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

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.

Analysis of the Forces Driving the Oscillations in 3D Fluidic Oscillators

“…From their applications in flow control, it is interesting to mention their use in combustion control [3], flow deflection and mixing enhancement [4], flow separation modification in airfoils [5], boundary layer modification on hump diffusers used in turbomachinery [6], flow separation control on compressors stator vanes [7], gas turbine cooling [8], drag reduction on lorries [9], and noise reduction in cavities [10].Despite the existence of particular fluidic oscillator configurations, like the one introduced by Uzol and Camci [11], which was based on two elliptical cross-sections placed transversally and an afterbody located in front of them, or the one proposed by Huang and Chang [12], which was a V-shaped fluidic oscillator, most of the recent studies on oscillators focused on two main, very similar, canonical geometries, which Ostermann et al [13] called the angled and the curved oscillator geometries. Some very recent studies on the angled geometry are [13][14][15][16][17][18][19][20][21][22][23], while the curved geometry was studied by [4,10,13,[23][24][25][26][27][28][29][30][31][32][33]. Ostermann et al [13], compared both geometries, concluding that the curved one was energetically the most efficient.One of the first analyses of the internal flow on an angled fluidic oscillator was undertaken by Bobusch et al [17].…”

Velocity ratio effect on flow structures of non-parallel planar starting jets in cross-flow

“…Here, we follow the method introduced by Ostermann et al. (2019) and consider virtual seeding particles emitted through the PJA outlet that are advected according to the measured time-resolved velocity data. We then define the trajectory as the connecting line between particle locations with the largest wall distance for all streamwise positions.…”

Acoustic and flow data of fluidic and piezoelectric ultrasonic transducers

“…The wire was aligned with the z axis. The anemometer was calibrated in an open-return, suction wind tunnel at TU Berlin [4] , following the calibration curve given in Fig. 10 .…”