Experimental Evaluation of Air Flow at Honeycomb of a Vertical Wind Tunnel

Honeycomb is one of the major components of a wind tunnel, which is used to make the air flow uniform and reduce the flow angle. A honeycomb is installed upstream of the nozzle in the settling chamber. As high costs are incurred for construction of honeycomb in large vertical wind tunnels, and in view of the difficulties in installation of these units, it is necessary to reduce the ratio of length to hydraulic diameter of the honeycomb. However, reduction of this ratio may affect the honeycomb performance. In this paper, various honeycomb designs have presented and flow quality has been experimentally investigated for each case. A hot wire anemometer (HWA) and a device for measurement of flow angle (yaw head) have been used to study the flow downstream of the honeycomb. Results show that with decrease in length to hydraulic diameter ratio from 7 to 2, the honeycomb performance is adequate for change in flow angle from -20 to 20º. These results have been used in the design of a vertical wind tunnel, namely Tofan Vertical Wind Tunnel, which will be used for the simulation of skydiving. Based on these results a square honeycomb of length to hydraulic diameter ratio of 2 has been selected, which has resulted in a reduction of up to 60% in the construction cost of the honeycomb.