混流式水轮机尾水管近壁湍流特性和流场结构研究

采用滑移网格技术以及基于Vreman亚格子模型的全局动态大涡模拟方法,得到了HLA551-LJ-43型水轮机小开度工况下全流道内速度、压力以及涡量的分布,同时捕捉到尾水区域高强度的近壁湍流特性以及独特的分离流动现象。计算结果表明,当高转速、小开度工况时,流道内流体的圆周速度占有绝对优势,流体进入尾水管后"被甩出"呈旋转下泄趋势,在锥管段和弯管段内产生了明显的分流,同时在尾水管中心区域形成一个较大的空腔涡带。该涡带的流动形式与常规工况差异较大,反映出小开度工况偏离最优工况最远,流道中流体的漩涡、脱流、分离间断和回流等各种水力不稳定现象更为剧烈和复杂,具有独特的流动形式,容易导致机组异常振动的发生。

Numerical Study of Swirling Flow Fields in Francis Turbine under Small Opening Condition

The phenomenon that strong vibration of units occurred when the Francis turbine is operating under the small opening conditions, such as Gongzu, Shiquan, Liujia Gorges, Lijia Gorges and Three Gorges project. It was used the large eddy simulation (LES) method based on Vreman SubGrid Scale model to analysis the generation and evolution process of turbulence flow, captured the details of the flow structures and the dissipation of the turbulent kinetic energy. The SIMPIEC algorithm was applied to solve the coupled equation of velocity and pressure. The result shows that the small guide opening conditions deviated from the optimal conditions mostly. The unstable flow phenomenon including the swirl, flow separation, interruption and reflux was strong and complicated, which led to the abnormal vibration of the units.