Design and performance of an ultra-compact, low-speed, low turbulence level, wind tunnel for aerodynamic and animal flight experiments

Abstract

We present a novel closed-circuit ultra-compact wind tunnel with an 8:1 contraction ratio and high flow quality. Its overall footprint area is less than half that of a conventional tunnel with the same test section size and same contraction ratio, enabling significantly smaller material and construction costs. The tunnel’s key features which enable the small footprint include a two-dimensional main diffuser, a minimum-length contraction, and expanding turning vanes with a 1.167:1 ratio in corner two and an aggressive 1.875:1 ratio in corner four. Separation in the latter is prevented using a screen and honeycomb integrated into each vane passage—the first time this has been used in a wind tunnel. The tunnel exhibits excellent flow quality with less than pm 1% mean flow variation in the test section core and a freestream turbulence level of 0.03% at 12 m/s over a 4 Hz–20kHz bandwidth.Graphical abstract