Aspect ratio influence on the stability of Taylor-Couette flow

The study deals with the effect of the fluid height on the stability of the Taylor-Couette flow of a Newtonian fluid between two coaxial cylinders, the upper surface of the fluid system being free. The exploration of the flow regimes is carried out for different values of the Taylor number Ta and of the aspect ratio Γ. By means of polarographic technique, we have determined the temporal mean value of the gradient velocity at the inner wall of the outer cylinder maintained at rest. We also performed the spectral analysis of the fluctuations of the velocity gradient. In order to complete wall measurements, the LDA technique was used to measure particularly the axial velocity component and rotation speed of the azimuthal wave. In this wavy-mode regime, the analysis of the results associated with the fluctuations of the fundamental frequency shows a change in the circumferential wave number. We established that the appearance of the azimuthal wave is delayed when the aspect ratio decreases. In addition we found that below the critical value Γc, the azimuthal wave regime is no longer observed.