An active-controlled multi-blade facility to generate 2-D downburst-like outflows in the boundary layer wind tunnel

This study aims to design and calibrate an active-controlled multi-blade system (AMBS) that allows for reproducing downburst outflows in the boundary layer wind tunnel. The downburst-like wind profiles could be produced by adjusting the inclined angle of each blade independently. By controlling four blades to rotate at predefined angular velocities, downburst-like outflows with varying non-stationary characteristics can be generated. The experimental results indicate that the mean wind velocity profiles can well match the target profiles obtained in full-scale measurements and available experimental results, and the generated winds can be considered as two-dimensional (2D) flows. The power spectral density of the produced longitudinal wind velocity is consistent with the von Karman spectrum. The duration of the most intense part of the non-stationary winds and non-dimensional wind speed ratios can be well reproduced to match full-scale downburst events based on the designed AMBS. In addition, the primary vortex of the downburst can be reproduced by the AMBS based on flow visualization with smoke, which confirms the physical property of the produced flows. This work provides a developed facility to produce 2D downburst-like outflows in the boundary layer wind tunnel and the generated winds are verified to be reasonable.