Investigations On Characteristics Of Self-excited Vibration Of The Splitter Plate With A Cavity And Mixing In Supersonic Mixing Layer

This paper is based on the research background of greatly effective mixing of fuel and airflow in RBCC.Given the fact that mixing induced by forced vibration cannot be availiable in engineering,a new method to enhance mixing induced by self-excited vibration is proposed.The splitter plate of self-excited vibration is based on cavity configuration and its displacement can be measured by small vibration measurement system.The influencing factor of self-excited vibration characteristics can be analyzed combining theory analysis and experimental study.Large eddy simulation(LES)is employed to investigate the mixing characteristics under different configuration parameters of cavity.Passive and active mixing enhancement technologies are summarized both at home and abroad in past decades.Besides,this paper analyzes the features of mixing induced by forced vibration and self-excited vibration and then generalizes the investigation progress of unstable vortex induced by vibration.Self-excited vibration splitter plate is attached with a cavity on it in this paper.The cantilever plate with a cavity and proper experimental model are designed.Through calibrating the supersonic mixing layer nozzle,the Mach number of upper and lower flow are 1.96 and 2.78 respectively,with a convective Mach number of 0.18.Small vibration measurement system can realize non-contact measurement.The two-way fluid and solid interaction(FSI)is employed to investigate the interaction between supersonic flow and cantilever plate.Large eddy simulation is conducted to simulate supersonic flow.In addition,the case vertification is carried out to make sure that LES is valid in the simulation of mixing layer and cavity flow.The characteristics of splitter self-excited vibration are gained by experimental study combining with numerical simulation.It is indicated that the self-excited vibration of splitter is caused by fluctuation of pressure difference on upper and lower plate directly.The long cantilever plate with right free end loses stability in the supersonic mixing tunnel when experiment is going on.In order to avoid stability loss,constraint condition is exerted on free end.Experimental researches indicate that vibration frequency is negatively related to limit distance while effective amplitude of vibration is actively related to limit distance.Vibration frequency decreases with increasing static pressure difference in the outlet of nozzle while vibration amplitude takes exactly the opposite point of view.But both changes above are not greatly obvious.Configuration parameters of a cavity play an essential role in the characteristic of splitter self-excited vibration.It reaches maximum frequency when the length depth ratio K equal zero.Now turbulent pressure fluctuation is the main actuating source.With the increase of K,frequency decreases and amplitude grows up.The augment of rear ramp angle results in frequency growing of self-excited vibration but amplitude tends to the opposite.Large eddy simulation is conducted to get supersonic mixing layer flow structures with a cavity splitter and mixing characteristics are analyzed.Upper flow is actuated by a cavity and produce a large number of unstable vortexes,which results in an advancement of mixing layer transition position.Several small scale eddies come into being at the edge of large scale eddy,which indicates there are a few modes in the cavity.Through the analysis of mixing characteristic under different configuration parameters of cavity,we find that mixing efficiency grow up with the increase of K because cavity shear layer develops fully meanwhile we keep the cavity depth unchanged.Mixing efficiency decreases with abate of rear ramp angle because of the decline of oscillation intensity in a cavity.Self-excited oscillation of leads to mixing enhancement in supersonic parallel flow.A cavity is placed in the upstream of upper flow like a high frequency actuator whose oscillation intensity can determine mixing efficiency.Streamwise vortex produced by cavity can result in momentum exchange in spanwise direction and longitudinal direction,which is beneficial to mixing augmentation.