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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.

Airplane cabin ventilation is essential to ensure passengers' well-being. The conventional ventilation method is mixing ventilation with a statistically steady supply, which, according to former studies, has reached its limits regarding, for example, the ventilation efficiency. However, the effect of a statistically unsteady (time-periodic) supply on the mixing ventilation efficiency has remained largely unexplored. This research uses computational fluid dynamics (CFD) with the large eddy simulation (LES) approach to study isothermal time-periodic mixing ventilation in a section of a single-aisle airplane cabin model, in which the air exhaled by the passengers functions as (passive) contaminants. Two time-periodic supply strategies are evaluated. The induced time-periodic airflow patterns promote an efficient delivery of fresh air to the passenger zone and affect the passengers' expiratory plumes. This results in increased mean contaminant mass fluxes, causing a strong reduction of the mean contaminant concentrations in the passenger zone (up to 23%) and an increased contaminant extraction from the cabin. Mean velocities increase with up to 55% but remain within the comfortable range. It is shown that the ventilation efficiency improves; that is, the contaminant removal effectiveness and air change efficiency (in the full cabin volume) increase with up to 20% and 7%, respectively.

The uniformity of the environmental conditions in a vertical farm can be poor due to multi-layer cultivation shelves, crop resistance to airflow, and excessive heat generated by artificial lighting, decreasing overall crop yield and quality. This study evaluates the performance of two air distribution systems, i.e., long-side air supply and short-side air supply, in a generic multi-layer vertical farm using a validated computational fluid dynamics (CFD) modeling approach. The simulation results show that under identical airflow rates, the average air temperature in crop regions from short-side air supply is higher than the long-side case. In addition, stagnation regions exist in both scenarios, where the removal efficiency of water vapor and heat is low. Further study is required to improve the uniformity of air distribution in crop regions.

A sequentially coupled shape and topology optimization framework is presented in which the outer geometry and the internal topological layout of beam-type structures are optimized simultaneously. The outer geometry of the beam-type structures is parametrically described by non-uniform rational B-splines (NURBS), which guarantees a highly accurate description of the structural shape and enable an efficient control of the design domain with only a few control points. The computational efficiency of the coupled optimization approach is assured by applying a gradient-based optimization algorithm, for which the sensitivities are derived in closed form. The formulation of the coupled optimization approach is tailored toward 2.5D and full 3D representations of beam structures used in engineering applications. The 2.5D beam model, which has been taken from the literature, uses standard beam elements to simulate the beam response in the longitudinal direction, whereby the cross-sectional properties of the beam elements are calculated from additional 2D finite element method (FEM) analyses. A comparison study of a cantilever beam problem subjected to pure shape optimization and pure topology optimization illustrates that the 2.5D and 3D beam models lead to similar shape and topology designs, but that the 2.5D beam model has a significantly higher computational efficiency. Specifically, the computational times for the 2.5D model are about a factor 70 (shape optimization) and 1.4 (topology optimization) lower than for the 3D model, which indicates that in the coupled optimization approach the optimization of the shape provides the largest contribution to the higher computational efficiency of the 2.5D model. The coupled shape and topology optimization analysis subsequently performed on the 2.5D cantilever beam model demonstrates that the specific order at which the alternating shape and topology optimization increments are performed in the staggered update procedure turns out to have some influence on the computational speed and the value of the minimal compliance computed. Despite these differences, the final beam structures following from the different staggered update procedures illustrate how shape and topology can be efficiently optimized in an integrated, coupled fashion.

This contribution compares the performance of a monolithic and two staggered numerical update schemes for a coupled shape and topology optimization method for thin-walled beam structures. In order to limit the computational time of the optimization method, the thin-walled beam structures are modeled as 2.5D configurations. In this approach, 1D beam elements are used to simulate the beam response in the longitudinal direction, while the cross-sectional properties of the beam elements are calculated from additional 2D finite element method analyses. The sensitivities with respect to the shape and topology design variables are derived in closed form in order to take advantage of a computationally efficient, gradient-based optimization algorithm. The numerical examples concern basic circular and square thin-walled cantilever beam structures, as well as a more complex, non-prismatic thin-walled beam structure representative of a rotor blade used in a horizontal-axis wind turbine. For each numerical example the computational time and the solution computed by the monolithic and staggered update schemes are compared, which provides clear insight into the numerical efficiency of the solution procedure and the uniqueness of the computational result. Although the three different update schemes for the cases examined result in comparable optimized design concepts, the computational efficiency and the specific minimal compliance value found turn out to be rather sensitive to the algorithmic details of the numerical update scheme applied. Since the monolithic update scheme typically navigates a larger design space than the two staggered update schemes, for most cases examined it provides the lowest structural compliance. In the specific case whereby shape optimization (virtually) has no influence on the final, optimized beam configuration, the structural compliance computed by the monolithic scheme may relate to a local minimum that is less optimal compared to the value calculated by a staggered update scheme.

Building integrated photovoltaic (BIPV) is a key concept for the realisation of sustainable buildings. Despite the progress in BIPV modelling, the use of sensitivity analysis (SA) is still scarce in the BIPV literature. SA can help the modeller to identify which model inputs influence the model outputs the most. This paper presents a simulation framework that combines global SA methods with a multi-physics BIPV model. The analysis focuses on the performance of naturally ventilated BIPV facade elements (cell temperature and power). Building performance indicators, such as the total heat flux to the building interior and the building wall temperature, are also analysed. Inputs to the SA include convective heat transfer coefficients, cavity airflow rate, and weather conditions. As expected, the SA results were found to be highly dependent on the range selected for the inputs. For a narrow variation in weather conditions, the exterior convective heat transfer coefficient was identified as the input with the strongest influence on the BIPV performance. Results also showed that cavity ventilation becomes more important as the exterior convective heat transfer decreases. These findings indicate the need for accurate models to represent exterior convective heat transfer in BIPV facades and corroborate the importance of cavity ventilation.

Building integrated photovoltaic (BIPV) systems are considered a promising solution to increase the share of renewable energy in the built environment. To evaluate the BIPV performance at the building level, the implementation of BIPV models in building performance simulation tools is an essential step. This paper presents the development of a multi-physics BIPV model for the simulation of BIPV facades within the openIDEAS framework for building and district energy simulations. The model couples a high-resolution electrical model to physics-based thermal and airflow models. The combination of these two modelling approaches is not common in BIPV models, particularly for building performance simulations. The model predictions are compared to three months of experimental data from a naturally ventilated BIPV module installed in the facade of a test building in Leuven, Belgium. A good agreement is obtained in terms of both BIPV energy yield and temperature. The error in daily energy yield estimations is on average below 3 % and the error in the monthly energy yield is below 2%. The back-of-module temperature is predicted with a MAE lower than 2 °C and RMSE lower than 5 °C.

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.

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.

Air curtains (ACs) employ plane turbulent jets to separate two environments in terms of heat and mass transfer, while still allowing unrestricted access through the opening between these environments. Most previous studies focused on ACs discharged from nozzles located just above the opening. However, in some cases ACs have to be installed close to the ceiling at a substantial distance from the top of the opening. The AC blown downwards along the vertical wall then first resembles a wall jet and after reaching the top of the opening starts resembling a free jet. The present study analyzes the behavior and performance of an AC with upstream wall above the opening. 2D steady RANS CFD simulations are performed based on grid-sensitivity analyses and validation with experimental data for a wall jet and a free jet. The total opening height is 4 m and vertical walls of 0.5 m, 1 m and 2 m, partly closing this opening, are considered. AC performance is evaluated both with the separation efficiency η (based on infiltration) and the adapted separation efficiency η* (based on infiltration and exfiltration). It is shown that the presence of the wall reduces jet decay. The longer the wall, the larger the jet momentum over the opening height. This reduces infiltration and increases η, but it increases exfiltration and therefore decreases η*. In practice, the jet discharge velocity (jet momentum) will have to be adjusted to keep high η*.

© 2018 Elsevier Masson SAS The numerical modelling of impinging jet flows is not straightforward as it should not only solve the shear layer development in the free jet region, but also the near-wall behaviour (streamline curvature) and the resulting wall jets after impingement. This study presents a validation study of steady Reynolds-averaged Navier–Stokes turbulence models for predicting isothermal plane turbulent impinging jets at two different slot Reynolds numbers, i.e. Re = 8,000 (case I) and Re = 13,000 (case II), based on 2D particle image velocimetry measurements. In addition, an in-depth analysis of the results provided by the five different turbulence models: standard k−ε (SKE), realisable k−ε (RKE), RNG k−ε SST k−ω and a Reynolds stress model (RSM), is performed. The results show that: (1) for both Reynolds numbers the best agreement with measured velocities and turbulent kinetic energy in the region near the jet nozzle is achieved with SST; (2) the best predictions of potential core length are provided by RNG (case I) and RKE (case II); (3) centreline distributions of velocities and turbulent kinetic energy are most accurately predicted by RNG and RKE for case I, while for case II the best agreement with experimental data is obtained by SKE and RNG; (4) the best overall performance for both cases in predicting velocities is provided by RKE, and by RKE and RNG when considering turbulent kinetic energy; (5) all models more accurately predict the jet spreading rate in the intermediate region than in the potential core region; (6) for both Reynolds numbers SKE provides the most accurate estimation of jet decay rate. ispartof: EUROPEAN JOURNAL OF MECHANICS B-FLUIDS vol:75 pages:228-243 status: published

Building integrated photovoltaic (BIPV) applications are key to increase the share of renewable energy in the built environment. A large potential for BIPV deployment is related to building facades. The assessment of BIPV facades depends on the accurate modelling of exterior convective heat transfer coefficients (eCHTC). However, eCHTC models commonly used in BIPV modelling tend to be simplified. This paper proposes a simulation framework that combines detailed computational fluid dynamics with a multi-physics BIPV model to investigate the influence of eCHTC on the performance of BIPV facades (cell temperature and power). The evaluation is performed for different building geometries, wind speeds, wind directions, solar irradiations, and ambient temperatures. The results show that local variations in eCHTC can cause variations in cell temperature up to 42 ° C between the BIPV modules across the facade. These temperature differences are associated with differences in power up to 17% across the BIPV facade. In general, lower temperatures (and higher power output) occur near the edges of the facade while higher temperatures (and lower power output) occur at the middle and at the bottom of the facade. Therefore, a detailed assessment of wind effects is recommended in order to verify the local operating conditions of the BIPV modules. The framework and findings presented in this work are relevant for applications in which the knowledge of the local behaviour is important, such as degradation studies.

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.

Building integrated photovoltaic (BIPV) systems provide an opportunity for renewable energy generation in the built environment. In order to quantify the BIPV potential, numerical models of varying levels of complexity have been developed. This paper investigates how the complexity of BIPV models affects their predictions. The study starts with a detailed multi-physics BIPV model that combines a high-resolution one-diode model with physics-based thermal and airflow models. Next, simplifications are introduced into the model. The model predictions are compared to experimental data from a BIPV curtain wall installed in a test building in Leuven, Belgium. The results show that the detailed BIPV model is capable of estimating the BIPV daily energy yield with an average difference of 6.2 % (2.0 % for clear sky days) and the back-of-module temperature with an average difference of 1.74 °C. The use of a linear power model instead of a high-resolution one-diode model affects the average differences, but not significantly: 8.7 % for daily energy yield predictions (4.5 % for clear sky days) and 1.71 °C for temperature predictions. The use of two different empirical temperature correlations instead of a physics-based approach increases the average temperature difference to 3.5 and 4.4 °C. The average difference in daily energy yield increases to 10.2 and 10.4 %, respectively (5.9 and 5.5 % for clear sky days). These findings indicate that the detailed version of multi-physics BIPV model provides the best agreement with experimental data, but it is still possible to reduce the model complexity with acceptable accuracy.

This paper presents a numerical study on the required momentum flux ratio to prevent air curtain breakthrough in case of cross-curtain (i.e. cross-jet) pressure gradients. 2D steady Reynolds-averaged Navier-Stokes (RANS) CFD simulations with the RNG k-ε turbulence model are employed for jet Reynolds numbers ranging from 5,000 to 30,000. First, the computational model is validated based on particle image velocimetry (PIV) measurements. Second, the influence of several jet parameters on the separation efficiency is evaluated for a moderate cross-jet pressure difference of 10 Pa. These are the ratio of the jet discharge momentum flux to the jet cross-flow momentum flux (momentum flux ratio), the jet height-to-width ratio and the jet discharge angle. Finally, the minimum deflection modulus to prevent jet breakthrough and the corresponding momentum flux ratio by an analytical equation and by CFD are compared. The results show that, for the configuration under study: (1) jets with the smallest height-to-width ratios (β = 18) provide the highest separation efficiency; (2) inclined jets with discharge angles α0 = 5° and 10° provide slightly higher separation efficiency than straight jets (α0 = 0°) and jets with α0 = 20°; (3) the maximum modified separation efficiency is reached at lower momentum flux ratios for jets with smaller height-to-width ratios and for inclined jets; (4) the analytical and CFD values of the optimal momentum flux ratio differ with up to 31.2%. This study shows how the separation efficiency of air curtains can be improved by adjusting certain jet parameters.

It is crucial to accurately and efficiently predict transient particle transport in indoor environments to improve air distribution design and reduce health risks. For steady-state indoor airflow, fast fluid dynamics (FFD) + Markov chain model increased the calculation speed by around seven times compared to computational fluid dynamics (CFD) + Eulerian model and CFD + Lagrangian model, while achieving the same level of accuracy. However, the indoor airflow could be transient, if there were human behaviors involved like coughing or sneezing and air was supplied periodically. Therefore, this study developed an FFD + Markov chain model solver for predicting transient particle transport in transient indoor airflow. This investigation used two cases, transient particle transport in a ventilated two-zone chamber and a chamber with periodic air supplies, for validation. Case 1 had experimental data for validation and the results showed that the predicted particle concentration by FFD + Markov chain model matched well with the experimental data. Besides, it had similar accuracy as the CFD + Eulerian model. In the second case, the prediction by large eddy simulation (LES) was used for validating the FFD. The simulated particle concentrations by the Markov chain model and the Eulerian model were similar. The simulated particle concentrations by the Markov chain model and the Eulerian model were similar. The computational time of the FFD + Markov chain model was 7.8 times less than that of the CFD + Eulerian model., Highlights • A fast fluid dynamics (FFD) ＋ Markov chain model solver developed in OpenFOAM. • The solver is for predicting transient particle transport in transient indoor airflow. • The developed method had a similar accuracy to the CFD ＋ Eulerian model. • 7.8 times less computing time than CFD ＋ Eulerian model.

Traditionally, Aerodynamic Shape Optimization (ASO) and Structural Topology Optimization (STO) are considered as two separate, consecutive stages in the aerostructural design process of wind turbine rotor blades. Since such a modeling strategy does not adequately account for the coupling effects between the blade aerodynamics and its structural performance, in this paper a Coupled Multi-objective Shape and Topology Optimization (CMSTO) approach is presented, which simultaneously optimizes the outer shape and the interior structural layout of the turbine blade from aerodynamic and structural requirements. The framework uses the weighted sum method, whereby the sum of the aerodynamic and structural objectives multiplied by specific weighting factors is minimized employing an incremental-iterative update procedure. The coupled optimization process is performed by sequentially carrying out shape and topology optimization steps for beam-type structures, in accordance with a staggered scheme. For the aerodynamic and structural optimizations the rotor power coefficient and the blade structural compliance are considered as the objectives, respectively. The aerodynamic response of the blade is evaluated by the Blade Element Momentum (BEM) method, which, together with a reduced beam-type Finite Element Method (FEM) model that simulates the structural response, facilitates the application of a gradient-based algorithm with analytical sensitivities. Accordingly, the computational efficiency of the CMSTO framework is warranted. The shape design variables are characterized by the locations of Non-Uniform Rational B-Splines (NURBS) control points that parameterize the blade outer shape. The topology design variables are represented by the relative densities assigned to the finite elements modeling the blade cross-sections, in correspondence with the Simplified Isotropic Material with Penalization (SIMP) method. The CMSTO framework is used to optimize the NREL 5 MW reference rotor blade, whereby the results are compared to those obtained from a separate ASO-STO approach and a pure STO approach. The rotor power coefficients calculated by the CMSTO and ASO-STO approaches are about 4% larger than that of the reference rotor blade. In addition, the blade structural compliance computed by the CMSTO approach is reduced by an extra 16% and 41% compared to the compliances found by ASO-STO and pure STO approaches, respectively. Such significant improvements clearly demonstrate the benefits of the CMSTO approach in the quest of wind turbines with higher power output and better structural performance.

© 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

Quality assurance in computational fluid dynamics (CFD) is essential for an accurate and reliable assessment of complex indoor airflow. Two important aspects are the limitation of numerical diffusion and the appropriate choice of inlet conditions to ensure the correct amount of physical diffusion. This paper presents an assessment of the impact of both numerical and physical diffusion on the predicted flow patterns and contaminant distribution in steady Reynolds-averaged Navier–Stokes (RANS) CFD simulations of mixing ventilation at a low slot Reynolds number (Re≈2,500). The simulations are performed on five different grids and with three different spatial discretization schemes; i.e. first-order upwind (FOU), second-order upwind (SOU) and QUICK. The impact of physical diffusion is assessed by varying the inlet turbulence intensity (TI) that is often less known in practice. The analysis shows that: (1) excessive numerical and physical diffusion leads to erroneous results in terms of delayed detachment of the wall jet and locally decreased velocity gradients; (2) excessive numerical diffusion by FOU schemes leads to deviations (up to 100%) in mean velocity and concentration, even on very high-resolution grids; (3) difference between SOU and FOU on the coarsest grid is larger than difference between SOU on coarsest grid and SOU on 22 times finer grid; (4) imposing TI values from 1% to 100% at the inlet results in very different flow patterns (enhanced or delayed detachment of wall jet) and different contaminant concentrations (deviations up to 40%); (5) impact of physical diffusion on contaminant transport can markedly differ from that of numerical diffusion. ispartof: Building Simulation vol:10 issue:4 pages:589-606 status: published

High-rise buildings can significantly increase the wind speed at pedestrian level, and knowledge of building aerodynamics and pedestrian-level wind (PLW) conditions is therefore imperative in their design. This study aims at evaluating different building geometry modifications to reduce PLW speed around an isolated high-rise building. Numerical simulations with computational fluid dynamics (CFD) are performed to evaluate the effect of canopies, podiums and permeable floors. To the best knowledge of the authors, a systematic study on the impact of these modifications on PLW conditions using validated CFD simulations has not been reported before. Grid-sensitivity analyses are performed and sub-configuration validation is applied using wind-tunnel measurements from the literature. It is shown that a canopy or a podium can significantly reduce the area-averaged PLW speed (up to 29%) and maximum PLW speed (up to 36%) around the high-rise building. In general, the PLW speeds decrease with increasing canopy or podium size. The introduction of a permeable floor to the building can reduce the maximum and area-averaged mean wind speed. However, when low-floor building layers are removed, adverse effects are noted, i.e. the average PLW speed increases (up to 21%) and the lower-speed wake region behind the building is reduced in size.

Building integrated photovoltaic (BIPV) technology has gained attention as a solution to achieve low energy buildings. However, unlike conventional PV applications, BIPVs typically operate at non-optimal orientation, imposed by the building geometry. Moreover, the building integration reduces the heat exchange to the exterior, leading to higher temperatures. This paper investigates the performance of BIPV modules in different locations by simulating a representative office room in a high-rise building having a BIPV facade. The locations considered are Riyadh (Saudi Arabia), Seville (Spain), Naples (Florida, USA), Cape Town (South Africa), and Munich (Germany). The facade is vertical and faces the equator for all locations. Results show the highest annual BIPV energy yield occurs in Seville, followed by Cape Town, Riyadh, and Naples. In terms of monthly yields, the highest values are observed in Riyadh and Seville in wintertime. Monthly yield is more uniform over the year in Munich, while important differences between summer and winter have been obtained for Riyadh. These results confirm the influence of the latitude on the BIPV yield, with equator-facing facades in high latitudes receiving up to 40 % less irradiation compared to a horizontal surface, with important reductions especially in the summer. In these locations, the use of west and east facades may be necessary to achieve a balanced profile over the year. Moreover, the highest average cell temperatures occur in Riyadh, Naples and Seville, while lowest temperatures are verified in Cape Town and Munich, which is consistent with the corresponding ambient temperatures. Finally, with lower BIPV temperatures and relatively high solar irradiation, Cape Town achieves the highest performance ratio (PR) values. Conversely, the combination of high solar irradiation and high temperatures leads to lower PR values in Riyadh and Seville

© 2019, Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature. Windexchangers are relatively small structures located on the building rooftop to promote natural ventilation. This paper presents a Computational Fluid Dynamics (CFD) validation study, sensitivity analysis and performance comparison of three windexchanger (WE) configurations applied to a generic isolated building with a windward window. The study is limited to wind-driven (isothermal) ventilation, for wind perpendicular to the windward facade. The CFD simulations are based on the 3D-steady Reynolds-Averaged Navier–Stokes (RANS) equations. The validation study is performed with experimental results from a previously published water channel test. The sensitivity analysis focuses on the domain size, grid resolution and turbulence model. The performance evaluation of the three WE configurations is based on the mean velocity and mean static pressure coefficients in the vertical centerplane, the ventilation volume flow rate and the volume percentage of the living zone with air speed ratio equal to or above 0.10. The WE configuration with four openings and one duct shows the highest ventilation flow rate (0.232 m 3 /s) and the highest volume percentage (21%). This study shows that the assessment and selection of WE configurations should not only be based on volume flow rate or ACH but should consider the living zone air speed ratio as well, specifically concerning the flow distribution in the living zone. ispartof: BUILDING SIMULATION vol:12 issue:3 pages:475-488 status: published

© 2019 The Authors Natural ventilation can be used to improve indoor air quality, remove contaminants from spaces and to remove heat from a building during the day, or during the night. In some cases, openings for natural ventilation are equipped with shading devices – such as louvers – to reduce solar heat gains while allowing natural ventilation. This study presents wind-tunnel experiments and computational fluid dynamics (CFD) simulations of a cross-ventilated building equipped with louvers. Four opening positions are studied: (i) openings in the center, (ii) upper or (iii) lower part of the windward and leeward facades or (iv) one opening in the upper part of the windward facade and one opening in the lower part of the leeward facade. The 3D steady Reynolds-averaged Navier-Stokes (RANS) simulations are performed with three turbulence models (RNG k-ε, SST k-ω, RSM) and validated with the wind-tunnel experiments. The experimental results show that the largest velocities occur in a building with openings in the upper part of the facade. The best agreement with experimental data is provided by RSM. In addition, CFD simulations for buildings without louvers are conducted for the same opening positions to evaluate the effect of louvers on the dimensionless volume flow rate, age of air and air exchange efficiency. The highest dimensionless volume flow rate at reduced scale (0.69) is obtained in the building with louvered openings in the upper part of the facade and the highest air exchange efficiency is achieved for a building with louvered openings in the center of the facade (45%). ispartof: BUILDING AND ENVIRONMENT vol:154 pages:263-280 status: published

© 2018, The Author(s). The building energy demand for heating and cooling is changing due to climate change. The adoption of climate change adaptation measures at the building scale aims at limiting heating and cooling demands. In previous studies on adaptation measures little attention has been paid to lightweight semi-portable buildings, which are increasingly used to temporarily house the growing number of small households (1–2 persons) in peripheral and derelict areas. In this paper the impact of passive climate adaptation measures and building orientation on heating and cooling demands is assessed for a detached, lightweight, semi-portable residential building by means of building energy simulations (BES), considering two climate scenarios for the Netherlands: current climate and a future climate (2050). The results show that the most efficient adaptation measure consists in a combination of exterior solar shading and an increase of thermal resistance of the building envelope, which reduces the annual heating and cooling demand–averaged over eight building orientations – by 11% for the current climate and 15% for the future climate. The impact of building orientation varies according to the climate scenario. Compared to the average over the eight orientations considered, the annual cooling demand for a single orientation varies between about −31% and +22% and between about −24% and +18% for the current and future climate, respectively. For the case without adaptation measures, optimizing the building orientation leads to annual total energy savings of about 4% for the current and 3% for the future climate. ispartof: BUILDING SIMULATION vol:11 issue:6 pages:1163-1177 status: published

Traffic is one of the main sources of particulate matter (PM) inside urban areas. This paper provides a preliminary assessment of the potential to reduce outdoor PM concentrations by local removal inside semi-enclosed parking garages. The assessment is performed by computational fluid dynamics (CFD) based on the 3D steady RANS equations and an Eulerian advection-diffusion equation. First, an extensive CFD validation study is performed with gas dispersion wind-tunnel measurements. Next, the case study for Eindhoven city center is conducted on a high-resolution grid including 16 semi-enclosed garages. Traffic intensities on the streets and in the garages are converted to PM 10 source terms. The garages are ventilated with outdoor air. Simulations are performed with and without removal units in the garages. The case study is not intended to reproduce a particular pollution episode but to provide a preliminary indication of the potential reduction in PM 10 for representative meteorological and traffic conditions. The results show that 594 removal units allow reductions in local outdoor PM 10 by up to 50% close to the garages while reductions up to 10% are achieved further downstream. It is concluded that local removal in semi-enclosed parking garages can be an effective strategy towards improved outdoor air quality.

The use of computational fluid dynamics (CFD) to solve indoor airflow problems has increased tremendously in the last decades. However, the accuracy of CFD simulations depends greatly on user experience, the available validation data, and the effort made to verify solutions. This study presents the results of a conference workshop, which assessed user influence on the CFD results obtained for a generic non-isothermal flow problem; ie, a backward-facing step flow problem with a heated wall below the supply. Fifty-five simulation sets were submitted by 32 teams. The results showed a very large spread in predicted penetration length (xre /(H - h)), location of maximum velocity in the lower part of the recirculation cell (xrm /(H - h)), and maximum velocity at this location (urm /u0 ). The turbulence model seemed to very strongly influence the results, with a statistically significant difference in the predictions yielded by the k-ε and k-ω models. The results obtained using a single turbulence model generally also showed a spread in results; the level of spread depended on factors such as grid size and near-wall treatment. The statistical data strongly indicate the need for validation studies using experimental data (benchmarks) to ensure the accuracy, reliability, and trustworthiness of CFD simulations for indoor airflow problems. ispartof: INDOOR AIR vol:28 issue:6 pages:866-880 ispartof: location:England status: published

The transpirational cooling of vegetation as a measure to mitigate outdoor air temperatures was investigated for a street canyon in the city center of Arnhem, the Netherlands for the meteorological conditions of an afternoon hour on a hot summer day during a heat wave with wind of speed 5.1 m s −1 at 10 m above ground and direction along the canyon. Computational Fluid Dynamics (CFD) simulations with locally applied vegetation in the street, i.e. avenue-trees, facade greening, roof greening and all three combined, were performed. The 3D steady-state Reynolds-averaged Navier–Stokes (RANS) equations were closed by the realizable k-e turbulence model extended with source and sink terms to represent the effects of vegetation on air flow. By specifying a cooling power term in the energy equation, the transpirational cooling by vegetation was accounted for. The strongest cooling by a single vegetative measure was obtained with the avenue-trees with mean and maximum temperature reductions at pedestrian level of 0.43 °C and 1.6 °C, respectively. Facade greening resulted in rather small changes with mean and maximum reductions of 0.04 °C and 0.3 °C, respectively. For roof greening no noticeable reductions inside the canyon were found. In the case of a combination of all vegetative measures, cooling in terms of spatial distribution and intensity overall resembled a linear superposition of those of the vegetative measures solely applied with 0.52 °C mean and 2.0 °C maximum temperature reduction. Overall, the cooling was restricted to the vicinity of the vegetative measures, i.e. up to a distance of a few meters.

Urban sound propagation is influenced by multiple reflections on horizontal and vertical surfaces, either specular or diffusive in nature, diffraction around edges and meteorology, causing refraction and scattering of sound waves. This paper initiates multiple benchmark cases for urban sound propagation, with the purpose of comparing the suitability of computational methodologies. The benchmark cases are two-dimensional cross-sections of typical urban geometries, involving all of the effects mentioned above. The sound source is either geometrically screened or is in the line of sight from the receiver's position. When meteorological conditions are included, results obtained from computational fluid dynamics simulations are used. All details of the benchmark cases are concisely described, and results from two numerical methods for outdoor sound propagation are included. Both methods solve the linearized Euler equations (LEE). The first method is the Fourier pseudospectral time-domain method (Fourier-PSTD) ...

Apart from sports purposes, stadia are also increasingly being used for concerts and other events with large spectator attendance. The main aspect for spectator comfort in open stadia is protection from wind and rain. In the design of many existing stadia however, rain shelter has insufficiently been taken into account because most roofs have been designed with vertical rainfall in mind, while no consideration has been given to the possibility of rain being blown onto the stands and spectators by wind (wind-driven rain). Adequate rain shelter should be addressed during the design stage of new sports and football stadia. Currently however, almost no information or guidelines on this matter are available. This paper presents an investigation of the impact of roof geometry on rain shelter. 2D Computational Fluid Dynamics (CFD) simulations and Lagrangian particle tracking are performed to analyse the wind flow pattern and rainfall distribution in seven generic stadium configurations and to assess the performance of each roof type. Although most existing stadium roofs are built with a light to medium upward slope towards the field, the analysis indicates that roofs with a downward slope of 13° provide significantly better rain shelter. This paper will demonstrate that the reason is not only the well-known trigonometric shielding effect. This effect refers to the rain shelter that can theoretically be obtained by assuming that raindrop trajectories are straight lines. This study will show that, in addition to the trigonometric shielding effect, downward sloping roofs restrict the extent of the primary vortex in the stadium and generate a sufficiently strong counter-rotating secondary vortex below the roof that sweeps the rain away from the stands. This specific feature appears to occur only for roofs with a sufficiently large downward slope. As a result, downward sloping roofs are clearly superior in terms of rain shelter compared to traditional roof types with an upward slope towards the field.