Development of a Feedback Model for the Self-Excited Impinging Planar Jet
This article experimentally investigates the self-excited impinging planar jet flow, specifically, the development and propagation of large-scale coherent flow structures convecting between the nozzle lip and the downstream impingement surface. The invest
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Abstract This article experimentally investigates the self-excited impinging planar jet flow, specifically, the development and propagation of large-scale coherent flow structures convecting between the nozzle lip and the downstream impingement surface. The investigation uses phase-locked PIV measurements and a new structure-tracking scheme to measure convection velocity and characterize the impingement mechanism near the plate in order to develop a new feedback model that can be used to predict the oscillation frequency as a function of flow velocity (Uo), impingement distance (xo) and nozzle thickness (h). The resulting model prediction shows a good agreement with experimental tone frequency data.
Keywords Impinging jet Self-excited flow Acoustic tone Flow-acoustic interaction Feedback mechanism Coherent structure Vortices Convection speed
1 Introduction High-speed impinging planar jets are used in a myriad of important industrial applications; however, these flows are also known to be liable to the production of very intense narrow-band acoustic tones and strong self-excited flows. These phenomena are produced by a feedback mechanism between instabilities in the free shear layers of the jet and pressure fluctuations produced by the impingement
D. Arthurs (&) S. Ziada (&) Department of Mechanical Eng—JHE-316, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada e-mail: [email protected] S. Ziada e-mail: [email protected]
Y. Zhou et al. (eds.), Fluid-Structure-Sound Interactions and Control, Lecture Notes in Mechanical Engineering, DOI: 10.1007/978-3-642-40371-2_4, Springer-Verlag Berlin Heidelberg 2014
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D. Arthurs and S. Ziada
of large-scale coherent flow structures at the impingement surface. Previous investigations of the planar impinging jet have shown that the characteristics of the self-excited response of the system is different from other related geometries, such as the impinging axisymmetric jet, being self-excited over a much larger range of impingement ratio (1.5 B xo/h B 32.0 for the planar cases, compared with 1.5 B xo/D B 7.0 for round jets) and beginning at lower flow velocities (Arthurs and Ziada 2012). These distinctions result in significant differences in both the structure of the flow, as well as the form of the jet oscillation modes compared to related systems, and as a result, the existing feedback models lead to relatively poor predictions of the oscillation frequency.
2 Experimental Details Experiments were conducted using McMaster’s planar jet noise facility, which employs a planar nozzle with a thickness of h = 3 mm, a total span of L = 100 mm, and uses compressed air as a flow source. Acoustic measurements have been performed with GRAS " microphones, and flow measurements have been performed by means of a standard-speed PIV system using a phase-locked measurement technique, which acquires flow measurements at a specified point in the flow oscillation cycle using the periodic pressure signal obtained at the plate surface
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