Architectural: Wind Tower with Qanat

Wind Tower with Qanat CFD Simulation

Description

This project uses ANSYS Fluent to simulate a wind tower system paired with a qanat, a traditional passive cooling arrangement rooted in the architecture of hot, arid regions. Passive ventilation techniques rely entirely on natural driving forces rather than mechanical equipment, and they generally fall into two categories: wind-driven systems, where airflow is generated by pressure differences, and buoyancy-driven systems, where temperature-induced density differences create natural convection. The wind tower and qanat combination sits in a hybrid category, drawing on both mechanisms at once.

In this setup, a tall tower rises above the building and works together with an underground channel — the qanat — which acts as a natural cooling reservoir. When wind strikes the tall structure, it creates a pressure imbalance: high pressure builds on the windward face while a low-pressure zone forms behind it, driving suction that pulls air through the system. Meanwhile, inside the underground channel, incoming hot air passes over a body of cool water, picking up moisture and losing heat before rising into the building through the floor to condition the interior air.

To keep the model manageable, the water surface inside the channel wasn't explicitly represented; instead, a fixed-temperature boundary condition of 278 K was applied to the channel walls to represent its cooling effect. The incoming hot air enters the channel at 0.2 m/s and 300 K. Window surfaces exposed to sunlight and outdoor heat were assigned a constant temperature of 298 K. The geometry, built in Design Modeler, consists of three connected components: the room, the tower, and the underground channel. Meshing was carried out in ANSYS Meshing using an unstructured approach, producing 402,198 cells.

Methodology

The simulation was run as a steady-state, time-independent case using a pressure-based solver in ANSYS Fluent. Because natural convection plays a central role here, buoyancy effects were captured by allowing air density to vary with temperature rather than treating it as constant — warmer, lighter air rises, which is what drives hot air out through the tower. This density variation was modeled using the incompressible ideal gas law, where density depends on temperature and operating pressure rather than on local pressure fluctuations, consistent with the assumption of constant pressure throughout the domain.

Conclusion

The simulation produced temperature, pressure, and velocity contours in both 2D and 3D, along with velocity vector fields. The temperature results clearly show the cooling pathway: cool air drawn in through the underground channel and hot air escaping through the tower opening. The pressure field confirms the mechanism driving this exchange, with high pressure outside and lower pressure inside the room and tower pulling hot air upward and out. The velocity vectors trace this circulation clearly, showing cool air entering rapidly at floor level, circulating through the room, and exiting through the tower once conditioning is complete. Overall, the results confirm that this passive wind tower and qanat system successfully performs natural air conditioning without any mechanical input.