Flow-Sound Interaction Mechanisms and Control Strategies

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* * * *Flow-excited acoustic resonance is a design concern in many engineering applications such as tube bundles in heat exchangers, boiler plants, turbomachines, and piping systems. It occurs when the flow surrounding a bluff body, such as a circular cylinder, vibrates in a resonant manner. This often leads to the generation of acute noise problems and/or excessive vibrations. Since the acoustic resonance phenomenon is not yet fully understood, it can be dangerously unpredictable and may cause catastrophic failures. With the ever increasing demand on energy, expansion projects of existing power plants are becoming common practice. This means the construction of larger heat exchangers tube bundles with higher flow rates than what are currently used which, in turn, would make the heat exchangers more susceptible to noise and vibration problems. Considering the existing level of knowledge of flow-sound interaction in heat exchangers tube bundles it is extremely complex to predict the occurrence of acoustic resonance during the design stage. ***Due to the complexity of the flow-sound interaction mechanisms in tube bundles, the simplified cases of isolated cylinders in various arrangements have been investigated in some detail. However, this knowledge cannot be directly applied to the case of tube bundles. In addition, finned cylinders are widely used in heat exchangers tube bundles to increase the heat transfer rates. In this respect, previous experiments showed that adding fins to cylinders may enhance the process of vortex shedding, and therefore may increase the susceptibility to acoustic resonance excitation. However, the applicant's research established that the acoustic resonance for the case of a single finned cylinder in cross-flow depends on its aspect ratio. Although the cylinder's aspect ratio is not a factor in the excitation mechanism of acoustic resonance from bare cylinders, it is an important parameter that should be considered when investigating acoustic resonance excitation in finned tube bundles.***Therefore, the main objective of this research program is to investigate the fundamental mechanisms of flow-sound interaction in tube bundles with full arrays of both bare and finned cylinders, and develop practical control strategies to alleviate the occurrence of acoustic resonance. The findings of this research will lead to the development of reliable design guidelines that can be used to predict, control and avoid the occurrence of acoustic resonance in heat exchanger tube bundles. Such significant guidelines are currently not available in the literature. This will not only reduce unplanned shutdowns of power plants due to potential catastrophic failures of heat exchanger tube bundles but also will allow for the construction of larger and more efficient heat exchangers. Increasing the efficiency, safety and reliability of such equipment will directly benefit the Canadian economy.***