Flow Characteristics beneath Ice Blocks with Smooth and Rough Undersurfaces

Abstract

Separating and reattaching flows beneath semisubmerged ice blocks with smooth and rough undersurfaces were systematically studied using a planar particle image velocimetry system. The examined Froude and Reynolds numbers based on the incoming free-stream velocity and water depth were 0.06–0.24 and 55,900–204,000, respectively. The ratios between the submerged thickness of the ice block and water depth varied between 0.02 and 0.18. The results indicate that there exists a mean separation bubble beneath the head of an ice block. The mean reattachment length when scaled by the incoming water depth correlates very well with the Reynolds number based on the submergence thickness. The undersurface roughness tends to reduce the mean reattachment length, and this reduction diminishes as the submergence thickness increases. The streamwise mean velocity scales well with the mean reattachment length within the mean shear layer. The results also show that turbulence transition initiates at the leading edge of the ice block. Meanwhile, the magnitudes of Reynolds stresses are significantly elevated within the mean shear layer and peak in the rear part of the mean separation bubble. When properly scaled, the Reynolds stresses in the lower portion of the shear layer exhibit self-similar profiles. These self-similar profiles are close to a Gaussian function and are not sensitive to either the undersurface roughness or Reynolds number.