Exploring fields of turbulence generated by an active grid

With the invention of active grids, a tool for the manipulation of flows was developed that has fascinated the experimental turbulence community for decades. Different philosophies for the excitation of active grids have led to a large variety of parametric studies. Often, these experimental studies are carried out using hot-wires to investigate the evolution of small-scale turbulence structures. In contrast, here, we present a study of eight excitation protocols of an active grid with a mesh width of M=10cm that is installed in the wind tunnel at NTNU with dimensions of 1.8m x 2.7m x 10m. Measurements were performed 60M downstream of the active grid at 10m/s using particle image velocimetry with a sampling frequency of 1.5Hz and a field of view of 10M in streamwise and 3M in wall-normal direction. This allows for a detailed exploration of the instantaneous behavior of the velocity field. This will be complemented with analyses of the means of streamwise and wall-normal velocity, turbulence intensity and integral length scales with the objective of quantifying the turbulence evolution based on the excitation of the flow, possibly checking for anomalies in the behavior.