Wind engineers have two primary tools for modeling winds around buildings: computational fluid dynamics (CFD) and wind tunnel testing (WTT). RWDI has teams of engineers with significant experience using both tools, and we would like to share our views on the use of CFD and WTT for external flows.
Some firms have begun to argue that advances in CFD technology make it possible to perform a comprehensive study of external wind flows without the need for wind tunnel testing. We disagree. We believe the idea that CFD can displace rigorous wind tunnel testing is flawed and does not acknowledge advantages that each tool offers independently. Using CFD as a direct replacement for WTT also ignores the challenges inherent in numerically simulating complex urban wind flows.
Wind tunnel testing is the established tool used for modeling wind flow around buildings and structures in order to develop design data for cladding and structural loads; conduct local dispersion assessments; and assess pedestrian-level winds. In general, such modeling provides a good representation of both mean and gust effects.
CFD is an excellent tool for simulating flow behavior. In fact, CFD can be used to simulate some physics that cannot be achieved practically in a wind tunnel. However, although some consultants are using CFD modeling as a direct replacement for WTT, CFD is not suited to predicting wind patterns for safety-based design issues on buildings. It struggles to accurately predict separation, turbulent eddies and gusts within the urban environment, as well as flow around bluff bodies like buildings. It is these eddies that contribute to dilution of contaminants, peak structural wind loads on buildings and the gusts that can cause pedestrian discomfort and safety concerns.
RWDI are world-leading experts in wind engineering. We utilize CFD and WTT in a complementary manner. CFD excels as a tool for urban wind modeling by allowing us to provide early design advice; resolve complex flow physics like rain penetration; and help diagnose problematic wind conditions. Wind tunnel testing is the better tool when wind load design values are required; safety considerations are at play; and when turbulent mixing is a dominant factor.
Ultimately, CFD and WTT both have a role to play in helping developers, architects and engineers assess wind and environmental impacts. Using one tool to analyze an issue that should be done with the other, or applying either without an experienced specialist, may cause costly errors in the results. It is the responsibility of professional practitioners, that is both architects and engineers, to understand the limitations and undertake studies using the correct suite of tools.