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Instability Modal Behavior of the Acoustically Excited Impinging Plane Jet With a Small Cylinder

Published online by Cambridge University Press:  05 May 2011

Fei-Bin Hsiao ,
I-Che Hsu  and
Cheng-Chiang Hsu
Fei-Bin Hsiao*
Affiliation:
Institute of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan 70101, R.O.C.
I-Che Hsu*
Affiliation:
Institute of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan 70101, R.O.C.
Cheng-Chiang Hsu*
Affiliation:
Department of Aicraft Engineering, Air Force Institute of Technology, Kaohsiung, Taiwan 820, R.O.C.
*
*Professor
**Graduate student
***Assistant Professor
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Abstract

The Instability modal behavior of coherent structures in a jet-small cylinder impinging flow field is extensively studied by hot-wire anemometry measurements. The free jet is employed with a small cylinder of 3 mm in diameter located in the potential core region at the impinging length of L/H = 1.5 for the near field impingement and L/H = 4 for the far field impingement. The jet exit velocity is operated at 10 m/sec with the Reynolds number of 1.03 × 104 based on the nozzle exit width H = 15mm. The impinging jet is locally excited at the nozzle exit with varicose mode (m =0) and sinuous mode (m = 1) disturbances at the fundamental frequency of the natural jet flow. Data indicate that the jet flow is greatly altered and significantly enhanced by strengthening the coherent structures of the flow due to resonance according to the feedback mechanism. Although the original natural jet preferably exhibits the varicose mode, the strong sinuous mode is dominant in the flow field owing to the presence of the small cylinder in the potential core region. In the near field impingement, the wake region behind the cylinder preserves the pure sinuous mode to where the jet vortices merge and then mildly fades out. Whereas in the jet shear layer, the sinuous mode exists in the initial portion and gradually transforms to the varicose mode. In the far field impingement, the alternate mode dominates in each frequency stage in pure impinging case and the modal behavior follows the selected mode with the introducing acoustic waves in the acoustic excitation cases.

Keywords

JetWakeImpinging jetMode behaviorAcoustic excitationTurbulent shear flow
Type
Articles
Information
Journal of Mechanics , Volume 20 , Issue 2 , June 2004 , pp. 145 - 157
Copyright
Copyright © The Society of Theoretical and Applied Mechanics, R.O.C. 2004

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