Experimental study on the characteristics of longitudinal oscillating grid turbulence

Oscillating grid turbulence is an efficient way of studying complex turbulence and mass transport, while the turbulence generated by the existing vertical oscillating grid systems is quite different from the natural turbulence. A large scale grid turbulence experiment system is established, the grids conduct longitudinal oscillating rather than the traditional vertical oscillating, and the Particle Image Velocimetry is used to measure the flow fields. Tests of the instantaneous flow velocities show that the turbulence generated by this system has strong randomness and statistical regularity. All the longitudinal and vertical root mean square velocities vary rapidly near the grids, and tend to be stable at the middle of the grids. The longitudinal root mean square velocities are larger than the vertical values, and the ratio is about 1.5-2.0, which is close to the natural open channel flow. The fluctuation of the Reynolds stress near the grids is relatively large and decreases with the increasing distance from the grid, the Reynolds stress is about zero at the middle of the grids. The integral time and length scales near the grids are the smallest and increase linearly with the increasing distance from the grids, reaching the maximum at the middle of the grids. The flow velocity spectra obeys the Kolmogorov-5/3 theory. The statistical characteristics of the turbulence generated by this system are consistent with the traditional vertical oscillating grid turbulence, but the longitudinal and vertical turbulent intensities are more close to the natural open channel flow, laying the foundation for the studies of sediment and pollutant transports.