The Effect of Auxiliary Jets on Excited Tones in Gas Jet Wiping

It has been shown that the high intensity tonal noise generated in continuous galvanizing gas jet wiping is due to aeroacoustic feedback. This feedback occurs between the jet flow of the air knife and an acoustic wave generated by coherent flow structures impinging upon the substrate. This paper is presented as a proof of concept of the ability of a new design of multi-jet air knife geometry to suppress the tones generated in this manner. The new nozzle design comprises a main jet with two inclined auxiliary jets located symmetrically about the main jet nozzle. The results show that when the auxiliary jets are used in conjunction with the main wiping jet, the intense tones observed for the main jet alone are suppressed significantly. The introduction of auxiliary jets also increases the broadband noise of the jet and produces low amplitude tones at higher frequencies.