Vortex shedding and vorticity fluxes in the wake of cylinders within a random array

ABSTRACT

This work investigates the impact of the background turbulence generated by randomly placed cylinders on the vortex shedding regime and the mechanisms associated to vorticity fluxes. The goals are achieved by exploring velocity databases acquired with a two-dimensional particle image velocimetry system in two types of turbulent flow experiments: flow around a single infinite cylinder and flow within random array of infinite cylinders. Formation lengths, power spectral density functions and vortex distributions are employed to discuss the vortex shedding regime. The effects of background turbulence and vorticity cancellation, due to opposite sign vorticity, on the vorticity fluxes are discussed. The results show that the background turbulence reduces the formation length and consequently increase the shedding frequency. The stronger decay of longitudinal vorticity flux in denser arrays is not accompanied by an increase of the lateral flux of vorticity. Furthermore, it was concluded that the decay of longitudinal vorticity flux is mainly caused by the vorticity cancellation due to the vorticity of opposite sign of close downstream cylinders.

KEYWORDS:

• Array of cylinders
• wake disappearance
• vortex shedding
• Schiller-Linke regime
• vorticity flux

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was partially funded by FEDER, program COMPETE, and by national funds through Portuguese Foundation for Science and Technology (FCT) project RECI/ECM-HID/0371/2012 and grant number SFRH/BPD/93903/2013.