Multilaboratory Particle Image Velocimetry Analysis of the FDA Benchmark Nozzle Model to Support Validation of Computational Fluid Dynamics Simulations

Abstract

This study is part of a FDA-sponsored project to evaluate the use and limitations of computational fluid dynamics (CFD) in assessing blood flow parameters related to medical device safety. In an interlaboratory study, fluid velocities and pressures were measured in a nozzle model to provide experimental validation for a companion round-robin CFD study. The simple benchmark nozzle model, which mimicked the flow fields in several medical devices, consisted of a gradual flow constriction, a narrow throat region, and a sudden expansion region where a fluid jet exited the center of the nozzle with recirculation zones near the model walls. Measurements of mean velocity and turbulent flow quantities were made in the benchmark device at three independent laboratories using particle image velocimetry (PIV). Flow measurements were performed over a range of nozzle throat Reynolds numbers (Re(throat)) from 500 to 6500, covering the laminar, transitional, and turbulent flow regimes. A standard operating procedure was developed for performing experiments under controlled temperature and flow conditions and for minimizing systematic errors during PIV image acquisition and processing. For laminar (Re(throat)=500) and turbulent flow conditions (Re(throat)≥3500), the velocities measured by the three laboratories were similar with an interlaboratory uncertainty of ∼10% at most of the locations. However, for the transitional flow case (Re(throat)=2000), the uncertainty in the size and the velocity of the jet at the nozzle exit increased to ∼60% and was very sensitive to the flow conditions. An error analysis showed that by minimizing the variability in the experimental parameters such as flow rate and fluid viscosity to less than 5% and by matching the inlet turbulence level between the laboratories, the uncertainties in the velocities of the transitional flow case could be reduced to ∼15%. The experimental procedure and flow results from this interlaboratory study (available at http://fdacfd.nci.nih.gov) will be useful in validating CFD simulations of the benchmark nozzle model and in performing PIV studies on other medical device models.

A Quantitative Comparison of Mechanical Blood Damage Parameters in Rotary Ventricular Assist Devices: Shear Stress, Exposure Time and Hemolysis Index

“…For the VADs in this work the shear stress transport (SST)-kx turbulence model [45] was used since it was found to give accurate predictions of the pressure head in the VADs. Additionally in our calculations of flow through a simplified medical device, which we compared with published PIV results [46], it produced accurate velocity fields.…”

Large Eddy Simulation of FDA’s Idealized Medical Device

“…In 2011, Hariharan et al [6] studied the uncertainties related to experimental measurements in an idealized medical device. The goal of this FDA commissioned study was to compare experimental measurements between different laboratories in order to reference the key parameters that can influence experimental measurements.…”

“…RANS-based solvers were used with different turbulence models, and the results were compared to the experimental measurements from Hariharan et al [6]. For the laminar case, simulations were able to capture the absence of break down of the jet downstream of the sudden expansion.…”

“…An in-house code is used, hereafter ( W enoHemo ™ ), that combines high-order finite-difference schemes on structured staggered Cartesian grids with an IBM to facilitate flow over or through complex stationary or rotating geometries and employs a subgrid-scale (SGS) turbulence model that more naturally handles transitional flows [2]. Predictions of velocity and wall shear stress statistics are compared with previously published experimental measurements from Hariharan et al [6] for the four Reynolds numbers considered. …”

Classification of Unsteady Flow Patterns in a Rotodynamic Blood Pump: Introduction of Non-Dimensional Regime Map

“…9,21 For this reason, CFD and flow visualization have become common practice for designing and analyzing these devices and blood-wetted devices in general. 6,7,12,13,22 It is however astonishing that the vast majority of visualization studies with rotodynamic blood pumps are conducted under steady conditions in light of the dramatic effect of the pulsatility on the velocity fields. 10,20 Consequently, it behooves the developers of these devices to consider a representative range of pulsatile hemodynamic physiological conditions.…”