Effect of chevron tip count and shape on the subsonic jet mixing noise emitted from hot air lance

To mitigate jet-mixing noise emitted from a Mach 0.85 hot-air lance in iron manufacturing, we examined the effect of chevron tip geometry on large turbulence structure noise and fine-scale turbulence noise. The parametric variables are tip count (0, 4, 8 and 16) and tip shape (original chevron, tetragonal tip and round tip). To determine the tip effect quantitatively, we proposed the corrected jet noise spectrum equation and coefficient factor. Increasing the chevron tip count induced efficient jet mixing due to an increase in downstream jetmixing interface area. When the tip count was eight, large turbulence noise was reduced to the most. When the tip count was fixed at eight for round and tetragonal tips, jet mixing and noise reduction efficiency are both decreased owing to the non-uniform tip area decrease in the nozzle’s axial direction.