Intensifying fractal-grid-generated turbulence

Abstract 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 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 L₀/t₀ 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