基于LDV测速算法的多普勒频率测量不确定度分析和评定

Analysis and Evaluation on the Uncertainty of Doppler Frequency Measurement Based on LDV Velocity Measurement Algorithm

为了明确激光多普勒测速仪(LDV)通过转盘装置校准的低速结果在高速的适用性,分析得到LDV测量流速的不确定度与测量体中的干涉条纹间距和多普勒频率的不确定度相关。由于干涉条纹间距与被测流速无关,则高、低流速测量结果不确定度间的可能差异由多普勒频率算法引入。用基于蒙特卡洛法(MCM)传播概率分布评定测量不确定度的方法分析在不同流速下多普勒频率算法引入的多普勒频率测量不确定度,发现在流速为0.1~340 m/s时,由多普勒频率算法引入的多普勒频率相对不确定度均小于0.03%,且该相对不确定度在不同流速下基本保持不变。流速不同产生的多普勒频率不确定度差异对LDV测速结果的影响小于0.013%,验证了测速算法精度的适用范围。得到了LDV低速校准结果可以应用于高速测量的结论,解决了高流速测量的溯源问题。

In order to clarify the applicability of the low-speed results of the laser Doppler velocimeter(LDV)calibrated by the spinning-disc facility,it is analyzed that the uncertainty of velocity depends on the uncertainty of both the interference fringe spacing in the measuring volume and Doppler frequency.As the Interference fringe spacing is independent of the fluid velocity the possible difference of uncertainty in between the high velocity and the low velocity is only related with the Doppler frequency algorithm at different velocity.The uncertainty of Doppler frequency caused by the algorithm at different velocity is analyzed with Monte Carlo method(MCM)for evaluation of measurement uncertainty.The result shows that the relative uncertainty of the Doppler frequency caused by the algorithm is less than 0.03%in the range of 0.1~340 m/s.The obvious difference of uncertainty has not been found in the different points of velocity investigated.The budget resulting from Doppler frequency accuracy to the uncertainty of velocity measured is less than 0.013%.It is concluded that the calibration result at low velocity is also reasonable to be used at high velocity measurement.