平板和静叶表面气流-水膜耦合流动特性的数值研究

Numerical Investigation for Coupled Flow Behavior Between Gas Flow and Wall Film of Flat and Turbine Stator

针对平板表面的空气水膜和透平静叶栅中的水蒸气水膜耦合流动特性提出了分析气流与壁面水膜耦合作用的数值方法,即气相主流和液相水膜视为相对独立的开口系,通过在两相各自的控制方程中添加考虑相间动量和能量交换的源项,实现水膜和气流的双向耦合计算。研究表明:平板表面水膜厚度和进口水膜雷诺数近似呈1/2指数幂关系,与来流马赫数呈反比关系,与出口背压呈弱负指数次幂关系;水膜流速与出口背压近似呈线性关系;水膜附加损失对水膜流量的变化较为敏感,对来流马赫数并不敏感;透平静叶压力面侧水膜厚度分布较为均匀,在叶顶角区的叶片表面出现水膜聚积,吸力面侧水膜厚度变化较为剧烈,在叶顶和叶根角区的叶片表面出现水膜聚积。从而得出影响透平叶栅通道中水膜分布的机理是,壁面曲率通过影响相间剪切力来影响壁面水膜厚度和速度的分布,端壁上从压力面到吸力面的二次流引起水膜向吸力面侧聚积,通道涡和角涡引起的径向压力梯度导致叶片表面水膜沿叶高重新分布,水膜聚积对叶片表面的压力分布和出口气流角产生显著影响。

A numerical algorithm was employed to investigate the coupled flow behavior between gas flow and wall film. The air flow and wall film on a flat, and the water vapor flow and wall film in a turbine cascade were focused on. It is concluded that the film thickness is approximately proportional to the root of the inlet wall film Reynolds number, and inversely proportional to the mainstream flow Mach number. Film thickness and the outlet pressure have a weak negative exponential order relation, and the interface velocity is linearly related to the outlet pressure. The additional losses due to water film are sensitive to the change of water flow rate, but not sensitive to the flow Mach number. As for the turbine stator, the pressure surface film thickness is relative even, except that a film accumulation region appears at the tip corner region. In contrast, the suction side thickness changes obviously, and the film accumulation is observed at both the tip and root corner regions. The wall film distribution in a turbine cascade is affected by threefactors. The wall curvature influences the film thickness and velocity by influencing the interphase shear force. The endwall secondary flow from the pressure side to the suction side leads to film accumulation near the suction surface. The radial pressure gradient caused by passage vortex and corner vortex results in film redistribution along the blade height. On the other hand, the film accumulation on the blade exerts a significant impact on the surface pressure and outlet flow angle.