Experimental study on acoustic energy absorbers to suppress acoustic resonance in tube bundles of boiler plants

The present paper deals with acoustic resonance in tube bundles which occurred in actual boiler plants. A practical method to suppress the resonant noise is proposed based on scale model tests. In those experiments, besides the transverse modes which are relatively well-known, longitudinal modes which are known to be difficult to suppress, were realized. The relation of both kinds of acoustic modes to vortex shedding frequency was clarified. In the following step, a design method of the acoustic energy absorbers is proposed based on the feedback system stability theory. According to this theory, acoustic energy absorbers were equipped in the duct of the test model, and remarkable increase of the critical flow velocity was confirmed for both types of resonant mode. Based on these results, this method was applied to the actual boiler plants and it was confirmed that the proposed method is the effective countermeasure for both types of acoustic resonant modes.