| Glass fiber continuous strand mat is a new kind of glass fiber non-woven reinforced substrate with the advantages of isotropy,scour resistance and high mechanical strength.Its composite products are widely used in aerospace,wind power generation and military industry.Continuous strand mat is formed by throwing and stacking of several strands and bonding with adhesive.As one of the important molding processes of continuous strand mats,the throwing process of strands is an important checkpoint of product quality.However,the high-speed operation of the strand thrower is often accompanied by the production of air flow which is one of the main factors that cause the uneven spread of strands and then lead to the deterioration of the quality of continuous strand mat products.Therefore,it is very important to carry out the characteristic analysis and performance optimization of the strand thrower.At present,most of the research of domestic and foreign scholars on the strand thrower is about mechanical structure design and control system development,and the related research is not perfect,especially for the flow state and the distribution of parameters in the outer flow field of the strand thrower still need to be further explored,but the actual flow field measurement is relatively difficult.With the development of computer technology,the repeatability and visualization of flow field of the Computational Fluid Dynamics(CFD)technology make it possible to study the outflow field characteristics of the strand thrower.In order to realize the goal of thrown strands performance optimization,this article aimed at the problem of uneven strands spreading caused by high-speed air flow,using CFD numerical simulation technology,systematically analyzed the influence of the strand thrower rotating parts influence on flow field characteristics,revealed the main factors affecting the pull-wheel mechanism of action,and the unit structure to carry out the optimization design and numerical simulation.It provided theoretical foundation for optimizing throwing performance and improving the quality of continuous strand mat products.The main research contents and methods in this paper included the following aspects:1.Multi-fluid domains coupling numerical simulation method for strand throwerThe main structure of the strand thrower consists of finger-wheel and pull-wheel,both of which work in the way of rotation and revolution.In order to accurately capture the characteristics of the flow field,the RNG k-? model was used to simulate the turbulence structure of the strand thrower under 2D section and 3D characteristics based on the basic flow governing equation and turbulence characteristics in the rotating coordinate system.In this paper,the calculation method of multi-fluid domains coupling of strand thrower is studied,and the "meshing-like" characteristics of finger-wheel and pull-wheel were realized by using the moving grid technology in 2D scale.The flow between the finger-wheel and the pull-wheel at the interface was analyzed by a simplified 3D flow channel geometry model combined with the sliding mesh technology.2.Numerical simulation of 2D section of strand thrower and analysis of main influencing factorsIn order to clarify the main factors affecting the external flow field of the strand thrower,the numerical simulation results of the rotation of the finger-wheel and pull-wheel and the "meshing-like" of the finger-wheel and pull-wheel were analyzed and studied respectively,taking the radial distribution radius of the high-speed airflow area as the measurement standard.The calculation results showed that the influence degree of pull-wheel rotation is greater than that of finger wheel rotation,and the co-rotation phenomenon exists in the highspeed airflow area of pull-wheel rotation outflow.To pull wheel rotation and finger-wheel and pull-wheel and "meshing-like" velocity distribution on the contrast analysis,the results showed that the velocity superposition exists in the "meshing-like" of the finger-wheel and the pull-wheel,which resulting in the radial diffusion of the distribution range of the posthigh-speed airflow region.However,the phenomenon of co-rotation still existed,which further indicated that the pull-wheel is the main factor affecting the formation of the outflow field of the strand thrower.3.Research on the action mechanism of the pull-wheel of strand thrower based on square column flowAccording to the principle of flow around static boundary and moving boundary,pull rotation applied to stationary air can be regarded as flow around moving boundary.In order to verify the correctness of the turbulence model and the grid model,the flow around a twodimensional stationary square column with the same quasi-trapezoid feature length as the pull-wheel element structure was numerically simulated.The aerodynamic coefficients were monitored and compared with the published data,and the results were in good agreement.Based on the same boundary conditions,the wake field characteristics of static trapezoidal flow around the flow were explored,and the wake morphology of quasi-trapezoid flow moving in straight line and circular motion was compared and analyzed.The results showed that both wakes fluctuate along the trajectory,but the former dissipates gradually,while the latter collides and superposes to form a high-speed air flow region with the increase of the number of motion cycles.To analyze the action mechanism of the pull-wheel,according to the above wake flow characteristics,the wake field simulation analysis of multiple quasitrapezoid circular motion was carried out.The results showed that with the increase of quasitrapezoid number,the wake collision and stacking period is shortened,the wake width is increased,and the two high-speed flow regions are divided into inner and outer regions by the boundary of the pull-wheel,revealing the pull-wheel's action mechanism.4.Numerical simulation and structural optimization design and verification of 3D model of strand throwerTo optimize the performance of strand throwing,based on the wake flow field characteristics research and the pull-wheel mechanism,on the basis of the original pullwheel unit structure six kinds of different kind of quasi-trapezoid geometry model of width to height ratio were set up,for a variety of model under a single class wake flow characteristics of quasi-trapezoid with circular motion,this paper compared and analyzed preliminary evidence that wake width is proportional to the type of quasi-trapezoid radial height,and inversely proportional to the circumferential width.To further verify the above conclusions,four models were selected for numerical simulation verification of main factors.Combined with the verification results,the relative optimal model was determined and the numerical simulation of the optimized structure was carried out.The results showed that the reduction of quasi-trapezoid radial height can effectively improve the external flow field of the strand thrower,restrain the radial diffusion in the high-speed flow area of the external flow field,and reduce the air speed.It provided a certain basis for optimizing the performance of the strand thrower. |
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