| Complex flow exists in axial compressor,The interaction of various three-dimensional flow structures in the passage affects the overall performance of the compressor.The flow in the blade tip and near hub region of an axial-flow compressor is the most complex,which makes the compressor it easier to enter an unsteady flow state,and leading to stall.In order to ensure that the high load compressor has a wider stable working range,this paper mainly focuses on the passive flow control method of micro-vortex generator,and develops different combined flow control technology.Based on the characteristics of the corner separation and the stall mechanism of the axial compressor cascade/stator,the ability of different flow control technologies to control the corner separation is explored and analyzed in the theoretical research.The research includes four parts.After comparing the characteristics of the corner separation of the cascades under the steady working condition and stall condition,the optimization parameters of the micro-vortex generator under the design condition are obtained by the response surface optimization method,and the structure of the vortex generator is optimized.In the third part,an combined flow control technology with active and passive flow control are proposed,and the effects of different combined technologies on the performance of cascades are studied.In the fourth part,a multi-stage axial-flow compressor is taken as the research object to explore the performance of different flow control methods in the stage environment.The research situation and main conclusions of each part are as follows:1.Through the analysis of the three-dimensional flow field and flow topology in the cascade passage at the design condition and stall condition,it is found that because a strong radial pressure gradient exists the blade suction surface near the end-wall,the low energy fluid near the blade suction surface moves upward along the span.With the increase of the incidence,the initial position of the corner separation gradually moves upstream,and the accumulation of low energy fluid on the end wall near the leading edge of the blade gradually increases.When the low-energy fluid in the corner region is accumulated excessively,the structure of the flow field in the cascade changes suddenly,which leads to the sudden increase of the total pressure loss and the occurrence of corner stall.In the research object of this paper,more low energy fluid suddenly accumulated on the end wall near the leading edge of the blade,which trigger a pair of singular points far away from the blade suction surface appear in the end wall near the upstream of the blade passage.The change of the flow field marked the occurrence of stall in the corner region.2.Based on the numerical simulation method of cascade,the sample space points used to optimize the parameters of the micro-vortex generator are completed by using the experimental design method.After the approximate model is constructed,the optimization results of the micro-vortex generator at the design condition are obtained by using the response surface optimization method.In the study of the influence of the micro-vortex generator on the performance of the cascade,it is found that a strong radial pressure gradient exists the blade suction surface near the end-wall,the low energy fluid near the blade suction surface moves upward along the span.However,due to the limitation of its size and position,the action height of the micro-vortex generator is limited near the end-wall.Therefore,at the design condition,the induced vortex produced by the micro vortex generator can not act on the low-energy fluid which has been pushed to a higher position by the radial pressure gradient,so that the performance of the cascade becomes worse.With the increase of the incidence,the microvortex generator gradually showed its advantages and successfully delayed the corner stall point from 7.9° to 10.4°.3.Taking the cascade as the research object,the micro-vortex generator and the active flow control technology are combined to analyze the advantages of this method,and the following conclusions are drawn:(1)The micro-vortex generator is analyzed by the response surface method and the response relationship between the main structural parameters of the full span suction slot,it is found that the interaction between the micro-vortex generator and full span suction slot is not obvious,and the change of the parameters of one control method will not change the influence on cascade performance by using the other control method.Therefore,optimizing the two flow control methods separately can reduce the workload.(2)The active/passive combined flow control technology has the advantages of different control methods.The micro-vortex generator is combined with the full span suction slot,which can reduce the total pressure loss coefficient of the cascade by 13.77% at the design condition and13.85% at the stall condition.The stall incidence is delayed from 7.9° to 10.2°.The combination of the micro vortex generator and the segmented suction slot reduces the total pressure loss coefficient by 11.73% at design conditions,and 17.98% at stall conditions,and the stall incidence is delayed to 9.6°.4.The flow phenomenon in the axial compressor stage environment is more complicated than the flow in the cascade.The compressor stator will be affected by the wake vortex/tip leakage vortex of the upstream rotor,and the incoming flow boundary layer will be tilted by the rotation of the upstream hub.Therefore,in order to study the influence of flow control technology on the performance of compressor in complex environment,a 3.5-stage transonic axial compressor is taken as the research object,and the influence of flow control technology on the performance of compressor is analyzed,the following conclusions are obtained:(1)The occurrence of the stall in the corner region does not trigger the surge of the compressor,but causes the corner separation of the stator to suddenly change into an unstable flow structure,so that the aerodynamic performance of the compressor becomes significant drop with the decrease of the flow rate.(2)The direct cause of the corner stall in the stator of the compressor is the same as that of the cascade,which is caused by the excessive accumulation of low-energy fluid in the corner region.(3)Active/passive combined flow control technology still demonstrates a good ability to improve compressor performance in complex compressor environments.The stall margin improvement of the last stage can reach 2.46% and the highest efficiency can reach 1.83% when the micro vortex generator is combined with the full span suction slot.The stall margin improvement of the last stage can reach 2.71% and the highest efficiency can reach 1.63% when the micro vortex generator is combined with the segmented suction slot. |
PDF Full Text Request