轴流风机仿生耦合叶片降噪机理研究

Noise Reduction Mechanism of Bionic Coupled Blades of Axial Flow Fan

为降低传统叶型轴流风机的气动噪声,受鸮类翅膀翼型和非光滑边缘结构的启发,以原型轴流风机的中弧线分布为基准,提取具有静音飞行特性的长耳鸮40%翼展截面处的厚度分布,结合长耳鸮翅膀边缘的非光滑结构特征,在仿鸮翼叶片尾缘耦合了正弦型锯齿结构对轴流风机叶片进行仿生重构,并将其应用于降低轴流风机噪声叶片改型设计中。基于轴流风机内部流场的数值计算结果,采用大涡模拟(LES)结合Ffowcs Williams和Hawkings发展的FW-H声类比方法对轴流风机的声场特性进行了数值模拟。研究结果表明:与原型风机相比,仿生耦合叶片风机的整体降噪幅度为2dB,风量提升4.69%。风机内部流场及声场显示:仿生耦合叶片使气流从吸力面向压力面的过渡更为平缓,不仅改善了气流对叶片前缘局部的冲击性,且能减弱叶顶间隙处的泄漏涡强度。此外,仿生耦合叶片产生的紊流边界层及尾迹涡脱落引起的气流脉动和气流不均匀性程度减弱,宽频噪声和离散噪声在中低频范围内均有所降低,因此仿生耦合叶片不仅改善了叶片前缘的局部压力脉动,且能够减小尾缘锯齿处的声源强度,改善叶片尾缘的尾迹涡分布。

In order to reduce the aerodynamic noise of the traditional blade-type axial fan and inspired by the owl wing profile and non-smooth edge structure,the thickness distribution at the40%span of the long-eared owl with silent flight characteristics was extracted based on the medial camber line distribution of the prototype axial fan as a benchmark.Combined with the non-smooth structural features of the long-eared owl wing edges and coupled with a sinusoidal sawtooth structure at the trailing edge of the imitated owl blade,bionic reconstruction of the axial fan blade was performed and used in the modified blade design to reduce the noise of axial fans.Based on the numerical calculation results of the internal flow field of axial fan,the large eddy simulation(LES)combined with the FW-H sound analogy method developed by Ffowcs Williams and Hawkings was used to numerically simulate the sound field characteristics of the axial fan.The research results show that the overall noise reduction of the bionic coupled blade fan is 2 dB and the air volume is increased by 4.69%compared with the prototype fan.The internal flow field and sound field of the fan show that the bionic coupled blade makes the air flow transition from the suction surface to the pressure surface more smoothly,which not only improves the local impact of the air flow on the leading edge of the blade,but also reduces the leakage vortex strength at the tip clearance.In addition,the turbulence boundary layer generated by the bionic coupled blades and the degree of airflow pulsation and airflow unevenness caused by the wake vortex shedding are weakened,and both broadband noise and discrete noise are reduced in the low-mid frequency range.Therefore,the bionic coupled blade not only improves the local pressure pulsation at the leading edge of the blade,but also reduces the intensity of the sound source at the trailing edge serration and improves the trailing vortex distribution at the trailing edge of the blade.