Vortex Shedding in the Wake of a Dual Step Cylinder

TL;DR

This study visualizes vortex shedding phenomena behind a dual-step cylinder, revealing how aspect ratio influences wake structures and vortex interactions at a Reynolds number of 2100.

Contribution

It provides detailed flow visualization of vortex interactions in dual-step cylinders, highlighting the effect of aspect ratio on vortex shedding and wake development.

Findings

Vortex shedding occurs at distinct frequencies for 1 < L/D < 3.

Large cylinder vortex shedding ceases at smaller L/D.

Small cylinder vortices interact in the large cylinder wake at low L/D.

Abstract

A dual-step cylinder is comprised of a large diameter cylinder (D) with low aspect ratio (L/D) attached co-axially to the mid-span of a small diameter cylinder (d). The fluid dynamics video presented in this investigation is used to illustrate the effect of aspect ratio on dual step cylinder wake development for Re = 2100, D/d = 2, and 0.2 < L/D < 3. In addition, the video provides visualization of such flow phenomena as interaction of spanwise vortices, development of streamwise vortex filaments, and formation of Kelvin-Helmholtz rollers. The experiments were performed in a water flume at the University of Waterloo. A hydrogen bubble flow visualization technique was employed to visualize vortical structures downstream of each cylinder model. High-resolution images of the flow were obtained with a high speed Photron camera and post-processed using Adobe Photoshop CS4. The results show a plethora of vortices developing in the wake of the dual step cylinder. For 1 < L/D < 3, spanwise vortex shedding occurs from the large and small cylinders at distinct frequencies. However, for smaller L/D, large cylinder vortex shedding ceases and small cylinder vortices interact in the large cylinder wake.