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Development of Scan-Type Laser-Doppler Velocimeter and Some Examples of Measurement

扫描式激光多普勒测速仪的研制及部分测量实例

基本信息

批准号：
59850088
负责人：
HINO Mikio
金额：
$ 9.73万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research
财政年份：
1984
资助国家：
日本
起止时间：
1984 至 1985
项目状态：
已结题

项目摘要

LDV (Laser Doppler Velocimeter) has an excellent feature that it can measure velocity without inserting a prove into a flow field and thus without disturbing it. Nevertheless, it cannot be free from the defect common with the Eulerian type of velocimeters which are set at a fixed point in a flow field; i.e., these velocimeters cannot measure the instantaneous spatial feature of flow at a glance.On the contrary, the recently advanced various techniques of flow visualization can afford us a spatial feature of a flow field at a glance but they cannot give a detailed quantitative information of the flow, without expensive special equipments and tedious time consuming labor.We attempted in this project ot develop a novel type of instrumentation; i.e., SLV (Scan-type Laser Doppler Velocimeter) Hich can measure quantitatively and nearly continuously the spatial (one-dimensional and if the Taylor hypothesis of a frozen flow field is introduced, two-dimensional) flow field.Splitted laser beams which focus at a measuring point and make the interference fringes are scanned by a rapidly rotating polygon-mirror. An electronic processing unit receives, on the one hand, signals on the position of the moving measuring point from the driving unit and, at the same time, signals of velocity carried on the scattering laser beam from tracer particles passing through interference fringes. The maximum scanning period is 0.2s, and the maximum scanning width is 10cm.In order to test the performance of the SLV, three typical flow fields are measured, i.e., (1) Karman vortex street, (2) laminar oscillatory boundary layer and (3) vortex ring. The results were satisfactory.The instrument may be a powerful tool for measurement of flow fields which are non-steady or cannot be realized repeatedly such as an instantaneous structure of organized turbulence.

LDV（激光多普勒测速仪）具有无需在流场中插入探针就能测量速度，因而不会干扰流场的优良特性，但它也不能避免欧拉型测速仪的缺点，即在流场中设置固定点，这些测速仪不能一眼看出流场的瞬时空间特征，而近年来发展起来的各种流场显示技术，却不能给出流场的详细定量信息，而需要昂贵的专用设备和费时的劳动。SLV（Scan-type Laser Doppler Velocimeter）激光多普勒测速仪是一种能定量、近连续地测量空间（一维，如果引入冻结流场的泰勒假设，则为二维）流场的测速仪，它是将分裂的激光束聚焦在一个测量点上，通过一个快速旋转的反射镜扫描产生干涉条纹。电子处理单元一方面接收来自驱动单元的关于移动测量点的位置的信号，并且同时接收来自穿过干涉条纹的示踪剂颗粒的散射激光束上携带的速度信号。最大扫描周期为0.2s，最大扫描宽度为10 cm。为了测试SLV的性能，测量了三种典型的流场，(1)卡门涡街，（2）层流振荡边界层和（3）涡环。结果表明，该仪器可作为测量非定常流场或不可重复测量流场的有力工具，如有组织湍流的瞬时结构。