Active Control of flows using Thin Actuators

1)风洞实验首先，利用附着在平板表面的聚偏氟乙烯来控制气流。胶片是由来自工作站的信号操作的，并由高速功率放大器放大。该系统利用不同的信号分别控制每片薄膜产生不同扫描角度的二维Tollmien-Schlichting波和斜波，并将流量控制装置改为压电陶瓷装置。同时，通过减小器件尺寸和增加器件个数，增加了扫描角度的自由度，从而实现了在边界层中引入各种波的研究目的。然而，由于实验装置的限制，我们不能证明该系统具有改变转换点的能力。2)数值模拟采用正交网格，成功地再现了风洞实验的流场。结果揭示了在波发展之前紧接在控制装置之后发生的复杂机制。结果表明，执行器的边缘不一定要暴露在流动中，而且有可能使用平齐安装的装置来控制流动。

1) Wind tunnel experimentsFirst, PVDF attached on the surface of a flat plate was used to control the flow. The film was operated by a signal from a workstation, amplified by a high-speed power amplifier. Each film piece was controlled separately by different signals and it was shown that two-dimensional Tollmien-Schlichting wave and oblique waves of various sweep angles could be generated by this system.Next, the flow controlling device was changed to a piezo-ceramic device. As a result, the system became capable of generating oblique waves of small sweep angles, which was difficult with the PVDF.In addition, by reducing the size of the devices and increasing their number, the freedom in the sweep angle of the wave increased.The aim of the research which was to develop a technique to introduce various types of wave in the boundary layer was accomplished. However, due to the limitation in the experimental facility, we could not show that the system was capable of changing the transition point.2) Numerical simulationsBy using an orthogonal grid, the flow fields of the wind tunnel experiments were regenerated successfully. The result disclosed the complicated mechanism which takes place immediately after the controlling device before the wave develops. The result suggests that it is not essential for the edge of the actuator to be exposed the flow, and that there is a possibility that a flush-mounted device can be used to control the flow.