基于UDF的二维管束流弹失稳模拟研究

Simulation Study on Fluid-elastic Instability of Two-Dimensional Tube Bundle Based on UDF

针对现有流弹失稳模拟研究中的流固耦合模型存在计算精度较低、计算成本巨大的问题,建立了一种可以预测管束临界流速的二维单向流固耦合模型,该模型基于商用ANSYS Fluent软件,通过SST k-ω湍流模型进行流场计算,再由自编译的用户自定义函数(UDF)提取管子所受的流体力,并利用4阶Runge-Kutta法求解结构动力学方程实现单向流固耦合计算。利用该模型对节径比为1.5的转角三角形排布管束进行了流固耦合计算,得到了中心管的临界流速、振幅时程曲线及振幅频谱图,并通过水洞实验进行了验证。结果表明,本模型以较低的计算成本准确地预测了临界流速,同时也获取了管子真实的振动特征,模拟计算的中心管振幅时程曲线及振幅频谱均与实验相近。此外,模拟计算获取的阻力和升力系数数据表明,随着流速增大,阻力和升力系数时程曲线经历了从紊乱到规律的变化,换算流速达到2.44时,阻力和升力系数主频包含管子在静水中固有频率的成分。

In view of the low calculation accuracy and huge calculation cost of the existing fluid-solid coupling model in the simulation study of fluid-elastic instability,a two-dimensional unidirectional fluid-solid coupling model which can predict the critical velocity of tube bundle is established.This model is based on the commercial ANSYS Fluent software,the flow field is calculated by the SST k-ωturbulence model,and then the fluid force on the tube is extracted by a self-compiled user-defined function(UDF),and the fourth-order Runge-Kutta method is used to solve the structural dynamic equation and realize the unidirectional fluid-solid coupling calculation.Using this model,the fluid-solid coupling calculation is carried out on the triangularly-arranged tube bundle with a pitch-diameter ratio of 1.5,and the critical velocity,the amplitude time-history curve and the amplitude spectrum of the central tube are obtained,which are verified by water tunnel experiments.The results show that this model can accurately predict the critical velocity with low calculation cost,and also obtain the true vibration characteristics of the tube.The amplitude time-history curve and amplitude spectrum of the central tube calculated by simulation are similar to those of the experiment.In addition,the resistance and lift coefficient data obtained by simulation calculation show that the resistance and lift coefficient time-history curves change from disorder to regularity with the increase of the velocity.When the converted velocity reaches 2.44,the main frequency of the resistance and lift coefficient includes the component of the natural frequency of the tube in still water.