| As one of the kernel components of aircraft gas turbine engines,the compressor works mainly under adverse pressure gradient hence the flows in it are often of great complexity.Owing to this complexity,it is quite common for three-dimensional flow separations to occur,which is usually accompanied by strong secondary flows and would impact the aerodynamic performance of the compressor greatly.The developing trend of modern aircraft engines for higher thrust-weight ratio,efficiency and lower fuel consumption rate is putt ing higher and higher demands for the stage loading of compressors,which would definitely exacerbate the flow separations in the compressor passage.It is therefore necessary to take measures to get these separations under control.In this dissertation,vortex generator jets are utilized to control the flow separations of a high-speed compressor cascade whose inlet Mach number is 0.67.The vortex generator takes the form of a circular hole penetrating the blade and is able to produce jet flows using the pressure difference between the blade pressure surface and suction surface.Vortex structures are then induced by the interactions between the jet and the main flow.This flow control technique belongs to the category of passive flow control and possesses the advantages of structural simplicity and high control efficiency.According to the numerical results,vortex generators which are properly positioned and skewed could produce a jet vortex which is counter-rotating to the wall vortex.The interactions between the jet vortex and the vortex structures in the blade passage could enhance the momentum exchange between the main flow and the boundary layer while reducing the total pressure loss of the cascade.On the one hand,high-momentum fluid from the main flow is transported to the end wall boundary layer by the down-washing effect of the jet vortex,which relieves the blockage in the corner region and delays the corresponding flow separations.On the other hand,momentum exchange on the midspan side of the jet vortex is improved by its up-washing effect.Consequently,the midspan branch of the wall vortex is forced to migrate along the blade span and the flow conditions in the midspan areas are worsened slightly.The final influence of the jet vortex depends o n the sum of its two opposite effects.Effects of different jet parameters are one of the main topics of the present study.It is found that the best control effect is obtained when the vortex generator is located 40% chord downstream of the blade leading edge and 15% blade height from the end wall.The optimum skew angle is 60 ?.Under the designed condition,the total pressured is reduced by 5.2% with a jet-to-inlet mass flow ratio of only 0.27‰.In order to validate the effectiveness of the passive flow control technique under off-design conditions,the controlled flow fields under various incidences are investigated.The influences of different jet parameters are discussed in detail and the effect of incidence on the flow field are revealed based on the s elected jet parameters.Results show that the vortex generator jet has excellent adaptability and could enhance the cascade performance under a wide range of incidences.At the incidence angle of 2?,the total pressure loss of the cascade could be decrease d by as much as 7.8%.In practical application,jet parameters should be selected carefully according to the actual flow field of the cascade.The off-design characteristics should also be considered.To obtain ideal control effect,the vortex generator should be located in the near upstream of the separation line,pointing downstream and skewed towards the midspan.Also the spanwise position of the jet should be aligned with the high loss region clinging the blade suction surface. |
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