Bioreactor: Agitated by Rushton Turbine

Description

This project simulates fluid mixing inside a bioreactor agitated by a Rushton turbine using ANSYS Fluent, a mixing configuration widely used in pharmaceutical, food, biochemical, and perfumery applications wherever biochemical reactions require thorough fluid homogenization. The bioreactor is cylindrical, 0.8 m tall and 0.4 m in diameter, with a vertical stirrer mounted along its central axis. That stirrer is a Rushton-type turbine, a radial-flow impeller consisting of two rows of flat discs, each carrying six blades, chosen because radial-flow impellers of this type are a standard choice for mixing applications across process engineering. The geometry is built in Design Modeler and meshed in ANSYS Meshing with 3,558,726 elements, and given the inherently time-evolving nature of the mixing process, a transient solver is used.

Methodology

The rotational motion of the fluid around the Rushton turbine is defined using the Mesh Motion technique, with a distinct cylindrical inner region assigned a rotational velocity of 143 rpm about the vertical (Y) axis to represent the turbine's action on the surrounding fluid. Three rows of baffles line the interior of the bioreactor's cylindrical wall, breaking up the vortices that would otherwise form and reducing unwanted bulk rotation of the whole fluid volume. Turbulence is resolved using the RNG k-epsilon model.

Analysis

The results include 3D contours of pressure gradient, velocity, and turbulent kinetic energy throughout the bioreactor, along with 2D contours of pressure, velocity, and turbulent kinetic energy taken on two planes perpendicular to the stirrer axis, each passing through one of the turbine's disc rows. These fields show velocity and rotational flow intensifying around the impeller blades, exactly where the turbine imparts momentum to the fluid. Velocity vectors, examined in both 2D and 3D, trace how the fluid circulates fully around the stirrer's rotation axis, confirming the Rushton turbine is generating the s