Study On Flow Around Bluff Body Induced Structural Vibration Based On The Immersed Boundary Method

In the simulation process of fluid structure coupling problem,the conventional body fitted moving grid has high accuracy,but low efficiency.The immersed boundary method is a new fluid structure coupling method based on Cartesian grid coordinates.In this method,the whole calculation area is regarded as a pure fluid area,and the solid is divided into several Lagrangian grid points.The influence of the solid on the flow field is fed back by the effect of the force on the solid points.As the whole calculation process of the immersed boundary method does not change the grid,it avoids the process of updating the grid with time and saves the calculation time.In recent years,the research of fluid structure coupling is very popular with researchers.With the introduction of new energy ocean energy flow,the method of obtaining ocean energy flow from vortex induced vibration of structure has entered the public field of vision,and has become a hot spot of many scholars.In the process of vortex induced vibration,mass ratio,damping ratio,Reynolds number and other parameters will have a certain impact on its amplitude and lift resistance.Therefore,this paper will study the parameters that affect the process of vortex induced vibration based on virtual force immersion boundary method.The details are as follows:(1)The virtual force immersion boundary method is used to calculate the flow around a two-dimensional fixed cylinder.The results of this paper are compared with those in the literature.It is found that the error of the results is very small,closer to the experimental results,and the accuracy of the program is verified.(2)The single degree of freedom vortex induced vibration of the cylinder is simulated,and the transverse amplitude,the coefficient of lift resistance and the law of vortex shedding are obtained under different Reynolds numbers.(3)By changing the mass ratio and damping ratio,the effects of these two parameters on the process of vortex induced vibration are studied.When the mass damping ratio is equal,the effects of high mass ratio and low mass ratio on the process of vortex induced vibration are studied.It is found that the mass ratio has little effect on the lateral amplitude and locking interval,and the damping ratio has no effect on the locking interval,but the mass damping ratio is the same The mass ratio has no great influence on the lateral amplitude,but has a great influence on the range of the locking interval.(4)Based on the virtual force immersion boundary method,this paper makes a further comparative study on the influence of the ratio of the long axis to the short axis on the flow field and the vortex shedding characteristics at the end of the structure.The results show that with the increase of the ratio of the long axis to the short axis,the drag coefficient increases,while the vortex frequency decreases.(5)By changing the angle of attack of the elliptical cylinder,we can study the difference of the flow around the elliptical cylinder caused by different inflow conditions.The results show that the change of the angle of attack will have different effects on the lift resistance,vortex shedding frequency,and the law and shape of vortex shedding.