Study on the effect of the boundary layer on the generation of aerodynamic noise and its control method.

Experimental investigations were conducted in order to understand the characteristics of the Aeolian tone generated from two-dimensional square and circular cylinders with pressure transducers embedded on the surface。下面的组合是物体：1）方形回旋机当攻击角度为0°时，Aeolian音调的峰值水平是最大值，或者，一个平坦的表面是正常的，达到了平均流动。The separated flow from the leading edge corner of the square cylinder reattaches to the side surface for the angle of attack between 10°到13°。表面压力流动在这一攻击角度的最小化程度上成为Aeolian音调的最小化程度。（2）圆形圆筒形圆筒形圆形圆筒形（Re<3 x10 y D15 y D1）， super c#（3 x10 y D15 y D1<Re<10 y D16 y D1） and trans-c #（Re>10 y D16 y D1） regions。在亚临界地区，冲浪区 ... More ACE压力流动是统一的跨度和在Aeolian音调较高的音调之间的一致性，而Strouhal数为0.2。在超临界区域，Strouhal的数字跳跃到0.45，Aeolian音调下降的峰值水平将共享。表面压力流动显示出强大的三维尺寸，只有一个分形部分在西班牙显示出与Aeolian ire的高度一致性。在跨临界区域，Strouhal数字返回到0.2，表面压力流动的特殊特征和Aeolian音调显示某种随机性质与布朗特峰。从测量和预测的Aeolian音调水平从表面压力流动显示出很好的一致性，但预测的音调水平大约低于10分贝，低于跨临界区域的测量水平.3）减少Aeolian音调的一半圆形方形圆柱显示接近10分贝低Aeolian音调水平当圆形部分接近平均流动时，与相同直径的圆形圆柱体相比较。当一根直径d线在一个音高p处弯曲时，绕一根直径D的圆形圆柱体时，Aeolian音调在d/D>0.2和p/D=3时被认为退化。Less（低）

Experimental investigations were conducted in order to understand the characteristics of the Aeolian tone generated from two-dimensional square and circular cylinders with pressure transducers embedded on the surface. The following conclusions were obtainec.1) Square CylinderThe peak level of the Aeolian tone is maximum when the angle of attack is 0°, or, a flat surface is placed normal to the mean flow. The separated flow from the leading edge corner of the square cylinder reattaches to the side surface for the angle of attack between 10°to 13°. The surface pressure fluctuation becomes minimum at this angle of attack and consequently the Aeolian tone becomes minimum.2) Circular CylinderThe characteristics of the Aeolian tone radiated from a circular cylinder can be divided into three categories in the Reynolds number, Re, I.e. sub-critical (Re<3x10ィイD15ィエD1), super critical (3x10ィイD15ィエD1<Re<10ィイD16ィエD1) and trans-critical (Re>10ィイD16ィエD1) regions. In the sub-critical region, the surf … More ace pressure fluctuation is uniform spanwise and the coherence between the Aeolian tone is high and the Strouhal number is 0.2. In the super-critical region, the Strouhal number jumps up to 0.45 and the peak level of the Aeolian tone decreases sharply. The surface pressure fluctuation shows strong three-dimensionality and only a fractional part in spanwise shows high coherence with the Aeolian ire. In the trans-critical region, the Strouhal number returns to 0.2 and the spectra of the surface pressure fluctuation and the Aeolian tone show somewhat random nature with a blunt peak. The comparison between the measured and predicted Aeolian tone level from the surface pressure fluctuation shows good agreement for the sub- and super-critical regions but the predicted level is approximately 10 dB lower than the measured level for the trans-critical region.3) Reduction of the Aeolian ToneA half rounded square cylinder shows approximately 10 dB lower Aeolian tone level when the rounded part is faced to the mean flow, compared to the circular cylinder with the same diameter. When a wire of diameter d is wound in spiral with a pitch p,around a circular cylinder of diameter D, the Aeolian tone is considerably decreased when d/D>0.2 and p/D=3. Less