Experimental investigation of the wake behind a rotating sphere

TL;DR

This study experimentally explores how the wake behind a rotating sphere changes with different flow conditions, revealing various flow regimes depending on Reynolds number and rotation rate.

Contribution

It provides a detailed experimental analysis of wake regimes behind a rotating sphere across a range of Reynolds numbers and rotation rates, mapping the flow transitions.

Findings

Identification of flow regimes: axisymmetric, low helical, high helical.

Flow regime transitions depend on Reynolds number and swirl rate.

Experimental visualization of wake structures.

Abstract

The wake behind a sphere, rotating about an axis aligned with the streamwise direction, has been experimentally investigated in a low-velocity water tunnel using LIF visualizations and PIV measurements. The measurements focused on the evolution of the flow regimes that appear depending on two control parameters, namely the Reynolds number $Re$ and the dimensionless rotation or swirl rate $\Omega$, which is the ratio of the maximum azimuthal velocity of the body to the free stream velocity. In the present investigation, we cover the range of $Re$ smaller than 400 and $\Omega$ from 0 and 4. Different wakes regimes such as an axisymmetric flow, a low helical state and a high helical mode are represented in the ($Re$, $\Omega$) parameter plane.