INTRODUCTION

This paper presents an empirical and qualitative analysis of three wind simulation tools that were specifically developed to be used in the initial stages of the design process. 

In the last few years it has been well documented by engineers, geographers and architects that urbanization modifies natural wind circulation, generating turbulent flow around buildings (GANDEMER, 1978; OKE,1987).  According to Boris (2005) it is important to analyse the phenomenon of urban aerodynamics to determine environmental air quality, predict wind pressures on buildings, reduce urban heat islands, plan for pedestrian comfort, and calculate ambient noise level in the building’s surroundings. Bittencourt (1993) complemented this statement with a reminder that understanding wind dispersion through the city is essential to reducing the consumption of energy in indoor spaces with artificial mechanisms of comfort like air conditioning.

In some urban settlements, such as Hong Kong (NG, 2009), the government already applies methodologies and guidelines to promote a good wind flow inside and around buildings. Despite the fact that wind is an important environmental parameter to consider for a city’s sustainability, it is still neglected by most architects and urban planners in Brazil, compromising the welfare of the population (MARQUES, 2003). According to Assis (2006), there was an increase in the number of studies that relate wind flow to urban planning in Brazil, but in general the investigations are limited to a specific case study and there is lack of integration between the academic knowledge and the professionals that regulate and design the future of the city.

Nowadays, several tools can be applied to simulate wind-related phenomena in digital or physical models, providing visual and numeric information that can be used by urban planners to support their decisions.  Nevertheless, some of these tools are based on sophisticated technology and require high initial investment and running costs, challenging their use by architects in the early stages of the design process. This aspect has been identified as one of the reasons why it is so difficult to integrate wind analysis with architectural design exploration.

The purpose of the current paper is to present the results of a research that seeks to evaluate the advantages and limitations of wind simulation tools developed to be used by architects in the early stages of urban design. The study was designed to evaluate the following aspects:

i. How different are the stages of preprocess, simulation and post-process for each of these tools?

ii. How different are the results produced by Phoenics and the results produced by the less sophisticated wind analysis tools?

iii. What strategy should be used by architects and urban planners to incorporate these simulation tools in the initial project phases?

METHODOLOGY

The research was developed in three different phases. In the first phase, three wind analysis tools were selected, each of which were specifically developed to be used in the early stages of the design process and for educational purposes. The tools were two computer fluid dynamic (CFD) programs: Autodesk Flow Design, and ODS-Studio; and one mini wind tunnel developed by a PhD student for rapid visualisation and comprehension of air circulation. To collect the data from the mini wind tunnel it was set up a platform with eight environmental sensors connected to an Arduino board. This system  was designed to give real time feedback to the user by means of graphical visualisation, showing data such as wind speed in a digital interface via a Rhinoceros 3D modelling tool and Grasshopper visual algorithmic plug-in.

In the second step, a case study was selected to be used as a means of comparison with the simulations generated in the tools studied. For this purpose, the results of an urban ventilation research developed to study an urban area located in Recife, Brazil northeast were chosen. During this study a sophisticated and reliable CFD software (Phoenics VR 3.6.1), largely used by engineers and architects for professional and academic purposes, was used as simulation tool. The aim was to use the results obtained in the previous investigation as an analytic standard, seeking to identify a similar pattern of results between all tools. The scenarios simulated had three specific urban arrangements that varied according to land use rates, distance between buildings, and the height of buildings. These scenarios were selected from the previous research because they present distinct wind dynamics, namely different wind velocities around buildings at the pedestrian level due to different aerodynamic events. The first scenario demonstrated a continuous area of low wind speed at leeward, and acceleration of the wind speed on the streets parallel to the buildings that are exposed to the prevailing wind. The second scenario presented more than one place with wind velocity above six meters per second (to strong for pedestrian comfort) between the proposed buildings and low wind speed at leeward. The third scenario was the one that showed the most wide turbulence wake.

The last step, consisted on comparing and evaluating the performance of each tool according to the user experience and to the results generated in the simulations. The three wind analysis tools selected in the first phase of the methodology were used to simulate the three urban scenarios chosen as case study. Sixteen points on each scenario were selected and used as reference to evaluate the simulation results, generated on each tool, at the pedestrian level.

RESULTS

With this investigation it was possible to conclude that all the selected tools were relatively easy to manipulate and provide a real time interface. These two aspects are very important for the user as they deliver almost immediate feed-back, giving them the chance to visualise the air movement and be part of the simulation, as opposed to the experiment using Phoenics, where the results appeared only a few days later as a final numerical calculation. The interaction with the simulation is also a good incentive for architects to try different designs, so from this point of view these tools were more suitable for early design stages.  Despite this, all of them demonstrated constraints to producing an adequate simulation of wind. For instance, Autodesk Flow Design had very limited options to set up wind parameters, a grid and the exact coordinate or position to be studied in the model. The ODS-Studio, on the other hand, showed more options to regulate airflow, however it has a steeper learning curve than Autodesk Flow Design and does not provide an adequate interaction with other architectural software. The mini wind tunnel provided very detailed data but had some limitations in reproducing the boundary layer effect. Finally, the quality of the results generated by all simulation tools were not as precise as the ones shown on CFD program Phoenics, but the general air flow performance was similar.

DISCUSSION

The results obtained in all simulations reinforced the importance of studying and identifying advantages and restrictions of the new wind simulation tools that have been developed to be used by architects in the early design stages. Adopting these technologies in their process of design is essential to promoting the use of wind as a renewable energy source and reducing the formation of urban heat islands. Future work will seek to develop this analyses using other wind simulation systems and create a model for the ways in which architects should use these tools during the design process.