Abstract
In this study, the resilience of large cities and their built infrastructure in New Zealand to extreme winds, is investigated by coupling the outputs of a very high-resolution, 333-m resolution, numerical weather prediction (NWP) model with computational fluid dynamics (CFD) simulations. Following an extreme wind event on 18 September 2020 in Auckland, in which two trucks travelling over the Auckland Harbour bridge tipped over and damaged the bridge structure, a CFD simulation of airflow over the bridge using the Reynolds-averaged Navier–Stokes (RANS) method and NWP wind speed forecasts as the inlet profile is conducted. The 333 m NWP forecasts were validated against four nearby observation sites, showing generally high correlations of greater than 0.8 and low mean bias (±3 m s−1) and RMSE (<3 m s−1) values. The CFD-based estimates of the mean wind speed-up over the bridge showed that the mean wind speed could increase by a factor of 1.15–1.20 in the vicinity of the road where the toppled vehicles were travelling. Additionally, NWP forecasts and CFD estimates of wind gusts at the maximum bridge height, within the area not affected by the bridge structure, agreed well with a value of about 25 m s−1. An anemometer mounted at the top of the bridge arch measured a higher gust wind speed of about 35 m s−1 that could have been influenced by the gust speed-up resulting from the flow separation from the bridge arch, which is demonstrated in the CFD results. The results demonstrate the importance of understanding localised wind speed-up effects and distinguishing them from the approaching undisturbed airflow.
Highlights
Rapid increases in urbanisation and population of cities, as well as the design and construction of lighter and larger structures, necessitate a better understanding of the urban microclimate and associated hazards to fulfil a need for wind-resistant infrastructures and safer urban environments
The results showed that the variations of gust and mean wind speeds within the urban area were well represented in the large eddy simulation (LES)
The performance of the 333-m numerical weather prediction (NWP) forecasts during the extreme wind event on 18 September 2020 was validated against observation data from the four nearby stations (Table 1)
Summary
Rapid increases in urbanisation and population of cities, as well as the design and construction of lighter and larger structures, necessitate a better understanding of the urban microclimate and associated hazards to fulfil a need for wind-resistant infrastructures and safer urban environments. Large-scale meteorological disturbances and small-scale wind fluctuations produced by surface terrain and roughness elements are the two main factors characterising the highly variable atmospheric airflow [4]. Numerical weather prediction (NWP) models are commonly used to simulate and forecast atmospheric flows, they cannot produce the small-scale fluctuations induced by urban roughness elements and finer scale structures. The significant increase in numerical simulation capabilities over the last few decades has made it possible to develop high-resolution sub-km weather models and integrate fine-scale models with coarser models to have realistic initial and boundary conditions [5]. Coupling NWP and CFD models can provide an opportunity to investigate the strong winds over urban areas utilising real meteorological conditions, such as cyclones, thunderstorms, and fronts, as the initial and boundary conditions of the CFD simulations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
