Experiments in Fluids

, 56:38 | Cite as

Mixing enhancement of an axisymmetric jet using flaplets with zero mass-flux excitation

  • Hanns Müller-VahlEmail author
  • Christian Navid Nayeri
  • Christian Oliver Paschereit
  • David Greenblatt
Research Article


A novel active control concept aimed at mixing enhancement of an axisymmetric incompressible jet was investigated experimentally. The lip of the jet was equipped with evenly distributed small flaps, or flaplets, deflected away from the stream at an angle of 30°. Controlled attachment of the jet’s boundary layer to the flaps was achieved by introducing zero mass-flux perturbations through control slots located at the base of the flaps, yielding a radial deflection of the shear layer. As a result, pairs of strong streamwise vortices of a finite length were periodically generated and shed in phase with the control signal. At a Strouhal number of 0.3 based on the nozzle diameter, the perturbations also regulated the shedding of spanwise vortex rings. Hot-wire measurements in the vicinity of the flaplets as well as phase-averaged stereoscopic PIV measurements at various streamwise locations were employed to elucidate the mechanism of controlled attachment and to map the evolution of the coherent structures. The strength of axial vorticity was strongly dependent upon the control frequency. A semiempirical framework adopted to quantify the overall effect of control predicted a significant increase in mixing in the region close to the nozzle.


Vortex Vorticity Shear Layer Vortex Ring Streamwise Vortex 
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.



The authors gratefully acknowledge the financial support for the work provided by the Deutsche Forschungsgemeinschaft (DFG), project number Pa 920/4-1. The assistance of Yogesh Singh is greatly appreciated.

Supplementary material

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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Hanns Müller-Vahl
    • 1
    • 2
    Email author
  • Christian Navid Nayeri
    • 2
  • Christian Oliver Paschereit
    • 2
  • David Greenblatt
    • 1
  1. 1.Faculty of Mechanical EngineeringTechnion - Israel Institute of TechnologyTechnion City, HaifaIsrael
  2. 2.Institute of Fluid Dynamics and Technical AcousticsBerlin Institute of TechnologyBerlinGermany

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