Experimental and Numerical Studies on the Projective Dye Visualization Velocimetry in a Squared Vertical Tube*

In fluid flow experiments, there have been numerous techniques developed over the years to measure velocity. Most popular techniques are non-intrusive such as particle image velocimetry (PIV), but these techniques are not suitable for all applications. For instance, PIV cannot be used in examining in-vivo measurements since the laser is not able to penetrate through the patient, which is why medical applications typically use X-rays. However, the images obtained from X-rays, in particular digital subtraction angiography, are projective images which compress 3D flow features onto a 2D image. Therefore, when intensity techniques, such as optical flow method (OFM), are applied to these images the accuracy of the velocity measurements suffer from the 3D effects. To understand the error introduced in using projective images, a vertical square tube chamber was constructed to achieve multiple water flow rates with various dye injection points to capture dye visualization images. Two experiments were conducted with the dye inlet either in the center or against the tube’s wall. These images were then evaluated with OFM and compared with PIV measurements to quantify the error associated with dye visualization velocimetry. Results from dye visualization were comparable with PIV, but a correction method, more specifically the Levenberg-Marquardt algorithm, was needed to adjust the OFM results. Corrections matched well with the baseline velocity values with relatively low valued least-squares. CFD simulations were compared with PIV measurements and dye visualization images to validate proper boundary conditions and meshing. CFD simulation results provided more insights of the flow characteristics of the dye diffusion in the laminar vertical tube flow.