This is a summary of an extensive research project on natural ventilation and thermal comfort in courtyard buildings in the Historical Centre of Havana. Based on a morphological study, a field work and a comfort survey (reported in previous papers), Computational Fluid Dynamics (CFD) simulations, thermal simulations and a comfort analysis are performed in theoretical generic courtyard buildings inserted in the compact urban morphology of Old Havana. The results of this study can be useful in order to promote the design of comfortable low-energy residential buildings in Old Havana in particular and in other compact cities in tropical-humid regions in general.
Wind-driven rain (WDR) significantly affects buildings. Examples are the durability of building walls, the weathering and soiling of buildings and monuments, algae formation at building facades, mould growth at inside wall surfaces, indoor climate and energy consumption of buildings. In numerical simulation models to analyse the hygrothermal performance of building components, the WDR intensity on a building facade is traditionally implemented as a (uniform) moisture flux boundary condition. In reality however, WDR is the sum of individual raindrops, which do not only spread, but may also splash or bounce off the facade. In this paper, these phenomena, i.e. spreading, splashing and bouncing and their potential occurrence at raindrop impact on building facades are investigated. Laboratory measurements were made of water drop impact on a dry, clean and relatively smooth porous ceramic brick surface. Results show that—depending on impact angle, impact speed and diameter—raindrops impinging on porous material surfaces can show either spreading, splashing or bouncing, which results in variable shapes and sizes of wetted areas. The possibility and importance of splashing and bouncing at the windward facade of a building are investigated by combining the drop impact measurements with computational fluid dynamics (CFD) simulations of raindrop trajectories impinging on the windward building facade of a 10 × 10 × 10 m3 cubic building. It is shown that depending on the meteorological conditions, splashing and bouncing can occur at large parts of the facade. This implies that the current implementation of WDR as a boundary condition in numerical hygrothermal simulation models, which does not take into account these effects, can significantly overestimate the real moisture flux boundary condition.
Goede ventilatie van gebouwen en vervoersmiddelen is niet alleen van belang voor onze gezondheid en ons comfort, maar ook voor energiezuinigheid en duurzaamheid. Mengventilatie, gebaseerd op de toevoer van verse lucht bovenin een ruimte, wordt bet meest toegepast (figuur ia en ib). De impuls van de toegevoerde Iucht zorgt ervoor dat de verse lucht zich mengt met de in de ruimte aanwezige lucht, waarna de gemengde lucht wordt afgevoerd. Dat mag een eenvoudig proces Iijken, maar ondanks veel onderzoek, zijn er nog altijd heel wat vragen onbeantwoord.
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.
Three different calculation models for wind-driven rain (WDR) are compared: the semi-empirical model in the ISO standard for WDR (ISO), the semi-empirical model by Straube and Burnett (SB) and the CFD model by Choi, extended by Blocken and Carmeliet. This paper builds further on the comparison of these models for idealized building configurations and fixed wind and rain conditions in (Blocken et al., 2010. Comparison of calculation models for wind- driven rain deposition on building facades, Atmospheric Environment 44(14): 1714-1725). In the present paper, these models are applied to a high-rise monumental tower building, for a transient rain event, and the model results are compared with full-scale measurements. The agreement be- tween the CFD results and the measurements is quite good at the upper part of the facade, while the ISO and SB model show large discrepancies at these facade positions.
The expanding capacity of seaports for worldwide competitiveness is leading to an increased risk exposure. The increasing ship size causes larger wind forces that can render ship navigation difficult in stormy weather. The alert system for the suspension of port operations is usually based on the wind conditions measured by anemometers installed (i) on top of cranes/buildings often sheltered for some wind sectors; hence unable to provide reliable wind statistics, (ii) at undisturbed positions (far from quays); hence unable to catch the actual wind near cranes/mooring ships. Despite many efforts towards the safety management of seaports and waterways, the prediction of real-time local wind conditions in such environments is still challenging. The goal of this paper is the innovative development of an integrated tool to transfer the measured wind field (by on-site measurements) from an undisturbed position to the sea lock under investigation by transfer coefficients computed with CFD. The tool allows tugboat pilots to check in real-time the mean wind speed, wind direction and turbulence intensity in the newly built IJmuiden sea lock, in the Netherlands. This project is targeted at improving the awareness of risks and the prevention of detrimental accidents in seaports in stormy weather.
The last decades have seen an increasing interest in cycling aerodynamics, with the design of more aerodynamic bicycles and wearable equipment such as helmets and skinsuits and the development and application of new cyclist positions. Moreover, a better understanding of the flow topology around a cyclist and of the aerodynamic interaction between cyclists and other cyclists and nearby vehicles has been gained. However, some knowledge – albeit mainly empirical – of the impact of aerodynamics on cycling performance was already known in late 1800s and early 1900s; as shown by the design of recumbent bicycles and aerodynamic fairings, the adoption of dropped cyclist positions and the organization of drafting races. The goal of this paper is to demonstrate the evolution of aerodynamic knowledge in cycling from the early days to the most recent state-of-the-art to efficiently drive future studies. Therefore, this paper provides a comprehensive review of the history and state-of-the-art in cyclist aerodynamics, focused on three aspects: (i) cycling flow topology and the wind influence; (ii) the aerodynamics of a single cyclist and his/her wearable components; and (iii) the aerodynamic interaction between a cyclist and other cyclists or nearby vehicles. Finally, some future perspectives about cyclist aerodynamics are provided.
Abstract Large Eddy Simulation (LES) undeniably has the potential to provide more accurate and more reliable results than simulations based on the Reynolds-averaged Navier-Stokes (RANS) approach. However, LES entails a higher simulation complexity and a much higher computational cost. In spite of some claims made in the past decades that LES would render RANS obsolete, RANS remains widely used in both research and engineering practice. This paper attempts to answer the questions why this is the case and whether this is justified, from the viewpoint of building simulation, both for outdoor and indoor applications. First, the governing equations and a brief overview of the history of LES and RANS are presented. Next, relevant highlights from some previous position papers on LES versus RANS are provided. Given their importance, the availability or unavailability of best practice guidelines is outlined. Subsequently, why RANS is still frequently used and whether this is justified or not is illustrated by examples for five application areas in building simulation: pedestrian-level wind comfort, near-field pollutant dispersion, urban thermal environment, natural ventilation of buildings and indoor airflow. It is shown that the answers vary depending on the application area but also depending on other—less obvious—parameters such as the building configuration under study. Finally, a discussion and conclusions including perspectives on the future of LES and RANS in building simulation are provided.
Abstract The wind‐driven‐rain effect refers to the redistribution of rainfall over micro‐scale topography due to the existence of local perturbed wind‐flow patterns. Rainfall measurements reported in the literature point to the fact that the wind‐driven‐rain distribution can show large variations over micro‐scale topography. These variations should be taken into account in hillslope hydrology, in runoff and erosion studies and in the design of rainfall monitoring networks. In practice, measurements are often not suitable for determining the wind‐driven‐rain distribution. Therefore, a few researchers have employed numerical modelling. In order to provide confidence in using numerical models, experimental verification for a range of different topographic features is imperative. The objective of this study is to investigate the adequacy of a two‐dimensional Computational Fluid Dynamics (CFD) model to predict the wind‐driven‐rain distribution over small‐scale topography. The numerical model is applied to a number of topographic features, including a succession of cliffs, a small isolated hill, a small valley and a field with ridges and furrows. The numerical results are compared with the corresponding measurement results reported in the literature. It is shown that two‐dimensional numerical modelling can provide a good indication of the wind‐driven‐rain distribution over each type of micro‐scale topography that is considered in this study. It is concluded that more detailed verification procedures are currently inhibited due to the lack of available and detailed spatial and temporal rainfall data from field measurements. Copyright © 2005 John Wiley & Sons, Ltd.
The majority of numerical studies of room airflow using Computational Fluid Dynamics (CFD) are conducted with the steady Reynolds-averaged Navier-Stokes (RANS) approach. In this approach the averaged quantities are computed, and the effect of turbulence is modelled. Furthermore, the standardgradient diffusion hypothesis is often used to model the turbulent mass transport, which relates the turbulent mass flux to the mean concentration derivative. In this paper, a CFD analysis of pollutant dispersion in an enclosure ventilated by a transitional wall jet (Re ≈ 2,500) is presented, using validated high-resolution RANS and Large Eddy Simulations (LES). Although the LES computations show that a counter-gradient turbulent mass flux is present, indicating that the standard gradient-diffusion hypothesis used in RANS is not valid in the entire flow domain, it is shown that the convective mass fluxes dominate over the turbulent mass fluxes, and that therefore the pollutant concentrations predicted by RANS do not differ significantly.
