• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.1
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• pp.33-38
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• 2012

An experimental study was carried out to observe the characteristics of impingement of assist gas from a rectangular supersonic nozzle on kerf surface in laser machining. A micro-scale supersonic (Mach number 2.0) rectangular nozzle system was designed and fabricated for the purposes, and hot tests of the performance of the nozzle system was proceeded in the ITI corporation laboratory. For various related parameters such as laser powers, nozzle pressures and cutting speeds, the quality of the frontal view of cut edge surfaces was observed by a microscope. In the study, it was shown that the application of the present micro-rectangular supersonic nozzle in an off-axis configuration made it possible to cut a mild steel, by combinations of relatively low laser - powers, large standoff distances, and assist gas with no oxygen, which was not achieved by conventional laser cutting processes.

• Journal of computational fluids engineering
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• v.9 no.2
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• pp.30-35
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• 2004

A numerical study of underexpanded jet and impingement on a wall mounted at various distances from the nozzle exit is presented. The 3-dimensional Wavier-Stokes equations and κ-ω turbulence equations are solved. The grids are constructed as overlapped grid systems to examine the distance effect. The DADI method is applied to obtain steady-state solutions. To avoid numerical instability such as the carbuncle phenomena that sometimes accompany approximate Riemann solver, the HLLE+ scheme is employed for the inviscid flux at the cell interfaces. A goal of this work is to apply a number of two-equation turbulence models based on the w equation to the impinging jet problem.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.139-145
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• 2004

A numerical study of underexpanded jet and impingement on a wall mounted at various distances from the nozzle exit is presented. The 3-dimensional Navier-Stokes equations and $\kappa-\omega$ turbulence equations are solved. The grids are constructed as overlapped grid systems to examine the distance effect. The DADI method is applied to obtain steady-state solutions. To avoid numerical instability such as the carbuncle that sometimes accompany approximate Riemann solver, the HLLE+ scheme is employed for the inviscid flux at the cell interfaces. A goal of this work is to apply a number of two-equation turbulence models based on the $\omega$ equation to the impinging jet problem.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.285-288
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• 2007

Numerical study of the influence of the boundary layer of micro-supersonic jet impinging on a flat plate with a hole was performed, to investigate the role of gas jet to eject melted materials from the cut zone in the laser machining. The detailed shock structures and the information of the mass flow rate through the hole were compared to the results of the previous study, in which the effects of boundary layer inside nozzle was not accounted. It was found that the boundary layer inside the micro- nozzle introduced stronger Mach disc over the machining zone, and thus that the mass flow rate through the hole decreased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.233-240
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• 2012

An experimental study to improve the impingement characteristics of the assist gas in laser cutting was carried out. For various assist-gas pressures, and locations and installation angles of the nozzle, the characteristics of the impingement of the jet from a supersonic rectangular nozzle were compared to those previously observed for typical circular nozzles. Schlieren flow visualizations and Pitot pressure measurements downstream of the kerf surface were utilized for this purpose. The present rectangular supersonic nozzle decreased the strength of the Mach disc occurring at the corner of the kerf surface, and thus, could weaken the separation of the assist gas on the kerf surface and increase the Pitot pressures downstream compared to conventional circular nozzles.

• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1448-1456
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• 2002

The present study addresses the flow characteristics involved in the self-induced oscillations of the underexpanded jet impinging upon a cylindrical body. Both experiment and computational analysis are carried out to elucidate the shock motions of the self-induced oscillations and to find the associated major flow factors. The underexpanded sonic jet is made from a nozzle and a cylindrical body is placed downstream to simulate the impinging jet upon an obstacle. The computational analysis using TVD scheme is applied to solve the axisymmetric, unsteady, inviscid governing equations. A Schlieren system is employed to visualize the self-induced oscillations generated in flow field. The data of the shock motions are obtained from a high-speed video system. The detailed characteristics of the Mach disk oscillations and the resulting pressure variations are expatiated using the time dependent data of the Mach disk positions. The mechanisms of the self-induced oscillations are discussed in details based upon the experimental and computational results.