Video Library

Simulation of fluid motion, bubble transport, and oxygen saturation in a lab-scale bioreactor. Ongoing break-up and coalescence events (due to fluid shear and bubble collision) lead to a non-uniform bubble size.

Two-way coupling between the bubbles and the fluid make the flow-field inside a gas-lift bioreactor complex.

Simulation of velocity, bubble growth, and dissolved carbon dioxide accumulation in a tall bioreactor. The time-evolution of the dissolved carbon dioxide reflects the computation between production (via a reaction) and stripping (via transfer to the bubbles).

Here we use combine time-accurate large eddy CFD simulations with discrete particle tracking to predict particle suspension. The system here has 0.2 mm glass beads agitated by a 16″ PBT spinning at 60 RPM. This impeller speed is below the Njs.

Here we inject water into a tank contained a stratified mixture of water and brine. The competition between jet inertia, viscosity, and gravity lead to complex mixing profiles across the vessel.

Here we compare the predicted to measured vortex shape for an unbaffled, bottom-mounted bioreactor. Both systems operate at the same speed and with the same geometry. The only inputs to the model are the fluid density, viscosity, and surface tension.

Does increasing the resolution have a strong effect on simulation predictions? It depends on what you are trying to study. Many bulk flow and mixing processes in agitated vessels can be reproduced using only a few million grid points. Such simulations can provide very good predictions of system-level blend time, power draw, impeller pumping, etc. If you are trying to get more detailed insights into the local turbulence mechanics and micro timescales, you are going to want more resolution. I can send over some journal papers that discuss this point. Mechanistically speaking, within the context of LES, the fineness of the grid spacing informs how much of the turbulent energy spectrum is resolved explicitly by the simulation. That is, the grid spacing informs the minimum eddy length scale that is resolved explicitly by the solver. Sub-grid motions are still incorporated into the fluid mechanics via the eddy viscosity, but their effects are not resolved explicitly. Sometimes this matters, other times it does not.

The lack of baffling in this agitated tank leads to strong azimuthal flow and surface vortexing. Here we show the velocity along a slice through the vessel, as well as the time-evolution of the free surface interface.