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.
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.
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 PM10 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 PM10 for representative meteorological and traffic conditions. The results show that 594 removal units allow reductions in local outdoor PM10 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.
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•Assessment of potential to reduce outdoor PM by removal in semi-enclosed parking garages.•Extensive CFD validation study with gas dispersion wind-tunnel measurements.•Case study for Eindhoven city center on high-quality high-resolution grid.•Model includes buildings, semi-enclosed parking garages, and removal units.•594 removal units allow reductions in local outdoor PM10 by up to 50%.
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 multi-physics BIPV model is developed for building performance simulations.•High-resolution electrical model combined with physics-based thermal and airflow models.•Predictions are compared to ...experimental data from a naturally-ventilated BIPV module.•Naturally-ventilated BIPV module is integrated into the facade of a test building.•A good agreement is obtained for both BIPV energy yield and temperature.
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.
An appropriate design for air distribution systems is crucial for achieving optimal and uniform growth conditions while reducing energy costs in vertical farms. This study employs steady ...computational fluid dynamics (CFD) simulations to investigate the influence of several key design parameters of air distribution systems in a small generic vertical farm with a lateral air supply. The simulation results reveal that an air supply orifice of reduced dimensions, positioned proximally to the LED lamps, coupled with an exhaust mechanism integrated into the corridor ceiling, proves most effective in removing the excess heat generated by the LED lamps. Moreover, enhanced uniformity in air distribution is attained by positioning the air supply closer to the LED lamps, utilizing larger orifices, and eliminating the corridor space. In contrast, the vertical distance between the lateral air exhaust orifices and the cultivated regions is found to have a negligible effect.
•Comprehensive assessment of air distribution design in a vertical farm.•Momentum sink and air exchange from crop canopy are considered.•Configurations of air supply, air exhaust, corridor width are numerically evaluated.•Uniformity in crop regions across different growth layers is examined.•Suggestions for optimizing air distribution in vertical farms are provided.
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.
•Literature review on computational and physical parameters in the CFD simulation of snow drift is provided.•Snow transport over flat, uniformly rough, open terrain, is successfully simulated.•Detailed sensitivity analysis for CFD simulations of snow transport in open terrain is conducted.•The falling velocity and the turbulent Schmidt number have largest impact on the CFD simulation results.
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.
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.
•Detailed analyses of influence of inlet boundary conditions in CFD simulations.•Validation of RANS CFD simulations with measurement data from the literature.•ω-based turbulence models perform better than the ε-based turbulence models.•The inlet flow conditions can have a very strong effect on overall flow pattern.•Care should be taken in validation studies when inlet conditions are not known.
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.
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