Numerical Study Of Flow Around A Circular Cylinder With Longitudinal Slats Abstract

Cylindrical structures have been widely used in ocean engineering, such as pile groups, oil and gas pipelines, rises of drilling, oil extraction and water injection on platforms, and so on. Studying omnidirectional suppression methods of vortex-induced vibration which can both reduce drag force and vibration is significant in theory research and engineering application.This paper examines numerically the performance of a circular cylinder with longitudinal slats for drag force and vibration reductions in low Reynolds number range. The FLUENT software is used as the solver of the two-dimensional Navier-Stokes equation, and the Semi-Implicit Method for Pressure-Linked Equation (SIMPLE) is adopted. The time-averaged drag coefficient, the fluctuating lift coefficient and the Strouhal number are calculated at the laminar flow with Reynolds number = 100 300. The variations of theses parameters with Reynolds number and the flow field around the cylinder are carefully examined. Some useful results are presented for engineering design and physical model tests.The numerical simulation for the 2-D unsteady flow around a single cylinder is performed to examine the grid independence and validate the calculation method. The time-averaged force coefficient, the fluctuating lift coefficient and the Strouhal number for a single circular cylinder are calculated. The calculated results agree well with the experimental data.The time-averaged force coefficient, the fluctuating lift coefficient, the Strouhal number and the vortex shedding frequency of cylinder with longitudinal slats are calculated, and the vortex quantity, the speed, the pressure and other flow characteristics are analyzed. For Re = 100 300, the time-averaged force coefficients of the cylinder protected by longitudinal slats are reduced by 2.8% 14.2% compared to that of single cylinder without slates. With the increasing value of the Reynolds number, the drag force decreases first and then increases. The drag reduction effect is worst at Re = 175. For Re > 175¹80, the fluctuating lift coefficient of the single cylinder without slats increases with the increasing value of the Reynolds number. However, the fluctuating lift coefficient of cylinder with longitudinal slats decreases significantly with the increasing Reynolds number. The corresponding reduction value is 20% at Re = 200 300. In one word, when Re > 175¹80, the longitudinal slats is very useful for reducing the vibration and force on a circular cylinder.For a circular cylinder with or without longitudinal slats, the variations of the Strouhal number versus the Reynolds number are similar. The frequency of vortex off is reduced overall. For Re = 100 300, we obtain the following relationship: S₁^c≈0.873Sts, where S₁^s is the Strouhal number for a single cylinder, and S₁^c is the Strouhal number for a cylinder with longitudinal slats. This relationship may be useful for calculating the Strouhal number of a cylinder with longitudinal slats.