Research On Unsteady Characteristics Of Flow Field And Fluid-Structure Coupling Of Pipeline Cavitation Cleaner

Cavitation water jet cleaning technology is widely used in pipeline cleaning.It has the advantages of low working pressure,strong adaptability,environmental-friendly,and suitable for online cleaning.It is becoming an important method of pipeline cleaning with increasingly strict environmental protection policies.The core of the cavitation water jet pipeline cleaning technology lies in the cavitation capacity of the pipeline cleaner.The previous research mainly focused on the steady flow field characteristics of the cleaner.Due to the instability of cavitation,steady-state analysis of the flow field of the cleaner can't accurately descript the flow field characteristics and cavitation performance of the cleaner.Besides,the cleaner will deform elastically due to its structure and affect the flow field.To analyze the influence of the deformation on the flow field,a two-way fluid-structure coupling analysis is performed.The research content of this paper is as follows:(1)A two-dimensional simplified symmetrical flow field model of the cleaner is established to conduct simulation analysis,and the unsteady cavitation characteristics of the cleaner flow field at an inlet pressure of 1MPa is studied.The research results indicate that at an inlet pressure of 1 MPa,the cavitation structure of the flow field of the cleaner changes periodically,the cycle is 14ms,and its change process can be divided into three stages:the incipient,development,and contraction.In the development stage of cavitation,the area of the high-intensity cavitation area remains unchanged,and the shape of the downstream cavity continuously changes with time.The position of the near-wall surface in the middle of the flow field of the scrubber forms a local high-pressure area due to the sudden change of the radial flow velocity of the water flow and causes the abrupt change of the vapor content there.There are two vortices in the flow field area of the scrubber and the position of the downstream flow field.The former is due to the re-entrant jet and the latter is due to the formation of a velocity gradient caused by the increase in the flow area,and cavitation enhances re-entrant jet velocity.(2)The effect of parameters such as inlet pressure,bending angle,and cleaner diameter on the cavitation evolution period is analyzed.The results indicate that increasing the inlet pressure can enhance the cavitation intensity of the cleaner.There is no periodic change of the cavitation structure when the inlet pressure is low.As the inlet pressure increases,the cavitation structure of the flow field of the scrubber begins to gradually change,the velocity of the flow field increases,the turbulence increases,the period gradually decreases.The reduction of the bending angle will increase the throttling effect of the flow field,the average velocity of the flow field will increase,the cavitation intensity will increase,the cavitation period will decrease.When the bending angle is 85°,the cavitation structure doesn't change periodically.As the cleaner diameter increases,the gap between the cleaner and the pipe decreases,the pressure los's at the inlet of the cleaner increases,the flow resistance increases,the cavitation intensity decreases,and the cavitation period decreases.(3)A two-way fluid-structure coupling method is used to perform simulation analysis on the cleaner to research the deformation of the cleaner and its influence on the flow field.The research results indicate that the stress of the cleaner is similar to that of a simply supported beam with one end is fixed and the other is supported.The maximal deformation position is located is about 1/3 away from the entrance of the cleaner and the maximum stress is at the bottom.The elastic deformation of the cleaner causes the flow area of the cleaner to be reduced and the throttling effect to be enhanced.The cavitation area of the cleaner is significantly larger than that it was undeformed.Among them,area 2 near the pipe wall has the most obvious change.At the same time,the influence of parameters such as working parameters,blade thickness,and bending angle on fluid-structure coupling was analyzed.The results show that the deformation trend of the cleaner is consistent under different pressures,and the amount of deformation is linear with the inlet pressure.The deformation can effectively enhance the cavitation capacity of the cleaner.The amount of deformation of the cleaner decreases with the increase of the thickness,and the cavitation capacity of the flow field increases with the increase of the thickness.These two trends must be considered comprehensively at larger working pressure.The larger the bending angle,the greater the elastic modulus of the cleaner.The amount of deformation decreases with the increase of the bending angle.The cavitation performance of the cleaner is significantly improved with the increase of the bending angle.The larger bending angle is beneficial to improve the cavitation ability of the cleaner,but excessively large bending angles will reduce the passing ability of the cleaner and reduce the adaptability in complex pipelines,which will make it more prone to jam.(4)The cleaning effect of the cavitation jet is tested by the erosion method.Erosion and destruction are carried out by placing the polished samples in the cavitation area and monitoring the surface morphology of the eroded samples.The results show that the surface morphology of the sample changes significantly as the working pressure increasing.Both the number of surface pits,the average height,and roughness of the surface increase,indicating that with the increase of pressure,the destruction ability of cavitation bubbles enhanced.This also indirectly indicates that the cavitation intensity of the cleaner is enhanced.