High-resolution CFD results, supplemented by extensive experimental validation, are presented for Newtonian laminar flow fields in a stirred tank equipped with three Rushton turbines. Flow fields are computed using the ORCA software suite for Reynolds numbers ranging from 20 to 200 with an unstructured tetrahedral mesh containing roughly 2 million tetrahedra. Each of the flow solutions takes less than 8 h to converge when running in parallel on eight desktop workstations. Excellent agreement is obtained between computed velocity fields and planar velocity vectors obtained using particle image velocimetry. Planar laser-induced fluorescence was used to expose persistent poor-mixing regions, in excellent agreement with numerical results. The computational results used illustrate strong flow compartmentalization and significant spatial heterogeneity with respect to local deformation rates within the vessel.