Flow simulations are performed on single-phase flow in a baffled tank stirred by a Rushton turbine at a Reynolds number of 40000. The flow physics are discussed, and the benefits of a scale-adaptive simulation (SAS) compared with classical unsteady Reynolds-averaged Navier-Stokes (URANS) models are highlighted. The effect of geometry simplifications, i.e., infinitely thin blades, is illustrated. Furthermore, due to the existence of low-frequency flow instabilities, the necessity of utilizing a full 360° computational domain and the consideration of up to 150 impeller revolutions in the simulation is demonstrated. By a zonal grid refinement within the blade and wake region, the successively resolved portion of the turbulent spectrum is investigated. Even on computational grids typically employed for URANS simulations, the SAS shows a considerably improved prediction of mean velocity and turbulence statistics, compared with conventional URANS models, and should thus be preferred, e.g., to an under-resolved large eddy simulation (LES).