Effect of a Boundary Layer Leak Slot on Improving the Test Section Flow Quality in an Open Return Meteorological Wind Tunnel

A boundary layer leak slot is devised to improve flow quality in an open return wind tunnel and is tested in the large meteorological wind tunnel of the Meteorological Research Institute. The feature of the slot is that the forcible exhaust, as adopted in many automobile wind tunnels, is not used. The most effective width for improvement is determined to be 40 cm, by an experiment in which the slot width defined as the streamwise opening length is varied from 0 cm to 100 cm. Installing the boundary layer leak slot upstream of the test section remarkably improved the wind velocity uniformity in the cross-direction to the centerline of the wind tunnel in the upper reaches of the test section. The improvement is not clear in the lower reaches, however. The deterioration of uniformity downstream was caused by irregular floor-surface roughness resulting from long-time use. It can be concluded that the boundary layer leak slot is an effective low-cost method of improving flow quality in an open return wind tunnel.