A visual observation of the air flow pattern for the high speed nozzle applicable to high power laser cutting and welding

In this study, the flow pattern and pressure variation of the nozzles applicable to high power laser cutting and welding were studied. A total of five nozzles are made and tested with nozzle diameter ranging from 0.8 to 4 mm. The depth of focus and the width of focus are measured based on the flow visualization. It is found that the depth of focus is increased with the rise of exit Mach number while the width of focus is increased with the nozzle diameter. The visual results indicate that the supersonic nozzle reveals a more concentrated jet flow pattern even the flow has passed through the depth of focus. On the other hand, appreciate deviation of the flow pattern is observed for the subsonic nozzle after the depth of focus. As far as more concentrated air flow pattern is concerned, a supersonic nozzle with an exit diameter less than 3.0 mm is recommended. The total pressure decreasing tremendously with the exit Mach number is encountered while moderate decline of the static and dynamic pressure for supersonic nozzles is seen. However, its corresponding dynamic pressure is still higher than that of the subsonic nozzle.