摘艾灸仪 要
针对镁合金表面防腐、耐磨的需要，利用冷喷涂技术在镁合金表面制备了耐磨和防腐涂层。为了提高冷喷涂效率，本文根据流体力学和空气动力学的相关理论对超音速喷进行优化设计。应用FLUENT软件对拉瓦尔喷内的气固两相流动过程进行数值模拟，并对喷内气相和固相颗粒的速度、温度和压强分布进行分析，跟据模拟结果改进喷结构，使强化材料流出速度达到最佳。 冷喷涂技术的关键是通过拉瓦尔喷加速气流提高粉末的喷出速度，实现在基体表面的沉积。气体进口参数对出口气流速度有一定影响。在相同的喷结构下，进口速度的变化对出口速度的影响较小，尤其是进口速度低于50m/s时，其变化基本上不会使出口速度有大的改变。并且让进口气流压强有大的提高不易实现。提高出口速度的方式是以提高进口气体温度为主，适当提高进口压强。通过对模拟数据的分析，适当延长喷渐扩段的长度既可以降低出口温度，又可以提高出口速度。为了对喷内气体流动过程有更深入的分析，应用重整化(RNG)k–ε模型对喷内流动过程进行数值模拟，对喷流道形状的变化，采用不均匀网格划分计算区域，并用二阶差分格式离散通用微分方程的对流相；然后用SIMP LE算法来求解气体的运动。跟据上述原理应用fluent软件对喷内的压强、温度、速度的分布做分析后，设计出最优的喷结构为：入口直径D1=15.2mm，出口直径D2=14mm，喉部半径Rcr=3.5mm；渐缩角α=30°，长度L1=20.9mm；渐扩角 β=10°，渐扩段长度L2=55mm；总长L=75.9mm。然后，对优化设计的喷进行数值模拟，得出最后的结果。
关键词：镁合金；拉瓦尔喷；(RNG)k–ε模型；SIMPLE算法
丝绵机
压力检测器Abstract
In order to study the cold spray technology on Mg alloy surface, the designed supersonic nozzle is optimized according to the theory of hydrodynamics and aerodynamics. The FLUENT software is used to simulate the gas-solid flow. The velocity, temperature and pressure of gas and solid particles are analyzed in the Laval Nozzle. According to the simulation results, the nozzle structure is improved to make the velocity of gas and particle best.
The key of Cold Spray technology is accelerating the velocity of materials to supersonic in the Laval nozzle, then the powder of materials is deposited on the surface effectively. The speed of outlet was impacted by inlet parameters. At the same Laval nozzle structure, the speed of inlet less impact on outlet speed, particularly inlet velocity blow 50m / s. And increasing air pressure of inlet deeply is difficult realization. The main method of raising the speed of outlet is getting up the gas temperature of inlet with suitable pressure. Through analysis the data of simulation, appropriately extending the length of expanding nozzle’s zone can obtain both lower temperature and higher speed at outlet. A k-ε (RNG) model was used in the simulation in order to understand the character of the flows in Laval-Nozzle. According to the shape variation of the Laval-Nozzle, a structured non-uniform grid system has been used to divide the computation domain. The second-order difference style was selected for the discrimination of the convection in the differential equation, and the SIMPLE method is used to solve the gas phase flow. According to the application of this principle, the pressure, temperature and velocity's distribution are analyzed with FLUENT software. Optimal designing structure of
the nozzle is: Inlet diameter: D1 =15.2mm; outlet diameter: D2 = 14mm; throat radius: Rrfid读写器芯片cr = 3.5mm; Diverging angle: α= 30 °; L影像处理1 = 20.9mm; expanding angle: β= 10 °; L2 = 55mm; Total length: L = 75.9mm. Then, the optimized nozzle properties were simulated and get a reasonable result.
Keywords箱包手把: Mg alloy; Laval Nozzle; SIMPLE method; k-ε (RNG) model
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