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产生高强度和大尺度湍流。由于气流是由一组小型99风扇驱动的，因此可以产生各种气流。然而，如何同时产生高强度和大规模湍流的问题仍然没有解决。作为基本的驱动方法，我们有(1)均匀主动模式和(2)准网格模式，但得到的湍流与真实的大气湍流相差甚远。结合驱动模式(1)和(2)，我们尝试了一种主动网格方法。通过输入一些正弦波动，我们测量了湍流场，并关注了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峰外，所得光谱几乎没有变化。在更新风洞后，通过反向旋转风扇可以获得吸力。研究发现，吸力的作用是最大限度地提高吹风下游的混合，并且每个风扇的随机相位差异可以增强混合。然而，我们还没有去除来自外部波动的脉动分量。此外，我们还尝试了扇形的分形排列。所产生的湍流在一定程度上满足各向同性，但在一定的流向距离上仍然存在非均匀性。

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.