Theoretical Analysis And Numerical Simulation Of Hydraulic Performance Of Horizontal Self-cleaning Mesh Filter

Object: Self-cleaning mesh filter is one of the most widely used filter types in Northwest China.And filters play a vital role in water-saving irrigation.However,the tank body of the self-cleaning mesh filter is closed during operation.The inside of the filter has complex hydraulic characteristics,especially the water flow conditions,which cannot be observed intuitively through physical experiments.This thesis takes the horizontal self-cleaning mesh filter as the research object.The variation law of its internal flow field under different working conditions is obtained.Then systematically analyze the complex hydraulic characteristics of the filter.This provides a reference for the design and structure optimization of the horizontal self-cleaning mesh filter.Method: Through theoretical analysis of the filtration process and sewage discharge process of the horizontal self-cleaning mesh filter,the influencing factors affecting the pressure drop and sewage effect are determined,and the relevant theoretical formulas are obtained.Using Fluent software,the filtration process and sewage discharge process of the horizontal self-cleaning mesh filter under different working conditions were numerically simulated,and the distribution law of the internal flow field was obtained.Results:(1)The filter pressure drop expression in cylindrical coordinates is deduced.The maximum error between the theoretical value and the experimental value is 10%.Theoretical formulas of swirling power,adsorption suction and their relationship of sewage system are deduced and established.Secondly,combined with the filter pressure drop expression,the mathematical expression model of adsorption suction and filter cake layer parameters is established.(2)Under the condition of no filter screen,the water flow velocity from the inlet pipe to the outlet pipe shows a trend of decreasing first and then increasing under the conditions of clear water and muddy water.The greater the flow rate of the inlet water,the greater the pressure difference between the inlet and outlet.The flow field in the tank in both clear water and muddy water conditions is symmetrical in the horizontal direction,but the pressure in the muddy water condition is more uniform than that in the clear water condition.Under the condition of filter screen and under the condition of clear water and muddy water,the same inlet water flow,the larger the filter screen aperture,the smaller the average flow rate through the filter screen,and the smaller the pressure difference between the inside and outside of the filter screen.Under the condition of constant inlet water flow,the larger the particle size,the higher the concentration of particles near the front of the filter.As the flow rate of the inlet water increases,the particle content at the outlet increases,and the concentration of particles near the rear of the filter also increases.(3)Under the conditions of clear water and muddy water,the pressure at the suction nozzle of the sand suction assembly is the largest,but the pressure of hydro rotary nozzle is the smallest.With the increase of the inlet water flow rate,the internal flow velocity distribution is more uneven,and the pressure difference between the inlet and outlet is larger.With the increase of the influent flow rate,the average particle concentration of the section decreases gradually.The particle size increases,and the average particle concentration in the section increases gradually.Comparing the six groups of schemes,comprehensively considering the results of the pressure and flow rate of each suction nozzle,the opening widths of the suction nozzles 1～4 of the sand suction assembly are 2 mm,4 mm,6 mm,and 20 mm,respectively,and the opening diameter of the rotary nozzle is 20 mm.The proposed scheme is the recommended optimal structure scheme.Conclusion: Based on theoretical analysis and numerical simulation,the hydraulic performance and internal flow field of the horizontal self-cleaning mesh filter were studied.The theoretical results and numerical simulation results are in good agreement with the experimental results.It can provide theoretical reference for the determination of filter head loss,structure optimization,selection of particle size and influent flow rate in practical engineering.