Computational hemodynamics: Hemolysis and viscoelasticity
Behr, Marek; Pasquali, Matteo
Doctor of Philosophy
Computational Fluids Dynamics (CFD) has emerged as a viable and reliable design tool for the analysis of blood-handling devices. The CFD-based design is simple, time- and cost-effective; the method predicts accurately the hydraulic performance of these devices. However, the CFD-based hematologic design is in its infancy. This thesis presents a holistic design approach for centrifugal blood pumps. The flow through the pump is simulated with a novel finite element method that accounts efficiently for deformable domains and moving parts while retaining desirable scalability on distributed-memory computers. The method is validated successfully against literature results in a benchmark problem of flow past a stirrer in a square cavity. Blood is treated as a Newtonian fluid in these initial simulations. However, blood is known to display shear-thinning and viscoelasticity; a generalized Newtonian model is employed to capture the shear-thinning blood viscosity, and the flow through the GYRO pump (Baylor College of Medicine) is simulated in typical operating conditions. The overall hydraulic performance predicted by the shear-thinning model show little difference compared to the Newtonian results. However, the shear-thinning model predicts smaller recirculation regions and higher values of wall shear stress. For simulating viscoelasticity, a new family of three-field Galerkin/Least-Squares stabilized finite element methods is constructed and evaluated in the benchmark flow past a cylinder placed in a channel. The results are compared with the state-of-the-art numerical results and good agreement is found for the drag predictions. Mesh convergence is demonstrated for the new methods. Finally, a new tensor-based blood-damage model is proposed; the model is based on the analogy between red blood cells and fluid droplets. The model is compared with the traditional method of hemolysis prediction in homogeneous steady and unsteady flows and inhomogeneous time-dependent flow in two-dimensional and three-dimensional blood pump. The predictions of hemolysis by the tensor-based method are found to agree well with flow-loop experimental results on bovine blood in the GYRO pump.
Biomedical engineering; Chemical engineering; Mechanical engineering