Assessment of CFD Performance in Simulations of an Idealized Medical Device: Results of FDA’s First Computational Interlaboratory Study

Abstract

While computational fluid dynamics (CFD) is commonly used for medical device development, its usefulness for demonstrating device safety has not been proven. Reliable standardized methods for this specialized need are lacking and are inhibiting the use of computational methods in the regulatory review of medical devices. To meet this need, participants from academia, industry, and the U.S. Food and Drug Administration recently completed a computational interlaboratory study to determine the suitability and methodology for simulating fluid flow in an idealized medical device. A technical working committee designed the study, defined the model geometry and flow conditions, and identified comparison metrics. The model geometry was a 0.012 m diameter cylindrical nozzle with a conical collector and sudden expansion on either side of a 0.04 m long, 0.004 m diameter throat, which is able to cause hemolysis under certain flow conditions. Open invitations to participate in the study were extended through professional societies and organizations. Twenty-eight groups from around the world submitted simulation results for five flow rates, spanning laminar, transitional, and turbulent flows. Concurrently, three laboratories generated experimental validation data on geometrically similar physical models using particle image velocimetry. The simulations showed considerable variation from each other and from experiment. One main source of error involved turbulence model underestimations of the centerline velocities in the inlet and throat regions, because the flow was laminar in these regions. Turbulence models were also unable to accurately predict velocities and shear stresses in the recirculation zones downstream of the sudden expansion. The wide variety in results suggest that CFD studies used to assess safety in medical device submissions to the FDA require careful experimental validation. Better transitional models are needed, as many medical devices operate in the transitional regime. It is imperative that the community undertake and publish quality validation cases of biofluid dynamics and blood damage that include complications such as pulsatility, secondary flows, and short and/or curved inlets and outlets. The results of this interlaboratory study will be available in a benchmark database to help develop improved modeling techniques, and consensus standards and guidelines for using CFD in the evaluation of medical devices.