A Development of a Two-component Velocity Profiler using an Advanced-Multi-Point LDV Technique and a Particle Image Technique

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The summary of this study for three years from 2000 to 2002 is as follows.A novel method to measure two-component velocity profile simultaneously was developed by using the combined system of a CCD area image sensor (CAIS) and a multi-point LDV. The benefits of this method are shown by pursuing the compact and convenient over the system. The results of some measurements such as the flow field behind the cylinder shows the reliability of the measurement for turbulence field. The basics techniques of this method are established and the applicability for the measurement of flow field is shown.Many experiments have been performed to study the flow structure around the reattachment region of a two-dimensional backward facing step. This flow field has a large-scale vortex structure with low-frequency fluctuation involving one of instantaneous reattachment point. To clarify these structures time series velocity profile is measured using an advanced multi-point LDV system and behavior of separated shear layer and reattachment phenomena is visualized clearly. A velocity at the vicinity of the step wall increases rapidly when the separated shear layer reached to the step wall passes the measuring region. A frequency of this event is in good agreement with the one of the flapping of the separated shear layer. There are two patterns of when the velocity direction changes from positive to negative on the step wall around a reattachment region.