Development of Fiber-Bundle-Image-Guided PIV

The present work involves the development of a particle imaging velocimetry system using an optical fiber bundle scope as shown in Figure 1. Applying a fiber scope to PIV system, the resolution of particle images is spatially poorer than those taken directly by a CCD camera, which leads to an inadequate result of cross-correlation between a pair of particle images from the fiber scope. With a conventional cross-correlation PIV, the results processed by images transmitted through a fiber scope show the direction of the vectors along the orientation of fiber elements of bundle scope, because they have a strong correlations in one frame image to the other reference frame image due to the stationary image while the particles show the intermittent images in their trace. A distribution of correlation coefficients used to obtain particle displacements has many random correlation peaks, so it is necessary to reduce background noise from the frame images. In the present study, the pattern of the fiber scope was eliminated by subtracting an initial reference image from the image with particles and using the cross-correlation PIV with a hierarchical interrogation technique could reduce erroneous vectors. Further the more improvement was tried to obtain vectors even in the case of lean particle concentration using particle streak tracking method as shown in Figure 2. Figure 2 Particle Streak Image and Velocity Vectors Laser Diode Laser Driver Timing Scheduler CCD camera Fiber Bundle Network PC Frame Grabber Figure 1 Fiber-Bundle-Image-Guided PIV system