Turbulence modeling in the numerical estimation of hemolysis in hemodialysis cannulae

In recent years, CFD has become an increasingly used tool in the design of blood-based devices. Particularly, the estimation of red blood cells damage (hemolysis) becomes a very important challenge to CFD scientists since the blood is a complex fluid present in turbulent regime in most pumping devices. Thus, previous CFD studies on blood hemolysis lack of appropriate turbulence modeling and consequently, reliable relationships between hydraulic results and hematological responses. Cannula geometries were studied to numerically assess a relatively simple flow with well documented laboratory hematological data. For benchmarking purposes, numerical data from a coaxial jet array direct numerical simulation (DNS) was used in the selection of the most appropriate and economical turbulence model to be used in the cannula numerical analysis. Velocity and stress time-averaged profiles were compared between DNS results and RANS simulations with different turbulence models. These results, pointed to the Shear Stress Transport with Gamma-Theta transition model as the appropriate turbulence model in that geometry. Accurate and reliable hydrodynamic CFD results were obtained for the cannula as an important previous step to the study and development of further hematological calculations with a minimum degree of uncertainty in the flow field. These hematological calculations led to interesting results about the important role played by turbulence modeling in hemolysis estimation.