MRF Method: Mixing Tank

MRF Method — Mixing Tank CFD Simulation, ANSYS Fluent

Description

This project simulates a stirred mixing tank in ANSYS Fluent using the Multiple Reference Frame (MRF) method — the first of three mixing-tank studies that model the same tank with three different rotating-frame approaches. A mixing tank uses a rotating impeller to blend fluid, and it's a workhorse of chemical, pharmaceutical, food, and wastewater processing. The MRF method represents the spinning impeller through a rotating reference frame while the tank stays stationary, giving a steady-state picture of the flow at a fraction of the cost of a fully transient simulation. Within the Rotary Equipment: Beginner CFD Training Package, this project opens the three-part mixing-tank method comparison, establishing the MRF approach as the baseline against which the SRF and mesh-motion methods that follow are compared.

Methodology

The 3D model is created in ANSYS Design Modeler and meshed in ANSYS Meshing with 229,177 unstructured elements. The domain is divided into multiple zones for the MRF method — a rotating zone around the impeller and a stationary zone for the rest of the tank. The case is set up as a steady-state analysis with the k-ε turbulence model, and the boundary conditions define a 500 rpm impeller rotation within the stationary tank. This arrangement captures the effect of the rotating impeller on the surrounding fluid without physically moving the mesh, keeping the analysis steady and efficient.

Analysis

Post-processing extracts pressure, velocity, and turbulent-intensity contours along with flow vectors around the impeller. The pressure field shows the variations around the impeller and their effect on mixing across the different zones; the velocity profiles reveal the flow patterns, particularly behind the impeller, and how they correlate with mixing effectiveness; and the turbulence-intensity field shows where the mixing is most vigorous, especially near the impeller. The flow vectors reveal the vortex formation that governs mixing efficiency. By the end of this project, you'll be able to set up a multi-zone MRF simulation of a stirred tank, define the rotating and stationary zones and impeller speed, and interpret the pressure, velocity, and turbulence fields to assess mixing performance — the baseline for comparing the SRF and mesh-motion methods in the next two projects.