SUMMARY

A lattice-Boltzmann based suspension solver has been developed to simulate whole blood with deformable red blood cells (RBCs) and rigid platelets. A coarse-grained (Pivkin and Karniadakis, 2008) spectrin-link method has been coupled with a lattice-Boltzmann suspension flow solver (MacMeccan et al., 2009) to capture RBC membrane deformations and dynamics in isolation and in dense suspensions characteristic of whole blood. The standard bounce-back lattice-Boltzmann boundary condition was used to enforce the no-slip condition on the surface of each RBC membrane and on vessel walls. Simulations were performed to study rheological effects in unbounded shear using the Lees–Edwards boundary condition and compared to rotational viscometer results. Hagen–Poiseuille flow simulations were performed in rigid vessels for investigating the change in cell-depleted layer thickness with shear rate, the Fahraeus–Linqvist effect, and the process of platelet margination. The method has been parallelized to perform simulations on as many as 4,096 cores with as many as 12,288 deformable red blood cells using the parallelization methodology of Clausen et al., 2010. The particle-phase normal stress tensor was analyzed for suspensions in unbounded shear, which demonstrated a change in sign of the particle-phase pressure from low to high shear rates due to the RBCs transitioning from a compressive state to a tensile state in the flow direction. Non-Newtonian effects such as viscosity shear thinning were observed for shear rates ranging from 14-440 sec-1 as well as the dependence of viscosity on hematocrit. An increase in membrane bending energy was shown to be an important factor for determining the orientation of RBCs in a suspension, which ultimately affects rheological properties. The shear stress on platelets was observed to be higher than the average shear stress in blood. The process of platelet margination was shown to be sensitive to platelet shape, hematocrit, and suspending fluid viscosity.