Brayton D B, Kalb H T, Crosswy F L
Appl Opt. 1973 Jun 1;12(6):1145-56. doi: 10.1364/AO.12.001145.
A dual-scatter laser Doppler velocimeter (LDV) system designed for measuring wind tunnel flow velocity is described. The system simultaneously measures two orthogonal velocity components of a flowing fluid at a common point in the flow. Essential single-velocity component dual-scatter concepts are presented to simplify the description of the more sophisticated two-component system. To implement the two-component system three laser beams with a 0 degrees , 45 degrees , and 90 degrees polarization plane relationship are focused to a common point in the flow by the system-transmitting optics. The beams interfere to form two perpendicular sets of interference fringe planes that are orthogonally polarized. The system-receiving optics collect and separate the orthogonally polarized components of laser radiation scattered from micron-size particles moving with the flowing fluid through the ringes. The system requires no artificial seeding, since intrinsic test section aerosols are utilized for radiation scattering. The passage of each scatter particle through the interference fringes simultaneously produces two frequency-burst-type photodetected signals, the frequencies of which are directly proportional to two perpendicular components of particle velocity. The system photodetection, signal-conditioning, and data acquisition instrumentation is specifically designed to process the frequency burst information in the time domain as opposed to spectrum analysis or frequency domain processing. The system was initially evaluated in an AEDC wind tunnel operating over a Mach number range from 0.6 to 1.5. The LDV and calculated wind tunnel mean velocity data agreed to within 1.25%; flow direction deviations of a few milliradians were resolved.
本文描述了一种用于测量风洞流速的双散射激光多普勒测速仪（LDV）系统。该系统可同时测量流体中某一共同点处的两个正交速度分量。文中介绍了基本的单速度分量双散射概念，以简化对更复杂的双分量系统的描述。为实现双分量系统，系统发射光学装置将具有0度、45度和90度偏振面关系的三束激光聚焦到流场中的一个共同点。这些光束相互干涉，形成两组相互垂直的干涉条纹平面，且条纹平面相互正交偏振。系统接收光学装置收集并分离由随流体流动的微米级颗粒通过条纹时散射的激光辐射的正交偏振分量。该系统无需人工撒种，因为利用了试验段内的固有气溶胶进行辐射散射。每个散射颗粒穿过干涉条纹时，会同时产生两个频率猝发型光电检测信号，其频率与颗粒速度的两个垂直分量成正比。系统的光电检测、信号调理和数据采集仪器专门设计用于在时域中处理频率猝发信息，而非频谱分析或频域处理。该系统最初在AEDC风洞中进行评估，风洞运行的马赫数范围为0.6至1.5。LDV测量结果与计算得到的风洞平均速度数据的误差在1.25%以内；几毫弧度的流向偏差也能分辨出来。
