Physical Insights from Active Grid Turbulence

Active turbulence grids have reshaped laboratory turbulence research by shifting experiments from passive generation toward controllable forcing. Originally introduced to extend the Reynolds number range of grid-generated turbulence, active grids enable systematic control of turbulence intensity, integral scales, and shear within a single setup. This capability expands the accessible parameter space and reframes the questions that can be addressed experimentally. In canonical flows, active grids permit high–Reynolds number investigations of turbulence scalings and controlled studies of turbulence interacting with walls and free shear flows. In multiphase and Lagrangian systems, they provide well-characterized conditions to probe clustering, settling, and interfacial transfer at previously unattainable Reynolds numbers. In engineering contexts, they enable reproducible coherent inflow structures, e.g., gusts. Together, these advances have expanded the experimental parameter space and changed how universality, forcing, and flow development are investigated in turbulent flows.