Hydrodynamic Characteristics Of Viscous Flow Past Two Side-by-side Cylinders

Cylindrical marine structures (marine riser, subsea pipeline) have been widelyapplied on the deep ocean development. With the wave and current flowing around acylinder, periodic vortex-shedding occurs. Furthermore, the periodic vortex inducesperiodic force act on the cylinder which may vibrate under the effect of the force, thatphenomenon is called VIV (vortex-induced-vibration). Recently, with theconsideration of technique and economy, multiple-pipelines, such as the piggybackpipeline, have been widely used in the deep sea oil and gas explorations. A piggybackpipeline is compose of a small cylinder and a large cylinder. The multiple-pipelinescan be more easily damaged because of its tight arrangement compared with thesingle cylinder. Therefore, more attention should be paid to the multi-pipelines. Thephenomenon of the flow around multi-pipelines is influenced by the G/D, d/D, and Re.However, in most numerical simulations, the range of G/D and d/D is narrow, thedivision of G/D interval is larger, and the effect of Re has not been researchedextensively. For that reason, this study aim to investigate how G/D, d/D influence thephenomenon of flow around two side-by-side cylinders and investigate the Re effectis also investigated by comparing with others’ research results. In this study, Re is3900,G/D is0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0,1.5,2.0,2.5. d/D is0.5,1.0,0.25,0.75,and the research method is numerical simulation.The vortex characteristics and hydrodynamic forces (lift coefficient, dragcoefficient and St) were analyzed based on the simulation. The obtained results showthat:(1) single vortex shedding at small G/D (0<G/D0.2), biased flow atintermediate G/D (0.2<G/D0.5~1.0), symmetric flow at large G/D (0.5~1.0<G/D2.5);(2)At small G/D, lift and drag coefficients change sharply and St issmaller than the single cylinder’s St. At immediate G/D, drag coefficients fluctuate，lift coefficients decrease with G/D increase and change sharply at the critical G/D, Stchanges between two extreme values. At large G/D, lift and drag coefficients and Sttends towards stability.With the difference of d/D, the critical G/D,the range of G/D of biased flow,the width of the wake and the deflection angle of gap flow are different.By comparing with the existing research results, the Re effect is investigated. Itis found that: with the difference of Re, the length of vortex and the changingregulation of lift force and drag force as the G/D changes are different. Anotherconclusion is the biased flow does not always occur under the condition of any Re.