Characterization of flow structures generated by an active grid

Active grids are widely used in wind tunnel experiments to generate turbulence with tailored characteristics, particularly for achieving high Reynolds numbers. While many studies have focused on the statistical properties of the resulting turbulence, fewer have explored how the frequencies interact to create a cascade of dominant structures in the spectral domain through the variation of actuation parameters. This work investigates the frequency structures generated by an active grid composed of off-the-shelf components, operated at different flapping frequencies. Experiments were conducted in the University of Houston’s wind tunnel using hot-wire anemometry to capture the velocity fluctuations. The results demonstrate that varying the flapping frequency significantly affects the spectral content of the flow, revealing the emergence of distinct frequency structures associated with different actuation patterns. These findings contribute to a better understanding of how active grid control can be used to shape turbulence for experimental and modeling purposes.