Evaluation of Wind Comfort Levels Around Building Developments

WSP Environmental – A Case Study

As an established environmental and energy consultancy, WSP Environmental advises designers on the environmental impacts of new development schemes and helps designers achieve excellent BREEAM ratings. BREEAM (Building Research Establishment’s Environmental Assessment Method) is the world’s most widely used means for auditing and improving the environmental performance of buildings and is established as offering best practice in environmental design and management.

When planning a new development, designers need to understand the local wind environment and what impact, if any, it will have on pedestrian comfort and safety. A pedestrian wind study, along with other wind environment studies, is required by planners as part of the Environmental Impact Assessment for new large developments.

IDAC has carried out several wind engineering analyses using the ANSYS CFD capabilities for many large development projects for WSP Environmental. One such project has been the prestigious Shanghai Plaza. A major commercial office and entertainment complex, it is situated in Shanghai’s south-western Hongqiao business-diplomatic-residential district, over a major underground rail station.

The aim of these analyses has been to establish the comfort levels that a pedestrian will experience under certain wind velocities.

Analysis

A geometric model of both the buildings and the terrain was provided by WSP Environmental. These were imported into ANSYS and ‘subtracted’ from an encompassing cylindrical volume, leaving the total air surrounding the buildings and terrain. This air volume that was then used for analysis. The air volume was meshed, with a refined mesh being generated on the surface of the buildings and at ground level, to enable a better resolution of the boundary layer flow. Based on previous analyses, an RNG turbulence model was used. Consequently, the boundary layer thickness and number of layers were adjusted to account for predominantly turbulent flow around the building development.

The wind loading conditions were characterised by a formula involving the average wind speed, a terrain factor and a height index and by the direction of wind. Knowing the wind direction meant that certain nodes on the outer boundary of the air domain were selected, so that the wind velocity could be applied to them as a load. The programme then calculated the wind velocities along the ground, through and around the buildings.

The calculated wind velocities were presented as velocity contours at a height specified by WSP. Carrying out these types of analyses can, for example, highlight how the addition of mitigation features can significantly reduce the wind speed around the corner of the building.

Design benefit

IDAC has automated the analysis procedure so that new geometry supplied by a client can be input very quickly and there is a rapid turnaround of results. As such, IDAC has been able to carry out a great many of these analyses for WSP Environmental and they have proved to be a very valuable design tool. The analyses are quick and cheap compared with wind tunnel testing, and have provided IDAC’s clients with significant cost and timesavings.

CFD is becoming increasingly popular as a tool for predicting air flows and is particularly effective for assessing internal conditions such as ventilation air flow. Choosing an environmental system to control the indoor climate without assessing its suitability can be costly. IDAC is able to use the CFD technology within ANSYS to simulate heating ventilation and air conditioning (HVAC) problems, so that the performance or suitability of a HVAC system can be established.

Another similar application of the CFD technology within ANSYS is to analyse nitrous oxide (NOx) problems. Nitrous oxide emissions from cars in an enclosed space such as a car park can be a real problem. CFD can be used to assess where best a ventilation system is to be situated for the most effective ventilation of nitrous oxide emissions from cars in car parks.

The full case study, including images, can be found on the IDAC website.

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