Notes on the design and construction of a (relatively) cheap wind tunnel for the Daniel Lab.
I designed the Daniel Lab's wind tunnel as a virtual model in 3D CAD software (Google SketchUp: http://sketchup.google.com). Such a model was very useful for exploring and testing various design options before any actual structure was ever built. In addition, creating a parts list from the 1:1 model greatly simplified the ordering process. The wind tunnel design consists of three separable, but tightly attached, sections.
- Air intake: air enters the system through a 1.5 x 1.5 m air straightener consisting of aluminum honeycomb (1/4 in. honeycomb cell size, 2 in thick; HoneyCommCore. LLC, Cattaraugus, NY). The cross-sectional area of the wind tunnel constricts to 1 x 1 m over a distance of 1.2 m, at which point another air straightener is encountered.
- Midsection: this is the working area of the wind tunnel. The cross section is 1 x 1 m, and the length is about two meters, about 1 m of which is usable.
- Fan section: a large air circulator (Multifan TURBO36/120, Bloomington, IL), providing a maximum air throughput of $12,000 ft3/minute (ca. 5.7 m3/s) powers the wind tunnel. It is attached to a ca. 1 m long module with a honeycomb air straightener to buffer oscillations due to the revolving fan blades.
The structural skeleton of the wind tunnel consists of 80/20 extruded aluminum profiles (80/20 Inc.: http://www.8020.net/). The bottom support structure is constructed of heavy-duty 80/20 15-series profiles. It elevates and holds the upper frame of the actual wind tunnel, which is constructed of lighter 80/20 10-series profiles.
The walls of the mid-section, which have to allow an undistorted view of the inside, as well as IR and visible illumination from the outside, are of clear, high-quality acrylic sheets of 6 mm thickness. Sections that don't require a view of their inside volume are walled with black Sintra PVC, also 6mm thick. (Sintra is lightweight, yet rigid, expanded polyvinyl chloride (PVC) extrusion.)
Wind speed measurements
The following image shows the wind speed measured at 9 different locations with an anemometer. The right side, looking upwind, experiences slightly lower velocities because of the proximity of a wall to the intake. The wind tunnel has just moved to a new room, where such wall effects will be far less important.