Verification Benchmarks to Assess the Implementation of Computational Fluid Dynamics Based Hemolysis Prediction Models

Abstract

As part of an ongoing effort to develop verification and validation (V&V) standards for using computational fluid dynamics (CFD) in the evaluation of medical devices, we have developed idealized flowbased verification benchmarks to assess the implementation of commonly cited powerlaw based hemolysis models in CFD. The verification process ensures that all governing equations are solved correctly and the model is free of user and numerical errors. To perform verification for powerlaw based hemolysis modeling, analytical solutions for the Eulerian powerlaw blood damage model (which estimates hemolysis index (HI) as a function of shear stress and exposure time) were obtained for Couette and inclined Couette flow models, and for Newtonian and nonNewtonian pipe flow models. Subsequently, CFD simulations of fluid flow and HI were performed using Eulerian and three different Lagrangianbased hemolysis models and compared with the analytical solutions. For all the geometries, the blood damage results from the Eulerianbased CFD simulations matched the Eulerian analytical solutions within ∼1%, which indicates successful implementation of the Eulerian hemolysis model. Agreement between the Lagrangian and Eulerian models depended upon the choice of the hemolysis powerlaw constants. For the commonly used values of powerlaw constants (خ±  = 1.9–2.42 and خ²  = 0.65–0.80), in the absence of flow acceleration, most of the Lagrangian models matched the Eulerian results within 5%. In the presence of flow acceleration (inclined Couette flow), moderate differences (∼10%) were observed between the Lagrangian and Eulerian models. This difference increased to greater than 100% as the beta exponent decreased. These simplified flow problems can be used as standard benchmarks for verifying the implementation of blood damage predictive models in commercial and opensource CFD codes. The current study used only a powerlaw model as an illustrative example to emphasize the need for model verification. Similar verification problems could be developed for other types of hemolysis models (such as strainbased and energy dissipationbased methods). And since the current study did not include experimental validation, the results from the verified models do not guarantee accurate hemolysis predictions. This verification step must be followed by experimental validation before the hemolysis models can be used for actual device safety evaluations.