caa a22 4500 606198903 CHVBK 20210128100936.0 cr unu---uuuuu 210128e20150201xx s 000 0 eng 10.1007/s00348-014-1889-z doi (NATIONALLICENCE)springer-10.1007/s00348-014-1889-z Mixing enhancement of an axisymmetric jet using flaplets with zero mass-flux excitation [Elektronische Daten] [Hanns Müller-Vahl, Christian Nayeri, Christian Paschereit, David Greenblatt] 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. Springer-Verlag Berlin Heidelberg, 2015 Müller-Vahl Hanns Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, 32000, Technion City, Haifa, Israel aut Nayeri Christian Institute of Fluid Dynamics and Technical Acoustics, Berlin Institute of Technology, 10623, Berlin, Germany aut Paschereit Christian Institute of Fluid Dynamics and Technical Acoustics, Berlin Institute of Technology, 10623, Berlin, Germany aut Greenblatt David Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, 32000, Technion City, Haifa, Israel aut Experiments in Fluids Springer Berlin Heidelberg 56/2(2015-02-01), 1-22 0723-4864 56:2<1 2015 56 348 https://doi.org/10.1007/s00348-014-1889-z text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00348-014-1889-z text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Müller-Vahl Hanns Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, 32000, Technion City, Haifa, Israel aut NATIONALLICENCE 700 1- Nayeri Christian Institute of Fluid Dynamics and Technical Acoustics, Berlin Institute of Technology, 10623, Berlin, Germany aut NATIONALLICENCE 700 1- Paschereit Christian Institute of Fluid Dynamics and Technical Acoustics, Berlin Institute of Technology, 10623, Berlin, Germany aut NATIONALLICENCE 700 1- Greenblatt David Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, 32000, Technion City, Haifa, Israel aut NATIONALLICENCE 773 0- Experiments in Fluids Springer Berlin Heidelberg 56/2(2015-02-01), 1-22 0723-4864 56:2<1 2015 56 348