Water entry dynamics of hydrophilic spheres through particle-laden free surfaces

We advance the seminal topic of water entry by documenting splash features generated by the impact of hydrophilic spheres through particle-laden free surfaces. Proximal interaction with small, buoyant particles is yet another means to manipulate splash dynamics. In this experimental study, we systematically investigate the fluid-structure interactions between floating particles and hydrophilic spheres for Froude numbers in the range of 20-94. Thus, we observe previously undocumented sub- and supersurface fluid interactions. Generally, hydrophilic spheres entering a liquid bath below the threshold of 8 m/s produce minimal fluid displacement and no cavity formation. The presence of floating particles atop the free surface with respect to impacting spheres promote flow separation, yielding a radially expanding splash crown just above the free surface, simultaneously with an air-entraining cavity into the body of the fluid, and a vertically-protruding Worthington jet following cavity collapse. The resulting splash metrics differ from those of purely hydrophobic spheres based on the size of the impacted particles. Such observations augur well for fluid-structure interactions where flow separation warrant control.