发动机喷流与襟翼侧缘干扰的流动结构演化及降噪研究

High-speed jet and flap side-edge are main noise sources of a civil aircraft. Interference between the jet and vortex induces more intensive noise. The interaction of the jet and the side-edge vortex contributes to both mid- and high-frequency noise, and also induces narrow-band noise peaks. One possible reason is that the vortex system of the flap side-edge changes the flow structure evolvement of the high-speed jet and increases turbulence intensity of the shear layer. The other reason might be the destruction and merging of the original streamwise double-vortex system of the flap side-edge caused by the jet impingement. Currently the jet/vortex interaction is rarely studied by researchers at home and abroad. This project is aiming at the specific flow and aero-acoustic problem of the interaction of the high-speed jet and the side-edge vortex. A simplified coaxial jet with a simple wing/flap model is used for turbulence structure study. By applying advanced wall-modelled large eddy simulation method, the generation and evolvement of the turbulent structure of the high speed jet under inducing of streamwise vortex, as well as wavepacket, vortex system and flow topology, will be numerically investigated. The connection between the evolvement of the turbulence structure and sound generation will be analyzed. Based on the analysis of the noise emission mechanism of the high speed jet under inducing of streamwise vortex, an empirical prediction method of the noise spectrum will be proposed, and novel noise reduction method will also be analyzed.

发动机喷流和襟翼侧缘旋涡是民用飞机的重要噪声源，二者的相互干扰还会诱导产生更强的噪声。喷流在襟翼侧缘旋涡的诱导和二者相互干扰下，会对中频和高频噪声都有贡献，并会诱发窄带噪声峰值。其原因可能一是侧缘流向涡对高速射流核心区的诱导，使射流剪切层的流动结构演化过程发生改变，使混合层的湍流强度增加；二是高速射流对侧缘原有的流向“双涡”结构的破坏，促进旋涡结构的融合。目前国内外研究人员对流向涡诱导下的发动机喷流的流动结构演化过程的研究还很少。本项目聚焦喷流与襟翼侧缘的干扰现象，以喷流在旋涡诱导下所诱发的复杂湍流结构的演化为切入点，建立模型问题，应用新型的壁面模化的大涡模拟方法，研究其射流的波包、旋涡等湍流结构在旋涡诱导下的相互干扰和演化的流动图谱，分析流动结构演化过程与气动噪声之间的关联，探索高速射流在旋涡干扰下的湍流结构演化和发声机理，发展噪声的经验预估方法，并发展新型的降噪措施。

本项目基于先进非定常流场预测方法与噪声分析方法，重点瞄准喷流、襟翼旋涡以及相互干扰的流动结构演化与发声机理，发展降噪方法。研究成果有几个方面：（1）提出一种基于壁模型大涡模拟的流场计算方法，结合FW-H进行远场噪声处理，采用圆柱-翼型干扰算例、多段翼型标模、起落架标模等标模，验证了数值模拟方法预测流场及噪声的可靠性。（2）在平直翼/半展长襟翼构型上研究了襟翼侧缘涡结构及其演化机理，探明侧缘双涡的演化规律并定位声源；针对侧缘双涡特点，发展了侧缘修型和侧缘挡板等降噪方案，获得一种具有良好控制双涡且尺寸较小的降噪挡板，A计权声压级降低1.6dBA；该降噪方案应用于MA700飞机襟翼侧缘上，通过噪声风洞实验验证了降噪效果。（3）发展并测试了多种喷流噪声的锯齿降噪方案，结果表明锯齿对主流的插入深度对喷流降噪影响明显。（4）利用射流结合机翼/襟翼模型，探明侧缘涡影响下的喷流与噪声演化规律，发现干扰旋涡区域是主要声源；研究了射流的前后位置、上下高度对噪声的影响，表明上下位置对于噪声影响较大，分析了侧缘修型方案的降噪效果，相比基本构型获得2dBA的噪声降低。项目通过四年的研究实施，完成了相关研究内容，并取得了良好的成果。