Heat exchangers and boilers are widely used in various plants such as power plants and chemical plants. In heat exchangers and boilers, tube banks are set in a duct such that water passes through inside the tubes and warm gas outside the tubes. Due to the external flow around tube banks, the resonance phenomenon called the self-sustained tone occurs at a certain velocity. The self-sustained tone might cause noise problems in the surroundings, cause losses due to plant shutdown, etc. The self-sustained tone has been studied, and the generation mechanism has been experimentally and numerically clarified. In this paper, we have performed numerical simulations of high level sound generated in boiler tube bank duct with the flow and an acoustic simulation without the flow for a practical generation prediction of a self-sustained tone. The results show a good agreement with measurement data, and that acoustic resonance phenomenon has been numerically captured and clarified. There is the slight difference in the resonance frequencies obtained from the acoustic simulation (without the flow) by means of BEM and the CFD simulation or the experiments due to the absence or presence of the flow.