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The interaction between a spatially oscillating jet emitted by a fluidic oscillator and a cross-flow

Published online by Cambridge University Press:  23 January 2019

Florian Ostermann*
Affiliation:
Technische Universität Berlin, Berlin 10623, Germany
Rene Woszidlo
Affiliation:
Technische Universität Berlin, Berlin 10623, Germany
C. Navid Nayeri
Affiliation:
Technische Universität Berlin, Berlin 10623, Germany
C. Oliver Paschereit
Affiliation:
Technische Universität Berlin, Berlin 10623, Germany
*
Email address for correspondence: florian.ostermann@tu-berlin.de

Abstract

This experimental study investigates the fundamental flow field of a spatially oscillating jet emitted by a fluidic oscillator into an attached cross-flow. Dominant flow structures, such as the jet trajectory and dynamics of streamwise vortices, are discussed in detail with the aim of understanding the interaction between the spatially oscillating jet and the cross-flow. The oscillating jet is ejected perpendicular to the cross-flow. A moveable stereoscopic particle image velocimetry (PIV) system is employed for the plane-by-plane acquisition of the flow field. The three-dimensional, time-resolved flow field is obtained by phase averaging the PIV results based on a pressure signal from inside the fluidic oscillator. The influence of velocity ratio and Strouhal number is assessed. Compared to a common steady wall-normal jet, the spatially oscillating jet penetrates to a lesser extent into the cross-flow’s wall-normal direction in favour of a considerable spanwise penetration. The flow field is dominated by streamwise-oriented vortices, which are convected downstream at the speed of the cross-flow. The vortex dynamics exhibits a strong dependence on the Strouhal number. For small Strouhal numbers, the spatially oscillating jet acts similar to a vortex-generating jet with a time-dependent deflection angle. Accordingly, it forms time-dependent streamwise vortices. For higher Strouhal numbers, the cross-flow is not able to follow the motion of the jet, which results in a quasi-steady wake that forms downstream of the jet. The results suggest that the flow field approaches a quasi-steady behaviour when further increasing the Strouhal number.

JFM classification

Type
JFM Papers
Copyright
© 2019 Cambridge University Press 

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Ostermann et al. supplementary movie 1

Flow field visualization that shows the finite-time Lyapunov exponent (FTLE) for three velocity ratios.

Download Ostermann et al. supplementary movie 1(Video)
Video 6.2 MB

Ostermann et al. supplementary movie 2

Time-resolved cross-section through the phase-averaged flow field for two velocity ratios.

Download Ostermann et al. supplementary movie 2(Video)
Video 12.1 MB