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The tube-bank exhaust gas economizer can be usually considered as a series of tubes arranged in a rectangular duct. The tube arrays in cross flow sometimes excite the acoustical vibrations of sound fields in the duct of the exhaust gas economizer. It is very important, for practical applications, to understand the conditions of the acoustical resonances in the duct with the tube bundles. A staggered array of closely paced rigid tubes has been tested, in a exhaust gas economaizer of varying the flow velocity, to investigate the conditions under which acoustical resonances do or do not materialize. Among the aspects which have been investigated are: the Strouhal numbers at which flow periodicities occur; the relation between these Strouhal numbers and those at which acoustical resonances occur. The resonances occur when the frequencies of the flow periodicities inside the array coincide with those of the acoustical modes. At resonances, the intense pure tone noises, which may reach 120 dB, are produced. When the shedding frequency of the vortex formed in the wake of the flow behind the individual tubes happens to be near the natural frequency of the gas column perpendicular to the flow and the tube axis, a strong transverse acoustical oscillation of the gas column is excited. Acoustical resonance in the economizer tube arrays has been suppressed by detuning the resonance with baffles that shift the acoustic natural frequency upwards. We have successfully employed a single baffle to suppress resonance.

An Experimental Study on the Acoustical Resonance and Its Suppression in the Exhaust Gas Economizer Employed in the Ship