Research On Supersonic Flow Velocity Measurement And Shock Wave Structure Visualization Based On Femtosecond Laser

With the rapid development of aerospace technology,the visualization of supersonic and hypersonic flow field structures and the accurate parameters measurement of flow field have become one of the urgent problems with the urgent need for the development of high-speed aircraft.And they have practical significance to promote the development of supersonic flight.With the emergence and development of lasers,optical diagnostic technology has developed rapidly.Compared with traditional diagnostic techniques,optical diagnostic technology is widely used in flow field because of its advantages of noninterference,high resolution,high precision,and visualization.Because supersonic flow is affected by many factors such as shock,compressibility,instability,and turbulence,there are many difficulties when using the flow visualizing technology.The quantitative measurement of the temperature,velocity and density of the flow field under hypersonic complex flow and high temperature conditions is more difficult.At the same time,with the study of the supersonic complex flow,the requirements for optical measurement results are higher.Therefore,it is of great significance to develop and study optical diagnostic techniques that are suitable for supersonic flow field.In view of the above problems,this paper studies and discusses the feasibility of Femtosecond Laser-Induced Cyano Chemiluminescence(FLICC)for imaging the shock structure.Then the experimental verification of the velocity measurement in the supersonic flow field by Femtosecond Laser Electronic Excitation Tagging(FLEET)is carried out.Firstly,the principle of FLICC is studied.Then the technique is applied to the axisymmetric supersonic flow field to explore the feasibility of imaging the shock structure.The experimental results show that the fluorescence signal of FLICC mainly comes from the excited CN particles generated by chemical reaction between femtosecond laser and methane nitrogen mixture.Compared with the experimental results of Rayleigh Scattering,it is shown that the results of shock wave structure measured by FLICC are accurate and reliable.The measured image has a high signalto-noise ratio and can present clear shock structure in the flow field.This technology has the potential to be applied to shock wave fine structure imaging research.Based on the above experiments,this paper uses FLEET to quantitatively measure the velocity of the axisymmetric supersonic flow field.The accuracy of the measurement results of the technique in the supersonic flow field is studied.Centerline velocity,axial velocity at different radial position and One-dimensional velocity distribution at different axial heights are measured.FLEET can realize one-dimensional velocity measurement.The two-dimensional axial velocity field of supersonic flow field is measured by scanning the flow field,which provides a reference for the subsequent research.