The flow energy efficiency of different impellers for stirring rheologically complex fluids (yield stress fluids) in cylindrical tanks has been investigated in this paper. Four impellers have been used: a Maxblend, an anchor, a gate and a double helical ribbon impeller. Our investigations were achieved via numerical simulations with the help of a CFD (computational fluid dynamics) computer program CFX 13.0. It was found from the predicted results that the Maxblend impeller gives the best performance. The effects of some design parameters on the flow energy efficiency and the power consumption have been also studied; it concerns the Maxblend impeller: its grid size and its paddle curvature. (C) 2015 Elsevier Ltd. All rights reserved.