Three-Dimensional Measurement Of A Stress Field In A Rectangular Channel Flow Using A Photoelastic Method
K. Nakamine (1), Y. Yokoyama (1), M. Muto (2), Y. Tagawa(1)
(1) Dept. Mech. Sys. Eng., Tokyo University of Agriculture and Technology, Japan
(2) Dept. Mech. Sys. Eng, Nagoya Institute of Technology, Japan
The hydrodynamic stress field of a steady laminar flow in a rectangular channel was experimentally measured by using a photoelastic method. For this purpose, following two issues for a mixed solution of photoelastic material, cellulose nanoctystal (CNC), were extensively investigated. The first is to elucidate whether there are any phenomena (trends) peculiar to a CNC mixed solution that differ from those to the solid case. The second is to elucidate the extent to which the stress-optic law holds for CNC mixed solution. As a verification method for the first question, we measured retardation distributions by using a high-speed polarization camera. We compared distributions of measured retardation of a CNC mixed solution (0.5 wt %) (Newtonian fluid) and theoretical secondary-principal stress difference derived from the analytical solution of steady lam- inar flow in a rectangular channel. The results showed that a retardation, which was not affected by stress-oriented phase retardation, appeared in the CNC mixed solution. The reason is considered to be retardation induced by aggregations of CNC particles. This phenomenon is peculiar to CNC mixed solution and does not occur in solids cases. As a method of verification of the second issue, 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 within a relative error of 3.84 %. This indicates that the stress-optic law holds for the retardation offsetting the retardation specific to the CNC mixed solution. To evaluate the validity of the above validation results, we measured the retardation fields of flows at different flow rates (10, 20 ml/min). The measured results agree with theory with relative errors 5.67 % and 3.24 % for flow rates of 10 and 20 ml/min, respectively.