PIV measurements using refraction at a solid/fluid interface

TL;DR

This paper introduces a novel refracted PIV (R-PIV) technique using laser refraction at a solid/fluid interface, supported by ray tracing and an extended cross-correlation model, to improve flow measurements in optically limited environments.

Contribution

It develops a new R-PIV method with an extended cross-correlation model to address optical refraction limitations in flow measurements.

Findings

Ray tracing quantifies laser sheet propagation and illumination intensity.

The extended CCM analyzes image pairs considering optical refraction effects.

Comparison with P-PIV in a known flow validates the R-PIV approach.

Abstract

Laser light sheet refraction at the fluid flow/window interface is proposed to proceed fluorescent PIV measurements, in particular for cases for which optical access limits the possibilities of illuminating a flow with a planar collimated light sheet. The study of the laser sheet propagation for the present measurement method is led with ray tracing to quantify the illumination intensity. To describe the limitations of this developed PIV version (the R-PIV), we proposed a cross-correlation model (CCM) for analysing image pairs and that is an extension of the ones used in the cases of $\mu$-PIV or P-PIV techniques. This cross-correlation model accounts for the R-PIV optical constraints as 1) in-depth and longitudinal inhomogeneities of the light sheet refraction at the location of the object plane or 2) integration in depth of the fluorescence from seeding particles. This refracted PIV (R-PIV) and the P-PIV techniques are further compared in the case of an academic pipe flow whose analytic solution is known. Our extended cross-correlation model function is finally applied, knowing the theoretical flow velocity, the flow illumination and the seeding flow parameters, to analyse some error levels in determining the real flow velocity field.