Characterization of the Free-Surface Turbulent Wakes of Surface-Piercing Bluff Bodies

The free-surface wake flows behind surface vessels and offshore structures exhibit complex multiphase turbulent transport processes. This research aims to advance the fundamental understanding of anisotropic turbulent free-surface wake flows generated by surface-piercing bluff bodies with uniform cross-sections. Experiments conducted in a free-surface water tunnel utilized fluorescent dye visualization and 2D digital particle image velocimetry (DPIV) in multiple 2D planes to characterize the highly anisotropic wakes under varied Reynolds and Froude numbers. Two models were selectively tested: a blunt equilateral triangle (Wedge I) and a more slender geometry (Wedge II). Dye visualization reveals that the formation and shedding of wake vortices are suppressed and delayed in regions near the unsteady free surface. Within this region, DPIV results show that the wake widens and forms an extended recirculation zone with reduced convective velocity. The Reynolds shear stress, as the dominant agent of momentum transfer, is also reduced by the unsteady free surface. Directly below this region, shear layer measurements show a distinct peak in convective velocity, influencing both wake width and recirculation. This anisotropy is more pronounced with the bluff Wedge I geometry, likely due to the large Froude number. The present results lay a foundation for further research into the three-dimensionality and geometry dependence of free-surface wake flows, which is crucial for optimizing the design of naval vessels, amphibious aircraft, and maritime structures, and for advancing the development of high-fidelity turbulence models.