| Air jet looms are widely used because of their high speed,long width and wide adaptability.The weft guidance system of air jet looms consists of a main nozzle,an auxiliary nozzle and a profiled reed,of which the auxiliary nozzle is the core component that determines the weft insertion velocity,stability and energy consumption of the machine.The aim of the study is to design a new type of auxiliary nozzle with a multi-hole array method.Based on computational fluid dynamics theory,the steady state and non-constant flow characteristics of the combined flow field of the auxiliary nozzle jet and the profiled reed are simulated numerically,and then an experimental setup is designed to verify the correctness of the numerical simulation.Finally,the aerodynamic noise characteristics of the external radiation of the auxiliary nozzle jet are investigated based on the theory of aerodynamic acoustics.The research in this paper is as follows.(1)Two types of triple elliptical-hole array auxiliary nozzles(M1 and M2)were designed with a single circular-hole auxiliary nozzle(S1)as the prototype,and the hydrodynamic models of S1,M1 and M2 auxiliary nozzles were established,and the steady-state flow field distribution of the auxiliary nozzle free jet was obtained based on Reynolds Average Navier-Stokes numerical simulations.The numerical simulations are validated by experiments.The velocity distribution of three types of auxiliary nozzle jets was analysed,and the results showed that the designed M2 auxiliary nozzle jet has the slowest velocity decay along the mid-axis of the weft flight and the best weft guidance stability.(2)Taking S1,M1 and M2 auxiliary nozzles as the objects,based on Large Eddy Simulation(LES)combined with sub lattice stress model,numerical simulation of the non-constant flow characteristics of the three types of auxiliary nozzle jets,the model simulation of the weft insertion jet transient flow field,analysis of the transient velocity fluctuations of the three auxiliary nozzles in different axial directions at different times,the turbulent vortex evolution and shedding process at different times,revealing the influence of different auxiliary nozzle structures on the decay of airflow velocity under the same airflow outlet area.(3)Based on the Broadband Noise Sources model and the Ffowcs Williams and Hawkings model,we simulated the changes in the sound field of the induced airflow,compared the experimental test data and studied the attenuation of the airflow noise of different types of auxiliary nozzles in the profiled reed,as well as the changes in turbulence,turbulent energy and the distribution of sound power level in three-dimensional space at different times.The changes in turbulence,turbulent kinetic energy and the distribution of the sound power level in three-dimensional space are investigated to obtain the auxiliary nozzle with better overall performance.The velocity,sound power level and flow field parameters at different cross-sections are monitored at the central axis of the main nozzle(A1)and the central axis of the first auxiliary nozzle outlet(A2).The results show that,compared to single round-hole auxiliary nozzles,the array auxiliary nozzles have better airflow collectivity,and a suitable array arrangement method can improve the weft drawing speed,reduce turbulence and reduce noise in the near outer wall area,which can achieve the purpose of green textile.The research results of this project have important reference value and wide engineering application background for optimizing the design of auxiliary nozzles,improving the auxiliary nozzle weft drawing speed while reducing air consumption and noise. |
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