Trial production of a new wind tunnel with directly controlled fans to simulate fluctuations in velocity and direction of natural wind

本项目旨在开发一种新的风洞，以模拟自然风的速度和方向的波动。我们做了一个由交流电机驱动风扇的风洞进行试验。伺服电机由计算机生成的电压历史控制。最大风速为13 m/s。用热线风速仪测量了产生的风速，电压阶跃变化下的实测风速历史表明，风速可以在小于1/4秒的微小时间内发生突变。然而，在目标速度为零的情况下，由于即使在风扇已经停止旋转之后风也由于其惯性而不能停止，因此需要大约一秒。正弦电压变化下的实测风速历史表明，除了最低风速为零的情况下，风速的正弦变化。我们接下来进行了一系列的实验，目标速度波动服从卡门谱。实测的速度历程及其功率谱表明，新风洞不仅能再现目标速度脉动的细节，而且能再现其统计特性。特别是，可以很容易地实现相当大的湍流长度尺度的速度脉动。结果表明，这种新型风洞具有足够的模拟自然风速度脉动的能力。作为控制风向的初步研究，我们研究了两个串联风洞的吸气效应，发现吸气效应是无效的。现在计划通过合并来自两个水平角度对齐的风洞的气流来控制风向。

The present project has been conducted to develop a new wind tunnel to simulate fluctuations in velocity and direction of natural wind. We made for trial a wind tunnel of which fans are driven by an AC servomotor. The servo motor is controlled by computer-generated voltage histories. The maximum wind velocity is 13 m/s. The generated wind velocity is measured by a hot wire anemometer.The measured velocity histories under step-wise voltage changes show that the wind velocity can change abruptly within a infinitesimal time less than a quarter second. However, in the cases that the target velocity is zero, it takes about one second because the wind is not able to stop due to its inertia even after the fan has stopped rotating. The measured velocity histories under sinusoidal voltage changes show that the wind velocity varies sinusoidally, except for the cases that the lowest velocity is zero.We have next conducted a series of experiments where the target velocity fluctuations obey the Karman spectrum. The measured velocity histories and their power spectra show that the new wind tunnel can reproduce not only details of the target velocity fluctuation but also its statistics. Especially, velocity fluctuation with quite large turbulence length scale can be achieved easily. There is a limitation in generating high frequency fluctuation beyond several cycles per second.These results show that the present new wind tunnel possesses sufficient ability to simulate velocity fluctuation of natural wind as far as the longitudinal fluctuations are concerned.As a preliminary investigation to control wind direction, we investigated the effect of inhalation by two wind tunnels in tandem alignment, and found that it is not effective. It is now planned to control wind direction by combining air flows from two wind tunnels aligned with a horizontal angle.