Knowledge of the fluid dynamic characteristics in a stirred vessel is essential for reliable design and scale-up of a mixing system. In this paper, 3D hydrodynamics in a vessel agitated by a Rushton turbine were numerically studied (with the help of a CFD computer program (CFX 13.0)). The study was carried out covering a wide Reynolds number range: 104 - 105. Computations, based on control volume method, were made using the k-ε model. Our main purpose was to investigate the effect of vessel configuration and agitation rates on the flow structure and power consumption. Three types of vessels were used: unbaffled, baffled and a vessel with slots placed at the external perimeter of its vertical wall. The effect of slot length has been investigated. The comparison of our predicted results with available experimental data shows a satisfactory agreement.