A semi-implicit immersed boundary method and its application to viscous mixing

• A semi-implicit finite volume immersed boundary method based is developed.
• It is parallel and compatible with unstructured meshes and dynamic mesh refinement.
• Its accuracy is similar to that of sliding mesh and single reference frame techniques.
• It is flexible enough to simulate flows in stirred tanks with overlapping impellers.
• It can be part of solid–liquid mixing CFD-DEM models.

Computational fluid dynamics (CFD) simulations in the context of single-phase mixing remain challenging notably due the presence of a complex rotating geometry within the domain. In this work, we develop a parallel semi-implicit immersed boundary method based on Open∇FOAM, which is applicable to unstructured meshes. This method is first verified on academic test cases before it is applied to single phase mixing. It is then applied to baffled and unbaffled stirred tanks equipped with a pitched blade impeller. The results obtained are compared to experimental data and those predicted with the single rotating frame and sliding mesh techniques. The proposed method is found to be of comparable accuracy in predicting the flow patterns and the torque values while being straightforwardly applicable to complex systems with multiples impellers for which the swept volumes overlap.