基于能量耗散率的低速扩压叶栅损失研究

针对无化学反应和热流输入的叶栅有黏不可压流模型,推导出能量耗散率的组分分解式,根据叶栅流场仿真结果进行分析简化,得到由轴向涡量、轴向阻力和剪切力组成的能量耗散率分解式。结合总压损失,分析了耗散各组分在前缘损失、叶表损失和通道损失中的主导因素:轴向涡量项反映旋涡结构,在通道损失中占主要部分,集中在通道涡和分离面附近;轴向阻力项反映扩压和叶表边界层转折造成的流动损失,在前缘损失和叶表损失中占主要部分,集中在叶栅前部的叶表边界层和主流区;剪切力项反映轴向截面速度不均匀性,在叶栅后部的叶表损失和通道损失中占主要部分,集中在叶表、端壁边界层和分离面附近。旋涡结构和耗散各组分分布特征揭示了叶栅通道中旋涡结构与能量耗散之间的分布关系,分离区并不是主要能量耗散区,高能量耗散区主要分布在叶表边界层(叶栅前部由轴向阻力项主导,后部由剪切力项中的υ(∂V_x/∂y)²项主导)、分离面附近(受剪切力项中的υ(∂V_x/∂y)²项和轴向涡量项影响)。大攻角情况下,叶栅通道损失显著增加,正攻角促使轴向涡量项的增长点提前,负攻角则使得叶表边界层的速度剪切加剧。

Energy loss in a low-speed compressor cascade with dissipation function

A viscous incompressible flow model in compressor cascade is set up without chemical reaction and heat input. Each of these components is resolved from the energy dissipation function with the derivation of the formula and simplified according to the simulation result in compressor cascade. These main factors are summarized as streamwise-vorticity item, axial resistance and shear force. Then, the axial characteristic of each component of the energy dissipation function is discussed in leading-edge loss, profile loss and passage loss with total pressure loss efficient. The streamwise-vorticity item, as the primary factor in passage loss to reflect the vortex structure in cascade, is concentrated near the passage vortex and separation surface. The axial resistance is concentrated on the boundary layer in the front of cascade passage, which is the key factor in leading-edge loss and profile loss to reflect the flow loss in diffusion and turning of boundary layer. The shear force item is concentrated on the separation surface and the boundary layer near the suction surface and endwall, which is the key factor in passage loss and profile loss to reflect the inhomogeneity of velocity. The relation between vortex structure and the energy dissipation is investigated with the distribution characteristic. One large dissipation zone is also found between main flow and corner separation region, which is influenced by υ(∂V_x/∂y)² and the streamwise-vorticity item. Another is developed because of boundary layer near blades, which is influenced by flow resistance at the front part and υ(∂V_x/∂y)² in the rear part. Governing factors on each axial plane are found while the key factor to energy dissipation is the shear item. The passage loss is significantly increased with high angle of attack, while the induction of streamwise-vorticity item is earlier in positive incidence and the shear force in boundary layer is higher in negative incidence.