On behaviors of pressure and velocity in duct with tube bank at onset of high level sound

Abstract

Vortices occur when gas flow passes through a duct with a tube bank of the heat exchangers, such as a gas heater and a boiler. Very high level sound called a “self-sustained tone” occurs due to the interference of the vortices and the sound field in the duct. There are many investigations concerning the generation mechanism and countermeasures of the self-sustained tones. However there are few investigations focusing on the behaviors of the pressure and the velocity in occurrence of the self-sustained tones. In the past, we experienced the failure of the fan blade used in the experiment. In this paper, the experiment was carried out to examine the behaviors of the pressure and the velocity in the duct with tube bank. As a result, the static pressure changes along the squared curve when the self-sustained tone does not occur. But it suddenly rises up when the self-sustained tone occurs and it is possible for this pressure rise to cause the blade failure due to the generation of the rotating stall. In addition, it was clarified that the flow velocity does not increase in proportion to the inverter frequency and its gradient decreases when the self-sustained tone occurs.