Design of a Low-Turbulence, Low-Pressure Wind-Tunnel for Micro-Aerodynamics

Abstract

A novel wind-tunnel facility has been designed for measurement of lift and drag on micromachined airfoils. The tunnel is designed to operate with pressures ranging from 0.15 to 1.0 atmosphere, over a velocity range of 30 to 100m∕s, allowing for independent control of Reynolds and Knudsen number. The tunnel is designed for testing of airfoils with chords of 10 to 100 microns, giving a range of Reynolds numbers from 10 to 600, with Knudsen numbers reaching 0.01. Due to the structural constraints of the airfoils being tested, the wind tunnel has a 1cm cross-section. This small size allows the use of a 100-1 contraction area, and extremely fine turbulence screens, creating a low turbulence facility. Computational fluid dynamics is used to show that an ultra-short 100-1 contraction provides uniform flow without separation, or corner vortices. Velocity data obtained with impact and hot-wire probes indicate uniform flow and turbulence intensities below 0.5%.