磨料射流与电火花复合加工技术喷嘴内流场速度分布研究Study on Velocity Distribution of Flow Field in Nozzles for the Composite Machining Technology of Abrasive Jet and EDM

DOI: 10.12677/IJFD.2017.54017, PDF, HTML, XML, 下载: 740  浏览: 1,557  科研立项经费支持

Abstract: The composite machining technology (CMT) of abrasive jet (AJ) and electrical discharge machining (EDM) is used to improve the machining quality and efficiency of the workpiece, and the velocity distributions of flow felid of jet fluid in the nozzle and at nozzle exit have important influences on machining process of the workpiece. By establishing the finite element model of the flow field in the nozzle and changing the inlet diameter and inlet velocity of the nozzle, effects of inlet diameter for working fluid, inlet diameter for abrasive, outlet diameter for nozzle, inlet velocity for working fluid, inlet velocity for abrasive, on the velocity distributions of flow fields in nozzle and at nozzle exit, are studied. The results show that the velocities at the nozzle exit increase with the increase of inlet diameters for working fluid and abrasive, however, the distributions of velocity uniformity are worse in these cases; the velocities decrease with the increases of the outlet diameter for the nozzle, and the distributions of velocity uniformity are not much changed; the velocity distributions of flow field in nozzle change a little with the increases of inlet velocity for abrasive at low speeds, however, influences are greater at the high speed cases; for different inlet velocities of working fluid, the velocity distributions of flow field in nozzle have almost the same trend, and the velocities with great values locate mainly below the line between the working fluid inlet and the nozzle outlet. The results in this paper can be used to optimize the internal geometry of the nozzle.

1. 引言

2. 计算模型

2.1. 磨料射流与电火花复合加工技术原理

2.2. 湍流流动的理论基础

Figure 1. Schematic diagram of the CMT of AJ and EDM

Figure 2. The machining area of EDM

$\left\{\begin{array}{l}\frac{\partial \rho }{\partial t}+\frac{\partial \rho {v}_{j}}{\partial {x}_{i}}=0\\ \frac{\partial \rho {v}_{i}}{\partial t}+\frac{\partial \rho {v}_{j}}{\partial {x}_{i}}=-\frac{\partial P}{\partial {x}_{j}}+\frac{\partial }{\partial {x}_{j}}\left[{\mu }_{e}\left(\frac{\partial {v}_{j}}{\partial {x}_{j}}+\frac{\partial {v}_{i}}{\partial {x}_{i}}\right)\right]-\rho {g}_{i}\beta T\\ \frac{\partial \left(\rho k\right)}{\partial {x}_{j}}+\frac{\partial \left(\rho {v}_{j}\right)}{\partial {x}_{j}}=\frac{\partial }{\partial {x}_{i}}\left(\frac{{\mu }_{e}}{{\epsilon }_{k}}\frac{\partial k}{\partial {x}_{j}}\right)+{P}_{k}+{P}_{b}-\rho \epsilon \\ \frac{\partial \rho \epsilon }{\partial t}+\frac{\partial \rho {v}_{k}\epsilon }{\partial {x}_{k}}=\frac{\partial }{\partial {x}_{k}}\left(\frac{{\mu }_{e}}{{\epsilon }_{k}}\frac{\partial \epsilon }{\partial {x}_{j}}\right)+\frac{\epsilon }{k}\left(c{\epsilon }_{1}Pk-\rho c{\epsilon }_{2}\epsilon \right)+c{\epsilon }_{3}\frac{\epsilon }{k}{P}_{k}\end{array}$ (1)

2.3. 喷嘴内流场有限元计算模型

3. 结果与讨论

3.1. 喷嘴内部流场的速度分布

Figure 3. Schematic diagram of the nozzle geometry

Figure 4. The finite element grids of the nozzle

Table 1. Geometric dimensioning for the internal structure of the nozzle

3.2. 几何尺寸对出口处流场速度分布的影响

Figure 5. The velocity distribution of flow field in the nozzle: (a) The velocity distribution of flow field for the abrasive-working fluid; (b) The velocity distribution of flow field for the abrasive; (c) The velocity distribution of flow field in the nozzle

Figure 6. Effects of inlet diameter for working fluid on the velocity distribution of the exit

Figure 7. Effects of inlet diameter for abrasive on the velocity distribution of the exit

Figure 8. Effects of the exit diameter on the velocity distribution of the exit

3.3. 入口速度对喷嘴内部和出口处流场速度分布的影响

Figure 9. Effects of inlet velocity for abrasive on the velocity distribution of the flow field in the nozzle

Figure 10. Effect of inlet velocity for abrasive on velocity distribution of nozzle outlet

Figure 11. Effects of the inlet velocity for working fluid on the velocity distribution of the flow field in the nozzle

Figure 12. Effect of inlet velocity for working fluid on velocity distribution of nozzle outlet

4. 结论

1) 在相同磨料入口速度和工作液入口速度情况下，随着工作液入口尺寸和磨料入口尺寸的增加，喷嘴出口处速度值都会增加，但速度分布均匀性却相应变差；喷嘴出口尺寸的增加，会导致喷嘴出口处速度值的降低，但速度分布均匀性变化不大。

2) 低速时，磨料入口速度增加，对喷嘴内部流场的速度分布状况影响不大；对于不同的工作液入口速度，喷嘴内部流场的速度分布大致一致，速度较大部分主要分布在工作液入口与喷嘴出口连线下部区域。磨料入口速度和工作液入口速度增加，都会导致喷嘴内部流场相应位置流速的增加。

3) 喷嘴几何尺寸、入口速度都会对喷嘴内部流场的速度分布以及喷嘴出口处速度分布产生影响。

4) 在磨料射流与电火花复合加工过程中，针对不同的入射速度，应该设计出具有不同结构尺寸的喷嘴。

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