Convergence study and uncertainty quantification of average and statistical PIV measurements in a matched refractive index 5×5 rod bundle with mixing vane spacer grid

A new combination of materials with matched indices of refraction was used in average and statistical PIV analysis of a 5×5 rod bundle with prototypical pressurized water reactor (PWR) mixing vane spacer grids. The new combination of materials shows improved matching of refractive index which enabled detailed PIV measurement of subchannel flow, even when viewed through a relatively large number of material interfaces. Convergence of average full field PIV measurements at ∼27,000 Reynolds number was demonstrated as independent of measurement plane depth relative to camera view window. A method for average vector post-processing elimination is proposed using validation statistics from PIV. The proposed method shows potential for eliminating vectors in areas of poor-convergence for planes with little interfering geometry. A full uncertainty quantification was performed on the full field of each PIV measurement planes. Similar to convergence rates, uncertainty demonstrated independence from measurement plane depth. Additional material interface between camera and measurement plane does not appear to have affected instantaneous velocity measurements' contribution to average vector fields. Symmetric measurement planes were compared between 2 rod pitch intervals of the spacer grid. Velocity and statistically derived quantities show good coherence between symmetric planes. Measurements near and even below the tips of the mixing vanes were collected and analyzed.