Lagrangian-Based Characterisation of Aerated Stirred Tank Reactors

Industrial-scale bioreactors expose cells to complex and continuously changing hydrodynamic conditions that are difficult to reproduce at laboratory scale. Conventional scale-down approaches are often developed under single-phase conditions and evaluated primarily using mixing times. This work combines experiments and validated Lattice-Boltzmann Large-Eddy Simulations to characterise the multiphase hydrodynamics of a 15 m³ mammalian cell culture stirred tank reactor. A Lagrangian, cell-centred perspective is used to quantify the conditions experienced by cells through velocity distributions, circulation times, residence times, and lifelines. Finite-Time Lyapunov Exponent fields additionally reveal coherent flow structures and transport barriers. The methodology is applied to evaluate the Single Multi-Compartment Bioreactor as a representative scale-down system. The results show that similarity achieved under single-phase conditions does not necessarily persist during aeration, highlighting the need to incorporate multiphase lifeline metrics into scale-down development and evaluation.