Experimental And Numerical Investigations On Internal Flows And Sound Radiations Of Control Valves With Various Internal Trims

Control valves are extensively used in power generation plants. Although some reports on the general performances of control valves are available in literatures, the noise generation and its mechanism behind it for the control valves are still very unclear. Such noises radiated by these valves are generally on a high level; they are harmful and may damage the listening of the workers. Meanwhile, the noise tremendously affects the daily life of the inhabitants in around. Seeing from the reasons of control valve noises, they are closely related to internal unsteady flows and structural vibrations, therefore, strong noise may also cause structural fatigue and failure of the valves, which means disastrous to the nearby apparatuses.In this thesis, numerical simulations of the control valves with 3 kinds of internal trims (window, labyrinth and single-sleeve), are carried out. The flow fields are obtained by solving the three-dimensional Navier-Stokes equations, combined with the k-s turbulence model for initial flow fields and then with the large eddy simulation for the unsteady flow. The calculations are performed using a commercial package, the CFX. The distributions of velocity, pressure, turbulent kinetic energy and vorticity with the valve have been calculated to analyze the causes of the valve noise. Calculation results indicate that compared with other valves, labyrinth valve has the weaker vorticity in the internal section. On the other hand, the vorticity distributions in inlet and outlet for the four control valves are similar.Further to the experiments, the noise emissions of a control valve equipped with these internal trims, are experimentally measured in an acoustical laboratory, where the over-all sound pressure level and the noise spectra of the control valve with all these internal components are obtained. The experiment results show that the noises generated by the control valve consist of low frequency tones and broad band frequency noises. Different internal components have produced little influence on the low frequency tones. This is possibly a result of the similar scales of vorticies in the inlet and out flow passage of the valve. However, the broad band noise for the labyrinth valve is on a lower level, and its general SPL has some advantages over the valves with other internal components. The measurements of the noise agree well with the flow fields.