The turbulent gas-liquid flow field in an industrial 100-m(3) stirred tank was calculated by using computational fluid dynamics based on the finite-volume method. Turbulent effects were modeled with the shear stress transport model, and gas-liquid bubbly flow was modeled with the Eulerian-Eulerian approach using the Grace correlation for the drag force interphase momentum transfer. The relative motion between the rotating impeller and the stationary baffled tank was considered by using a multiple frames of reference algorithm. The effects of Rushton and pitched-blade impeller design parameters such as blade geometry, location, and pumping direction on the mixing performance were investigated. It was found that a combination of Rushton turbines with up-pumping pitched-blade turbines provides the best mixing performance in terms of gas holdup and interfacial area density. The approach outlined in this work is useful for performance optimization of biotechnology reactors, as typically found in fermentation processes.