On the Vortical Structure Developments of a Plane Jet under Long-wave Excitation

Yung-Lan Yeh

《Journal of Aeronautics, Astronautics and Aviation. Series A》 45卷1期 (2013/03) Pp. 1-11

https://doi.org/10.6125/12-1203-719

並列摘要

In order to control and influence the far field flow structures, the vortical characteristics of a low-speed plane jet under low-frequency, anti-symmetric excitation are well investigated experimentally by means of hot-wire anemometric measurements. The jet is normally operated at 10 m/sec, which has the corresponding Reynolds number of 8.2×10^3 based on the nozzle exit width. The perturbations for flow excitation are introduced with two oscillating mental strips which are flush mounted right at the nozzle exit, and two kinds of excitation frequencies are conducted, which are 5 and 10 Hz. In addition, because the wavelength of the oscillating perturbations is larger than the initial momentum thickness and initial instability wavelength at least two orders of magnitude, this kind of excitation method can be claimed as long-wave excitation. The spatial developments will be spread out from the experimental data of mean velocity distributions and spectral evolution under bi-modal excitation. The results indicate that the evolution of coherent structures and jet flapping motion are significantly influenced by long-wave excitation in the downstream, but it is similar to the natural jet in the near field and they also indicate that the preferred mode frequency is suppressed by the low-frequency excitation mode. In addition, the developments of large-scale vortices in the far field which are indicated by the phase-averaged technique show that their occurrences are the main cause of the large spreading increment.

並列關鍵字

Plane jet ； Vortical structure ； Long-wave excitation ； Bi-modal ； Flapping motion

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