全尺寸起落架的气动及声学特性分析

Analysis of aerodynamic and aeroacoustics of full scale landing gear

起落架气动噪声是机体噪声的一大重要来源,其噪声特性的研究分析对于低噪声起落架的设计具有重要作用。基于FL-52声学风洞实验测试技术和耦合尺度自适应模型/声扰动方程的高精度混合数值方法,针对某支线飞机全尺寸起落架模型,开展了气动噪声实验测试和数值预测结果对比分析。该起落架模型是一个高保真的详细模型,包含了横向支杆、扭力臂、活塞杆、机轮等部件。对比分析了起落架机轮壁面静压分布、脉动压力功率谱密度、气动噪声源分布、总声压级指向性等特征,并比较远场传感器和安装在机轮凹腔中局部传感器的测量与数值结果,以表征机轮凹腔纯音的方向性,了解它们对远场噪声的贡献。结果表明,所采用的气动噪声混合数值方法可准确量化起落架近/远场的气动噪声。起落架机轮内、外侧凹腔存在560 Hz和960 Hz频率的纯音,最大声压级峰值可达136 dB,且纯音可辐射到起落架机轮非分离区域的表面。而位于起落架机轮湍流区域的测点,其壁面压力频谱曲线呈宽频特征,未出现明显的纯音。从远场噪声指向性来说,起落架前传噪声总体趋势上大于后传噪声,并且在65°和110°位置存在较小的总声压级区域。当远场测点达到一定距离后,起落架远场噪声呈现宽频特征,并未出现明显的纯音。该研究结果也为起落架噪声预测和低噪声起落架设计提供了依据。

The aerodynamic noise of a landing gear is an important source of airframe noise. The analysis of its noise characteristics plays an important role in the design of a low-noise landing gear. Based on the FL-52 acoustic wind tunnel test technology, the coupled scale adaptive model and the acoustic disturbance equation, the results on aerodynamic noise of a full-scale landing gear model are analyzed. The high-fidelity model includes transverse strut, torsion arm, piston rod, wheel and other parts. The characteristics of static pressure distribution, power spectrum density of pulsating pressure, aerodynamic noise source distribution and directivity of overall sound pressure level are analyzed. The noise characteristics of the far-field microphone are compared with the local microphone installed in the wheel cavity. In this way, we characterize the directivity of pure tone in the wheel cavity and understand its contribution to the far-field noise. The results show that the aerodynamic noise of the landing gear can be quantified accurately by the hybrid numerical method. The pure tone has two frequencies inside and outside the wheel of the landing gear: 560 Hz and 960 Hz. The peak of the loudest sound pressure level reaches 136 dB, and the pure tone radiates to the surface of the non-separation area of the wheel of the landing gear. However, the wall pressure spectrum of the points located in the turbulence region shows a wide-frequency characteristic, and there is no obvious pure tone. From the point of view of the far-field noise directivity, the forward noise of the landing gear is larger than the rear noise, and there is a small overall sound pressure level area at the points of 65 and 110 degrees respectively. When the monitoring points are far away, the far-field noise of the landing gear shows the characteristics of wide frequency, and no obvious pure tone appears. The method can provide the technical support for predicting the aeroacoustics of a landing gear and designing a low-noise land gear.