Research On The Aerodynamic Noise Of A Control Valve

As an important part of control system, control valve is widely used in all kinds of flowsystems. Because of its throttling control method, control valve is always a high noise sourcein the system. High noise not only seriously affects the health of surrounding workers, butalso can reduce the accuracy of equipments, and even may cause damage to mechanical parts.According to the aerodynamic noise problems, this paper takes a marine steam turbinecontrol valve as the research object, and conducts the following study:Firstly, the control valve flow field simulation analysis is made by the computationalfluid dynamics software FLUENT, including the steady flow field analysis and the transientflow field analysis. Through the steady flow field analysis, the relationship between thevalve flow field distribution and the pressure ratio is obtained. The most severe condition ofturbulence is also identified initially. Then, according to the most severe condition ofturbulence, the transient analysis of the valve flow field is made by large eddy simulation. Inthis way, parameters related to the time-varying characteristics are obtained. According tothe transient flow field calculation, causes of aerodynamic noise in the control valve areanalyzed. The position of the highest noise inthe valve is also confirmed.Secondly, characteristics of the maximum noise in the control valve are analyzed. Bysolving the FW-H equations, aerodynamic noise spectrum characteristic in the relevantposition is obtained. After that, combining with the shock wave appeared in the analysis ofthe flow field, the effect of shock wave on the aerodynamic noise is analyzed.Thirdly, the structure and acoustic modal analysis are conducted separately from theview of structure and acoustic resonance. Based on that, the vibration and acoustic couplingrelationship between aerodynamic noise in the valve and the valve body structure is verified.Finally, according to the above analysis, the valve structure was optimized. Then, thenoise reduction effect of the new control valve is verified by methods above.Based on the numerical simulation of flow field in valve, the velocity peak is found inthe annular channel between the valve disc and the valve seat. Flow parameters varyseverely in the area of valve seat diffuser, below valve disc. That is the main area ofaerodynamic noise. Obvious shock wave is found in the exit of the annular channel of thevalve disc and the valve seat.Shock wave causes the separation of the boundary layer. Interacting with supersonic jet, shock wave makes the jet expansion rate increased rapidlyand the complex shock structure and different scale turbulent structure formed in the flowfield. Through the aerodynamic noise analysis in valve, it is found that the aerodynamicnoise has significant broadband characteristics. Along the axial direction of the valve outletsection, aerodynamic noise amplitude is reduced gradually and the main noise frequencybands decreased gradually.High noise and the flow patterns are closely related, and the working medium flowpatterns is influenced by the structure of flow channel. Through repeated simulation, it isproved that the curvature of valve throat is an important parameters which influence the flowpattern. If the curvature is too large, the flow can separate from the wall. In this way,impinging jet type is formated and aerodynamic noise will be increased rapidly. This articlereduces the low frequency noise by20dB above through the throat curvature modification.High frequency noise decreases some extent.