凹壁不稳定性流动的数值计算

Numerical Calculation of Flow Instability of Concave Wall

凹壁结构在工业应用的多个领域中都是很常见的,由于离心力不稳定性,流体流过凹壁面附近时可能会产生G?rtler涡。为了研究这些涡的特性及对流场产生的影响,采用CFD技术对曲率半径为2 m的弯曲渠道的流动过程进行数值模拟。用有限体积法对模型进行空间离散,采用大涡模拟中Smagorinsky-Lilly模型进行计算。通过与实验结果进行对比发现,计算结果能较准确的反应G?rtler涡随流动的发展过程。在此基础上进行的分析表明:在速度3 m/s,湍流度0.35%的进口条件下,沿流向流过一段距离后,在靠近凹壁的边界层中产生了G?rtler涡;涡轴平行于流动方向并且相邻涡轴之间的距离保持不变;随着涡在展向和法向空间的增长,速度等值线出现"蘑菇状"结构;靠近出口位置"蘑菇状"结构破裂,流动发生转捩。

Concave wall structures are very common in industrial application fields,Gortler vortices may generate in the concave wall boundary layer due to the centrifugal instability. In order to study the characteristics of Gortler vortices and impact on flow field,numerical simulations are made on the bending rectangular channel which radius is 2 m. Finite volume method was employed during the spatial discretization and the calculation was carried out in term of Smagorinsky-Lilly model of large eddy simulation（ LES）. Results show that,on the inlet conditions of 3 m / s in speed,turbulence 0. 35%,G？rtler vortices generate in the concave wall boundary layer along streamwise. Vortex axis is parallel to the flow direction and the distance between adjacent Vortex axis remains the same. With the development of eddy in normal and spanwise space,the speed contour lines appear ＂ mushroomshaped＂ structure. Near the position of exit, ＂ mushroom-shaped＂ structure breaks down and flow transitions.