Statistical characteristics of spanwise vortex in open-channel turbulence with step-shaped spur dike

The step-shaped spur dike is a common waterway regulation structure. Based on the PIV (Particle Image Velocimetry) open-channel experiment, the distribution laws of turbulence lateral vortex density, vortex area, vortex shape parameters, vortex rotation intensity along the longitudinal direction and the transverse direction in the step-shaped spur dike area are studied. The results show that the distribution of vortex density along the water depth direction shows fluctuating peaks near the top and the bottom of the spur dike, and the farther away from the spur dike along the flow direction, the smaller the fluctuation of vortex density. The area of the prograde vortex at the same location near the spur dike is generally larger than that of the retrograde vortex. The peak of the vortex area on the vertical distribution appears at the top of the spur dike and decreases with the distance from the central axis of open-channel. The spanwise vortex near the spur dike is mostly elliptical in shape, and the retrograde vortex at the bottom of the open-channel in the spur dike area and the prograde vortex at the water surface are both flat. The rotation intensity of the retrograde vortex at the same location near the spur dike is much larger than that of the prograde vortex. From the upstream of the spur dam to the spur dam area, the spanwise vortex rotation intensity shows a sharp decrease along the path. From the spur dam area to the downstream, the spanwise vortex rotation intensity gradually stabilizes along the path.