External Flow around an Atrium

External Flow Around an Atrium — ANSYS Fluent CFD Simulation

Description

This project presents a complete CFD simulation of the external airflow around a building atrium — a structure rooted in ancient Roman architecture and reborn in modern multi-story buildings as a glass-roofed space used for daylighting and natural ventilation. Atriums rely on two fundamental natural phenomena — the greenhouse effect and the chimney effect — and understanding the airflow around them is the first step in designing them effectively. At the urban scale, this kind of external-flow analysis matters because the wind around large buildings shapes pedestrian comfort, natural ventilation, and how structures interact with the surrounding built environment. Within the Urban Microclimate: All Levels CFD Training Package, this project builds on the tall-buildings case, applying external-flow analysis to a single architectural structure and establishing a reusable building-aerodynamics workflow.

Methodology

The 3D external-flow domain (3.35 m × 2.21 m × 3.9 m) is designed around the atrium structure in Design Modeler, then meshed in ANSYS Meshing with a refined unstructured grid of roughly 1.95 million elements — with finer cells near the building walls for accurate boundary-layer resolution. A pressure-based, steady-state solver suited to external aerodynamic problems is configured with the RNG k-ε turbulence model and standard wall functions — a combination well-suited to the separated and recirculating flows that form around bluff bodies. The external-flow boundary conditions are an 8 m/s velocity inlet, a 0 Pa gauge pressure outlet, and stationary walls. Pressure–velocity coupling uses the SIMPLE scheme with second-order discretization for pressure and momentum, and the domain is initialized with atmospheric pressure (101,325 Pa) and a uniform freestream velocity.

Analysis

Post-processing generates 2D and 3D contours of pressure and velocity, pathlines, and velocity vectors on the XY plane, along with the pressure distribution over the building's wall surfaces. These results reveal how the 8 m/s wind interacts with the atrium walls — generating regions of high pressure, flow separation, recirculation, and acceleration around the structure. External flow analysis of this kind is a backbone of modern architectural and urban engineering, informing decisions about façade design, pedestrian wind comfort, natural ventilation, and structural wind loading. By the end of this project, you'll have a reusable external-flow workflow — designing the domain, refining the mesh near the walls, configuring the solver and turbulence model, and interpreting the pressure and velocity fields — that you can apply to virtually any external building-flow problem in the built environment.