Study on the behavior of fluid acoustic device by numerical simulation

This paper describes computational study to investigate the aero-acoustic mechanism observed in Hartmann generator when under-expanded supersonic jet is blown from a convergent nozzle. The Hartmann generator, composed of a nozzle and a resonance tube with small distance, is known to radiate much higher amplitude of tonal sound than a free jet without any interaction. Aiming at establishing compact and efficient fluidic actuators, the authors tried to clarify the fluid-dynamic and acoustic behaviors of this special device by use of computational tool, i.e., UPACS-LES of Japan aerospace exploration agency（JAXA）. The computational results suggested existence of the JRG mode, an alternative flow motion between the nozzle and the resonance tube. This flow motion drives strong pressure fluctuation and forms sound field in the far field. The computational results complied with the fundamental acoustic characteristics in the former studies, such as far-field sound directivity and radiated acoustic power. Based on the results, it was confirmed that some parameters such as nozzle pressure ratio are predominant to intensify the acoustic power in the far field. Especially, the open-end location of the resonance tube governs the acoustic power when it is between Mach disk and shock cell end in the under-expanded supersonic jet.