Study On The Correlation Between Turbulence Structure And Flowinduced Noise In Circular Cylinder Wakes

Flow-induced noise widely exists in aviation,navigation,ground transportation,building environment and many other fields of industrial production and social life.In recent years,with the development of modern industry,the problem of flowinduced noise has attracted more and more attention of industry and academia.Therefore,the study of flow-induced noise is of great significance.The flow around a cylinder is one of the classical research paradigms of bluff body.When the fluid flows around the cylinder,the shear layers fall off alternately and form Carmen vortex street behind the cylinder,accompanied by the generation of noise.This thesis focuses on the correlation between turbulent structure and flow-induced noise in circular cylinder wakes.In this thesis,the acoustic source of flow-induced noise in the wake of a blunt body is analyzed theoretically by using previous theories,and the phase averag ing analysis of the Curle equation is carried out.Therefore,it is qualitatively inferred that the contribution of coherent structure ?? to noise is more significant than the contribution of coherent structure ?? and coherent structure ?? in quadrupole sources.In this thesis,a noise amplification device with depth-adjustable cavities can amplify the acostic signal of a specific frequency.The device provides a new means for the research of flow-induced noise.Through the simultaneous measurement of the flow field and flow-induced noise in the single circular cylinder wake,the correlation coefficient between the turbulence structure and the noise is analyzed.In the wake of a single cylinder,the flow-induced noise is mainly generated in the near field within streamwise 10 d.The contribution of Reynolds stress to the acoustic source mainly comes from the turbulence structure between-2.1d to 2.1d in spanwise direction,and the contribution of Reynolds stress to the quadrupole source mainly comes from the turbulence structure in the range of spanwise-1.3d to 1.3d.In addition,the flow field and flow-induced noise in the wake of the identical side-by-side cylinders in engineering practice are measured simultaneously.The results show that the acoustic source in the wake of side by side cylinders with equal diameter is mainly from the turbulent structure in the clearence region,where the contribution of Reynolds shear stress uv to noise is more significant than others.With the decrease of the spacing ratio of two cylinders,the interference between the two vortex streets in the wake gradually increases.Meanwhile,the flow-induced noise intensity decreases,and the contribution of Reynolds stress to the noise also decreases.The flow-induced noise is drowned in the background noise at the Reynolds number 12500,where there is a bistable flow in clearence region.