计及叶片前缘周向不均匀源项的弯掠叶片流动机理

Flow mechanism of bowed and swept blades with consideration of circumferential fluctuation source term before blade leading edge

目前弯掠叶片被广泛应用于现代叶轮机设计,以协调高负荷、高通流、高效率和喘振裕度之间的矛盾,但同时也会引发应力、振动和稳定性等问题。因此,为更好地发挥弯掠叶片的气动优势,同时减少其空间结构复杂性,需要对弯掠空气动力学有更深的机理认识。利用周向平均降维方法,推导获得了可定量描述的周向不均匀源项,揭示出周向不均匀性会诱发叶轮机进气流场产生不同于直叶片的再平衡,进而影响弯掠叶片各基元的设计迎角,并使叶轮机内部流场和性能特性产生变化。采用数值仿真和Stereoscopic Particle Image Velocimetry(SPIV)实验的方法对弯掠叶片的这一机理进行了验证。结果表明弯掠叶片中,周向不均匀源项会打破原有的进气流场的径向平衡,导致进气流场的径向迁移,使进气流场关键参数产生展向差异,改变迎角的展向分布,进而影响整个流场性能。同时,对影响进气流场的周向不均匀源项构建解析模型及机器学习代理模型,解除叶轮机进气均匀流场的传统假设,以利于三维弯掠叶片的气动设计与分析。

Bowed and swept blades have been widely used in the transonic fan/compressor of aircraft engines to harmonize the conflicts between high loading, high through-flow, high efficiency, and acceptable stall/surge margin. However, these blades can also induce stress, vibration, and stability problems. Therefore, to better apply the advantages of bowed and swept blades to fans/compressors and reduce the complexity of their spatial structure, we need a deeper mechanistic understanding of bowed and swept aerodynamics. In this paper, the circumferential averaging method is used to derive a quantitatively describable circumferential fluctuation source term, which reveals that the circumferential fluctuation induces a re-equilibrium of the fan/compressor inlet flow field different from that of a straight blade and which in turn affects the design incidence angle of each base element of the bowed and swept blade and produces changes in the flow field and performance characteristics of the fan/compressor. This mechanism of the curved(bowed and swept) blade is verified by numerical simulation and Stereoscopic Particle Image Velocimetry(SPIV) experiments. The results show that the circumferential fluctuation source term in the curved blade can break the radial equilibrium of the original inlet field, leading to the radial migration of the inlet field, generating the spanwise differences of the key parameters of the inlet field, changing the spanwise distribution of the incidence angle, and thus affecting the overall flow field performance. Meanwhile, an analytical model and a machine learning model are constructed for the circumferential fluctuation source terms affecting the inlet flow field to release the traditional assumption of a uniform flow field of inlet air, to facilitate the aerodynamic design and analysis of the 3D bowed and swept blade.