论文标题
翼型过渡流中的音调噪声产生机制的转换
Switch of tonal noise generation mechanisms in airfoil transitional flows
论文作者
论文摘要
进行大型的涡流模拟以通过NACA0012的机翼以攻击角度$ {α= 3} $ deg来研究音调噪声。和$ {m _ {\ infty} = 0.3} $的自由式马赫数。分析了跨越$ {0.5 \ times 10^5 \ le re \ le \ le 4 \ times 10^5} $的不同雷诺数。结果表明，导致噪声产生的流动模式来自不同的层流分离气泡，包括在压力侧的翼型吸力侧观察到的流动模式，在翼型吸气侧观察到的气泡。对于较低的雷诺数，吸气侧的间歇性涡旋动力学会导致连贯的结构或湍流数据包朝向后边缘。这种流动动力学还会影响压力侧的分离气泡，这变得间歇性。尽管层流动力过渡的不规则发生，但噪声光谱描绘了具有多种等距次级音调的主音调。增加雷诺数的数量会导致吸力侧的永久性湍流状态，从而降低了相干水平，从而仅观察到小规模的湍流涡流。此外，吸力侧的层流分离气泡几乎消失了，而压力侧的层状则变得更加明显和永久。结果，主要的噪声产生机制变成了沿尾流的涡流。
Large eddy simulations are performed to study tonal noise generation by a NACA0012 airfoil at an angle of attack ${α= 3}$ deg. and freestream Mach number of ${M_{\infty} = 0.3}$. Different Reynolds numbers are analyzed spanning ${0.5 \times 10^5 \le Re \le 4 \times 10^5}$. Results show that the flow patterns responsible for noise generation appear from different laminar separation bubbles, including one observed over the airfoil suction side and another near the trailing edge, on the pressure side. For lower Reynolds numbers, intermittent vortex dynamics on the suction side results in either coherent structures or turbulent packets advected towards the trailing edge. Such flow dynamics also affects the separation bubbles on the pressure side, which become intermittent. Despite the irregular occurrence of laminar-turbulent transition, the noise spectrum depicts a main tone with multiple equidistant secondary tones. Increasing the Reynolds number leads to a permanent turbulent regime on the suction side that reduces the coherence level causing only small scale turbulent eddies to be observed. Furthermore, the laminar separation bubble on the suction side almost vanishes while that on the pressure side becomes more pronounced and permanent. As a consequence, the dominant noise generation mechanism becomes the vortex shedding along the wake.
