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

点击翻译按钮获取中文摘要

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.