Kelvin - Helmholtz and streamwise vortices in the near wake of a single-lobe forced mixer

R.H. Mao, Ching Man Yu, L.P. Chua

Research output: Journal article publicationJournal articleAcademic researchpeer-review

19 Citations (Scopus)

Abstract

In the present experimental investigation, the characteristics of two types of vortices, namely the normal Kelvin-Helmholtz (K-H) and streamwise vortices, generated in the near wake of a lobed forced mixer were examined and evaluated at two velocity ratios (r = U1:U2 = 1:1 and 0.4:1). The lobed forced mixer has only one lobe and was designed to eliminate any possible interactions between the neighbouring vortices generated by the adjacent lobes. Hot-wire anemometer was used to study the K-H vortices via the spectrum analysis. Laser-Doppler anemometer was employed to examine the streamwise vortices. It was found that there were two main frequencies for the K-H vortex in the wake of the forced mixer (fLM_C and fLM_L); both were higher than the case of plane-free shear layer (fFP), i.e., fLM_C > fLM_L > fFP, where f LM_C represents the K-H vortex shedding frequency in the behind the semi-circle part of the trailing edge, whereas fLM_L represents the frequency in the near wake behind the parallel side-walls of the trailing edge. The velocity ratio appeared to have more important effects at point C than at point L. The Strouhal numbers (StLM_C and StLM_L) reached constant values at the Reynolds number greater than 5 × 105. The K-H vorticities for the velocity ratio r= 0.4 was ?30 and 110 per cent stronger than for case r=1 for points L and C, respectively. The K-H vortices were also found to be more contributive to the production of the turbulent kinetic energy in the near wake of the single-lobe forced mixer than the streamwise vortices. The streamwise vortices at r = 0.4 accelerated the breakdown of the K-H vortices, which happened at about one wavelength earlier than r = 1. Finally, the effects of geometry parameters, including lobe height (or penetration angle) and wavelength, were examined. © IMechE 2006.
Original languageEnglish
Pages (from-to)279-298
Number of pages20
JournalProceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering
Volume220
Issue number4
DOIs
Publication statusPublished - 1 Dec 2006
Externally publishedYes

Keywords

  • Hot-wire anemometry
  • Kelvin-Helmholtz vortex
  • Laser-Doppler anemometry
  • Lobed forced mixer
  • Streamwise vortex
  • Two-stream mixing
  • Vortex shedding frequency

ASJC Scopus subject areas

  • Aerospace Engineering
  • Mechanical Engineering

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