Plasma Arc Cutting: PNU And KIMM Scientists Together Decode Gas Flow Dynamics

(MENAFN- PR Newswire) The quality of workpieces cut using PAC depends on various factors: kind of plasma gas and its pressure, nozzle hole shape and size, arc current and voltage, cutting speed, and distance between the plasma torch and the workpiece. While most of these factors are well understood in the context of PAC, the impact of gas flow dynamics on cut quality remains less clearly known. This is mainly due to challenges in visualization of the flow dynamics.

To bridge this knowledge gap, a team of researchers, led by Dr. Upendra Tuladhar, currently based at HD Hyundai Mipo after the completion of his Ph.D. studies under Professor Seokyoung Ahn from the Department of Mechanical Engineering at Pusan National University, in collaboration with the Korean Institute of Machinery and Materials, devised novel experimental and computational methods to visualize and understand gas flow dynamics in PAC. Their findings were made available online on 14 September 2024 and published in Volume 159, Part A of the journal International Communications in Heat and Mass Transfer on 1 December 2024.

Dr. Tuladhar explains the motivation behind their research. "Our goal was to assess the gas flow behavior inside the kerfs or grooves of various geometries derived from an actual PAC workpiece. The shape of the cutting front in the kerf varies with the changing cutting speed: high speed yields a curved cutting front. This results in unwanted gas flow behavior, which adversely influences the cutting performance. We carried out further analyses to better understand the mechanism behind this observation."

In this study, researchers proposed an innovative computational fluid dynamics simulation model to explore the impact of a curved cutting front on flow behavior in PAC. Moreover, they performed Schlieren imaging of the gas flow. Herein, fluid flow is photographed by imaging the deflections of light rays refracted by a moving fluid, enabling the visualization of normally unobservable changes in a fluid's refractive index. Lastly, the team compared the gas flow patterns predicted by the simulations with the Schlieren imaging results.

They found that the cutting front curvature resulted in oblique shockwave structures, which significantly reduced flow velocity. Notably, weak shock structures present at the curved cutting front lowered the velocity gradually. In addition, it was possible to achieve a critical flow velocity in kerf with a highly curved cutting front. The workpiece cannot be penetrated vertically beyond this velocity.

Furthermore, the researchers validated their numerical results by noting that the shear stress lines matched the striation patterns on kerf walls.

Reference
Title of original paper: Numerical analysis and Schlieren visualization of gas flow dynamics inside the plasma arc cut kerf with curved cutting fronts
Journal: International Communications in Heat and Mass Transfer
DOI: href="" rel="nofollow" 1016/j.2024.10807

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