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Direct Numerical Simulations of the Free, Unsteady, Round, Unforced Jet at Low Reynolds Numbers

  • Ionut Danaila
  • Jan Dušek
  • Fabien Anselmet
Conference paper
Part of the ERCOFTAC Series book series (ERCO, volume 5)

Abstract

Three-dimensional direct numerical simulations of unforced, incompressible, free, spatially evolving round jets are used to investigate the onset of instability at low diametral Reynolds numbers (Re ≤ 500). Compact, coherent structures are identified by means of iso-surfaces of vorticity and pressure fields. The Reynolds number proves to be the decisive parameter for the selection of the most amplified unstable mode once the inflow velocity profile is given. (A ‘top-hat’ profile is used). At the upper limit of the investigated range of Reynolds numbers, the present simulations are consistent with the widely accepted scenario of the space and time development of a round jet instability. For lower Reynolds numbers, a superposition of symmetry-breaking (helical) modes is shown to characterize the instability of the round jet. The Fourier decomposition of the fluctuating flow field allows to extract the helical modes and to identify them as the modes predicted already by Batchelor as possible linearly unstable modes in an axisymmetric parallel and inviscid jet. The dynamics of the unstable axisymmetric jet present some particular features that might be characteristic of axisymmetric flows in general: absence of a limit cycle and sensitivity of the asymptotic state to initial conditions.

Keywords

Reynolds Number Direct Numerical Simulation Unstable Mode Spectral Element Momentum Thickness 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media Dordrecht 1997

Authors and Affiliations

  • Ionut Danaila
    • 1
    • 2
  • Jan Dušek
    • 3
  • Fabien Anselmet
    • 2
  1. 1.Parc Tech. AlataI.N.E.R.I.S.Général LeclercFrance
  2. 2.I.R.P.H.E.Général LeclercMarseilleFrance
  3. 3.I.M.F.StrasbourgFrance

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