Proper Orthogonal Decomposition used for determination of the convection velocity of the initial zone of the annular jet. Aerodynamic study and control of instabilities

International audienceThe annular jet is an example of complex shear flow situations. Two axisymmetric shear layers, originating at the jet exit, one at the nozzle lip and the other at the centre body, eventually meet downstream or interact with each other. This study also proposes to apply P.O.D on P.I.V velocity fields. We propose especially a determination of the convection velocity of the primary vortices of an annular jet. In this study, we want to investigate two ways to reduce the stagnation point instabilities of an annular jet with a large diameter ratio (r=0.91). This article discusses the application of Proper Orthogonal Decomposition to the P.I.V. velocity fields of an annular jet and on a statistic of time-resolved tomographic images of the initial zone of the annular jet. In the second part of the study, the influence of the internal obstacle shape is studied. We will also use P.I.V. measurements to see the effects of three internal obstacles: a disk, a cone and a spheroid. The main aim of this study is to observe and analyze the effects of different annular jet configurations, in order to find a new way to reduce jet instabilities, using passive or active control. The second method consists in applying a sound wave to obtain an active control of these instabilities. With different frequencies (fundamental, first harmonic...), we will see the effect on the flow by the P.I.V. measurement technique (Particle Image Velocimetry). Measurements are conducted with a Reynolds number ReDo=107800. The fluctuation frequency of the stagnation point is known for this Reynolds number. The Strouhal number corresponding to this frequency is StDo = 0.27. Active control has already been used with round jets and has given promising results, but only a few studies have been conducted on annular jets in this field. This work will permit us essentially to have a better knowledge of annular jets and to meet manufacturers' needs