Physics of free-surface turbulent wake flow uncovered by three-dimensional defocusing particle image velocimetry (PIV)

The turbulent free surface wake is extremely complicated due to its multi-scale unsteady nature across two phases (air and water). The transport of mass, momentum, and energy results in phenomena such as air bubble entrainment, which critically affects the safety and performance capabilities of many maritime technologies. Here we present the physics of turbulent wake flow behind a partially submerged triangle wedge. Measurement results obtained by both the conventional 2D-PIV and the more advanced 3D defocusing PIV will be present. It was discovered that the wake flow has a wider wake angle with higher turbulence intensity when close to the free surface. These observations are likely due to the amplification of instability in the 3D wake flow caused by the unsteady free surface. These fundamental discoveries pave the way towards high-fidelity modeling of free surface turbulent wake.