Experimental Study On Plasma Active Control Of Acoustic Excitation Of Compressor Rotor Plane Cascade Blades

Acoustic excitation is one of the important sources of vibration of aeroengine rotor blades.The compressor will break the blades when they are excited by sound,which seriously affects the safety of the engine.Therefore,it is urgent to explore the mechanism of acoustic excitation and study the control method.In this thesis,the mechanism of blade acoustic excitation is studied by wind tunnel test of rotor blade plane cascade.Based on the clear mechanism,the plasma jet is used to control the tip leakage vortex to restrain the intensity of acoustic excitation.Firstly,the phenomenon of blade sound excitation is reproduced and its mechanism is revealed.The wind tunnel test model of the rotor blade plane cascade is developed.The vibration and noise in the tip area are measured synchronously by wind tunnel test.Compared with the simulation results,the acoustic excitation phenomenon occurs when the flow velocity is 30 m/s and the blade installation angle is 15°.The mechanism of the sound excitation is revealed by combining the stress changes of the root and the noise spectrum of different positions in the tip area.The aerodynamic noise of blade has the characteristics of single peak and its frequency increases with the increase of the flow velocity.When the peak noise frequency is close to the third order mode frequency(488.3 Hz),the blade vibration mode is excited and the acoustic excitation occurs.Then,based on the control requirements,the flow characteristics of tip leakage vortex are studied.The flow field of different tip cross-section was measured by PIV,and the generation and development of tip leakage vortex were clarified.The results show that the flow structure of tip leakage vortex is similar to that of Bindon.It is clear that the important node positions in the development of tip leakage vortex are 0.25c and 0.5c,which is the active control position of plasma synthetic jet.The peak velocity of leakage flow in sections 0.25c,0.5c and 0.75c was measured with the flow velocity.It is found that the peak velocity of leakage flow in section 0.75c is similar to that of 488.3 Hz peak noise,which increases first and then decreases.When the acoustic excitation occurs(30 m/s),it reaches the maximum,which reflects the positive feedback effect of vortex sound under the acoustic resonance state.When the acoustic excitation occurs,the cross-section velocity of 0.25c and 0.5c is 26.7 m/s and 40 m/s respectively,which provides guidance for the selection of the jet velocity parameters.Finally,the plasma synthetic jet is used to control the blade sound excitation and its control mechanism is clarified.Compared with the scheme of jet towards the tip and back of blade,the scheme of inclined jet towards the blade basin at 0.5c section has the best control effect.Under the optimal discharge frequency of 220 Hz,the noise suppression is 3.2 dB and the vibration stress of the blade is 31.6%.The control mechanism is to use jet to interfere with the start of leakage flow between tip gaps,reduce the pressure gradient of blade pressure surface and suction surface,weaken the driving force of tip leakage flow movement,inhibit the formation and development of tip leakage vortex,and then reduce the strength of leakage vortex.The decrease of leakage vortex strength causes the corresponding noise intensity to decrease,the positive feedback effect of vortex sound is weakened,the excitation force of induced blade vibration decreases,and the blade vibration strength decreases,thus the intensity of blade acoustic excitation is restrained.The research results of this thesis can provide reference for the design of compressor and provide a new method for active control of acoustic excitation of compressor blades.