Establishment, validation, and application of thixotropic fluid startup flow algorithms

Thixotropic fluids are prevalent in industrial processing, medical applications, and everyday consumer products, and accurate prediction of their transient startup flow between flat plates is crucial for ensuring the stability of processes such as food and drug delivery, three-dimensional printing, and lithium battery electrode coating. Owing to their time-dependent structural breakdown and recovery, along with the complex coupling with viscoelasticity and viscoplasticity, most existing studies focus primarily on rheological experimental characterization or on the computation of simplified models, making it challenging to accurately simulate the startup flow field of constitutive thixotropic models at a fine-grained level. This study develops a numerical algorithm for pressure-driven startup flow between flat plates based on the isotropic–kinematic–hardening (IKH) thixotropic viscoelastic–plastic model. An analytical solution for the steady-state flat-plate Poiseuille flow is derived for both this model and conventional fluid models to validate the algorithm's accuracy. The algorithm decouples the governing equations from the constitutive relations by iteratively updating the wall shear stress, enabling robust computation of transient flows in complex fluid–structure dynamics, and allows visualization of the flow field at any time using a self-developed data conversion tool. Results indicate that IKH fluids exhibit pronounced structural evolution and distinct startup flow behaviors under varying model parameters, and that the relationship between model parameters, startup flow success, and steady-state flow rate can be quantitatively characterized. Furthermore, the proposed computational framework offers a reliable basis for predicting and optimizing processes involving thixotropic structural dynamics models.