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Particle image velocimetry (PIV) has been used in order to measure the three mean components and turbulence intensities of the velocity vector in a swirling decaying¯ow induced by a tangential inlet in an annulus. This kind of¯ow motion is found to be very complex, exhibiting three-dimensional and non-axisymmetric characteristics coupled with a free decay of the swirling intensity along the¯ow path, thereby making it dif®cult to study. A method allowing the measurement of the three components of the velocity¯ow-®eld with a standard PIV system with two-dimensional acquisitions, is presented. The evolution of each velocity component between the inlet and the outlet of the annulus is obtained. Furthermore, the PIV technique is extended to the measurement of turbulent characteristics such as turbulent intensities and dimensionless turbulent energy. The main characteristics of the swirling¯ow are discussed and the swirl number is estimated as a function of the axial distance from the tangential inlet.

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