Eulerian flow field estimation from particle trajectories: Numerical experiments for stirred tank type flows

The computer automated radioactive particle tracking (CARPT) and positron emission particle tracking (PEPT) techniques have been developed to characterize opaque multiphase flows. In CARPT and PEPT, the Eulerian flow field is inferred from the knowledge of reconstructed tracer particle trajectories. The present study was undertaken to assess the strengths and limitations of the process of estimating the Eulerian flow field from particle trajectories. A two-dimensional problem, which mimics the characteristics of flow in a stirred tank reactor equipped with a standard Rushton turbine, was considered. The Eulerian flow field was numerically simulated. Care was taken to minimize effects of numerical issues on the computed flow field, which was then used to calculate particle trajectories. Standard CARPT data processing was carried out on the simulated particle trajectories to estimate the Eulerian flow field. This estimated flow field was compared with the original flow field used for trajectory simulations to evaluate possible errors associated with the CARPT data processing and flow follow-ability of the particles. Influence of grid used for data processing, sampling frequency, and particle size and particle density on the estimated flow field was examined. The study highlights several issues pertaining to the estimation of the Eulerian flow field from Lagrangian information. The results provide guidelines for selecting appropriate parameters in processing of CARPT or PEPT data.