Experiments in Fluids

, Volume 40, Issue 2, pp 177–187 | Cite as

An analysis of unsteady highly turbulent swirling flow in a model vortex combustor

  • E.C. Fernandes
  • M.V. Heitor
  • S.I. Shtork
Research Article


This paper reports an experimental investigation of a non-reacting turbulent swirling flow in a practical vortex combustor. The flow was examined for the conditions characteristic of the presence of a breakdown zone and a strong flow instability appearing at swirl numbers S>0.5. Flow visualization techniques, LDA measurements and acoustic probes were employed to study the unsteady flow characteristics. Based on the experimental results a positive first helical mode of instability was identified with a wavelength and frequency depending on swirl. The wavelength was confirmed to grow monotonically with S, while the dominant frequency of the flow pulsations was found to have an unusual parabolic evolution with swirl, with a minimum at S min=0.88. This finding was interpreted using a proposed kinematic model based on the contribution of two mechanisms: rotation and axial motion of the helical vortex. It was concluded that for S<S min the instability frequency is essentially dominated by the axial translation of the spiral vortex being inversely proportional to S and therefore giving a decreasing trend. For S>S min the frequency of the flow precession is more dependent on the angular transportation of the vortex core, which resulted in the expected growing dependence on S.


Vortex Flow Pulsation Spiral Structure Pressure Probe Vortex Breakdown 
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List of symbols


axial phase velocity, ω/k


angular phase velocity, ω/n


nozzle diameter


precession frequency


axial wavenumber, 2π/λ


azimuthal number

r, θ, z

cylindrical coordinates


radius of maximum tangential velocity


Reynolds number, u 0 d/ν (ν is the kinematic viscosity)


geometrical swirl number


Strouhal number, fd/u 0


mean axial velocity in the nozzle


centerline axial velocity

um, wm

maximum axial and tangential velocities, respectively


angular frequency, 2πf

Φ(z, θ, t)

phase function


axial wavelength



The authors are pleased to acknowledge support from the Portuguese Science and Technology Foundation through Research Grant PCTI/1999/EME/34768 and Fellowship SFRH/BPD/1641/2000 provided for S.I. Shtork. The authors are also grateful to their colleagues Profs. P.M. Anacleto and A.L.N. Moreira, for their kind attention to this work.


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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  1. 1.Department of Mechanical Engineering, Instituto Superior TécnicoLaboratory of Thermofluids, Combustion and Energy Systems, Center for Innovation, Technology and Policy Research, IN+LisbonPortugal
  2. 2.Institute of ThermophysicsNovosibirskRussia

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