曲率连续造型方法对激波噪声的影响机理

激波噪声是大涵道比涡扇发动机噪声的主要来源。为降低风扇/压气机叶片叶尖产生的激波噪声，对轴向亚音、相对超音的基元级叶型前缘脱体激波系进行研究。基于几何Hermit差值法（GHI）思想，提出一种3段式贝塞尔（Bezier）曲线构造曲率连续前缘叶型的方法，在完成改型设计时拥有更高的自由度。通过改变前缘上3段Bezier曲线间过渡点位置，探究局部曲率优化、整体曲率优化及带厚度补偿的改型方式对前缘处外伸激波强度和激波噪声的影响。通过对比研究不同数值模拟，结果表明：曲率连续前缘设计能减小叶型前缘处过膨胀区大小，减小由此产生的逆压梯度；局部曲率优化和整体曲率优化的方式能够分别在距前缘1倍弦长处降低噪声1.6 dB和4.6 dB。

Influence mechanism of continuous curvature shaping method on buzz-saw noise

Buzz-saw noise generated by fan/compressor blade tips is one of the main noise sources in high bypass ratio Turbofan engine. To reduce the noise, the detached shock-wave system at the blade leading edge of a relative supersonic and subsonic axial two-dimensional cascade is studied. First, based on the geometric hermit interpolation (GHI) method, a three-segment Bezier curve was proposed to construct a continuous-curvature leading edge, which has higher degree of freedom in modification design. Next, by changing the position of the transition points between the three Bezier curves on the leading edge, the effects of local curvature optimization, overall curvature optimization, and optimization with extra thickness upon the strength of the shock-wave and noise level at the leading edge were explored. A comparison of numerical results showed that the continuous curvature design could decrease the size of the over expanded zone at the leading edge of the blade, thus reducing the reverse pressure gradient. Through local curvature optimization and overall curvature optimization, noise level at one chord length upstream from the leading edge could be lowered by 1.6 dB and 4.6 dB.