Numerical Investigation Of Flow Around Cylinders

The flow around a cylinder has always been one of the classic problems in the field of fluid mechanics,and the phenomenon of flow around a cylinder is also widely present in practical engineering,such as bridge piers,offshore structure,and cooling towers for nuclear plants,etc.In recent years,with the development of deep-sea oil and gas,the laying of submarine pipelines often adopts multi-cylinder systems,and densely arranged multi-cylinders are prone to structural damage under the action of fluid,especially when the natural frequency of the cylinders and the vortex breakaway frequency are close,the resonance is likely to occur,which will accelerate the fatigue damage of the structure.In the current work,the flow around single cylinder and double cylinder arrangements has been studied in depth,but there are fewer studies on the flow around multiple cylinders with more arrangements.Therefore,in this paper,the cases that seven-array cylinders with equidistant staggered arrangement and nine-array cylinders with equidistant regular quadrilateral arrangement are chosen for numerical simulations.This paper provides a reference for studying the flow characteristics of multi-cylinder complex structures.In this paper,the laminar flow model is used to solve the momentum equation and the mass equation based on finite element method.In the numerical investigations of the flow patterns around multi-cylinder,the Reynolds number is 200 and the spacing ratios is between1.1 and 5.The wake patterns of the cylinders at different spacing ratios are analyzed.Based on the different hydrodynamic characteristics and vortex street arrangements,the wake patterns are identified.In order to further in-depth study of the characteristics of different wake patterns,the variation of the hydrodynamic forces on seven cylinders and the underlying mechanism are analyzed,and the wake structures were found.The analysis results show that the gap flow under different wake patterns has different effects on the change of hydrodynamic characteristics.It is found that the change of the wake structure is closely related to the change of wake pattern.The information entropy and time series analysis are employed to quantitatively analyze the characteristics of the wake in the sampled areas in the flow field.The information entropy changes and the time series models under different spacing ratios are given.These analysis provide a feasible and effective measure of the characteristics of flow around multiple cylinders and quantitative measurement the change of flow field.