Performance of an Unsteady, Low-Speed Wind Tunnel with an Upstream Louver System for Longitudinal Velocity Modulation

The experimental simulation of unsteady flow can be obtained by moving a model relative to a flow or modifying the flow itself. In this study, the latter approach was used, utilizing the opening and closing of flow-impeding louvers at the far upstream end of a low-speed, open-return wind tunnel. These louvers can rapidly tune the flow speed in the test section without altering the blower speed. Fixing the louvers in the fully closed position results in a 53% to 60% drop in flow speed from fully open, with the larger reductions at faster blower speeds. During dynamic louver operation, the test section flow speed does not instantly track with louver position. Additionally, the flow speed responds more quickly as the shutters are closed, dropping the speed, than when opened at the same rate. When commanding louver motion with equal opening and closing times, the flow speed can spend as much as 62% more time accelerating than decelerating. This effect is most pronounced for faster louver motions and lower blower speeds. Ultimately, this project aims to accurately predict the flow speed in the test section for any arbitrary louver position schedule.