Wake interaction of two disks falling in tandem

TL;DR

This study visualizes and analyzes how two disks falling in tandem interact through their wakes at a Reynolds number near 100, revealing different wake behaviors and fall configurations based on disk thickness.

Contribution

It provides experimental visualization of wake interactions and identifies how disk thickness influences wake merging and fall patterns in tandem falling disks.

Findings

Thicker disks lose their initial wakes and fall side by side.

Thinner disks' wakes merge, leading to a stable Y-configuration.

Trailing disks can accelerate and catch up due to wake entrainment.

Abstract

The fluid dynamics video illustrates the interaction of two disks falling in tandem at Reynolds number close to 100. Two fluorescent dyes were used to visualize the wake of each body. We can observe that the trailing body accelerates thanks to the entrainment provided by the wake of the leading body and eventually catches up the leadind body. Then, thick disks (diameter/thickness = 3) lose their initial wakes, separate laterally and fall side by side. On the contrary, the wakes of thinner disks (d/t = 10) merge in a single wake and the bodies continue their fall together adopting a stable Y-configuration.