Homogeneous turbulence in an octagonal tank stirred by four synthetic jet arrays

We inspect high Reynolds number homogeneous turbulence with a negligible mean flow in the octagonal tank created by four synthetic jet arrays. Each array has 40 pumps, and more pumps are placed in the vertical direction to generate a vertically large turbulence region. The individual pump firing zero-net- mass flux jet flow turns on and off repeatedly. The durations of the ON / OFF period are chosen from two different Gaussian distributions. In order to improve homogeneity and isotropy, we investigate the effects of placing a grid and a cylindrical obstacle at each jet exit, whose effects on the jet flow is first characterized by time-resolved particle image velocimetry (PIV) measurements in a single jet flow. The obstacle is designed to increase stirring in the vertical direction while diluting the signature of the jet flow. The turbulent quantities such as turbulent kinetic energy, correlation, structure function, and energy spectra from two experimental configurations, with/without the obstacles, are compared using statistically independent velocity snapshots taken with PIV. We also perform time resolved velocity measurements to understand large scale spatiotemporal velocity correlations within the flow.