Numerical Investigation On Effects Of Inlet Boundary Layer Characteristics On Aspirated Compressor Cascade

With the rapid development of modern aero-engine，the efficiency and stability ofcompressor which is an important part of the engine constraints and affects the entireengine performance．Under the condition that the total pressure ratio is met，we canreduce the compressor stages as far as possible in order to promote the thrust-weightratio and lower the expense．Stage load is increased by enlarging the turning angle incompressor design．Large turning angle always leads to separation as the strong adversepressure gradient in the diffuse cascade．In recent years，boundary layer suctiontechnique-a kind of active flow control strategy，is widely used in high load in thedesign．The inlet boundary layer characteristics of the aero-craft change often as it istaking off，landing or in a state of fighting．How will the change of inlet flow boundarylayer influences the flow field and the load for the aspirated compressor cascade？Thestudies about it are rare at present．The purpose of this paper is to study the influencecaused by inlet boundary layer on flow field and performance for a aspiratedcompressor cascade by using numerical simulation method and to explore the optimalamount of boundary layer suction in the varying working conditions (thickness of inletboundary layer，flow turbulence，and attack angle)．In this paper，the research contents are mainly divided into two parts．In the firstpart，the thickness of inlet flow boundary layer are classified into displacementthickness and momentum loss thickness．The influence to the limiting streamline in thesuction side，the three-dimensional flow field and outlet losses in the design attack angleand under the moderate turbulence intensity (5%degree of turbulence) condition causedby the two types of boundary layer are researched respectively．The paper alsodiscussed how the changes of the inlet flow turbulence intensity will affect the cascadeflow field and its performance．In the second part，based on the two boundary layerthickness distribution schemes（A11and A24），which lead to the biggest loss and have been discussed in the first part，the paper has studied the influences on the flow fieldand outlet losses under the medium turbulence intensity (5%degree of turbulence)leaded by the attack angle．Secondly，according to the maximum flow boundary layermomentum loss thickness，the influence of the turbulence intensity to the flow field andoutlet losses are considered and researched at-6°and+6°angle of attackrespectively．At the end，the paper discusses the influence on diffusion cascade flowfield and the losses contributed by the suction flow rate in the extreme air inletconditions(large angle of attack and large inlet flow boundary layer thickness) in orderto achieve better control over the flow field and losses with reasonable suction flow ratein the variable working condition．We draw some conclusions after a large number of simulation schemes．1）Theincrease of boundary layer thickness will deteriorate the flow situation in the cascadeand enlarge the scope and extent of the corner separation；2) As the angle of attackincreases，the three-dimensional separation is augmented and the flow becomes morecomplicated；3) When at a large angle of attack，the cascade performance is moresensitive with a large inlet boundary layer momentum loss thickness．As the inletboundary layer momentum loss thickness is small，the cascade performance is relativelygood at different turbulence intensities of the inlet flow in the variable workingcondition；4) Increasing the amount of suction appropriately can narrow the scope of thecorner separation and reflux effectively，improve the air flow turning ability and reducethe losses in the extreme air inlet conditions(large angle of attack and large inlet flowboundary layer thickness).