The use of high-speed PIV and holographic cinematography in the study of fiber suspension flows

High-speed particle image velocimetry (PIV) and digital holography were applied to dilute, rigid fiber suspensions without floc formation. PIV is suited to study the instantaneous interaction between the flow and the fiber motion down to the scale of the fiber. Based on the size difference between fibers and tracers, fibers were masked in the PIV images. However, this method is not always sufficient, and we propose a more elaborate method based on local cross-correlation between successive cropped images to track and remove fibers from the PIV images. Digital, inline holographic cinematography has the advantage of a relatively easy optical setup. Exploratory experiments were performed using a single-view, inline setup tracking fibers in 3D. Fiber holographic reconstructions were clear and enable accurate determination of fiber length and orientation. This is in contrast to the PIV images, where the fiber optical signature suffers from intensity saturation and reflections. However, to obtain the accurate 3D fiber orientations, a two-orthogonal view holography setup is needed. We propose combined PIV and holography to study the basic fiber-flow interaction mechanisms in turbulent flows.