Numerical Investigation Of Flow Past Circular Cylinders With Rotation And Oscillation By The DFD Method

The DFD(Domain-Free Discretization) method is an immersed boundary method. Using the local domain-free discretization(DFD) method to solve the incompressible Navier-Stokes equations,the two dimensional viscous flow past rotating circular cylinders with cross-flow oscillation are investigated, including forced and free oscillation. The moving-boundary flows are simulated on a fixed mesh and there is no need to update the mesh at each time step. After verifying the accuracy of the DFD method, simulations are firstly conducted for the flows past a rotating cylinder with cross-flow oscillation at different rotational speeds, oscillating amplitudes and oscillating frequencies.Both in lock-on and non-lock-on regions, effects of the oscillation and rotation on the vortex shedding,the mean drag and lift coefficients are analyzed in detail. When the rotational speed is increased, the lift coefficient increases and the drag coefficient decreases. Beyond a critical non-dimensional rotational speed, the vortex shedding is highly suppressed. Then, the calculations of flow past two rotating circular cylinders in tandem with cross-flow oscillation are carried out. The gap is set to be2 D. The flow separated from the upstream cylinder is captured by the downstream one and there is a reattachment of the shear layers emanated from the first cylinder to the wall of the second one. The variations of aerodynamic coefficients have been discussed. After that, the flows past a free-oscillating cylinder with rotation are simulated. It is found that the phenomenon of hysteresis and lock-in still exist. The mode of vortex shedding and effects of rotation on cylinder response in different branches are investigated. Finally, the flow-induced oscillations of two rotated circular cylinders in tandem arrangement are calculated. The cylinders are free to oscillate only in transverse direction. The gap between two cylinders is 1.5D. Lock-in and hysteresis are observed for both upstream and downstream cylinders. It is also found that the rotation may delay the variation of amplitude with the reduced velocity.