Computational Bio-FSI Laboratory, Department of Mechanical Engineering, School of Engineering & Computing Sciences, New York Institute of Technology, United States
Corresponding author details:
Computational Bio-FSI Laboratory Department of Mechanical Engineering
School of Engineering & Computing Sciences New York Institute of Technology
Copyright: © 2018 Toma M. This is an openaccess article distributed under the terms of the Creative Commons Attribution 4.0 international License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Validation is the assessment of the accuracy of computational simulations by comparison
with experimental data. A well validated computational fluid dynamics model can be of
high importance when assessing the safety of medical devices. However, its validation
and verification must be conducted before the results can be considered credible. The U.S.
Food and Drug Administration has completed a computational inter-laboratory study that
showed relatively negative current state of numerical methods used for simulating fluid
flow in an idealized medical device, even by self-ascribed experts. Yet, the same numerical
methods are commonly used to simulate fluid flow in much more complex geometries,
especially when patient-specific geometries need to be used. The study presented here recreated these results with larger number of participants and confirmed the need for proper
validation of the numerical methods used. Moreover, the results were analyzed with respect
to the use of grid refinement study by the participants.
Computational Fluid Dynamics; Medical Device; Fluid Flow; Validation; Simulation
To assess the current state of methods used for simulating fluid flow in an idealized medical device, the U.S. Food and Drug Administration (FDA) has completed a Computational Fluid Dynamics (CFD) inter-laboratory study [1,2]. The FDA’s study used generic medical device consisting of a 0.012 m diameter cylindrical nozzle followed by a sudden contraction and 20° conical diffuser, on either side of a 0.04 m long, 0.004 m diameter throat (Figure 1). Planar particle Image Velocimetry (PIV) measurements performed at three laboratories were used to validate the data provided by 28 computational results from around the world. In the FDA study, model dimensions, volumetric flow rates, and fluid properties were specified; while flow solver, mesh density, element shape, inlet/outlet, length, boundary condition details, and laminar or, turbulence models, were left up to participants. Participants were asked to do a grid refinement study to confirm the convergence of their results. Consequently, the CFD results were compared to PIV data obtained in three laboratories. To show the results of the above mentioned study, two of the graphs were recreated (traced) based on the data from  (Figure 2). The FDA study-predicted centerline axial velocities in the entry region and conical contraction were in good agreement with the experimental results, but considerable scatter was observed in the throat region and downstream of the sudden expansion. Interestingly, a self-ascribed level of expertise by the project participants did not correlate qualitatively with the success of the validation, i.e. comparing axial centerline velocity predicted by CFD to that measured by PIV.
Figure 1: The geometry of the generic medical device consisting of a 0.012 m diameter
cylindrical nozzle followed by a sudden contraction and 20° conical diffuser, on either
side of a 0.04 m long, 0.004 m diameter throat