The interaction between a spatially oscillating jet emitted by a fluidic oscillator and a cross-flow
The interaction between a spatially oscillating jet emitted by a fluidic oscillator and a cross-flow
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DOI：
10.1017/jfm.2018.981
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发表时间：
2019-03-25
影响因子：
3.7
通讯作者：
Paschereit, C. Oliver
中科院分区：
文献类型：
--
作者：
Ostermann, Florian;Woszidlo, Rene;Paschereit, C. Oliver
本实验研究了射流振荡器产生的空间振荡射流进入附壁横流的基本流场。主要的流动结构，如射流轨迹和流向涡的动力学，进行了详细讨论，以了解空间振荡射流和横流之间的相互作用。振荡射流垂直于横流喷射。采用可移动的立体粒子图像测速（PIV）系统进行流场的逐面采集。通过基于流体振荡器内部的压力信号对PIV结果进行相位平均来获得三维时间分辨流场。速度比和Strouhal数的影响进行了评估。与常见的稳定壁面法向射流相比，空间振荡射流穿透到横流的壁面法向方向的程度较小，有利于相当大的展向穿透。流场主要由流向涡主导，这些涡以横流的速度向下游对流。涡动力学表现出强烈的依赖于Strouhal数。对于小的Strouhal数，空间振荡射流的行为类似于具有随时间变化的偏转角的涡流生成射流。因此，它形成随时间变化的流向涡。对于更高的Strouhal数，横流不能跟随射流的运动，这导致在射流下游形成准定常尾流。结果表明，进一步增加Strouhal数时，流场接近准稳态行为。
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.