External Flow Around Tall Buildings: Transient

External Flow Around Tall Buildings (Transient Solver) — ANSYS Fluent CFD Simulation

Description

This project uses ANSYS Fluent to simulate wind flow through a domain containing three tall buildings that act as flow barriers — a representative example of the common "flow-around-obstacle" problems found throughout wind engineering (buildings, wings, propellers, and rigs all belong to the same family). A horizontal airstream enters the domain and interacts with the buildings, letting you examine how the wake develops behind each structure and how vortices form in their lee. As the opening project of the Urban Microclimate: All Levels CFD Training Package, it establishes the external-aerodynamics foundation of urban wind flow — the bluff-body behavior that underlies pedestrian wind comfort, building loads, and pollutant dispersion — before any pollutants are introduced.

Methodology

The 3D geometry, built in DesignModeler, is a large rectangular region of 120 m × 300 m × 100 m containing three buildings, each 75 m tall. Meshing in ANSYS Meshing is unstructured with 128,893 elements, with local refinement near the building surfaces for accuracy. The analysis is transient — run over 1 s with a 0.01 s time step — and solved with a pressure-based approach. A horizontal airstream of 5 m/s enters the domain and interacts with the buildings, with the transient setup capturing the unsteady wake and vortex behavior that a steady solution would miss.

Analysis

The results include pressure and velocity contours, turbulent kinetic energy (TKE), pathlines, and velocity vectors. The highest pressure occurs on the windward faces, where the flow first impinges on the buildings, while vortices form in the leeward wakes behind them. All reported fields are evaluated at the final simulation time (t = 1 s). From these results you can assess the wind loading on the building faces, trace the wake structure and vortex shedding between and behind the buildings, and understand the flow patterns that govern wind comfort and dispersion in the built environment. By the end of this project, you'll be able to set up a transient external-flow simulation around bluff bodies, apply local mesh refinement near solid surfaces, and interpret the pressure, velocity, and turbulence fields that characterize urban wind flow.