拦污栅结构流固耦合理论与流激振动机理研究

The flow-induced vibration problem of the trash-rack is very complicated, being closely related to the flow conditions, the boundary conditions and the structural dynamic characteristics. In practical trash-rack engineering projects, structural damage examples, caused by the flow-induced vibration phenomena, have been frequently reported at home and abroad. This project aims at analyzing the flow-induced vibration problem for the trash-rack with the aid of theoretical analysis, numerical simulation and physical model test, and the main research contents include the following three aspects: Firstly, independently developing the three-dimensional computational codes in a generalized curvilinear coordinate system in order to accurately solve the fluid-structure-interaction problem of the trash-rack, within which either the dynamic Smagorinsky sub-grid scale LES model or the K-Omega-SST RANS model is used to calculate the turbulence variables, and the Level-Set method is utilized to capture the free surface of water. Secondly, with the help of the LingYun supercomputer system of DUT, exploring the feasibility and the practicability of directly numerically solving the accurate hydroelasticity three-dimensional governing equations, and obtaining the spatial and temporal distribution characteristics of various physical quantities, such as the flow velocity, the fluctuating pressure, the vibration displacement/frequency, the vibration mode, the stress distribution, and so on. Thirdly, acquiring the dynamic properties of the trash-rack with the aid of the ‘model-test & numerical-simulation’ joint prediction method. This project aims to quantitatively compare the respective advantages and disadvantages of the aforementioned two kinds of solution schemes and explore the inner damage mechanism for the flow-excited vibration problem of the trash-rack.

拦污栅的流激振动现象涉及水流条件、边界条件以及结构自身动力特性等方面，问题十分复杂。拦污栅因流激振动失事的工程实例在国内外均屡有报导。本项目以拦污栅的流固耦合流激振动问题为研究对象，主要内容包括：（1）自主开发求解拦污栅流固耦合问题的基于一般曲线坐标系的三维计算程序，该程序采用动态Smagorinsky亚格子尺度LES大涡模拟和K-Omega-SST双方程模型求解紊动变量，并采用Level-Set方法捕捉自由水面。（2）借助大连理工大学“凌云”超级计算机系统，探索“直接数值求解”水弹性力学三维控制方程组的可行性和实用性，得到包括流场速度、脉动压力、结构振动的位移、频率、振型、应力等物理量的时空分布特征。（3）通过采用水工模型试验（仅满足重力相似准则）与结构动力数值分析相结合的“物模-数模联合求解”获得拦污栅的流激振动特性。对前述两种求解方法进行对比分析，探索拦污栅流激振动破坏的内在机理。

拦污栅的流固耦合流激振动问题涉及水流条件、边界条件及结构自身动力特性等方面。首先，本项目对圆形、正方形、长矩形、前缘为半圆形的长矩形、前/后缘均为半圆形的长矩形五种截面栅条在不同运行工况下的受力特征、压力分布、过栅流速分布以及旋涡脱落频率进行研究。结果表明：前/后缘均为半圆形的长矩形截面栅条的栅后流速分布最为均匀，其可减少或避免吸气漩涡的产生、可避免局部冲刷等不利因素；圆形与正方形截面栅条不满足刚度条件要求，其余三种长矩形截面满足刚度条件；通过比较栅条不同部位的漩涡脱落频率与栅条在水中的固有频率，发现前/后缘均为半圆形的长矩形截面拥有最大的避免共振的安全阈值。其次，本项目进一步分析了栅条在不同水流攻角下的流场特性，并进行共振分析和疲劳计算。结果表明：针对长宽比为5:1的栅条，随着水流攻角的增大，水流流态更加复杂，栅条对来流的阻碍作用增强。在0°~15°之间的漩涡融合类型包括U-D模式、U-T模式和U-DT模式；在15°~45°之间的漩涡融合类型包含UL-T-U-DT模式和UL-T-UTb-DT模式。针对蒲石河电站长宽比7.27:1的栅条，对0°~45°的水流攻角进行流场分析、共振分析和疲劳计算。栅条主频为400.58Hz，远大于不同水流攻角下的脱涡频率，不会发生共振破坏。但当水流攻角大于12°时，栅条易发生疲劳破坏。此外，本项目计算了长宽比为L/D=1、2、4、6、8、10、12、14和16的矩形栅条在Re=22000时的流场特征和旋涡脱落特征。结果表明，当L/D=1~6时，脱涡频率对应的St呈现阶梯性变化，当L/D⩾8时，St与L/D呈现近似线性变化。存在四种类型的前后缘涡耦合模式，即L/D=1~2时的L-Vortex模式、L/D=4~8时的L-T-Vortex模式、L/D=10~14时的T-L-Vortex模式和L/D⩾16时的T-Vortex模式。当L/D>4时,前后缘涡的对流速度不随着L/D值的发生显著变化。本项目研究成果对拦污栅优化设计、合理选择其运行条件、采取措施避免其因流激振动而遭受破坏等具有重要指导价值。本项目已发表论文共18篇（其中SCI论文10篇），已授权国家专利8项（其中发明专利2项、实用新型6项）。此外，还有与本项目相关的6篇SCI论文正处于审稿阶段。