3-D Particle Tracking Velocimetry: Development and Applications in Small Scale Flows
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The thesis contains two parts of studies. In part I, a novel volumetric velocimetry technique is developed to measure the 3-D flow field of small-scale flows. The technique utilizes a color-coded pinhole plate with multiple light sources aligned to each pinhole to achieve high particle image density and large measurable depth on a single lens microscope system. A color separation algorithm and an improved particle identification algorithm are developed to identify individual particle images from each pinhole view. Furthermore, a calibration-based technique based on epi-polar line search method is developed to reconstruct the spatial coordinates of the particle, and a new two-frame tracking particle-tracking algorithm is developed to calculate the velocity field. The system was setup to achieve a magnification of 2.69, resulting in an imaging volume of 3.35 × 2.5 × 1.5 mm3 and showed satisfactory measurement accuracy. The technique was then further miniaturized to achieve a magnification of 10, resulting in a imaging volume of 600 × 600 × 600 µm3. The system was applied to a backward-facing step flow to test its ability to reconstruct the unsteady flow field with two-frame tracking. Finally, this technique was applied to a steady streaming flow field in a microfluidic device used to trap particles. The results revealed the three-dimensional flow structure that has not been observed in previous studies, and provided insights to the design of a more efficient trapping device. In part II, an in-vitro study was carried out to investigate the flow around a prosthetic venous valve. Using 2-D PIV, the dynamics of the valve motion was captured and the velocity fields were measured to investigate the effect of the sinus pocket and the coupling effect of a pair of valves. The PIV and hemodynamic results showed that the sinus pocket around the valve functioned as a flow regulator to smooth the entrained velocity profile and suppress the jet width. For current prosthetic valve design a shorter leaflets is advantageous because it prevents flow stasis and reduce the energy loss. Valve pairing tests showed that an orthogonal configuration of the valve pair result in a complicated 3-D flow around the valve, which can increase the mixing of the blood flow and prevent reversed flow in between the valves. The tests of different valve separation distance showed that the coupling effect of two valves was weakened as the separation distance increased, suggesting the existence of a separation distance between the two valves to maximize the coupling effect and keep the flow structure stable.