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

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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.