Measurements of turbulence generated by oscillating grid

Turbulence generated by a vertically oscillating grid in a water tank was i nvestigated using the digital particle image velocimetry technique. The sta tistical turbulence characteristics computed based on the experimental data agree well with the two main findings reported in the literature: (1) The turbulence decays following the power law; and (2) the integral length scal e increases linearly with the distance from the grid. In addition, the flow structure near the grid was observed in detail with the advantage of the p lanar measurements. It was found that the velocity fluctuations in the regi on near the grid vary depending on the grid geometry. The fluctuations imme diately over the bar position are significantly different from those over t he grid openings. Turbulence with the highest intensity occurs above the in tersection of the square bars that constitute the grid. The results imply t hat shear flow clearly exists near the grid and homogeneity of the turbulen ce can only be achieved at a distance from the grid greater than about thre e mesh sizes. In addition, it was found that at least 400 vector maps shoul d be taken to ensure the accuracy of the measured velocity fluctuations.