Research And Application Of High Temporal And Spatial Resolution Particle Image Velocimetry In Hypersonic Flows

Hypersonic aircraft is the commanding height of national defense technology in the aerospace field in the new century.The measurement of hypersonic flow is the basis and key to the test of hypersonic aircraft.Because of that the air is compressible,the hypersonic flow field has complex aerodynamic structures,such as shock waves,expansion waves,and recirculation zones,and its precise measurement is extremely challenging.Particle image velocimetry(PIV)is one of the measurement technologies with great application prospects for the current hypersonic flow measurement.In fields of imaging and image processing,PIV cannot meet the high spatiotemporal-resolution measurement requirement of hypersonic flow,which has highly unsteady and non-uniform characteristics.To resolve with thi problem,this dissertation develops a nanosecond straddling weak-light imaging technology,proposes a PIV reconstruction method based on gradient prior and multi-frame displacement information,and a hybrid optical flow method based on circulant-matrix.A PIV system suitable for supersonic flows is developed and applied to corresponding measurement applications.The main research contents include:(1)To realize high temporal resolution measurement of hypersonic flows,which has highspeed and highly unsteady characteristics,this dissertation develops a nanosecond straddling weak-light imaging technology,controlling several sensors collecting particle images to achieve high time resolution imaing of hypersonic flow.The desined nanosecond straddling weak-light imaging equipment can output particle images with frame rate of 200 Hz,image pixel resolution of 2 560×2 160 pixels and time resolution up to 10 nanoseconds,solving the 1 μs even ten nanoseconds level measurement requirements for the time resolution of the PIV measurement system caused by the fast and drastic changes of the hypersonic flow.(2)Aiming at solving the problem of insufficient imaging resolution in hypersonic flow,resulting in low accuracy of small-scale structures,this disservation combines the gradient prior and the spatial information of multi-frame low-resolution particle images,and proposes a gradient prior based super-resolution technology using multi-frame displacenment information(GPMFSR).Compared with existing reconstruction methods,this method improves the peaksignal-to-noise by more than 3%,reduces RMSE by 20%,AAE by 30% and obtains a higher estimation accuracy,solving the problem of high imaing spatial resolution measurement of small-scale structures in the hypersonic flow.(3)In view of the high spatial resolution measurement requirement that nano-tracer particles in hypersonic flows has large dynamic range of velocity field,this disservation proposes a circulant-matrix based hybrid optical flow method(CM-HOF),estimating the coarse velocity with a circulant-matrix based correlation to improve the measurable velocity range and estimating the finer velocity with an adaptive weighted optical flow to output one velocity vecotor per pixel.Compared with existing cross-correlation and optical flow methods,CMHOF can achieve velocity with large dynamic range and one velocity vector per pixel,solving the problem of spatial resolution measurement caused by the intereference of complex waves,such as shock waves and expansion waves,generated by the highly non-uniform characteristics of the hypersonic flow.To meet the measurement requirement of high temporal and spatial resolution of hypersonic flow,the hardware devices of an instrument named real-time adaptative PIV(RTAPIV)is developed,including the designed imaging equipment and high-speed image processing equiment,along with RTA-PIV software development integrating GPMFSR and CM-HOF.The desired RAT-PIV instrument realizes the measurement of hypersonic flow at March 5 and above,with resolution of 2 560×2 160 pixels,frame rate of 200 Hz and time resolution up to 10 nanoseconds.It provides a velocity output of one vector per pixel.The measurement error in the 5Ma hypersonic flow of a twenty-eight degrees wedge model is within 1%,indicating that RTA-PIV instrument can be used for the measurement of the applications of hypersonic flow enginerrring model.