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Properties of a sweeping jet emitted from a fluidic oscillator

Published online by Cambridge University Press:  19 October 2018

Florian Ostermann Open the ORCID record for Florian Ostermann [Opens in a new window] ,
Rene Woszidlo ,
C. Navid Nayeri  and
C. Oliver Paschereit
Florian Ostermann*
Affiliation:
Hermann-Föttinger-Institut, Technische Universität Berlin, Berlin 10623, Germany
Rene Woszidlo
Affiliation:
Hermann-Föttinger-Institut, Technische Universität Berlin, Berlin 10623, Germany
C. Navid Nayeri
Affiliation:
Hermann-Föttinger-Institut, Technische Universität Berlin, Berlin 10623, Germany
C. Oliver Paschereit
Affiliation:
Hermann-Föttinger-Institut, Technische Universität Berlin, Berlin 10623, Germany
*
†Email address for correspondence: florian.ostermann@tu-berlin.de
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Abstract

This experimental study investigates the flow field and properties of a sweeping jet emitted from a fluidic oscillator into a quiescent environment. The aspect ratio of the outlet throat is 1. Stereoscopic particle image velocimetry is employed to measure the velocity field plane-by-plane. Simultaneously acquired pressure measurements provide a reference for phase correlating the individual planes yielding three-dimensional, time-resolved velocity information. Lagrangian and Eulerian visualization techniques illustrate the phase-averaged flow field. Circular head vortices, similar to the starting vortex of a steady jet, are formed repetitively when the jet is at its maximum deflection. The quantitative jet properties are determined from instantaneous velocity data using a cylindrical coordinate system that takes into account the changing deflection angle of the jet. The jet properties vary throughout the oscillation cycle. The maximum jet velocity decays much faster than that of a comparable steady jet indicating a higher momentum transfer to the environment. The entrainment rate of the spatially oscillating jet is larger than for a steady jet by a factor of 4. Most of the mass flow is entrained from the direction normal to the oscillation plane, which is accompanied by a significant increase in jet depth compared to a steady jet. The high entrainment rate results from the enlarged contact area between jet and ambient fluid due to the spatial oscillation. The jet’s total force exceeds that of an idealized steady jet by up to 30 %. The results are independent of the investigated oscillation frequencies in the range from 5 to 20 Hz.

JFM classification

Flow Control: Flow Control Wakes/Jets: Jets Flow Control: Mixing enhancement
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 857 , 25 December 2018 , pp. 216 - 238
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Copyright
© 2018 Cambridge University Press 

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Ostermann et al. supplementary movie

The three-dimensional flow field of a sweeping jet emitted from a fluidic oscillator visualized by the backward finite time Lyapunov exponent. Note that the top half of the boundary wall is omitted to provide unobstructed view.

Download Ostermann et al. supplementary movie(Video)
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