13th Int Symp on Applications of Laser Techniques to Fluid Mechanics Lisbon, Portugal, 26-29 June, 2006 - 1 - Characterization of vortex flow transition using PIV in the Couette Taylor system Nizar Abcha, Noureddine Latrache, Olivier Crumeyrolle & Innocent Mutabazi LMPG, University of Le Havre, France nizar.abcha@univ-lehavre.fr Abstract We have developed a Particle Image Velocimetry (PIV) adapted to the Couette-Taylor system in order to measure the axial and radial velocity components, vorticity fields, and their spatio-temporal dependence. The comparison between spatio-temporal diagrams obtained by flow visualization and PIV indicates that the intensity of light reflected by Kalliroscope platelets is related to the radial velocity component. 1. Introduction The Couette-taylor system is composed of two coaxial differentially rotating cylinders; it represents a good prototype for investigation of centrifugal instabilities and the transition system to turbulence in closed flows. This flow system has been subject of intense studies since the pionneering work of G.I. Taylor of 1923. Since then, many theoretical and experiments studies have been performed (Chandrasekhar S (1961), Coles D (1965)). Using visualization by means of anisotropic particles (aluminium powder (Taylor GI (1923), Coles D 1965), kalliroscope (Gorman M et al(1982), Andereck CD et al (1986),...), it was shown that the Couette-Taylor system possesses a rich variety of pattern depending on geometrical (aspect ratio and radius ratio) and physical (flow viscosity, cylinder rotation speeds) parameters (Coles D (1965), Andereck CD et al (1986)). Because of the intensive use of these particles in the investigation of flows in closed systems, theoretical and experimental attempts have been made to relate flow properties with visualization using these particles (Savas Ö (1985), Gauthier G et al(1998), Kalliroscope Corporation, Domnguez-Lerma et al (1985), Matisse P et al (1984), Thoroddsen et al (1999), Prigent A (2000). Since two decades, the visualization techniques have been complemented with of Laser Doppler Velocimetry (LDV) (Wereley ST et al (1994), Ultrasonic Doppler Velocimetry (UDV) (Takeda et al (1993), Takeda (1999)) and Particle Image Velocimetry (PIV) (Wereley ST et al (1998), Hwang JY et al (2004), Wereley ST et al (2002), and Wereley ST et al (1999)). Unfortunately, no clear answer has been provided so far to the following question: which flow information is given by the Kalliroscope particles? In this paper, we address this question using simultaneously a comparison of space-time diagrams obtained using both visualization technique and PIV. 2. Experimental apparatus and procedure The experimental system consists of two vertical coaxial cylinders immersed in a large square plexiglass box filled with water maintained at a controlled temperature. This square box allows for minimization of distortion effects of refraction due to curvature of the outer cylinder (Fig.1) during optical measurements. The inner cylinder has a radius a = 4 cm, the outer cylinder a radius b = 5 cm, the gap between the cylinders is d = b-a = 1 cm and the working length is L = 45.9 cm. Therefore the radius ratio η = a/b = 0.8 and the aspect ratio is Γ = L/d = 45.9. The inner cylinder is rotated by a motor at the angular rotation frequency Ω while the outer cylinder is fixed. The control