Bifurcation scenario in wide gap Spherical Couette Flow

In wide gap Spherical Couette Flow a complex route into chaos can be observed experimentally. By increasing the Reynolds number Re=R-1(2) omega/v with the angular velocity omega of the driving inner sphere (radius R-1) the flow bifurcates laminar axisymmetric basic flow to the periodic motion of non-axisymmetric secondary spiral waves for relative gap width beta=R2-R1/R1 greater than or equal to 0.3, with R-2 as the radius of the outer spherical shell [1]. In the present study a relative gap width of beta=0.5 is chosen. The spiral waves exist over a wide range of the Reynolds number. In this range a change in shape and periodicity can be detected by visualization with small aluminum flakes and also measured by Laser Doppler Measurement (LDV) technique. At high Reynolds numbers, the flaw undergoes a bifurcation to low-dimensional chaotic motion before it eventually becomes turbulent. The dynamic behaviour is discussed by spectral bifurcation diagrams, reconstructed attractors and their Lyapunov exponents as a quantitative parameter. These quantities are calculated from the measured LDV time series.