Abstract

Extensive studies have been conducted, both experimentally and numerically, in the last decades, however mostly on relatively low Reynolds numbers. The flow field around a sphere in an uniform flow is investigated by the numerical simulations using Large Eddy Simulation (LES) with a dynamic Smagorinsky type subgrid stress (SGS) model at the subcritical regimes (Re = 104 and 105) based on the freestream velocity and sphere diameter in the present paper. The CFD solver adopted in the simulations is Fluent and the fluid is water. Numerical results have verified the grid independence using three different grid quantities at Re=104 in the current paper. Compared with existing data, the LES can simulate accurately the flow field around a sphere at Re= 104 and 105. The hydrodynamic coefficients and Strouhal numbers are consistent with the experimental results. The structures of wake and the separation angle are also satisfied with experimental results.

Introduction

The study about the flows over a sphere that have a complex nature depending on the Reynolds number is of great interest to computational fluid dynamics (CFD). The vertical structure around it, depending on the Reynolds number, has been known to show diverse flow characteristics such as the axi-symmetric flow, and irregular rotation of separation points, unsteady flows, periodic vortex shedding, etc. A sphere is considered as an idealized model of three-dimensional axisymmetric bluff bodies. For engineering applications, typical bluff bodies whose shape resembles a sphere are balloons, wings at the high attack, thrusts of ship, bombs, oil-storage tanks, etc. In fact, the study about turbulent flows that exhibit massive separation over a sphere can be essential to investigate these complex flow structures as well as to provide useful information for validating CFD models (e.g. LES model). Because a sphere is a basic body, which has a large potential for various applications, many researchers have studied the flow over a sphere.

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