Design and Flow Characterization of the Compressed Air Wind Tunnel

Systems with large physical size such as wind turbines, aircraft, and ships are dominated by the inertia of the flow. In conventional experimental facilities, a reduction in scale is required, which can introduce viscous effects that are not present at full size. However, if the wind tunnel is operated with a heavy gas, the reduction in scale can be counteracted by an increase in density, and the flow that exists at full size can be recreated accurately. This work describes the design, construction, and basic flow characterization of a heavy gas wind tunnel facility, known as the Compressed Air Wind Tunnel (CAWT), that utilizes pressurized air as the working fluid at pressures up to 35 bar. The tunnel was designed to accommodate relatively large models inside the 1.04 meter-diameter test section while having improved optical access compared to existing facilities of this type. A series of flow characterization tasks were carried out on the completed facility, including quantifying the turbulence intensity and flow uniformity in the tunnel test section. Measurements showed a maximum turbulence intensity of 0.46% and an average of 0.22% across all conditions and locations tested. The maximum velocity non-uniformity between four locations in the test section was 0.36%, which occurred at the lowest tested wind speed of 2.4 m/s. The average non-uniformity across all tested conditions was less than 0.093%. Mapping the facility operating space has now enabled ongoing work examining rotorcraft, marine propeller, and wind turbine performance and wake development with the aim of answering long-standing questions regarding how the fluid dynamics depend on scale or Reynolds number effects.