Analysis Of Flow Field Uniformity And Structure Optimization Of Self-mixing Concrete Nozzle

With the rapid development of science and technology,the technological level of large-scale engineering equipment for supporting infrastructure construction continues to improve.The most typical representative is the application of full-face tunnel boring machine(TBM).TBM can realize tunnel boring,support,slag removal and other processes.Parallel and continuous operation,in which the concrete nozzle for support can spray the accelerator and concrete mixture to the inner wall of the initial support tunnel,and cooperate with TBM to complete the initial support.The mixing uniformity of concrete and accelerator after passing through the nozzle seriously affects the quality of concrete spraying,which in turn affects the construction progress and safety of TBM tunnelling.Based on the problem of uneven mixing of concrete and accelerator sprayed by traditional nozzles,this paper innovatively proposes a self-mixing concrete nozzle.According to the working characteristics of the nozzle and concrete flow characteristics,the flow field characteristics of the self-mixing concrete nozzle are developed.Research.On the basis of theoretical analysis and research,numerical calculation and simulation analysis of the internal flow field of the new nozzle are carried out to obtain the velocity distribution law of the flow field in the concrete nozzle,the distribution law of turbulent flow energy and the cloud diagram of the volume fraction distribution of the concrete phase on the nozzle outlet section.Based on orthogonal experiments,carry out research on the influence of nozzle structure parameters on concrete mixing uniformity,optimize the new concrete nozzle structure,manufacture prototypes,and carry out performance tests to verify the rationality and feasibility of the new nozzle structure design.The main work carried out are:(1)Analyze and summarize the development status of concrete wet spraying technology,and put forward the importance of the influence of concrete nozzle structure on the mixing uniformity of concrete and accelerator.In-depth analysis of the research status of hybrid nozzles at home and abroad is carried out,and the main research content,research methods and main technical routes of this dissertation are put forward.(2)Analyzed the structure and working principle of the concrete wet spraying machine,studied the flow characteristics of the concrete in the nozzle,combined with the related professional knowledge of fluid mechanics and material transportation,and innovatively proposed a concept of a self-mixing concrete nozzle.The force analysis,dynamics and kinematics analysis of the concrete flow in the nozzle were carried out,the differential equation of the fluid motion of the concrete flow in the nozzle was established,the movement law of the concrete flow in the new nozzle was studied,and the concrete flow in the nozzle was analyzed.The pressure loss provides a theoretical basis for the design of the concrete nozzle and the numerical calculation of the internal flow field.(3)Innovatively proposed a self-mixing concrete nozzle structure,and completed the structural design of the new self-mixing concrete nozzle through three-dimensional software,analyzed the possible structural parameters that affect the mixing uniformity of the concrete nozzle,and established different The three-dimensional model of the concrete nozzle with structural parameters,and the internal flow channel models of the concrete nozzle with different structural parameters were extracted and meshed.According to the actual operating conditions of the concrete nozzle,the boundary conditions of the inlet and outlet of the concrete nozzle were determined,and the simulation study of the internal flow field of the new concrete nozzle was carried out.The velocity distribution law at each position of the flow field in the nozzle,the distribution law of turbulent kinetic energy and the distribution law of the volume fraction of the concrete phase on the nozzle exit section are analyzed.(4)Based on the basic principles of the orthogonal test method,the influence of the concrete nozzle structure parameters on its flow field characteristics is analyzed,and the influencing factors of the orthogonal test are determined to be the effective mixing length of the nozzle,the outlet diameter,the spray angle,and the mixing The number of columns to determine the orthogonal test table.The basic theory of concrete mixing uniformity is studied.Based on the concept of mixing uniformity,through orthogonal test analysis method,it is obtained that when the concrete nozzle is at its nozzle effective length of 475 mm,outlet diameter of 75 mm,spraying angle of 50°,and mixing column setting 6 It is the best combination plan to determine the concrete nozzle prototype machining plan.(5)Based on the research results of the orthogonal test of the new self-mixing concrete nozzle,in order to further improve the uniformity of concrete and accelerator after passing through the nozzle,it is innovatively proposed to add a baffle structure to the nozzle and carry out a baffle.Research on the characteristics of the flow field by the front profile of the flow plate.The research results show that adding a baffle with a suitable profile can effectively increase the mixing uniformity of the nozzle outlet.When a baffle with a size of 20 mm is set,the mixing uniformity of the nozzle outlet is increased by 0.0632.(6)The self-mixing concrete nozzle prototype was processed and trial-produced.Relying on a domestic large-scale diversion tunnel TBM construction project,the developed new self-mixing concrete nozzle was installed on the TBM host,and the concrete nozzle mixing uniformity verification test was carried out.The strength of the equipment self-spraying concrete after 1 hour was measured and compared with the strength of concrete sprayed by the new self-mixing concrete nozzle.The results show that the developed new self-mixing concrete nozzle can achieve sufficient concrete and quick-setting admixture.Mixed,shotcrete has a fast solidification speed,which achieves the expected research purpose.The research method of self-mixing concrete nozzles in this article can provide reference for the research of similar concrete nozzles.Relevant research results can guide construction units to carry out research on new lining technology,effectively improve construction efficiency,ensure construction period,and reduce construction costs,which have important research significance.