基于双向流固耦合的贯流式水轮机动力特性分析

Dynamic characteristics analysis of tubular turbine based on bidirectional fluid-solid coupling

为了深入研究流固耦合作用对贯流式水轮机转轮动力特性及内部流场的影响,文中采用商业软件CFX和ANSYS APDL对贯流式水轮机流体域和固体域进行耦合求解,分析了耦合作用对结构应力及应变的影响,并将耦合数值计算得到的转轮外特性与实测值进行了对比。结果表明:考虑耦合作用后,转轮的效率、水头与耦合前相比都有不同程度的下降,最大值分别为0.6%、0.21 m。同时在靠近叶片出水边轮缘附近,耦合后压力面与吸力面压力差有所下降,说明耦合作用会降低转轮的水力性能。2种耦合计算方法求解得到的叶片的等效应力分布基本一致,应力集中都出现在转轮叶片与枢轴法兰联接处,同时双向耦合下最大等效应力的主频与单向耦合相比有明显下降的趋势,由于双向耦合考虑了结构在运动过程中周围水体与结构的相互影响。该研究为实际工程中准确地进行转轮的水力性能预估和叶片结构在水中瞬态响应计算提供了参考。

In order to study the stress, displacement and flow characteristics of flow field of the tubular turbine under the effect of coupling, the flow field and the structural response of the runner blade in the tubular turbine are calculated in one-way and two-way coupling by using the commercial software ANSYS 12.0 CFX and ANSYS APDL. The flow field is based on RANS control equation, two-equation SST-ωturbulence model and runner blade structure of the solid domain using the equations of the motion of elastic structure. The fluid-structure coupling numerical calculation of the tubular turbine under different working conditions is carried out for stress and displacement of the runner blade and the distribution of the pressure field of the runner in this paper. The calculated structural stress, the displacement distribution and the variation trend of the structure are compared. The difference of equivalent stress and displacement of the runner is analyzed under one-way and two-way coupling. The pressure distribution of the flow field inside the runner is also analyzed. The results show that under different working conditions, the equivalent stress, displacement distribution and variation trend of the one-way coupling and two-way coupling are basically same. The maximum equivalent stress occurs on the runner blade near the hub; the maximal displacement occurs on the blade trailing edge at blade tip. The maximum equivalent stress values of the two-way coupling are separately increased by 0.16%, 0.38% and 0.82% than the one-way coupling under 3 different conditions. In the maximum displacement position, the equivalent stress difference between uncoupled and coupled systems is more significant and the equivalent stress of the two-way coupling is increased by 1.71%, 1.90% and 2.51% respectively than the one-way coupling. The maximum deformation displacement of the two-way coupling is separately increased by 0.3%, 0.43% and 0.61% than the one-way coupling. Also in the position of maximum deformation displacement, the deformation displacement is increased by 0.52%, 0.88% and 1.08% respectively. With the increase of the guide vane opening, the maximum equivalent stress and the deformation displacement are also decline. At the same time, the difference of the equivalent stress values calculated under the 2 kinds of coupling is even more significant with the increase of the maximum displacement difference between unidirectional and bidirectional coupling. It is verified that the size of displacement and the relative displacement difference in solving the runner dynamic stress is a key factor to the difference between two methods of coupling. The maximum equivalent stress peak appears 4 times within a time period, just the same as the number of blades under 3 kinds of conditions. It shows that the maximum equivalent stress with time is affected by the number of blades. The maximum equivalent stress calculated by two-way coupling is volatile and stronger than one-way coupling. The frequency domain graph shows that the maximum equivalent stress frequency is 16 times rotation frequency by the one-way coupling, while 4 times by the two-way coupling. All in all, the difference of maximum equivalent stress between one-way coupling and two-way coupling is small. At the same time, the main frequency of the maximum equivalent stress is also different. The internal geometric boundary caused by blade displacement can also affect the change of flow field. Compared with uncoupling, the pressure difference between pressure side and suction side of blade decline near blade tip. This paper provides certain reference for further numerical study of fluid-structure interaction and hydraulic performance on tubular turbine.