Three-dimensional stress measurement of a laminar flow in a rectangular channel using integrated photoelasticity*

The purpose of this study is to measure the shear rate distribution of a laminar flow in a rectangular by using integrated photoelasticity. We measured a mixed solution of photoelastic material, cellulose nanoctystal (CNC), to elucidate whether there are any phenomena peculiar to CNC mixed solution that differ from integrated photoelasticity in the solid case. In addition, we examine the stress-optic law for CNC mixed solution using a high-speed polarization camera to measure the retardation and orientation angles of polarized lights. We compare the measured retardation and theoretical secondary-principal-stress-difference distribution based on the analytical solution in steady laminar flow. Results show that retardation, which was not caused by stress, appeared in the CNC mixed solution. We compared the secondary principal stress difference distribution with the retardation distribution offsetting the effect of the retardation specific to the CNC mixed solution. The result showed that the spatial intensity distributions of both agreed well. We conducted additional verification for various flow rates.