Research On The Calibration Method Of Laser Doppler Velocimeter Based On Adjustable Speed Spinning-Disc Facility

With the advantages of non-contact measurement,high accuracy and quick dynamic response,Laser Doppler Velocimeter(LDV)is widely applied to measure air velocity in the world and used as the standard to calibrate other velocimeters to ensure accurate and reliable measurement values transmission.However in practical applications,the fringe distortion is a key factor which affects the measurement accuracy of LDV,the existing research mainly concentrated in the experiment,which directly affects the reliability of the quantity-transfer system of the air velocity.In this work,the calibration method of LDV based on adjustable speed spinning-disc facility was investigated.The measurement accuracy of LDV was improved fundamentally.The reliable technology foundation and quantity-transfer basis of new air velocity standard was provided.Finally the LDV measurement values effective trace to the SI units of meter and second.In this paper,a new spinning-disc facility was established for the investigation on the calibration method of LDV.It can be applied to(0.2-25m/s)speed range,and the relative expanded uncertainty was 0.1%(k=2).The main work and innovations are as follows:(1)Acording to the main causes of the fringe distortion,through detailed theoretical analysis,the mechanism of the fringe distortion which affects the measurement accuracy of LDV was revealed firstly.The relationship between the Gaussian beam propagation characteristics and its interference fringe distribution are established.The parameters influencing the interference fringe distribution are determined.(2)The relevant parameters were measured by experiment.The interference fringe spacing and gradient distribution of green and purple beams in the measuring volume at any locations are quantified by using measured parameters.In the measuring volume of green and purple beams,maximal normalized fringe gradient can reach 0.46% and 0.60%.(3)A new spinning-disc facility was established firstly,fixing the scattering particle on the glass spinning-disc to simulate the tracer particles in the fluid,which can realize the accurate measurement of fringe spacing in LDV.The scheme of calibration system was designed independently.The structural design of the whole facility,accessories selection,software design and hardware design were accomplished.(4)By measuring the fringe spacing and its distribution under the different laser wavelength and the focal length on the spinning-disc facility,green and purple light of the maximum relative error are 0.87% and 0.78% respectively compared with the theoretical analysis results.The calibration method was verified,and the LDV measurement accuracy was improved fundamentally.(5)The uncertainty of measurement results was analysed detailed.