Investigation Of Tip Leakage Flow In Low-Speed Axial Compressor Cascade

Tip leakage flow has significant effects on the performance and stability of compressor operation. In recent years, it has been found that tip leakage flow is closely related with the phenomena of rotating stall. And tip leakage flow will oscillate unsteadily when compressor is throttled close to the stability limit. In order to develop effective control techniques to delay the onset of rotating stall, the research on the unsteady flow features of tip leakage flow, its triggering mechanism and relationship with rotating stall is motivated.Tip leakage flow is driven by the pressure difference between pressure and suction sides of compressor blade, and is affected by many other factors, such tip clearance size, blade loads, blade shape, inlet flow angle and annular boundary layer. Due to the great difficulty to measure the compressor inner flow field in real rotating environment, and also to consider the effects of different factors, the compressor plane cascade is an important method to study the unsteady tip leakage flow.In this dissertation, the research is mainly conducted by experiments on compressor plane cascade, and numerical simulation also is adopted to validate the experiment results. For two sets of compressor plane cascades with large turning angles, the existence of tip leakage flow unsteadiness is confirmed, and its unsteady flow field features, occurrence condition and triggering mechanism are also explored.In the first section, the construction of the experiment test rig and development of corresponding measurement systems are introduced, during which the inlet boundary layer of wind tunnel is treated by the diaphragm, the adjustable device of cascade tip clearance size is designed and manufactured, the flow quality of the wind tunnel is checked, the ink traces method is used for flow visualization, the three-hole and seven-hole pressure probes are designed and manufactured and a standard wind tunnel is built to calibrate the two probes, the steady and unsteady pressure sensors are calibrated, the data acquisition program is written by the computer language of Labview.In the second section, the steady features of tip leakage flow are investigated. The effects of tip clearance size, attack angle, inlet flow velocity and turning angles on the tip leakage flow is studied by the ink traces method, measurement of seven-hole pressure probes and numerical simulation. The results showed that:(1) The originating location of tip leakage flow moves downstream obviously when the tip clearance size increases. The trajectory of tip leakage flow moves toward the neighboring blade pressure side. And at the same time, the radial range of tip leakage flow also expands. When the tip clearance size is increased to a certain extent, the trajectory of tip leakage flow impinges on the neighboring blade pressure side. (2) The effects of stack angle and velocity of inlet flow on tip leakage flow are equivalent to that of mass flow rate. With mass flow rate decreased (stack angle increased or inlet velocity decreased), the originating location of tip leakage flow moves upstream towards blade leading edge. And the trajectory of tip leakage flow also moves toward the neighboring blade pressure side. (3) When the turning angle is increased, the trajectory of tip leakage flow is not sensitive to the change of tip clearance size, stack angle and inlet velocity.In the third section, the unsteady features of tip leakage flow are studied. The casing pressure is measured by Kulite unsteady pressure transducers. And the numerical simulation is also the conducted for the corresponding operating points. It has been found that:(1) The unsteadiness of tip leakage flow occurs under some certain conditions. The changes of inlet velocity and stack angle will affect the unsteady frequency of tip leakage flow, and the effect of inlet velocity is relatively larger. (2) It is necessary for the occurrence of tip leakage flow unsteadiness that the trajectory of tip leakage flow arrives at the neighboring blade pressure side. (3) The large turning angle will restrain the occurrence of tip leakage flow unsteadiness. For the cascade with large turning angle, even if the tip clearance size and inlet stack angle are larger, the trajectory of tip leakage flow is still restrained within the blade passage. And thus the triggering of tip leakage flow unsteadiness is controlled.