Architectural: Windcatcher

Octagonal Windcatcher Natural Ventilation — ANSYS Fluent CFD Simulation

A windcatcher is a tall rooftop tower used for passive, energy-free ventilation — a centuries-old design still relevant in sustainable architecture. It captures ambient wind at roof level and channels it down into the building below, flushing out warm, stale indoor air and replacing it with fresh outside air. Internal walls and channels trap the incoming flow and guide it downward from the upper intake panels into the occupied space. This project uses ANSYS Fluent to simulate the airflow through an octagonal windcatcher and confirm that it ventilates the room beneath as intended.

The windcatcher is placed inside a large open-domain environment with a horizontal wind of 10 m/s at atmospheric pressure. The geometry is built in Design Modeler and meshed in ANSYS Meshing with an unstructured grid of about 2.33 million cells.

This is a fluid-only analysis with no heat transfer — the focus is purely on how the tower's geometry drives air movement. The key feature is the internal layout above the windcatcher: barrier surfaces are arranged so that some upper inlets face the wind directly while others are shielded from it. This sets up a pressure difference across the tower — the windward openings push air in, while the leeward openings generate suction — and that differential is what drives circulation down through the windcatcher shaft and into the room below.

At the end of the solution, you generate velocity and pressure contours, along with velocity vectors and path lines. The windward side shows higher pressure than the leeward side, exactly as the design relies on. The flow visualizations confirm the intended behavior: air enters through the top panels, is guided and trapped by the interior walls, then descends and discharges through the lower panels into the interior space — showing the windcatcher works as designed. By the end of this project, you'll be able to set up an external-flow ventilation simulation in a large open domain, use barrier surfaces to create a driving pressure differential, and interpret pressure and flow fields to verify that a passive ventilation system performs as intended.