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Proper Orthogonal Decomposition application on the aerodynamic study of controlled annular jets

Abstract : Proper Orthogonal Decomposition (P.O.D.) is a technique used for analysis of vortex structures in a turbulent flow. In this study, complex shear flows are observed by P.I.V. measurements (Particle Image Velocimetry) of a large diameter ratio annular jet. These jets present a lot of strong instabilities which become a real handicap on industrial processes (burners, glass fibers process, cooling system...). The fundamental interest of the P.O.D. technique is to observe each structure building the flow in order to understand what structure is responsible for what instability, and how we can apply an active forcing or a passive control to change the flow and its time evolution. P.I.V. measurements allow us to have a high spatial resolution and P.O.D. can complete these pieces of information with a temporal reconstruction. We focus our study on the initial zone of the annular jet. This zone extends from the outlet of the nozzle to the end of the recirculation zone which is formed downstream an obstacle in the middle of a round jet flow. At the end of the recirculation zone, the stagnation point is submitted to periodic fluctuations around the jet axis. We try to apply an active control using acoustic waves with different frequencies (fundamental, first harmonic...). Measurements are conducted with a Reynolds number ReDo=107 800 for which the stagnation point fluctuates with a frequency of 150Hz (the associated Strouhal number StDo is equal to 0.27) . This study will permit us essentially to have a better knowledge of annular jets and to meet manufacturer's needs. The P.O.D. analysis applied on a natural annular jet and an excited annular jet enables us to see the significance of the triggering of the acoustic wave with the stagnation point motion. An active control is therefore necessary to use acoustic excitation to reduce instabilities in the initial zone of these turbulent jets. The position of the excitation affects the efficiency of the acoustic forcing. Then this study indicates that an excitation using an acoustic wave with a frequency equal to the inherent frequency of the stagnation point fluctuations reduces these instabilities while a double harmonic excitation frequency seems to have the inverse results.
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Submitted on : Thursday, December 20, 2012 - 2:38:34 PM
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  • HAL Id : hal-00767786, version 1

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Amélie Danlos, Béatrice Patte-Rouland. Proper Orthogonal Decomposition application on the aerodynamic study of controlled annular jets. 14th International Symposium of Laser Techniques to Fluid Mechanics, Jul 2008, Lisbon, Portugal. pp.1-13. ⟨hal-00767786⟩

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