Development of a driving method for high-intensity turbulence through independent controllability of multi-fan wind tunnels

本研究的目的是利用多扇风洞来产生高强度和大尺度的湍流。由于气流是由99个小风扇组成的阵列驱动的，所以可以产生各种流动。然而，如何同时产生高强度和大尺度的湍流仍然是一个悬而未决的问题。作为基本的驱动方法，我们有(1)均匀活动模式和(2)准网格模式，但所产生的湍流与真实大气湍流相差甚远，我们尝试了主动网格方法。在输入几个正弦波动的情况下，我们测量了湍流场，重点关注湍流强度是否可以被放大。这意味着我们试图产生高雷诺数的湍流，通过提供外部波动来放大湍流能量。除了与输入波动相关的尖锐峰值外，所产生的光谱几乎没有变化。在使用的风洞更新后，可以通过反向旋转的风扇来获得吸力。研究发现，吸力的作用是在吹风后立即使混合达到最大，每个风机的随机相位差可以增强混合。然而，我们还没有去除来自外部波动的脉动分量，而且我们还尝试了对风扇进行分形排列。由此产生的湍流在一定程度上满足各向同性，但非均匀存在于一定的流向距离上。

The purpose of the present research is to generate both high-intensity and large-scale turbulence by using a multi-fan wind tunnel. Since air flow is driven by an array of small 99 fans, various flows can be generated., However, the question as to how to generate both high-intensity and large-scale turbulence is still open. As basic driving methods, we have (1) uniformly active mode and (2) quasi-grid mode, but the resulting turbulence is far from the real atmospheric turbulence.By combining driving mode (1) and (2), we have tried an active-grid method. With a few sinusoidal fluctuations fed, we have measured turbulent fields with attention focused on whether turbulence intensity can be amplified. That means we try to generate high-Reynolds number turbulence to amplify turbulent energy by providing external fluctuations. Except a sharp peak associated with input fluctuations, there is little change in the resulting spectra.After an update of the wind tunnel used, suction becomes available by rotating fans in the reverse direction. It was found that the effect of suction is to maximize mixing immediately downstream of blowing, and random differences in phase of each fan allow mixing to enhance. However, we have not removed pulsating component originated from the external fluctuations yet.Furthermore, we have attempted fractal arrangement of the fans. The resulting turbulence satisfied isotropy to some degree, but non-uniformity survives over some streamwise distance.