Faculty of Aerospace Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel.
J Acoust Soc Am. 2013 Apr;133(4):1934-44. doi: 10.1121/1.4792246.
Acoustic signature of a rigid wing, equipped with a movable downstream flap and interacting with a line vortex, is studied in a two-dimensional low-Mach number flow. The flap is attached to the airfoil via a torsion spring, and the coupled fluid-structure interaction problem is analyzed using thin-airfoil methodology and application of the emended Brown and Michael equation. It is found that incident vortex passage above the airfoil excites flap motion at the system natural frequency, amplified above all other frequencies contained in the forcing vortex. Far-field radiation is analyzed using Powell-Howe analogy, yielding the leading order dipole-type signature of the system. It is shown that direct flap motion has a negligible effect on total sound radiation. The characteristic acoustic signature of the system is dominated by vortex sound, consisting of relatively strong leading and trailing edge interactions of the airfoil with the incident vortex, together with late-time wake sound resulting from induced flap motion. In comparison with the counterpart rigid (non-flapped) configuration, it is found that the flap may act as sound amplifier or absorber, depending on the value of flap-fluid natural frequency. The study complements existing analyses examining sound radiation in static- and detached-flap configurations.
刚性机翼的声学特性研究，配备可动的下游襟翼，并与线涡相互作用，在二维低马赫数流动中进行。襟翼通过扭转弹簧连接到翼型上，通过薄翼型方法和修正的 Brown-Michael 方程的应用分析耦合流固相互作用问题。结果表明，在翼型上方的入射涡旋通道以系统固有频率激励襟翼运动，放大了所有其他包含在激励涡旋中的频率。远场辐射采用 Powell-Howe 类比进行分析，得到系统的主导偶极型特征。结果表明，直接襟翼运动对总声辐射的影响可以忽略不计。系统的特征声学特征主要由涡旋声组成，包括翼型与入射涡旋的前缘和后缘相互作用较强，以及由诱导襟翼运动引起的尾迹后期声音。与刚性（无襟翼）配置相比，发现襟翼可以作为声音放大器或吸收器，具体取决于襟翼-流体固有频率的值。该研究补充了现有的静态和分离襟翼配置的声辐射分析。
