확장관 형상에 따른 유체유기진동기반 방사소음 특성에 관한 연구

Abstract

Flow characteristics inside an expanded cavity under high Reynolds number containing noise and vibration have recently been highlighted in connection with the strict regulation maintaining a comfortable environment. Noise and vibration phenomena occurring in a pipe is usually accompanied by a complex flow and structural interaction. Although it can be estimated in an even simple case of the expanded pipes having complex turbulent flow, the radiated noise caused by the size, shape and thickness of the given model propagates and makes serious interference effect and instability of the surrounding systems, and it finally gets a fatigue fracture and failure. Formulation of a coupled Fluid-Structure system can be expressed by the combination of Navier-Stokes equation governing flow structure inside a duct, elastic wave equation governing dynamic momentum motion and suitable boundary conditions. The flow interaction between surrounding bodies and small-scale flow eddies in a high speed turbulent flow is highly complicated to predict so that the fluid-structural interaction(FSI) analysis must be coaxially performed to ensure the reliability of the upcoming results. In this study, the user-defined FSI modules are developed by the combination of several commercial codes. They include 3 representative codes such as FLUENT known as the flow solver, NASTRAN as dynamic motion solver of complex structures and finally radiated noise solver - SYSNOISE - which is based on BEM(Boundary Element Method) scheme. The study undertakes the flow characteristics inside an expanded pipe and establishes some procedures analyzing the flow-induced vibration of body/surface and finally get a radiated noise from the vibration source. In the results, the expanded pipe having a resonator cavity with a bottle neck has the SPL(Sound Pressure Level) around -30dB, which is the lowest value among other four cavities.