Low-speed wind tunnel: Design and build

In this chapter the authors deal with a procedure for the design and build of a low speed wind tunnel for airfoil aerodynamic analyses and micro wind turbine studies. The designed closed-circuit wind tunnel has a test chamber with a square cross section (500 mm x 500 mm) with a design average flow velocity of about 30 m/s along its axis. The designed wind tunnel has a square test chamber, two diffusers (one adjacent to the test section and one adjacent to the fan to slow the flow), four corners (with turning vanes) to guide the flow around the 90o corners, an axial fan to guarantee the mass flow rate and balance any pressure loss throughout the circuit, a settling chamber with a honeycomb (to eliminate any transverse flow), a series of ever-finer mesh screens (to reduce turbulence) and a nozzle to accelerate flow and provide constant velocity over the whole test chamber. The pressure losses of single components were evaluated as well as the global pressure loss (the sum of pressure losses of all the single components). Once the pressure losses were evaluated, the axial fan was chosen to guarantee the design's volumetric flow, balance pressure losses and above all maximise its performance. The definitive dimensions of the wind tunnel are 10.49 m x 3.65 m. Once the design targets were defined, the test chamber dimensions, maximum wind speed and Reynolds numbers were calculated. At the end of the design process, the wind tunnel energy consumption was estimated and on-design and off-design performance was evaluated to obtain the wind tunnel circuit characteristics for a defined velocity range (0 - 50 m/s). The best circuit and axial fan matches were performed in both the open and closed test section configurations. Using the matching procedure between the fan and wind tunnel's mechanical characteristics (global pressure loss as a function of wind velocity), the fan operating parameters were set up for optimum energy conservation.