| Summary: | This thesis reports the results of an experimental investigation of vortex induced acoustic resonances in a rectangular duct containing two plates located in tandem. The effects of varying the plate spacing and the leading edge shape were investigated. Tests were conducted in both an open channel and in a rectangular wind tunnel. Measurements were made of acoustic amplitude, frequency and phase relationship between the acoustic field and cortex shedding. Short tests were also conducted with an absorber unit mounted in the wind tunnel wall. Results of tandem plate configuration showed in most cases the presence of two discrete resonances during which the phase of shedding of the first resonance is similar to that of the upstream plate alone while during the second resonance, there was a much smaller variation in phase. In between the two resonances, there was a sudden jump in phase and amplitude as the flow velocity was further increased due to the re-excitation of the resonance. The effect of varying the plate spacing has a marked effect on both the velocity range at which the resonances were excited and the natural Strouhal number. At some plate spacings, these two resonances were excited alternately while at other spacings, there was a wide break between them. The application of tandem plates as a general means to suppress resonance was unsuccessful. It was also found that resonance can be totally suppressed by using an absorber unit.
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