Study on Vibration Mechanism of Connecting Pipe of Medium and Low Pressure Cylinder in Steam Turbine

The zero-output technology of low-pressure cylinders is widely used in the heating expansion and electric peak regulation transformation of heating units in thermal power plants. The problem of large vibration of the connecting pipe under small volume flow is generally present, and it is very important to find out its vibration mechanism for the development of the vibration suppression technology of the connecting pipe. In this paper, a 600 MW heating unit was taken as the research object to establish a three-dimensional model, and CFD was used to carry out a constant numerical simulation of the butterfly valve at different openings. According to the calculation results and field measurements, the butterfly valve opening of 10° was determined to be the maximum vibration condition. According to the unsteady numerical simulation of the maximum vibration and the statistics of the flow excitation force in three directions, it is clear that the main flow of steam flowing out of the open side of the butterfly valve plate under a small opening will produce unstable flow. It will “slap” the valve plate, impact the inner wall of the valve shell and the connecting pipe and produce unstable flow excitation, which is the main reason for the vibration of the connecting pipe. This study provides a theoretical basis for the development of vibration suppression technology for connecting pipe.