Test of Airflow in a Mono-directional Wind-catcher for various Wind Conditions using Computational Fluid Dynamics

Wind-catchers are one of the most extensively used passive technologies in history of arid climatic regions, engaged to supplement airflow and maintain indoor comfort ventilation. It was meant to catch the air flow high above the ground, which is greater in speed compared to the flow at lower levels due to ground conditions. This study aims to analyse wind-catchers with respect to different speeds and its orientation to prevailing winds for effective airflow.

A simple test case is considered where the geometry and physical parameters of the wind catcher are fixed while wind speed and its incident angle are varied. Also the atmospheric boundary layer is considered for terrain roughness in the analysis. CFD (3D) analysis was carried out to find the efficiency of the wind catcher in terms of velocity at the outlet, pressure differential between inlet and outlet and massflow rate at the outlet. The test site is chosen in a typical urban topography considering the atmospheric boundary layer and its roughness height which impedes the airflow near the ground region and modifies the airflow pattern in a power law profile. Multiple parametric analyses of the aforesaid parameters, i.e., flow speed and different orientation were carried out.

The analysis shows that, in general the air speed near the inlet of wind catcher is greatly reduced (almost by half in magnitude) due to the terrain roughness. The air speed at the outlet increases with the increase in outdoor air speed and is optimum when the incident angle of later is normal or up to an angle of 300 to the surface of the inlet area of wind catcher.