  Flows through medical devices as well as in anatomical vessels despite being
at moderate Reynolds number may exhibit transitional or even turbulent
character. In order to validate numerical methods and codes used for biomedical
flow computations, the U.S. food and drug administration (FDA) established an
experimental benchmark, which was a pipe with gradual contraction and sudden
expansion representing a nozzle. The experimental results for various Reynolds
numbers ranging from 500 to 6500 were publicly released. Previous and recent
computational investigations of flow in the FDA nozzle found limitations in
various CFD approaches and some even questioned the adequacy of the benchmark
itself. This communication reports the results of a lattice Boltzmann method
(LBM) based direct numerical simulation (DNS) approach applied to the FDA
nozzle benchmark for transitional cases of Reynolds numbers 2000 and 3500. The
goal is to evaluate if a simple off the shelf LBM would predict the
experimental results without the use of complex models or synthetic turbulence
at the inflow. LBM computations with various spatial and temporal resolutions
are performed - in the extremities of 44 million to 2.8 billion lattice cells -
conducted respectively on 32 CPU cores of a desktop to more than 300'000 cores
of a modern supercomputer to explore and characterize miniscule flow details
and quantify Kolmogorov scales. The LBM simulations transition to turbulence at
a Reynolds number 2000 like the FDA's experiments and acceptable agreement in
jet breakdown locations, average velocity, shear stress and pressure is found
for both the Reynolds numbers.

Fluid Dynamics;Distributed, Parallel, and Cluster Computing;Cellular Automata and Lattice Gases;Biological Physics