Experimental And Numerical Study On Flow-Induced Acoustic Resonance In Square Closed Side Branch

Flow-induced acoustic resonance in closed side branch is aflow-acoustic-coupling phenomenon caused by the interaction of flowand acoustic field in special structure. It may cause structure destructionto those components in the system if occurred in nuclear power station.Taking the safety aspect of components into account, it is of veryimportant engineering value to gain adequate understanding of themechanism and discipline of acoustic resonance for structural design.The non-visualization, visualization experiments and computationalfluid dynamic (CFD) research are carried out for closed side branchstructure with square cross section in this thesis. The resonancecharacteristics are obtained in the experiment. And the influence ofvelocity and length of side branch on flow-induced acoustic resonance arealso investigated through experiments. Based on the experiment results,the mechanism and discipline of acoustic resonance are discussed. Theexperiment results are also utilized to validate the CFD simulation whichcan be applied in the subsequent study on acoustic resonance andengineering design.The experiment results show that the vortex shedding from theleading edge of side branch moved downstream and does not vanish untilimpacting the trailing edge. This impact of those vortices on the trailingedge can be regarded as the cause of acoustic resonance in the studiedstructures. When acoustic resonance occurred, the fluctuating pressureapproaches pure tone with high amplitude, and the major frequency areclearly observed. The fluctuating pressure generated in the side branchmainly transmitted downstream, partly upstream. The results revealedthat resonance frequency shows a stair-wise lock-in phenomenonregarding the flow velocity. There exists, insignificant though, hysteresis phenomenon in structures studied.As the length of side branch increases, the amplitude of acousticpressure and resonance frequency decreases. In the structure considered,acoustic resonance occurred when Strouhal number was in the range of0.3to0.6and0.7to1.0. The strongest resonance occurred in each lengthof side branch (L=250mm,300mm and350mm) at St=0.45,0.41and0.43separately, and the amplitude decreased.The flow field around the mouth of side branch, the fluctuatingpressure in acoustic resonant condition, the lock-in phenomena as well ashydrodynamic mode have been successfully captured through the CFDsimulation. But the amplitude of acoustic resonance obtained from CFDwas higher than that from experiment.Comprehensive researches were carried out in this thesis,experimentally and numerically. Non-visualization and visualizationexperiment were carried out for certain test condition and local flow field,and utilizing CFD study as complement. The cause and characteristics offlow-induced acoustic resonance and influence from velocity and lengthof side branch were revealed to some extent, providing foundation forsubsequent deep research.