| The unsteady flow in turbomachinery belongs to the most complex flow phenomena in engineering. Main character of the flow is the complex vortex system. The formation, development and breakdown of vortex, the interaction between vortex and main flow and the interactions among vortices dominate the elementary characters of the flow and the force on the bodies. In compressor, the vortex development directly affects not only the efficiency, but also the stability.In this thesis, the author obtained the distribution of velocity and vortex structure in the compressor cascades by using two-dimensional measurement technique of PIV. The measurement on the S1 stream surface was performed within the flow passage and at the outlet of the cascade at five different radial positions. The S2 stream surface at the leading edge was measured in order to obtain the horse-shoe vortex (HV). The measurement on the S3 section was carried out at fifteen different axial locations to capture the passage vortex (PV).The experimental results indicate that under large positive attack angle, the flow is totally unsteady and unsymmetrical with the large flow separation area near the suction surface and all kinds of vortex in the cascade. The flow field changes largely at different time. In positive dihedral cascade, the flow separation area at the mid-span of the blade is remarkably smaller than that near the end-wall. At the same time, the variability of the flow separation at different blade height in negative dihedral cascade is completely opposite. At the positive dihedral blade trailing edge, the direction of the flow changes more largely at different span-wise position, compared to that at the negative one. At the leading edge of the positive dihedral blade, there is a strong HV, which is also observed in negative dihedral cascade, but weaker. Further more, the passage PV appears earlier, and is also steadier in positive dihedral cascade than that in negative dihedral cascade.
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