Research On Calibration Method Of Particle Image Velocimetry(PIV)

Particle image velocimetry(PIV)is a flow field measurement technology which uses high-speed camera,laser and tracer particles to measure the flow velocity.Compared with the traditional measurement technology,PIV technology does not interfere with the measured flow field,and can realize the whole field transient measurement with high measurement accuracy.It has been applied into many fields,and gradually become an important flow field measurement technology.In practical application,PIV measurement accuracy is always the most concerned problem of users,but there is no general PIV calibration method at present.Therefore,it is urgent to establish a set of PIV calibration method,improve the value transmission and traceability system of PIV measurement results,and polish the measurement ability of PIV,so as to realize the application of PIV in more fields.In order to enhance the measurement accuracy of PIV and realize the quantitative analysis of the PIV measurement results,the paper obtains two important factors affecting the measurement results through the study of PIV measurement principle and system composition,which are: particle displacement(35)s and frame straddling time(35)t.The research carries out the evaluation of the uncertainty of the two factors and designed the experimental scheme of PIV calibration based on laser Doppler velocimeter,then its uncertainty was evaluated systematically.The main research results are as follows:(1)The main influencing factors of uncertainty evaluation of particle displacement(35)s are image distortion,laser sheet thickness,optical performance of tracer particles and camera calibration.The results of the investigation are as follows: The image distortion of the CCD camera used in the experiment has little influence on(35)s and can be ignored;In the experiment,the thickness of the laser sheet is set as around 1 mm,which can eliminate the influence of the thickness of the laser sheet on(35)s to the maximum extent;According to the requirements of the optical properties of the particles,the experiment selected the tracer particles with different materials and sizes.Therefore,the main source of uncertainty of particle displacement is camera calibration,and the team performed the evaluation of uncertainty of camera calibration,and the expanded uncertainty of particle displacement(35)s is 0.08mm(k = 2).(2)The team further conducted uncertainty evaluation of frame straddling time(35)t.After the investigation on its working principle,we have known that the major influencing factors are:synchronizer working frequency,synchronizer time interval,CCD camera response delay,laser response delay.We conducted the uncertainty evaluation of these four influencing factors respectively and we finally derived the relative expanded uncertainty of frame straddling time for(35)t is 1.3%(k = 2).(3)A set of PIV calibration experiment scheme based on LDV is designed.Taking the open-ended wind tunnel as the flow field generator and LDV as the standard etalon,the calibration experiment scheme is designed by studying the flow field quality evaluation,LDV measurement position and PIV post-processing parameters in the experimental section of the wind tunnel.After the calibration experiment,the uncertainty of measurement results was analyzed in detail.The expanded uncertainty of PIV measurement is 1.549%(k = 2)in the flow rate range of(1 ? 30)m/s.