Comparative simulations of the pedestrian-level wind environment using structured and unstructured meshes

Understanding the characteristics of wind at pedestrian level is important to ensure pedestrian safety and comfort in urban environments. Pedestrian-level wind characteristics are mainly affected by the average characteristics of surrounding buildings such as plan and frontal area densities and mean building height, and the shape of each building also has a big impact on the wind characteristics. In particular, the various shapes of buildings, including curved surfaces, complicate the wind environment in urban areas. Currently, various computational fluid dynamics (CFD) models are being utilized to study the complex flows in urban areas. Many CFD models use cartesian grids to simulate flows in urban space by converting the urban space made up of buildings into a set of cuboids. The OpenFOAM (Open Field Operation And Manipulation) model, an open source CFD model, has the advantage of being able to represent the curved shape of building to the greatest extent possible by generating unstructured meshes using the mesh generation utility called snappyHexMesh.

In this study, we simulate the campus space of University of Seoul located in Seoul, South Korea using structured (cartesian grid) and unstructured meshes for OpenFOAM simulations, and compare the results over the two meshes. To implement realistic flow conditions, a mesoscale weather model (WRF) are used as the initial and lateral boundary conditions. In this study, we analyze the differences in the generation of turbulent eddies specially around the curved building surfaces according to the two types of meshes and compare the simulation results with observations. We expect that using the unstructured mesh will allow us to more accurately simulate flow separation, wakes around buildings, and turbulence statistics at pedestrian level. This study can be used to identify detailed features of pedestrian-level wind (e.g., gustiness), thereby providing a basis for pedestrian environmental impact assessment.