Research On Laser Doppler Technique For One-dimensional Particle Flow Measurement

With the continuous development of science and technology,the requirements for flow field information in various fields,such as aerospace and biomedicine,are becoming higher and higher.As a classical flow field measurement technology,laser Doppler measurement technology has great scientific research needs.However,at present,the instruments and equipment formed abroad are expensive and difficult to maintain,while the domestic demand for this measurement technology is only increasing.The cost of foreign instruments is very high,in order to develop a low-cost laser Doppler velocimetry system,this paper has carried out experimental research on the Doppler measurement technology,designed and manufactured a preliminary principle prototype.The main work is as following:Based on the Doppler principle of light wave,the basic theory of laser Doppler velocity measurement technology is analyzed.A Doppler measurement system which can be used for velocity measurement is built by using the double beam double scattering model,and the processing program based on MATLAB platform is completed.Experimental measurements are carried out on a variety of objects.Subsequently,the droplet flow generator is used to measure the accuracy of the velocity measurement system.The experimental results are in good agreement with the calibration results of the high-speed camera,showing a high measurement accuracy.Subsequently,in order to improve the number of available signals in the system experimental measurement,five window functions,namely rectangular window,Kaiser window,Hamming window,Hanning window and Blackman window,are used to preprocess the collected data.After a large number of experimental comparisons,the corresponding algorithm of Blackman window is selected as the signal preprocessing method,which improves the availability of system signals from 44% to 82%.Then a frequency shift Doppler measurement system is built using an acoustooptic frequency shifter and relevant experiments are carried out.The reasonable experimental data are obtained,and the corresponding solutions and prospects for the problems are put forward.Based on the previous experimental basis,the current experimental system is integrated and designed.The special adapter is obtained through mechanical design and processing,and the principle prototype of one-dimensional velocity measurement system is obtained.At last,this paper measured the actual spray scene using the designed and machined principle prototype.Firstly,the axial velocity of the low-speed ultrasonic atomizer was measured under multiple working conditions,and the reasonable experimental results were obtained.Then,the axial velocity of the swirling spray flow field produced by a swirl cup is measured by using the principle prototype,and the experimental results are analyzed and compared with the measurement results of the commercial PDA under the same working conditions,which confirms the measurement reliability of the principle prototype designed in this paper,and analyzes the shortcomings between the prototype and the commercial PDA.