Effects of surface microstructures on cavity dynamics during vertical water entry of cylinders

This study experimentally and theoretically investigates the effects of surface microstructures on cavity dynamics during vertical water entry of cylindrical bodies. Experimental results indicate that surface microstructures enable rapid cavity expansion during the initial phase of water entry and overcome original characteristic length constraints. Furthermore, the Froude number (Fr) is a critical parameter influencing cavity morphology. Over the tested range, the pinch-off depth of the cavity formed by the cylinders with microstructures still obeys the Fr13scaling law, the microstructured surfaces mainly accelerate the formation of larger cavities. Consistently, as Fr increases, the pinch-off depth, pinch-off time, and cavity growth rate significantly increase, facilitating the formation of a complete cavity envelope in water. This cavity evolution, resulting from the enhanced slip effect identified in our theoretical analysis, transforms the no-slip boundary condition at the solid–liquid interface into a slip condition at the gas–liquid interface, thereby enhancing cavity-liquid coupling dynamics and enriching subsequent water entry behavior. Overall, these findings indicate the role of microstructured surfaces in modulating hydrodynamic interactions, offering insights for designing advanced microstructured surfaces to optimize drag reduction, enhance stability, and improve performance in trans-media vehicles.