在選擇性雷射熔融製程中，成功地移除製程中產生的飛濺金屬粉末是改善其產品品質的主要目標之一。 一吹氣及兩抽吸的裝置應用在大尺寸之SLM工作腔體，需要小心地控制腔體內的流動結構且通過氣體移除飛濺的金屬粉末。 在本研究中，粒子圖像測速儀（PIV）技術用來觀測兩個不同長寬比的橢圓形噴嘴之SLM工作腔體內流動特性。 分析平均速度分布、紊流強度、渦度以及雷諾應力，以評估兩個噴嘴的性能表現。 根據實驗結果得知，較高長寬比的橢圓形吹嘴更適合應用於SLM製程。

Successfully removing the ejected metal powders during the manufacturing process of Selective Laser Melting (SLM) has been one of the major targets for improving the quality of its product. One blowing and two suction devices are applied to the large-scale SLM working chamber for removing the ejected metal powders through the carrier gas, which the flow structure within the chamber needs to be carefully taken care of. In this study, the technique of particle image velocimetry (PIV) was used to observe the flow properties inside the SLM working chamber, for examining two elliptical blowing nozzles with the different aspect ratio (AR). The mean velocity distributions, turbulence intensities, vorticities and Reynolds stress were analyzed to evaluate the performances of the two nozzles. According to the experimental observations, the elliptical blowing nozzle with higher AR was more suitable for applying to SLM manufacturing.

1. Ladewig, A., et al., Influence of the shielding gas flow on the removal of process by-products in the selective laser melting process. Additive Manufacturing, 2016. 10: p. 1-9.
2. Ferrar, B., et al., Gas flow effects on selective laser melting (SLM) manufacturing performance. Journal of Materials Processing Technology, 2012. 212(2): p. 355-364.
3. Anwar, A.B. and Q.-C. Pham, Selective laser melting of AlSi10Mg: Effects of scan direction, part placement and inert gas flow velocity on tensile strength. Journal of Materials Processing Technology, 2017. 240: p. 388-396.
4. Wang, W.-C. and C.-Y. Chang, Flow analysis of the laminated manufacturing system with laser sintering of metal powder. Part I: flow uniformity inside the working chamber. The International Journal of Advanced Manufacturing Technology, 2017. 92(1-4): p. 1299-1314.
5. Gauntner, J.W., P. Hrycak, and J. Livingood, Survey of literature on flow characteristics of a single turbulent jet impinging on a flat plate. 1970.
6. Gutmark, E. and F. Grinstein, Flow control with noncircular jets. Annual review of fluid mechanics, 1999. 31(1): p. 239-272.
7. Aleyasin, S., et al. Low Reynolds number effects on jets issuing from round and elliptic orifices. in ICHMT DIGITAL LIBRARY ONLINE. 2015. Begel House Inc.
8. Aleyasin, S.S., M.F. Tachie, and M. Koupriyanov, Statistical Properties of Round, Square, and Elliptic Jets at Low and Moderate Reynolds Numbers. Journal of Fluids Engineering, 2017. 139(10): p. 101206.
9. Sz-Jia Tzeng, X.-X.C., Wei-Cheng Wang, Numerical and Experimental Observations of the Flow Field inside the Selective Laser Melting (SLM) Chamber through Computational Fluid Dynamics (CFD) and Particle Image Velocimetry (PIV). 2018.
10. Long, J. and T. New, Vortex dynamics and wall shear stress behaviour associated with an elliptic jet impinging upon a flat plate. Experiments in Fluids, 2016. 57(7): p. 121.
11. Khayrullina, A., et al., PIV measurements of isothermal plane turbulent impinging jets at moderate Reynolds numbers. Experiments in Fluids, 2017. 58(4): p. 31.
12. New, T., T. Lim, and S. Luo, A flow field study of an elliptic jet in cross flow using DPIV technique. Experiments in Fluids, 2004. 36(4): p. 604-618.
13. Hsu, C. and R. Huang, Phase-resolved and time-averaged puff motions of an excited stack-issued transverse jet. Journal of Fluids and Structures, 2013. 40: p. 302-316.
14. Hsu, C.M., R.F. Huang, and M.E. Loretero, Unsteady flow motions of an oscillating jet in crossflow. Experimental Thermal and Fluid Science, 2014. 55: p. 77-85.
15. Wang, H., S. Lee, and Y.A. Hassan, Particle image velocimetry measurements of the flow in the converging region of two parallel jets. Nuclear Engineering and Design, 2016. 306: p. 89-97.
16. Zhang, X., et al., PIV measurement and simulation of turbulent thermal free convection over a small heat source in a large enclosed cavity. Building and Environment, 2015. 90: p. 105-113.
17. Lee, S.-J. and S.-J. Baek, The effect of aspect ratio on the near-field turbulent structure of elliptic jets. Flow Measurement and Instrumentation, 1994. 5(3): p. 170-180.
18. Quinn, W., On mixing in an elliptic turbulent free jet. Physics of Fluids A: Fluid Dynamics, 1989. 1(10): p. 1716-1722.
19. Quinn, W., Experimental study of the near field and transition region of a free jet issuing from a sharp-edged elliptic orifice plate. European journal of Mechanics-B/Fluids, 2007. 26(4): p. 583-614.
20. Lee, J. and S.-J. Lee, The effect of nozzle aspect ratio on stagnation region heat transfer characteristics of elliptic impinging jet. International journal of heat and mass transfer, 2000. 43(4): p. 555-575.
21. Hashiehbaf, A. and G. Romano, Particle image velocimetry investigation on mixing enhancement of non-circular sharp edge nozzles. International Journal of Heat and Fluid Flow, 2013. 44: p. 208-221.
22. Maurel, S. and C. Solliec, A turbulent plane jet impinging nearby and far from a flat plate. Experiments in Fluids, 2001. 31(6): p. 687-696.
23. Narayanan, V., J. Seyed-Yagoobi, and R. Page, An experimental study of fluid mechanics and heat transfer in an impinging slot jet flow. International Journal of Heat and Mass Transfer, 2004. 47(8-9): p. 1827-1845.
24. Deo, R.C., J. Mi, and G.J. Nathan, The influence of nozzle aspect ratio on plane jets. Experimental thermal and fluid science, 2007. 31(8): p. 825-838.
25. Zhou, D. and S.-J. Lee, Forced convective heat transfer with impinging rectangular jets. International Journal of heat and mass transfer, 2007. 50(9-10): p. 1916-1926.
26. Quinn, W., Turbulent free jet flows issuing from sharp-edged rectangular slots: the influence of slot aspect ratio. Experimental thermal and fluid science, 1992. 5(2): p. 203-215.
27. Melling, A., Tracer particles and seeding for particle image velocimetry. Measurement Science and Technology, 1997. 8(12): p. 1406.
28. Flagan, R.C. and J.H. Seinfeld, Fundamentals of air pollution engineering. 2012: Courier Corporation.
29. Adrian, R.J., Image shifting technique to resolve directional ambiguity in double-pulsed velocimetry. Applied Optics, 1986. 25(21): p. 3855-3858.
30. Rajaratnam, N., Turbulent jets. Vol. 5. 1976: Elsevier.
31. Pope, S.B., Turbulent flows. 2001, IOP Publishing.