基于流固耦合作用的柔性体流噪声降噪机理研究

舵体与流体相互作用产生的流噪声是水动力噪声的主要来源之一,这种噪声以宽频噪声为主,一般的降噪措施难以对其进行有效控制,而柔性舵体提供了解决的技术方案。以柔性NACA0018翼型为对象,基于流场大涡模拟、考虑任意运动固体边界的声学FW-H方程、并进一步利用弱耦合流固耦合算法考虑流体与柔性体的相互作用,对柔性翼型绕流非定常流场及流致噪声进行仿真,系统地分析不同攻角下柔性体的变形对流动、声源特性及流噪声辐射特性的影响。仿真结果表明:柔性体的变形延缓了壁面的流动分离,减小了湍流区,并抑制了壁面的压力脉动;降低了转捩区和湍流区的壁面声源强度,层流区的声源强度在大攻角下减小,而在小攻角下增大;随着攻角的变化,远场辐射噪声总声压级在翼型弦长方向和法线方向上呈现不同的变化规律,噪声频谱特性也表现出不同的规律。

Study on Noise Reduction Mechanism of Flow Induced Noise for Flexible Body Based on Fluid-structure Interaction

The flow induced noise by the interaction between structure and fluid for rudder is one of dominant sources of hydrodynamic noise, featured by broadband noise, which is difficult to be controlled by ordinary noise reduction measures, but a solution is provided by flexible rudder. The unsteady flow field and flow induced noise of a flexible NACA0018 airfoil are simulated using large eddy simulation method, along with the FW-H equation which considers the arbitrary boundary movement. The interaction between flexible body and fluid is taken into account by weak coupling method. Then the influence of airfoil’s flexible deformation on flow field, noise source, and sound radiation characters under different attack angles are analyzed systematically. The simulation results show that flow separation is postponed by the deformation, turbulence region is contracted, and wall pressure fluctuation is suppressed. The sound source intensity of transitional boundary-layer and turbulent flow are decreased, and it is reduced for laminar flow under large angle of attack, but increased under small attack angle. With attack angle increasing the radiated far-field overall sound pressure level varies in different ways in chord-length and normal directions, and their sound frequency properties are also affected by the flexible deformation unlikely.