BIOMEDICAL RESEARCH AND REVIEWS

ISSN 2631-3944

Computational Fluid Dynamics Simulations Using FDA’s Idealized Medical Device Demonstrating the Importance of Model Validation

Milan Toma*

Computational Bio-FSI Laboratory, Department of Mechanical Engineering, School of Engineering & Computing Sciences, New York Institute of Technology, United States

CitationCitation COPIED

Toma M. Computational Fluid Dynamics Simulations Using FDA’s Idealized Medical Device Demonstrating the Importance of Model Validation. Biomed Res Rev. 2018 Jul;1(1):104.

Abstract

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.

Keywords

Computational Fluid Dynamics; Medical Device; Fluid Flow; Validation; Simulation

Introduction

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 [3] (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