Investigation On Aerodynamics Performance Of Application Slot Injection Technology In Compound Lean Compressor Cascades

A compression system of high-efficiency, high-loading, and high-reliability has always been the objectives for the modern aircraft engine development. Therefore, investigating in depth the compressor internal flow structure, exploring how to control the large-scale flow separation which is caused by high loading within the compressor flow passages becomes a key issue in compressor aerodynamics. The application of slot jet to the compound lean blade used in the highly-loaded compressor to control boundary layer flow has a great potential to solve this key issue.The flow field structures of the compound lean linear compressor cascades with/without slots were measured in the large scale low-speed wind tunnel. Under design and off-design conditions, the cascade flow field parameters were measured by five-hole probe in detail. The static pressure was measured by"U"pitot traverse on the cascade surfaces and endwall. Ink-trace flow visualizations was also conducted. On the basis of the experimental study, the hybrid approach based on the genetic algorithms and numerical simulation was used to investigate the relation between the slots location in radial and the inflow incidence. Furthermore, combined with the experimental and numerical results, the flow mechanics of boundary layer in highly-loaded compound leaned compressor cascade with/without slots was studied in depth via the qualitative analysis theory of the differential equation and topological theory.The experimental results show that under design condition, the air jet penetrating through the pressure and suction surfaces in the highly-loaded compound-lean compressor cascade with slots can not only control the boundary layer separation and shedding on the suction surface effectively, thus increases the flow turning capacity, but also destroy the axial vortex turbulence coherent structure early, hence increases the kinetic enery of the low enery fluid in the wake region, and restrains the high entropy fluid to concentrate exceedingly to wake center. The wake mixing, wake intensity and the momentum thickness of free vortex layer in wake region are therefore reduced, so the cascade aerodynamic performance is improved. When the slot axial location starts near the separation line and extends into the separation region on the suction surface, the slot injection can control the flow separation more effectively. In addition, slot injection can further reduce the compressor cascade total loss by a reasonable selection of the radial location for the single slot configuration or of the combination manner for the multi-slot configuration. The boundary layer separation is weakened on the suction surface and the aerodynamic load is increased simultaneously near the slot in the positively compound lean cascade. However, the boundary layer separation is weakened remarkably on the suction surface in the negatively compound lean cascade.Under off-design conditions, the mechanism which slot-jet improved boundary layer flow is similar to that under design condition. And the operating range with low loss level is widened in the highly-loaded compressor cascade. At negative incidence, the slot jet reduces the wake momentum thickness, and prevents the low-energy fluid near the endwall from migrating in the radial direction, so the total loss is reduced. At positive incidence, the slots jet with a high speed effectively improves the boundary layer flow behavior within the separation region on the suction surface, restrains the high entropy fluid to concentrate exceedingly after the cascade, therefore the aerodynamic performance of compressor cascade is improved greatly. The radial migration of boundary layer from the endwall to the midspan due to the positively compound lean effect, on the one hand, improves the flow conditions in the endwall region, on the other hand, deteriorates the flow in the middle region. The case is opposite in the negatively compound lean blade. Slot jet can weaken or even eliminate the local flow deterioration resulted from the boundary layer migration in the compound lean blade. Slot jet with a high speed can introduce the locally concentrated high entropy fluid into the mainstream in time, thus the boundary layer shedding from the suction surface is reduced, and the quasi-ordering structure of the concentrated shedding vortex is destroyed, therefore the exceeding accumulation of the low energy fluid is restrained. This effect is gradually increased when the incidence varies from negative to positive. This indicates that a reasonable combination of the slot jet and blade compound lean is an effective way to improve the aerodynamic performance of highly-loaded compressor cascades, to expand their application, and to enhance the effect. Furthermore, based on the experimental and numerical simulation samples, the relation between the radial location of the slots and the inflow incidence was obtained for the highly-loaded compound leaned compressor cascade.In addition, in order to better understand the flow control mechanism due to the blade compound lean and slot jet used in the highly-loaded compressor cascade, the topological rules which are applicable to the wall friction force spectrum, to the flow patterns on the cross-section of the cascade as well as on the blade-to-blade surface were deduced in detail for the turbomachine cascades with/without slots according to the topological principle. The mathenatic expression between the number of singular points and the number of slots were obtained based on the flow patterns, which provides a feasible analysis method for the turbomachine flow field. Applying the vortex dynamics theory, the qualitative analysis theory of the differential equation and the singular point bifurcation principle, the mechanisms of the blade compound lean and slot jet to reduce the secondary flow loss in the highly-loaded compound lean compressor cascade was studied. It shows that the saddle point?spiral separation structure is converted into the saddle point?node structure via the degradation node or critical node on the blade suction surface region through the flow control technology, which suppresses the large-scale flow separation or vortex generation, thus aerodynamic loss in cascade is reduced effectively. This is also the most essential reason why the slot jet can control the concentrated shedding vortex starting at the highly-loaded compressor cascades suction surface. Based on the above studies, the vortex structure, and the boundary layer migration and controlling mechanism in the highly-loaded compound leaned compressor cascade with/without slots was studied in depth. The vortex models in which the blade compound-lean effect and the jet through the slots were coupled, were presented. These models show that the passage vortex and the concentrated shedding vortex are two main factors that affect the aerodynamic performance of the highly-loaded compressor cascade.