Develpment of Karman Vortex Velocimeter by Use of Laser Diode

研制了一种适用于气液两相流的流速仪。测量了垂直于流动方向放置的小直径金属丝（0.3mm、0.5mm和1 mm）下游卡门涡的频率。来自激光二极管的平行光（直径：1 mm）被涡旋折射，并被光电二极管检测到。通过施加低压电荷来加热电线，以加强光的折射。用FFT分析仪测量了卡门涡的频率，卡门涡的频率与速度几乎成线性关系。实验证实，在3 ~ 200 m/s的速度范围内，可以测量到速度，并认为更高的速度也是可行的。一种是通过使激光沿着导线（涡流发生器）扫描来测量频率的方法。另一种方法是移动测频丝的方法，对于0.3mm和0.5mm的小直径测频丝，该方法与皮托管的测量结果基本一致。随着直径变大，两个测量值之间的差异变大。此外，小直径的金属丝还具有扰动小、波形好、功耗低等优点，并以此为基础研制了小直径管道（直径为5 mm）水流流量计。涡流发生器选用直径为0.1 ~ 0.5mm的细钢丝。流量和频率之间的关系几乎是线性的。利用F/V转换器成功地实现了频率的测量。该转换器可用于测量高达40 Hz的正弦流量。

A velocimeter which is applicable to gas and liquid flow was developed. The frequency of the Karman vortex downstream of a small diameter wire (0.3mm, 0.5mm and 1mm) set perpendicular to the flow is measured. The parallel light (diameter : 1mm) from a laser diode is refracted by the vortex and it is detected with a photo diode. The wire is heated by applying a low-voltage electrical charge in order to strengthen the refraction of light. The frequency is measured with FFT analyzer.The frequency of the Karman vortex and the velocity are almost linear. It was confirmed experimentally that the velocity range between 3m/s and 200m/s could be measured, and it is supposed that higher velocity is also avairable.Two methods were carried out to measure the velocity profile. One is a method which measures the frequency by scanning the laser light along the wire (vortex generator). The another is a method which measures the frequency by moving the wire.Almost same results between this method and Pitot tube were obtained as for the wire of a small diameter such as 0.3mm and 0.5mm. As the diameter became larger, the difference between the two measurements became higher. Beside, the wire of small diameter showed favorable results in a smoll disturbance of the flow, a fine wave form and a low electrical power consumption.A flowmeter for water flow in a small diameter pipe (diameter : 5mm) was also developed in a same way to the velocimeter. The wire of small diameter from 0.1mm to 0.5mm were used as the vortex generator. The relation between the flow rate and the frequency which is almost linear. F/V converter was also used successfully to measure the frequency. The converter was available to measure a sinusioidal flow rate up to 40Hz.