Flow-Sound Interaction Mechanisms with Application to Bluff Body Wakes and Separated Shear Flows

自由剪切流，如钝体后面的尾迹，空腔和侧分支上的分离剪切层，以及通过孔和阀的射流，都是高度不稳定的。自由剪切流的不稳定性产生周期性涡度脱落，其频率随流速线性变化。在紊流中，这是许多工业应用的典型，如热交换器、锅炉、涡轮机器、管道系统和反应堆容器中的管束，涡度脱落是弱的和高度无组织/不连贯的。然而，当涡度脱落与声模耦合时，会发生反馈机制，涡度脱落变得更强，更连贯。这就产生了严重的噪音问题，通常与过度振动有关，这可能导致操作中断，在某些情况下可能迅速升级为灾难性故障。由于声学共振现象尚未被完全理解，它可能是危险的不可预测的。本研究的目的是促进对流声相互作用机制和流声共振发生条件的认识。在未来五年的研究计划中，重点将放在两种主要的流动配置上，其中钝体尾迹和分离剪切流将遇到，以阐明管束（焦点区域I）中流声耦合的基本机制和来自翅片圆柱簇（焦点区域II）的共振激励。此外，将开发一种可用于预测管阵列中声共振发生的声阻尼准则（焦点区域III）。该研究的结果将有助于解决一些重要工业应用中与流动引起的突然激发噪声和振动问题相关的挑战，以及在设计阶段缺乏预测其发生的指导方针。这不仅可以减少由于潜在的灾难性故障而导致的工程应用程序的意外停机，还可以建造更大、更安全、更高效的设备。

Free shear flows, such as wakes behind bluff bodies, separated shear layers over cavities and side branches, and jet flows through orifices and valves, are highly unstable. The instabilities of the free shear flows generate periodic vorticity shedding with frequencies that vary linearly with the flow velocity. In turbulent flow, which is typical in many industrial applications, such as tube bundles in heat exchangers, boiler plants, turbomachines, piping systems, and reactor vessels, the vorticity shedding is weak and highly unorganized/incoherent. However, when the vorticity shedding couples with an acoustic mode a feedback mechanism occurs and the vorticity shedding becomes stronger and much more coherent. This leads to the generation of acute noise problems that are often associated with excessive vibration, which could result in operation interruption and in some cases may escalate rapidly to catastrophic failures. Since the acoustic resonance phenomenon is not yet fully understood, it can be dangerously unpredictable. The objective of the proposed research is to advance the state of knowledge of the flow-sound interaction mechanisms and the conditions under which flow-induced acoustic resonances materialize. In the next five years of the research program the focus will be on two main flow configurations where bluff body wakes and separated shear flows are encountered to elucidate the fundamental mechanisms of flow-acoustic coupling in tube bundles (FOCUS AREA I) and resonance excitation from cluster of finned cylinders (FOCUS AREA II). Moreover, an acoustic damping criterion that can be used to predict the occurrence of acoustic resonance in tube arrays will be developed (FOCUS AREA III). The findings of the proposed research will help to tackle challenges associated with the sudden excitation of flow-induced noise and vibration problems in several important industrial applications and the lack of guidelines to predict their occurrence during the design stage. This will not only reduce unplanned shutdowns of these engineering applications due to potential catastrophic failures but also will allow for the construction of larger, safer, and more efficient equipment.