The purpose of this study is to make clear the behavior of the swirling pipe flows with non-circular section. Transitional swirling flows in a rectangular channel with aspect ratio of 1.3 and a short channel length, which is one of typical pipe flow with non-circular section, were investigated experimentally and numerically. In this experiment with water circulation flow, LDV measurement system was used in order to obtain the mean velocity fields and turbulent quantities. The flow visualization of the swirling flows was carried out in order to understand the oscillating motion of vortex core. Also, large eddy simulation of the flow fields was made at the same conditions as the experimental ones. As results of these investigations, the computational results showed good agreement with experimental ones quantitatively, it was found that the vortex core region moves to the swirling direction with deformation and interactions of secondary flow at the corners.

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A new optical image analyzing technique for the flow visualization image has been proposed. The technique is based on the optical cross-correlation which is using Multiplexed Matched Spatial Filter (MMSF). In order to obtain the image for the optical analysis, Particle Tracking Velocimetry (PTV) under deformed double exposure has been applied. In the image, the loci of the particle displacement by the deformed double exposure represent the direction and the magnitude of the flow velocity. In the technique of MMSF, cross-correlation between the visualized image and the reference image i.e. the pattern matching between the shape of the locus of the particle displacement and the reference locus has been performed. As the result of the correlation, spatial distributions of the correlation peaks which are the spatial distributions of the particles displacement in each direction and the magnitude have been obtained. In addition, a Spatial Light Modulator (SLM) and a CCD camera have been installed in the optical system of MMSF. The real time image capturing and analysis can be realized by the MMSF optical system with a SLM and a CCD camera. As a first trial, the technique of the real time monitoring of the flow has been developed.

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