Numerical Simulation Of Flow And Vortex Induced Virbration Of Two Circular Cylinders By Using Discrete Vortex Method

In this paper,discrete vortex method(DVM),a computational fluid dynamics numerical method,is used to simulate the two-dimensional and three-dimensional flows around two cylinders and related vortex-induced vibration(VIV)problems.The results are verified by comparing the lift coefficient,drag coefficient and Strouhal number with classic experimental results and a good agreement with previous research.Simulations are performed for two cylinders with different arrangements,spacing ratios and diameter ratios.It shows that different arrangements of the two cylinders have different effects on the flow around the cylinders.When the attack angle of the system which is consisted of two cylinders is small,the drag coefficients vary greatly in relation to the attack angle.While the attack angle is relatively large,the lift coefficients may vary greatly.Also when the attack angle is small,the two cylinders will have the same vortex shedding frequency.The characteristics above hold when the two cylinders have different diameters.It is found that as the diameter ratio increases,the critical distance increases.When the two tandem cylinders vibrate in 2DOF,the cylindrical center trajectory of the upstream cylinder is similar to the figure “8”,while the cylindrical center trajectory of the downstream cylinder is too complex.For the two side by side cylinders,the cylindrical center trajectory of both the upstream cylinder and the downstream cylinder are similar to the figure “8”.Considering that most of the practical engineering problems are three-dimensional(3D)problems,it is necessary to expand the two-dimensional(2D)DVM to calculate three-dimensional problems.Present work uses a strip slice method to calculate 3D problems.The dimensionless amplitudes of vibration in the cross-flow direction are evaluated under different velocities.The results show that DVM can be used to efficiently simulate the 3D riser VIV problems.Present work provides a research foundation for engineering applications.