The Investigation Of Vortex Structure In Straight And Compound Lean Compressor Cascades Via PIV

Particle Image Velocimetry (PIV) is a whole-field laser measurement technique, which can give the instantaneous on-line velocity distribution by a non-intrusive approach. Although this technique came into use not long ago, it has been widely used in many kinds of areas because of its outstanding merits. As this technique become more mature, it has a good prospect in the application of turbomachinery. This thesis presents a research on the flowfield of compressor cascades under large positive attack angles via PIV. The cascades are composed of conventional straight blades and positive curved blades.In this thesis, first, the author studied the key PIV techniques involved in the two-dimensional flow field measurement, such as the calibration of the sheet light, the relationship between the laser's pulsed time interval and flow velocity, and the selection of the tracking particle. Second, the distribution of velocity and vortex structure in the compressor cascades was successfully obtained. The measurement on the S1 stream surface was performed within the flow passage and at the outlet of the cascade at five radial positions. The measurement on the S3 stream surface was carried out at fifteen axial locations to capture the passage vortex.The experimental results indicate that under large positive attack angle, the flow is totally unsteady. The flow field changes largely at different time. The distribution of the time-averaged velocity and time-averaged vorticity shows the presence of the large flow separation area near the suction surface, which is larger near the midspan than that near the endwall. The flow behavior at the midspan of the positive curved blade becomes slightly worse than that at the midspan of the straight blade due to the"C"type static pressure distribution along the blade height. On the contrary, the flow condition near the endwall of the positive curved blade improves in comparison with that near the endwall of the straight blade for the same reason. In addition, the passage vortex in the positive curved cascade is steadier than that in straight cascade.Numerical simulation was performed on the two cascades under the experimental conditions to supplement the aerodynamic parameters besides...