Intensifying fractal-grid-generated turbulence

For the past twenty years, fractal grids have shown their efficiency at generating long-lasting broad-band turbulence. So far, reference studies have mainly sought to develop the most canonical self-similar turbulence far downstream of the grid. The production region was stretched out, and the maximum turbulence intensities at the peak have remained limited. We explore a new part of the parameter space of \textit{fractal square grids} to accelerate turbulence production, shorten the wake interaction length, and consequently, enhance kinetic energy in the early stages of the turbulence in decay. The length/thickness ratio $L_0/t_0$ of the first iteration is much lower than that of typical grids in the literature. The experiments were conducted in a recirculating hydro-channel facility by means of Particle Image Velocimetry for spatially extended data and Laser Doppler Velocimetry for time-resolved centreline data. Based on the turbulence theory framework and comparing with the recent literature of grid-generated turbulence, the study focuses on characterising the production region and early stage of the decaying region, that is, within the wake interaction length ($x