Chemical process industries use stirred tank reactors (STR) for a variety of mixing and blending operations. Turbulent flow inside a baffled stirred tank reactor with a 45° pitched blade impeller is numerically studied using a large-eddy simulation (LES) technique with a body-fitted curvilinear mesh. The moving impeller geometries are modeled using an immersed boundary method (IBM). The instantaneous as well as time-averaged flow field suggests formation of trailing vortex due to the interaction of the fluid streams from the side and top edges of the blade. An enhanced distribution of turbulent kinetic energy has been observed in the vicinity of the trailing vortices. Instabilities occurring at a frequency lower than the frequency of impeller rotation are noticed from the time signal of the velocity components. The growth and break-up of the trailing vortices with this macro-instability frequency is observed. Turbulence is shown to be strongly anisotropic.

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