Flow patterns and red blood cell dynamics in a U-bend

The flow of cells in curved vessels is often accompanied by a secondary flow, which plays an important and practical role in various biomedical and bioengineering applications. However, there have been few attempts to investigate how the cells affect the development of the secondary flow in those curved microvessels. In this work, we use a particle-based model, smoothed dissipative particle dynamics, to numerically simulate the flow of red blood cells (RBCs) in a U-bend, with a diameter comparable to the RBC diameter. We first carry out three validation studies on the flow field, the cell deformation, and the cell aggregation, respectively, to establish the model predictive capability. Then, we study the formation and development of the secondary flow in a U-bend for the suspending (Newtonian) fluid, followed by exploring the disturbance of a single RBC and multiple RBCs to the secondary flow. The simulation results show that a secondary flow is developed in the U-bend for the suspending fluid, with a pair of Dean vortices. When a single RBC is suspended in the fluid, the secondary flow is disturbed, which is implemented by a transition from two to four and then back to two vortices again. This is the first time to show that cells can initiate such transition in a curved bend. When multiple RBCs are suspended in the fluid, the secondary flow becomes less likely to occur as the RBC number increases. On the contrary, the flow becomes more developed with increasing intercellular interactions. Published by AIP Publishing.