Exploration of geometric constraints in laboratory-generated homogeneous isotropic turbulence via random jet arrays

Laboratory generation of mean shear free homogeneous isotropic turbulence (HIT) has progressed significantly since the 1950s. Since the creation of the random jet array by Variano et al. (2004), in which grids of randomly-actuated recirculating pumps produce HIT, refined control of turbulence statistics is possible by changing both the geometry of the facility and actuation of the stochastic forcing algorithm. While prior studies have shown turbulence metrics (e.g. turbulent kinetic energy, dissipation, integral length scale) correlate to the mean on-time of the jets specified in the algorithm, questions remain regarding the importance of jet spacing and jet diameter in producing mean shear free HIT of targeted turbulence levels. We perform a laboratory study to explore the relative importance of the arrangement of jets (jet spacing), algorithm parameters (mean on-time; percentage of active jets), and jet outlet velocity on the energetics of the turbulence produced, as well as implications for determining the distance from the jet array at which HIT is generated. We use particle image velocimetry to quantify the flow dynamics produced by 8x8, 12x12, and 16x16 arrays, and we perform extensive dimensional analysis to thoroughly characterize turbulence generation.