Analyse de la turbulence pariétale de l'écoulement annulaire tourbillonnaire non entretenu généré par une entrée tangentielle du fluide

This work is dedicated to an experimental study of the wall shear stress in a turbulent swirling decaying flow induced by means of a tangential inlet in an annular cell. The flow pattern near both cylinders of the annulus is analyzed by means of measurements of wall velocity gradients using an electrochemical method involving micro-electrodes working in inert wall. The analysis of the axial and circumferential evolutions of the mean wall velocity gradient and of its power spectral density emphasizes the complexity and highly three-dimensional nature of the flow pattern of the annular swirling decaying flow induced by means of a single tangential inlet. Near the inner wall of the annulus, a recirculating zone, consisting of several pairs of contra-rotating cells, develops following the main helical motion of the fluid along the flow path. Near the external wall of the annular cell, high local velocities and energetic turbulent structures are detected in the vicinity of the tangential inlet. These eddies rapidly decay along the flow path because of the decrease of the swirl intensity. The setup of a recirculation bubble near the inner wall induces a quasi-axisymmetric flow behavior at the outer cylinder of the annulus. Near both walls, the power spectral densities of the velocity gradient reveal a superposition of small turbulent eddies having a low energetic level in the high-frequency domain.