The turbulent flow between two rotating stirrers: similarity laws and transitions for the driving torques fluctuations

Instantaneous torques driving the turbulent flow between two rotating disks equipped with blades and enclosed in a fixed cylindrical cell are measured. The flow is studied by varying the rotational frequency of one stirrer while the other is set to a fixed rotational frequency. Many flow configurations, defined as the rotational frequency ratio S of the disks are studied from the co- to the counter-rotating regimes. For the entire range of S, the driving torques, means and fluctuations give a satisfactory match with similarity laws having no dependence on the Reynolds number. This allows the study to be restricted in the range S = [- 1 ; + 1]. In the detail, the counter-rotating regime seems to be insensitive to the Reynolds number in the range - 1.33 < S < - 0.69 that correspond to the well known two cell structure configuration. On the contrary, a significant dependence with the Reynolds number is found for the co-rotating regime. Flow transitions marked by strong torque fluctuation crisis are observed for both the co- and counter-rotating regimes. Mean flow visualization elucidates the flow topology corresponding to these transitions.