| One of the key problems in research of long range and high impact fire monitor is the optimal design of flow path, nozzle and straightener, then the internal flow loss can be reduced as much as possible, and better flow state and longer range of fire monitor can be got in the same inlet condition. Two kinds of large flow fire monitor nozzles – jet-type nozzle and diversion-type nozzle were designed in this paper, and the flow paths of the two kinds of nozzles were optimized and researched deeply.The main research contents and results were as follows:(1) According to the requirements of the project to determine the performance parameters of fire monitor. Then structure and hydraulic parameters of large flow jettype nozzle and diversion-type nozzle were designed respectively. Flow passages of the two nozzles were analyzed by ICEM and Fluent software. The results indicated that: pressure and velocity distributions of jet-type nozzle and diversion-type nozzle that been designed in this paper are not uniform, these factors could influence jet effect and shorten the range of fire monitor. Thus the structure of the two nozzles should be optimized. With the jet-type nozzle, the structure style of the straightener has an important effect on jet; with the diversion-type nozzle, the internal flow passage is complex, so the key size combinations should be improved and optimized.(2) Small model of two kinds of nozzles were designed according to the principle of similarity theory and the experimental study was carried out. The trajectories of the two small fire monitor models were gained under different elevation and working pressure. To research the calculation method of fire monitor trajectories, four-order Runge-Kutta method was used with the combination of single water drop hypothesis model and index growth model. Comparing the calculation results and experimental data, the calculation result using index growth model was found better. Finally, the trajectories of large flow fire monitor were calculated, and the range of large flow fire monitor was predicted.(3) In order to optimize the fire monitor nozzle passage structure, RSM model and numerical simulation were carried out. First, the throat diameter, throat length and throat contraction angle of nozzle were selected as design variables. The lowest turbulent kinetic energy and the highest average velocity in outlet were taken as objectives. Then, combined with optimal Latin hypercube design and numerical simulation, the RSM model was constructed. Finally, multi-objective optimization for the water channel of fire monitor nozzle was performed with NSGA-Ⅱ algorithm, and the pareto optimal solution set was obtained. The conclusion was drawn that the RSM model with high fitting accuracy could significantly improve the optimization efficiency of fire monitor nozzle. Moreover, in the three chosen variables, the throat diameter performed the highest influence of fire monitor nozzle. The optimization results suggest that the two objectives were better than those of the original model.(4) Three types of straightener were designed which have approximately the same cross section area. In the two cases where straighteners take up the same volume and surface area as the flow passage, the numerical simulations of flow in the fire monitor are studied at design flow rate. The suitable straightener of large flow fire monitor was chosen with the combination of orthogonal experiment and numerical simulation. The results show that the flow pattern is improved evidently when straighteners are installed, and the axial velocity near the outlet increases more greatly than the case without straightener.The total hydraulic loss is ranged from 0.10 to 0.13 MPa, and its 55% occurs across the straightener. The surface area of straightener exhibits a more significant rectifying effect than the volume does.However, there is a suitable length for a straightener, once this length is selected, the position of straightener in fire monitor tube has little influence on the rectifying effect. |
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