Development of a High Dynamic Velocity Range Processing Scheme for Time-Resolved Particle Image Velocimetry Measurements
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The development, validation, and demonstration of a novel computational procedure to supplementally process time-resolved particle image velocimetry (TR PIV) measurements are described. The motivation for such work stems from an experimental investigation to characterize the near-nozzle velocity field in a high-temperature, shock-containing jet. The computational procedure, termed dynamic evaluation via ordinary least squares (DEVOLS), offers substantial improvements over conventional processing methods for its ability to increase the dynamic velocity range. Unique to DEVOLS is an iterative validation scheme that enables a variable number of displacement results to be utilized in the determination of a single velocity vector. This approach is significant since it provides enhanced robustness in the presence of significant image noise. Validation of the procedure is provided through the use of temporally resolved, synthetically generated particle images simulating the fluid dynamics of a Hamel-Oseen vortex. Following such validation, the experimental investigation is described wherein TR PIV measurements were acquired for a flow field centered axially at the end of the jet potential core and radially along the lower half of the shear layer. For all cases the nozzle was operated at over-expanded conditions, and images were acquired through the combined use of a pulse burst laser and a high-speed, gated intensified CCD framing camera. Results achieved by the DEVOLS processing scheme are presented for both the experimental jet as well as a synthetic jet derived from computational fluid dynamics. Estimations of the measurement errors associated with these results are also given. Finally, steps for improving the quality of the experimental data as well as the analysis procedure are offered as suggestions for future investigations.