The Effects And Analysis Of Compressibility On Pulsed Jet Control Flow Separation

The stage pressure ratio is a very important target to compressor performance, while increasing thestage pressure ratio will lead to flow separation in cascade passage. Aims at controling flowseparation, the unsteady active flow control technology manipulating flow instabilities, withperiodical addition of momentum the cost could be decreased by an order of magnitude comparable tothat of steady blowing. Based on a micro pulsed jet concept used in compressor cascade to suppressflow separation, the numerical investigation is presented. The main work is as follows:1、The study of the cascade passage flow characteristics at typical subsonic velocity show that,when inflow attack angle is fixed, increase inlet mach number will delay the location of separation,raise the characteristic frequency of the separated vortex，and enlarge the flow instabilities.Application of the Proper Orthogonal Decomposition to analyze the unforced flow, consider a flowcontaining both density and velocity, we use complex number to express vector and couple thevelocity and density in the POD kernel. Studies showed that, different modes reflect differentfluctuation structure except the first mode represents average-flow. The time coefficient of2ndand3rdmode has the same period with separation vortex. The kinetic energy concentrate low order mode.When increase the inlet velocity, high velocity main flow compress area of fluctuation structure tosuction side, the period of2nd and3rd mode time coefficient become shorter.2、The study of unsteady flow control at inlet mach number0.6and0.1was carried out to analyzingcompressibility effect. The result of different cases show that，when the excited frequency is close tothe characteristic frequency of the separated vortex， the total pressure loss is lowest. Compared withincompressible flow, the control result is weaken at compressible flow. The effective excitationfrequency can enlarge the characteristic frequency. By inducing the negative vorticity flow attach thesurface and reducing accumulated vorticity at leading edge, which decrease scale of next vortex, theeffective frequency pulsed jet suppress flow separation at compressible flow. The effective pulsed jetbe able to make the flow more uniform through contribute to the growth of vortex matching atincompressible.3、The result of different cases analyzed through application of the POD show that，the excitationtransform the kinetic energy of fluctuation into average-flow kinetic energy. By coupled with largescale coherent structures in whole flow field, the most effective frequency of pulsed jets reduce theenergy of fluctuations even better. Study of reconstructing the flow field with the first five modes alsofully confirmed the analysis of vorticity field. 4、With electrical motor diver the rotation valve to control excited frequency, and research ofunsteady flow control above, the coupling effect between unsteady pressure fluctuates in separationarea and pulsed jet devices was investigated. The numerical result demonstrates the pulsed jet devicescan generate163m/s peak velocity at required frequency（inlet mach0.6）. When choosing theoptimum reduced frequency F+=1.1(2000Hz), a reduction in pressure losses of up to16.9%wasreached. The required mass flow for actuator was about0.35%of the passage mass flow.