English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The onset of turbulent flow around an oscillating sphere is known to occur ata critical velocity vc ~ sqrt(kappa omega) where kappa is the circulationquantum and omega is the oscillation frequency. However, in a small interval ofdriving force amplitudes F (or corresponding velocity amplitudes of few percentabove vc) the turbulent flow is found to be unstable. The flow pattern switchesintermittently between potential flow and turbulence. The lifetimes of theturbulent phases have an exponential distribution and the mean lifetimes taugrow very rapidly with increasing driving force, namely as tau(F) ~ exp[(F/F1)^2]. In this work this experimental result is analyzed in more detailthan before, in particular the force F1 is identified. As a result, theturbulent drag force F(v) ~ (v^2 - vc^2) can be ascribed quantitatively to theshedding of vortex rings having the size of the sphere. Moreover, we can inferthe average number of vortex rings that are shed per half-period at any givenvelocity v on the turbulent drag force.

Shedding of Vortex Rings from an Oscillating Sphere in Superfluid He-4 below 0.5 K - The Origin of the Turbulent Drag Force