低速轴流涡轮叶片层流分离流动的数值模拟方法比较

Comparisons of Numerical Simulation Methods of Laminar Flow Separation on Blade Surface Within a Low Speed Axial Turbine

在低雷诺数进口条件下,低速涡轮叶片绕流可能存在大范围的层流流动、层流分离流动、边界层转捩和显著的径向二次流动,流动结构复杂,给精确的数值模拟提出挑战。本文对AIST低速轴流单级涡轮内部流动进行数值模拟,其中静叶通道分别采用全层流模型、全湍流模型、AbuGhannam&Shaw(AGS)转捩模型和分离涡模拟(DES)方法,动叶通道求解RANS方程,湍流模型为Spalrat-Allmaras一方程模型。与实验结果对比显示,层流模型准确地捕捉到了静叶叶片吸力面层流分离的分离位置。三维流动结构分析显示,在很低的雷诺数条件下,静叶吸力面层流分离流产生很大的径向运动,没有再附于叶片表面,被卷入叶片根部的通道涡中。

Under inlet conditions with a low Reynolds number, laminar flow, laminar flow separation, transition flow and radial secondary flow may exist in large range on the blade surface of a low speed turbine. The complex flow structure makes accurate numerical simulations a chall- enges. Numerical simulations are perform- ed on internal flows within the low speed single stage axial turbine of AIST. Different models, such as fully laminar flow model, fully turbulent flow model, Abu-Ghannam ＆ Shaw （AGS） transition model, and detached eddy simulation（DES） are used respectively within the stator blade pass- age. The RANS equations are solved in therotor blade passage. One equation turbulence model, the Spalart-Allmaras model, is employed for turbulence modeling. According to the validation with experimental result, the laminar simulation accurately captures the position of laminar separation on the stator blade＇s suction surface. The three-dimensional flow struc- ture analysis reveals that the laminar sepa- rated flow has large spanwise movement, which is wrapped into the hub passage vortex rather than reattaching the blade surface.