PIV Experiments on Turbulence Characteristics of Double-Layer Oscillating Grid

To construct a controllable turbulence environment, experiments on a double-layer oscillating grid were conducted using Particle Image Velocimetry (PIV). Two-dimensional velocity fields were obtained using Particle Image Velocimetry (PIV) over oscillation frequencies of 1–6 Hz and strokes of 4, 6, and 8 cm. Mean velocities, RMS velocity fluctuations, Reynolds shear stress, and power spectral densities were subsequently analyzed. The mean velocity in the central region of Window II was generally close to zero. A central 10 cm × 10 cm area was therefore selected as the working region for flow-statistics analysis and turbulence-intensity calibration. As the horizontal and vertical root-mean-square (RMS) velocity fluctuations differed in magnitude, their relationships with the grid operating parameters were established separately. Under the analyzed operating condition, the integral timescale of the horizontal velocity fluctuations in the central working region was approximately 0.846 s. The dimensionless spectral analysis further characterized the frequency distributions of velocity fluctuations at different measurement locations. This study provides a basis for apparatus calibration and a reference for setting operating conditions for subsequent laboratory experiments on fine-grained sediment flocculation and settling under controlled turbulence conditions.