling in building facades with ventilated cavities requires information on the cavity air change rates, which can be a complex function of the building and cavity geometry and the meteorological conditions. This paper applies Reynolds-averaged Navier–Stokes (RANS) CFD to study wind-induced airflow in the narrow (23 mm) ventilated facade cavities of an isolated low-rise building. Both coupled and decoupled simulations are performed. In the coupled simulations, the atmospheric boundary layer wind-flow pattern around the building and the resulting airflow in the cavities are calculated simultaneously and within the same computational domain. In the decoupled simulations, two separate CFD simulations are conducted: a simulation of the outdoor wind flow around the building (with closed cavities) to determine the surface pressures at the position of the cavity inlet and outlet openings, and a simulation of the cavity airflow, driven by these surface pressures. CFD validation is performed for the external and internal (cavity) flows. It indicates an important modelling limitation: while both laminar and turbulent cavity airflow can be accurately reproduced with low-Reynolds number modelling, this method fails in the transitional regime. The valid CFD results (outside the transitional regime) are analysed in terms of cavity airflow patterns and cavity air change rates per hour (ACH) for different cavity positions, wind speeds and wind directions. The CFD results of cavity air speed and ACH compare favourably with values from previous experimental studies. The coupled and decoupled simulation results are compared to provide an indication of the local losses. It is concluded that future work should focus on adapting RANS CFD low-Reynolds number models to accurately model cavity flow in the transitional regime.

Natural ventilation of buildings refers to the replacement of indoor air with outdoor air due to pressure differences caused by wind and/or buoyancy. It is often expressed in terms of the air change rate per hour (ACH). The pressure differences created by the wind depend – among others – on the wind speed, the wind direction, the configuration of surrounding buildings and the surrounding topography. Computational Fluid Dynamics (CFD) has been used extensively in natural ventilation research. However, most CFD studies were performed for only a limited number of wind directions and/or without considering the urban surroundings. This paper presents isothermal CFD simulations of coupled urban wind flow and indoor natural ventilation to assess the influence of wind direction and urban surroundings on the ACH of a large semi-enclosed stadium. Simulations are performed for eight wind directions and for a computational model with and without the surrounding buildings. CFD solution verification is conducted by performing a grid-sensitivity analysis. CFD validation is performed with on-site wind velocity measurements. The simulated differences in ACH between wind directions can go up to 75% (without surrounding buildings) and 152% (with surrounding buildings). Furthermore, comparing the simulations with and without surrounding buildings showed that neglecting the surroundings can lead to overestimations of the ACH with up to 96%.

Experimental wind tunnel and smoke visualization testing as well as CFD and analytical modeling were conducted to investigate the performance of a two-sided wind catcher. This type of wind catcher is divided internally into two halves for the purposes of air supply and extract. In this study, the two-sided wind catcher model was constructed of two similar one-sided wind catcher models, which were attached together back to back. These one-sided models are 1:40 scale models of Kharmani's School wind catcher in the city of Yazd. Experimental investigations were carried out using an open-circuit wind tunnel and both the induced volumetric airflow into the building and the pressure coefficients around all surfaces of the wind catcher model were measured at various wind angles. Furthermore, the CFD simulation was also used to evaluate the pressure coefficient distribution and airflow pattern around and through the wind catcher. Additional experimental tests and computational fluid dynamics simulation of the wind catcher in the wind tunnel were also conducted in order to assess the accuracy of measurement procedures and the uncertainty of experimental results. This article also represents a semi-empirical approach in which experimental data were used for a detailed analytic model, in order to provide an accurate estimate of the performance of wind catchers. It was found that for an isolated two-sided wind catcher model, the maximum efficiency is achieved at the angle of 90°. At this air incident angle the wind catcher efficiency increases approximately 20% more than the one at zero angle. The experimental investigations demonstrated the potential of two-sided wind catcher for enhancing the natural ventilation inside buildings. It can be seen that CFD simulation and analytical modeling results have a good agreement with the experimental results. Theoretical modeling can also help to assess the accuracy of measurement procedures and the uncertainty of experimental results.

Wind-driven rain (WDR) is one of the most important boundary conditions governing the hygrothermal behaviour of building facades, which is usually numerically analysed with the so-called Heat-Air-Moisture (HAM) transfer models. In the traditional approach of HAM transfer models, WDR is implemented in a simplified manner: the total mass of all raindrops impinging on a certain surface area of a building facade during the time interval of the meteorological input data (typically 1 h) is spatially and temporally averaged and is supplied to the facade as an averaged moisture flux. However, real WDR is the sum of individual raindrops that impinge on the facade in a spatially and temporally discrete modus, and that do not only spread at impact, but may also splash or bounce off the facade. Therefore the reliability of this simplification can be questioned. To investigate its validity, a new experimental set-up was developed at a full-scale test building. It allows simultaneous and continuous measurements of the reference wind speed and direction, WDR intensity, outdoor air temperature and humidity, as well as the response of facade material samples to these environmental conditions. For this purpose, a measuring device was developed that monitors the weight change of the sample with a resolution of 5 mg. Temperatures at the interior and exterior material surfaces are also monitored. The whole measurement data set is used to check the validity of the traditional numerical approach. Large differences are found between the measurement and simulation results, which cannot solely be attributed to the uncertainty in the convective moisture transfer coefficient, but may be due to two additional reasons: the occurrence of splashing and bouncing at raindrop impact on the facade, which is not included in the model, and/or errors in surface moisture evaporation and absorption due to modelling the actual random and discrete raindrop impingement as a simplified averaged moisture flux.

Wind-driven rain (WDR) is one of the most important moisture sources that affect the hygrothermal performance and the durability of building facades. The facades of the Dutch monumental building St. Hubertus show severe deterioration caused by WDR. Assessment of the amount and intensity of WDR falling onto the facades is necessary as input for numerical heat-air-moisture (HAM) transfer models to analyse the causes of the moisture problems and the impact of remedial measures. In this study, a numerical simulation method based on Computational Fluid Dynamics (CFD) is used to predict the amount of WDR impinging on the south-west facade of the tower of the building. The paper focuses on the numerical simulation results, the validation of these results and their sensitivity to two parameters: the level of geometrical detailing of the computational building model and the upstream terrain aerodynamic roughness length. Validation is performed by comparison of the numerical results with a dataset obtained from on-site WDR measurements. It is shown that the CFD simulations provide fairly good predictions of the amount of WDR impinging on the south-west facade of the tower, except for the lower part. It is also shown that the local effects of geometrical facade details are significant and can yield differences in WDR exposure up to 40%, while their effect at other positions is negligible. Finally, the sensitivity of WDR simulations to the upstream aerodynamic roughness length is discussed.

Experimental wind tunnel and smoke visualization testing was conducted to investigate the performance of a two-sided wind catcher. This type of wind catcher is divided internally into two halves for the purposes of air supply and extract. In this study, the two-sided wind catcher model was constructed of two similar one-sided wind catcher models, which were attached back to back. These one-sided models are 1: 40 scale models of Kharmani's School wind catcher in the city of Yazd. Experimental investigations were carried out using an open-circuit wind tunnel, and both the induced volumetric airflow into the building and the pressure coefficients around all surfaces of the wind catcher model were measured at various wind angles. Additional experimental tests and computational fluid dynamics simulation of the wind catcher in the wind tunnel were also conducted in order to assess the accuracy of measurement procedures and the uncertainty of experimental results. To evaluate the stack effects on the natural ventilation performance of a two-sided wind catcher system, the results were compared to the corresponding results of a one-sided one. As a result of placing urban full-scale wind catchers in the boundary layer of atmospheric winds, the effect of this phenomenon was also examined experimentally. The experiments were performed when the wind catcher model with an adjoining house was placed in the wake of upstream objects, resembling neighbouring buildings. It was found that for an isolated two-sided wind catcher model, maximum efficiency is achieved at an air incident angle of 90°, and this can only be explained by the domination of a stack effect rather than dynamic pressure. At this air incident angle the wind catcher efficiency is ≈20 per cent more than the one at zero angle. The results show that the approaching air incident angles, the presence of an object upstream of the structure, and the blowing of atmospheric wind, influence phenomena such as pressure coefficients, induced airflow rate, and the airflow pattern of the two-sided wind catcher. The results show the potential of the two-sided wind catcher as a passive device for providing natural ventilation in buildings.

Hydrodynamic performance of a one-sided wind catcher was investigated by experimental wind tunnel and smoke visualization testing. Wind catchers or what is called Baud-Geers in Persian language was a main component of buildings in central region of Iran and the neighboring countries. A Baud-Geer is a tower used to capture wind from external air stream and induce it into the building in order to provide natural ventilation and passive cooling. Due to geographical coordinates of the region, wind power and the direction of blowing wind, wind catchers are employed in different heights, cross sections of the air passages and the places and the number of the openings. The one-sided wind catcher has only one channel as a passage of induced air and is often related to the areas where there is prevailing wind. These Baud-Geers are employed to catch the wind blowing at higher elevations and direct it to the building, causing it to leave through windows, doors or other exhausted segments. In this study a 1:40 scale model of Kharmani's School Baud-Geer was employed and the induced air flow rate into the test room and the pressure coefficients around all surfaces of its channel were measured for different values of approaching air incident angles. Using measured pressure coefficients, the theoretical values of ventilation air flow were estimated to evaluate ability of simplified models in natural ventilation studies. Due to placing of urban full-scale wind catchers in the boundary layer of atmospheric winds, the effect of this phenomenon was also examined. The experiments were conducted when the wind catcher model with adjoining house was placed in the wake of upstream objects, resembling neighboring buildings. It was found that for an isolated wind catcher model, the maximum efficiency is achieved at zero air incident angle. Also it was concluded that the angle of incidence of the wind, the presence of an upstream building around the structure and blowing of atmospheric wind influence the pressure coefficients, the rate and the direction of ventilation air flow.

Cycling races contain a multitude of cars including team cars. During parts of the race, the cyclists can ride in close proximity of these cars. An earlier study indicated that there is a drag reduction for a cyclist by a following car. However, to the best of our knowledge, there is no information in the scientific literature about the impact of a car on cyclist drag when the cyclist is positioned either in-line behind the car or in parallel or staggered position with the car. This paper presents wind tunnel measurements and CFD simulations of cyclist drag for 29 different cyclist-car arrangements. It is shown that drafting in-line behind a car at a distance of 10 and 40 m leads to substantial drag reductions of about 20 and 7%, respectively. The staggered positions can lead to either a large drag increase up to almost 9% or a moderate drag decrease up to 1.4%. These drag changes can induce time gains or losses that go up to several seconds per kilometer, which is large enough to potentially influence the outcome of cycling races.

Anecdotal evidence suggests that the correlated color temperature (CCT) of light can affect thermal comfort. Previous literature mostly investigated this effect over a short duration (2 h; 2700 K vs. 5700 K with 500 lux illuminance at the eye) in office -like settings during mild cold exposure (17 degrees C) using a within-subject design (N = 16). The results indicate that CCT did not significantly affect thermal sensation in mild cold, which may be explained by the large interin-dividual variation in the color-temperature association. Interestingly, 5700 K even improved thermal comfort, decreased perceived shivering, and, after 1-h exposure, increased energy expenditure. Moreover, visual comfort was not significantly moderated by CCT, but 5700 K improved comprehensive cognitive performance. Concur-rently, arousal and alertness were higher in 5700 K, potentially indicating greater non-visual effects in 5700 K. Further analysis revealed that thermal comfort significantly correlated with perceived shivering and visual comfort, but not with the color sensation of the light. Together, the results provide no support for the hue-heat hypothesis under mildly cold conditions and suggest that high CCT enhanced thermal comfort, alertness, arousal, and cognitive performance, likely via non-visual mechanisms that built up over longer exposure durations.