Quantitative Flow Field Imaging about a Hydrophobic Sphere Impacting on a Free Surface

TL;DR

This study visualizes and quantifies the flow dynamics of a hydrophobic sphere impacting water, revealing splash formation, cavity collapse, and flow fields using high-speed imaging and Particle Image Velocimetry.

Contribution

It provides detailed flow field measurements during sphere impact on a free surface, combining visual impact analysis with quantitative PIV data under specific impact conditions.

Findings

Visualization of splash crown and air cavity formation.

Quantitative velocity and vorticity fields around the impact.

Insights into cavity collapse and pinch-off dynamics.

Abstract

This fluid dynamics video shows the impact of a hydrophobic sphere impacting a water surface. The sphere has a mass ratio of m* = 1.15, a wetting angle of 110 degrees, a diameter of 9.5 mm, and impacts the surface with a Froude number of Fr = 9.2. The first sequence shows an impact of a sphere on the free surface illustrating the formation of the splash crown and air cavity. The cavity grows both in the axial and radial direction until it eventually collapses at a point roughly half of the distance from the free surface to the sphere, which is known as the pinch-off point. The second set of videos shows a sphere impacting the free surface under the same conditions using Particle Image Velocimetry (PIV) to quantify the flow field. A laser sheet illuminates the mid-plane of the sphere, and the fluid is seeded with particles whose motion is captured by a high-speed video camera. Velocity fields are then calculated from the images. The video sequences from left to right depict the radial velocity, the axial velocity, and the vorticity respectively in the flow field. The color bar on the far left indicates the magnitude of the velocity and vorticity. All videos were taken at 2610 fps and the PIV data was processed using a 16 x 16 window with a 50% overlap.