Isotropic turbulence apparatus with a large vertical extent

n experimental flow facility for sustaining a column of nearly isotropic turbulence in air has been developed. Four arrays of synthetic jet actuators are arranged along the walls of a vertical tower, producing a homogeneous region spanning 13 integral length scales in the vertical direction. The isotropy, homogeneity, and various turbulence properties are quantified using optical measurement techniques. At the highest jet power setting, a root-mean-square velocity of 0.73 m/s and a Reynolds number Re_λ of 240 are attained. Although the mean flows are not negligible, their contribution to the turbulence kinetic energy production is insignificant, given the small magnitude of the measured Reynolds stress. The flow exhibits a high degree of isotropy when comparing the longitudinal autocorrelation functions, although some anisotropy is observed in the large scales according to the rms velocity ratio, which ranges from 0.90 to 1.33 over the measured regions. Despite these deviations from ideal isotropic turbulence, the experimental design is well-suited for the study of inertial particle agglomeration during gravitational settling. Graphical abstract