TRANSITION TO TURBULENCE ON A ROTATING FLAT DISK

Experimental data from one-point measurements obtained in a transitional flow on a rotating flat disk are presented and analyzed by using biorthogonal decomposition techniques. The analysis is performed at various Reynolds numbers from slightly above the onset of the first instability to the transition to turbulence. As Reynolds number increases, biorthogonal spectra become broader and the entropy characterizing the distribution of energy among the various biorthogonal modes increases. Details of this increase are studied by analyzing local entropy maxima corresponding to eigenvalue degeneracies. At these values of the Reynolds number, internal bifurcations, responsible for a lack of smoothness in the dependence of the flow with Reynolds number, are shown to occur.