Numerical Simulation of High Level Sound Generated in Boiler tube Bank Duct

Abstract

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.

Countermeasure for High Level Sound Generated from Boiler Tube Bank Duct

“…The resonance frequencies obtained from the theory (without the flow) and the CFD simulations or the experiments are slightly different because of the absence or presence of the flow. Figure 1 shows that the slight increase of the resonance frequency occurs with an increase of the gap flow velocity [24]. The predicted SPL of the dominant tone at 740 Hz reasonably agrees with the measured one.…”

“…Mori et al [24] performed compressible CFD simulations to capture the selfsustained tone and compare the simulation results with the measurements [13]. They confirmed that the self-sustained tone at the acoustic mode in the width direction of the duct occurs, and the sound pressure level does not follow the 5th power law when the gap velocity is high, as in the experiments.…”

“…Instantaneous snapshots of vorticity fields at Z = 0 plane are shown in Figure 8 shows that the value of the static pressure on the upstream side of the tube bank is larger than that on the downstream side, and distinguishing the sound pressure from the static pressure seems to be difficult. Thus, the fluctuation pressure is defined as follows to distinguish easily between the sound pressure and the static pressure [24].…”

“…(2) Figure 6. CFD model [24]. Here, p s denotes the static pressure which is defined by The frequency spectra of SPL are monitored on the wall of the duct near the outflow boundary, and represented in Figure 10.…”