Unsteady Characteristics Analysis And Flow Control Of Supersonic Inlet Buzz

Starting of a supersonic inlet is the premise of the normal operating of the propulsion system,otherwise complex flow field oscillation will occur.The starting issue has always been an important research field of the supersonic propulsion system.In this paper,high confidence numerical simulations of typical buzz states are carried out.The proper orthogonal decomposition(POD)and dynamic mode decomposition(DMD)methods are introduced to analyze the flow field.A one-dimensional(1D)mathematical model is then proposed based on the classical acoustic theory using parameters of inlet buzz obtained from numerical results.Therefore,the oscillation mechanism of the buzzed flow is clarified and the variation of flow stability between the little buzz and the big buzz is revealed.Finally,based on the 1D model,a preliminary exploration of buzz suppression is performed,which provides a useful theoretical support and method basis for the improvement of the supersonic inlet starting performance.The main contents of this paper are as follows:(1)The POD method is introduced for the analysis of the buzzed flow characteristics.Dominant flow patterns and characteristics of the buzzed flow are obtained by decoupling the computed pressure field into spatial and temporal sub-parts using the POD method.On the basis of POD results,a 1D model,which approximates the original flow field,is proposed by taking into account only the first-order POD mode.The supersonic inlet buzz phenomenon studied in this work can be approximated as a product of decoupled temporal and spatial terms.(2)The DMD method is introduced to analyze the dynamic features of the buzzed flow.The results show that the first order DMD mode reflects the time-averaged flow field characteristics,and the second order DMD mode represents the flow field features of the main frequency oscillation.The flow of the little buzz contains the oscillation characteristics of the big buzz,and the little buzz regime is a transitional state from the steady flow field to the big buzz regime.During the evolution from the little buzz to the big buzz,some flow structures in the inlet are gradually weakened and tend to be stable,hence the overall flow field of the big buzz is more stable than that of the little buzz.(3)Based on the understanding of the buzz oscillation mechanism obtained by POD and DMD,a 1D mathematical model is proposed using classical acoustic theory.The results show that frequency of inlet buzz is closely related to the resonant mode of acoustic wave,and the pressure oscillation of computational results along the internal flow passage is in good agreement with the acoustic wave fluctuation characteristics as well.Limited pressure distribution phase discrepancy was observed between numerical results and analytical predictions.Influential factors which lead to this minor discrepancy can be viscous effect in real flow,unsteadiness of acoustic source and slight area variation of inlet duct.Since the flow of the little buzz contains the oscillation characteristics of the big buzz,the acoustic model of the little buzz contains an acoustic model item of the big buzz.(4)Based on the 1D acoustic model,the mathematical modeling and numerical simulation analysis of unsteady jet control are realized,and the control effects under different jet phase,amplitude and frequency are compared.The numerical simulation results of unsteady jet control are basically consistent with the theoretical prediction results,which further proves the reliability of the 1D mathematical model proposed in this paper and provides a new analytical method for improving the starting performance of supersonic inlets.