| The high-pressure reducing valve is widely used in process industries such as nuclear power,petrochemicals,and coal chemical engineering.Its main function is to reduce pressure.Taking nuclear power engineering as an example,the main feed water pressure reducing valve and bypass pressure reducing valve in the secondary circuit use cooling water as the medium,form flow cavitation during pressure reduction,and the collapse of bubbles can further induce flow-induced vibration and noise,which are important factors affecting the performance and reliability of key units in the nuclear power industry.Due to the complex structure and harsh working conditions of the high-pressure reducing valve,the mechanism of flow cavitation and the factors affecting flow-induced vibration and noise are unclear,making it difficult to develop effective prediction and adjustment methods.Therefore,it is necessary to conduct research on the flow mechanism and damage characteristics of this type of reducing valve,providing theoretical basis and guidance for failure prediction and prevention of similar equipment.This paper takes the high-pressure differential space transfer ant-hole type reduction valve as the research object,and uses a combination of experimental and numerical simulation methods to construct a numerical solution model for cavitation,flow-induced vibration,and noise.Research on the cavitation,vibration,and noise characteristics under pressure reduction flow is carried out.The use of vapor phase fraction and surface condensation rate is used to characterize cavitation damage,stress and modal resonance are used to characterize vibration damage,and sound pressure level under different noise sources is used to characterize noise damage.Based on the above methods,targeted structural optimization design schemes have been proposed.The main research content and conclusions include:(1)An experimental device for the depressurization characteristics of a circulating multi-stage hedge channel was built.The influence of the structural design of the hedge channel on the depressurization flow was obtained,the energy dissipation mechanism of the hedge channel was revealed,and the reliability of the internal flow numerical simulation method was verified.The results show that the multi-stage hedge channel design mainly completes the step-by-step depressurization through the dissipation of hedge energy caused by multiple frontal hedging of fluid and the dissipation of turbulent energy and velocity gradient shear dissipation caused by turbulence and vortex structure formed by steering and turning angles,and the first two stages play a dominant role in pressure reduction.(2)In regards to the space transfer ant-hole type reduction valve,a numerical solution model for flow cavitation was developed,with parameters such as pressure velocity,turbulent intensity,and vortex simulation used to characterize flow characteristics,while vapor phase fraction and wall condensation rate were used to characterize cavitation damage.Research results show that the greater the pressure difference,the stronger the turbulence,and the higher the Q value under vortex simulation recognition,while the buffer design of the inlet cavity significantly reduces the pressure of the lowermost flow channel.The flow outlet of the spool sleeve is the high-risk area for cavitation damage,where the vapor phase fraction and wall condensation rate are the highest,and the degree of cavitation damage is negatively correlated with the outlet pressure.(3)In response to the vibration characteristics under flow excitation of the space transfer ant-hole type reduction valve,a one-way fluid-structure coupling was employed to analyze the effects of internal flow on the deformation,stress,and modal resonance response of the entire valve and flow path static structure.Research results show that the overall valve was subjected to high-stress intensity,where vibration damage was mainly caused by the normal stress generated by fluid impact.The resonant response frequency was a low-frequency 440 Hz,and had a significant impact on the valve stem and upper valve body.The vibration damage of the flow path was jointly caused by normal stress and shear stress,with the resonant response frequency range around 40000 Hz,which belongs to high frequency resonance.(4)In response to the noise characteristics induced by multi-stage hedge channel flow,different noise characteristics were analyzed under various noise sources and their noise levels were determined in conjunction with internal flow to carry out noise characteristic analysis.Research results show that the turbulent flow noise generated by the quadrupole noise source had the greatest impact on the channel noise level,with a noise level of approximately 188 dB.The maximum noise area has consistency with the area of high turbulent intensity,confirming that unstable fluid flow is the main cause of channel noise.The noise exhibits a continuous broadband characteristic dominated by medium to high frequencies,and monitoring points at different distances behind the valve show certain periodic pulsation characteristics.The normal distance is the main factor affecting the sound pressure level.(5)The optimization design of flow channel structure has been completed based on the characterization study of internal flow and damage.Firstly,the structure selection of multi-stage hedge flow channels was carried out based on the pressure reduction process,with different number of stages and orifice sizes being considered.It was determined that the five-stage hedge gradual expansion orifice had a more significant pressure reduction effect and a smoother pressure reduction process.Secondly,the structure optimization of the above-mentioned flow channels was conducted under a three-factor-three-level orthogonal test to address the issues of noise and outlet erosion damage.The optimal flow channel structure parameters were analyzed and determined to be: U-shaped groove of 3.5 mm,outlet diameter of 15 mm,and equidistant stage spacing.Therefore,theoretical basis was provided for the optimization design of multi-stage hedge flow channel structure of pressure reducing valve.The main innovations of this paper include:(1)Based on experimental verification and numerical simulation calculation techniques,the turbulent dissipation and pressure reduction flow characteristics within the multi-stage pressure reduction flow channel of the pressure reducing valve were analyzed,and the influence mechanism of different structural parameters such as impingement levels and aperture sizes on the pressure reduction characteristics inside the valve were determined.(2)Based on the fluid-structure interaction calculation method,the stress distribution characteristics of valves under the impinging turbulent flow dissipation and the flow-induced vibration rules were studied.A technical method for predicting the risk of valve flow-induced vibration damage using parameters such as stress intensity and modal resonance was proposed. |
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