Development of Aeroacoustic Cavity Noise Controlling Devices Utilizing Strong Fluctuation into Turbulent Flows

本研究旨在发展一种能有效控制腔体噪声的主动控制装置。我们的策略是在空腔的前缘提供流动分离的相位控制，在那里流动的感受性变得最高。所安装的控制装置可以将具有180度相位差的并排速度波动的波浪图案引入到流动中。压力波动以及由此产生的声波也是180度异相的。在我们的研究中，我们尝试用合成射流来抑制空腔噪声。首先，合成射流产生的扬声器和谐振器的集合。由于发现扬声器的贡献不是对流体颗粒的运动而是对压力波动的贡献，因此确定了产生合成射流的有效位置。因此，通过调节扬声器的声音频率，成功地降低了空腔噪声。此外，另一种控制装置，利用射流振荡器的开发。对于层流分离流，空腔噪声的峰值被成功地抑制到背景噪声水平，谐波分量也从频谱中消失。此外，我们成功地实现了有效的抑制空腔噪声，即使当分离流是湍流时，使用两个同步的射流振荡器沿展向沿着安装。

The purpose of this study has been to develop an energy efficient active control device that can control the cavity noise. Our strategy was to provide the phase control of the flow separation at the leading edge of the cavity, where the receptivity of the flow becomes the highest. The control devices installed can introduce wavy patterns of the velocity fluctuations side-by-side with 180 degrees phase difference into the flow. The pressure fluctuations and hence the sound waves coming out are also 180 degrees out of phase. As a result, the opposite-signed sound waves eventually cancel each other faraway from the source.In our study, the suppression of the cavity noise has been tried by synthetic jets according to the strategy. First, the synthetic jets were generated by the sets of the loudspeakers and the resonators. Because it was found that a loudspeaker's contribution was not to the motion of the fluid particles but to the pressure fluctuation, the effective location to produce the synthetic jets was determined. Consequently, the cavity noise was successfully reduced by adjusting the sound frequency of the loudspeakers.Furthermore, another control device utilizing a fluidic oscillator was developed. For the laminar separating flow, the peak of the cavity noise was successfully suppressed to the background noise level and the harmonic components also disappeared from the spectrum. Moreover, we were successful in achieving an effective suppression of the cavity noise even when the separating flow was turbulent using two synchronized fluidic oscillators installed side by side along the spanwise direction.