Research and Development of Fiber L2F

为了实现小型化、低成本、操作方便的特点，研制了一种新型激光双焦点测速仪（L2 F）。设计并搭建了基于光纤和半导体激光器的光学系统和信号处理系统。在风洞或旋转叶轮的流量测量中，对新系统的设计指标进行了测试。第一步，开发了在激光源和光学头之间使用的光纤长度为8 m的光纤L2 F。与原始L2 F相比，纤维L2 F的尺寸在重量上减小到一半，在体积上减小到三分之一。当根据光纤中偏振光的特性将光闸安装在光纤前面时，光纤L2 F的光学S/N比对于应用于旋转叶轮中的流量测量没有恶化。 ...更多信息 研制了长324 mm、宽98 mm、高140 mm、重5 kg的微型微型电动自行车。使用波长为840 mm的二极管激光器作为光源，并且使用雪崩光电二极管检测来自颗粒的散射光。设计了一种对半导体激光器具有高灵敏度的电子放大器。二极管L2 F的测量体积是用一个直径为5 μ m的细线和一个机械横移系统测量的，即使当激光束垂直于壁插入一个小型风洞时，也可以在靠近底壁1 mm处进行流量测量，这证实了二极管L2 F系统的高S/N比。在低湍流度情况下，最大采样率为2kHz，粒子穿过两焦点的概率超过80%，从而通过将两焦点之间的距离缩窄到0.1mm而显著缩短了测量时间。即使在横向湍流强度为20%的高湍流流中，二极管L2 F也适用于流量测量。少

A new type laser-2-focus velocimeter (L2F) was developed to materialize a small size, a low price and an easier operation. An optical system and a signal processing system based on an optical fiber or based on a diode laser were designed and were built up. The design specifications of new systems were tested applying to a flow measurement in a wind tunnel or in a rotating impeller.At the first step, a fiber L2F with an optical fiber of 8 m in length used between the laser source and the optical head was developed. The size of the fiber L2F was reduced to a half in weight and a third in volume compared with the original L2F. The optical S/N ratio of the fiber L2F was not deteriorated for application to a flow measurement in a rotating impeller, when the optical shutter was installed ahead of the optical fiber according to the behavior of polarized light in an optical fiber.At the second step, a diode L2F with a transmitter optics of 48 mm in diameter and of 120 mm of measuring distance … More was developed, the size of which is 324 mm in length, 98 mm in width and 140 mm in height, and the weight is 5kg. A diode laser of 840 mm in wave length was used as a light source, and the scattered light from a particles was detected using an avalanche photodiode. An electric amplifier was designed with high sensitivity against the diode laser. The measuring volume of the diode L2F was measured using a fine wier of 5 mum in diameter with a mechanical traversing system.It was possible to make a flow measurement at I mm close to the bottom wall even when the laser beam was inserted into a small-sized wind tunnel normal to the wall, and this confirmed a high S/N ratio of the diode L2F system. In the case of low turbulence flow, the maximum sampling rate was 2kHz and the probability of a particle traveling through the two foci was beyond 80 percent so that a measuring time was reduced significantly by narrowing the distance between the two foci to 0.1 mm. Velocity distribution in a two-dimensional wake behind a circular cylinder was measured. The diode L2F was applicable to a flow measurement even in a high turbulence flow with 20 % in transverse turbulence intensity. Less