Numerical modeling and Schlieren visualization of the gas-assisted laser cutting under various operating stagnation pressures

• Published in: International journal of heat and mass transfer 2020-02, Vol.147, p.118965, Article 118965
• Main Authors: Darwish, Mohamed, Mrňa, Libor, Orazi, Leonardo, Reggiani, Barbara
• Format: Article
• Language: English
• Subjects: Cut kerf; Cutting parameters; Gas dynamics; Gas-assisted laser cutting; Jet flow; Laser beam cutting; Machining; Mathematical models; Nozzle geometry; OpenFOAM; Over-expansion; Schlieren visualization; Stagnation pressure; Supersonic nozzles; Under-expansion; Visualization
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2019.118965

•Gas assisting flow plays an essential role in laser cutting where it helps to improve both quality, by ejecting the molten material, and capability by increasing the allowable operational speed and thickness.•The effect of both nozzle configuration and operating condition on the dynamic characteristics and the behavior of the exit jet have been investigated.•The gas-assisted laser cutting flow through different supersonic nozzles has been numerically modelled using an open source software, under various operating conditions.•The numerical results have been compared with the experimental observations made by Schlieren visualization and they are quantitatively in high agreement in terms of the flow structure. The uniformity of the exit jet pattern in high pressure gas-assisted laser cutting represents the main feature in order to achieve high cutting quality and capability. Therefore, the effect of both inlet stagnation pressure and nozzle geometry on the behavior of the exit jet has been investigated in this research. Quasi 1-D gas dynamics theory has been used to calculate the exact-design operating conditions for three different supersonic nozzles that were fabricated by means of Wire Electrical Discharge Machining. The jet flow through these nozzles has been numerically modeled and experimentally checked, using Schlieren visualization, under exact-design, over-expansion and under-expansion operating conditions coming to a good numerical-experimental agreement in terms of flow structure. As main result, the exit jet was found to preserve its uniform distribution with parallel boundaries and low divergence under the exact-design operating condition, differently to what observed for the others two conditions, especially for nozzle with small divergence angle.