Decay of turbulence generated by oscillating grid

Turbulence generated by a vertically oscillating grid in a water tank was investigated using the DPIV technique. The statistical turbulence characteristics computed based on the experimental data obtained agree well with the two main findings reported in the literature, i.e., the turbulence decays following the power law and the integral length scale increases linearly with the distance from the grid. The flow structure near the grid was particularly observed in details utilising the advantage of the planar measurements. It was found that the velocity fluctuations in the region near the grid vary depending on the grid geometry. The velocity fluctuations immediately over the bar position are significantly different from those over the grid openings. Turbulence with the highest intensity occurs above the intersection of the square bars that constitute the grid. The results imply that shear now clearly exists near the grid and the homogeneity of the turbulence can only be achieved at a distance from the grid greater than about three mesh sizes. In addition, it was found that the number of velocity vector maps from the data sampling should be large enough to ensure the accuracy of the measured velocity fluctuations.