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Simulated time-dependent data to estimate uncertainty in fluid flow measurements

Abstract:

Positron Emission Particle Tracking (PEPT) is an emerging measurement technique for Lagrangian data collection in experimental fluid flows. The nature of the measurement extends the study of turbulent flows to applications lacking optical access. A simulated pipe flow PEPT measurement is used in this work to verify reconstruction algorithm and identify novel sources of uncertainty. Simulated measurement occurs in a 38 mm diameter pipe with 0.55 m/s mean flow velocity and Reynolds number equal 21,000. Flow is simulated using computational fluid dynamics (CFD), generating 1000 time-dependent trajectories of tracers from CFD to prescribe movements of 40 µCi, fluorine-18-point sources. Geant4 Application for Tomographic Emission (GATE) simulates the response of the Inveon Pre-Clinical scanner model and produces an array of coincidence lines for the prescribed sources. The array is provided to a multiple PEPT (mPEPT) code reconstructing the position of simulated tracers and assigns positions to coherent trajectories. The mPEPT reconstructed trajectories are compared to prescribed positions. Reconstruction of 754 trajectories is achieved with measurement bias centered at 0.0 mm in all directions and standard deviation of 0.29 mm, 0.29 mm, and 0.30 mm in the x, y, and z component respectively using 2.0 ms time-steps. Two instances of position misassignments induced by the close-approach of two tracers in measurement volume are identified. This is a novel reconstruction error to PEPT measurements, unable to be identified without prior knowledge of tracer trajectories provided by these simulation tools.