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This paper discusses the application of proper orthogonal decomposition (POD) to the particle image velocimetry (PIV) velocity fields of the recirculation zone of an annular jet. The annular jet is an example of complex shear flow situations. Two axisymmetrical shear layers, originating at the exit of the jet, one at the lip of the nozzle and the other in the centre of the body, eventually meet downstream or interact with each other. In this study we propose use of the POD on PIV velocity fields of the recirculation zone of this annular jet. According to POD analysis, the primary objective of this paper is to describe the mode effects on the understanding of the nature of the flow and especially the link between the first eigenfunctions of POD and the motion of the stagnation point at the extremity of the recirculation zone of the annular jet. In particular, this allows us to dissociate the oscillation and velocity fluctuations due to the turbulent flow behaviour.

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This article presents an experimental investigation of a large diameter ratio annular air jet by Particle Image Velocimetry (P.I.V.), Laser Doppler Anemometry (L.D.A.), hot wire anemometry and time-resolved tomography. Annular jets consist in a round nozzle with an obstacle placed in its center. These jets are thus defined by an external and an internal diameter corresponding to the round nozzle lips and the diameter of the obstacle respectively. The ratio between these two diameters defines the behavior of the flow across a characteristic diameter called diameter ratio. In most industrial applications these jets have large diameter ratios, superior to 0.7.

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