多排凹坑对叶片气动及噪声特性的研究

Study on Aerodynamic and Noise Characteristics of Blades with Multiple Rows of Pits

摘要: 本文通过改变叶片两种凹坑的排列方式，采用大涡模拟(LES)方法探究相对长度和排列方式对叶片的气动特性的影响，声场上采用LMS Virtual.lab直接边界元法研究了相对长度和排列方式对叶片的噪声特性的影响，并揭示了多排凹坑设计对叶片边界层流动控制及噪声抑制的机理。研究结果表明：排布方式对卵圆形凹坑的影响不大，采用矩形排布的圆形凹坑时叶片尾缘压力脉动明显下降。多排凹坑引起高频段窄带噪声增大，其中圆形凹坑模型的总声压级下降约3 dB。当采用菱形排布时降噪效果更好，此时额外诱导的周期性涡脱落噪声较小。通过进一步研究分析，认为多排凹坑降噪的机理为：吸力面表面凹坑设计对叶片湍流流动具有一定的控制效果，坑面处形成的反向涡流干扰了边界层内相干结构的展向联系，一定程度上可以抑制尾缘处大尺度脱落涡形成，削弱壁面分离流结构，可以有效降低与大尺度相干涡关联的中低频噪声。

Abstract: In this paper, by changing the arrangement of the two pits of the blade, the large eddy simulation (LES) method was used to investigate the influence of relative length and arrangement on the aerodynamic characteristics of blades. The effects of relative length and pit arrangement on blade noise characteristics were studied by LMS Virtual.lab direct boundary element method, and the mechanism of multi-row pit design on flow control and noise suppression of blade boundary layer were revealed. The research results show that: the arrangement has little effect on oval pits blades, the pressure pulsation at the trailing edge of the blade decreases obviously when the circular pit is arranged in a rectangular pattern. Multiple rows of pits cause high frequency narrow-band noise to increase, and the total sound pressure level of the circular pit model decreased by about 3 dB. The noise reduction effect is better when diamond layout is adopted. At this time, the additional induced periodic vortex shedding noise is smaller. Through further research and analysis, it is concluded that the noise reduction mechanism of multi-row pits is that: the design of the pit on the suction surface can control the turbulent flow of the blade; the backward eddy currents formed at the pit surface interfere with the spanwise relations of the coherent structures in the boundary layer; to some extent the formation of large scale shedding vortex at trailing edge can be restrained, and wall separation flow structure is weakened, that can effectively reduce the low and medium-frequency noise associated with large scale vortices.