Study On Flow-induced Vibrations Of Two Tandem-arranged Circular Cylinders In Larminar Flow With Low Reynolds Number

Ocean current energy is abundant in the global scope. However, the flowvelocity of ocean currents is generally below1.5m/s. Conventional ocean energyharvesting devices, such as turbines and watermills, can extract energy only forcurrent stronger than2.0m/s, below which they do not function efficiently. TheVIVACE array, utilizing the flow-induced vibration (FIV) of a cylinder/cylinderarray to capture ocean current energy, is a novel energy harnessing device withhigh energy density and has attracted great interest from both acadmia andindustry. For VIVACE, larger cylinder vibration amplitude and faster cylindervibration velocity mean more vibration energy, i.e., higher ocean current energyharnessing rate. Wider velocity range of large cylinder vibration responseindicates a broader current velocity range can be utilized by VIVACE. To this end,this paper numerically investigates the FIV of two tamdan-arranged circularcylinders and its underlying mechanisms.The numerical method applied in this paper is an immersed boundarymethod (IBM) with buit-in iterations. The governing equation for fluid motion isthe Navier-Stokes equation which is discretized using the second order temporaland spatial schemes. The conjugate gradient method is used to solve the pressurePoisson equation. The structure motion is governed by the Newton’s second law.A second order temporal scheme is adoped to solve this problem. The iterativeIBM is applied to solve the fluid-structure interaction (FSI) problem. In theframework of IBM, additional body forces are imposed on the immersedboundary points to mimic the FSI boundary conditions.The FIV of two tandem-arranged circular cylinders (mass ratio m*=2.0) inincompressible fluid with different cylinder spacings of L/D=2.0,3.0,4.0and5.0and a low Reynold number of Re=100has been numerically investigated. Twodifferent cases are considered, i.e.,1) the upstream cylinder is fixed and thedownstream cylinder is elastically supported and2) both upstream anddownstream cylinders are elastically supported. The time history of cylinders’displacement, lift and drag force together with the curves of non-dimensionalcharacteristic parameters (St, CL, CD, Y/D) versus the reduced velocity arepresented. The effect of cylinder spacing on these parameters are systematicallyanalyzed. In some typical cases, the interaction between upstream anddownstream cylinders, the wake modes and the effect of sheded vortice on cylinder responses have been investigated. Comparsion of these results betweencase1and case2have been porformed. Three forms of the wake mode of thedownstream cylinder are found in this paper; And the relationships between effectof sheded vortice on cylinder with the vibration mode of cylinder are summarized.Finally, from the view point of wake mode and the lift force, the mechanism ofthe FIV of two tamdem-arranged circular cylinders is discussed.