Flow-Sound Interaction Mechanisms and Control Strategies

*在热交换器、锅炉、透平机械和管道系统中的管束等许多工程应用中，流动激励的声学共振是一个设计问题。当绕着钝体(如圆柱体)的流动以共振方式振动时，就会发生这种情况。这通常会导致产生严重的噪音问题和/或过度振动。由于声学共振现象尚未完全了解，它可能是危险的不可预测的，并可能导致灾难性的故障。随着能源需求的不断增长，对现有电厂进行扩建已成为一种普遍现象。这意味着建造更大的换热器管束，其流速高于当前使用的管束，这反过来又会使换热器更容易受到噪音和振动问题的影响。考虑到换热器管束中流-声相互作用的现有知识水平，在设计阶段预测声学共振的发生是非常复杂的。*由于管束中流-声相互作用机理的复杂性，本文对不同布置形式的孤立柱体的简化情况进行了较为详细的研究。然而，这一知识不能直接应用于管束的情况。此外，翅片圆柱体被广泛应用于换热器管束中，以提高换热效率。在这方面，以前的实验表明，在圆柱体上加装翅片可以加强涡流的脱落过程，因此可能会增加对声学共振激励的敏感性。然而，申请人的研究证实，横流中单个翅片圆柱体的声学共振取决于其长径比。尽管圆柱体的纵横比不是裸圆柱声共振激励机制中的一个因素，但它是研究翅片管束中声共振激励时需要考虑的一个重要参数。*因此，本研究计划的主要目的是研究完整排列的裸圆柱体和翅片圆柱体管束中流声相互作用的基本机理，并开发实用的控制策略来减少声共振的发生。这项研究的结果将导致开发可靠的设计指南，可以用于预测、控制和避免换热器管束中发生声共振的发生。这种重要的指南目前在文献中是不可用的。这不仅将减少由于热交换器管束潜在的灾难性故障而导致的发电厂计划外关闭，而且还将允许建造更大、更高效的热交换器。提高此类设备的效率、安全性和可靠性将直接惠及加拿大经济。*

* * * *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.***