EXPERIMENTAL INVESTIGATIONS OF THE SPHERICAL TAYLOR- COUETTE FLOW USING ELECTRODIFFUSION TECHNIQUE M. Mahloul 1, 2 , A. Mahamdia 2 and M. Kristiawan 3 1 Departement of Physics, Preparatory School “Science and Technology” of Algiers, B.P 474, Place des Martyrs, Algiers, Algeria. 2 Departement of Energetics and fluid mechanics, Faculty of Physics, University of Sciences and Technology Houari Boumediene, BP N° 32 El Alia 16111 Algiers – Algeria. 3 INRA, UR 1268 Biopolymers Interactions and Assemblies, 44316, Nantes, France. Abstract In this paper, we study the hydrodynamic instabilities between two concentric spheres, the inner rotating while the outer is at rest, through visualization and electrodiffusion technique. The exploration of the flow regimes is carried out for different values of the Taylor number Ta and the aspect ratio Γ, but with one dimensionless gap width δ = 0.107. The bifurcation diagram of the flow is determined by classical visualization. On the other hand, by means of electrodiffusion technique, we measured the friction factor at the inner wall of the outer sphere. Time series obtained by the electrodiffusion technique, using FFT, permitted the identification of the fundamental frequencies and confirmed part of the bifurcation diagram obtained by the classical visualization. Keywords: Spherical Taylor-Couette, visualisation, electrodiffusion, instability. 1 Introduction The understanding of dynamic systems manifested in spherical geometry flows is still increasing concern of researchers. Particularly considerable progress has been realize in recent years to study the various instabilities and the transition to the turbulence of an incompressible viscous fluid between two concentric spheres in rotations. (Wimmer, [1] ; Bühler, [2] ; Mamun and Tuckerman, [3] ; Nakabayashi et al, [4] ; Yuan, [5] ; Tigrine et al, [6] ; Loukopoulos, [7] ; Feudel et al, [8] ; Lalaoua and Bouabdallah, [9] ; Mahloul et al, [10, 11]. The observation of the spherical flow and the description of the successive structures during the changes of the regimes is necessary for the understanding of the dynamics of the concerned phenomena. In this type of flow, the transition to turbulence is a repetition of bifurcation phenomena. Mahloul et al [11] studied experimentally the evolution of flow structures during the laminar–turbulent transition in the spherical Couette system. The hydrodynamic instabilities were investigated by spectral analysis of time series recorded for different flow regimes. Different flow structures were also simulated numerically by Allaoua and Bouabdallah [9]. They presented the velocity time series and power spectral density corresponding to three type of instabilities, i.e. the spiral mode and wavy mode (SM+WM), the wavy mode (WVF) and the chaotic fluctuation (CF). The relaminarization phenomenon has been experimentally investigated in spherical Taylor–Couette system by Nakabayashi et al [4, 12] and Mahloul et al [10]. These studies have shown the similarity of evolution of the fluctuation intensity in this flow by the use of two different methods. The aim of this work is experimental investigation of the spherical Taylor-Couette flow by classical visualization and electrodiffusion technique. The results obtained allow us to present the evolutions of the mean friction coefficient f * as a function of the Taylor number Ta. Spectral analysis of the time series permitted the identification of several bifurcation path obtained by the classical visualization during the laminar–turbulent transition. 2. Experimental apparatus and electrodiffusion technique The experimental apparatus shown in Fig. 1 consists of two concentric spheres made of transparent Plexiglas. The inner one is rotated and the outer one remains at rest. The inner and outer spheres have a radius of R ih = 49.6mm and R oh =54.9 mm, respectively, resulting in the gap width d = R oh – R ih = 5.3 mm TOPICAL PROBLEMS OF FLUID MECHANICS 221 _______________________________________________________________________ DOI: https://doi.org/10.14311/TPFM.2017.028