Comparative CFD analysis of flow direction in the FDA benchmark nozzle

Computational fluid dynamics (CFD) is a widely used method for analyzing and optimizing blood-contacting medical devices. Standardized CFD methodologies are crucial for modeling physiological flow conditions. Therefore, benchmark models such as the FDA nozzle play an essential role in validating simulations across various flow regimes. This study investigates the effect of two distinct flow directions, as defined by the FDA standard geometry (gradual cone, GC, and sudden contraction, SC), on hemodynamic parameters. Previous studies mainly focused on a single configuration of the FDA nozzle, and no analysis directly compares the GC and the SC under the same experimental conditions. Five different flow conditions, with throat Reynolds numbers from 500 to 6500, were analyzed for both configurations using ANSYS Fluent. Velocity, turbulence intensity, dynamic pressure, and wall shear stresses were computed and compared. Differences in the spatial distribution of peak velocity were observed between the GC and SC configurations. In contrast, lower maximum wall shear stress and dynamic pressure values were observed in the SC configuration. Hemodynamic loads stayed elevated over longer axial distances in the SC, while these peaks were localized more sharply in the GC configuration. These findings demonstrate the effect of flow direction on stress distributions in the FDA nozzle and provide insight into CFD validation and blood damage modeling.