Numerical Investigation Of Vortex Induced Vibration Of Square Cylinder With Splitter Plate At Low Reynolds Numbers

Flow over a bluff body in nature is a widespread physical phenomenon, whichinvolves flow separation, vortex shedding and vibration of the bluff body and so on. Theflow in the wake is extremely complex, and contains many complex physicalmechanisms. When vortices are shedding from both sides of the bluff body, whichresults in periodic fluctuating forces acting on the bluff body, the body cause vibrationswhen elastically mounted or allowed deformation. The vibration further affects thenature of the vortex shedding mode in the wake. The interaction between the fluid andsolid is called Vortex Induced Vibration, VIV. On the one hand VIV has a significantinfluence on the stability and security of the structure, it is so important to prevent theoccurrence of a strong VIV and improve the safety performance of the structure. On theother hand, the clean energy from VIV has also been widespread concern in recent years.Therefore, it has very important significance to explore and understand the mechanismof flow over a bluff body. In the VIV passive control technology, a rigid thin splitterplate attached normal to the rear surface of the cylinder is the most effective to changevortex shedding and wake characteristics.In this paper, a numerical study of square cylinder with (and without) splitter plateis conducted at low Reynolds number. The cylinder mounted on elastic supports, withlow mass ratio, is allowed to undergo transverse vibration. The vibration and wakecharacteristics are investigated, including drag and lift coefficients, the vibrationfrequency ratio, non-dimensional vortex shedding frequency, amplitude and amplitudespectra,“beat” and “phase switching” and vortex shedding modes in the wake.The VIV mechanisms of square cylinder, such as locked-in and galloping, are exploredas well. The passive control mechanism of splitter plate in the galloping regime isestimated. The results showed:Firstly, a numerical study of the transverse motion of a spring-mounted squarecylinder is conducted at low Reynolds number (60≤Re≤250). According to thenon-dimensional vortex shedding frequency, the VIV characteristics can be divided intofour regimes, including the VIV initial and locked-in branch, transition and gallopingbranch. The energy collection of VIVACE system is efficient in locked-in and gallopingbranch. The closer the vibration frequency ratio is from one, the greater thedisplacement amplitude is. The top displacement amplitude does not appear in the point of f*=1, but near the left end of the locked-in branch. So the “detuning” phenomenain the locked field are acquired. When the vibration frequency ratio approximately equalone, and then the lift coefficient Cl is floor, the “phase switching” is also acquired. Ingalloping branch, the “beat” phenomena of displacement and lift coefficient oncylinder are investigated. Vortex shedding in the wake shows typical2S mode in initial,locked-in and transition branch. Vortex shedding mode is still2S mode for170≤Re≤231. However, wake vortex shedding mode change from the2S mode to P+S mode atReynolds number of Re=232, which is fully developed in galloping branch.Furthermore, a numerical study of the transverse motion of square cylinder withsplitter plate is conducted in galloping branch (only reference to Re=200). The vibrationand wake characteristics and the free shear layers are discussed. It is found that thesplitter plate has significant effects on the flow downstream of the square cylinder,which inhibits wake interactions between the shear layers. When L is variedsystematically from0D to7D, the flow characteristics can be divided into threeregimes.In the first regime of the flow over cylinder with plate, the vibration amplitude andfrequency are high, which is good for VIVACE harvesting. In the initial part of thesecond regime, the amplitude is greater than the square cylinder when galloping, but thevibration frequency is lower. This is not conducive to energy harvesting and passivecontrol. However, the lower amplitude and vibration frequency is beneficial to passivecontrol in the other part of the regime. In the last regime, the vibration frequency ishigher, but still lower than the flow of stationary cylinder. This is conducive to passivecontrol.