Active control of coaxial jet mixing with manipulation of primary vortical structures by arrayed micro flap actuators

Abstract

Active mixing control of a methane/air isothermal coaxial jet was achieved using micro magnetic flap actuators arranged on the inner surface of the outer annular nozzle. The spatio-temporal evolution of vortical structures and the scalar mixing were studied through the particle image velocimetry and planar laser-induced fluorescence methods. In contrast to studies on jet control using acoustic forcing, the mechanical movement of the flap directly generated large-scale intense vortices. The mixing was enhanced significantly by the vortices formed in the inner shear layer, although the control input was given to the outer shear layer. It was found that the primary vortex rings dominated the near-field mixing, while streamwise vortices were responsible for the downstream mixing. It was also demonstrated that the radial range of the inner fuel transportation could be manipulated flexibly by adjusting the shedding interval of the vortices. Especially, the mixing was enhanced most significantly when the primary vortices were most densely populated near the nozzle exit at the control Strouhal number of unity.

Keywords:

• coaxial jet
• flow control
• micro actuator
• laser-induced fluorescence
• particle image velocimetry

Acknowledgements

This work was supported through the research project on Micro Gas Turbine/Fuel Cell Hybrid-Type Distributed Energy System by the Department of Core Research for Evolutional Science and Technology (CREST) of the Japan Science and Technology Corporation (JST).

Disclosure statement

No potential conflict of interest was reported by the authors.