Publications

Using integrated 3D canopy architecture and porous media models for prediction of orchard pesticide applications.

Numerical simulation of convective heat transfer at the surfaces of a cube

Knowledge of the convective heat transfer coefficient (CHTC) on building walls is important for research on building energy and building component durability. In building aerodynamics, steady RANS is frequently used to model air flow, rather than unsteady RANS (URANS) or Large-Eddy Simulations (LES). To gain insight into the performance of LES compared to steady RANS, this paper presents LES and RANS CFD simulations of the temperature distributions at the surfaces of a reduced-scale cubic model measured in turbulent channel flow. The evaluation is based on a grid-sensitivity analysis. The results show that LES can accurately predict the surface temperature distributions of the cube walls. Steady RANS, however, indicates a satisfactory agreement with the experiments only for the windward surface.

modelling and boundary-layer modelling approaches

17 18 Computational Fluid Dynamics; turbulence model; cyclist; aerodynamics; wind tunnel 19 20 Word count (Introduction to conclusions): 3494 words 21 22 23 Abstract 24 This study aims at assessing the accuracy of Computational Fluid Dynamics (CFD) for applications in sports 25 aerodynamics, for example for drag predictions of swimmers, cyclists or skiers, by evaluating the applied 26 numerical modelling techniques by means of detailed validation experiments. In this study, a wind-tunnel 27 experiment on a scale model of a cyclist (scale 1:2) is presented. Apart from three-component forces and 28 moments, also high-resolution surface pressure measurements on the scale model's surface, i.e. at 115 locations, 29 are performed to provide detailed information on the flow field. These data are used to compare the performance 30 of different turbulence-modelling techniques, such as steady Reynolds-averaged Navier-Stokes (RANS), with 31 several k-� and k-� turbulence models, and unsteady Large-Eddy Simulation (LES), and also boundary-layer 32 modelling techniques, namely wall functions and low-Reynolds number modelling (LRNM). The commercial 33 CFD code Fluent 6.3 is used for the simulations. The RANS shear-stress transport (SST) k-� model shows the 34 best overall performance, followed by the more computationally expensive LES. Furthermore, LRNM is clearly

Optimization of the energy performance of multiple-skin facades

This paper describes how the energy performance of single storey multiple-skin facades can be optimized by changing the settings of the facades and HVACsystem. The energy performance is analyzed with a yearly whole building energy analysis under Belgian climatic conditions. Three multiple-skin facades are scrutinised: a mechanically ventilated airflow window, a naturally ventilated double-skin facade and a mechanically ventilated supply window. Their performance is compared against the performance of a traditional cladding with exterior and interior shading device. It is shown that both the heating and cooling demand may significantly be improved by implementing control strategies such as controlling the airflow rate and recovery of air returning from multiple-skin facades.

Wind-driven rain in urban areas: field experiments and CFD simulations with turbulent dispersion of raindrops

Numerical modelling of urban microclimate in a compact urban area : a case study for Rome

Large-Eddy Simulation of Pollutant Dispersion in Downtown Montreal: Evaluation of the Convective and Turbulent Mass Fluxes

Large-Eddy Simulation of pollutant dispersion from a stack on the roof of a low-rise building in downtown Montreal is performed. Two wind directions are considered, with different wind flow patterns and plume behaviours. The resulting mean concentration field is observed and analysed with the computed (mean) convective and turbulent mass fluxes. These two concepts allow gaining some insight into the dispersion process and analysing the deficiencies of less sophisticated turbulence models. When the emitting building is located downstream of a high-rise building (case SW), the turbulent mass flux is directed from the high to low levels of mean concentration and the gradient diffusion hypothesis often used with steady models is verified. However, when the influence of the surrounding buildings is smaller (case W), a counter-gradient mechanism is observed in the streamwise direction, confirming the results obtained on isolated buildings. The present study supports the use of generic, simplified cases to investigate environmental processes; the conclusions can subsequently be applied to real and more complex cases.

Driving Rain on Building Envelopes— II. Representative Experimental Data for Driving Rain Estimation

A practical numerical method for driving rain estimation was presented in “Driving Rain on Building Envelopes—I” (Blocken and Carmeliet, 2000). An important prerequisite in employing this method is that the climatic data used as input are representative. In this paper, the attainment of representative experimental data for driving rain estimation is analysed. The importance of a sufficiently small time step to obtain representative climatic data measurements is indicated. It is shown that representative averaged values for wind speed and rainfall intensity for longer time steps can be obtained by averaging the measured data with the rainfall amounts as weighting factors. The effects of using different averaging techniques on the accuracy of the calculated driving rain results are investigated. It is found that the presented weighted averaging technique can provide accurate representative averaged data, whereas commonly used averaging techniques can give rise to large errors.

Numerical investigation of evaporative cooling provided by a mist spraying system

Reduction of particulate matter concentrations by local removal in a building courtyard: Case study for the Delhi American Embassy School

A numerical study of non-isothermal mixing ventilation in an enclosure to evaluate RANS turbulence model performance

Local-scale forcing effects on wind flows in an urban environment: Impact of geometrical simplifications

Wind flow in urban areas is strongly affected by the urban geometry. In the last decades most of the geometries used to reproduce urban areas, both in wind-tunnel (WT) tests and Computational Fluid Dynamics (CFD) simulations, were simplified compared to reality in order to limit experimental effort and computational costs. However, it is unclear to which extent these geometrical simplifications can affect the reliability of the numerical and experimental results. The goal of this paper is to quantify the deviations caused by geometrical simplifications. The case under study is the district of Livorno city (Italy), called "Quartiere La Venezia". The 3D steady Reynolds-averaged Navier-Stokes (RANS) simulations are solved, first for a single block of the district, then for the whole district. The CFD simulations are validated with WT tests at scale 1:300. Comparisons are made of mean wind velocity profiles between WT tests and CFD simulations, and the agreement is quantified using four validation metrics (FB, NMSE, R and FAC1.3). The results show that the most detailed geometry provides improved performance, especially for wind direction α = 240° (22% difference in terms of FAC1.3).

Impact of Disc Wheel Geometry on Aerodynamic Performance: A Computational Fluid Dynamics Investigation

Abstract 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.

Modélisation couplée de transfert convectif de masse et de chaleur avec CFD d’un écoulement laminaire au-dessus du gypse

L’analyse du comportement hygrothermique de l’enveloppe du bâtiment est requise pour evaluer les problemes relies a l’humidite et la chaleur. Les coefficients de transfert convectif sont particulierement importants pour ces calculs. Des guides, standards, et relations semi-empiriques existent pour la determination des coefficients de transfert convectif de chaleur, mais il y a peu d’information pour les coefficients de transfert convectif d’humidite. Les equations pour la chaleur, l’air, et l’humidite dans la couche limite sont analogues pour des conditions particulieres, et en consequence les coefficients de transfert convectif d’humidite sont souvent calcules avec des equations d’analogie, i.e. Lewis et Chilton-Colburn. Les analogies sont surtout applicables pour des ecoulements d’aire dans le regime laminaire, mais certaines etudes indiquent que les equations pourraient aussi etre valides pour des ecoulements d’aire turbulents. Par contre, les comparaisons entre les donnees experimentales et les coefficients calcules a l’aide des analogies montrent des differences pouvant atteindre 300%. Les parametres influencant les resultats sont, entre autres, l’echange radiatif, la chaleur latente, des materiaux au-dessous du point de saturation, etc. La dynamique de fluide computationnelle (CFD) est souvent utilisee pour etudier le transfert de chaleur entre un materiel et une lame d’air, puisque la CFD peut calculer avec precision le profil de vitesse dans la couche limite. Plusieurs limitations sont presentes dans les programmes commerciaux de CFD pour modeliser l’humidite dans des materiaux poreux. Consequemment, un modele a ete developpe par les auteurs pour simuler le transfert d’humidite entre une lame d’air et un materiau poreux en utilisant la CFD integree a un modele de transfert de diffusion de l’humidite.

APPLICATION OF EXTERNALLY-COUPLED BES-CFD IN HAM ENGINEERING OF THE INDOOR ENVIRONMENT

The high importance of indoor environment performance aspects such as surface condensation, mold growth, thermal comfort, etc., is widely recognized. High-resolution simulation of heat, air and moisture (HAM) transfer can be used to enhance the prediction and analysis of these aspects. For this purpose, a coupling mechanism has been developed in order to perform run-time external coupling between Building Energy simulation (BES) and Computational Fluid Dynamics (CFD). This paper presents the results of indoor humidity calculation using the new coupled tool for the BESTEST case600. The results are compared with stand-alone BES results and the need and importance of coupled simulations is discussed.

CFD study on aerodynamics of a train passing an underground railroad platform

The Dutch railways provide transport for more than 1.2 million passengers a day, resulting in more than 5200 train rides. In order to avoid overcrowded trains during rush hours, it is planned to increase the amount of passenger and freight trains, and their running velocities. Pedestrian discomfort or danger on platforms can be caused by trains which are allowed to pass small railway stations at high speed of up to 140 km/h. A number of these railway stations lay underground and it is known that space confinement increases the slipstream forces and results in augmented velocities behind the running train (Gilbert et al., 2012). The purpose of this study is to evaluate the effect of a passing train on the wind flow induced inside a tunnel by means of CFD using LES simulation and to validate the simulations by wind-tunnel measurements.

Wind-driven rain assessment on buildings using climatic datasets: what time resolution is needed?

Overview of challenges and achievements in the climate adaptation of cities and in the Climate Proof Cities program