Study on the Calculation Method of Correlation Length of Power Spectral Density Function of Two-Phase Flow in Heat Transfer Tube of Steam Generator

In nuclear reactors, turbulent excitation is an essential mechanism of flow-induced vibration. Turbulence exists everywhere in the heat transfer tubes, fuel rods and valves. Among three main research methods for turbulence excitation, the first is the fluid-structure coupling method, which can fully consider the fluid structure coupling effect but has not yet obtained a strict mathematical solution. The second is to make reasonable assumptions and use the classical random vibration theory to calculate the vibration response of the structure. This method is simple and efficient, but it cannot consider the nonlinear factors such as clearance, collision and friction. Thirdly, the transient analysis method is used to calculate the vibration response of the structure. This method can consider nonlinear factors, and the difficulty is to obtain the time history of turbulent excitation force acting on the structure. This paper presents a calculation method of the correlation length of the power spectral density function of two-phase flow in the heat transfer tube of steam generator based on global optimization fitting, which can determine the correlation length of the power spectral density function of two-phase flow in the heat transfer tube of steam generator efficiently and conveniently. It provides necessary input for the time history of power spectral density to turbulent excitation forc, and lays a foundation for more accurate transient analysis method for random turbulent excitation vibration analysis, design improvement, and safety evaluation of tube bundle equipment.