Phase-resolved particle image velocimetry measurements were carried out to assess the flow dynamics occurring in orbitally shaken bioreactors of cylindrical geometry when working fluids of increasing viscosity are considered. Study of the phase-resolved flow characteristics allowed to built a Re-Fr map, where four quadrants associated to different flow regimes are identified: in-phase toroidal vortex (low Fr and high Re), out-of-phase precessional vortex (high Fr and high Re), in-phase single vortex (low Fr and low Re), out-of-phase counter-rotating toroidal vortex (high Fr and low Re). Turbulence levels are found to be significant only in the top right quadrant (high Fr and low Re) and scaling of the turbulent kinetic energy obtained with fluid of varying viscosity is obtained using the ratio of the operating Froude number to the critical Froude number associated to the mean flow transition, Fr/Fr-c. Estimates of the mean flow strain deformation as well as of the flow dissipative scale are provided, while a comparison is made between the flow circulation times obtained for different regimes. (C) 2014 American Institute of Chemical Engineers